What is Extra dimensions: Definition and 78 Discussions

In physics, extra dimensions are proposed additional space or time dimensions beyond the (3 + 1) typical of observed spacetime, such as the first attempts based on the Kaluza–Klein theory. Among theories proposing extra dimensions are:
Large extra dimension, mostly motivated by the ADD model, by Nima Arkani-Hamed, Savas Dimopoulos, and Gia Dvali in 1998, in an attempt to solve the hierarchy problem. This theory requires that the fields of the Standard Model are confined to a four-dimensional membrane, while gravity propagates in several additional spatial dimensions that are large compared to the Planck scale.
Warped extra dimensions, such as those proposed by the Randall–Sundrum model (RS), based on warped geometry where the universe is a five-dimensional anti-de Sitter space and the elementary particles except for the graviton are localized on a (3 + 1)-dimensional brane or branes.
Universal extra dimension, proposed and first studied in 2000, assume, at variance with the ADD and RS approaches, that all fields propagate universally in the extra dimensions.
Multiple time dimensions, i.e. the possibility that there might be more than one dimension of time, has occasionally been discussed in physics and philosophy, although those models have to deal with the problem of causality.
String theory has one notable feature that requires extra dimensions for mathematical consistency. Spacetime is 26-dimensional in bosonic string theory, 10-dimensional in superstring theory, and 11-dimensional in supergravity theory and M-theory.

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  1. P

    B String theory suggests that dark matter is hiding in extra dimension

    Here is the article titled "In a ‘Dark Dimension,’ Physicists Search for the Universe’s Missing Matter" by Quanta Magazine https://www.quantamagazine.org/in-a-dark-dimension-physicists-search-for-missing-matter-20240201/
  2. V

    A Small and large extra dimension(s) of the physical space

    Trying to make sense of small and large extra dimension(s) of phyiscal space in a simple intuitive example. Consider a two dimensional manifold like R2 and we are trying to add a small and a large extra dimension. Do we mean by smale extra dimension in this case something like (0,1)×R (the...
  3. Safinaz

    A The scale of an extra dimension

    Any help to understand how the authors of this paper Fine Tuning Problem of the Cosmological Constant in a Generalized Randall-Sundrum Model calculted this size of the extra dimension Equ. (3.8) from the scale factor defined by Equ. (3.3) ? Specifically, this paragraph after Equ. (3.8) -...
  4. ohwilleke

    I Trying To Conceptualize Two Dimensions Of Time

    Some BSM theories, often but not exclusively string theory inspired, have an extra time dimension, as well as extra spatial dimensions. I'm trying to make sense of what it even means to have more than one time dimension, ideally, with a concrete example that illustrates how the second time...
  5. T

    I Do extra dimensions lead to expansion of our universe?

    https://arxiv.org/abs/hep-th/0303031#:~:text=In%20gravitational%20theories%20with%20extra,of%20our%20four%2Ddimensional%20world. This paper seems to suggest that if there are extra dimensions , then they are unstable and can expand turning our 4d universe into a higher dimensional space.
  6. T

    I What Shapes Can Extra Dimensions Take in String Theory?

    I read Brian Greenes book "The Elegant Universe". In it there is one chapter talking about extra dimensions. The first idea was proposed by Kaluza and Klein. They suggested that the extra fifth dimension exists as a circle, is it right. Is this called a KK circle? Now Greene also mentioned that...
  7. S

    I Brane cosmology without string theory?

    There are several models of brane cosmology (https://en.wikipedia.org/wiki/Brane_cosmology) and several physicists working in this field (e.g Lisa Randall and Raman Sundrum), but as you will notice, apparently they are all directly related to string theory. This has several consequences, for...
  8. A

    I Are these descriptions about extra dimensions really true?

    I have been trying to imagine extra dimensions for a long time now. I came across this article and it is certainly the most vivid pictures I have ever seen painted of the extra dimensions: https://phys.org/news/2014-12-universe-dimensions.html For example, it describes "In the sixth, we would...
  9. T

    B Any proof of extra dimensions?

    As of 2020 is there any proof of tiny extra dimensions or observations of them?
  10. DuckAmuck

    A Compactification of spatial extra dimensions

    Hi everyone, I am looking at a paper on compact dimensions. Equation 65 makes sense except for the term of 4*pi*n*R in the denominator. Why is it 4*pi and not 2*pi? I cannot rationalize this. Please help. Thank you. https://arxiv.org/ftp/hep-ph/papers/0609/0609260.pdf
  11. G

    B Strong nuclei force and extra dimensions

    Sorry for my speculative question, i just wondered, is there any sensible theory that thinks strong nuclei force is so weak in the distance, because it isn't three dimensional? Again i don't intend to say my speculations are facts, but i think the above question needs a bit explanation. I would...
  12. A

    B Exploring Extra Dimensions: Time, 2D & 3D Space

    Why do physicist presenting extra dimensions with 2d creature experiencing 3d space with object falling through 2d dimension. And that, that 2d creature can see only a slice of the 3d dimension. If time == space that means that 2d creature also experiences time because objects are moving...
  13. MathematicalPhysicist

    A Max number of extra dimensions

    Is there an upper bound for the number of curled-up extra spatial dimensions and perhaps also temporal dimensions? I just wonder how many more theories with extra dimensions are possible... infinite?
  14. K

    I Testing string/m-theory extra dimensions prediction

    String theory and M-theory and Kaluza Klein theories predicts additional extra dimensions at least 2 recent papers proposed tests these predictions of extra dimensions String theory phenomenology and quantum many body systems Sergio Gutiérrez, Abel Camacho, Héctor Hernández (Submitted on 24...
  15. AuntyMatter

    I Black holes and extra dimensions

    We often hear about string theory requiring extra dimensions over and above our 4D spacetime. Does this shed any light on the singularity which is supposed to exist at the centre of a black hole? Does our normal spacetime simply join the other dimensions in their hidden (curled-up) form? This...
  16. K

    I Signatures of extra dimensions in gravitational waves

    Signatures of extra dimensions in gravitational waves David Andriot, Gustavo Lucena Gómez (Submitted on 24 Apr 2017) Considering gravitational waves propagating on the most general 4+N-dimensional space-time, we investigate the effects due to the N extra dimensions on the four-dimensional waves...
  17. I

    Particle What are some introductory texts for extra dimensions and branes?

    Hello all I hope you can help me with this query. I would like to find an introductory text in extra dimensions. I am taking a course in BSM and I have been referred to: C. Csaki, TASI lectures on extra dimensions and branes, hep-ph/0404096, but I was hoping to find something more...
  18. P

    Extra Dimensions: Are They Large or Tiny?

    Large Extra Dimensions I watched a video with Brian Greene explaining string theory and he said that extra dimensions may be curled up very tiny and that's why we don't see them. Is it possible that some extra dimensions may be very large but we don't see them or are all of them very tiny?
  19. A

    Wilson Loop and spontaneous symmetry breaking.

    I would like to ask about the case of: ##SU(2)\otimes U(1) \rightarrow U(1)\otimes U(1),## spontaneous symmetry breaking. It is given that the Wilson Loop: ##W \equiv exp[ig \oint dy H T^1]= diag(−1,−1,1).## Where ##y## is the ##S^1/Z^2## fifth/extra dimension, ##H = \frac{1}{g R}## and...
  20. H

    Why can't we perceive extra dimensions?

    String theorists postulate that our world has 9 dimensions and these extra dimensions are very twisted up such that they are too small to be seen. Question 1: Why don't we postulate, instead, that the reason we can't see these extra dimensions is because we are not genetically wired to do so...
  21. K

    Extra Dimensions: Lorentz Covariance, String Theory, Symmetries & More

    We know that the 3+1 dimensions all fit together in a nicely with Lorentz covariance. We can rotate and apply Lorentz boosts without breaking the laws of physics. How do string theory's extra dimensions fit in with this? Does it make sense to rotate between a normal space dimension and one of...
  22. BiGyElLoWhAt

    How Did Clifford's Theories Influence Modern Physics and String Theory?

    http://en.wikipedia.org/wiki/Kaluza–Klein_theory ##http://link.springer.com/article/10.1007/BF01390677 (original german paper, Ich kan nicht Deutsche) http://www.scientificexploration.org/journal/jse_21_3_beichler.pdf (this author makes some interesting arguments) Also, a lot (if not all...
  23. CaptDude

    Dark Matter and extra dimensions

    I have considered the possibility that dark matter is so hard to find because it exists in extra dimensions. Before posting here I googled this, and found that some scientists postulate this exact possibility, while others consider that extra dimensions themselves cause the effects that are...
  24. ChrisVer

    Are We Missing Hidden Dimensions in Our Universe?

    I've heard that extra dimensions can be (due to gravitational experiments) of dimensions ~some millimeters... I'm quiet skeptical about this issue... Why would someone choose gravity (such a weak force for those experiments) to determine the scale? why not use Electromagnetism , that has...
  25. N

    Are extra dimensions provable?

    I understand that we live in a 3D world. X,Y,Z...Up-Down, Left-Right, Frontwards-Backwards. But I hear theoretically ideas of the 4th dimension, time? As well as String Theory with as many as 11-dimensions. Are any of these higher/lower dimensions provable? And is the 4th dimension that is...
  26. K

    Extra dimensions and weakness of gravity

    I often read about the weakness of gravity being explained by gravity leaking into extra space dimensions. But, if there is a large 4th space dimension that only gravity can access, that would make gravity follow an inverse cube law. Observation clearly shows an inverse square law that Newton...
  27. S

    Quantum Entanglement and extra dimensions?

    I recently heard one theory of parallel universes simply being extra dimensions (one thing string theory requires I believe). Well I also happened to be thinking about quantum entanglement. It is still unknown how this phenomenon works right? Well I had this idea that I suppose can't be...
  28. L

    Is another form of time one of the extra dimensions?

    Sorry. I know I must sound like a hick. Time is ... the 4th dimension of our conventional reference? If so, are one or more of the other dimensions posited by String Theory considered possibly to be an additional time dimension(s)?
  29. H

    Does String Theory tell us the size of Extra Dimensions.

    Does the math in string theory tell us anything about the size of any of the extra dimensions?
  30. K

    Brane cosmology and extra dimensions

    I have a few questions so I hope it is okay if I ask them all here in this thread. They are all related somewhat. According to brane cosmology, our 4-D universe is embedded inside a higher dimensional space, a hyperspace if you will, called the bulk. The reason we cannot perceive or interact...
  31. K

    Quantum tunneling and extra dimensions

    Hello. Okay, so there are some theories like string theory that say that there are extra dimensions of space that we cannot see. Extra dimensions if they exist would allow more degrees of freedom in movement. This website demonstrate how barriers insurmountable in a lower dimension would be...
  32. S

    Visualizing seven extra dimensions

    Hi, I am a sculptor working with glass. I have come to this forum for some information. Several years ago I read an article on sting/M-theory that gave a description of one of the possible shapes the the 7 compact extra dimensions of m-theory. I have been unable to find the article again. I...
  33. T

    Exploring Symmetry in Extra Dimensions: SO(n,1) & SO(3,1)xG

    Hi how, in my master project I am working on extra dimensions and I am asking my self why is it common to start most of the theories with a space time symmetry given by SO(n,1) (n>4) and then compactify the obtained spectrum to SO(3,1)xG (where G is an abitrary symmetry group). Because...
  34. D

    Extra Dimensions: Real or Mathematical Constructs?

    When physicists talk about 4+ dimensional space are these real spatial/temporal/something dimensions or just mathematical constructs that are the only known way to accurately describe the observed behavior? Take the flatland example... We live on a 2D Plane and see a 3D Object (say a sphere)...
  35. L

    Symmetries of Higher Dimensions & Extra Spacetimes

    Is it true to say that most higher dimensional spacetimes have symmetries amongst their n extra dimensions? Thanks.
  36. humanino

    A Slant on Warped Extra Dimensions

    I often read claims that string theory cannot possibly break Lorentz invariance. Whether people have feedback right now, or for future reference, I would like to open a thread on the following paper. A Slant on Warped Extra Dimensions
  37. N

    Do the extra dimensions really make sense?

    Is it just me, or are dimensions supposed to simply add another coordinate, i.e., I can move 1m in x, y or z direction and be 1m away from where I started, are the dimensions in string theory based on this concept or do I not understand what a dimension is? The most confusing part is how these...
  38. bcrowell

    Large extra dimensions ruled out?

    Search for Microscopic Black Hole Signatures at the Large Hadron Collider Authors: CMS Collaboration http://arxiv.org/abs/1012.3375 (BTW, slashdot is running this as a falsification of string theory, based on a jokey summary on the Not Even Wrong blog. Not Even Wrong has posted an update...
  39. N

    How Would I Visualize the Extra Dimensions of String Theory?

    Greetings. My question comes in two parts. Part one - In most "low-level - made for t.v." explanations of the extra dimensional space they describe these extra dimensions as "curled-up". If I were to visualize the extra dimensions of string theory would it be better to think of these extra...
  40. Spinnor

    Surface waves on a balloon and our possible extra dimensions.

    Think about the dimensionality of a balloon with surface waves. Say these waves are of small amplitude compared with the radius of the balloon. Two coordinates label points on the balloon and a third labels radial position. Creatures who lived on the surface could make measurements that...
  41. R

    Tell me how string theory works and about extra dimensions in (laymen terms)

    Iv'e scene the documentary about string theory and i just have a few questions about it.(laymen terms) : 1.How does string theory contribute to a unified field theory? 2.Is matter really made of "vibrationg strings"? 3.What does string theory actually mean or what has been the impact...
  42. M

    What is Compactified Extra Dimensions?

    Hi, I have a question about extra dimensions. I don't understand what means that a dimension is compactified. Thanks a lot! Sorry it's the wrong forum. It belongs to Beyond the Standard Model , but I don't know how to remove it!
  43. K

    Extra Dimensions: What Caused Compactification?

    waht caused compactification of the extra dimensions in the early universe?
  44. K

    Extra dimensions vs. dark matter in the LHC

    It is my understanding that physicists hope to use conservation of energy in the LHC to determine if there are multiple dimensions AND if there is dark matter. Let's suppose that through conservation of momentum, we detect a particle that apparently only reacts through gravity, and there is some...
  45. K

    String thoery - extra dimensions

    Why does string theory need so many dimensions? i know in our 3 it would break special relativity but i don't know why
  46. K

    Extra dimensions -> power law lowering unification?

    Is it true that the existence of extra dimensions can lower the unification scale to the GeV scale? Does this mean that the LHC would be in range to detect a unification of couplings if this were true?
  47. T

    Planck scale in extra dimensions

    Hi everybody, it's my first post on here but as i seem to have hit a brick wall with my work I'm hoping somebody might be able to help me :) Homework Statement I'm looking at how the Planck scale is reduced in higher dimensions (ADD theories) and I've managed to reproduce an expression...
  48. K

    Unification of guage couplings in the presence of extra dimensions

    Hi guys, I'm reading about unification of gauge couplings in the presence of extra dimensions but I'm coming unstuck in my understanding of what a Kaluza-Klein mode/excitation/tower is. I've looked ont he net and in string theory books but have been unable to find mcuh that is helping my...
  49. T

    Ontological status of extra dimensions

    M-theory, the latest version of string theory, posits 11 dimensions (ten space dimensions, one time dimension). Earlier versions posited ten or fewer dimensions. Brian Greene and other string theory proponents envision the first three "extra" space dimensions (beyond the three space...
  50. marcus

    Extra dimensions don't go with dark energy (new Steinhardt no-go theorems)

    This applies to the small extra dimensions. The rolled-up compact kind that we wouldn't see if they were there. Paul Steinhardt has just posted a paper proving no-go theorems that exhibit an impressive degree of incompatibility between compact extra dimensions on the one hand versus the...