Quantcast
  • Register
PhysicsOverflow is a next-generation academic platform for physicists and astronomers, including a community peer review system and a postgraduate-level discussion forum analogous to MathOverflow.

Welcome to PhysicsOverflow! PhysicsOverflow is an open platform for community peer review and graduate-level Physics discussion.

Please help promote PhysicsOverflow ads elsewhere if you like it.

News

PO is now at the Physics Department of Bielefeld University!

New printer friendly PO pages!

Migration to Bielefeld University was successful!

Please vote for this year's PhysicsOverflow ads!

Please do help out in categorising submissions. Submit a paper to PhysicsOverflow!

... see more

Tools for paper authors

Submit paper
Claim Paper Authorship

Tools for SE users

Search User
Reclaim SE Account
Request Account Merger
Nativise imported posts
Claim post (deleted users)
Import SE post

Users whose questions have been imported from Physics Stack Exchange, Theoretical Physics Stack Exchange, or any other Stack Exchange site are kindly requested to reclaim their account and not to register as a new user.

Public \(\beta\) tools

Report a bug with a feature
Request a new functionality
404 page design
Send feedback

Attributions

(propose a free ad)

Site Statistics

205 submissions , 163 unreviewed
5,082 questions , 2,232 unanswered
5,353 answers , 22,786 comments
1,470 users with positive rep
820 active unimported users
More ...

  Measuring extra-dimensions

+ 6 like - 0 dislike
1692 views

I have read and heard in a number of places that extra dimension might be as big as $x$ mm. What I'm wondering is the following: How is length assigned to these extra dimensions?

I mean you can probably not get your ruler out and compare with the extent of an extra-dimension directly, can you? So if not how can you compare one dimension with the other? Does one have some sort of canonical metric? Could one also assign a length (in meters) to time in this way?

This post imported from StackExchange Physics at 2014-03-17 03:59 (UCT), posted by SE-user Sam
asked Mar 18, 2012 in Experimental Physics by sam (45 points) [ no revision ]
retagged Apr 19, 2014 by dimension10
Related: physics.stackexchange.com/q/4079/2451 and links therein.

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user Qmechanic

3 Answers

+ 7 like - 0 dislike

In addition to what dmckee said, another hint at ("large") extra dimensions would be the detection of Kaluza-Klein particles at the LHC for example.

Kaluza-Klein particles are in principle nothing but the known standard model particles which can propagate into the extra dimensions if these are large enough. It can be shown that the angular momentum in these extra dimensions is quantized. This leads to the effect that particles propagating into the extra dimensions would be observed as heavier versions of the known standard model particles due to the additional momentum in the otherwise not directly visible dimensions. The energy (or mass squared) spectrum of the corresponding expected particle tower would have a step size proportional to 1/r (where r is the radius of the extra dimension).

As Prof. Strassler explains here, to determine the shape and extent of such large extra dimensions it would be necessary to measure the whole mass spectrum using more than one KK particle.

Up to now no KK particles have shown up at the LHC so far (which was run only at 7TeV and now continues at 8 TeV). But note that even if there could be such large extra dimensions leaving hints at themselves at the "LHC scale" (up to 14 TeV), this does not have to be the case for ST to work; the "large" extra dimensions are only a feature of certain (phenomenologica) models ...

answered Mar 19, 2012 by Dilaton (6,240 points) [ revision history ]
That Strassler turned out to be a traitor to "speculative" Supersymmetry! . . . +1 .

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user Dimensio1n0
@Dimension10 since quite some time I had an increasing strang feeling when reading his explanations about BSM physics concepts, like he is explaining things he does not really approve. Since this discussion things are clear now, and the feeling has turned from strange to foul...

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user Dilaton
+ 5 like - 0 dislike

I'll start with your last question. " Could one also assign a length (in meters) to time in this way? " Yes! In the (Minkowki) spacetime infinitesimal interval,

$$\mbox{d}s^2=\left(ic_0\mbox{d}t\right)^2+\left(\mbox{d}x\right)^2+\left(\mbox{d}y\right)^2+\left(\mbox{d}z\right)^2$$

$\left(ic_0\mbox{d}t\right)$ has units of ?? Meters! Exactly! You could think, (very "hand-wavily") that time is like "imaginary space", except for the $c_0$ factor, but if you use natural units $c_0=1$, then, even that factor drops out!.

Now, for the second (really the first) part. How does one measure these compactified extra dimensions? Simply (well, kind of, in principle), by measuring the inverse square law at sub-milimeter scales. It has been done in an arXiv paper by C. Hoyle, U. Schmidt, B. R. Heckel, E. G. Adelberger, J. H. Gundlach, D. J. Kapner, H. E. Swanson Looks like they got a positive result (for the inverse square law) :(


This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user Dimensio1n0

answered Jun 18, 2013 by dimension10 (1,985 points) [ revision history ]
what do you mean positive result? They see no deviation from newtonian physics.from abstract of your link " We improved previous short-range constraints by up to a factor of 1000 and find no deviations from Newtonian physics. "

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user anna v
@annav: By positive result, I didn't mean one that supports extra dimensions, nor one that is somehow good for physics. I was referring to the fact that they were testing the inverse square law, and they got a positive result about the inverse square law. I made it clear by editing my post.

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user Dimensio1n0
thanks. One tends to think as positive the answer to the primary question: "measuring extra dimensions".

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user anna v
+ 4 like - 0 dislike
  • Make some assumptions about the physics associated with the dimensions in questions (say electric field strength goes by $r^{-(n-1)}$ over distances in which $n$ dimensions are significant).

  • Make predictions on that basis

  • Compare to experiment

Many predictions can be made and tested in the realms of high energy particle physics, but so far all are null.

This post imported from StackExchange Physics at 2014-03-17 04:00 (UCT), posted by SE-user dmckee
answered Mar 18, 2012 by dmckee (420 points) [ no revision ]

Your answer

Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead.
To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL.
Please consult the FAQ for as to how to format your post.
This is the answer box; if you want to write a comment instead, please use the 'add comment' button.
Live preview (may slow down editor)   Preview
Your name to display (optional):
Privacy: Your email address will only be used for sending these notifications.
Anti-spam verification:
If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:
p$\hbar$ysicsOverf$\varnothing$ow
Then drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds).
Please complete the anti-spam verification




user contributions licensed under cc by-sa 3.0 with attribution required

Your rights
...