What are the dimensions of strings?

[ShadowVegan]

According to string theory, are strings Planck length in 1 dimension and 0 in all other dimensions? Or more than Planck length in 1 dimension and exactly Planck length in all other dimensions? Or something else? Thanks.

 

[bapowell]

The string is exactly 1-dimensional. I don't believe the length of the string is bounded to be at or below the Planck scale (obviously it must be close, but there is typically some wiggle room of an order of magnitude or so).

 

[Naty1]

Presumably you are thinking of fundamental strings...that's what's usually discussed in these forums...there are a different "brand" of string that makes up elementary nuclear particles...called QCD strings and those are huge maybe 10²⁰ times longer. Strings can also be thought of as 1 branes...one dimensional (length only) branes...particles would be zero branes (no dimensions). So strings are a special class of branes. (I think this depends on the particular string theory.)

The former are supposedly near the Planck scale, so one dimension and largr than Planck scale, yet there IS a type of unity between the two types of strings. Leonard Susskind says "you could suspend 10⁴⁰ trucks from a fundamental string"...(gotta love THAT measurement unit!) they don't expand (extend) very easily.

Susskind points out that black holes, even the supersized giants at the center of galaxies, DO have the energy needed to extend strings to immense size..such that a black hole might consist of a single string! As an example, one theory posits the horizon of a black hole as a single tangled string with quantum fluctuations...when a bump in the string appears on the horizon, it appears to an outside observer as an open string...ends connected to the horizon...and when one breaks off due to quantum zero point energy...carrying gravitational energy, voila, Hawking radiation!

 

[Naty1]

Now that I think about it again, I know I read there are hints that cosmological scale strings that might stretch across the universe might be remnants of a big bang...don't recall the source...so "strings" might vary in size from just above Planck scale to cosmological size.