Question about fourth and fifth spatial dimensions

Post Reply New Topic

I'm not sure what you mean. According to M-theory, we may be stuck on brane embedded in a higher dimension space but I'm not sure if that's what you're talking about.

I think?

I mean that we consider our dimensions to be the first through fourth, but they might be the 113th through 117th(or whatever).

That's a matter of labelling. If our four conventional space-time dimensions were just four of 117 in total it would matter neither mathematically nor physically if we called them the first through fourth dimensions or if we called them 113th through 117th dimensions. The mathematics is the same and the physics is the same, so we might as well call them the first through fourth by convention. In any case, M-theory has a maximum of 11 space-time dimensions to self-consistent. So if M-theory is correct, there can never be as many as 117 dimensions.

Yes I knew it was limited, just didnt care to look the actual limits up.

As far as labeling goes, I didnt mean it in that sense.

Does the first(arbitrarily named) dimension appear as in inaccessible to the 11th as the fifth is from us? Are we talking about a mobius strip here?

Ill let him answer in detail since hes more comfortable with the subject than I, but no.

A 'compactified' dimension is cyclic on a finite scale - our normal 3 dimensions are not. How I interpreted his question was, what if ours were 'compactified' on a scale far greater than our observable universe exists? Then our entire universe could, hypothetically, be present (at a specific point within) another. But thats just the speculative fiction nerd in me bleeding through!

OK, there are two possible answers to this question. One is the braneworld scenario, in which matter and energy is constrained to move on brane embedded in an extra-dimensional space and the other one is that the extra dimensions are compactified into an extremely small size. Most string theorists think the reality would be a combination of the two. In the braneworld scenario, the end points of open strings are constrained to only move around on the brane whereas the closed stings (the ones form closed loops) can leak off the brane into the bulk (i.e. the rest of the extra-dimensional space). In string theory, all the known matter and force carrying particles are open strings except the graviton. So in the case of the braneworld scenario, the extra-dimensions outside the brane are indeed inaccessible to all matter and energy except for gravity, sort of like the following illustration:

[img][800:1000]http://tena4.vub.ac.be/beyondstringtheory/braneworld.jpg[/img].

If the extra-dimensions are not outside a brane but are just compactified into a small space, then technically they are not inaccessible and on microscopic scales matter would move through them all the time but they would just be too small for us to see or detect them. Before branes became part of string theory, stings theorists mostly assumed that the extra dimensions had to be compactified at the Planck scale (i.e. 16.163×10^−36 m) but since the introductions of branes they realised they could be larger. That's why people at the LHC would want to measure gravitation at atomic scales, to detect the extra dimensions. It is rather difficult to probe small distances with gravity because it's extremely weak compared to the other forces but the other forces would not be able to detect the extra dimensions.

Not really, rather it would mean that our universe is finite without an edge. What this means is that in principle if you send a spaceship into space from the north pole and let it continue travelling in a straight line forever, it would eventually approach Earth's south pole from the opposite direction, sort of like how you can circumnavigate the world without falling off the edge.

time is considered as the fourth dimension

This thread was referring to spacial dimensions though.