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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42 views

Relation between units , quantities and dimensions [closed]

If two quantities have the same dimensions, do they represent the same physical content then?
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1answer
38 views

Gravity creating other dimensions [duplicate]

It is a well known fact that gravity can bend space, kind of like a rock placed on a sheet of paper, bending the paper. But, doing this will make another third dimension, that the marble actually ...
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3answers
57 views

Are black holes 0 dimensional? [duplicate]

If black holes are mass of the star concentrated on a single point then how can it be moving through a 3-dimensional space? How can they spin?
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Does Birkhoff's theorem generalize to higher dimensions without additional assumptions?

In the Newtonian theory of gravity, the shell theorem says that the gravitational field inside a massive and spherically symmetric shell is zero. The conclusion is the same in general relativity, as ...
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Dimension of scale, or depth - does it exist?

Description of an object in 3 standard space dimensions seems not to be its full description. Say, the placement of a molecule is described by $x=2N$, $y=4N$, $z=7N$ measurement units in the Descartes ...
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Is there an equivalent of Kaluza-Klein for fermionic dimensions?

Taking GR in $D$ dimensions, one can use the process of compactification to turn this into GR in $D-1$ dimensions coupled to a Yang-Mills field. i.e. you start with spin-2 fields and you and up with ...
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Can one derive charged black hole solution of GR using Kaluza-Klein?

Kaluza-Klein showed that a 5 dimensional gravitional theory with one dimension on a circle, is equivalent in the limit to a 4 dimensional gravitational theory with electromagnetism. So for the ...
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Second dominate phenomenon to effect the speed of time? [closed]

Part of Einstein's Theory Of Relativity is that the faster an object and/or person moves through space, the slower they move through time. What other phenomenon could potentially effect the passage ...
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What evidence exists to show that hyperdimensions are spacially perpindicular to the dimensions before it?

I've heard of a tesseract which is supposedly spacially perpendicular to the other 3 dimensions. Is there evidence this is possible in our universe or another?
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Is there a theory that proposes the universe is a spacetime bubble within a higher dimensional reality? [closed]

I have heard that one proposal/interpretation of string theory is that, perhaps, extra dimensions exist at minuscule scales. I would conjecture that it is possible for the opposite to be true, akin to ...
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Why is the normal argument for fermions/bosons wrong?

If we have a state $\psi(x_1,x_2)$ of two identical particles and an exchange operator $O$ which swaps the particles. Obviously the physics must be the same and hence $O$ can only introduce an ...
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Is the dimensionality of space considered a universal constant? [duplicate]

What if the dimensionality was something like 3.0001 or 2.999? Would we be able to tell the difference? I heard about fractional dimensionality in 3b1b and was wondering about its implications for ...
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Models of accelerated expansion

Are there models of accelerated cosmological expansion that involve a changing number of spatial dimensions? I think I've seen a version of string theory that posits a reduction to quasi-3 dimensions ...
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1answer
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Do Black Strings Violate Black Hole Uniqueness in Higher Dimensions?

Most black string solutions are obtained by adding flat directions to lower dimensional black holes, for instance in the Gregory-Laflamme instability argument. I had the following question; Is this ...
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How can extra dimensions be small?

I have a super basic gap in my understanding of the theory of extra spacial dimensions - one piece of the explanation that never felt right. As I've heard it, it's theorized that there may be extra ...
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1answer
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Trajectories of Free Particle in (3+1) Dimension

It is often mentioned that due to long range attractive forces in 4D spacetimes, the particle trajectory at large time t looks like: $$r(t) = v*(t+ c_1 \ln(t)).$$ I'm interested in understanding how ...
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Displacement of “Space” [duplicate]

To the extent that matter has volume, is that volume permeated by "space", or does matter displace the "space" it occupies? I understand that limiting factors and conceptual issues abound in the ...
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How exactly does spacetime change inside a black hole? [closed]

There are a few coordinate systems to describe the inside of the BH: Schwarzschild, behaves oddly inside the BH Kruskal-Szekeres, space and time do not swap Gullstrand-Painlevé, $t$ is the time ...
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Do physical fields always have dimension of the Tangent Space at a point?

Say we only consider classical fields in 3 dimensions. In a 3 dimensional space you have scalar or vector fields, where scalar fields can be understood as vectors of one dimension. The other physical ...
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Why Coulomb's law goes with inverse of square radius?

I've seen many similar questions, but none of them were appropriated to me. I was reading about an answer that used the Gauss' law. I don't think that's wise because, of course, the electrostatic ...
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0answers
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How to derive the perturbativity condition of a simple Kaluza-Klein theory?

I thought that the simple $\lambda\phi^4$ theory in 4D is always perturbative if $\lambda<1$. Below equation 107.1, PDG review of extra dimensions says that the 5D Kaluza-Klein theory $$S_5=-\int ...
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In 4 spatial dimensions, would motion under a central force law be confined to a plane?

In dimension $3$, we have the angular momentum $\omega = q \times v$, and since $$\frac{d}{dt} \omega = v \times v + q \times (F/m)$$ from the fact the force is central (so $F$ is parallel to $q$) we ...
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How we can measure speed with time, when the rate at which time passes depends on speed?

I was thinking about relativity, specifically about how we travel at the speed of light in 4 dimensions. The higher one’s velocity in space, the lower one’s velocity in time. Inversely, the lower one’...
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Casimir Force and bosonic String Theory dimensions

I was reading the lecture notes on Quantum field theory by David Tong. In the section on Casimir force he derived the force of attraction felt by the plates due to the field vacuum energy in $1+1$ ...
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1answer
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Question about quantum fields, elementary particles, and quantum numbers, and fundamental forces

As I understand it the allowable spin states of elementary particles is tied to the number of space and time dimensions, so for any two universes with the same number of space and time dimensions the ...
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1answer
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'Complex dimensions' in a metric

In Special Relativity the metric is (with $\eta=\text{diag}(1, -1, -1, -1)$) $$ \text{d}s^2 = \text{d}t^2 - \text{d}\mathbf{x}^2. $$ What sets time apart from space in this equation is the "$-$" in ...
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What is the $R$-symmetry group for ${\cal N}=6$ supergravity in $D=4$ dimensions?

What is the $R$-symmetry group for ${\cal N}=6$ supergravity in $D=4$ dimensions?
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Dimension in the universe [closed]

I was researching on a project ,that is I have to prepare a lecture on 4d.While browseing in youtube I found myself in this question, 1st and 3rd dimensions have fundemental forces acting on objects ...
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3answers
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Does sound travel in other dimensions?

Recently I have been watching Youtube videos regarding dimensions. It wasn't clear to me whether sound travels in the other dimension (excluding 1d,2d and 3d). If so, how would it sound? If no, why?
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3answers
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If extra dimensions are out there, why don't/can't we see them? [duplicate]

String theory proposes the existence of extra space dimensions. Very brilliant minds believe in their existence. Of course, I could appreciate that they are consequences of mathematical ...
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2answers
54 views

Travel and locate extra dimensions

I'm a newbie to String Theory. String Theory says there are extra dimensions apart from the 4 known ones (space and time). Even if the extra dimensions are very small, what makes the theory say they ...
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1answer
51 views

Is Time a container of Space, or separate from Space? [duplicate]

Those of you more learned than me in this topic, please bear with me here. Hopefully it presents an interesting and enlightening discussion for those of us who are just readers of science and may ...
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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 ...
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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 ...
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1answer
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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_{...
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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 ...
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1answer
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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, ...
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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, ...
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1answer
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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. ...
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11answers
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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 ...
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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 ...
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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 ...
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2answers
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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 ...
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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 ...
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1answer
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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 ...
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1answer
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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 ...
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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 ...
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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 ...
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70 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 ...
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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 ...

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