Is there a 4th dimension

[magma]

Is there such a thing? I've seen it used to explain how the Universe is not infinite (i.e. it is unbounded). But i have always thought x, y and z was it.

Thanks.

[TheOncomingStorm]

Yes it is called time, also according to some string thoeries there could be 11 or more dimensions.

[gGriffeth]

This should clear things up a little, it did for me.

[OUAstrPhys]

Other than the 4 obvious dimensions that make up space-time, some theoretical physists believe that for every single point in space, there are 7 more "curled" up dimensions that are too small for our eyes to render. Imagine an ant walking across a tight rope, our small friend can traverse back and forth, but also around the cylindrical rope. If you viewed this situation from a far(very far) it would not seem obvious that the second type of movement I discussed could be possible. But when you zoom back in on the situation it becomes apparent. I hope that analogy helps a little bit. It was used by Brian Green in one of his books, I can't remember which one at the moment but "The Fabric of the Cosmos", and "The Elegent Universe" are both books that address this situation.

[Neverfly]

According to Michu Kaku in his book 'Hyperspace'( I have it around here somewhere but know not where at the moment) There are theoretically 26 dimensions.
After 11 dimensions the additional dimensions are Curled up in similar fashion to if you are stretching an elastic sheet over a bed- and a side slips off- and the sheet springs on itself curling up. If i recall correctly- the 26th dimension is not curled up.