Use this tag for dimensions of a manifold, typically the space-time. DO NOT USE THIS TAG for dimension of a physical quantity.

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3
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2answers
358 views

String theory: why not use $n$-dimensional blocks/objects/branes?

I have a basic question: if we use 1d string to replace 0d particle to gain insight of nature in string theory, and advanced to use 2d membranes, can we imagine that using $3$- or $n$-dimensional ...
5
votes
1answer
388 views

Is this explanation of “Why nine space dimensions?” correct?

In Gordon Kane's Supersymmetry and Beyond (p. 118), he states: String theory has to be formulated in nine space dimensions or it is not a consistent mathematical theory. There doesn't seem to be a ...
5
votes
1answer
789 views

Critical Dimension of Bosonic Strings and Regularization of $\sum_{n=1}^\infty n$

If $D$ is critical dimension of Bosonic strings, a particular derivation goes like the following, where we arrive finally at $$ \frac{D-2}{2}\sum_{n=1}^\infty n + 1 = 0. $$ Now mathematically this is ...
6
votes
2answers
743 views

Einstein Field Equations in other space-time dimensions than 3+1?

This question is apparently quite simple but I can't seem to find an answer to it, so I was hopping anyone could clarify me. Are the Einstein field equations (EFE) only valid for a 3+1 dimensional ...
1
vote
1answer
133 views

the meaning of epsilon in this operator $ \epsilon $

Consider the dimensional regularized integral $$ \int d^{d}k (k^{2}-m^{2}+i\epsilon)^{-\lambda} $$ For positive $ \lambda $ this integral has a pole at $ k=m $. Is this the reason we we insert the $ ...
6
votes
1answer
178 views

Critical dimension in quantization of p-branes

So I have what might be a fairly basic question, but my understanding that in the quantization of the the string, or the 1-brane, there are conditions on the number of spacetime dimensions to ensure ...
4
votes
1answer
119 views

Are there real life applications for Hausdorff dimensions, specifically crack formations?

I was curios about Hausdorff dimensions. They seem to neatly describe rough surfaces. So I was wondering if there are common applications of Hausdorff dimensions in things like complicated friction ...
6
votes
1answer
225 views

A Game Of The Number Of Space-Time Dimensions

Holger Bech Nielsen, one of the founders of string theory, has apparently just played some sort of game between different potential dimensions for space-time and reached the conclusion that D4 wins in ...
2
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2answers
2k views

Units and Dimensions - Use of proportionality constant

In units and dimensions we learn about Establishing a Formula : (example) : to establish a relationship between T (Time Period) , m (Mass) , l (length of the string) and g(acc. due to gravity) - ...
5
votes
3answers
8k views

Is imagining 10 dimension video by Rob Bryanton has any invalid/wrong information? [closed]

I just watched this youtube video by Rob Bryanton and am wondering that is there anything invalid/wrong in term of real physics. I search for Rob Bryanton and it look like he has not-so-good ...
1
vote
2answers
294 views

Imaginary time and string theory

Is imaginary time an extra dimension? In other words, are time and imaginary time considered two separate dimensions? If so, does imaginary time appear (as a separate dimension) in string theory (thus ...
13
votes
2answers
765 views

Why one-dimensional strings, but not higher-dimensional shells/membranes?

One way that I've seen to sort-of motivate string theory is to 'generalize' the relativistic point particle action, resulting in the Nambu-Goto action. However, once you see how to make this ...
1
vote
1answer
315 views

parallel=time, perpendicular=space? on multiple time dimensions

There are some discussions on more than one time dimensions, e.g., Intuition for multiple temporal dimensions and More than one time dimension. If we define that the parallel direction is time, of ...
2
votes
1answer
136 views

Can we project a 4D world using 3D video technology?

Traditional movies, TV, etc, faithfully show our 3-dimensional world using 2 dimensions. So can we have a movie that shows a 4-dimensional world using 3D technology?
2
votes
2answers
262 views

Do we live in an integer dimension?

I have read that there exist non-integer fractal dimensions and the images generated from these dimensions look organic and they seem to provide a new way of describing the world around us, which ...
-1
votes
1answer
139 views

Are more/other colors posible with other dimensions?

Like these impossible colors (yellow/blue and green/red) or these imaginary colors, for example saturated red more intense than pure spectral red can be viewed in ordinary viewing conditions. Can ...
11
votes
5answers
3k views

Could negative dimension ever make sense?

After some quick check I found that negative dimensions are not used. But we have negative probability, negative energy etc. So is it so likely that we won't ever use negative dimension(s) ? Update ...
0
votes
1answer
123 views

Do we reside in any particular dimension(s)?

In other words does it make sense to say that we live or exist in dimension x? Or do dimensions not apply to reality the universe its self?
11
votes
3answers
3k views

Gravity in other dimensions than 3 and stable orbits

I have heard from here that stable orbits (ones that require a large amount of force to push it significantly out of it's elliptical path) can only exist in a three spatial dimensions because gravity ...
1
vote
1answer
605 views

What is the apparent diameter of the sun as seen from earth?

I know this may not be physically accurate. For my purposes, basically 3D renders, I am assuming the sun rays are parallel rays from an infinitely far lamp. If the sky is clear, what size would that ...
2
votes
0answers
222 views

Higher dimensions

1) How we determine whether the higher dimensions are Unstable or Unpredictable? Or on the basis of what assumption we make this prediction? (Source of Image: Max Tegmark. See also this Wikipedia ...
1
vote
2answers
488 views

How exactly do superstrings reduce the number of dimensions in bosonic string theory from 26 to 10 and remove the tachyons?

In bosonic string theory, to obtain the photon as the first excited state, the ground state must have a negative mass (tachyon). By applying $1 + 2 + 3 + \cdots = -1/12$, it can be shown (in a ...
17
votes
4answers
2k views

Why are so many forces explainable using inverse squares when space is three dimensional?

It seems paradoxical that the strength of so many phenomena (Newtonian gravity, Coulomb force) are calculable by the inverse square of distance. However, since volume is determined by three ...
12
votes
1answer
323 views

How can two time theories be compactified to 3+1 without any Kaluza-Klein remnants

I have recently been looking into the two-time theories and the implied concepts. For me this seems slightly hard to grasp. How can I see the basic concept in this theory in a fundamental way based ...
3
votes
1answer
1k views

Why does the universe exhibit three large-scale spatial dimensions? [duplicate]

Possible Duplicate: Is 3+1 spacetime as privileged as is claimed? Regardless of your favorite theory of how many dimensions the universe has in total, the universe seems to have a deep ...
2
votes
2answers
293 views

Did the universe always have 4 space time dimensions?

Is the dimensionality of spacetime in all usual models constant?
1
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1answer
189 views

Is there a relation between the number of dimensions of space time and the number of fundamental forces?

Is there a relation between the number of dimensions of space time and the number of fundamental forces? Also, did the universe always have 4 space time dimensions? And could there exist a world ...
11
votes
6answers
607 views

More than one time dimension

We know that space-time dimensions are 3+1 macroscopically, but what if 2+2? Obviously it is tough to imagine two time dimensions, but mathematically we can always imagine as either having two ...
13
votes
1answer
904 views

Intuition for multiple temporal dimensions

It’s easy, relatively speaking, to develop an intuition for higher spatial dimensions, usually by induction on familiar lower-dimensional spaces. But I’m having difficulty envisioning a universe with ...
0
votes
2answers
557 views

When and how do you represent a two body state as a tensor product?

I have read that in quantum mechanics, compound systems are constructed as tensor products. But on page 177 of Griffith, for example, a two body wavefunction is introduced as Psi ...
7
votes
1answer
132 views

Is the LEP B meson asymmetry evidence for higher dimensions and/or string theory?

According to this blog, new standard model calculations have changed the 3 sigma B meson forward and backward production asymmetry observed at LEP into two anomolies: A 2.5 sigma B meson production ...
4
votes
1answer
141 views

Limit on space-time dimension from susy

I read an argument saying that it would be impossible to write down a super-symmetric theory in more than 11 dimensions, this limit coming from the dimension of the Clifford algebra that goes as ...
0
votes
3answers
2k views

If we had three eyes, would our visual perspective be fourth dimensional?

If one covers up one eye, then he loses depth perception (two dimensional perspective). When we uncover that eye, we can now see depth (three dimensional perspective). My question is if we had four ...
1
vote
0answers
131 views

Folded and/or compacted dimensions in M-theory?

I've on many occasions that there are various numbers of 'extra' dimensions above the 4th. However, I've heard that they are 'compacted' or 'folded' tightly and unimaginably small. Now, as I ...
0
votes
1answer
181 views

what to use for mass in a 2D FEM simulation

I am trying to find the energy of a wave travelling through a solid material in a 2D Finite Element Method (FEM) - Simulation. As a general approach I would try to use $E_{kin}=\frac{1}{2}mv^2$ at ...
8
votes
2answers
316 views

Why would a particle in an extra dimension appear not as one particle, but a set of particles?

I was reading an article in this months issue of Physics World magazine on the three main theories of extra dimensions and stumbled across something I didn't quite understand when the author began ...
4
votes
2answers
4k views

Do we live in a world with 4 or more dimension?

A NOVA show have told the audience that we are live in 3 dimensional world, the world we lived in is compose by 3 element: the energy, matter, space. By the time Einstein have invented the ...
2
votes
2answers
165 views

What's the meaning of dimensionality?

I got amazed with this answer and as you can see, I had a little talk with joriki. He suggested me some examples such as the 2DEG. I'm stuck with some aspects on dimensionality, see this line: A ...
4
votes
2answers
176 views

What is the minimum number of co-ordinates used to perfectly describe the shape,orientation and position of an n-dimensional object?

What is the minimum number of co-ordinates used to perfectly describe the shape,orientation and position of a n-dimensional object? How do I make an approach to this problem? I am confused with the ...
-2
votes
2answers
161 views

Dimensions of obstacle needed to block light?

How many dimensions are required minimum for an object to block light? in 1d I doubt it's possible. in 2d I think it could do it if only the light was limited to a dimension perpendicular to the ...
18
votes
3answers
1k views

Can light exists in $2+1$ or $1+1$ spacetime dimensions?

Spacetime of special relativity is frequently illustrated with its spatial part reduced to one or two spatial dimension (with light sector or cone, respectively). Taken literally, is it possible for ...
2
votes
4answers
4k views

Why does string theory require 9 dimensions of space and one dimension of time?

String theorists say that there are many more dimensions out there, but they are too small to be detected. However, I do not understand why there are ten dimensions and not just any other number? ...
5
votes
2answers
955 views

Does the Hilbert space of the universe have to be infinite dimensional to make sense of quantum mechanics?

Does the Hilbert space of the universe have to be infinite dimensional to make sense of quantum mechanics? Otherwise, decoherence can never become exact. Does interpreting quantum mechanics require ...
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votes
1answer
1k views

Total Number of Dimensions in the Universe? [duplicate]

I have often heard that there are more than 4 (3 space and 1 time) dimensions of spacetime. What are the theories that say so, and how many does each predict? Has any experimental evidence been ...
1
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0answers
35 views

How can we know the size of a dimension? [duplicate]

Possible Duplicate: Measuring extra-dimensions I was watching a layman's documentary and it said: "The 11th dimension is incredibly small, like a long tube about $10^-30m$ in diameter". ...
-2
votes
1answer
892 views

What do scientists believe about existence in dimensions? [closed]

I couldn't really think of a suitable question title, I'm not sure if it's completely related or not. But this is as far as I know (well, I thought it all up last night and it seemed extremely ...
-1
votes
2answers
2k views

Regarding possibility of infinitely many spatial dimensions

Recently I was taking a look at a video explaining the existence of fourth spatial dimension and thereupon that infinitely many spatial dimensions are possible. Also it showed that what Einstein told ...
5
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2answers
126 views

Is the “dimension” in dimensional analysis the same as the “dimension” in “three spatial dimensions”?

When we talk about the dimension of a quantity (e.g. the dimension of acceleration is$[ L \ T ^ {-2}]$) are we talking about the same "dimension" as when we talk about three dimensional space? Are ...
3
votes
2answers
388 views

About space-time and its four dimensions

I explained to someone I know about General Relativity (as much as I know). He said that he didn't see how it could be correct. He argued: How is 4-dimensional space-time space different to ...
2
votes
2answers
972 views

Why does the force of gravity get weaker as it travels through the dimensions?

Some theories predict that the graviton exists in a dimension that we of course can't see, and that is why the force of gravity is so weak. Because by the time gravity has got from the dimension in ...