The Stack Overflow podcast is back! Listen to an interview with our new CEO.

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.

Filter by
Sorted by
Tagged with
0
votes
4answers
57 views

Can motion be considered a dimension?

Okay, go easy on me, I’m in no way any kind of physicist, or even a scientist, I graduated High School and that’s it, but I do have a very mechanically based mind, (probably why I wound up a Diesel ...
0
votes
0answers
54 views

Does string theory really associate 6 dimensions to electromagnetism & the nuclear forces?

1) I understand string (superstring) theory often ends up with 10 dimensions, 9 space-like and 1 timelike. Typically I read that these are all associated to space-time. 2) So, I was interested when I ...
5
votes
0answers
139 views
+50

Magnetic field “lines” in $D \ne 4$ spacetimes

The electromagnetic field is represented by an antisymetric tensor $F_{ab} = -\, F_{ba}$ (the faraday). In $D = 4$ spacetimes, it has 6 independent componenents: 3 describing the electric field: $F_{...
1
vote
0answers
85 views

Could dark matter actually be matter which resides in a different spatial dimension? [closed]

I have at best a rudimentary understanding of the math in this side of physics, so bear with me. I am also aware of this question, but it was asked and answered 4 years ago and I don't want to ...
3
votes
1answer
87 views

Can a “time dimension” be part of a spherical topology?

I've heard it speculated that the spatial dimensions of the universe is a 3-sphere. Or a 3-torus. But usually, I guess, it's assumed that the "time" dimension just has its own geometry, like a line, ...
-3
votes
1answer
81 views

Bending light by warping space? [closed]

If I ask what is space, space is purely a mathematical abstraction, an area described by a set of dimensions defined with numbers, space is devoid and has no physical properties what so ever, ...
0
votes
0answers
48 views

Critical dimension from the symmetries of the string action

(Related: This post and this post.) In this thesis it is said (on page 13) that just by assuming that we have some general action with the same symmetries as the Polyakov action (Poincare invariance, ...
1
vote
1answer
42 views

Counting independent components of the Riemann curvature tensor

In 4D spacetime, we may choose a locally inertial frame at point P, that is we always have a transformation such that $g_{{\mu'}{\nu'}}(P) = \eta_{{\mu'}{\nu'}}$ and its first derivatives vanish. ...
30
votes
10answers
8k views

Is the “spacetime” the same thing as the mathematical 4th dimension?

Is the "spacetime" the same thing as the mathematical 4th dimension? We often say that time is the fourth dimension, but I am wondering if it's means that time is like the fourth geometrical axis, or ...
0
votes
0answers
44 views

Count degrees of freedom of gauge tensors

For degrees of freedom (dof) it is said that spin-1 massless boson like photon has 2 dof in 4d, like U(1) gauge theory. it is said that spin-2 massless boson like photon has 2 dof in 4d, like ...
0
votes
0answers
26 views

Gravity in a spacetime with 2 indistinguishable dimensions, with all spacetime directions equivalent

A spacetime with 2 indistinguishable dimensions and all spacetime directions equivalent would have the signature (++) meaning that there would be no difference between spacelike and timelike ...
0
votes
2answers
60 views

Connected and disconnected dimensions

The usual way of determining the dimensionality of space is from the number of values needed to define a unique point. However, when choosing a ski, my body is defined by two numbers - my mass and ...
4
votes
3answers
1k views

When exactly is a dimension spatial?

I every so often hear claims like: M-Theory predicts that there are 10 spatial dimensions! Now I'm not really sure what these claims mean. There are three spatial dimensions that I normally ...
7
votes
1answer
158 views

How do we know the laws of physics remain the same in different dimensions?

Section on Wikipedia dealing with the possibility of different dimensions. When reading this section it feels like there's a giant elephant in the room that is not addressed. For example, here's a ...
3
votes
1answer
53 views

Should the 4D normalization constant $8\pi$ in Einstein field equations (EFE) be changed to $(n-2)S_{n-2}$ in other spacetime dimensions?

Should the 4D normalization constant $8\pi$ in Einstein field equations (EFE) be changed to $(n-2)S_{n-2}$, where $S_{n-2}$ denotes the area of a $n-2$-sphere, in higher dimensions? The reason is that ...
0
votes
1answer
67 views

If there exists a universe with other than 3+1 dimensions, could we quantum tunnel to it?

Section of Wikipedia article on the possibility of universes with space & time dimensions other than 3 and 1 respectively. If one of these other universes exist, could we in principle quantum ...
-1
votes
1answer
67 views

What exactly is dimension?

In class 11th, I studied in first chapter of physics (that is unit and measurement) that dimension is an expression of a physical quantity in terms of fundamental quantity. But immediately in second ...
0
votes
0answers
68 views

Intuitive way to get 10 dimensions in string theory?

To get the 26 dimensions is sort of intuitive (in a handwavey sort of way). Basically we solve: $$(D-2)\frac{1}{2}(1+2+3+4+...)=-1$$ Where $1+2+3+..$ times $\frac{1}{2}\hbar$ are the ground energy ...
1
vote
1answer
76 views

Is there a cosmological constant $\Lambda$ in 2D?

It is well known that the Einstein tensor is trivially 0 in any two dimensions spacetime: \begin{equation}\tag{1} G_{\mu \nu}^{(2)} \equiv 0. \end{equation} Thus, it is not possible to formulate the ...
1
vote
0answers
23 views

Standard References for 5d or 6d SUSY theories?

I'd like to learn more about them, but I need a text that I know is worth reading to start!
-2
votes
2answers
107 views

Why time is 4th dimension not 1st? [closed]

Yeah we can not define a line without a point but why time is not 1st. Also time exist in 1st dimension as well doesn't it?
1
vote
1answer
87 views

What does QCD look like in higher dimensions?

It was pointed out as a comment on my question on atomic physics in higher dimensions that that question implicitly rests on an assumption that QCD, and thus the structure of atomic nuclei, is pretty ...
5
votes
0answers
63 views

Plum-pudding atomic physics in higher dimensions?

It is established that "normal" electron orbitals are not stable in more than 3 spatial dimensions, as the available energy levels become unbounded from below. However, this result only applies given ...
1
vote
1answer
55 views

Dark matter's effect in 2+1 GR?

In the appendix to The Planiverse, it is acknowledged that GR in 2 dimensional space implies no gravitational forces between separated masses--only in the interior of extended massive bodies. The ...
1
vote
0answers
38 views

Why are we in 3 spatial dimensions? [duplicate]

I am very curious to find if there is any reason that why are we in 3 dimensions not in any other like 1D would be hard almost impossible but 2D could have been possible, or what about 4D or in ...
0
votes
1answer
42 views

Conversion of the nonlinear schrodinger equation from $\partial_zE$ to $\partial_tE$

While reading some papers about the nonlinear schrodinger equation (NLS) I noticed that the authors sometimes use (for the linear case) $$\partial_zE=\frac{i}{2k_0}\nabla^2E$$ and sometimes $$\...
7
votes
1answer
1k views

Does the CPT theorem hold for all spacetime dimensions?

I can't find any reference which mentions the dependence of the theorem on spacetime dimension, but it would be very interesting to know what if any it has!
4
votes
1answer
123 views

What is dimension? What is the size of dimension?

Recently I heard a TED talk by Brian Greene where he was speaking about String Theory working on $(10+1)$ dimensions. Plus he said that we live in only in $(3 +1)$ dimensions. So where are others? ...
0
votes
0answers
46 views

Does gravity exist in higher dimensions? [duplicate]

I’m very curious to know whether gravity exists in higher dimensions. Because it follows the inverse square law it seems to me that it should be 3D only (just intuition). Is there any mathematical ...
1
vote
0answers
45 views

longitudinal and transverse components in higher dimensions

I am familiar with the Helmholz decomposition of a vector field in three dimensions: $$\vec{V}=\vec{\nabla}\wedge\vec{A}+\vec{\nabla}\phi$$ But I am interested to show that something similar can be ...
4
votes
1answer
160 views

Dimensional reduction of higher-dimensional Einstein-Hilbert action

I take a spacetime of the form $\mathcal{M}_{d+1}\times \mathbb{S}^n$, with $\mathcal{M}_{d+1}$ some generic non-compact $(d+1)$-dimensional spacetime and $\mathbb{S}^n$ an $n$-dimensional sphere, so ...
0
votes
1answer
47 views

Do particles go into the 4th dimension in 3d waves?

Let's say you create a pulse on a string. The wave moves in 1d(in a straight line) but the particles of the string itself extend into 2 dimensions. The same goes for ripples in water. The wave ...
0
votes
1answer
55 views

Application of Weyl's method in $D$ dimension

I am reading the paper "Shortcuts to high symmetry solutions in gravitational theories" written by Deser and Tekin, http://cds.cern.ch/record/625743/files/0306114.pdf and I am having troubles to ...
1
vote
0answers
21 views

What would it look like to be inside a small space with positive curvature?

Say you're floating in an empty void with a light source. The space you are in has a positive curvature, so going forwards will bring you back to the place you started after about 20 meters. What do ...
2
votes
1answer
95 views

Einstein-Palatini action in $d$-dimensions

The tetradic Einstein-Palatini action can be written as (see, for instance, arXiv:1804.09685) $$S=\epsilon_{IJKL}\int_{\mathcal{M}}e^I\wedge e^J\wedge\Omega^{KL},$$ where $e^I$ are the frame ...
4
votes
1answer
67 views

Would Color Confinement apply in higher dimensions?

As I understand it color confinement comes from the fact that as the distance between two color charges increases the color potential energy increases, instead of decreasing, and the energy needed to ...
0
votes
0answers
6 views

basic question about irrelevance in statements about absorptive and spectral absorptive power

I have read that spectral absorptive power(a...
3
votes
2answers
108 views

Finding the dimensions of a spacetime given the Riemann tensor

The question is: For a spacetime the Riemann tensor is given below: $$R_{\mu \nu \rho \sigma} = \frac{R}{6} (g_{\mu \rho} g_{\nu \sigma} - g_{\mu \sigma} g_{ \nu \rho} )$$ What is the dimension of ...
1
vote
4answers
132 views

Extra Dimensions (in String Theory) - What does it mean?

I have been reading a lot about string theory and the necessity of extra dimensions (particularly as visualized in Calabi-Yau spaces), as "curling-ups" in our apparently 3-dimensional (or 4-...
0
votes
1answer
45 views

Observable higher dimensional geometry?

I recently watched a video where in VR someone was manipulating a 4D geometry in 3D space that was changing into all kinds of different shapes as it was moving through space. What i found strange is ...
0
votes
0answers
22 views

Visualizing higher dimension [duplicate]

Why can't we visualize Higher dimensions greater than 3? Is it just because the dimensions doesn't exist (Certainly I know that space-time is four dimensional) or any other physical reasons.
3
votes
2answers
112 views

Is there a higher dimension analogue of Noether's theorem?

So I have recently read the proof of Noether's theorem from the book variation calculus by Gelfand. Basically, what I have already seen is that for any single integral functional, if we have a ...
2
votes
1answer
102 views

Interacting conformal field theories in spacetime dimensions higher 6?

Are there any papers which directly tackle the question of whether or not there exists interacting CFTs in spacetime dimensions higher than 6? It has been proven that there do not exist any ...
3
votes
2answers
96 views

Meaning of $n+1$ dimensions

Is there anything mathematically significant about studying a theory in $n$ dimensions or $m+1$ dimensions if $n=m+1$? For instance in the context of general relativity I hear people talk about the ...
4
votes
1answer
83 views

Nonrelativistic Quantum Mechanics Results Implying Analogous QFT Results?

One particularly fascinating example of this I have found is the following. The delta function potential has no effect in nonrelativistic quantum mechanics in spatial dimensions greater than or equal ...
3
votes
2answers
136 views

Triviality of Yang Mills in $d>4$?

It has been proved that the $\phi^4$ theory is trivial in spacetime dimensions $d>4$. By trivial I mean that the field $\phi$ is a generalized free field, or in other words, it's only nonzero ...
4
votes
2answers
114 views

Spatial and temporal dimensions orthogonality

It seems that the spatial dimensions are orthogonal: a particle can move along one axis without changing its position in relation to other two axes. It seems that the temporal dimension is somewhat ...
-2
votes
1answer
56 views

Time difference between all particles and waves [closed]

Since all elementary particles and waves were created simultaneously in the big-bang (t0) would there be any time difference between any interacting elementary particles and/or waves after t0? I'm ...
0
votes
0answers
24 views

What is the simplest possible explanation of the String Theory? [duplicate]

I was recently reading through 'The Little Book of String Theory' by Steven S. Gubser, and found it too complicated. Now, some people may say that the string theory is meant to be complicated as even ...
2
votes
2answers
122 views

Relativity in 2+1 or 4+1 dimensions

Whereas we have experience of relativity working with 3 spacial dimensions and one of time would there be similar rules affecting a two dimensional space and one of time or even with a 4 space and 1 ...