Sense Perception and Reality


By Rochelle Forrester


© All Rights Reserved


Published in 2002


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††††††††††† This paper is intended to investigate the nature of reality. It will do so by looking at the philosophical debate between realism and idealism and at scientific investigations in quantum physics. The concept of perceptual relativity will be examined and this will involve looking at sense perception in other animals and various examples of perceptual relativity in science. It will be concluded that the universe is sense dependant and that there is no reality independent of the observer, which is knowable to the observer. Several experiments in quantum physics will be examined and the results of those experiments will also show an observer dependant universe. The paper concludes by an investigation of what an observer dependent universe would be like.

††††††††††† The paper will attempt to describe the nature of reality as we can understand it through our sensory apparatus. It will argue that it is only through our sensory apparatus that we can know the real or external world. It will also argue that there are many and possibly an infinite number of realities each as valid and true as any other. Each reality is not something which is out there in the physical world, if such a world exists, but consists of a relationship between our sensory apparatus and the physical world. The world is observer dependant and changes in the sensory apparatus used to perceive the world will result in changes in the world. This situation exists both in our macro-world and in the micro-world of quantum entities. Animals with different sensory apparatus receive different sensory percepts from each other and from those received by human beings. Each animals sense percepts can be regarded as a set and each set of sense percepts constitute that animals world. Every individualís world within a species will be very similar but the worlds of different species may vary greatly. However each species world is as valid as any other species so that there is no single objective reality but rather a great variety of realities each as valid as the other.

††††††††††† Philosophers have been studying the problem of how we can know the world for thousands of years. Our method of knowing about the world is primarily and perhaps exclusively through out sensory apparatus. The senses of sight, hearing, touch, taste and smell all provide us with information as to what there is in the world. This information, widely called sensations, lets us know the colour and shape of things, any sound they may make, how hard or soft things are and what they taste or smell like. They allow us to be aware of certain qualities of the things in the world. There appears to be no way in which we can find out about the world external to ourselves, other than through our sensory apparatus.

††††††††††† In this paper I shall refer to sensations, by which I mean the colours, shapes, sizes, smells, tastes and feelings which our senses provide us with. Sensations are the raw material of perception; it is that which is perceived with no inference or judgment being made upon it. It is something about which we cannot be mistaken, it is simply that which is given by our sensory apparatus, without it being processed in any way. It would be unwise to deny the existence of sensations as that would involve denying we see colours, shapes, sizes, hear sounds and perceive smells, tastes and feel things.


The Problem


††††††††††† However, as has been noted in the past sensations can be inconsistent and contradictory. This is sometimes called the problem of perceptual relativity. A fine example of this is provided by Bertrand Russell, in "The Problems of Philosophy" when, referring to a table he states:


"To the eye it is oblong, brown, and shiny, to the touch it is smooth and cool and hard; when I tap it, it gives out a wooden sound. Any one else who sees and feels and hears the table will agree with this description..."




"Although I believe that the table is really of the same colour all over, the parts that reflect the light look much brighter than the other parts, and some parts look white because of reflected light. I know that, if I move, the parts that reflect the light will be different, so that the apparent distribution of colours on the table will change. It follows that if several people are looking at the table at the same moment, no two of them will see exactly the same distribution of colours, because no two can see it from exactly the same point of view, and any change in the point of view makes some change in the way the light is reflected...."


Russell goes on to say:


"It is evident from what we have found, that there is no colour which pre-eminently appears to be the colour of the table, or even of any one particular part of the table-it appears to be of different colours from different points of view, and there is no reason for regarding some of these as more really its colour than others. And we know this even from a given point of view the colour will seem different by artificial light, or to a colour-blind man, or to a man wearing blue spectacles, while in the dark there will be no colour at all, though to touch and hearing the table will be unchanged. This colour is not something which is inherent in the table, but something depending upon the table and the spectator and the way the light falls on the table. When, in ordinary life, we speak of the colour of the table, we only mean the sort of colour which it will seem to have to a normal spectator from an ordinary point of view under usual conditions of light. But the other colours which appear under other conditions have just as good a right to be considered real; and therefore, to avoid favouritism, we are compelled to deny that, in itself, the table has any one particular colour.

†††††† The same thing applies to the texture. With the naked eye one can see the grain, but otherwise the table looks smooth and even. If we looked at it through a microscope, we should see roughness and hills and valleys, and all sorts of differences that are imperceptible to the naked eye. Which of these is the 'real' table ? We are naturally tempted to say that what we see through the microscope is more real, but that in turn would be changed by a still more powerful microscope. If, then, we cannot trust what we see with the naked eye, why should we trust what we see through a microscope? Thus, again, the confidence in our senses with which we began deserts us.

†††††† The shape of the table is no better. We are all in the habit of judging as to the 'real' shapes of things, and we do this so unreflectingly that we come to think we actually see the real shapes. But, in fact, as we all have to learn if we try to draw, a given thing looks different in shape from every different point of view. If our table is 'really' rectangular, it will look, from almost all points of view, as if it had two acute angles and two obtuse angles. If opposite sides are parallel, they will look as if they converged to a point away from the spectator; if they are of equal length, they will look as if the nearer side were longer. All these things are not commonly noticed in looking at a table, because experience has taught us to construct the 'real' shape from the apparent shape, and the 'real' shape is what interests us as practical men. But the 'real' shape is not what we see; it is something inferred from what we see. And what we see is constantly changing in shape as we move about the room; so that here again the senses seem not to give us the truth about the table itself, but only about the appearance of the table.

†††††† Similar difficulties arise when we consider the sense of touch. It is true that the table always gives us a sensation of hardness, and we feel that it resists pressure. But the sensation we obtain depends upon how hard we press the table and also upon what part of the body we press with; thus the various sensations due to various pressures or various parts of the body cannot be supposed to reveal directly any definite property of the table, but at most to be signs of some property which perhaps causes all the sensations, but is not actually apparent in any of them. And the same applies still more obviously to the sounds which can be elicited by rapping the table.

†††††† Thus it becomes evident that the real table, if there is one, is not the same as what we immediately experience by sight or touch or hearing. The real table, if there is one, is not immediately known to us at all, but must be an inference from what is immediately known."

†††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† (Russell, 1912, 2-4)


††††††††††† The example given by Russell relates only to human sensory apparatus, yet it is apparent many other animals perceive things differently than humans perceive them. Some animals can see colours humans cannot see, while others can see only in black and white. Dogs can sense smells and hear sounds that are not perceivable by humans; other animals appear to be able to detect the earth's magnetic field; while some fish generate electric fields and are able to detect disturbances in their fields. What is perceived seems to vary with the sensory apparatus used for the perception.

††††††††††† One reason for considering animal senses is that it raises certain questions of what may be considered to be standard observers. Some philosophers consider that a standard observer in relation to colours would be a human with no colour blindness. This observer will obtain the correct view of colours; he or she would see reality as it is. However some animals are naturally colour blind and others see a different range of colours from humans, so their view of colours will differ radically from that of the standard human observer. It would be difficult to justify why the human view should be preferred over that of other animals and be considered the real or correct view of the world.

††††††††††† Astronomy provides us with other examples of the unreliability of our senses. Our naked senses tell us the earth is motionless and each day the sun travels around the earth. Kepler, using information obtained from the Danish astronomer Tycho Bathe, suggested the earth spun on its axis and orbited the sun in an elliptical orbit. This view was later confirmed by observations made by the newly invented telescope. Einstein using still more accurate observations concluded the earth orbited the sun in circular orbits in curved four dimensional space-time. We also believe the earth is travelling through space as part of an expanding universe. Each view of the earths motion was based on the best observations possible at the time. Different instruments, naked senses, telescopes and superior telescopes produced different observations which produced different views as the earth's motion. It may be one day we will be able to establish a completely certain view of the earth's movement, but considering the way in which previous theories were completely accepted and then later discarded, it would seem unwise to regard any theory as the correct and final view.

††††††††††† The Doppler effect provides a further example of differing observations by different observers. The Doppler effect shows up both in our senses of hearing and vision. We experience it in everyday life as the increase in the pitch of a police siren as it approaches us and the fall in the pitch after it has passed and is moving away from us. This is because as the police car approaches the sound waves are bunched up or shortened and as the car moves away the sound waves are stretched out. Our ears interpret different lengths of sound waves as different pitches, the shorter the wave the higher the pitch. A similar effect applies if the source of the sound is stationary and the perceiver is moving. The Doppler effect also applies to light and all other electro-magnetic radiation, but does not show up as a visible difference in colour, but can be seen as a shift in the spectral lines within electro-magnetic radiation. As the universe seems to be in continuous motion, so the Doppler effect will always apply. It cannot be said that sound has any single true or real pitch or radiation has any single true or real spectral lines. It may be argued that there are single real or true pitches or spectral lines at particular motions for observers of light or sound sources. This however does not give real spectral lines or real pitches. Spectral lines and pitches still vary with the observer.

††††††††††† A further illustration of the problem is shown by the phenomena of space contraction in the theory of special relativity. If an observer is moving away from a scene at the end of a street at the speed of light the scene will remain fixed and all activity in the street will cease. Such an observer will only see the scene available to the observer immediately before the observer began moving away at the speed of light. If the observer is moving at close to the speed of light the objects in the street will appear to change shape. They will tend to appear thinner and taller, buildings and people will seem crowded together as horizontal distances will appear shorter. The same effect is seen by the stationary observer when observing the person moving away at close to the speed of light. The person moving at the speed of light will appear to contract along the direction of motion, the person will appear thinner and taller. This effect has been observed in particle accelerators where protons which normally behave as spheres tend to flatten out as they get closer to the speed of light and assume the shape of a flattened ellipsoid. Space contraction is actually taken into account when constructing particle accelerators; without it particle accelerators would not work. One situation when space contraction does not occur is when the observer watching the object moving at close to the speed of light, is also moving at the same speed.

††††††††††† The fact that objects change shape when moving at close to the speed of light and objects in any stationary scene observed by a person moving at close to the speed of light change shape, again raises the question of what is the real shape of the objects involved. Their shape seems to alter with the movement of the observer and due to the movement of the objects themselves. In a universe where everything seems to be moving, the earth spins on its axis and orbits the sun and our galaxy flies through the universe as part of an expanding universe, it does not seem possible to give a privileged position to stationary objects and observers. Of course objects and observers in our world do not move at the speed of light but if you are trying to discover the nature of the universe it is the principle that matters. This is because although our instruments and sensory apparatus are unable to detect the effects of special relativity at slow speed those effects are still there. The problem is that our instruments and sensory apparatus are just not good enough to pick up relativistic effect at slow speeds.

††††††††††† A further example of perceptual relativity is time dilation. Time dilation is another consequence of special relativity and involves time passing at different speeds for observers travelling at different speeds. If an observer is travelling away from a scene at the speed of light the scene will remain motionless and time will have ceased for that observer. This is because light reflected from the scene and other things in the street will never reach an observer moving away from the clock tower and the street at the speed of light. Yet for a stationary observer the scene will change and time will pass at a steady rate. An observer travelling at half the speed of light will observe time passing but at a different and slower rate than the stationary observer. The effect of this is that there is no universal time, time varies according to the motion of the observer. Identical clocks carried by the three observers, would all record different times. None of these times would be any more correct than the other times.

††††††††††† The only thing that is the same for all observers are the laws of nature. However we can not use the laws of nature or our scientific laws to tell us about reality, because those laws are dependent upon our observations and our observations are unreliable and contradictory. Our observations are necessarily a priori to our scientific laws and any defects in our observations would be carried over into our scientific laws. The fact that human sensory apparatus give all humans a very similar (but not identical) view of the world, but a view similar enough for most humans to be able to agree on the scientific laws, does not mean that those laws are necessarily correct and will enable us to understand the real world. A completely different sensory apparatus would produce different observations and would result in a quite different scientific laws than those produced from observations made with the human sensory apparatus.

††††††††††† It is quite apparent that our sense perceptions do not provide us with a single objective view of the world. However, we may get, some idea of what the universe is like by imagining what the world would be like if our sense organs were different or if we had no sense organs at all. Let us imagine first a person born with no sense organs. What would such a person be like? Obviously such a person would have no sense perceptions nor would he or she be capable of any sort of language. This person would not be able to think, as our thoughts are in words, and would be incapable of imagining any thing, because with no sense perceptions, there would be nothing to base any images on. To such a person there is no world, nothing exists, there is no awareness of anything, including self awareness.

††††††††††† Let us now suppose our person could see, but had no other sense perception although his or her sight was exceptional. Such a person could perhaps see distant planets such as Pluto and Neptune and microscopic life forms invisible to the normal unaided human eye. It could be argued that such a person lives in a different world from normal humans as that person is able to see things other humans are not directly able to see, while being quite unaware of all the sounds, tastes, smells and touch sensations other humans take for granted.

††††††††††† Let us now consider a being with none of the usual human senses, but with the ability to perceive:


a) gases contained in the atmosphere on earth and the ability to differentiate between those gases.

b) infra-red radiation thus giving the ability to detect warm objects.

c) echoes of sounds sent by the being and bouncing off certain objects, similar to that possessed by bats.


If such a being existed its world would consist of certain colours emitted from warm objects (but not from colder objects) echoes and an awareness of certain gases. Such a being could live on the planet earth and yet be in a sense living in another world from the humans on the same planet. It would perceive things in this world that humans do not see, it would fail to perceive things which humans perceive and would perceive some things in one way that humans see in a totally different way. Yet such a being could live amongst us and view the world quite differently from human beings. Yet there seems to be no reason why such a being's view of the world should be regarded as being less real than those of human beings. To treat human sense perceptions as special or better than those of other species is simply a form of human centricity that seems impossible to justify.

††††††††††† A further illustration of our world being observer dependent can be seen in the old question if a tree falls in a forest and there is no one there to hear it, does it make any sound. The answer to this is no it does not. This is because a tree falling in the forest will make vibrations in the air, but vibrations in the air are not sound. Vibrations in the air only get converted into sound by the mechanism and processes of the human (or some other) ear and if there is no ear to carry out this process the falling tree will make no sound. Sound requires both vibrations in the air and a hearing apparatus (ears) for it to be heard. Remove the hearing apparatus and you only have vibrations in the air and vibrations in the air are not sound.

††††††††††† The same situation exists with the sense of sight. If light is reflected of an object and there is no one there to observe the reflected light can it be said that the reflected light amounts to a visual event for example to the visual equivalent of a sound. Again the answer is no. This is because what we see is not light reflected of an object but an image created by the eye and brain of the observer using the reflected light. When light is reflected of an object it passes through the cornea which bends the light waves. The amount of light that enters the eye is controlled by the iris which allows more light in when there is insufficient light and less when there is to much light. Then the light passes through a lense which focuses an image on the retina. The retina contains receptor cells that change the physical energy of a light wave (or light particles) into neural energy which the brain interprets as seeing. The receptor cells, called rods and cones, receive light stimuli and send impulses along the optic nerve to the area of the brain that deals with sight. Here the impulses are converted into the images that we see. Just as with sound, the raw data that enters the eye, reflected light, goes through such a process of change when it enters the human (and other animals) sense organs that it is not at all clear that the images we receive bare any more relation to the reflected light that enters our eyes than vibrations in the air have to sound. The human brain is inadequate to take note of all the stimuli the body senses. It is estimated a brain the size of a cubic light year would be required to process all the information received by the eyes alone. A human being must therefore ignore the majority of the stimuli he or she senses and in turn these stimuli vie for attention. (Mckeachie & Doyle, 1966, 171). No one has actually "seen" reflected light, all we know about it are what the physicists tell us for example that it consists of particles called photons or of waves or both. What we see are images processed out of reflected light that may have no more relation to reflected light than a cow has to a hamburger. Furthermore if one removes the observer all that will remain will be the reflected light as the images the observer would normally see will disappear with him as there will no longer be any mechanism available to convert the reflected light into the images an observer might see.

††††††††††† Our senses have evolved over millions of years in order to help us to survive. They give us information as to whether food is safe to eat, where potential prey may be and whether potential predators are around. They are designed to give us information relevant to our survival. Information not relevant to our survival will not normally be available to us. Our senses are not designed to give us an accurate objective view of the world. They require a certain amount of energy to operate and human survival requires that energy is not wasted in providing us with information not relevant to our continued survival as a species. It is hardly surprising our senses do not give an accurate or objective view of the world. They are simply not intended for that purpose.

††††††††††† The problems disclosed by Russell, special relativity, the Doppler effect and by other animal perception, often called the problem of perceptual relativity, have been the subject of much philosophical discussion. George Berkeley suggested that these problems show there is no real table and no such thing as matter. All that could be said to exist were sense perceptions which vary according to which observer is making the observation, the position of the observer and the circumstances of the observation (such as the amount of light). Such a variety of contradictory sense perceptions (the table can not be of different colours, sizes and shapes at the same time) suggests there could not be a real table there but only a set of sense perceptions with no continuing identity. Berkeley suggested that these sense perceptions existed only in the mind, they were mental entities only and could only exist when an observation is made. He considered "To be, is to be perceived" and that no world existed beyond our sense perceptions.

††††††††††† However the Berkeley interpretation is not the only possible interpretation of perceptual relativity. If one looks at the problems shown above it would appear that what we see varies with the sensory apparatus used to make the observation and the conditions within which the observation is made. If one changes the position of the observer, the shape and colour of things change; if a different sensory apparatus is used, such as another animals sensory apparatus, there may not be any colours at all or there may be additional colours that humans are not aware of. Sounds, smells, taste and touch vary with the sensory apparatus and the conditions under which they operate. Sounds are vibrations in the air, but if there is no air, for example in outer space, no sounds can be heard. The ability of dogs to detect smells and sounds not perceivable by humans shows that different sensory apparatus will produce different sense data. Tastes appear to vary from person to person and from species to species. What is poisonous to one species may be food for another. Touch varies with the conditions available, for example a cold hand placed in cold (but less cold than the hand) water, will feel warm. The feelings obtained by touch also vary with the part of the body used for the touch as some parts of the body are more sensitive than others. If the sensory apparatus or the conditions of the observation are changed, then different sensations will be produced. This suggests the sensory process involves a relationship between the sensory apparatus, the conditions of observation and whatever, if anything, is out there. If any of these are altered different sensations will be produced. There seems no basis on which we can claim any of these sensations are more real than any other of the sensations.

††††††††††† This suggests that Berkeley's interpretation may be wrong in some respects. One is that he seem to go beyond what can be inferred by the facts of perception. He does this when he claims there is no such thing as matter and that sense perceptions are mental entities only. In order to claim there is no such thing as matter, it would be necessary in some way to go beyond our sense perceptions to see whether matter exists or not. This, known as going beyond the veil of perception, is something we are not able to do. The appropriate attitude to matter is agnosticism, rather than atheism. Equally the claim that what we see are only mental entities is doubtful, when what we see seems to involve a relationship between the sensory apparatus, the conditions of observation and whatever, if anything is out there.

††††††††††† What is observed when an observation takes place is sense percepts or sensations. Given that the sensations change if different sensory apparatus are used to make the observation, that suggests there is no single objective reality available to us. It may be that such a reality exists, but we can never know it as our sensory apparatus does not give us any special privileged way of observing the world that allows us to get beyond the sensations. We have no idea what is beyond the veil of perception. Berkeley suggested there was nothing, while Kant suggested there was "noumena" or the "thing in itself" and simply stressed the unknowability of the noumena. In effect Berkeley claimed matter did not exist (i.e. nothing beyond the veil of perception) an ontological matter, while Kant considered it to be an epistemological matter i.e. we have no way of knowing what is beyond the veil of perception. I think Kant's view is much to be preferred as we are not in a position to say there is nothing beyond the veil of perception and the acceptance of an idea such as noumena helps to explain why people with similar sensory apparatus see different things at different times. If there was nothing beyond the veil of perception, perceivers would always, subject to some variation caused by the conditions of observation, perceive the same sensations. Nothing is uniform, and would tend to produce the same sensations wherever and whenever one looked, while our sensations vary considerably.

††††††††††† Sensations will vary if you change any of:


i) the observer or sensory apparatus used; or

ii) the conditions of the observation; or

iii) the point in space and time that is being observed egg the observed


When I refer to a relationship between the observer, the conditions of observation and the observed, I mean you will get different sensations if you alter any of the observer, the conditions of observation or the observed.

††††††††††† One consequence of perceptual relativity and our inability to get pass the veil of perception is that it is necessary to distinguish between phenomena and noumena. Noumena, due to our inability to get pass the veil of perception, is something we cannot know about and we can not even be sure it exists at all. Noumena is largely irrelevant to us except as being a contributing factor in the creation of phenomena. It is phenomena which is the world in which we live. Phenomena comes in maybe an infinite number of forms and is produced by the inter-relationship of the perceivers sensory apparatus, the conditions of observation and whatever, if anything, that lies beyond the veil of perception. Phenomena cannot exist without an observation being made. Noumena can exist independently of observers. When one talks about an observer dependant universe, it is phenomena which one is talking about.

††††††††††† The idea that phenomena cannot exist unless an observation is made can be seen if one traces what happens to observed and unobserved reflected light. We could imagine a beam of light striking an object and then being reflected off into empty space. No observation is made of the reflected light so the object is never observed. In this situation the object is never part of a perceived reality, although in principal it is perceivable, unlike noumena. This is the sense in which we mean objects do not exist unless they are perceived; they do not exist as part of a perceived reality. Next imagine a beam of light reflecting off an object and entering the retina of being A who sees the same colours, sizes and shapes as a human. This brings the object into existence as part of a perceived reality and in particular to the perceived reality of being A. Next imagine a beam of light reflecting of the same object and entering the retina of being B who is unable to perceive colours and who is also unable to clearly differentiate boundaries with any precision and simply sees things in shades of grey that gradually merge into each other, so the boundaries between things are indistinguishable. This would bring the object into existence as part of the perceived reality of being B. However B's perceived reality will not be the same as A's perceived reality.

††††††††††† In these circumstances the object will not be part of any perceived reality until observed. When observed it will take what form the observers sensory apparatus is able to give it. Being A will see it in one form, being B will see it in another form. In other word it is indeterminate until an observation has been made. The observation both brings the object into existence in a perceived reality and gives it its particular from.

††††††††††† The idea of noumena and our inability to perceive the real world (if there is one) seems consistent with other philosophical theories such as Popperís falsificationism, Humeís analysis of cause and effect and the problem of induction. Popper suggested a scientific theory could never be proved correct but could only be falsified by observations that contradicted the theory. This is because while we can observe phenomena that contradict the theory, we can never look beyond or behind the theory to check it was correct as this would involve observing the noumena which is impossible. Hume noted that we can never prove cause and effect, all we can do is observe the co-relation of phenomena. We can observe one billiard ball hitting another and the second ball being set in motion, but we can never prove the second ball was set in motion by the first. We can never prove a necessary connection between the first ball hitting the second ball and the second ball being set in motion. We can merely show the one event, the first ball hitting the second was followed by the second ball being set in motion. The inability to show the first ball caused the second ball to move is because we can only see the phenomena and we cannot see the noumena. The problem of induction is also consistent with the idea of noumena. With induction all we have is repeated examples of the same phenomena in a particular situation, but we can never be certain that in the same situation the phenomena will always be repeated. This is because we are unable to see behind the phenomena to see the cause of the phenomena. This would involve observing the noumena which cannot be done.

††††††††††† The reason why humans have difficulty in accepting their world is observer dependent and that different sensory apparatus will produce different worlds is that humans have only one set of sensory apparatus (egg the five normal human senses) that give a more or less coherent view of the world. Coherence among our senses is the result of evolution and it has the effect of fooling us into thinking there is only one world, our world. We are unable to use an alternative sensory apparatus that will show different views of the world. The problem is a form of human centrism, the belief that the way humans see the world, is the way the world is and the only way it is or could be. Anthropologists have observed the same phenomena in different cultures around the world. Nearly all cultures believe that their view of the world is the right and only view of the world. They tend to be culturally centristic or as it is often expressed ethno-centric. This was because there was little contact between different cultures, so the people in one culture could agree amongst themselves that their view of the world was correct with little to challenge that view. However in the modern and especially the western world cultural centrism has to some extent broken down and new concepts such as cultural relativism have emerged. This is because we have come to see that there are a considerable number of alternative and in many ways contradictory views of the world and it is often difficult and sometimes impossible to rationally choose between them. What gave rise to cultural relativism was the realisation that different people saw the world differently. What gave strength to ethno-centrism is that everybody within a culture tendered to see the world the same way. All human beings have more or less the same sensory apparatus so we all see the world in more or less the same way and we tend not to be aware that there may be other ways of seeing the world.


Arguments against the argument from perceptual relativity


††††††††††† It is sometimes considered that we see objects rather than sensations and that perceptual relativity does not apply to our perception of objects. A person lacking a word for a particular object can still see, smell, touch and taste the object. Perception of objects does not depend upon and is not relative to the perceivers, linguistic, conceptual, cognitive or scientific knowledge.( Audi (ed), 1995, 569). If we see objects and perceptual relativity does not apply to objects then that enables us to see a single real world, to see the world as it is.

††††††††††† There are a number of problems with this argument, the first is that it fails to consider that perceptual relativity is not based solely upon the perceiverís linguistic, conceptual, cognitive or scientific systems. It is also based on the sensory apparatus available to the perceiver and this may vary widely between perceivers. In particular different animals with different sensory apparatus may well perceive as different objects, what we perceive as the same object and what we perceive as the same object, as different objects. It may well be that what I see as a computer keyboard on a table, as two different objects, my cat may not make any distinction between keyboard and table. My cat will not know the keyboard and table have different functions and is not able to examine the keyboard to see that it is not attached to the table. Much as I see two separate objects, my cat may regard the keyboard and table as a single object of two different colours. The view that perceptual relativity does not apply to objects is a human-centric view that assumes the human view of the world is in someway special. It is hard to see how this view could be justified.

††††††††††† A further objection to the view that we see objects rather than sensations and perceptual relativity does not apply to objects, is that it is not clear what an object is. There seems to be no objective criteria for deciding whether what is observed is an object. In practise we often make such distinctions based on criteria such as attachment and function. If what we are observing is not attached to anything we often regard it as an object. However even if what we are observing is attached to another thing it may well be regarded as an object, as an object can be made up of other objects. If what we are observing has a particular function then we may well regard it as a separate object. A pen sitting on a table has a particular function, namely writing, so it will be regarded as a separate thing from the table which has a different function. A ashtray sitting on a table will be an object, but what if it is nailed or glued to the table. It would be attached the same way as the tables legs might be attached, but whereas the tables legs would be regarded as part of the table, as well as possibly being objects in their own right, it is not clear whether an ashtray glued to a table would be regarded as part of the table. What if the ashtray was simply a hole cut into the table top, so it is not attached to the table but an integral part of the table, but has a function quite different from the rest of the table?

††††††††††† When I look at my door I see a brown vanished door of different shades of brown corresponding to the grain of the wood. Some parts of the wood are darker than other parts. I also see a brown wooden door handle. Most people would say the different colours of parts of the wood do not constitute separate objects, but the door handle could be considered a separate object from the door. The only way we could say the door handle is a different object from the door is that we know the function of the door handle is different from that of the door and that we know the door handle is screwed on. However knowledge of the function of the door handle and of screws is cultural relative. It is not at all obvious to people unfamiliar with doors and screws that the door handle enables people to open the door and that the door handle is attached to the door. People in a non-door culture would have no reason to think that the brown wooden shape, which we would call a door handle, has any more specific function or any different function than the different colours that constitute the wooden part of the door. They would also have no reason to believe that the door handle was connected to the door and would see it as part of the door as much as the differently coloured parts of the wooden door. The knowledge as to whether a particular item is attached to another item or is part of that item would be culturally relative as it would involve knowledge of how items can be attached for example glued, nailed or screwed together. Knowledge of function is often necessary to decide whether a particular colour and shape constitutes an object, but knowledge of function will certainly vary across cultures so the perception of whether a particular colour and shape is an object will vary across cultures. If knowledge of function is not necessary to decide whether a particular shape and colour is an object, then even in a particular culture there will often be disagreement as to what is an object.

††††††††††† If function is an important criteria for deciding whether something is an object, there would be many problems with humans from non-western cultures having the same view as to what is an object as people in western societies. Hunter-gatherers and many other non-western peoples would have no idea what the function is of a vast range of products used in western societies. This would mean their judgment as to what is an object would be quite different from that of most western people. An example of this was when Cortez and his Spanish horsemen landed on the coast of Mexico, the indigenous Americans believed his horse riders were a single animal rather than a man on top of a horse. They were quite astonished when they saw a man dismount, to them it looked as though the animal was coming apart before their eyes. The Americans thought the horse and rider were a single animal and a single object. The Spanish would have considered the horse and rider were one object on top of another.

††††††††††† This suggests what we regard as an object is a learnt experience, rather than something that is directly known through perception. Our most immediate sensory experiences are sensations rather than objects and we construct the objects from the sensations using our knowledge of what is being observed. What is an object will vary from culture to culture depending on what knowledge is possessed by the culture about that which is being observed.

††††††††††† The behaviour of babies also gives an indication that we immediately perceive sensations rather than objects and objects are constructed out of our sensations. Babies can distinguish colours and shapes but they can not tell whether what they see is an object or not unless they have put it through a series of tests. They will typically try to pick things up or push them around to see whether they are attached to other things. Until it has done such tests a baby will have no idea whether something is attached to something else. A baby will have no idea of the functions of things until it has learnt the function from watching adults and from its own experience. Adults when seeing something for the first time may well be able to guess whether or not it is attached to something else and possibly its function, but this is only because they have had prior experience of similar things.

††††††††††† The baby can distinguish colours and shapes, which are of course sensations, immediately simply by looking, but distinguishing objects requires learning on its part for example of function and attachment. If distinguishing objects requires learning, then they cannot be what is immediately seen when perceiving, but are constructed out of sensations. Obviously once one has learnt to distinguish objects, one does not have to repeat the learning every time the object is perceived, but it is the prior learning that enables us to distinguish objects. The ability to distinguish objects is not immediately known to us in the same way that colours and shapes are, it is based on our prior experience. This means that we immediately perceive sensations and that the objects are built out of the sensations using information obtained from prior experience.

††††††††††† A further curious factor when considering what is an object is the state of matter involved. Our ideas as to what is an object usually relate to solids, but less clearly to liquids and gases. A block of ice may be an object, if it is heated and turned into a puddle of water, is that puddle an object? Maybe , maybe not. Are the oceans an object or objects? If the puddle is further heated and turns into a gas, is this gas an object? It is certainly possible to perceive gases, such as smoke and steam, and other gases are felt when the wind blows. Perceptual relativity applies to these gases and yet calling them an object seems quite odd.

††††††††††† It is also doubtful that perceptual relativity does not apply to objects. While there may be some doubt as to exactly what is an object, if one chooses a typical object, say, with a total lack of originality a table, one can say perceptual relativity applies to it. Its colour shape and size will still vary with the position and motion of the observer and the amount and angle of the light falling upon it. This is because perceptual relativity allies to all of the properties of an object and the object is nothing more than the sum of the properties of the object. If perceptual relativity applies to the properties of an object then it must apply to the object. It is hard to imagine an object without its properties and when we talk about an object all we are talking about is the totality of its properties. Even if objects are something more than the totality of their properties, is that something more, something which will stop perceptual relativity applying to objects?

††††††††††† The whole concept of an object is murky. It is likely that other animals would not have the same view as to what is an object as would human beings. Obviously they will have little idea of the function of many human objects and would also often be unaware of the degree or manner of attachment objects may have to other objects. However even between human cultures what is an object will often not be clear as people from non-western cultures will have no idea of the function of many western objects or how they are put together and their degree of attachment to other objects. In this situation it would appear that people see colours and shapes first and their interpretation of what is an object is dependent upon their prior knowledge and experience. It also seems as though perceptual relativity does apply to objects as objects can only be the sum of their properties and perceptual relativity applies to all of the properties of objects.

††††††††††† There are three essential points that need to be understood when trying to understand the universe we perceive. The first is that what we see varies with the sensory apparatus used to make the observation. The second is that it is not possible to get past the veil of perception to see things how they are; if there is any particular way that they are. The third is that there is no special or standard or normal means of or conditions of observation that can show us how things really are. If there is any special or single way things are, it is not available to us. One problem with many arguments about our perception of the universe is that they assume we can somehow know how things really are, when this is in fact impossible.

††††††††††† An example of this is provided by Don Locke (Locke, 1967, 98-101) where he suggests that the real colour of something is how a thing looks to "normal perceivers" under "standard conditions" of observation. Standard conditions of observation would for example be in daylight, with no interfering sources of light and no coloured objects between the perceiver and the object being observed. The standard conditions of observation are those that are most common. A normal perceiver would be a human being with normal vision, for example a person who was not colour blind.

††††††††††† There are however problems with this view. Colours still look subtly different at different times of day, they look different on cloudy days and they vary depending on whether the observer is inside looking out, outside looking in or in the shade and upon a host of other variables. The brightness of an object will vary under these different conditions due to the different amount of light available at any given time. While there may be an average amount of light available there does not seem to be a normal amount of light. Colours will also vary with the angle at which the light is reflected of an object and it is hardly likely there is any normal or standard angle for the reflection of light.

††††††††††† A second problem is that normal perceivers will still perceive colour slightly differently from each other. They might all agree the colour is red but if analysed sufficiently closely it would be discovered they are still not seeing exactly the same colour. It is only the width of the concept "red" that allows it to encompass a range of different visual stimuli all of which we describe by using the term red. Each perceiver will perceive a slightly different version of red when seeing a red object. There may be an average perceiver but it is doubtful that any perceiver is any more normal than any other perceiver.

††††††††††† A third problem is that some species are normally colour blind and still other are able to distinguish a wide range of colours, some of which are not observable by human beings. This means that the same object will appear differently coloured to normal perceivers of different species, so it is hard to say it has any real colour. There seems to be no reason to claim that the human view of an objects colour should prevail over those of any other species.

††††††††††† The forth problem with Don Locke's attempt to find real colours is that normal and most common does not mean, entail or imply reality. Something may be normal or most common but that does not mean that it is necessarily real or leads to reality. Lockes choice of normal and most common are simply arbitrarily selected conditions to which he chooses to claim possess some special status that makes them the conditions under which we are able to perceive real properties. However there does not seem to be anything so special about those conditions that enable us to say that properties seen under those conditions are real while properties seen under other conditions are not real. It does not follow from normal perceivers and standard conditions that you will get real colours. Normality and most common have nothing to do with reality. It seems there are no normal perceivers or standard conditions under which we are able to perceive the real properties of objects, such as their real colours.


Reid's solution


††††††††††† A different view of the problems posed by perceptual relativity has been offered by Thomas Reid who suggested that, that the table had a different appearance from different positions, and that it changed with perspective is exactly what you would expect from a real table. Reid distinguishes between the real and apparent magnitude of the table. The real magnitude of the table could be obtained by applying the rules of geometry and perspective to the apparent magnitudes derived from the sense of sight.

††††††††††† Reid considered that the table appears to vary in size and shape depending on the position of the observer shows only variations in its apparent magnitude, but not its real magnitude. The tables real magnitude may be a rectangle of 1 metre by 2 metres but it will appear to become smaller as I move away from it, but its real magnitude will always remain a 1 metre by 2 metres rectangle. The real magnitude has three dimensions and is measured by a line, the apparent magnitude has two dimensions and is measured by an angle. The relationship between real and apparent magnitudes can be determined by the rules of geometry and perspective. If the table and the observer are placed in any particular positions, it is possible to calculate the apparent magnitude of the table from any position by using the rules of geometry and perspective. Equally given the apparent magnitude of the table and the position of the table and the observer it is possible to calculate the real magnitude of the table.

††††††††††† Reid considered the distinction between real and apparent magnitude explained why the table appeared different from different perspectives and that this was simply what would be expected of a real table seen from different positions. However Reid's theory can be questioned in a number of respects. Might not Reid's real magnitude be simply another apparent magnitude and should not be considered special or any different from any other of what Reid calls apparent magnitudes. The question is, "Is there any such thing as a real magnitude?" If I put a tape measure on the table to measure its size I will obtain a certain measurement. If I move back the size of the table will appear to reduce. Reid would say the tape measure touching the table would give its real magnitude while the reduced size at a greater distance from the table is its apparent magnitude. The problem is that the tape measure is still at a distance from the table even though it is touching the table. The tape measure cannot occupy the same position in space as the table so it is always a distance from the table even when touching the table, so such a measurement is just another example of apparent magnitude. It is impossible to measure the size of the table in any perfect sense. Any such perfect measurement can only be a theoretical concept relevant to pure mathematics rather than to our imperfect world.

††††††††††† Reidís arguments concerning the shape of the table also have their problems. The table may be a geometric shape with two parallel sides two metres long and two other parallel sides one metre long with the sides meeting at four right angles. Such a shape would normally be considered to be a rectangle due to the measurements of its sides and angles. (See Figure 1). However when observed from a particular position as in Fig 2 it may appear to be an isosceles trapezium with the near side appearing to be longer than the far side and the other two sides appearing to converge away from the observer. (See Fig 2). The four angles as with the rectangle will still equal 360 degrees but there will be two acute angles and two obtuse angles.


††††††††††††††††††††††† Figure 1††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Figure 2












††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† †† observer



††††††††††† Reid would say the real shape of the table is a rectangle rather than an isosceles trapezium and that the far side and the near side are of the same length and the other two sides are not in fact converging. The appearance of an isosceles trapezium that the rectangle gives is just the rectangles apparent shape rather than its real shape. The apparent shape of the rectangle i.e. its isosceles trapezium appearance is related to the visual angle from which the observer sees the shape. The visual angle is the angle formed by the rays of light from the shape and projected on to the observer's retina. (See Fig 3).


††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Figure 3




The angle, B, is the visual angle subtended by the target, S that lies at the distance, D, from the retina along the line of regard.(Source: Sensation and Perception, Schiffman)


The visual angle precludes specifying both an objects size and distance and is based on the following formula


tan B/2 = S/2D


where:Tan††††† =the trigonometric function for 1/2 of the visual angle

††††††††††† S††††††††† =size of object

††††††††††† D†††††††† =distance of the object from the observer


Where the visual angle is relatively small for example 10 degrees or less the formula tan B=S/D applies. (Schiffman,1982,224-225). If we know the visual angle and size of the object one can calculate the distance to the object, or if we know the visual angle and distance we can calculate the size of the object. More particularly the visual angle from which we see the far side of the table is different from the visual angle of the near side. However when we calculate the size taking into account the visual angle we always get the same result, so the mathematics would be the same regardless of the position of the observer. This would probably be accepted by Reid.

††††††††††† There are however some problems with Reid's theory. One is that Reid cannot show why the mathematics based on the measurements of the shape made at the point where the shape is, which are points at which no observer can be present at the same time, as no observer can be at all four sides of the shape at the same time, should prevail over the mathematical description of the shape which takes into account the position of the observer and the visual angle at which the observer sees the shape. The mathematics are equivalent in both cases and there is no more reason to believe that Reid's real magnitude is any more real than the apparent magnitudes, than to believe seven is more real than three plus four. Seven and Reid's real magnitude may be simpler than three plus four and the apparent magnitudes but that does not make them more real. Simplicity and reality are quite different concepts and it is not the case that that simplicity entails or leads to reality. It is also inevitable that some descriptions of the size of the table will be simpler than others and that there will be a simplest description, but there seems no reason why the simplest description should have any special status.

††††††††††† A second problem is that what Reid calls the real shape is one which can never actually be observed. It exists only as an abstract mathematical idea. However can a figure which is never seen, a figure that is only a mathematical construct, be regarded as real. Reid is trying to say there is a world external to our minds, and a mathematical construction, a rectangle that is never seen cannot possibly provide Reid with the external world he wants to show exists. The Reid view of nature is a God like view, he looks at nature from a single privileged position and that is from a position no human being can ever occupy. In a sense it is the view from nowhere. It is a position akin to that Newton took when describing his cosmology and can be compared to Einstein's view of the universe which describes it from a position in which human beings could actually see the universe.

††††††††††† The third problem for Reid is that his theory rests upon the correctness of the geometry he proposes to use to discover the real table. Reid's geometry would have been classical Euclidean geometry which assumes flat three dimensional space. If this assumption is wrong then we are unable to use Euclidean geometry to discover the real table even if all the mathematics based on the assumption are correct. Since the publication and acceptance of general relativity we would now consider we are living in a world of curved four dimensional space-time. In principle it should still be possible to use Reidís theory using the geometry of curved four dimensional space-time to arrive at his real table. However while the mathematics may be reliable if the calculations are correctly made, we still would not be lead to the real table if the assumptions that the mathematics rest on are unreliable. The view that geometry and the assumptions upon which it is based is dependant upon our perception is quite common place. Morris Kline states:


The dominant view today as to the nature of mathematical activity is, then that the concepts and axioms are derived from experience, the principles of reasoning used to deduce new conclusions were most likely derived from experience and insofar as the applicability of mathematics to the physical world is concerned, the conclusions must be checked against experience. (Kline, 1959, 472).


These assumptions whether of flat three dimensional space or curved four dimensional space-time are necessarily based upon our observations of our world and as we have seen these observations are not necessarily reliable and may vary with the observer.

††††††††††† In Euclidean geometry it is considered if there is a line "A" and a point not on that line then there was only one other line which could pass through the point and not meet line "A". This was known as Euclid's parallel axiom and was sometimes represented by the claim parallel lines never meet. However if space-time is curved as suggested by the theory of general relativity, then parallel lines will meet much as lines of longitude meet at the poles on the curved surface of the earth. There are many geometrical consequences of curved space-time the most commonly cited being triangles whose angles equal more or less than 180 depending exactly on what curvature exists. The same situation occurs with our table. The Euclidean rectangular table is shown as (a) below and non Euclidean rectangles as (b) and (c) below.


(a)††††††††††††††††††††††††††††††††††††††††††††††††††††††† (b)††††††††††††††††††††††††††††††††††††††††††††††††††††††† (c)


††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† †††††††††††††††††††††††††††


The angles, area and length of the sides of the rectangle will vary with the type and degree of the curvature of space-time. The curvature of space-time varies with the strength of gravity at any particular point in the universe. The strength of gravity varies at different points in the universe, so the curvature of space-time varies with it and so will the shape and size of any given object. As bodies which exert gravitational force are constantly moving through the universe the strength of gravity and the curvature of space-time at any particular point is constantly changing. It would seem that the size and shape of the table would vary at different points in the universe which suggests the table has no single size or shape.

††††††††††† It is not just the shape of space that is problematic. Space appears to be three dimensional but there has been considerable scientific speculation in recent years that there may be more than three dimensions of space. Superstring theories have suggested there may be ten or twenty six dimensions, these additional dimensions being known as hyperspace. The existence of the extra spatial dimensions will considerably simplify the laws of physics and all matter and forces in the universe can be explained as vibrations in hyperspace. Obviously we are unable to see these extra dimensions. It has been suggested the extra dimensions are curled up into a space so small we are unable to detect them. It would seem impossible for us to visualise more than three dimensions. It is however possible to image life in one or two dimensions. In a single dimension a being could see and move only along a line, while beings in two dimensional space would be able to see and move across a plane having both length and breadth. Such a two dimensional being would have no concept of height and if a three dimensional being reached into the two dimensional world and lifted a two dimensional being out, it would appear to the other two dimensional beings that their friend had disappeared into thin air. The two dimensional being carried into a three dimensional world, would only be able to see a two dimensional slice of everything in the three dimensional world. If two dimensional beings could only see in two dimensions and could not conceive of a third dimension, even when such a third dimension exists, this would suggest that a fourth or more dimensions could exist even though third dimensional beings (such as us) could not see the other dimensions or conceive of their existence.

††††††††††† There is an important difference between our perceptions of space and qualities such as colours. Colours are often considered to be secondary qualities of objects in that they are sense dependant as they vary with the sensory apparatus used to observe them and with the conditions of observation. Qualities such as shape and size are considered by some to be primary qualities of objects in that they are not considered to be sense dependant and exist independently of any observer. The reason colours are considered to be secondary qualities is because we note that the colour of an object will look different to the same observer under different conditions of light and to different observers under the same conditions of light. We also note that some people may be partially or totally colour blind and some animals can see more colours than humans and others will see less colours or may be naturally colour blind. Our observations of space are quite different from our observations of colour. All humans under all conditions see space as flat and three dimensional. As far as we know all other animals see space as flat and three dimensional. This means that unlike with colours we cannot show that our perceptions of space vary with the sensory apparatus used to perceive it. What we are able to show is that we see space as flat and three dimensional and that science suggests space is very likely curved and possibly has more than three dimensions. This suggests our naked senses gives us a false view of space if one accepts the scientific view or at least a doubtful view if one accepts there is evidence for both views of space. It is not clear whether there is a single correct view of space and even if there is, it is not clear what that correct view is. Without knowing how many dimensions space has and the shape of space it is not possible to know the real size and shape of things. It is also not possible to exclude the possibility that space is entirely sense dependant and that things either have no single size and shape or that size and shape are in principle unknowable to human beings whose only access to the physical world is through a sensory apparatus of doubtful reliability.

††††††††††† There is something circular about Reidís argument. His theory relies on the certainty of geometry in order to pass the veil of perception and to allow us to discover the real world. However the geometry itself is based upon our observations of our perceived world and so is subject to all the problems that perception of our world involves. Our very view of space itself may be dependant upon our sensory apparatus and there is no reason why other beings with different sensory apparatus would not see space as being quite different from the way we see it. They might for example see curved space or possibly other dimensions. Different sensory apparatus may provide different observers with totally different concepts of space. Different concepts of space will result in quite different geometries. The different geometries when applied to our sense data of the table will each produce a different real table. There is no limit to the number of geometries that may potentially exist, so there is no limit to the number of potential tables that may exist. This shows that Reid's method does not lead us to any single real table or any single reality. The very fact that flat three dimensional flat space has been replaced by curved four dimensional space-time shows the unreliability of the assumptions underlying our view of space. Our geometry may be analytic and true by definition, but the assumptions upon which it is based are not and are subject to all the problems of perceptual relativity and perceptual unreliability.

††††††††††† The problem for Reid is that size and shape may be as dependant on our sensory apparatus as all other qualities. It is perfectly conceivable that there could be beings that have no concept of size and shape simply due to not having the appropriate sensory apparatus to detect size and shape. A blind being with only the senses of smell and hearing could be such a being. This suggests that qualities such as size and shape maybe as equally sense dependant as qualities such as colour. Colour is a sense dependant quality because the ability to sense colour requires the presence of certain rods and cones within the observers eyes. However the sense dependence of size and shape is not based on certain qualities of the sensory apparatus as it is for colour, but on the very existence of the sense of sight.

††††††††††† A similar situation applies with other qualities of objects, such as their colour. It could be argued in relation to the colour green:


1) I have a sensation of green.

2) Green is produced when material has an atomic structure x and there are light conditions y.

3) Therefore the single objective reality, the real world, the real thing we are observing is atomic structure x.


But our knowledge that green is produced by atomic structure x in light conditions y has to be derived from somewhere. Inevitably it is derived from scientific experiments that show if we have some material with atomic structure x and we place it under light conditions y then we produce the colour green for normal human senses. We have moved from saying the material has the colour green to saying it has atomic structure x. But how can we say the material has atomic structure x? Not by observing it with human senses they only tell us it is green. We can only tell it has atomic structure x by means of a scientific experiment that is just as much a way of observing the material as looking at it with human senses is a way of observing the material. If I look at it with my human senses under lighting conditions y I see green. If I look at it through a certain scientific experiment I will detect atomic structure x.

††††††††††† The problem for the realist who wants to find the "real colour" to get around the problem of perceptual relativity is that the atomic structure of the material is the result of an observation itself and the process of that observation and the conditions under which it was made can be analysed in the same way as the process that showed the material to be coloured green. Why should it be more real to describe the material as having atomic structure x, than to describe it as being green? Of course the green view has the problem of perceptual relativity in that if the lighting conditions change, or if the observer is colour blind, as many animals are, then the green will change shade or may completely disappear. However the same problem exists for the scientific experiment that shows the atomic structure of the material. Concerning the scientific experiment we can always say:


1) Material m has atomic structure x.

2) Atomic structure x is shown by scientific experiment a carried out on m.

3) Therefore something (possibly unknown) in scientific experiment a and material m produces the observation, that material m has atomic structure x.


It is quite possible to see the atomic structure of the material as just another property of the material, just as green is a property of the material. Furthermore the atomic structure of the material is as subject to the problem of perceptual relativity in that it is revealed to us only through a particular experiment, much in the same way as green is only revealed to us under particular conditions, such as material with atomic structure x and the right lighting conditions. The point is one can always ask "what causes the colour green?" and one can equally ask "what causes atomic structure x?" For thousands of years humans saw the colour green without knowing what caused green. We now know what caused green, but it is just as reasonable a question to ask what causes atomic structure x as it is to ask what causes green. The cause of atomic structure x is the experiment carried out on material m (or something in the experiment) that allows us to detect that the material m has atomic structure x. That scientific experiment is just another way of observing the material; there seems to be no reason to give it any special epistemological status by saying it is real. It is just another way of viewing the material.

††††††††††† Perceptual relativity in the sub-atomic world is shown by the various experiments that show electro-magnetic energy and entities such as electrons, protons, neutrons and atoms to be both particles and waves. One experiment will show both the energy and entities to be waves, but if the experiment is altered they will appear to be particles.

††††††††††† Is it possible however to claim that the scientists view of matter that it consists of electrons, neutrons, protons etc is more real than the normal human view that it consists of objects of various sizes, shapes and colours. It seems it all comes down to a matter of size. As Russell noted with the table to a human observer it appeared smooth, but if placed under a microscope it will appear to be rough and contain various hills and valleys and if placed under a more powerful microscope, the roughness, hills and valleys will change and one will eventually see cells, or cell walls as the matter is dead. If one looks in even more detail one will see atoms and in more detail still electrons, protons and neutrons and other sub-atomic particles. The scientific view itself is subject to perceptual relativity in that how one observes an object determines what one sees. There are numerous equally correct and equally valid scientific ways of seeing the table which are no more or less valid than the method of observing the table with unaided human senses.

††††††††††† Could one argue that the real table is the table as it is constituted at its most basic level; the level of elementary particles usually though at the current time to be electrons and quarks. However what appears to be the elementary particles keeps changing. It is currently quarks and electrons, previously it was electrons, protons and neutrons, before that atoms and before that individual molecules. There seems no reason why the discovery of new elementary particles will not continue displacing the particles previously regarded as elementary particles. It cannot be argued that electrons and quarks are so small, that surely nothing could be smaller. Electrons and quarks are not small, they are relatively small compared to us. They may well be quite large compared to some smaller elementary particle much in the same way that atoms which we would regard as small are actually large compared to electrons. To regard sub-atomic particles as small, in any way other than a relativistic way is to adopt a human centric point of view which would seem to be impossible to justify. There seems no reason to regard size whether in largeness or smallness as being anything other than infinite, so there may be no limit to the range of sub-atomic entities that may be discoverable by means of appropriate experiments. There may be an infinite procession of so called elementary particles yet to be discovered. This means there will be no real table at some fundamental basic level.

††††††††††† It could also be argued that even if there was a final elementary particle or group of particles, that would not necessarily mean that these particles somehow constitute the "real" table. This would amount to confusing, in a manner similar to the geometric description of the table, the simplest or most basic view of the table, with the view of the table as being real. Simplicity and reality are two quite different concepts. One relates to whether things exist, the other to their degree of complexity. If they amounted to the same thing the universe would probably consist of nothing, or be a single dot or particle, or could be described in some very simple way. The universe however appears to be very complex and may be infinitely complex so there is no reason to believe there is any connection between the concepts of reality and simplicity. Reality does not follow from or is derived from simplicity. This means there is no reason to consider a description of the table at the level of some sort of elementary particle or entity amounts to a description of the "real" table.

††††††††††† The conclusion it seems necessary to draw is that there is no single objective reality that we can be aware of. It may be that such a reality exists, but we can never know whether this is correct or not. There seems little point in speculating about that which we cannot know. We can only know the world through the sensory apparatus available to us and it seems clear they provide us with a variety of perceptions many of which seem contradictory and may only be explained by an acceptance that there is a variety of worlds each existing as a result of a relationship between sensory apparatus and whatever (if anything) that is out there.


Some Quantum Mechanics


††††††††††† The problem of perceptual relativity does not just arise in the macro-world. It also appear to exist when making observations of the quantum world. The orthodox interpretation of the quantum world is known as the Copenhagen Interpretation. The Copenhagen Interpretation comes in a number of versions, but they commonly provide for a version of the quantum world that is in one way or another, observer dependant. This view is derived from the results of a series of experiments using quantum entities and electro-magnetic radiation. These experiments are the double slit experiment, the EPR-Aspect experiment, the Stern-Gerlach experiments, polarisation experiments and barrier experiments involving quantum tunnelling. We will look at the first two of these experiments in more detail.

††††††††††† The double slit experiment according to Nobel Prize winning physicist Richard Feynman shows all the mysteries of quantum mechanics. (Feynman,1965,1). The experiment involves shining light of a single wave length, from a single source onto a screen with two slits. Light passes through the slits onto another screen where it produces a pattern of alternative light and dark patches on the second screen. There will be a light patch on the second screen equidistant between the two slits on the first screen, then on both sides of this light patch there will be a dark patch followed by another light patch and so on. This is considered to be evidence that light is a wave, the light patches showing where the light waves were in unison and reinforced each other, the dark patches showing where the waves were not in unison so they cancelled each other out and so produced the dark patches. (Experiment 1). This interference pattern, so called because it results from light waves interfering with each other, was considered in the 19th century as showing that light consisted of waves.

††††††††††† There are a number of variations on this experiment that can be performed. Suppose one of the slits is closed. This causes the interference pattern to disappear and it is replaced by a light patch immediately behind the open slit. (Experiment 2). Now suppose both slits are open and the intensity of the light was reduced so that only a single


††††††††††† Experiment 1††††††††††††††††††††††††††††††††††††††††††††††††††† Experiment 2

††††††††††† Both slits open††††††††††††††††††††††††††††††††††††††††††††††††† Single slit open


Light†††††††††††††††† First†††††††††††††††† Second

Source ††††††††††† screen††††††††††††† screen††††††††††††††††††††††††††††††††††††† Light†††††††††††††††† First†††††††††††††††† Second

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photon of light will be sent through the experiment at a time. A photon is the smallest unit of light possible and is indivisible. This would seem to eliminate the possibility of interference happening, as how could a single photon go through both slits and interfere with itself. As one would expect the single photon arrives at the second screen as a single dot rather than as an interference pattern. One would expect each photon to follow the path of the previous photon and end up on the same spot. However as more and more photons are passed through the experiment they gradually build up the same interference pattern as they would if they had all been sent through the experiment at the same time. (Experiment 3). Somehow there has been interference which suggests the photon has gone through both slits and interfered with itself. This does not seem possible as photons are the smallest discrete packages of light possible so that a single photon should not be able to divide itself and go through both slits at the same time. This has lead to the claim that "light travels as a wave but departs and arrives as a particle". (Baierlein, 1992, 170).

††††††††††† A further variation on the double slit experiment is to place detectors at the holes to see whether the photons pass through both holes at once or through just one of the holes. What we find is that each photon behaves as a particle travelling through one hole or the other. The interference pattern disappears and is replaced by a light patch directly behind each hole.(Experiment 4). This is the same pattern observed if only one of the holes was open. The act of observing the photons at the holes seems to make the


††††††††††† Experiment 3††††††††††††††††††††††††††††††††††††††††††††††††††† Experiment 4

††††††††††† One photon at a time††††††††††††††††††††††††††††††††††††††† Detectors at both slits



Light†††††††††††††††† First†††††††††††††††† Second

Source ††††††††††† screen††††††††††††† screen††††††††††††††††††††††††††††††††††††† Light†††††††††††††††† First†††††††††††††††† Second

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photons behave as particles when going through the holes. If there were no detectors at the holes we would obtain an interference pattern on the second screen suggesting that the photons were acting as a wave when going through the holes. The act of observation seems to turn the photons from being waves into being particles. Furthermore we need only look at one of the two holes to cause this result. If a detector is placed at one hole the light behaves as a particle and produces a pattern on the second screen of a bright patch behind each hole. (Experiment 5). It is as if the photons passing through the hole with no detector "know" there is a detector at the other hole and this causes them to behave like particles.

††††††††††† Our final variation is known as the "delayed choice experiment". In this experiment a detector is placed between the slits and the second screen and a decision whether to turn the detector on is made only after the photons have passed through the slits. Quantum theory tells us, if the detector is on that the photons will behave as particles at the slits and there will be no interference pattern on the second screen. If it is off the photons will behave as waves at the slits and we will detect an interference pattern on the second screen. As the decision to turn the detector on or off can be made after the photons have passed through the slits, the form the photons take at the slits can be determined after the photons have passed through the slits. This means the behaviour of the photons at the slits is effected by how we are going to look at them even though


††††††††††† Experiment 5††††††††††††††††††††††††††††††††††††††††††††††††††† Experiment 6

Detector at one hole†††††††††††††††††††††††††††††††††††††††††††††††††††† Delayed choice experiment-with detector on†††† with detector of


Light†††††††††††††††† First†††††††††††††††† Second†††††††††††††††††††††††† Light†††††††††††††††† First†††††††††††††††† Second†††††††††††† Second

Source ††††††††††† screen††††††††††††† screen††††††††††††††††††††††††† Source†††††††††††† Screen††††††††††††† Screen††††††††††††† Screen

††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††††† Detector on††††† Detector of



we have not made up our mind as to how we are going to look at them when the photons are at the slits. The photons seem to be able to predict in advance whether the detector will be on or off. This experiment began as a thought experiment but has been performed using a beam splitting mirror (rather than the screen with two slits) and the result was as predicted by quantum theory. (Experiment 6). (Gribben,1995, 138-140, Lindley, 1996,62-66).

††††††††††† Interference certainly suggests that light is a wave, while the fact that light hits the second screen in a single spot and the pattern produced when only a single slit is open suggests light is a particle. There is furthermore plenty of other evidence light consists of particles. The photo-electric effect where electrons are knocked out of metals was explained by Einstein in 1905 as showing that light consists of particles. The Compton effect involves an x-ray beam (high frequency light) being shone into a gas and it is possible to detect both an electron being ejected from the gas and the recoiling photon. This involves the x-ray acting as a billiard ball and knocking the electron out of the gas. So light appears to be both a particle and a wave.

††††††††††† However it is not just light that behave in this way. The double slit experiment has been done using electrons and atoms both of which are normally regarded as particles. Unlike photons, both electrons and atoms have mass. Yet when fired one at a time towards the screen with the double slits in, they arrive at the second screen as particles, making just a single dot on the screen. However, as more and more electrons (or atoms) arrive the interference pattern produced by photons soon builds up. The experiment with electrons was first performed in 1987 and with atoms in the early 1990's. (Gribben, 1995, 7-9). However the results were very much as expected as it had long been known that electrons can behave as waves. In 1927 experiments were performed which directed beams of electrons at crystals of nickel causing the electrons to scatter. As the crystal lattice is arranged with geometric precision the crystal acts as a coherent source of electrons, the spaces between the atoms in the lattice acting as the slits, and the electrons create an interference pattern on a detector placed adjacent to the nickel crystal. (Lindley, 1996, 53). The results shown by the double slit experiment can also be seen in other experiments such as the Stern-Gerlach experiments involving electron spin and experiments concerning the polarisation of photons.

††††††††††† The question arises as to how can light, electrons and atoms be both particles and waves. As Nick Herbert in "Quantum Reality" says:


"Three wave attributes are especially discordant with the particle notion. 1. A wave can spread out over an enormous area, while a particle is confined to a tiny region. 2. A wave is easily split in an infinite variety of ways, some parts going in one direction, some another, while a particle is confined to a single direction. 3. Two waves can interpenetrate like ghosts and emerge unchanged where particles would crash together."(Herbert,1985,38)


It is hard to see how anything can be both a wave and a particle.

††††††††††† There are however other strange happenings in the double slit experiment. When photons (and electrons and atoms) are sent through the set-up in the experiment one at a time how do you get the interference pattern? Is each photon going through both slits at the same time, which seems impossible as photons and electrons can not split themselves in two. If not how is the interference pattern being produced? A further problem is to determine how does the photon or electron "know" where to place itself on the second screen to produce the interference pattern. Why doesn't each photon follow the same path and end up in the same place on the second screen? If each photon or electron is put through the experiment individually you would expect them to behave in the same way, given that no interference should be possible and even if the photon or electron interferes with itself it should do so in a manner that would be the same for each photon/electron.

††††††††††† Yet another problem is why interference patterns arise in the sub-atomic world but not in the macro world. If a machine gun is fired at a screen with two slits the pattern that would build up on the second screen would be a concentration of bullets immediately behind the two slits. There would be no sign of an interference pattern or of an other wave like behaviour. If it is argued that the sub-atomic world is different from the macro world, why do atoms which by definition are not part of the sub-atomic world and which are big enough to be photographed exhibit wave/particle duality? If there is a difference between the macro and the sub-atomic worlds exactly where does the difference begin and why is there such a difference?

††††††††††† A further puzzle is why should an act of observation or measurement cause a photon, electron or atom to behave differently? Why should they behave as waves if no detector is present and as a particle if a detector is present?

††††††††††† Yet another puzzle is how does an electron, photon or atom passing through one hole of the double slit experiment "know" whether or not the other hole is open. Each photon/electron "chooses" how it will behave at one hole dependant upon whether or not the other hole is open. It is as though the photon/electron is "aware" of whether the hole at which it is not present is open or closed at the time when it passes through the other hole. This is an example of non locality which Einstein referred to as "spooky action at a distance". (Gribben, 1995, 12-13). However maybe the explanation is that with one hole closed, nothing can get through the hole and the electron, photon or atom passing through the other hole has nothing to interfere with, so there is no interference pattern. This after all is simply the same as the experiment with only one slit open and there is nothing surprising or odd about that experiment. A further example of non locality is where a detector is placed at one of the holes causing the electron/photon going through the other hole to behave as a particle. It is as though the photon/electrons going through the second hole "know" we are looking at the first hole. (Gribben, 1995, 13). But maybe it is simply the case that the detector at one hole causes the electron/photon to behave as a particle at that hole and this leaves the electron/photon going through the other hole without a wave to interfere with, so there is no interference pattern or evidence of wave-like activity. Maybe these are not genuine cases of non-locality at all.

††††††††††† Needless to say considerable efforts have been made to explain these extraordinary quantum mechanical effects. The most generally accepted interpretation is known as the Copenhagen Interpretation, so called because a lot of the work on its development was done in that city. The Copenhagen Interpretation however has a number of different versions each providing a different emphasis on the varying aspects of the explanations of the puzzles produced by experiments such as the double slit experiment. The Copenhagen Interpretation has a number of aspects such as the collapse of the wave function, the uncertainty principle and complementarity all of which are illustrated by the double slit experiment.

††††††††††† The collapse of the wave function is a process which occurs whenever an observation or measurement is made of a quantum entity. It involves the quantum entities wave function collapsing to form a photon or a quantum particle. The wave function is not a real wave like waves in the ocean. Rather the wave function is an abstract mathematical concept representing "a complex form of vibration in an imaginary mathematical space called configuration space." (Gribben, 1984, 116). The picture of physically real waves in quantum mechanics is wrong (Gribben, 1984, 117) the waves are simply mathematical concepts based on probability. The mathematics produced by the wave function can be provided in a non-wave manner by the quantum algebra produced by Paul Dirac and the matrix mechanics produced by Heisenberg, Born and Jordan. (Gribben, 1984, 114). The wave function, based on work by Erwin Schrodinger and Max Born provides a measure of the probability of finding a particular particle at any given place. In the double slit experiment a given electron may be anywhere in the universe, but it is more likely to turn up in the dark patches of an interference pattern.

††††††††††† The uncertainty principle concerns the impossibility of obtaining precise measurements of certain pairs of properties of quantum entities. The example usually given is that of the position and momentum of an electron, the principle stating the more precisely we try to measure the position of an electron the less precisely we will be able to measure its momentum. The principle is sometimes explained on the basis that the only way we can observe an electrons position is by bouncing photons off it which will tell us the electrons position. However the collision between the photon and the electron will disturb the electron's momentum making it impossible to measure both position and momentum at the same time.

††††††††††† This however is not the full story. The mathematics of quantum theory make it clear that electrons and other quantum entities simply do not have a precise position and a precise momentum. It may have a precise position but then it will not have any knowable momentum at all, or it may have momentum, but its position will not be knowable. (Gribben, 1984, 157).

††††††††††† The uncertainty principle can be seen in the double slit experiment, in experiments (4) and (5) when we can see through which slit a photon/electron went through or you can observe an interference pattern, but you cannot do both. Detecting which slit the photon/electron went through is a measurement of its position which is a particle measurement as particles may have a definite position. An interference pattern is a wave measurement and momentum is a wave property as waves must be moving or they would not be waves. By observing the quantum entities position, we observe it as a particle, by observing its momentum we see it as a wave. This means we may measure the quantum entity as a particle and observe its position or as a wave and see the interference pattern, but it is not possible to see it as a wave and particle at the same time.

††††††††††† Complementarity is simply the idea that the quantum world can be seen in alternate ways. One can for example see it in terms of waves by performing the double slit experiment (experiment 1) or in terms of particles by placing detectors at the slits (experiment (4)). Both the wave view and the particle view are necessary to understand the quantum world. They can be seen as different sides of the same coin. Any experiment designed to show waves, will show waves, any experiment designed to show particles will show particles, however no experiment will be able to show both wave and particle pictures of the quantum world at the same time. It should be mentioned however that an experiment has been performed in Japan which shows the same photons acting as both wave and particle at the same time. (Gribben, 1995, 119-120).

††††††††††† The consequences of the Copenhagen Interpretation is that the observer plays a critical role in determining how the world is. The behaviour of atoms electrons and light depend on whether an observation is being made. If it is, then the wave function collapses and they behave as particles. If no observation is made, then electrons, atoms and light behave as waves as is shown by the phenomena of interference in the double slit experiment. The waves however are probability waves which do not have any material form; they are just mathematical concepts. Heinz Pagels in "The Cosmic Code" p144 states "There is no meaning to the objective existence of an electron at some point in space, for example at one of the two holes, independent of actual observation. The electron seems to spring into existence as a real object only when we observe it". Based on the results of the double slit experiments, Niels Bohr, the most prominent proponent of the Copenhagen interpretation, considered that whether you get waves or particles depends on the whole experimental set up including the electrons atoms or light, the holes, the detector screen and the human observer. If you set up the experiment in certain ways (egg one or two slits open, detectors at one or other of the two holes or no detector at the holes, deciding to have the detectors on or off after the electrons or photons have gone through the holes) you will get certain results. (Gribben, 1995, 14). The background to Bohrís Copenhagen interpretation of the quantum world and its questioning by Einstein is given in the paper Bohr v Einstein.

††††††††††† There is however a problem as the observer and the experimental apparatus are all made up of quantum entities, so how can the observation take place without another prior observation collapsing the wave function of the observer to bring the observer into existence. Who observes the observer?

††††††††††† The problem of quantum mechanical effects in the macro world is most dramatically shown by the paradox of Schrodinger's Cat. This can be illustrated in a number of ways. The simplest way concerns a closed box containing a single electron. The Copenhagen interpretation tells us the electrons probability wave fills the entire box. If a partition was lowered through the box to divide it into two, the probability wave would be evenly distributed between the two halves of the box as there is an equal possibility the electron will be in either half. Yet "common sense" tells us the electron must be in one half of the box or the other. However the Copenhagen interpretation tells us it is only when we look into the box, that the wave function collapses and the electron appears in one particular half of the box. The puzzle remains why should an act of observation collapse the wave function and cause the electron to come into existence.

††††††††††† A similar problem at the macroscopic level is revealed by the puzzle of Schrodingers cat. Quantum mechanical effects are assumed to apply at macroscopic level as macroscopic objects are made up of quantum entities. Schrodingers cat is placed in a chamber with a radio-active substance of which there is a 50% chance one of its atoms will have decayed within an hour. Should the atom decay a Geiger counter will detect this event and cause a hammer to break a flask containing a poisonous gas and so kill the cat. The common sense view is that after one hour the cat will be either alive or dead. However the Copenhagen interpretation considers that as the Geiger counter is made up of microscopic entities it is subject to the quantum mechanical rules and does not exist until an observation collapses its wave function. It is not until an observer opens the chamber that the wave function of the whole system collapses and the atom may or may not decay, the Geiger counter may or may not detect the radiation and the hammer may or may not break the flask and the gas may or may not kill the cat. Before the observer opens the chamber the Copenhagen interpretation considered the cat to be neither alive or dead but to be in suspended animation or a superposition of states. Alternatively the cat can be considered to be both alive and dead at the same time. Obviously a cat at any one time must be either dead or alive and it certainly cannot be both dead and alive. So what is happening in the box before it is opened and the wave function collapses? One view is that the cat itself is able to collapse the wave function so the cat is never both alive or dead or in a superposition of states. If the cat is able to do this would an ant, a bacterium or a computer also be able to collapse the wave function. If there was a human, sometimes called Wigner's friend, in the box instead of the cat no doubt he or she will collapse the wave function. After an hour when we open the box, Wigner's friend will either report nothing has happened or we will find the corpse of Wigner's friend. There is no case of a superposition of states here, but to a human outside the box the superposition of states remains. If the human opening the box is not actually being observed, if for example the building was sealed off to protect the experiment, then his or her wave function will not have collapsed. To the people outside the building, everything within the building will be in a superposition of states and this situation continues in an infinite regression. Is anyone observing the planet earth to collapse its wave function? Possibly any conscious being will be able to collapse its own wave function, in effect to be self actualising and to bring itself into existence.

††††††††††† A further variation of the experiment is to have an inflated balloon in the box and a sharp instrument that pops the balloon if the Geiger counter detects radiation. There is no question of a conscious observer collapsing the wave function before the box is opened, so the balloon, whether it is popped or not, remains in a superposition of states for conscious beings outside the box.

††††††††††† The Schrodinger's cat paradox is designed to show how ridiculous quantum theory is when applied to the macro-world. Yet as entities in the macro-world are all made up of quantum entities it would appear that quantum theory must apply in the macro-world. How can a macro entity, like a cat, exist if the quantum entities that make up the cat do not exist? Furthermore the phenomenon of superconductivity shows quantum effects operating in the macro world. It is possible to observe quantum effects on macro level instruments such as superconductor rings which may be several centimetres across and are of course made up of a vast number of atoms. This means it is not possible to say the rules of quantum mechanics apply only in the quantum world. (Davies, 1980, 128-129; Lindley, 1997, 176). It appears the same set of rules should apply to both the macro and quantum worlds and the rules that should apply are the quantum rules. So macro level measuring devices such as geiger counters, bubble chambers, photographic plates, cats and humans should not exist until they are observed.

††††††††††† If one accepts the standard Copenhagen view of the quantum world, quantum entities do not exist until they are observed. If one accepts the standard common sense view of the macro-world things continue to exist regardless of whether they are being observed. An attempt to accept both views would mean there must be a level where the rules of quantum theory cease to apply and the rules of classical physics begin to apply. It is however hard to pinpoint exactly where this level is and why it should apply.

††††††††††††††††††††††† There may however be a way around this problem. One way of seeing the macro world is that existence or reality can be seen as a relationship between the observer, the conditions of observation and the observed. Such a view would appear to reflect the facts of perception much better than either the idealist view that locates our perceptions exclusively in our minds and the realist view that there is a single objective reality "out there". Perceptual relativity shows the world varies with the observer and the conditions of observation creating insoluble problems for the realist single objective reality view while the complexity and variety of percepts suggest the presence of an external world. However if such an external world has a single form we can never know it. Rather all we can know off is the variety of worlds created by the relationship between our sensory apparatus, the circumstances of the observation and that unknown and unknowable entity, the external world, if it exists at all.

††††††††††† This is a view of the macro world but in many ways it is consistent with the Copenhagen interpretation and of the results of experiments, such as the double slit experiments, that reveal the quantum world to us. In the double slit experiment if only one slit is open or detectors are placed at one or other of the slits you obtain an observation that show light or a quantum entity to be a particle. If both slits are open we observe light and quantum entities as waves and the wave view also prevails if quantum entities or photons go through the experiment one at a time. Changing the means of observation, the experiment, results in a change in what one sees which is very like perceptual relativity in the macro world.

††††††††††† The view of the atom given to us by science also seems to be subject to perceptual relativity. John Gribben in Schrodinger's Cat says:


not only do we not know what an atom is "really" we cannot ever know what an atom is "really". We can only know what an atom is like. By probing it certain ways, we find that under those circumstances, it is "like" a billiard ball. Probe it another way and we find it is "like" a solar system. Ask a third set of questions, and the answer we get is it is "like" a positively charged nucleus surrounded by a fuzzy cloud of electrons. (Gribben, 1995,186).


Again we see that changing the method and conditions of observation, changes what we see.

††††††††††† The uncertainty principle is consistent with such a view of reality. The uncertainty principle as noted earlier states we cannot observe properties of quantum entities such as position and momentum at the same time as the measurement of one will disrupt the other, so making its measurement impossible. In other words the methods and conditions of observation determines what we will see. If we engage in one experiment we will observe the position of the quantum entity; another experiment will show its momentum.

††††††††††† One experiment that supports the Copenhagen Interpretation and the idea of an observer dependent reality began as a thought experiment in the 1930's but was actually carried out in 1981. The thought experiment was invented by Einstein, Podolsky and Rosen and became known as the EPR paradox. It was considerably refined and developed by John Bell in the 1960's. Bell worked out a way, known as Bell's Theorem, in which in principle it would be possible to carry out the experiment. Subsequently a number of attempts were made to carry out the experiment the most successful being that carried out by Alain Aspect in 1981.

††††††††††† The experiment was carried out on photons (particles of light) which have a property known as polarisation. Polarisation is the angle at which light waves vibrate in relation to their direction of motion. In practise they can vibrate at any angle but for the purposes of the EPR/Aspect experiment we can use just three angles of polarisation which we can describe as up, down and sideways.

††††††††††† The Aspect experiment involved an atom emitting two photons in opposite directions and then measuring the polarisation of each photon. The photons move apart at the speed of light so according to the theory of special relativity there is no possibility of a measurement carried out on photon 1 immediately effecting photon 2 as that would mean a signal has travelled faster than the speed of light. The polarisation of the photons is co-related in that if one knew the polarisation of one photon you also knew the polarisation of the other. Quantum theory holds that the photons do not have any definite polarisation until a measurement is made to detect their polarisation and that measurement brings the polarisation into existence. Einstein and his colleagues when inventing the thought experiment hoped to show that the photons had a particular polarisation from the time they were emitted from the atom so that there existed a reality independent of the act of measurement. Such a theory is known as a hidden variables theory as it assumes there is something not known to us which will ensure photons and their polarisation exist independently of the act of measurement. Einstein argued that if we looked at one of the photons and saw its polarisation then we would know the polarisation of the other photon as the polarisations were co-related. This showed the polarisation of photon 2 had a physical reality independent of the act of measurement. The requirement that there is no faster than light signalling stops the suggestion that photon 2 acquires its polarisation as the result of the act of measurement of the polarisation of photon 1.

††††††††††† Until John Bell produced Bell's Therom there was no practical way to carry out the experiment. The problem was that if one looked at the polarisation of the photons you could not tell whether the photons had their polarisation from the time they were emitted from the atom (Einstein's and the common sense view) or whether they only acquired it when we looked at the photons. Bell worked out that if we worked with three connected polarisation measurements, but only measured two of them it could in principle be possible to do the experiment. The measuring device would be set so that the photons had to have anyone of three possible polarisations, say up, down or sideways. The measuring device would give one of two possible measurements. If set to measure up polarisation it would give an answer of up or not up, if set for down it would give an answer of down or not down, or if set for sideways it would give an answer of sideways or not sideways. When a measurement was made on one photon, for instance its polarisation is found to be up, then we know the polarisation of the second photon must be either sideways or down and there is a 50% chance of it being either. Alternatively if the measurement of the first photon is not up, then the measurement of the second photon would be either up, down or sideways, but there would be a greater chance it would be up, rather than down or sideways. This is because the first photon may be down in which case the second measurement could be up or sideways or if the first photons measurement is sideways, then the second photons measurement would be either up or down. In this situation there is four alternatives and a 25% chance of each. However two of the alternatives are up, so the probabilities of the photon being up are 50% as against 25% for each of down and sideways.

††††††††††† The act of measuring the first photon changes the odds on obtaining a particular polarisation when measuring the second photon. Many measurements are required to be made to disclose a statistical pattern which is different if the photons acquired their polarisation when emitted from the atom from that which would apply if the photons acquired their polarisation at the time of measurement of the first photon. If the photons acquired their polarisation when emitted from the atom the particular pattern of measurement results that occurs would be produced more often than the pattern that results if the photons only acquired their polarisation when the measurement takes place. However the Aspect experiment and a number of similar experiments show that this does not happen. This result known as a violation of Bell's inequality means that when the photons are emitted they do exist in a superposition of states without any specific polarisation until a measurement is made of one of them.

††††††††††† The Aspect experiment is usually considered as eliminating any possible local hidden variable theories and leaving two possible alternatives for how the photon acquires its polarisation. One of these is non-locality, that a faster than light signal went from photon 1, due to the measurement of photon 1, to photon 2 and this is how photon 2 acquires its polarisation. This is the view supported by John Bell (Davies & Brown, 1986,48-50). The other alternative is that in conformity with special relativity, no faster than light signal happens and photon 2 does not acquire its polarisation until photon 2 is measured. This is the view suggested by Alain Aspect. (Davies & Brown,1986,42-43). Bernard d'Espagnat suggests, when considering the EPR experiment, that the common sense world view was based on three assumptions. The first is realism, that there is a physical reality independent of human observers. The second is induction and the third is locality. d'Espagnat suggests as a result of the violation of Bell's Inequality at least one of these three assumptions needs to be abandoned, modified or constrained. (Scientific American, November 1979, 128). Considering the substantial experimental support for locality and the widespread and usually successful use of induction it could be argued that realism should be abandoned.

††††††††††† One element of the Copenhagen interpretation that appears to be under threat is complementarity. Complementarity refers to the dual nature of quantum entities, such as wave/particle duality and states an experiment may show photons acting as waves or as particles but never as both at the same time. However an experiment suggested by Indian scientists and carried out by Japanese scientists has shown individual photons acting as particle and wave at the same time. The experiment involved sending individual photons towards two right angle triangular transparent prisms with a tiny gap between them of less than the wavelength of the light involved. Some of the light was reflected while some of it tunnelled across the gap between the two prisms. Detectors recorded the reflected and tunnelled light and counters were used to measure the reflected light and the light that tunnelled. The counters clicked in perfect anti-coincidence (never at the same time) confirming the photons were behaving as particles. If the clicks were at the same time this would mean the photons had split which means they would have had to be behaving as waves, as particles cannot split. As the clicking was anti-coincident the photons must have been behaving as particles. However half the photons tunnelled between the prisms and tunnelling involves acting as a wave. The same photons were acting both as a wave and particle at the same time which contradicts the idea of complementarity. (Gribben, 1995, 118-120). However such an experimental result would still be quite consistent with the view that our perception of reality is determined by a relationship between the observer, the observed and the condition of the observation. The experiment acts as an extension of our sensory apparatus and just as changes in our sensory apparatus will give us a different view of that which is observed, changes in an experiment will produce a different view of whatever is being observed. In these circumstances there is no great surprise in seeing photons appear as particles and waves at the same time. Experiments may well produce apparently contradictory results much in the same way that the size and shape of objects in the macro world vary with the position of the observer and colours vary depending on the sensory apparatus used to observe them and the light conditions.

††††††††††† The two qualities of wave and particle appear to be contradictory as particles are limited in space, may be at rest and rebound when they collide, while waves are spread out, inherently in motion and can merge together when they collide. It would be a contradiction to say "Light is both a wave and a particle" but there is no contradiction in the statement "Light observed by experiment a appears as a particle and light observed by experiment b appears as a wave." The different experiment, the different method of observation explains why the same phenomena appears differently under the different situations. Equally it would be a contradiction to say the table before us has a number of different shapes but it would not be contradictory to say "The table has different shapes when observed from different positions."

††††††††††† The idea that it is the act of observation that brings quantum entities into existence is quite consistent with the idea that reality (or the only reality available to us) consists of a relationship between the observer, the observed and the conditions of the observation. The reason why things in the macro world, such as tables, only exist when they are observed is that the only reality known and knowable to us exists in the form of phenomena (egg sense perceptions) and phenomena requires the participation of an observer for it to come into being. If the observer is not present, or looks away or closes his or her eyes then the phenomena or sense percepts disappear. Some might argue that even though the sense percept disappears the table remains. But they cannot tell us what it is that exists apart from the sense percepts. The only awareness we have of the table is the sense percepts and when they disappear we are left with nothing.

††††††††††† The situation in the quantum world differs from that in the macro world as in the macro world evolution has provided us with a set of senses that tend to give us a coherent view of that world. In the quantum world we have a variety of rather disjoint ways of seeing that world, so we can get contradictory and puzzling views of that world. When quantum mechanics says that electron spin or photon polarisation is indeterminate until observed it just means that one sensory apparatus or experiment will show spin or polarisation in one state, another will show it in a different state. We have different experiments and hence different sensory apparatus so we can see various different pictures of spin and polarisation.

††††††††††† There are a number of arguments that can be made against the view that the world is observer dependent. Alistair Rae in Quantum physics: illusion or reality suggests such an argument when he suggests that as different observers agree in their description of external reality the idea of the physical world not having an objective existence appears unreasonable. He gives the example of people driving cars at traffic lights, where the drivers all receive the same sensory impressions of red and green lights. He suggests that it is much more likely that the lights really exist than by coincidence the drivers brains and consciousness all change in similar ways so they all stop and go at the right time. (Rae,1986,68). This is quite true but there is a third explanation, that as all the drivers have very similar sensory apparatus they will all see the lights in the same way so they will all stop and go at the right time so there will be no accidents. Obviously if the sensory apparatus were different for instance if some of the drivers were colour blind then the red and green lights would be indistinguishable to those drivers and there would be plenty of problems at the traffic lights. However, generally drivers are not colour blind, their sensory apparatus work in more or less the same manner so they all see the colours the same way.

††††††††††† A further problem for the idea of an observer dependent world is that things are usually assumed to continue to exist when not observed. If I cease to look at a table, I lose my sense impressions of the table, but if I look back again I will see the table again. It is however going beyond what we can tell from such an experiment that the table exists when it is not being observed. All we can say is that the sense impressions disappear when you cease to look at something but that they return when you look at it again. If we look at the table again, after having turned away from it, we will see it again. This is known as the permanent possibility of perception, that whenever a certain sensory apparatus is directed at a certain point in space and time it will always produce the same sense percepts. This is not evidence that a table exists other than as the sense percepts but that the relationship between the observer, the table and the conditions of observation is consistent over time. (Mill, 1889, 230-234).

††††††††††† A further criticism of the observer dependent world is contained in Paul Davies Other Worlds. He gives the example of a Geiger counter measuring the decay of a radioactive nucleus with a pointer on the Geiger counter indicating whether or not the decay has taken place. Two successive photographs are taken of the Geiger counter pointer at time of the experiment. The first photograph was given to scientist A and pocketed, the second photograph is given to scientist B who looks at it and according to the Copenhagen Interpretation collapses the wave function of the Geiger counter pointer. Davies suggests that when A looks at his photograph and it shows the same as the second photograph given to scientist B, there is a case of backward causation. (Davies,1980,134-135). This however is not necessarily the case. If one observer makes an observation and collapses the wave function of any quantum or macro system, he or she does not necessarily collapse it for any observer other than him or her self. In short the collapse of the wave function is a personal matter between the observer and the observed. When scientist B looks at the photograph it only brings the Geiger counter pointer into existence for scientist B. Scientist A remains ignorant of the result of the experiment until he or she looks at the photograph given to his or her self. The causation chain runs not from photo 2 to photo 1 but from the taking of photo 1 to scientist A looking at photo 1. No backward causation is involved.

††††††††††† Yet another problem suggested for an observer dependent universe is that the observer must exist before the observer can make an observation. This means something must observe the observer to collapse his or her wave function before he or she makes an observation. Equally who or what observes or collapses the wave function of the being that observes the original observer. This obviously goes on in an infinite regress with no solution to the problem. (Davies,1980,134-135, Gribben,1984,205-207). A related problem is when the first conscious being evolved what collapsed its wave function and brought it into being. The answer to these problems is that conscious beings are self actualising, they collapse their own wave function, they bring themselves into existence. The first thing any conscious being must be conscious of is itself or possibly consciousness of self occurs simultaneously with the first observation of anything external to itself. If a being can observe something external to itself, there is no reason to believe it cannot observe itself and that both observations can be simultaneous.

††††††††††† A further problem sometimes posed for the observer dependent world is that there was once a time when there were no human or other observers of any kind so how could events such as the big bang and the formation of stars and galaxies take place? This question was put to Rudolf Peierls in The Ghost in the Atom (Davies & Brown,(ed),1986,75) who suggested the information we had now of such events allows us to be aware of what has happened before observers were present and so in a sense we are still able to observe the past. More particularly what is being talked about when an observer dependent universe is discussed is the world of phenomena, which is the only world available to us. This however does not exclude the possibility of things happening outside of our world. Our world, the phenomena and sense perceptions we perceive is limited to the information that can be provided to us by our five senses and to any additional information that may be obtained by scientific experiment. There is however good reason to believe there may be plenty going on beyond our world and things such as the big bang and the formation of galaxies before we became aware of them would be examples of such things beyond our sensory perception and scientific experimentation.

††††††††††† The view that reality consists of a relationship between the observer, the observed and the conditions of the observation has a number of advantages. It avoids the necessity of having different rules for the macro and micro worlds; having to draw a line between them and having to explain why the two worlds are different. It avoids the problem of how macro entities such as people exist while unobserved, while their constituent sub atomic parts do not exist until they are observed. It explains the puzzle of perceptual relativity in the macro world and gives the same account for puzzles in the quantum world such as wave/particle duality.

††††††††††† Many scientists however seem reluctant to abandon realism, usually it seems due to a misunderstanding of what the abandonment of realism would mean. This was actually expressed by d'Espagnat when he suggested the abandonment of realism would "trivialise the entire scientific enterprise". (Scientific American, November 1979, 139). However this is not the case as science can be carried out perfectly as it has been in the past regardless of whether one accepts realism or not. As David Lindley suggests, what is necessary for science is that scientists doing the same experiments will get the same results. There is no need to assume that those results relate in anyway to an underlying single objective reality. The assumption of an underlying single objective reality is totally unsupported by any experimental or other evidence and is described by Lindley as a leap of faith, rather than of scientific necessity. (Lindley,1997,159-161). In fact there is plenty of evidence from quantum mechanics and from perceptual relativity in the macro world to suggest there is no single observer independent reality knowable to us. The facts support an observer dependent world, only prejudice or "leaps of faith" support the observer independent realist world.


The consequences of perceptual relativity


††††††††††† The effect of perceptual relativity in the macro-world and the Copenhagen Interpretation of the quantum world is that it is necessary to distinguish two different types of reality. The first type of reality concerns whatever causes light to be reflected or vibrations in the air, the "thing in itself" or "noumena" referred to by Kant. We have no idea what this type of reality is like and in principle this world is unknown to us.

††††††††††† The second type of reality consists of sense perceptions themselves, the sights we see, the sounds we hear etc. This is the reality that exists for human beings and all other living things. We can call this reality, again using Kant's terminology, phenomena. This reality is totally based upon our sense perceptions. Our sense perceptions are all we can know and phenomena is the only reality available to us. Phenomena has no fixed form, it changes with the sense organs used to observe it. There is no reason to believe there is any relationship at all between what we perceive in phenomena and what possibly causes the sense perceptions in noumena. If we remove the observer then phenomena will vanish while noumena (whatever that is) may continue to exist. Phenomena is however fixed in that if we perceive it with the same sense organs it will always be the same. If the perceiving apparatus remains the same, phenomena remains the same. This gives coherence and consistency to our sense perceptions.

††††††††††† There are three states of existence or of a conscious beings relationship with reality. They are:


1) that which cannot be perceived when a sensory apparatus attempts to observe it.

2) that which could be perceived if observed by a sensory apparatus, but is not currently being observed.

3) that which is being observed.


A clear distinction needs to be made between that which is not being observed but which could be seen when looked at and that which could not be seen even if it was looked at. The former we do not have a sense perception of but we could have if an act of observation was made. The latter can be considered as not existing for the particular sensory apparatus attempting to make the observation. This however does not mean another sensory apparatus may not be able to make the observation. The failure to make the distinction has caused some confusion in the past some philosophers claiming that if there is no sensory perception of something, such as the moon, then it does not exist. This would be true in the sense of existence referred to in 2) above, but not true in the sense of existence in 1) above. The moon remains perceivable by ordinary human senses even when not being observed so it cannot be said to not exist in the sense of 1) above but it could be said not to exist in the sense of 2) above.

††††††††††† The situation appears to be that if human senses are increased or decreased in any way the human view of the world is altered. If a sense is eliminated, for example, through blindness, deafness or some other cause the person's view of the world will be different. If an additional sense is added the persons world view is changed by the information received through the additional sense. Equally if an existing sense is improved for example sight or smell we would be able to see things we could not previously see and perceive smells that we could not previously smell. This means the world is sense dependent. If you alter the sense, you alter the world. The reality we perceive seems to be totally sense dependant and is in fact not "that which is out there" but is a relationship between "that which is out there" and our sense organs. If there is an infinite number of types of senses, then there must be an infinite number of types of worlds. There seems to be no reason why we should regard the range of senses as being limited to the five human senses. That a range of sense organs much wider and different from our own exist can be seen most easily from the animal world. It is well known that many animals can sense things that humans cannot. Dogs for example can hear sounds and perceive smells that humans would be completely unaware of. This however merely involves an extension of senses that humans have. Some animals have senses quite different from anything humans possess and live in a world way beyond our imagination. Dolphins and bats have a form of sonar and radar which enables them to detect obstacles and prey. Some snakes such as pit vipers have temperature receptors sensitive enough to detect objects 0.1 warmer or cooler than their background. They can detect the warmth of a human hand from a distance of one foot. Many fish are able to generate electric currents and have organs capable of detecting any distortion in the electric field caused by objects in the electric field. Other animals such as birds, lobsters and even bacteria appear to be able to detect the earth's magnetic field and in the case of birds and lobsters are able to use this ability to assist their migrations over considerable distances.

††††††††††† An important property of all senses is that they have thresholds. Furthermore different senses have different thresholds, for example cats dogs and humans will all have different visual, aural and nasal thresholds; each will perceive the world differently from the others, each will perceive things the other will not and will fail to perceive things the others will perceive. This means that if you change sense organs the effect is to obtain a different set of sense perceptions, than if something is observed by a single sense organ or set of sense organs. The effect of thresholds is that for each individual and each species there is a reality that each individual and species can perceive and other realities lying beyond the individual or species sense perception.

††††††††††† Each sensory world can be described in a number of ways. A world can be described as a set, the sum total of all sensory perceptions produced by a given sensory apparatus, will constitute the set. Within a given species there will be a great overlap between each individuals set of sensory perceptions due to individuals having very similar sensory apparatus. Insofar as individuals sensory worlds within a species vary the variation is mainly but not exclusively caused by those individuals different positions in space and time. Between species there will be much less overlap due to the rather more varied sensory apparatus between species or there may be no overlap if the sensory apparatus are sufficiently different. Let us for example look at being A, a human being. Being A can see certain shapes and colours, can perceive a rather limited range of smells, can hear certain sounds, taste various tastes and feel certain things and not others. Being B for example a cat will see some things that the human will not see, but will fail to see some things the human will see. The cat will certainly smell things the human can not and taste and feel things that humans can not and fail to taste and feel things that humans can. The end result is that there is an overlap between the humans and cats sense perceptions, but there are also some sense perceptions only the human will receive and other sense perceptions only the cat will receive. Another being might have sensory apparatus sufficiently different from those either of a human and a cat so there is no overlap between its sensory perceptions and those of a human or a cat. This can be represented diagrammatically as follows:


††††††††††††††††††††††† Human†††††††††††† Cat†††††††††††††††††††††††††††††††††††††††††††††††††††††† Other Being






and analysed in accordance with set theory.

††††††††††† Sense perceptions can also be analysed mathematically by using the threshold levels for sight, hearing, smell, touch and taste all of which can be, or can potentially be, given numerical values. Everything within the thresholds will be in an individuals world or species world; everything outside the thresholds will, subject to the use of science and scientific apparatus to extend sensory perceptions, be outside the individuals or species world. These threshold based worlds are similar to the set of sensory perception worlds referred to earlier and illustrated by the above diagrams, but the threshold based worlds are based on the capacity of the individual or species sensory apparatus while the sets of sensory perception are based upon what the individuals or species actually perceive.

††††††††††† It is possible to conceive of a continuum of possible sensory apparatus, infinite if the range of sensory apparatus is unlimited and finite if the range of sensory apparatus is limited. In principle it should be possible to map the total possible sensory apparatus potentially available to any being and to be able to place any individual being or species (or sensory apparatus) on a particular position on that map. A separate map could be produced for each separate sensory apparatus and it may be possible to combine such maps, in some multi-dimensional way, to produce a map of the total sensory universe and each individual's and species position on the map. This would mean each being or species could be placed on a map grid showing where their sensory world is and the grid as a whole would show the total possible sensory universe.

††††††††††† In physics an event is something that takes place at a particular point in space and a particular point in time. It can be specified by three spatial co-ordinates and a single time co-ordinate to give its position in space-time. However for an event to have its position more completely stated it should have its position in the sensory perception continuum specified. This is because an event may occur at a particular point in space and time but may be perceivable by certain beings and not by others. More particularly an event may occur in space-time and be perceivable by human beings and another event may occur in space-time and may not be perceivable by human beings, but each event would be as real as the other. For the location of an event to be specified exactly it must not just have its position in space-time established but also its position in the sensory continuum. This would enable us to know in which or whose sensory world the event took place and what sensory apparatus may be used to detect the event.

††††††††††† It is necessary to add the sensory position (or situation) of an event to its position in space-time. This enables us to explain why one observer can look at a table and see a solid brown object while another, say a scientist, would conclude that it is largely empty space sparsely inhabited by particles such as protons, neutrons and electrons. By adding the sensory position of any event, to its position in space-time, it is possible to explain why something, such as a brown table, is seen by human beings and something else such as electrons, protons and neutrons are not seen even though they occupy the same position in space-time. The sensory position of an event is the same as its position in space-time in that if one observed a point in space at different times or made observations at the same time but directed to different points in space you would observe different events. Equally with different sensory apparatus observing a single point in space-time, the observer will see a different event. One obtains a different event by changing any of the co-ordinates of space, or of time, or of the sensory situation of the event.

††††††††††† A more formally logical way of presenting the above argument, with "a world" being defined as that which can be perceived by a conscious being through its senses, is as follows:


††††††††††† 1) There is no way in which we can know the world, other than through our senses. The only reality we can know is phenomena.

††††††††††† 2) Our senses give us only some information about the world.

††††††††††† 3) The things we can perceive can be considered to be in our world, the things we can not perceive can be considered to be in other or different worlds.

†††††††† 4) As there are many things we cannot perceive there are many worlds other than our own.

††††††††††† 5) There is no reason to consider that any world is more real, more true, more valid than any other world.

†††††††† 6) Any one world is as valid and real and true as any other.

††††††††††† 7) There is a wide variety of senses and each sense has thresholds which limit perception.

†††††††† 8) There must be a wide variety of worlds.

††††††††††† 9) As the senses of different people and species overlap some of the worlds overlap.

††††††††††† 10) As any being may have senses which are quite unlike those of any other being many of these worlds will not overlap. Such beings will live in totally separate worlds from those of other beings.

††††††††††† 11) There seems to be no reason to believe there is a finite limit on the range of potential sense organs.

†††††††† 12) There is no finite limit on the number of potential worlds that may exist.


††††††††††† There seems to be no such thing as a single reality available to human beings. There are in fact an infinite number of realities as there are an infinite possible range of senses and an infinite range of perceptions by each sense. In order to understand this it is necessary to distinguish that which is capable of being perceived by senses and that which is not. That which is capable of being perceived by our senses exists in our world and that which is not is in another world.

††††††††††† A categorisation of the range of worlds that can exist is as follows:


1) Each person has their own individual world. This is the world they perceive which is always different from the world perceived by others. Variations exists from person to person due to each person occupying different points in time and space and due to the quality of the individual persons sense organs.

2) Each species has its own world due to the tendency for each species to have the same sense organs which will tend to function in the same manner and to the same degree within each member of the species. This we could call the species world which can be sub-divided into each species world egg, the human world, the dog world, the bat world, the ant world etc. Possibly one could also talk about plant worlds as plants to appear to have some ability to sense things around them for example, light.

3) In any particular environment there is likely to be a certain set of sense organs available to species inhabiting that environment. For example at the bottom of the ocean where no sunlight penetrates, the life forms do not have the sense of eyesight.

4) It is possible to imagine a being with any type or types of sense organs capable of detecting anything at all. Whether that being exists according to human sense organs matters not at all. It would be possible for a simple object such as an apple as perceived by human sense organs to be perceived by our imaginary being as nothing at all, if it was unable to perceive the apple, to absolutely anything at all depending upon what sense organs our imaginary being possesses.

††††††††††† All of the above worlds are equally valid or realistic. There seems to be no good reason for favouring any one of them (including the human view of the world) over any other of them. It seems impossible to claim that the human view of the world has any special claim to validity when an alteration of our senses will give us different sense perceptions. How can you say what you perceive is, when you can perceive the same thing with different sense organs and it can be something quite different? If the human view was to be preferred it would be no more than a case of a human centric view of the world that is not capable of any real justification.


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Philosophy and Perception


Armstrong, D. M. (1961) Perception and the Physical World, Routledge & Keegan Paul: New York

Audi (ed) (1995) The Cambridge Dictionary of Philosophy, Cambridge University Press, Cambridge

Ayer, A J (1956) The Problem of Knowledge, Penguin Books: London

Berkeley, G (1710) Treatise concerning the Principle of Human Knowledge

Broad, C D (1965) Some Elementary Reflexions on Sense Perception in Perceiving, Sensing and Knowing (ed) Swartz, R: University of California Press, Berkeley

Broad, C D (1965) The Theory of Sensa in Perceiving, Sensing and Knowing (ed) Swartz, R: University of California Press, Berkeley

Chisholm, R M (1965) The Theory of Appearing in Perceiving, Sensing and Knowing (ed) Swartz, R: University of California Press, Berkeley

Cresswell, M J Jackson on perception in Theoria Vol.XLVI (1980) Part 2-3

Davies, P C W (1977) Space and Time in the modern universe, Cambridge University Press: Cambridge

Hoffman, Donald D. (1998) Visual Intelligence, W.W. Norton & Co:New York

Jackson, Frank (1977) Perception, Cambridge University Press: Cambridge

Kaku, M (1994) Hyperspace, Oxford University Press: Oxford

Kelly, David (1986) The Evidence of the Senses, Louisiana State University Press: Baton Rouge

Kline, M (1959) Mathematics and the Physical World, Thomas Y Crowell Company: New York

Kline, M (1980) Mathematics, Oxford University Press: New York

Locke, D (1967) Perception and our Knowledge of the External World, George Allen & Unwin Ltd: London

McKeachie, Wilbert J and Doyle, Charlotte L, (1966) Psychology, Addison-Wesley Publishing Co Inc: Reading, Mass

Mill, J. S. (1889) An Examination of Sir William Hamilton's Philosophy: London

Russell, B (1912) The Problems of Philosophy, Oxford University Press, Oxford

Schiffman, H. R. (1982) Sensation and Perception, John Wiley & Sons: New York

Smart, J. J. C. (1963) Philosophy and Scientific Realism, Routledge & Keegan Paul: New York


Quantum Theory


Baierlein, R (1992) Newton to Einstein, Cambridge University Press: Cambridge

Cushing, James T. & McMullin, E. (1989) Philosophical Consequences of Quantum Theory, University of Notre Dame Press:Notre Dame, Indiana

Davies, Paul (1980) Other Worlds Penguin Group: London

Davies, P. C. W. & Brown J. R. ed (1986) The Ghost in the Atom, Cambridge University Press: Cambridge

d' Espagnat, Bernard The Quantum Theory and Reality, in Scientific American, November 1979, 128-140

Feynman, R, Leighton, R & Sands, M (1965) The Feynman Lectures on Physics, Mass: Addison-Wesley

Forrest, Peter (1988) Quantum Metaphysics, Basil Blackwell:Oxford

Gibbins, Peter (1987) Particles and Paradoxs, Cambridge University Press: Cambridge

Gribbin, John (1984) In Search of Schrodinger's Cat, Black Swan:London

Gribbin, John (1995) Schrodinger's Kittens, Phoenix: London

Healey Richard (1989) The Philosophy of Quantum Mechanics Cambridge University Press: Cambridge

Herbert, Nick (1985) Quantum Reality, Anchor Press/Double Day:Garden City, New York

Hey, Tony & Walters, P (1987) The Quantum Universe, Cambridge University Press:Cambridge

Krips, Henry (1987) The Metaphysics of Quantum Theory, Clarendon Press: Oxford

Lindley, David (1996) Where does the weirdness go, Vintage: London

Mermin, N. David (1990) Boojums all the way through, Cambridge University Press: Cambridge

Mermin, N David Is the moon there when nobody looks? Reality and the quantum theory in Physics Today April 1985 38-47

Rae, Alastair (1986) Quantum Physics: illusion or reality, Cambridge University Press:Cambridge

Ridley, B. K. (1976) Time, Space and Things, Cambridge University Press: Cambridge

Wolf, Fred Alan (1981) Taking the Quantum Leap, Harper & Row: San Francisco

Zohar, Danah (1991) The Quantum Self, Flamingo: London