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Would the concept of empty space exist without depth perception?

  1. Nov 2, 2003 #1

    Eh

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    For the past few thousand years or so, the philosophy of space has occupied a lot of time among philosophers. There is really no argument as to the traditional definition of "space" as it usually relates to volume, being length width and breadth. But the big debate has typically been over the concept of empty space. That is, space that exists but does not contain any matter. On one hand, you had folks like the atomists arguing that empty space does exist, and has independent existence of matter contained in it. On the other hand, there were the philosophers who argued that space was merely a property of physical objects, and so there could be no space without matter.

    This debate really went unsettled until the past 80 years or so with the findings of modern science. Descartes and friends would be happy with the results, because modern physics suggests that there can be no space where there is no "thing" present, or more precisely a field.

    But one interesting question is how the debate ever got started in the first place. In other words, what causes one to think about the notion of "empty" and "filled" space in the first place? This may sound more like a question of psychology, but it has importance in the philosophy of space as well. Here's what I'm thinking.

    If we start with our everyday experience of physical objects, we can see that space does appear to be a property of things. Actually, we never actually *see* volumes, and no known human being has experienced anything in 3 dimensions. We only ever experience a 2D image of the outside world, with 2D geometrics from the retina being processed in certain areas of the visual cortex. From this 2D slice of space we form the concept of different objects through the different colors. Different areas of the plane we experience have different colors, and so we can make out the difference between a tree and the sky. And so we come to relate "substances" or "objects" with color. Any time we imagine a physical object, it necessarily has a color. There is no concept of an empty area, because there is a color at each point in our viewing space.

    But area is not the whole story, because we also have the concept of volume. Even though we only experience 2 dimensions, visual cues such as the differing sizes of objects, shadows and motion gives us depth perception. Through this we have the concept of the 3rd dimension, and objects with volume. But because we are able to view objects at differing distances, we understand that there must be invisible space in between us and such objects. IOW, we imagine that in the outside world, there are large volumes of space which cannot be seen, and that in turn leads us to think there are no objects present in this distance. Of course, if our brains are processing the data from light hitting our retinas, then there must necessarily be regions of space which are not emitting light. So invisible space must be a fact.

    What I'm thinking is that humans have taken depth perception and mistakenly believed invisible and visible space to be fundementally ontologically different. It seems silly that we would do such a thing on the basis of mere vision. It would be like calling AIR nothingness or a void because we can't see it. This intuition seems to be hard to shake, because imagining empty space as just another thing is difficult. In order to think of some geometric object, we must give it a color, and giving empty space any kind of color (so as to imagine it as a substance) feels unnatural. We can only imagine an empty volume through the relations of 2 dimensional objects, so I can at least understand why inution alone would lead us to the idea of some ontologically different and "empty" kind of space. But this would be a case of intuition alone leading to horrible reasoning.

    So without our perception of depth, what would happen to the philosophy of space? What if we lived in a world where the air glowed bright, so as to prevent our ability to perceive depth? We would still see motion of objects through space, but only as other objects (colors) were displaced. I'm wondering if there would have ever been a debate between proponents of relationalism and substantialism. There might be no atomists void, no debates between Newton and Leibniz, and no theologians loosing sleep over the issue.

    Well, it's an idea anyway. Though it would seem silly that such a hotly debated issue with a long history could come from a simple trick of the brain.
     
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  3. Nov 3, 2003 #2
    You make an interesting point, Eh. I think that last part, about a world where we don't have depth perception, and we percieve things as moving only in that they displace something else, sort of coincides with the Relativistic philosophies. I mean, didn't Einstein say that there is no such thing as space independent of points of reference?
     
  4. Nov 3, 2003 #3
    Depth Perception

    Another pertinent point would be those humans suffering blindness.
    An astrophysicist friend of mine is blind, and as such, he has no visual depth perception at all and never has.
    He thinks of space and matter as being interchangeable and thus no different in substance or matter. He compares space to a reflection of matter (in crude English). Sometimes I think he sees things more clearly than those of use who can be “tricked” by our eyes.
     
  5. Nov 4, 2003 #4

    Eh

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    He said a great deal on the subject. On that point, one argument used by the ancients for empty space goes as follows: If everything was essentially the same substance, the universe would be a solid mass. No motion would be possible. If we only experienced 2 dimensions without depth, we'd probably be more inclined to believe that space is a dynamic property of all objects, rather than being a fixed background stage for things to move about on.
     
  6. Nov 4, 2003 #5

    Eh

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    Re: Depth Perception

    That's interesting because I've always wondered how a blind person would think of space. Sure, they feel it and can navigate through 3 dimensions, but without vision they surely must have a very different philosophy of it. The question is, how blind? A lose of depth perception is one thing (since you would still have at least some idea of what space is), total blindness is another.
     
  7. Nov 4, 2003 #6
    Maybe, except that we would be conscious of the Universe in terms of lines. IOW, we would not see ourselves as "flat", each figure would seem like a straight line, and thus we might still have the same imparements on our abilities to conceive of space as it really is.
     
  8. Nov 4, 2003 #7

    Eh

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    Only if we are talking about 2D people experiencing 1D vision. If there was some kind of fog or such (you'll have to use your imagination here) that prevented us from seeing depth, we could still see length and width.

    I guess the same would apply for someone with a vision problem but who is not quite blind. If you think of a species that evolved with such limited depth perception, we would have 3D people who still only have an intuition for 2 dimensions. It is hard to imagine how any intelligent life could survive without good sight, but it's a useful comparison anyway.
     
  9. Nov 4, 2003 #8
    And how would these have a better concept of the dynamics of spacetime?
     
  10. Nov 4, 2003 #9

    Eh

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    Consider that they wouldn't have any concept of depth or "empty" space. As a result, they wouldn't make the mistake of assuming the existence of a fixed background of space (which is somehow fundementally different)in which matter and physical objects move about in. That is the atomists void, and Newtons absolute space.

    In 2 dimensions, philosophers with no depth perception would see that space (in this case just area) is a property of all objects experienced. They would then skip the question of empty space and focus on how the different objects are actually different. A modern example would be, how is a quark fundementally different than a lepton? Only being able to see areas of substances would eliminate the concept of any kind of void, I think. Think back, and try to remember what your first reaction was the first time you heard about spacetime being curved. How many of us thought: how can space which is nothing, be curved?

    Without depth, we'd see space as a property of objects and the question of Non Euclidean geometry would be a lot easier to fathom.
     
  11. Nov 4, 2003 #10
    Very good points. I think you're right.
     
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