How Does String Theory Work ?

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Re: How Does String Theory Work ?

#21  Postby Preno » Sep 03, 2010 1:33 pm

newolder wrote:
Preno wrote:
newolder wrote:My understanding is that all (mathematical) groups are embedded in E8
No.

I've failed at rigour again. :doh: I meant the Lie groups.
Okay, but how can a 248+ dimensional Lie group be embedded in a 248 dimensional Lie group?
http://library.thinkquest.org/27930/stringtheory5.htm wrote:... The first step toward such a goal has been taken in the realization that Calabi-Yau spaces contain holes of various numbers of dimensions which can affect a string's vibrational pattern. This goes a long way toward answering one of particle physics' most intriguing questions: why are there three families of elementary particles? why not one, or four, or any other number? The answer proposed by string theory is as follows...
I see, you were talking about the dimension of the holes, not the manifold.
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Re: How Does String Theory Work ?

#22  Postby twistor59 » Sep 03, 2010 2:46 pm

String theory status update for anyone who's interested (couple of years old, but I doubt if there have been massive strides in those years).
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Re: How Does String Theory Work ?

#23  Postby newolder » Sep 03, 2010 3:47 pm

Preno wrote:
newolder wrote:
Preno wrote:No.

I've failed at rigour again. :doh: I meant the Lie groups.
Okay, but how can a 248+ dimensional Lie group be embedded in a 248 dimensional Lie group?

What name exists for a Lie group of greater scope than E8? EIX? :dunno:
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Re: How Does String Theory Work ?

#24  Postby Mononoke » Sep 03, 2010 4:41 pm

newolder wrote:
Preno wrote:
newolder wrote:
I've failed at rigour again. :doh: I meant the Lie groups.
Okay, but how can a 248+ dimensional Lie group be embedded in a 248 dimensional Lie group?

What name exists for a Lie group of greater scope than E8? EIX? :dunno:


E8 is the largest finite one. there is a whole bunch infinite dimensional lie algebras starting with E9
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Re: How Does String Theory Work ?

#25  Postby Mononoke » Sep 03, 2010 4:42 pm

twistor59 wrote:String theory status update for anyone who's interested (couple of years old, but I doubt if there have been massive strides in those years).


I always wanted to learn stuff about string theory. But never made the proper commitment to seriously sit down with pencil and paper and work on.
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Re: How Does String Theory Work ?

#26  Postby newolder » Sep 03, 2010 4:50 pm

Mononoke wrote:
newolder wrote:
Preno wrote:Okay, but how can a 248+ dimensional Lie group be embedded in a 248 dimensional Lie group?

What name exists for a Lie group of greater scope than E8? EIX? :dunno:


E8 is the largest finite one. there is a whole bunch infinite dimensional lie algebras starting with E9

Some of the connections in E8 projections to a 2-d plane are exponential. Their scope is cardinal. I do not know anything in physics that requires anything of larger scope. :scratch:

I would like to read more about E9. Where should I look, please?
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Re: How Does String Theory Work ?

#27  Postby Denny » Sep 03, 2010 4:54 pm

String Theory works like this. Two guys are hanging out. One says:



Dude #1: Hey, I have a pretty cool Idea! Suppose all matter and energy consisted of tiny vibrating strings!


Dude #2: Interesting, If that were the case, what would that infer?




Dude #3: .................. I dunno...........



lol. I saw this on some video I watched, awhile back.
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Re: How Does String Theory Work ?

#28  Postby GreyICE » Sep 03, 2010 6:22 pm

Denny wrote:String Theory works like this. Two guys are hanging out. One says:



Dude #1: Hey, I have a pretty cool Idea! Suppose all matter and energy consisted of tiny vibrating strings!

Dude #2: Interesting, If that were the case, what would that infer?

Dude #3: .................. I dunno...........

lol. I saw this on some video I watched, awhile back.
Oddly, it's similar to this, but with more math and less science than presented ;)
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Re: How Does String Theory Work ?

#29  Postby Denny » Sep 03, 2010 9:33 pm

GreyICE wrote:
Denny wrote:String Theory works like this. Two guys are hanging out. One says:



Dude #1: Hey, I have a pretty cool Idea! Suppose all matter and energy consisted of tiny vibrating strings!

Dude #2: Interesting, If that were the case, what would that infer?

Dude #3: .................. I dunno...........

lol. I saw this on some video I watched, awhile back.
Oddly, it's similar to this, but with more math and less science than presented ;)



;) Yep!
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Re: How Does String Theory Work ?

#30  Postby Preno » Sep 03, 2010 10:01 pm

Mononoke wrote:
newolder wrote:
Preno wrote:Okay, but how can a 248+ dimensional Lie group be embedded in a 248 dimensional Lie group?
What name exists for a Lie group of greater scope than E8? EIX? :dunno:
E8 is the largest finite one.
No, it's not. You probably mean "finite-dimensional", not "finite" (because there is no such thing as a finite Lie group), but it's still not. Trivially, Lie groups of every dimension exist - Rn, for example.
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Re: How Does String Theory Work ?

#31  Postby Mononoke » Sep 04, 2010 2:24 am

Preano your right i was being sloppy there. I meant to say out the lie algebras that are called En, E8 is the largest finite dimensional one. :sorry:
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Re: How Does String Theory Work ?

#32  Postby Severian » Sep 04, 2010 6:01 pm

The trouble with String Theory is that it doesn't really say anything about nature that we don't already know. It can produce gauge theories, and GR from within itself, which is great, but it doesn't tell us anything about these gauge theories. It makes no predictions about, for example, the Standard Model. It doesn't tell us what the particle masses are, or what representations they come in, or even which gauge groups we should have.

And you don't need String Theory to have Exceptional groups. You can fit all the SM particles (including the Higgs, but excluding the gauge boons of course, which stay in the adjoint) into the fundamental representation of E6 for example.
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Re: How Does String Theory Work ?

#33  Postby Slothhead » Sep 05, 2010 12:30 am

Ok well not to burst any bubbles, and i think i have posted this elsewhere with reference to language. How the hell can you expect the non-scientific to get the word use right and not get confused when people, including big name science presenters, dont get it right themselves.

String theory is NOT A FUCKING THEORY - it is a hypothesis. People deride creationists and so forth for saying things like, "o, evolution is just a theory, thats why it is called the THEORY of evolution".

So the question, how does string theory work is invalid for two reasons, firstly it isnt a theory at all, and secondly it doesnt work. There have been no tested predictions of string HYPOTHESIS as yet, because the guys working in the field, actually dont have it all together yet, so the hypothesis part isnt even complete. It has only been recently that the string community has come out and said that we might be able to test for gravitons etc etc and they might show extra dimensions. But these are all very speculative at the moment. I am not saying that it is wrong, the math behind it is so intruging that you would have to think that it has to be right because of the math, but if it doesnt provide any predictions that can be tested, then it is not a scientific theory. It may be that it is right and we just dont have the technology to test it, or as Neil Tyson said, we just may not be smart enough to actually work it out and it will be left for someone in the future.

Having said that, I personally think it is a very exciting field and i really would like to see predictions come out, that we test and work, but if not then that is ok too, but i also think at the same time that when we talk about these things that we be honest, both in language and in application.

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Re: How Does String Theory Work ?

#34  Postby Mononoke » Sep 05, 2010 3:15 am

Severian wrote: You can fit all the SM particles (including the Higgs, but excluding the gauge boons of course, which stay in the adjoint) into the fundamental representation of E6 for example.


Really, i didn't know that
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Re: How Does String Theory Work ?

#35  Postby twistor59 » Sep 15, 2010 1:44 pm

Just to prove I'm not (very) prejudiced against strings:

Here is an alleged testable prediction

Superstring theory involves a single unifying superstring current for bosons and fermions that in the low-energy limit generalizes the Klein-Gordon (not the Dirac) current. By adopting a relativistic-covariant probabilistic interpretation of the current, the low-energy limit implies electron interference patterns that, under certain conditions, differ from those predicted by the Dirac current.
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Re: How Does String Theory Work ?

#36  Postby Delvo » Sep 15, 2010 2:05 pm

Denny wrote:Dude #2: Interesting, If that were the case, what would that infer?




Dude #3: .................. I dunno...........
Maybe the only reason he's stumped is the fact that only a thinking mind can ever infer anything, since that's a mental process, and string theory isn't a mind. :D
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Re: How Does String Theory Work ?

#37  Postby Severian » Sep 15, 2010 5:23 pm

twistor59 wrote:Just to prove I'm not (very) prejudiced against strings:

Here is an alleged testable prediction

Superstring theory involves a single unifying superstring current for bosons and fermions that in the low-energy limit generalizes the Klein-Gordon (not the Dirac) current. By adopting a relativistic-covariant probabilistic interpretation of the current, the low-energy limit implies electron interference patterns that, under certain conditions, differ from those predicted by the Dirac current.


Do you understand where his claim "(ii) that it cannot be derived from low-energy supersymmetric field theory" comes from? I would have said that "bosonic and fermionic particles are different states of the same object" in any supersymmetric theory.
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Re: How Does String Theory Work ?

#38  Postby twistor59 » Sep 15, 2010 7:34 pm

Severian wrote:
twistor59 wrote:Just to prove I'm not (very) prejudiced against strings:

Here is an alleged testable prediction

Superstring theory involves a single unifying superstring current for bosons and fermions that in the low-energy limit generalizes the Klein-Gordon (not the Dirac) current. By adopting a relativistic-covariant probabilistic interpretation of the current, the low-energy limit implies electron interference patterns that, under certain conditions, differ from those predicted by the Dirac current.


Do you understand where his claim "(ii) that it cannot be derived from low-energy supersymmetric field theory" comes from? I would have said that "bosonic and fermionic particles are different states of the same object" in any supersymmetric theory.


No I can't really see the basis for that either to be honest. I wouldn't have objected to calling bosonic and fermionic members of the same supermultiplet "different states of the same object" in an ordinary (non stringy) supersymmetric theory.

I assume what he's getting at is the stuff around eqns (7)-(9) (incl the long para before eq 7) - that's the stuff that I think is uniquely string theoretic and gives rise to the observed effect. (Although I know nothing about string theory, so I'm not fully sure what's going on).
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Re: How Does String Theory Work ?

#39  Postby newolder » Sep 15, 2010 8:14 pm

http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1431v2.pdf , Hrvoje Nikoli´ wrote:Finally, we note that our prediction of secondary peaks is also interesting from the point of view of foundations of relativistic QM. For example, the existence of the secondary peaks is predicted also for photons (the Maxwell equations, of course, also can be viewed as a variant of the Klein-Gordon equation), which probably could be tested more easily than for electrons. Such a test with photons would say nothing about string theory, but would represent a test of the probabilistic interpretation of the Klein-Gordon current.

How does a doubly-interesting and testable prediction say nothing about the theory? :ask:
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Re: How Does String Theory Work ?

#40  Postby twistor59 » Sep 16, 2010 7:57 am

newolder wrote:
http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.1431v2.pdf , Hrvoje Nikoli´ wrote:Finally, we note that our prediction of secondary peaks is also interesting from the point of view of foundations of relativistic QM. For example, the existence of the secondary peaks is predicted also for photons (the Maxwell equations, of course, also can be viewed as a variant of the Klein-Gordon equation), which probably could be tested more easily than for electrons. Such a test with photons would say nothing about string theory, but would represent a test of the probabilistic interpretation of the Klein-Gordon current.

How does a doubly-interesting and testable prediction say nothing about the theory? :ask:


The double peak arises from a new interpretation of the KG current. This is would be relevant for Maxwell theory regardless of supersymmetry, so observing the effect in photons would say nothing about supersymmetry/strings.

However, obeserving it in electrons would automatically imply something supersymmetric because otherwise the KG current has nothing to do with fermions. What I don't understand (and I think neither does Severian) is why this is uniquely a statement about string theory and not supersymmetric theories in general. I've never studied supersymmetric theories, so I'm not familiar with what currents can be defined from supersymmetric Lagrangians. Maybe when I get bored with LQG....
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