Use this tag for dimensions of a manifold, typically the space-time. DO NOT USE THIS TAG for dimension of a physical quantity.

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14
votes
2answers
594 views

Has the concept of non-integer $(n+m)$-dimensional spacetime ever been investigated by theoretical physicists?

The following image serves to aid the reader in understanding the "privileged character" of $3+1$-spacetime. The wikipedia article on spacetime, and the sub-article "The priveleged character of ...
6
votes
2answers
408 views

Some questions regarding $n+m$-dimensional spacetime [duplicate]

Possible Duplicate: Has the concept of non-integer $(n+m)$-dimensional spacetime ever been investigated by theoretical physicists? The following image: serves to aid the reader in ...
8
votes
1answer
613 views

Why do chiral objects only come in pairs?

My question arise and is connected to the "strange" fact that many things seem to come in pair or in number of two similar "objects". Why are there chiral "pairs" and not groups of 3,4, or more? What ...
6
votes
0answers
96 views

String landscape in different dimensions

For D = 11 large (uncompactified) spacetime dimensions, the only "string theory" vacuum is M-theory For D = 10, there are 5 vacua. Or maybe it's more correct to say 4, since type I is S-dual to ...
1
vote
1answer
303 views

A quantum particle in a box (with a catch)

I am reading Shankar's Quantum Mechanics and I am looking at the case where there is one particle inside a box, where the potential is zero inside the wall and abruptly goes to infinity outside the ...
7
votes
1answer
226 views

Plausible explanations for 3 local space dimensions

Every now and then I see accounts of models that claim to explain why we experience only 3 space dimensions (locally, i.e. within cosmic horizons and outside black hole horizons). One such of course ...
4
votes
2answers
430 views

Consequences for causality if superluminal neutrinos were explained by extra dimensions

One suggestion for explaining superluminal neutrinos (assuming for the sake of argument that the OPERA results should hold up) is that the neutrinos have taken a route through extra dimensions, with ...
2
votes
3answers
242 views

Is there a single metric for a given system?

Let imagine a tunnel that connect two distant places at the globe (eastern-western or north-south) There are a lot of posible "distances" or metrics, defined by maps, routes, "as the crow flies", ...
-1
votes
2answers
200 views

length, width, and time

is it possible to have length, width and time. A 2D or 1D object with the 4th dimension (although then there would not be 4 dimensions so would it b 3D?) .
32
votes
6answers
1k views

Is 3+1 spacetime as privileged as is claimed?

I've often heard the argument that having 3 spatial dimensions is very special. Such arguments are invariably based on certain assumptions that do not appear to be justifiable at all, at least to me. ...
9
votes
8answers
2k views

Why are extra dimensions necessary?

Some theories have more than 4 dimensions of spacetime. But we only observe 4 spacetime dimensions in the real world, cf. e.g. this Phys.SE post. Why are the theories (e.g. string theory) that ...
2
votes
1answer
217 views

Could extra dimensions be or become clustered?

String theory - for example - requires extra spatial dimension. Say for example in 10 dimensional string theory, what theoretically prevents clustering of the extra 6 dimensions in 2 timeless 3 ...
13
votes
1answer
3k views

How to define angular momentum in other than three dimensions?

In classical mechanics with 3 space dimension the angular momentum is defined as $\mathbf{L} = \mathbf{r} \times \mathbf{p}$ In relativistic mechanics we have the 4-vectors $x^{\mu}$ and $p^{\mu}$, ...
8
votes
3answers
615 views

Understanding counterintuitive units like s^2

One of the things I never understood but was too afraid to ask is this: how should I think of things like kg/s^2. What exactly is a square second? Square foot makes sense to me because I can see it, ...
2
votes
4answers
360 views

Does time have a special status in general relativity?

In a lot of laymen explanations of general relativity it is implied that the four dimensions of the space-time are equivalent, and we perceive time as different only because it is embedded in our ...
2
votes
5answers
478 views

what are dimensions?

First, discrete examples. In a computer screen I can specify any "2D" point with just one single number (pixel order starting count from first at upper left, and going on, left2right and up2down ...
0
votes
1answer
658 views

What is the 4th dimension? [closed]

I have heard before that the 4th dimension is time, however, another theory makes a lot more sense to me. This is that the 4th dimension is the third dimension stacked on top of each other in a ...
6
votes
3answers
401 views

Why (in relatively non-technical terms) are Calabi-Yau manifolds favored for compactified dimensions in string theory?

I was hoping for an answer in general terms avoiding things like holonomy, Chern classes, Kahler manifolds, fibre bundles and terms of similar ilk. Simply, what are the compelling reasons for ...
10
votes
6answers
2k views

Experimental evidence of a fourth spatial dimension?

As human beings, we observe the world in which we live in three dimensions. However, it is certainly theoretically possible that more dimensions exist. Is there any direct or indirect evidence ...
37
votes
5answers
3k views

Does Coulomb's Law, with Gauss's Law, imply the existence of only three spatial dimensions?

Coulomb's Law states that the fall-off of the strength of the electrostatic force is inversely proportional to the distance squared of the charges. Gauss's law implies that a the total flux through a ...