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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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Can the space-time be a discrete lattice? [duplicate]

I would like to know how much conjectures about the space-time's being discrete are valid. There is a short article here: https://www.meta-religion.com/Physics/Quantum_physics/is_space.htm One ...
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What should I learn to understand 6d (2,0) theory? [on hold]

I'm a first-year graduate student, I heard that 6d (2,0) theories can provide various dualities between lower dimension field theories, and can give many beautiful results in mathematics. So I ...
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1answer
36 views

General question about dimensionality of the universe [duplicate]

I am a high school math teacher with some basic physic/lay person knowledge. Each year after the AP test, I show the movies Flatland and Sphereland to my calculus classes and talk about the ...
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2answers
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Are the units of energy the same in higher dimensions?

In 3 spatial dimensions, $$[E] = [ML^2 T^{-2}]$$ Would it change in higher dimensions? If yes, then what would be the dimensions for 4 spatial dimensions?
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Dimension and other worlds [closed]

I had a question that can there be an upside down which is actually a mirror version of this world but is dark? Another one , Is there any existence of multiverse?
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2answers
54 views

Distance between events at relativistic speeds

The problem: A spaceship is travelling between Mountain $A$ and Mountain $B$, both of which erupt simultaneously as recorded by a scientist on the ground. The mountains are $300 \; \text{km}$ apart on ...
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1answer
37 views

Dilatations and action on derivatives of fields

How do derivatives of fields transform under dilatations? Specifically I am interested on what I misunderstand with the example: Consider a theory that has a field $A_\mu$ that transforms under ...
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2answers
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How can 0-dimensional particles or 1-dimensional strings be 3D matter? [closed]

According to the latest information we got String theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings....
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3answers
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Why does the LIGO observation disprove higher dimensions?

I recently read this article which claims that last year’s LIGO observation of gravitational waves is proof that, at least on massive scales, there cannot be more than three spatial dimensions. I ...
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Kaluza-Klein theory metric

What are the physical dimensions of the 5x5 Kaluza-Klein metric? ( the metric should be dimensionless but doesn't look so with the inclusion of the four potential and the scalar field)
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1answer
28 views

Grassmann-odd extra dimensions and gravity

Take a world with $D=3+n$ space-time dimensions, where $n$ are extra space-like dimensions. With extra-dimensional newton gravity $$F=G_N(D)\dfrac{Mm}{r^{2+n}}$$ Can $n$ affect IF the extra ...
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Is simulating the interaction of multiple particles possible in $0$ spacelike and $3$ timelike dimensions?

In multiple time like dimensions it is possible for particles to effect it's own past, and two particles can both be effected by each others future. I tried to simulate the interaction of multiple ...
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1answer
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Why does only gravity leak into extra non-compact dimensions?

This article K. Pardo, et. al., Limits on the number of spacetime dimensions from GW170817, Journal of Cosmology and Astroparticle Physics, Vol. 2018, 2018. which was published recently in JCAP ...
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1answer
58 views

Is it possible to test the physical reality of extra dimensions predicted by string theory?

I have no business asking this question since I am not a string scientist but I like to follow science news in phys.org and I read an article dated today Gravitational waves provide dose of reality ...
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Density of states as a function of dimension: what happens between 3D and 4D?

Consider a parabolic dispersion $\varepsilon_{\boldsymbol q} = \frac{\boldsymbol |q|^2}{2m}$. The two-particle density of states $\rho_2(\boldsymbol k, \varepsilon)$ is zero for $\varepsilon < \...
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1answer
259 views

Why is there a maximum number of supersymmetries?

Where does the NO-GO theorem for a maximum number of supersymmetries come from? I read from here https://en.wikipedia.org/wiki/Supersymmetry that number is 32, and that fixes the number of spacetime ...
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1answer
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Does energy conservation take into account the dimension of time?

We know that there are only 3 spacial dimensions because if we light a light bulb, we are able to measure the energy at any point in the 3 spacial dimensions and we can see that no energy is leaking ...
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2answers
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Can you affect higher dimensions from lower ones?

To make it easier to explain, I'm going to use 2-D and 3-D. Imagine you have a stationary sphere in a 3-dimensional space crossing through a 2-dimensional space (meaning the 2-D perspective has a ...
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3 generations as extra unconventional dimensions?

Kaluza-Klein resonances arise in theories with extra dimensions like superstrings or old KK models. Usually, extra dimensions and KK states provide regular spacing in the spectrum. Question: can some ...
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1answer
54 views

Why can't our cognitive sense or five senses sense or fathom hyper-dimensional spaces? [duplicate]

Why can't our cognitive sense or five senses sense hyper-dimensional spaces? Is it because of the way our human body is built?
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0answers
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What is the critical string?

What is the critical string? From wiki, I found the definition of non-Critical string wiki The non-critical string theory describes the relativistic string without enforcing the critical ...
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0answers
153 views

How to best describe wave behavior on even dimensions?

Main source: http://www.mathpages.com/home/kmath242/kmath242.htm On this article, as far as I understand, the author claims that wave behavior on even dimensions would give rise to many waves with ...
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1answer
78 views

How can we be sure that there are only four dimensions? [duplicate]

Infants can only perceive in one dimension (closeness and farness). Young children can only perceive three dimensions (they can't plan or handle time). Teenagers and young adults can perceive 3+1 ...
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(2+2)-dimensional flat spacetime with neutral signature [duplicate]

Is there an example of (2+2)-dimensional flat spacetime with neutral signature (i.e. (+,+,-,-))? ...for example the metric $ds^2=(dt_1)^2+(dt_2)^2-(dx)^2-(dy)^2$, has been studied? Are there any ...
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1answer
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Is general relativity about Lorentzian manifolds only?

General relativity is often used in context of Lorentzian manifolds. But the texts which describe Einstein Field Equations discuss them in context of general pseudo-Riemannian manifolds. It seems ...
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1answer
70 views

Spatial dimensions inside the event horizon

Consider a test particle falling radially to a black hole. The radial direction toward the singularity inside the black hole becomes a direction in time while the dimension that used to be time ...
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1answer
115 views

How to define *dynamical* dimensions?

I'm considering a simple toy model. The spacetime is flat with $d$ space dimensions. Using cartesian coordinates, the spacetime metric is Minkowskian : $$\tag{1} ds^2 = dt^2 - dx_1^2 - dx_2^2 - dx_3^...
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1answer
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Path integral in even number of spatial dimensions: does it exist?

The path integral formulation of Quantum Mechanics is related to Huygens principle, as stated by Feynman in his seminal article [1] and widely commented since then. However Huygens principle does not ...
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Lienard-Wiechert fields in D-dimentions

I tried to calculate Lienard-Wiechert fields in D-dimentions and got some expression with sums of derivatives, very ugly. Does anybody have "nice" expression for it?
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1answer
55 views

Is time really a 1-dimensional object that we only traverse through? [duplicate]

Is time really a 1-dimensional object that we traverse || is it possible that time can also be traversed horizontally. I think the later would also put it on a 2 dimensional plane.
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3answers
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What generates the curvature which is necessary for curling-up extra dimensions?

To say it right away, I am not an expert in string theory, but I know well General Relativity. So I wonder how the curling up of extra-dimensions which is assumed in many "Kaluza-Klein" like theories (...
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0answers
31 views

Dimensions and superstring theory [duplicate]

While I was reading B. Greene 's "the fabric of the cosmos" , There he says that the theory of relativity and quantum mechanics are the two pillars on which modern physics stands, but these theories ...
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1answer
72 views

Why do we assume that Gauss' law of gravitation to remain same even when there are extra spatial dimensions?

Every kid knows that the magnitude of the gravitational force between two point masses is inversely proportional to the square of the distance $r$ between them i.e., $F\sim r^{-2}$. But experimentally,...
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2answers
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A three rank Levi-Civita tensor in four dimensional spacetime

Is it possible to construct a Lorentz invariant, three rank Levi-Civita tensor in Minkowski Spacetime? If not, why so? I am talking about something like this $\epsilon_{\alpha\beta\gamma}$ or $\...
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1answer
84 views

Is 3 spatial dimensions most suitable to life? [closed]

As we're 3 dimensional beings, it's easy to say that the 3rd dimension is the most suitable for life, because we have trillions of examples of 3 dimensional life and no examples for any other ...
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3answers
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How strict are the boundaries that divide dimensions? Is a single-layer sheet of graphene 2D or 3D? [closed]

I would like to know if there is any theory that describes a set of rules that define the boundaries of dimensions. For example, does a single layer sheet made of graphene considered a two or a three ...
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1answer
110 views

Spacetime dimension and the dimension of Clifford algebra

The dimension of the Clifford algebra $C_p$ generated by a vector space $V^p$ is given by $2^p$, where $p$ is the dimension of the vector space (T. Frankel, the geometry of physics). Based on the top-...
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Density of States General Formula

So I have this formula regarding the density of states in 3D and 2D respectively are given by a function of the dispersion relation: $N=\frac18 \frac{4\pi}{3}(V^{\frac13}\frac{k(\omega)}{\pi})^3$ $N=...
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Can Higgs mechanism happen in 1+1D?

How I understand the Higgs mechanism is that, although it is called “spontaneously breaking of the gauge symmetry”, the gauge symmetry is actually not broken in the higgs mechanism and it is the ...
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2answers
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Can we have bubbles of the tenth dimension in our universe?

If the gap between the branes in the Big Bounce theory is the 10th dimension, and branes have wrinkles as they collide, can our universe have 'bubbles' in the 10th dimension? This is in reference to ...
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1answer
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Newton's “Shell theorem” in higher dimensions

In Newtons's shell theorem, the net gravitational force is zero inside a hollow sphere, if the gravitational force is proporional to $1/r^2$. In 2D, the net force is zero inside if the force is ...
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1answer
149 views

What is the velocity of a photon through space-time? What is the 4-velocity of a photon?

What is the velocity of a photon through space-time? What is the 4-velocity of a photon?
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Higher dimensional supergravity d.o.f

From where do the antisymmetric tensor d.o.f. arises from superpoincare group in 10 and 11 dimensional ${\cal N}=1$ SUGRAs? I mean, beyond the d.o.f. matching. Why it need's to be antisymmetric?
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1answer
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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
67 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
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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
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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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Why so many dimensions? [duplicate]

I know that string theory requires at least 9 dimensions or something. Why so many? How do they fit in this 4d universe? How do they help string theory?