Exploring the Dimension of Space: The Beauty of Cosmology and Unsolved Mysteries

[Tom Mcfarland]

TL;DR Summary

propose a dimension-existence experiment

Motivated by some apparently intractible unsolved problems, I see cosmology
as a beautiful mathematical description of a strongly flawed paradigm.
This forum wisely does not allow laying out alternate paradigms, so I try to
ask questions to guide my immature understanding , in the spirit of

<Link to stackexchange deleted by mentor as being irrelevant>
http://www.nature.com/news/did-a-hyper-black-hole-spawn-the-universe-1.13743
Question:
Can you describe a future experiment, the results of which would either
affirm or falsify the existence of more than 3 "large" spatial dimensions ?

For example, if we asked in 1610 if the sun orbits the earth, you
might propose building a telescope to look for moons of Jupiter.

Cheers, Tom McFarland

 

[Mark44]

Question:
Can you describe a future experiment, the results of which would either
affirm or falsify the existence of more than 3 "large" spatial dimensions ?

You can't describe an experiment to test a theory if you don't have a theory first.

For example, if we asked in 1610 if the sun orbits the earth, you
might propose building a telescope to look for moons of Jupiter.

This doesn't make sense to me. Galileo didn't propose to his patron (Medici?) that he wanted to build a telescope to look for something he hadn't discovered yet. I don't see how this relates to the title of your thread, about a dimension-existence experiment.

 

[PeterDonis]

if we asked in 1610 if the sun orbits the earth, you
might propose building a telescope to look for moons of Jupiter

That wouldn't refute the theory that the sun orbited the earth; showing that there are some objects that do not orbit the Earth does not prove that all objects do not orbit the earth. (Such a proof, if there were one, would obviously prove too much, since it would "prove" that the moon doesn't orbit the earth.)

 

[PeterDonis]

Can you describe a future experiment, the results of which would either
affirm or falsify the existence of more than 3 "large" spatial dimensions ?

What difference would you expect the presence vs. absence of more than 3 "large" spatial dimensions to make?

Answering that question, as @Mark44 points out, would require a theory that predicts that there is a difference.

 

[DaveC426913]

Question:
Can you describe a future experiment, the results of which would either
affirm or falsify the existence of more than 3 "large" spatial dimensions ?

By 'large' you certainly mean 'extended'. I think that's the accepted term for it.

I'm not sure we need a future experiment; we can do it now.

I can describe - or "get to" - any point in space by defining three - and only three - coordinates in a degree of freedom (a dimension) that is at right angles to the others.

What do you propose that might invalidate that assertion?

 

[Ibix]

Summary: propose a dimension-existence experiment

Can you describe a future experiment, the results of which would either
affirm or falsify the existence of more than 3 "large" spatial dimensions ?

The problem with this approach is that you are proposing a hypothesis (there are 4+ spatial dimensions) and asking us to use that hypothesis to make testable predictions (up/down, left/right, forward/backward, and at least one more pair of directions) and propose a test that would distinguish this from today's understanding (only the three pairs of directions - so can we move in a fourth pair that isn't just a combination of the usual three?).

The only thing you can learn from this is scientific method. Fine. But that doesn't help you with cosmology. There, the problem is the application of that method. You need to understand our current model well enough to make quantitative predictions, and understand what experiments have been done and what constraints they put on what alternative hypotheses can look like. Then you need to develop your hypothesis to the point that it can make quantitative predictions and show that it is consistent with existing experimental data and where its predictions differ from the current model. Only then can we talk about experiments to test it.

It's an enormous challenge. Don't think scientists don't try it all the time (there are a great many competitors and extensions to general relativity that have been tried from time to time, for example). But this is how it usually goes.

 

[kimbyd]

The short version is that if there were large extra dimensions, then high-energy experiments could detect them.

Normally, without large extra dimensions, we wouldn't expect quantum gravity to occur in any Earth experiment we could ever reasonably do. The large extra dimensions make the fundamental strength of gravity stronger (the apparent weakness stems instead from gravity "leaking" into the extra dimensions), and because it's stronger it's possible to detect it at lower energies.

Current experiments haven't seen any evidence of large extra dimensions, and this lack of detection limits the maximum possible size of such dimensions to a few nanometers (the exact limit depends upon how many extra dimensions you have and what their shape is).

Wikipedia has an overview here:
https://en.wikipedia.org/wiki/Large_extra_dimension

You can see a detailed analysis combining multiple lines of evidence here:
https://arxiv.org/abs/1201.2460

 

[metastable]

I can describe - or "get to" - any point in space by defining three - and only three - coordinates in a degree of freedom (a dimension) that is at right angles to the others.

What do you propose that might invalidate that assertion?

What about spherical coordinates... vector and radius from a central point?

 

[Ibix]

What about spherical coordinates... vector and radius from a central point?

All three basis vectors in this system are orthogonal. Exactly three numbers are needed again.

 

[metastable]

Could it be said to specify a particle position, we not only need to specify its position on the 3 axis, but also the vector of its magnetic moment, relative to the vector of the magnetic moment of a given test particle we use as a basis at-rest particle? Is this vector not considered a separate dimension?

 

[Ibix]

No. That's its position and its orientation, not just its position.

Edit: and orientation can be specified in terms of the coordinate system used to express the position.

 

[metastable]

If there are 3 spaceships lined up in a row, and each sees the other 2 as spinning about the row's axis, but one of them measures no centrifugal forces... does spacetime have a "dimension" or "orientation" that decides which of the spaceships has a "roll rate" equal to zero?

 

[Ibix]

No. If I have my differential geometry straight, that's related to the metric and the connection (which together define geodesics, which the particles of the one ship are following and the others aren't). These are not dimensions.

 

[Tom Mcfarland]

Please allow me to simplify this dimension question by replacing 3 with 2.
Ibix and Kimbyd above recognize the issues, but I see no experiment. Others
outside of Physics Stack have proposed theories and experiments, but
it is not proper to review them here.

Thus . same question:

we now live within a 2-sphere S2 which is so large that it appears locally flat as far as we can see. The only information accessible to us is generated within S2, except gravity.

Can you now conceive of an experiment the results of which would either
affirm or falsify the existence of more than the visible 2 "large" spatial dimensions ?

Thank you, Tom McFarland

 

[Ibix]

Can you now conceive of an experiment the results of which would either

Exactly what I said before except with "third" replacing "fourth".

can we move in a fourth pair that isn't just a combination of the usual three

 

[PeterDonis]

Thread closed for moderation.