String Theory on One Page

Interesting!

I've always wondered: does the string's characteristic size of 10^-35 m (the Planck length) came out of string theory, or is it just that it's the smallest size that has any meaning?

Hi Jorrie,

I've read a couple of interesting books on unification theory. One thing that popped into to my mind mind while reading this post was an explanation given in Greene's "The Fabric of the Cosmos." He first debunks the possibility of gravitons being point particles (assumption of Quantum Mechanics). Then he continues with the following:

"In string theory, each graviton is a vibrating string - something that is not a point, but instead roughly a Planck Length ... And since the gravitons are the finest, most elementary constituents of a gravitational field, it makes no sense to talk about gravitational fields on sub-Planck length scales."

He then compares Planck length in a gravitational field to the pixels on a television set. From there, Greene makes an interesting point by discussing how the assumed sizing constraints of a string (Plank length) avoid a "catastrophic clash between quantum mechanics and general relativity."

The same book offers the following: "Planck Length: Size ... below which the conflict between quantum mechanics and general relativity becomes manifest ..."

However, I think M-theory actually calls out for strings that are much larger (and potentially measurable) in size. Some works I have read state that strings could be as large as 10^-18m. This relies large on what the size is of the "extra" dimensions that are the consequence of string theory.

Sorry so long, but it proves to be difficult to get your point across when trying to discuss string theory!

fm!

Hi FM, is M-theory not the one that puts all 6 or so super-string theories on a common footing? If so, I suppose it allows, but not calls for, 10^-18 m strings.

Interesting, I read in a current post on Physics Forums that LQC (loop quantum cosmology), a derivative from LQG, represents the standard cosmology much better than super-string theory. It apparently prevents a singularity by having a bounce at the Planck scale and goes over to the standard ΛCDM model once the cosmic scale reaches a few Planck lengths.

Hello Jorrie,

Of course, my mistake! M-theory (the theory unifying the 5 string theories + 11-D super gravity) simply allows for rather than calls for the larger strings. The general point I was trying to develop is that the larger strings are on a potentially detectable level, possibly allowing for some empirical insight to string / M-Theory.

I've heard of LQC before, but haven't really learned much about it. I'll try and do a bit of research on it sometime!

fm!

Interesting, both your post here, and Jorrie's reply. It would be nice if you could expand on these points and also the general subject matter from your reading. If indeed strings are the size suggested, what frequencies would their vibrations be? If elementary particles are the "ends" of a string, or a string in its entirity, how do we reconcile "Planck length" strings with elementary particles such as the vanishingly small electron with a Thomson cross section on the order of 0.665 x 10 exp-28? I would think there are a number of readers who would love to read further discussions on this! Look at how the string (no pun intended) on Black Holes expanded here. Nice post!

Hi Cardio,

Well, I feel I may have to respond to your inquiries in segments! I'll start with the question on the frequencies that strings may potentially vibrate at.

According to some of the research I have done, the resonances (frequencies) at which a string vibrates quantify the different charges (force) and mass that a particular string may have. Hence a particular particle would have an associated string resonance pattern that would provide it (the particle) with its inherent mass and charge properties. So, in general, this theory allows the vibrating frequencies to vary!

If I failed to elaborate on this portion of you reply let me know and I will try to expand my response!

fm!

Thank you. That's as good an answer as I could ask for. I'd also like to see some discussion re how strings were formed, if their numbers are static or if they are somehow continuously created and destroyed. If we assume that the life of a proton, say, is essentially infinite, then some strings should also be "infinite". But what about fleeting particles with extremely short lifetimes? What are we actually "creating" in a particle accerator collision event? Many thanks!

I think I subscribe more to the chaos theory.

Seems to fit into just about everything I deal with

I feel a cosmolograine coming on!

I can sympathize with that! Got any Black Holiprofen?

Too many strings attached and it full of holes.