How Does String Theory Work ?

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Re: How Does String Theory Work ?

#41  Postby newolder » Sep 16, 2010 3:54 pm

The double peak arises from stringy KG as per equation 1.
Clearly, (1) represents a stringy generalization of the Klein-Gordon equation.


Observing a double peak with photons shows the bosonic counterparts in this theory behave as if stringiness abounds - failure to observe the peaks with photons and, surely, it's time to bin the whole exercise? :ask:
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Re: How Does String Theory Work ?

#42  Postby twistor59 » Sep 16, 2010 4:25 pm

newolder wrote:The double peak arises from stringy KG as per equation 1.
Clearly, (1) represents a stringy generalization of the Klein-Gordon equation.


Observing a double peak with photons shows the bosonic counterparts in this theory behave as if stringiness abounds - failure to observe the peaks with photons and, surely, it's time to bin the whole exercise? :ask:


Well if the secodary peak is not observed for photons, it means that the new interpretation of the KG current is wrong. Since this is the foundation of the whole paper, it would kill everything. So yes, if the experiment is feasible to do with photons then it would be a good idea to do it and validate the whole thing regardless of strings.
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Re: How Does String Theory Work ?

#43  Postby newolder » Sep 16, 2010 7:16 pm

^ k. :)

...

The experiment: If points are strings then we observe double peaks in the probability density functions of both bosonic and fermionic states of matter-energy.

In units where h =c and equivalently, 8πG = 1,

a) Massless bosons.

Photons, γ, = f.

Fail here and the theory is binned.

b) Massive fermions

Electrons, Me- = f.

as f → ~ 1042 Hertz, any measurable difference between massless and massive vanishes.

The functional is non-linear and should begin to show measurable deviations from 'otherwise expected' values at around 1025 Hz. and higher.

Attosecond, 10-18 s, timing is still a factor 10 million from this realm, I fear. :( :dunno:
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Re: How Does String Theory Work ?

#44  Postby twistor59 » Sep 16, 2010 7:41 pm

I think you're right newwy, he does slip in the sentence:

A more difficult requirement is the measurement of the electron position with a precision better than it's Compton length m-1, as well as the measurement of the time of detection with roughly the same precision.
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Re: How Does String Theory Work ?

#45  Postby newolder » Sep 16, 2010 8:36 pm

My access to petajoule sources are limited, these days. :lol:
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Re: How Does String Theory Work ?

#46  Postby lucek » Sep 17, 2010 7:52 pm

Slothhead wrote: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.

D

First off it is a mathematical theory not a scientific one. Big difference there. Implying equivalence of the 2 is fallacious.
Next new work on the theory has dropped out a prediction on the behavior of entangled particles. The Experimental data isn't in yet and it won't be the be all and end all of proof, but if the predictions hold true then that would put some weight behind the theory. Beside that we still have LISA to wait for as you implied.

Edit: Forgot the link. :doh: http://www.sciencedaily.com/releases/2010/09/100901091938.htm
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Re: How Does String Theory Work ?

#47  Postby Nautilidae » Sep 30, 2010 3:26 pm

Bump/ :coffee:
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Re: How Does String Theory Work ?

#48  Postby twistor59 » Sep 30, 2010 3:49 pm

Nautilidae wrote:Bump/ :coffee:


Maybe you'd be interested in Zweibach's book

http://www.amazon.com/First-Course-String-Theory/dp/0521831431

Looks like a pretty good place to start. I have a copy, but haven't had time to read it yet - will maybe get to it by Christmas. I've had a skim through it and it seems to proceed with only undergrad level maths (a bit of vector/tensor analysis, calculus of variations... not much more).
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Re: How Does String Theory Work ?

#49  Postby Nautilidae » Sep 30, 2010 3:50 pm

twistor59 wrote:
Nautilidae wrote:Bump/ :coffee:


Maybe you'd be interested in Zweibach's book

http://www.amazon.com/First-Course-String-Theory/dp/0521831431

Looks like a pretty good place to start. I have a copy, but haven't had time to read it yet - will maybe get to it by Christmas. I've had a skim through it and it seems to proceed with only undergrad level maths (a bit of vector/tensor analysis, calculus of variations... not much more).


Have you read it? I've been interested in that book for quite awhile.
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Re: How Does String Theory Work ?

#50  Postby twistor59 » Sep 30, 2010 6:07 pm

Nautilidae wrote:
twistor59 wrote:
Nautilidae wrote:Bump/ :coffee:


Maybe you'd be interested in Zweibach's book

http://www.amazon.com/First-Course-String-Theory/dp/0521831431

Looks like a pretty good place to start. I have a copy, but haven't had time to read it yet - will maybe get to it by Christmas. I've had a skim through it and it seems to proceed with only undergrad level maths (a bit of vector/tensor analysis, calculus of variations... not much more).


Have you read it? I've been interested in that book for quite awhile.


Not yet, haven't had the time.

It starts off pretty basic, but gets to some reasonably meaty stuff (dualities, Ads/CFT) but without requiring too much on the heavy maths front. No need to be an expert in algebraic topology/differential geometry. It's quite expensive (don't think there's a paperback), but I think it's a good textbook to start with.

If you do go ahead, let me know and we can have a race through the exercises :dance:
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Re: How Does String Theory Work ?

#51  Postby twistor59 » Nov 07, 2010 3:20 pm

Nice little online tutorial here
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Re: How Does String Theory Work ?

#52  Postby tnjrp » Nov 23, 2010 10:38 am

I don't think this has been on the thread yet -- Edward Witten's audio lecture on "Duality, Spacetime and Quantum Mechanics":
http://online.itp.ucsb.edu/plecture/witten/
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Re: How Does String Theory Work ?

#53  Postby twistor59 » Jan 21, 2011 12:58 pm

Nice article (I think - only skimmed it so far), including testability:

http://particle-theory.physics.lsa.umich.edu/kane/String%20theory%20and%20the%20real%20world.pdf
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Re: How Does String Theory Work ?

#54  Postby twistor59 » Mar 31, 2011 12:13 pm

Here's a document containing a gazillion references - ranging from the popular level to the highly specialist level - on string theory:

http://arxiv.org/abs/hep-th/0311044
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Re: How Does String Theory Work ?

#55  Postby twistor59 » May 03, 2011 2:07 pm

Quite an old paper, but some of the discussion on loops vs strings is still interesting.

http://arxiv.org/PS_cache/gr-qc/pdf/0307/0307090v2.pdf

The aim of the present paper is to discuss in some detail established results on the field.
In some strong sense, the review could be finished at once, because there are none. There
are, nevertheless, some interesting attempts, which look promising from certain points of
view. Perhaps the two approaches that have attracted more attention have been the loop
approach, on the one hand and strings on the other. We shall try to critically assess
prospects in both. Interesting related papers are [21][40].
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Re: How Does String Theory Work ?

#56  Postby twistor59 » May 07, 2011 9:42 am

Interesting review article on landscape and uniqueness issues:

http://arxiv.org/pdf/0807.3249v3
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Re: How Does String Theory Work ?

#57  Postby lpetrich » Jul 20, 2011 11:01 pm

One can construct a sequence of enlarged symmetries:
Broken Standard Model: SU(3) * U(1) -- QCD, photon
Unbroken Standard Model: SU(3) * SU(2) * U(1) -- QCD, electroweak (weak isospin, weak hypercharge)
Georgi-Glashow: SU(5)
SO(10)
E6
E8

First, the (Minimal Supersymmetric) Standard Model.

Broken Standard Model: particles have quantum numbers (spin, QCD multiplet, electric charge)

Gluon, gluino: (1,8,0), (1/2,8,0)
Photon, W, Z: (1,1,0), (1,1,+-1), (1,1,0)
Neutralino, chargino: (1/2,1,0), (1/2,1,+-1)
Higgs: (0,1,0), (0,1,+-1)
Up quark antiquark / Sup qk aqk: (1/2,3,2/3), (1/2,3*,-2/3), (0,3,2/3), (0,3*,-2/3)
Down quark antiquark / Sdown qk aqk: (1/2,3,-1/3), (1/2,3*,1/3), (0,3,-1/3), (0,3*,1/3)
Neutrino antineutrino / Sneutrino santineutrino: (1/2,1,0), (1/2,1,0), (0,1,0), (0,1,0)

Unbroken Standard Model. Left and right handed parts of elementary fermions are separate in it. Quantum numbers: (QCD multiplet, weak-isospin multiplet, weak hypercharge)

Gauge: spins 1, 1/2
Gluon g: (8,1,0)
W: (1,3,0)
B (1,1,0)
Left-handed EF's, Higgs: spins 0, 1/2
Q: (3,2,1/6), U*: (3*,1,-2/3), D*: (3*,1,1/3)
L: (1,2,-1/2), N*: (1,1,0), E*: (1,1,1)
Hu: (1,2,1/2), Hd: (1,2,-1/2)
Right-handed EF's, Higgs: spins 0, 1/2
Q*: (3*,2,-1/6), U: (3,1,2/3), D: (3,1,-1/3)
L*: (1,2,1/2), N: (1,1,0), E: (1,1,-1)
Hu*: (1,2,-1/2), Hd*: (1,2,1/2)

Weak isospin works like angular momentum, meaning that WI value I gives multiplicity 2*I+1 and projected values I3 = I, I-1, ..., -I
Electric charge = (projected isospin I3) + (weak hypercharge Y)

The W breaks into I3 = +1 (Q = 1), I3 = 0 (Q = 0), and I3 = -1 (Q = -1)
The first and third are W+ and W-, the second mixes with the B to gives the photon and the Z
Their superpartners (winos, binos) mixed with the Higgs superpartners (higgsinos) to give charginos and neutralinos
Higgses break into into combinations of I3 = +1/2 or -1/2 and Y = +1/2 or -1/2, giving charges +1, 0, and -1

The U and the I3 = +1/2 part of the Q give the up quark (Q = 2/3)
The D and the I3 = -1/2 part of the Q give the down quark (Q = -1/3)
The N and the I3 = +1/2 part of the L give the neutrino (Q = 0)
The E and the I3 = -1/2 part of the L give the electron (Q = -1)
The U* and the I3 = -1/2 part of the Q* give the up antiquark (Q = -2/3)
The D* and the I3 = +1/2 part of the Q* give the down antiquark (Q = 1/3)
The N* and the I3 = -1/2 part of the L* give the antineutrino (Q = 0)
The E* and the I3 = +1/2 part of the L* give the positron (Q = 1)

I'm fuzzing over generations; up quarks include charm and top ones, down quarks include strange and bottom ones, and electrons include muons and tauons.
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Re: How Does String Theory Work ?

#58  Postby lpetrich » Jul 21, 2011 12:32 am

The unbroken (Minimal Supersymmetric) Standard Model seems as bad as the broken one. I'll now consider a series of GUT symmetries.

First, the Georgi-Glashow one: SU(5)

The elementary fermions go:
Right: 1 = N
Left: 5 = D* + L
Right: 10 = Q* + U + E
Left: 10* = Q + U* + E*
Right: 5* = D + L*
Left 1 = N*
So we have a nice alternating binomial sequence of degeneracies and chiralities (left vs. right handed):
1R, 5L, 10R, 10*L, 5*R, 1L

The Higgses go:
Left: 5 = Hd + (3*,1,1/3)
Left: 5* = Hu + (3,1,-1/3)
Right: 5 = Hu* + (3*,1,1/3)
Right: 5* = Hd* + (3,1,-1/3)
The (3,1,1/3) and (3*,1,-1/3) look like a down quark, and they form the "Higgs triplet". This particle can cause proton and bound-neutron decay, and it has to have a GUT-scale mass to keep proton decay from being observed.

Note that left-handed and right-handed sets have both 5 and 5* in them.

The gauge particles go:
24 = g + W + B + (3,2,-5/6) + (3*,2,5/6)
Only one multiplet, but it contains the familiar ones and some extra ones, which can also cause proton decay.

SU(5) unification has the interesting consequence that the EF-Higgs coupling is the same for electrons and down quarks; at GUT energies, m(tau) = m(bottom).

-

The next one up: SO(10), which breaks into SU(5) * U(1)
The second symmetry is related to (baryon number) - (lepton number) or B-L

Elementary fermions:
Left: 16 = (1,5) + (5,-3) + (10*,1)
Right: 16* = (1,-5) + (5*,3) + (10,-1)
One multiplet for all the elementary fermions in each generation

Higgses:
Left, Right: 10 = (5,2) + (5*,-2)
One multiplet for all the Higgses

Gauge:
45 = (24,0) + (1,0) + (10,4) + (10*,-4)
The SU(5) gauge multiplet + some extra ones

SO(10) predicts complete mass unification for each generation of EF's -- and forbids cross-generation decay. That sort of decay must therefore be the result of SO(10) breaking.

-

Now, E6. It breaks into SO(10) * U(1)

Elementary fermions:
Left: 27 = (16,1) + (10,-2) + (1,4)
Right: 27* = (16*,-1) + (10,2) + (1,-4)
SO(10) EF"s + possible SO(10) Higgs + extra
The Higgses can be included in one of the EF multiplets, which may explain why they couple to one generation much more than to the others. The others must be kept at GUT energies by symmetry breaking.

Gauge:
78 = (45,0) + (1,0) + (16,-3) + (16*,3)
The SO(10) gauge multiplet + some extra ones

-

Finally, E8, breaking into E6 * SU(3) in the E8 * E8 heterotic superstring

Gauge:
248 = (78,1) + (1,8) + (27,3) + (27*,3*)

The first one is the E6 gauge multiplet, while the third and fourth are E6 EF's and Higgses. The different spins are the result of "compactification" from 10 to 4 space-time dimensions. E8 gets broken into E6 * SU(3), and the compactification interacts with the SU(3) parts.

So one multiplet can contain all the Standard Model.
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Re: How Does String Theory Work ?

#59  Postby twistor59 » Oct 15, 2011 8:28 pm

Something concrete on AdS/CFT (but not great news !)

http://backreaction.blogspot.com/2011/10/adscft-confronts-data.html
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Re: How Does String Theory Work ?

#60  Postby twistor59 » Oct 23, 2011 11:00 am

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