Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

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 understand, we live in 3 dimensional space coupled with time. So, by extension, those four dimensions should be present all around us and in our universe. Now, if these hypothetical extra dimensions are folded and compacted, obviously smaller than our universe, doesn't that mean that the extra dimensions are 'somewhere' in the universe and contained within it rather than enveloping it?

share|cite|improve this question
Extra dimensions are at each point of the 4-dimensional spacetime. The whole 10- or 11-dimensional spacetime has the shape of ${\mathcal M}^{3+1} \times X$ where $X$ is the 6- or 7-dimensional manifold and the first factor is the 3+1-dimensional spacetime manifold we used to think is "everything". It's a Cartesian product. It may also be a warped product but I don't want to go into these things. – LuboŇ° Motl Sep 23 '12 at 5:36
@Lubos that would be the sort of thing to put in an answer – David Z Sep 23 '12 at 7:41

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.