Universe and dimensions

[rodger0531]

Just for my curiosity... is there 4th dimension? is there 2nd dimension? is there nth dimension? is 4th dimension just time, or is it an actual space full of creatures?

[fo3nix]

There are 4 known dimensions. 3 spatial (up and down, forward and back, and left and right), and time. Together this makes up spacetime.

nth dimension is a mathematical concept. There is (possibly) no such thing. Maths can describe anything, including abstract spaces with infinite dimensions (look up Hilbert space on wikipedia). Whether or not this sort of thing really exists is not known.

M-theory (a theory grouping the 5 'different' string theories) suggests a possible 11 dimensions. Though some of the other string theories suggest up to 25 dimensions.

However, don't think of a dimension in the sci-fi sense (as I think you may be). It's not some alternate world. It's just another direction that we can move in.

Food for thought: where are these other dimensions then that some of the theories predict? One possible solution is they're really small and everywhere. Imagine dimensions smaller than atoms, so that every time you wave your arm or move in any way, you move though these dimensions many times. That's one thought.

[jake-the-peg]

Imagine a closed universe.

For example you zoom off in one direction and end up where you started. You can do this in all 3 directions - a bit like the old asteroids game.

Now asteroids was played on a 2-d screen - how would the asteroids universe look?

Well if you think about it, it would be a torus, a bagel shape.

So for a closed 3-d universe you'd need a 3d hyper-torus.

What would that look like? well it's pretty hard to imagine but you can draw a cube on a piece of paper can't you? so in the same way we can construct a 3d projection of a 4d torus

There's some nice animations and descriptions of 4d opbjects here:
http://en.wikipedia.org/wiki/4-D_geometry

As for higher physical dimentions, as fo3nix says a number of string theories have been developed that require 10 physical dimentions - but there was no way to tell which if any were correct. Then a number od physicists including Ed Witten pointed out that if you assumed 11 dimentions all the seperate theories became aspects of a single theory which he named M theory.

The real challenge is to take this and force a prediction out of it that can actually be measured - until then it's just something to amuse theoretical physicists

[rodger0531]

But if it is a new direction other than up, down, forward, backward, left and right we can move in, that means it is a brand new world, isn't it?

[fo3nix]

No. Imagine a beach ball, with a small ant walking along it. To the ant, it's living in a 2D world, because the surface of the beach ball is 2D -- you can either move up and down, or left and right. However, the ball itself is in 3D; the ant just doesn't know it. The extra dimension isn't a whole new dimension.

If you're interested in this, Brian Greene explains this stuff pretty well in his book, The Elegant Universe.

[oxfordrocks]

There is a 5th dimension:

http://en.wikipedia.org/wiki/5th_Dimension

[rodger0531]

not funny............. :P

[kwicky]

This article caught my imagination concerning Islasmic Art. Although the mathematics involved in creating a tesselation involving many adjoining sides (about 256 dimensions) was not proved until fairly recently (in time scale) this islamic pattern had been designed hundreds of years ago.

http://news.bbc.co.uk/1/hi/world/middle_east/6 389157.stm