Why is String theory not taken seriously?

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Why is String theory not taken seriously?

#1  Postby LIFE » Apr 27, 2010 4:24 am

Note: This post will probably be full of dimwitted assertions, so please be so kind to point me to the fallacies as I cannot seem to spot them myself with my layman understanding of this realm ;)

As I understand it we have gravity which is explained by the general theory of relativity and we have electromagnetism, the weak and strong nuclear force which are explained by quantum mechanics. Now String theory comes along and tries to unify those 4 forces into one theory of everything.

Theoretical physicists claim that string theory makes astoningnishly accurate predictions but which cannot be tested in the laboratory, therefor do not follow the scientific method and are thus unfalsifiable(?).

If these predictions are that accurate, how come we cannot observe and verify/falsify these predictions?

As I understand it the last revised model of String theory barely has (or does it?) any anomalies left, ain't that evidence we're onto something serious here?

Is it a possibility that there does not have to be a unified field theory? Maybe the reductionistic search for such is a futile one?

And last but not least, why isn't the mathematical logic of String theory convincing evidence for its validity?

I keep reading and hearing that String theory should be treated as part of philosophy, yet it seems to be the only "scientific" approach to account for the various forces and their source?

Please enlighten me :dopey:
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Re: Why is String theory not taken seriously?

#2  Postby lpetrich » Apr 27, 2010 8:43 pm

I'll try.

What are those astonishingly accurate predictions?

There are three possibilities about string theory.
  1. It's not possible to get the Standard Model of particle physics out of it.
  2. It is possible to uniquely get the Standard Model out of it, to get it and no other possibility.
  3. It is possible to get the Standard Model out of it, but also oodles of other possibilities.
I've yet to see anyone come close to either (1) or (2) with string theory. One can get much of the Standard Model by a suitable choice of space-time topology, but it is far from unique, thus placing string theory in (3).

I think that string theory being in state (3) is what makes it seem unfalsifiable.

The Large Hadron Collider may eventually be able to help, by either discovering or ruling out some speculated-about physics beyond the Standard Model. This could supply additional constraints, making it possible to get closer to (1) or (2).
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Re: Why is String theory not taken seriously?

#3  Postby Sityl » Apr 27, 2010 8:50 pm

Life wrote:Theoretical physicists claim that string theory makes astoningnishly accurate predictions but which cannot be tested in the laboratory, therefor do not follow the scientific method and are thus unfalsifiable(?).


I'd like to know how one ascertains the accuracy of said predictions if they cannot be tested in the laboratory.
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Re: Why is String theory not taken seriously?

#4  Postby newolder » Apr 27, 2010 10:24 pm

num1cubfn wrote:
Life wrote:Theoretical physicists claim that string theory makes astoningnishly accurate predictions but which cannot be tested in the laboratory, therefor do not follow the scientific method and are thus unfalsifiable(?).


I'd like to know how one ascertains the accuracy of said predictions if they cannot be tested in the laboratory.

For example, a prediction (by a theory) about a distance, z metres, to the 1042th significant figure cannot be tested currently in any laboratory. Such a distance is 10 million times smaller than the realm where stringy physics is argued to begin and 10-27 times finer than the lhc's, femtometre resolution.
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Re: Why is String theory not taken seriously?

#5  Postby Sityl » Apr 27, 2010 10:28 pm

newolder wrote:
num1cubfn wrote:
Life wrote:Theoretical physicists claim that string theory makes astoningnishly accurate predictions but which cannot be tested in the laboratory, therefor do not follow the scientific method and are thus unfalsifiable(?).


I'd like to know how one ascertains the accuracy of said predictions if they cannot be tested in the laboratory.

For example, a prediction (by a theory) about a distance, z metres, to the 1042th significant figure cannot be tested currently in any laboratory. Such a distance is 10 million times smaller than the realm where stringy physics is argued to begin and 10-27 times finer than the lhc's, femtometre resolution.


Thanks for that, that's amazing lol. Are you then agreeing with me? I can understand that there are things that we can't test, but what I'm asking is, if we can't test it how can we know that it's accurate.
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Re: Why is String theory not taken seriously?

#6  Postby rEvolutionist » Apr 27, 2010 10:36 pm

Doesn't string theory have infinite solutions? That is, it relies on setting unknown constants that could have any value possible, to a predetermined value so as to give an accurate solution. I.e. it is made to fit reality after the fact. :dunno:
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Re: Why is String theory not taken seriously?

#7  Postby newolder » Apr 27, 2010 10:37 pm

num1cubfn wrote:
newolder wrote:
num1cubfn wrote:
Life wrote:Theoretical physicists claim that string theory makes astoningnishly accurate predictions but which cannot be tested in the laboratory, therefor do not follow the scientific method and are thus unfalsifiable(?).


I'd like to know how one ascertains the accuracy of said predictions if they cannot be tested in the laboratory.

For example, a prediction (by a theory) about a distance, z metres, to the 1042th significant figure cannot be tested currently in any laboratory. Such a distance is 10 million times smaller than the realm where stringy physics is argued to begin and 10-27 times finer than the lhc's, femtometre resolution.


Thanks for that, that's amazing lol. Are you then agreeing with me? I can understand that there are things that we can't test, but what I'm asking is, if we can't test it how can we know that it's accurate.

Yes and no. ;)

Such theory seems unfalsifiable at first glance (& hence has no part in science). Yet we may reject a particular theory if the theory is shown (maybe years down the road) to have internal contradiction or other, scaled-up, predictions do not match even at current scales of cruder measure.

In other words, the theory can be as accurate as it likes but if it fails by contradiction or by not matching what we already see - it'll remain only as an interesting, but failed, idea.
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Re: Why is String theory not taken seriously?

#8  Postby newolder » Apr 27, 2010 11:15 pm

rEvolutionist wrote:Doesn't string theory have infinite solutions? That is, it relies on setting unknown constants that could have any value possible, to a predetermined value so as to give an accurate solution. I.e. it is made to fit reality after the fact. :dunno:

I read at least 10500 solutions have been identified in the 'landscape' hitherto. The observable universe looks most like the loftier peaks in that landscape. As Weinberg notes, the Earth's precise orbit is not derivable from 1st principles yet there must be many earth-like orbits occupied by earth-like planets across the galaxies we see. Similarly, observable universes like ours may (or may not) be the rarest of peaks in a grander scheme, who knows?

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Re: Why is String theory not taken seriously?

#9  Postby twistor59 » Apr 28, 2010 7:36 am

LIFE wrote:
And last but not least, why isn't the mathematical logic of String theory convincing evidence for its validity?


I guess by "mathematical logic" you mean "mathematical rigour". If so then, no, mathematical rigour isn't sufficient evidence for it's validity. For example twistor theory is mathematically rigorous, but was unable to make as close a connection with physics as was originally hoped :oops: :oops: :oops:

It could be argued, however, that mathematical rigour is a necessary condition for a theory's validity.
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Re: Why is String theory not taken seriously?

#10  Postby twistor59 » Apr 28, 2010 7:39 am

Newolder, is that picture actually a representation of the string landscape ? Is there any info on what the x, y and z axes are representing there ?
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Re: Why is String theory not taken seriously?

#11  Postby newolder » Apr 28, 2010 10:24 am

twistor59 wrote:Newolder, is that picture actually a representation of the string landscape ? Is there any info on what the x, y and z axes are representing there ?

I simply searched google images on: string landscape : Results 1 - 21 of about 2,440,000 for string landscape. (0.13 seconds) 
I've linked that image to its blogosphere source but there's nothing there that answers your question. :(

This might help: The statistics of string/M theory vacua by Michael R. Douglas (Journal reference: JHEP0305:046,2003)
abstract wrote:We discuss systematic approaches to the classification of string/M theory vacua, and physical questions this might help us resolve. To this end, we initiate the study of ensembles of effective Lagrangians, which can be used to precisely study the predictive power of string theory, and in simple examples can lead to universality results. Using these ideas, we outline an approach to estimating the number of vacua of string/M theory which can realize the Standard Model.

Introduction wrote:... To explain our point, let us imagine the logically simplest possible discussion of “string phenomenology.” It would be to show that N different vacua of string/M theory lead to Standard Model-like physics, but with many different values of the couplings, uniformly distributed in the space of possible couplings (we will make this more precise in section 5). Now the basic number characterizing our observational knowledge of the Standard Model is the volume in coupling space consistent with observations, measured in natural units, O(1) for dimensionless couplings and O(Mnpl) for a coupling of mass dimension n. If we include as couplings the Higgs mass and the cosmological constant, this number is of order 10−120−40−10−9−9−50 ∼ 10−238, where we count as independent the probability for a model to realize the observed cosmological constant, Higgs mass, fine structure constant, electron and proton mass, and a product of all other Standard Model couplings (being generous in the assumed accuracy here). This is a very high precision, but suppose string/M theory led to 101000 vacua which matched the Standard Model gauge group and low energy spectrum. If so, it is likely that, in the absence of a selection principle, string/M theory would lead to no testable predictions at all.
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Re: Why is String theory not taken seriously?

#12  Postby twistor59 » Apr 28, 2010 11:00 am

newolder wrote:

This might help: The statistics of string/M theory vacua by Michael R. Douglas (Journal reference: JHEP0305:046,2003)


That paper looks interesting, thanks !

(So this is what he did after "Basic Instinct" ?)
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Re: Why is String theory not taken seriously?

#13  Postby Roger Allott » Apr 28, 2010 10:42 pm

As a non-physicist, the problem I have with string theory and/or M theory is the supposed existence of nanomicroscopic dimensions. It's a concept that makes absolutely no sense to me. How the heck can a dimension be "small", or "long", or "thin"? These are terms relevant to the primary spatial dimensions. A new dimension constrained by an existing dimension means, surely, that it's not a dimension, doesn't it?
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Re: Why is String theory not taken seriously?

#14  Postby lpetrich » Apr 28, 2010 11:53 pm

Imagine rolling up a sheet of paper. Its dimension along the rolling direction will be much shorter than that perpenducular to that direction. That sort of thing is what is meant by "small" or "long" or "thin" dimensions -- if they are curled up, what is the size of that curling?
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Re: Why is String theory not taken seriously?

#15  Postby Nautilidae » Apr 29, 2010 3:12 am

String theory makes testable predictions. They simply haven't been tested yet. For instance, if the extra dimensions that it predicts exist, physicists expect black holes and massive string-balls to be produced in LHC collisions. The LHC should shed a lot of light on string theory.
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Re: Why is String theory not taken seriously?

#16  Postby LIFE » Apr 29, 2010 3:17 am

Nautilidae wrote:String theory makes testable predictions. They simply haven't been tested yet. For instance, if the extra dimensions that it predicts exist, physicists expect black holes and massive string-balls to be produced in LHC collisions. The LHC should shed a lot of light on string theory.


Yes, I was thinking about that too. So once they discover the graviton particle actually does exist it should be evidence for at least another dimension?
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Re: Why is String theory not taken seriously?

#17  Postby Nautilidae » Apr 29, 2010 3:22 am

LIFE wrote:
Nautilidae wrote:String theory makes testable predictions. They simply haven't been tested yet. For instance, if the extra dimensions that it predicts exist, physicists expect black holes and massive string-balls to be produced in LHC collisions. The LHC should shed a lot of light on string theory.


Yes, I was thinking about that too. So once they discover the graviton particle actually does exist it should be evidence for at least another dimension?


Not necessarily. There are other models that predict the existence of the graviton. For instance, Loop Quantum Gravity doesn't require extra dimensions to be consistent, but because it is a quantum gravity theory, it predicts the graviton.
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Re: Why is String theory not taken seriously?

#18  Postby Zubin » May 02, 2010 7:56 pm

There are many physicists who are afraid of mathematics and wish to obscure knowledge such that mathematicians are unable to understand their work and do anything meaningful with it. A lot of physicists complain that string theory introduces too much math into physics, and thus should either: A) be considered a branch of mathematics, or B) ultimately be ignored.
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Re: Why is String theory not taken seriously?

#19  Postby Nautilidae » May 02, 2010 8:13 pm

Zubin wrote:There are many physicists who are afraid of mathematics and wish to obscure knowledge such that mathematicians are unable to understand their work and do anything meaningful with it. A lot of physicists complain that string theory introduces too much math into physics, and thus should either: A) be considered a branch of mathematics, or B) ultimately be ignored.


Mathematics has certainly been shown to be efficient at describing nature in the past. As long as the mathematics predicts effects that can be detectable in experiments, I don't see the problem with introducing a lot of mathematics into physics.
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Re: Why is String theory not taken seriously?

#20  Postby Zubin » May 02, 2010 9:49 pm

There are many reasons why physicists may scoff at the work of mathematicians, or string theorists. They could have an inferiority complex, or especially in the case of senior physicists, it's frustrating to have to adjust to the new times(e.g. going to the library and studying a bunch of math you never needed in your life). Many also feel mathematical rigor has no place in the physical sciences. Why adjust to the new times when we can hinder progress so we can feel comfortable, at least until we die?
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