Questions tagged [spacetime-dimensions]

Use this tag for dimensions of a manifold, typically the space-time. DO NOT USE THIS TAG for dimension of a physical quantity nor for the size of an object.

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159 views

If Hawking's last paper is correct, is it valid to assume that we live in a 5 dimensional universe?

If I understand Hawking's last paper, "A smooth exit from eternal inflation?" (2018-04-27), correctly it implies that the Big Bang generated more universes than our own. This means that to locate a ...
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1answer
116 views

Why does Kaluza-Klein theory or the Randall-Sundrum model propose only one extra dimension?

Reading popular accounts on string theory, I have the impression that the number of extra dimensions of string theory is not an ad hoc postulate; it's uniquely determined by mathematical consistency. ...
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1answer
58 views

Is it possible to measure the number of spacetime dimensions?

My question is pretty straightforward to be stated but I don't know whether the answer is as easily reported. It is remarkable and very interesting that Physics work in (almost) any number of ...
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Why is it interesting to study gravity in (2+1)D? [duplicate]

I often see people researching (2+1)-Gravitational theories such as Chern-Simons. Why is it interesting or what's the motivation underlying that study if there are 4 macroscopic dimensions?
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Can objects exist in spaces with different number of dimensions

Iam new to string theory and extra dimensions. Some string theories suggest objects with many dimensions, I was just wondering if the space they exist in has the same number of dimensions - and in ...
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3answers
328 views

Closed spacelike vs Closed timeline curves (or rather loops)

Reading John Rennie's answer, it made it very clear as to why it is justified to talk of time as a coordinate. So, for now we put time and space on the same footing i.e. consider them dynamical ...
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1answer
44 views

For the case where universe is not flat, has it got an extrinsic curvature towards (an)other spatial dimension(s)? [duplicate]

I got the idea that expansion of the universe is not to somewhere, it is just getting stretched of spacetime since a point of singularity. And I know that universe was calculated as flat (which means ...
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2answers
77 views

Interpretation of wave equation

We represent the wave function in complex form. But complex number gives us plane i.e. two dimension. Than how its possibel to represent a three dimensional quantity in a plane? Please some one ...
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294 views

Why does M-theory need 11 dimensions? [duplicate]

I have looked on the internet and no one can tell me why M-theory needs eleven dimensions?
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1answer
25 views

What is regular mass spacing?

In a book I'm reading, there is a sentence as follows: Muons and taus are not extra-dimensional versions of electrons, because they don’t have a regular mass spacing and don’t have the same weak-...
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76 views

Does space cause matter to move in a 3D fashion, or, does the movement of matter in a 3D fashion cause space to appear 3D? [closed]

What is the mechanism that allows matter (elementary particles) to move with three degrees of dimensional freedom of movement but no more or less? I know it's not a question that has been discussed in ...
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Scepticism regarding the exponent of -2 in Coulombs law? [duplicate]

So lately I was speculating why nature choose the number 2 in Coulomb's law like why not 2.$10^{100}$ trailing zeros and then 1 or anything else. I find 2 a bit arbitrary the given explanation being ...
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1answer
54 views

P-branes (extended objects) with multime time-like dimensions

Why M-theory/supestring theory restrict itself to one time-like (internal!) dimension (excepting F and S-theory)? After all a brane with $X^\mu(\sigma,\tau$) can be extended in principle to $X^\mu(\...
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How everything will act in a universe of two time dimensions? [duplicate]

As far as we know, we live in a universe with one and single dimension of time, we know that some events happens BEFORE or AFTER other events, we know that some events happens slower or faster then ...
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1answer
79 views

How can i create a position-time graph of a object which is moving in 3D space? Is it even possible?

As modelling position-time graph of a object 2D in motion requires 3 dimensions, is it possible to create a 3D object's position-time graph? Is there any intuitive idea through which it can be ...
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1answer
109 views

Effective action of IIB Calabi-Yau compactification

I'm currently reading K. Becker, M. Becker and John. H. Schwartz book on string theory. I have a question about Calabi-Yau compactifications of IIB string theory. In chapter 9 page 403, Why do we don'...
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4answers
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Is a shadow 2D?

I had always thought anything below third dimensions couldn't exist in our 3rd-dimensional world. Correct me if I'm wrong but anything 0d 1d or 2d is massless and also can't have energy so it just can'...
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References on how dimensionality relates to inverse square laws

https://en.wikipedia.org/wiki/Spacetime#Privileged_character_of_3.2B1_spacetime Does Coulomb's Law, with Gauss's Law, imply the existence of only three spatial dimensions? Why are so many ...
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91 views

Can physics of n dimensions work in n-1 or n+1 dimensions?

Can 3D physics work in 2D? I mean, could 3D laws of physics exist in a 2D space? In Ads/CFT duality, for example, laws of physics in a 3D space (AdS) work in analogy with 2D laws of physics (CFT). ...
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267 views

What justifies the use of Clifford spinors to describe higher dimensional fermions?

I like to think of QFT Weinberg-style: particles come first, and fields come later; and the latter are constructed so as to describe the former. Fields are not to be thought of as fundamental, but ...
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1answer
176 views

What would be the force law for the electric force between two electric charges in higher dimensions in the case of photons that have rest mass?

I was reading about if photons have rest mass https://galileospendulum.org/2013/07/26/what-if-photons-actually-have-mass/, and found that if photons have mass the force law for the electric force ...
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Experimental test on lower dimensional QFT's$.$

In principle, it is possible to formulate a quantum theory in an arbitrary number of spacetime dimensions. This is useful because it allows us to abstract general features of the theory from those ...
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Can a 2D universe be closed?

Consider a universe as a curved 1D line looped onto itself. The second dimension is time. On one hand, this line is easy to visualize as a circle embedded in a flat 2D plane. However, there is only ...
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1answer
267 views

Slopes of lines in Lorentz transformation

Came across this paragraph reading Philosophy Of Physics by Tim Maudlin. ”In our Euclidean space-time diagrams, the trajectories of comoving clocks are related to their equal-t slices in the ...
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1answer
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Could an holographic universe consist of 3d embedded in 4d instead of 3d embedded in 2d?

In the holographic model, information about a given dimension can be embedded in a lower dimension, so our 3d universe could be considered as a 2d one. Could it happen the other way? I mean, could the ...
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2answers
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Does time matter?

Aside from the second law of thermodynamics it seems physics just doesn't care about the direction of time. So does time really matter? What if instead of 3 spacial and one time dimension. 3+0 or 3+2....
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2answers
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What happens to matter when there's distortion in space

This is all hypothetical, but if you had control of space (to do distortions to space as very heavy objects do), what happens to the matter in the space? To have a concrete example, let's say that you ...
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3answers
99 views

What is Fourth Dimension?

Before people get pissed at me for asking a question that has likely been asked more than a few times, I just want to know a simple answer, if first dimension is that an object exists, (collision) ...
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1answer
150 views

Supersymmetry beyond $D=11$ spacetime dimensions

Taking into account the higher spin theories, from which string theory is an effective field theory, I just wondering if there is something to do to extend supersymmetry to any dimension without any ...
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1answer
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How many polarisation states does a spin $s$ particle have in $d$ dimensions?

Consider Wigner's classification of massive particles in $d$ dimensions. One is interested in the irreducible representations of the (double cover of the) little group of the reference momentum $p=(m,\...
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Multi-temporal theories: why are they no studied as space-like extra dimensions?

Beyond the initial value problem in multi-temporal wave-like equations, the existence of causality problems (we could give up if extra time directions are not too large, I think), or the instability ...
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2answers
243 views

What is the physical implication(s) of the isomorphism between ${\rm SO}(2)$ and $\mathbb{R}/\mathbb{Z}$?

In the book Mathematical physics by V. Balakrishnan, he says (on page 329) that the isomorphism between ${\rm SO}(2)$ and $\mathbb{R}/\mathbb{Z}$, and the fact that $\mathbb{R}$ is the universal ...
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1answer
60 views

Massless Tachyon in 2D

Referring to a large number of works on 2D bosonic string theory with particular attention on the worldsheet description of 2D black hole solution (cigar CFT) I don't understand why the tachyonic ...
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1answer
128 views

Spacetime Of Flatland

I'm trying to really get the intuition of spacetime. This video explains how Minkoswki was the first to think that maybe our universe does not consist of a 3d space which evolves in time, but ...
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1answer
91 views

A detailed explanation of the new light-in-4D-with-quantum-Hall-effect experiments?

I have read several recent articles regarding the two experiments that were done that reveal the effects of a fourth spatial dimension via the quantum Hall effect using lasers and whatnot. I found ...
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99 views

Maximum number of dimensions in string/M-theory

M-theory low energy limit is eleven-dimensional supergravity. However I understand that Itzhak Bars and others have been working in generalizations of string theories of 12, 13 and 14 dimensions with ...
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1answer
250 views

Why are critical dimensions and central charge linkable?

From wikipedia: "In order for a string theory to be consistent, the worldsheet theory must be conformally invariant. The obstruction to conformal symmetry is known as the Weyl anomaly and is ...
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1answer
321 views

What is enstrophy and how to understand it in higher dimensions?

What is enstrophy and how can we generalize that notion to higher dimensions? Comment: a formulation using differential forms (and/or tensors/multivectors) is preferred!
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1answer
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Are the 3 generations of matter somehow connected to 3 dimensions of space? [duplicate]

I notice that each generation of matter is associated with a Lie group with that many degrees of freedom. Does that imply that 3 generations of matter is a direct result of 3 spatial dimensions?
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923 views

Why are the generators of rotation in the 4-dimensional Euclidean space correspond to rotations in a plane?

In three-dimensions, the rotation generators are represented by $J_1$, $J_2$ and $J_3$ where $1,2,3$ respectively stands for the generator of rotation about $x,y,z$ axes respectively. In general, in ...
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3answers
332 views

Where are the infinite-dimensional spaces of Quantum Mechanics?

There are two questions here: One of the confusing points about String Theory is the existence of extra dimensions. These are explained by saying that the these extra dimensions are compactified. ...
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2answers
224 views

Coulomb Potential in 1+1 and 1+2 dimensions?

It is know that in 1+1 dimensions, the Coulomb potential is of linear form: $$ V(x) = Cx$$ and in 1+2 dimensions, of the form: $$V(x,y) = - \ln\left(\frac{L}{\sqrt{x^2 + y^2}}\right).$$ And I am ...
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2answers
456 views

Rotation in Higher Dimensions

In a world of three spatial dimensions plus time, every atom rotates around a line, the axis of rotation. In a world of $N$ spatial dimensions where $N$ is greater than 3, must every atom rotate, ...
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1answer
162 views

Why is 11D supergravity part of M-theory?

11D Supergravity is a field theory, while the varieties of superstring theories is not. Why would M-theory include theories of two different framework?
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157 views

$D$-dimensional Schrodinger's equation with a Dirac delta potential

I know that for $D\geq 2$, there is no bound state for a Dirac potential $V=-\alpha \delta(\textbf{x})$ unless we use an ultraviolet cutoff $k_{max}=1/a$. I showed this by solving the Schrodinger's ...
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Can superstring theories predict our 4 dimensions? [duplicate]

Popular science literature is replete with the necessity for superstring theories to live in at least 10 dimensions, requiring at least 6 of them to be compactified so that they are not observable. ...
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1answer
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Fundamental string theory questions

Can anyone answer some basic string theory questions for me? The Veneziano Amplitude is celebrated for predicting the scattering amplitude of mesons and for practically giving birth to string theory....
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1answer
771 views

Zero dimensional field theory

I went through several books regarding zero dimensional path integral formulation. Can anyone please explain it to me what is that more physically. I read in the book that the formulation in 0+0D made ...
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58 views

5-dimensional electrodynamics [duplicate]

In the traditional 3+1 spacetime, Maxwell's equations také the following form: $\nabla × \mathbf E = -\frac 1 c\frac {\partial \mathbf B} {\partial t}$ $\nabla \cdot \mathbf B=0$ $\nabla \cdot \...
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Compactification of spacetimes always possible?

Consider a metric in a $n+1$ dimensional spacetime given by \begin{equation} g=\underbrace{g_{tt}(r,t)dt^2 + g_{rt}(r,t)drdt + g_{rr} dr^2}_{g'} +h(t,r,x^A)dx^Adx^B \end{equation} where $h$ is a $n-1$ ...