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Dimensions and relative magnitude

  1. Jun 16, 2011 #1
    Why is it that things appear smaller the farther they are away and bigger the closer they are away? It is almost as if the magnitude of their dimensions (length, width, and height)changes. But in reality it is still the same object.

    My cup x distance closer to me than the door may appear 1/6th size of the door itself. It is not as if the object got bigger but it seems as if.

    Why do things seem bigger or smaller in relative distances through space? It is interesting because things seem to change size close to the speed of light (lorentz contraction).
  2. jcsd
  3. Jun 16, 2011 #2


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    The two effects are not related. The difference in size due to distance is simply caused by angles. Drawing two lines from your eye to opposite sides of an object, you can see that the closer an object is, the greater the angle between the lines, meaning it takes up more of your field of view.

    Lorentz contraction is the result of an object not being able to travel faster than c. I can't explain very well, but I'm sure that a search on Lorentz Contraction here on the forums would yield plenty of good results.
  4. Jun 16, 2011 #3
    I'm aware of the triangle and angle explanation. It does not satisfy me. I feel that its too simple, there is might be more to it.

    For examples, what causes you to interpret different sizes? Well first you must see the objects, for that your neurons register photons. But how does photons coming from different angles causes the object to appear larger or smaller?

    Is this just simple three dimensional physics or are there other implications of it...
    Last edited: Jun 16, 2011
  5. Jun 17, 2011 #4
    The apparent linear size of the object is relative to the background or other objects near by.
    Your eye only produces information about the angular size of the object. When there is no reference around you cannot tell if you see a big object far away or a small one much closer.
    So there is no direct information about the linear size of the objects in the raw signal from the eyes and even less in the photons. It's all in the software (and training of it).
  6. Jun 17, 2011 #5


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    I would say simple 3d physics.
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