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Thread: 4th dimension

  1. #1 4th dimension 
    Forum Ph.D.
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    i dunno, i thought this was interesting:

    http://teamikaria.com/hddb/classic/introduction.htm

    learned a bit. its also interesting that the 2d world can be represented with 2 world axis and a third one for time. so time in 2d space would effectively be moving through the 3rd dimension, and seeing this, would more or less be "tubes" in a 3d world
    does that mean time is essentially our universe moving through the 4th dimension?


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  3. #2  
    Forum Radioactive Isotope MagiMaster's Avatar
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    It's not that simple. The 2d universe your talking about is like a flat sheet of paper moving straight upward. Our 3d universe isn't flat. It's more like a wavy sheet of rubber and it isn't even moving straight upwards.


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  4. #3  
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    I remember a lecture of Carl Sagan on this matter.It was really good how he explained the concept of dimensions.Here take a look
    http://www.youtube.com/watch?v=UnURElCzGc0
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  5. #4  
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    Quote Originally Posted by MagiMaster
    It's not that simple. The 2d universe your talking about is like a flat sheet of paper moving straight upward. Our 3d universe isn't flat. It's more like a wavy sheet of rubber and it isn't even moving straight upwards.
    but the general concept is similar thats what i'm getting at.
    when you have eliminated the impossible, whatever remains, however improbable, must be the truth
    A.C Doyle
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  6. #5  
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    Quote Originally Posted by mr.science
    I remember a lecture of Carl Sagan on this matter.It was really good how he explained the concept of dimensions.Here take a look
    http://www.youtube.com/watch?v=UnURElCzGc0
    yes, i've seen it. the link that i posted uses sagans concepts and goes into further detail in explaining the differences between thinking in 3d and 4d, as well as some very interesting concepts, like a 4-dimensional being being able to pick up a 3-dimensional object, manipulating it and putting it back, in a way that seems impossible for a lower-dimensional being. like the example of plucking a piece of chainlink from a chain whole, and putting it somewhere else, or using a hypernail to nail a 3-dimensional object like a safe in mid-air.
    when you have eliminated the impossible, whatever remains, however improbable, must be the truth
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  7. #6  
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    Quote Originally Posted by dejawolf
    Quote Originally Posted by MagiMaster
    It's not that simple. The 2d universe your talking about is like a flat sheet of paper moving straight upward. Our 3d universe isn't flat. It's more like a wavy sheet of rubber and it isn't even moving straight upwards.
    but the general concept is similar thats what i'm getting at.
    Almost.

    The problem is that the sheet represents now, but in GR, now isn't so straightforward. So yeah, it's similar, but with some important differences.
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  8. #7  
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    Quote Originally Posted by MagiMaster
    Quote Originally Posted by dejawolf
    Quote Originally Posted by MagiMaster
    It's not that simple. The 2d universe your talking about is like a flat sheet of paper moving straight upward. Our 3d universe isn't flat. It's more like a wavy sheet of rubber and it isn't even moving straight upwards.
    but the general concept is similar thats what i'm getting at.
    Almost.

    The problem is that the sheet represents now, but in GR, now isn't so straightforward. So yeah, it's similar, but with some important differences.
    ok. just had to make sure i was going in the right direction, and not getting lost.

    by wavy sheet of rubber, you're talking about time dilation, and such?
    when you have eliminated the impossible, whatever remains, however improbable, must be the truth
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  9. #8  
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    In this analogy, time dilation would be how different parts of the sheet are travelling upward at different relative rates, and the waviness would be from gravity. Of course, the two are related. This is near the edges of my understanding, so I'm hesitant to try and extend this analogy any further.
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  10. #9 Re: 4th dimension 
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    Quote Originally Posted by dejawolf
    does that mean time is essentially our universe moving through the 4th dimension?
    In GR time is much more subtle than that. Except as an approximation in simplified models there is no such thing as a global time. Time is a local concept and one cannot compare "time here" with "time there". Similarly space is also a local concept.

    On a local basis, as an approximation, time is "the 4th dimension". But the space is Minkowskian, not Euclidean. That is the perspective of special relativity. Special relativity is a local approximation to general relativity, so this can all be fit together in the big picture.
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