
#1
Dec1704, 10:31 AM

P: 170

Do we live in a 4 or 5 Dimensional Universe?
If Einstein had been told before writing SG and GR, that we live in a 5 Dimensional Universe, in which we can only see or detect the properties of the 4th Dimension, at speeds approaching the light speed. Would he have given another name to the 4th Dimension, to what we now call Time? In the quantum world is a clock not just another ruler? In a quantum world if you try to measure something you affect the result you are trying to measure, including time.  but the same can be said inside every black hole, where there is a singularity, the 4th Dimension is zero, but the Gallaxies still move on. Any answer to one or all above questions would be appreciated. Regards Terry Giblin 



#2
Dec1704, 01:23 PM

Emeritus
Sci Advisor
P: 7,436

It should be pretty clear, I think, that the universe has only 4 directly measurable dimensions  3 space and one time.
KaluzaKlein theory points out that if you consider that there is an unobservable fifth dimension, one can explain electromagnetism in geometric terms. The hypothetical fifth dimension is not directly observable, however . One often considerers the hypothetical, unobservable fifth dimension in KK theory to be "rolled up". This idea has found further expression in string theory, where the universe is considered to have 10 (or maybe it was 11) dimensions, with most of them "rolled up", and not directly observable. But for directly observable dimensions, we have only four. I'm not sure what you are thking of as the "fifth dimension", though I suspect you are taking embedding diagrams too seriously. Why you think high velocities has anything to do with dimensional structure is also a bit of a mystery. 



#3
Dec1804, 12:41 PM

P: 170

Dear Pervect,
Thank you for your comments, I agree with the comments you made but have tried to consider an alternative interpretation. If I could form a singularity in my hand, according to currently accept theory, relative to the singularity, time would come to a stop, which means it would have a time measurement of zero. If fact all 4 dimensions of a singularity are zero, if they are zero  which dimension are they existing in, for us to observe occurring  if not the 5th Dimension? If a singularity formed in a cloud, up in the sky, ignoring gravitational affects, or assume it was a super cloud, or as in the case of every blackhole which forms at the center of every galaxy, can someone please describe is motion? I would like to go back to first principles which is why I would like a copy of the Kalusa Papers, which he sent to Einstien. Regards Terry Giblin 



#4
Dec1804, 07:24 PM

Emeritus
Sci Advisor
P: 7,436

Is universal "time" the 4th or 5th Dimension?The singularity itself is a point, so it has no dimension. Spacetime in the neighborhood of the singularity is still 4 dimensional. The singularity itself is a "removed point" from the 4d spacetime, one that has no dimension Now let's talk about the event horizon. Time can be said to stop at the event horizon, but that does not mean that spacetime is not 4dimensional there. Here is an anology. If you stood at the north pole of the Earth, all directions would be south. So you would say "East and west stop at the north pole". But the Earth is round, and the north pole is not physically different from the rest of the Earth. You can see, I hope, that the surface of the Earth is two dimensional everywhere, even at the north pole. So it is with time at the event horizon. The problem turns out to be an issue of the coordinates used  lattitude and longitude are not well behaved at the north pole, and the Schwarzsachild coordiantes are not well behaved at the event horizon. But the structure of spacetime itself is whole at the event horizon, nothing is different there. Only at the center of the black hole itself, at the singularity, is there any difference, and even there the singularity is just a missing point. 


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