# The Validity of an 11- or 26-Dimensional Universe

**URL:** <https://boards.straightdope.com/t/the-validity-of-an-11-or-26-dimensional-universe/284829>\
**Category:** Great Debates\
**Created:** [January 15, 2005, 5:57am UTC](https://boards.straightdope.com/t/the-validity-of-an-11-or-26-dimensional-universe/284829 "2005-01-15T05:57:30Z")\
**Posts on this page:** 3\
**Page:** 3

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**Author:** ![chefurbo](https://avatars.discourse-cdn.com/v4/letter/c/e19b73/32.png) [@chefurbo](https://boards.straightdope.com/u/chefurbo)\
**Post date:** [January 31, 2005, 4:22am UTC](https://boards.straightdope.com/t/the-validity-of-an-11-or-26-dimensional-universe/284829/41 "2005-01-31T04:22:22Z")

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> [@chefurbo](#):
>
> It has long been a mystery to me as to what physical medium electromagnetic and gravity waves acted on. Gravitational forces obviously act with the presence of air (Me sitting on this chair on Earth), but they also act with the absence of air (The Earth orbiting around the Sun). Light obviously travels just fine with or without air, just as magnetic waves can attract/repel other magnetic waves in a vacuum.
> 
> So I once inquired of a physics professor…“How can gravity and electromagnetism act in the absence of a physical medium?” I suggested that these waves might act on a medium of 4+ dimension(s). He seemed to disagree and simply said that “electromagnetic and gravitational waves don’t need a physical medium to travel on”. I was unsatisfied… and so the mystery still remains. ☹

any ideas?

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**Author:** ![FriendRob](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@FriendRob](https://boards.straightdope.com/u/FriendRob)\
**Post date:** [January 31, 2005, 1:52pm UTC](https://boards.straightdope.com/t/the-validity-of-an-11-or-26-dimensional-universe/284829/42 "2005-01-31T13:52:12Z")

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> [@QuarkChild](#):
>
> For example, a large cosmological constant (one too large to allow galaxy formation, say) would falsify string theory **if** it was found that 99.999% percent of string theory solutions required a cosmological constant at least that large.

(Bolding mine)

That **if** is the rub, of course. Right now, no one (that I know of) can say that 99.999% of string theory solutions have any one particular testable property in common. I know there are many people working on this, but many people have been working on it for twenty years, and there’s _still_ no good experimental test available.

Good luck to you, QC, but I wish some of you bright young things would focus on areas where there’s real physics to be done, like solving QCD…

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**Author:** ![FriendRob](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@FriendRob](https://boards.straightdope.com/u/FriendRob)\
**Post date:** [January 31, 2005, 2:01pm UTC](https://boards.straightdope.com/t/the-validity-of-an-11-or-26-dimensional-universe/284829/43 "2005-01-31T14:01:40Z")

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**chefurbo** , if you imagine a physical medium that supports (say) EM waves, then you should be able to detect our motion _with respect to the medium_. Especially, the speed of light would no longer be constant for all observers, since the light would be moving at a particular speed with respect to the medium. This was the importance of the Michealson-Morley experiment.

You can fix up the problem by posulating some bizarre consequences of being in motion with respect to the medium (length contraction and so forth) - but why bother? Why introduce a medium and a bunch of arbitrary postulates about it, just to end up with the same predictions you have with the mediumless theory? It’s a matter of Occam’s razor: don’t introduce additional postulates unless you need to.

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