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Question about Space -- Is Space itself a 4th dimensional object?

  1. Dec 16, 2014 #1
    Ok, so I was just in physics class today and we were talking about special relativity... anyways, the instructor refered to how the universe is expanding, and so much so that there are places we could never ever get to because it's expanding fasterling than the speed of light. Anyways, this got me thinking about Space itself and I was wondering. Is Space in of itself a 4th dimensional object? Because clearly it can't be NOTHING if it is expanding... right? It's just intangible to us... so couldn't it just be a really big object perpendicular to the 3d matter on/in/around it?
  2. jcsd
  3. Dec 16, 2014 #2
    The local topology of our universe is 3-dimensional so spacetime also has 3 spacial dimensions.
  4. Dec 16, 2014 #3


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    Science Advisor

    This is not quite correct. See:

    Space-time is 4D, space is 3D

    See this similar question:
  5. Dec 17, 2014 #4
    Space is 3D where we have (x,y,z), then we add the third component, time or t, then we have (t,x,y,z) a 4D; which is why we call it Space-time. This t is most affected by massive objects such as black holes which not only bent space but also time.
  6. Dec 17, 2014 #5


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    Gold Member

    No, space is not a thing. The expression 'space is expanding' is a misnomer. It is more accurate to say the distance between distant objects is expanding.
  7. Dec 17, 2014 #6
    So what I'm getting... that time is the 4th dimension, which is what I always thought. But then I saw several other places that changed the way I saw it. The first dimension would be considered a line. 2nd dimension is a square, which is simply a shape perpendicular to the 1st dimension. We can all agree with that as well, yes? So the third dimension is perpendicular to a square, or the second dimension. So the fourth dimension must be perpendicular to the third. That's where the tesseract come from. A 4d cube. If I'm correct, this is what the string theory operates on, 11 dimensions, all perpendicular to the dimension before it. So how then is time the 4th dimension... these 2 theories, einstein's and the string theory seem to conflict...
  8. Dec 17, 2014 #7


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    Staff: Mentor

    Those dimensions are all spatial dimensions, and some of the string theory ones are very weird indeed. String theory is not an accepted mainstream theory (meaning that there's not enough evidence to use it over competing theories) at this time, so even though string theory and GR conflict, we don't have a problem. GR has plenty of observational evidence to support it over competing theories. String theory has little if any.
  9. Dec 17, 2014 #8
    Ok, thanks, that helps alot!
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