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-   -   How Credible Is M-Theory? (http://www.physicsforums.com/showthread.php?t=99248)

Gold Barz Nov9-05 10:00 PM

How Credible Is M-Theory?
 
Is it a pretty good theory thats holding up or is it about to go down the drain?

ahrkron Nov10-05 07:39 AM

I should point out first that there is still no theory with that name. People believe (some strongly, some not) that many string theories will eventually merge into that "M", but that is not so yet.

Regardless of that, talking about string theories, you will listen very varied opinions on this matter (holding up versus going down the drain).

dubmugga Nov10-05 08:29 PM

they say string theory makes no predictions...

...but doesn't it predict a fundamental building block of a 1d point/loop, the vibrational signature and dimensionality of which determines the nature of particles, elements, light, mass and gravity ???

only trouble is it can't be tested because we are eternally locked into 5 sense in 4 dimensions...

selfAdjoint Nov11-05 10:00 AM

Quote:

Quote by dubmugga
they say string theory makes no predictions...

...but doesn't it predict a fundamental building block of a 1d point/loop, the vibrational signature and dimensionality of which determines the nature of particles, elements, light, mass and gravity ???

only trouble is it can't be tested because we are eternally locked into 5 sense in 4 dimensions...


They mean checkable predictions. Things that could be measured at Tevatron or the next collider, LHC.

dubmugga Nov11-05 05:24 PM

so how does one test for extra dimensions or symmetric particles operating in quantum fields ???

Isn't strings extra dimensionality the equivalent of unseen fields operating wavelike within 4d spacetime which particles couple to and gain mass/gravity ???

is the search then is for the mechanism or is that what the LHC is supposed to replicate ???

daniel_i_l Nov12-05 12:33 PM

One way to search for extra dimensions (if they're very small) is to check if the force of gravity per distance is differant on very small scales than what it is on very large scales. Some people think that the reason that gravity is so weak over large macroscopic (and sofar microscopic) distances is that some of it goes to the other dimensions while what's left is very weak.

ahrkron Nov12-05 12:41 PM

Quote:

Quote by dubmugga
...but doesn't it predict a fundamental building block of a 1d point/loop, the vibrational signature and dimensionality of which determines the nature of particles, elements, light, mass and gravity ???

It does not predict the 1d loop; it starts from there.

But it does not make a clear, unique prediction of the output of an experiment.

dubmugga Nov12-05 10:57 PM

you mean like some models don't predict a singularity, it just starts from there...

...isn't the proof for string in the maths and that is fundamentally sound, i mean isn't eveything maths based and as long as that stacks up then it's sweet ???

I don't get why it has to make a clear and unique prediction of the output of an experiment ???

...and just cos it doesn't people want to bin it in favour of what ???

surely there has to be some sort of fundamental minimum scale particle that operates string like in 4d ???

so perhaps a rose by another name...

selfAdjoint Nov13-05 08:26 AM

Quote:

Quote by dubmugga
you mean like some models don't predict a singularity, it just starts from there...
...isn't the proof for string in the maths and that is fundamentally sound, i mean isn't eveything maths based and as long as that stacks up then it's sweet ???
I don't get why it has to make a clear and unique prediction of the output of an experiment ???
...and just cos it doesn't people want to bin it in favour of what ???
surely there has to be some sort of fundamental minimum scale particle that operates string like in 4d ???
so perhaps a rose by another name...

The one great thing that String physics has going for it is the sweet math. It is impressive, but then the mathematicians have gobs of sweet math, and that isn't physics. The point is that if the only things you can say about the universe are things that can't possibly be checked, then what good is your theory? Is it only an art form, to be admired without doing anything?

Juan R. Nov13-05 08:31 AM

Quote:

Quote by Gold Barz
Is it a pretty good theory thats holding up or is it about to go down the drain?

Last advances prove that string theory is unable to predict anything. Therefore has failed like a theory of physics.

The problem of string thorists is that was not sincere in the past. They claimed that are computing this and this other when was not true. For example in comutation of black hole entropy they begin from a well defined geometry then split it by hand and choose by hand the correct 4D manifold compatible with GR (that is not a prediction) then write the equations for the action and next modify they again by hand by compatibility by thoughts from GR.

Next they write a model of Black hole what is NOT the model of GR (it is a theoretical model invented by string theorists) and compute the entropy. They obtain a correct result, but the way was forced. It was not a derivation.

They wait that in a future they could do a ab initio computation from first principles of string theory. BUt those principles nwer were found and recent advances proven that due to vacua degeneraty, string theory CANNOT predict anything. One may complement the theory with experimental data because there is a minimum of 10000 parameters that are not fixed by theory and that in prinple cannot even be experimentally measured.

The Standard Model of particle physics contained less than 20 parameters that are obtained from experiment. Once you know the parameters (somewhat as you know what is the value of constants as c, G, etc.) you can predict things

Juan R. Nov13-05 08:38 AM

Effectively, string theory does not predict building block of a 1d point/loop, string theory begin from that postulate.

But that postulate is WRONG. As proved in brane theory (yes people does not know it), the strings are NOT fundamental (string theorists were wrong) and the simplicity of 1d loops is missed.

Brane theory is based in p-branes, where p is an index goes from 0 to 9. The string is not fundamental except as approximation.

Still more interesting is the ONLY formulation of M-theory known. I refer to Banks M(atrix) theory.

In M(atrix) theory, the fundamental object are pointlike objects in 10D, doing the traditional idea of that pointlike objects are approximations just outdated.

It is more M(atrix) theorists have proven that the string (an 1-brane) arise like an approximation from a pointlike object.

Remember that during decades string theorists claimed that the string was fundamental and that pointlike objects of Standard Model of particle physics an approximation.

M(atrix) theory is not complete.

Rake Nov13-05 02:42 PM

Quote:

Quote by dubmugga
...isn't the proof for string in the maths and that is fundamentally sound, i mean isn't eveything maths based and as long as that stacks up then it's sweet ???
I don't get why it has to make a clear and unique prediction of the output of an experiment ???

because that is the only way other than direct observation that string, or any other theory for that matter, is able to make the leap from philosophy to physics or more to your point from math to science.

mccrone Nov13-05 03:04 PM

Quote:

Quote by Juan R.
Effectively, string theory does not predict building block of a 1d point/loop, string theory begin from that postulate. But that postulate is WRONG. As proved in brane theory (yes people does not know it), the strings are NOT fundamental (string theorists were wrong) and the simplicity of 1d loops is missed.

An alternative view is that stringiness emerges via a system of constraint. So the fact that it is "approximations" all the way down the hierarchy is simply a reflection of the fact that physical reality is constructed by an asymptotic approach to limits.

String theories model the harmonics of symmetries. LQG theories are focusing on the self-organisation of the spaces that can sustain the harmonies. One models figure, the other ground, perhaps. But I agree that fundamental mistakes are being made because people don't see that the universe is a system and systems have their own science as well.

Cheers - John McCrone.

dubmugga Nov13-05 10:30 PM

Quote:

Quote by Juan R.
the strings are NOT fundamental (string theorists were wrong)

...then what is ???

Is not the initial postulate proven by the sweet maths which then predicts a string like object ???

Is there no fundamental minimum scale building block or if there is what would YOU call it, how would you have it work and what would you have it do ???

me, i like bubbles, where a 3dsphere is the membrane made of light flickering on and off causing time and motion...

...but then again I'm just a simple know nothing dumbugga

:rolleyes:

Juan R. Nov14-05 05:33 AM

Quote:

Quote by dubmugga
...then what is ???
Is not the initial postulate proven by the sweet maths which then predicts a string like object ???
Is there no fundamental minimum scale building block or if there is what would YOU call it, how would you have it work and what would you have it do ???
me, i like bubbles, where a 3dsphere is the membrane made of light flickering on and off causing time and motion...
...but then again I'm just a simple know nothing dumbugga
:rolleyes:

String theory is outdated. Today it was substituted by brane theory. In brane theory the fundamental object is the so called p-brane. with p = 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.

Some authors (e.g.Banks and his M-theory) claim that the fundamental object is really a D0-brane.

It is all pure confusion. String theory is a waste of time.

dubmugga Nov14-05 09:21 AM

so what's your alternative Juan R. ???
Is not the initial postulate proven by the sweet maths which then predicts a string like object ???
Is there no fundamental minimum scale building block or if there is what would YOU call it, how would you have it work and what would you have it do ???

I don't think it's enough to say something is a waste of time if you don't offer up something else to occupy one's time productively

Juan R. Nov14-05 10:14 AM

Quote:

Quote by dubmugga
so what's your alternative Juan R. ???
Is not the initial postulate proven by the sweet maths which then predicts a string like object ???
Is there no fundamental minimum scale building block or if there is what would YOU call it, how would you have it work and what would you have it do ???

I don't think it's enough to say something is a waste of time if you don't offer up something else to occupy one's time productively

For understand elementary particles?

An approach based in a non-perturbative quantum gravity study of topological regions in a 4D universe. Particles are studied in a similar way to the theory of pre-spinors in the sense of D. Finkelstein, the link with Coxeter groups...

For understand interactions?

A generalization of Fokker/Dirac/Wheeler/Feynman/Hoyle/Narlikar theory.

And yes, one can call string theory a waste of time because that is it really is. In fact, it is just that as have called by many many people. For example, Nobel Prize for Physics P. W. Anderson called string theory

Quote:

a futile exercise as physics
at beggining of this year in a popular magazine.

dubmugga Nov14-05 04:05 PM

I wish I'd never asked now...

:confused: :biggrin: :wink:


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