What Determines the Number of Dimensions in String Theory?

[shipreckdpenguin]

Ive been reading about string theory recently and obviously came across the many dementions it proves to have. My question is how do the equations point to 6 extra dementions. What is to say there arent 4 extra or 104 extra.. Why 6??

 

[selfAdjoint]

The six extra dimension are required for string theory to be consistent. In setting up the equations they put in a constant, usually denoted by D, for the dimensions of spacetime. Then they work through the math and find they can only get a theory that hangs together if D = 10 (for superstring theory, the original "bosonic" string theory reuired 26 dimensions).

 

[Aridea]

Ive been reading about string theory recently and obviously came across the many dementions it proves to have. My question is how do the equations point to 6 extra dementions. What is to say there arent 4 extra or 104 extra.. Why 6??

If you want a nice understandable but pretty in depth explanation for string theory and extra dimensions I would suggest reading "Parallel Worlds" & "Hyperspace" both by Michio Kaku, and "The Elegant Universe" by Brian Greene. These three books, besides being wonderful reading, and being written by two very brilliant and respected Physicts explain String Theory and the "extra" dimensions very well. "Hyperspace" in particular gets pretty detailed about the equations and dimensions explaining how the equations "simplify" with the addition of more spatial dimensions. "Parallel Worlds" is almost an expansion of "Hyperspace", giving more updated information about string theory. I would say this in no way means that someone should not read them both, they both have a wealth of information. "The Elegant Universe" is also great for anyone interested who either isn't a physicist, or who doesn't know too much about physics as the first part of the book gives a lot of the basics of physics in general. It's also very interesting even if you are quite familiar with the subject.

There's also a lot of information on the web about the extra dimensions and string theory as well. Actually if you go to Nova's website you can watch "The Elegant Universe" over the web. this is a three hour long series of programs that Brian Greene did with Nova to explain string theory. It's really convenient too, each three hour prograam is broken down to chapters so you can either just watch what you are interested in or break it up in a few sittings if you don't have the time to watch for three hours at once.

 

[shipreckdpenguin]

Interesting. I barely started into parallel worlds when i came up with my question for this thread but i have both parallel worlds by kaku and greenes elegant universe. The Nova special was what made me wonder about the 6 dimentions. It says the string level consists of 6 extra dimentions but i guess it didnt explain why. I can tell that in time and after i finish kaku and greene's books i will have a better understanding of the matters. Thank you very much for the sourses though. (by the way how do you pronounce michio kaku? i have wondered this for a while now)

 

[f-h]

Try here:

http://cosmicvariance.com/2006/02/04/why-10-or-11/