I have heard that there are 12 spatial dimensions. Does this mean that this many are possible, or that 12 dimensions actually exist? If the latter, then do the same things that exist in 3 dimensions exist in 4 or 5 dimensions as well? Or are the other dimensions a whole new world, like an alternate universe? I'm confused!

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    $\begingroup$ Related: physics.stackexchange.com/q/10527/2451 , physics.stackexchange.com/q/83492/2451 and links therein. $\endgroup$ – Qmechanic Oct 22 '14 at 21:24
  • $\begingroup$ As usual, we'd need to know what you think "actually exist" means before we could answer this question even if we had string theory fully tested and the proper variant identified. Is it sufficient that the theory requires them? $\endgroup$ – dmckee Oct 22 '14 at 22:01
  • $\begingroup$ When I say "actually exist", I mean that there is actually a place that exists in 4 or 5 dimensions. By "possible", I mean something scientists could somehow great in a lab $\endgroup$ – Henry V Oct 22 '14 at 22:30
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    $\begingroup$ You just defined what you mean by "actually exist" by saying that it should actually exist. Define what consequences you think are required for an extra dimension to be "actual". I'm being persnickty about this because I sometimes get the idea that people asking this question don't have a clear idea what it means for a dimension to exist---especially in the context of string theory where the extras are currently presumed to be compact and small. $\endgroup$ – dmckee Oct 23 '14 at 0:15

An informal answer until you get one from an expert: the extra spatial dimensions are spatial dimensions conceptually similar to the ones in our 3D space, and the objects exists in this higher dimensional space. The reason you do not notice them macroscopically (such as why an object cannot change direction into the fourth spatial dimension and disappear from your view is that these extra dimensions are assumed to be curled into very small loops, so their effect will be only observed for particles small enough to be able to actually move or interact into those extra dimensions (of course, this is just one of the current theories, there might be no extra dimensions at all).

  • $\begingroup$ And, I remember reading somewhere or hearing about this somewhere, that there is a theory that our 3-dimensional space is actually composed of broken and fragmented one-dimensional space at the super small (Planck Scale) size. I totally lost track of this reference so if anyone knows of this theory and can put a name to it, I would appreciate their efforts. $\endgroup$ – K7PEH Oct 23 '14 at 0:39
  • $\begingroup$ @K7PEH do you mean this by any chance?: en.wikipedia.org/wiki/Quantum_foam $\endgroup$ – Wolphram jonny Oct 23 '14 at 0:41
  • $\begingroup$ I know (and, knew) of Wheeler's Quantum Foam theory. In fact, I still have a book on Physics published in 1965 that has a nice article by Wheeler in it describing this theory. But, this one-dimensional thing, which I believe might have been on a Nova TV show a year or two ago or something like that, is different from Quantum Foam (I think) because the idea of One Dimensional space was paramount in the description, not foam like. Here is an article I just found but I am not sure if it is the same thing: universetoday.com/85159/… $\endgroup$ – K7PEH Oct 23 '14 at 0:47

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