# 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.

565 questions
Filter by
Sorted by
Tagged with
2k views

### Why is quantum mechanics called 0+1 dimensional QFT?

I know that quantum mechanics is sometimes called 0+1 dimensional quantum field theory. What is the meaning? How should we understand it?
1k views

### If I say time is the fourth dimension am I wrong?

As far as I know the prevailing view is that time is the fourth dimension, but I've read there is also a spatial fourth dimension and even higher spatial dimensions after that so I hesitate to say ...
54 views

### How to extend the notion of pressure to lower dimensional spaces?

Consider the pressure at each point in three dimensional space being given by the scalar function $P(\vec{x})$. By definition, the total force perpendicular to a given surface $S$ in this space due to ...
234 views

### The Lorentz group in three dimensions; Parity operator?

In three dimensions the Lorentz group is defined as \begin{align} \text{O}(2,1)=\{\Lambda\in\text{GL}(3,\mathbb{R}),~~~ \eta=\Lambda^T\eta\Lambda,~~~ \text{det}(\Lambda)=\pm 1\},~~~\eta=\begin{...
219 views

### Is Yang-Mills theory confining in any dimensions?

What is the current understanding of Yang-Mills theory (pure non-Abelian gauge theory without matter field) in the infrared limit? (To avoid the subtlety of renormalizability, we may restrict our ...
158 views

### Radial direction is one dimensional or two?

When students were asked a question, give example for one dimensional physical quantity, a student writes radial acceleration. He argues that in polar coordinates, just with $r$ one can give the ...
100 views

### How to visualize multi-dimensions in topological periodic table?

This is a question for those who are familiar with topological periodic table. The first row and right side columns represents dimensions of topological materials in periodic table. I know that for ...
194 views

395 views

### Why are extra timelike dimensions seldom considered? [duplicate]

There are a number of models (String theory, Cascading Gravity, Emergent Dimensions) that contain extra space like dimensions. Why do people tend to avoid considering extra timelike dimensions? The ...
177 views

### Does string theory give any values for the predicted “leakage” of gravity into extra spatial dimensions?

Sorry if this is a duplicate. I have read that string theory has a good explanation for the "hierarchy" problem of the force strength disparity between the fundamental forces because as gravity ...
435 views

### $2+1$-dimensional Einstein gravity is topological and only non-trivial globally

$2+1$-dimensional Einstein gravity has no local degrees of freedom. This can be proved in two different ways: In $D$-dimensional spacetime, a symmetric metric tensor appears to have $\frac{D(D+1)}{2}$...
46 views

### Metre Definition from speed of light [duplicate]

Why is 1 metre defined as the distance travelled by light in 1/299792458 seconds rather than 1/300000000 seconds?
196 views

### Can someone explain the basics of Kaluza-Klein Theory (with as minimal math as possible) and why it was discredited?

Most of what I know about Kaluza-Klein Theory comes from a book I read a while back by Brian Greene called "The Elegant Universe". What he said was that Kaluza had figured out a way to incorporate a ...
110 views

### Things in 2D world, i.e. a world with 2 spatial dimensions [closed]

There are many question about life and physics in higher dimensions. but is there any physical thing (i mean things like force, momentum, speed,...) that cannot exist in 2D world? could 2D world have ...
35 views

### States of equilibrium in an n-sphere

A mass at the center of two points (or a 0-sphere) that is gravitationally attracted to both would be in a state of unstable equilibrium; any disturbance would increase the attraction to one and ...
168 views

### Large $D$ limit of (Anti) de Sitter Space is Minkowskian Space?

As is well known, the solution of the vacuum Einstein equations with a non-zero cosmological constant, $G_{\mu\nu}+\Lambda g_{\mu\nu}=0$, is an asymptotically (anti) de Sitter space based on the sign ...
55 views

### Why was there a need of defining spatial dimensions more than 3? [duplicate]

3 dimensional universe looks like the limit for me. I can't even imagine a fourth dimension, and there are physicists talking of 11 dimensional spacetime. There are even mathematical generalisations ...
358 views

### Any nice interpretation of differentiating $j(j+1)$ to get $2j+1$?

If $j$ is a continuous variable, then differentiating the function $f(j)=j(j+1)$ with respect to $j$ gives $f'(j)=2j+1$. Of course I've chosen the letter to evoke quantum mechanical angular momentum, ...
132 views

### Instability of higher dimensional universes

According to superstring theory, there are at least 10 dimensions in the universe (M-theory actually suggests that there are 11 dimensions to spacetime; bosonic string theories suggest 26 dimensions). ...
2k views

### Basis for the Generalization of Physics to a Different Number of Dimensions

I am reading this really interesting book by Zwiebach called "A First Course in String Theory". Therein, he generalizes the laws of electrodynamics to the cases where dimensions are not 3+1. It's an ...
289 views

### In Einstein's General Relativity, do the space-time dimensions curve?

In Einstein's General Relativity, do the space-time dimensions curve according to the positions of stars, planets, and masses?
195 views

### Are there superconformal field theories in 10D?

I've heard that there is a belief that interacting conformal field theories do not exist in dimensions greater than 6, and in 6D the only known nontrivial CFTs are superconformal field theories. What ...
147 views

### Reference recommendation： QFT in arbitary dimensions $D=1+d$

When I self-study the QFT, I found that many results in textbook heavily rely on the dimension $1+3$. For example, I heard "In 3+1 dim, Majorana fermion cannot have well-defined handedness. But in ...
336 views

### Does the derivation of the Lorentz transformation depend on space having at least two spatial dimensions?

Eisberg's 'Fundamentals of Modern Physics' derives the space contraction formula from a mirror experiment in which A reflects a light beam in a direction perpendicular to the motion of B, both ...
266 views

80 views

### Query regarding bent space-time in General Relativity [duplicate]

I am just a beginner in this topic and I accept I haven't gone through whole of the content of GR. However after going through some of the basic ideas, I encountered a problem. If I did my homework ...
262 views

### How could we know that the relativistic curvature of universe is intrinsic?

General relativity tells us that the universe is bent by gravity, but this curvature is intrinsic to the universe (the universe bends, but not in a fourth spatial dimension, the universe having only ...
344 views

### In string theory why are the “extra” dimensions super-compact?

Is the only reason the "extra" dimensions of string theory are considered to be super-compact, so we can avoid dealing with the question "why can't we experience them?"?
129 views

### Dimension of an equipotential surface

How many dimensions has an equipotential surface? My book says it has $3$ dimensions but I think it has $2$ dimensions because a plane is an object of dimension $2$ as well. From linear algebra, I ...
164 views

### Dimension of Representation of Majorana Fermions with Euclidean Metric?

It is possible to represent the Dirac matrices in the Majorana basis using $N= 2^{⌊d/2⌋}$-dimensional matrices, as shown here. This source uses a Minkowski metric. It would then be possible to move to ...
84 views

### Does nature have more than four dimensions? [duplicate]

Does nature have more than four spacetime dimensions? If so, what is their size? Are dimensions a fundamental property of the universe or an emergent result of other physical laws? Can we ...
47 views

### Inverse square laws & dimensionality [duplicate]

I have been thinking about the famous Inverse square-laws and how they came out to be that way. Gauss's law elegantly describes the square law for electricity to spherical distribution. Now I am ...
130 views

### Is there a negative dimensional object similar to a black hole / singularity?

My view of negative dimensional objects is one where different objects are all stacked up one on top of the other within the same co-ordinates. Multiple objects may occupy the same space in negative ...
334 views

### How would Newtonian gravity work in a 1-dimensional universe?

I have come across the idea of gravity in different dimensional space. From the standard formula for gravity $F=\frac{GMm}{r^2}$ I have found that the $1/r^2$ term is a result of a three dimensional ...
362 views

### Dimensions of a tensor product space

Susskind, in his 'Theoretical Minimum' book about QM says that given two 2-dimensional spaces, the product state of two vectors, one from each space, is determined by four real parameters. But, he ...
178 views

### Why a 3D Universe?

The universe as it stands is perceived by us to be 3 dimensional. Why is it that the universe formed into 3D space and not 4D or 5D space for example?