Will string theory ever be proven wrong?

[Stringyguy0788]

Will string theory ever be proven wrong?

can string theory ever be proven wrong? will or do we have the equipment to find out?

 

[fffbone]

Originally posted by Stringyguy0788
can string theory ever be proven wrong? will or do we have the equipment to find out?

As far as proof is concerned, it can't even be proven right. All they have is the math formulas, that's why some physicians consider it a metaphysics theory rather than physics theory.

 

[meteor]

Yes, it can be proven wrong. If they're not able to find the supersymmetric particles (gravitino, gluino, etc), the theory will collapse like a house of cards

 

[selfAdjoint]

Yes it is falsifiable. There is astrophysical work going on right now to confirm or falsify some of its predictions.

As for finding supersymmetric partners, supersymmetry has developed as much as string theory has, and when you combine supersymmetry with string theory, you no longer have the simple minded particle picture of the popular accounts. The "low energy particle spectrum" is different for different superstring theories (and M-theories and Matrix theories, etc.). For each of them the matching of their low energy particle spectrum to testible physics is the holy grail, and many have and will fall by the wayside therough predicting false particles or not being able to predict phenomenological particles at all.

It's ironic that the SST critics have resurrected the old "unfalsifiable" canard just when actual falsification of SST theories becomes possible.

 

[marcus]

Originally posted by selfAdjoint
Yes it is falsifiable. There is astrophysical work going on right now to confirm or falsify some of its predictions.

...It's ironic that the SST critics have resurrected the old "unfalsifiable" canard just when actual falsification of SST theories becomes possible.

please share whatever links you have about ongoing astrophysical work able to make some substantial part of SST fall by the wayside (as you say)

when I have heard people worry about falsifiability it has sounded like a sincere concern and not just a phoney distraction ("canard").

please give us a link or two to some paper showing how
SST has become falsifiable. It seems to me to be an urgent and legitimate concern to have about such an extensive body of
theorizing.

I wonder if you are thinking about the possibility that LHC, soon to produce data, may discover evidence of SUSY? If it does that would be a great boost for string theory. But if it does not, where is it written that string theory would collapse (as meteor says) "like a house of cards." If the approaching LHC data is relevant, or even decisive, please explain a bit for those of us who don't know what different scenarios to expect.

 

[Nereid]

I'm not sure there are highly-focused, dedicated efforts under way to find experimental/observational evidence that will directly contradict SST (SMT?). Rather, there is a wide range of astronomical and astrophysical research whose results may play a significant role in falsifying (or supporting) SST.

AFAIK, SST/SMT has yet to make clear-cut predictions which can be directly tested, e.g. the mass of the Higgs, or the that of the LSSP. Of course, there are SST post-dictions, but they don't really count.

The Stecker paper which we've discussed elsewhere in PF gives some indication of what may be discovered in the high-energy regime (cosmic rays, ultra-high energy gammas). Other areas of active research which may be good tests of SST include:
- on-going cosmology research (WMAP, distant galaxy - and cluster - distributions and compositions, expansion rate of the universe at high z, ...)
- the ESSENCE project ("Equation of State: SupErNovae trace Cosmic Expansion" aka "the w project")
- searches for local dark matter, e.g. that associated with the growing list of small galaxies being cannibalised by the Milky Way
- GRBs
- gravitational waves (LIGO, VIRGO, ...)
- neutrino telescopes (esp AMANDA II)
- the next generation of space-based gamma-ray observatories (SWIFT, GLAST, ...)

Perhaps most exciting will be the serendipitous discoveries

 

[marcus]

Nereid, as you probably realize you are saying what was my impression too---unhappily enough, there is a lack of hard and fast string predictions.

Just to point up the contrast with how it's been in the past, in 1915 Einstein proposed the theory of General Relativity which predicted that light passing close to the sun would be bent by a certain angle. This was promptly tested (by Eddington in 1919)

If a substantially different bending angle had been observed in 1919 it would have shot down the whole GR theory.

20th Century physics has plenty of examples of observation advancing hand-in-hand with theory----or you might say killing off some theories and guiding the development of others. For this traditional type of scientific progress to work, theories must make firm predictions and the theorists must be willing to discard those which cannot be tested or which are tested and proven false. For a scientific theory to have meaning it must be falsifiable---must be subject to empirical disproof. That's the rule Western Science is played---you must know this as well or better than the rest of us.

If a theory is so amorphous or multiformed that it can adjust to any and all future empirical results, then ultimately it is not a part of predictive science but belongs to some other field of endeavor----fantasy, art, entertainment, philosophy, religion, metaphysics, intellectual recreation, pure mathematics, scholasticism, whatever.

Lets hope that the string folk come up with some "make or break" predictions soon and that these can be tested in a timely manner!

BTW the same urgent hope goes for Loop Gravity! I have a feeling that
several of the things you mentioned----like GLAST starting in 2006---
are going to have a bigger impact on Loop Gravity than on string!
Cant say for certain, but looks to me like astrophysical observations in near future are going to trash some versions of LQG and drive development of others in ways determined by how the observations go. Loop looks more exposed and vulnerable to empirical guidance, to me at least. (Even tho Loop has not been worked on as much as String, it is already on the brink of engaging with reality.) But this is just a side comment---the topic of the thread is String testability, so let's focus on that one.

 

[selfAdjoint]

Originally posted by marcus
please share whatever links you have about ongoing astrophysical work able to make some substantial part of SST fall by the wayside (as you say)

when I have heard people worry about falsifiability it has sounded like a sincere concern and not just a phoney distraction ("canard").

please give us a link or two to some paper showing how
SST has become falsifiable. It seems to me to be an urgent and legitimate concern to have about such an extensive body of
theorizing.

I wonder if you are thinking about the possibility that LHC, soon to produce data, may discover evidence of SUSY? If it does that would be a great boost for string theory. But if it does not, where is it written that string theory would collapse (as meteor says) "like a house of cards." If the approaching LHC data is relevant, or even decisive, please explain a bit for those of us who don't know what different scenarios to expect.

No I wasn't thinking about SUSY. I rebutted the simple SUSY failure idea and I think the way SUSY interfaces to stringy physics is sufficiently "special" that failures of low energy SUSY (and remember LHC will be ultra low energy wrt SST) wouldn't be fatal to SST.

What I was thinking mainly was the ongoing attempts to find theories that predict a believable low energy particle picture. Only some SST theories will wind up being able to do this. The trouble is there might be a google of them, but that's a bridge to be crossed when we really get to it, not a club to be waved at SST in our present state of ignorance.

I had noticed, browsing the astro-ph arxiv, a couple of papers promising tests of SST, as of LQG, via quasar light properties. I'll look them up. Hey, you're as bad as a thesis advisor about finding things for me to do! :=)

 

[notevenwrong]

The problem with string theory is not that
"all they have is the math formulas".
M-theory/non-perturbative string theory is
a purely conjectural theory, it is not known
what the dynamical degrees of freedom or
equations governing them are.

There are no predictions of string theory,
astrophysical or otherwise, since there
is no theory. Anyone who claims otherwise
doesn't know what they are talking about,
or is using a non-standard definition of
"prediction" (as in "string theory
predicts that X may happen, but then
again maybe it won't")

You're not going to find string theorists who
know what they are talking about claiming
predictions of the theory. People like Ed
Witten and David Gross are quite explicit
that the present state of the theory is such that it can't predict anything. They hope
this will change and they will find a
way to make predictions. They have been
hoping this without success for 20 years.

 

[marcus]

Originally posted by notevenwrong
The problem with string theory is not that
"all they have is the math formulas".
M-theory/non-perturbative string theory is
a purely conjectural theory, it is not known
what the dynamical degrees of freedom or
equations governing them are.

There are no predictions of string theory,
astrophysical or otherwise, since there
is no theory. Anyone who claims otherwise
doesn't know what they are talking about,
or is using a non-standard definition of
"prediction" (as in "string theory
predicts that X may happen, but then
again maybe it won't")

You're not going to find string theorists who
know what they are talking about claiming
predictions of the theory. People like Ed
Witten and David Gross are quite explicit
that the present state of the theory is such that it can't predict anything. They hope
this will change and they will find a
way to make predictions. They have been
hoping this without success for 20 years.

I was hoping someone here might take issue with your assessment, which amounts to concluding that string theory remains physically meaningless: that it is still amorphous daydreaming---not a "grown up" theory one could say.

(According to scientific convention, theories only have meaning to the extent that they are falsifiable: to the extent that experiment could cause them to be scrapped----no meaning without risk. If you ask a theorist "What experimental result would cause you to reject your theory?" and he cannot think of one, then the theory is empty.)

 

[marcus]

Originally posted by selfAdjoint
... failures of low energy SUSY (and remember LHC will be ultra low energy wrt SST) wouldn't be fatal to SST.

Then, to illustrate the point I think Mr. "notevenwrong" is making, according to you String Theory does not predict Supersymmetry will be found by the LHC.

In this case, since it does not predict, it is not at risk. Its credibility is not on the line. It does not get the credit if SUSY is found, nor does it get the ax if SUSY fails to appear.

 

[alexsok]

Originally posted by meteor
Yes, it can be proven wrong. If they're not able to find the supersymmetric particles (gravitino, gluino, etc), the theory will collapse like a house of cards

It won't get a great deal of a credit even if SUSY is discovered! Although i do believe that strictly from this vantage point, LQG is a much safer bet, since it quite elegantly subsumes and extends the much appraised GR framework.

 

[yanniru]

Is string theory falsifiable?

Lee Smolin claims that the cosmological constant observed cannot be predicted by any consistent superstring theory. His statement copied from his book is given below. Is he correct? Has there been any more recent work in this area? If true, does it falsify string theory?

Lee Smolin, pg. 220 in the Postscript of "Three Roads toQuantum Gravity" (2001)

"However, the apparent fact that the cosmological constant is not zero has big implications for the quantum theory of gravity. One reason is that it seems to be incompatible with string theory. It turns out that a mathematical structure that is required for string theory to be consistent- which goes by the name supersymmetry- only permits the cosmological constant to exist if it has the opposite sign from the one that apparently has been observed."

 

[polarstarus]

String Theory is aonly an approximation. It isn't the an absolute unifying theory.

 

[yanniru]

That did not answer any of my questions. Besides, can you name me a theory in physics that is not an approximation?

 

[selfAdjoint]

I wish someone who knows a lot about string physics would address this cosmological constant issue, or give a link to a competent discussion of it. I've never seen it covered on s.p.r, for example.

It just seems to have fallen into a black hole. Even Smolin, in his recent essays, doesn't seem to refer to it.

 

[Nereid]

cosmological constant vs dark energy

Not wishing to make things too much more complicated, however ...

The astronomical observations do not give an unambiguous value of 'the cosmological constant', nor are dark energy and the cosmological constant the same thing. Further, dark energy is just one of the proposed explanations for the observed acceleration of the expansion of the universe (and the WMAP and SDSS data, though the connection is more model-driven with these data).

Also, a request: by 'cosmological constant' are we referring to the number which is 120 OOM (or merely 59 ) too large?

{to quote Greene (Elegant Universe, p225): "Observations show that the cosmological constant is either zero (as Einstein ultimately suggested) or quite small; calculations indicate that quantum-mechanical fluctuations in the vacuum of empty space tend to generate a nonzero cosmological constant whose value is some 120 orders of magnitude [...] larger than experiment allows!"}

 

[marcus]

Originally posted by selfAdjoint
I wish someone who knows a lot about string physics would address this cosmological constant issue, or give a link to a competent discussion of it. I've never seen it covered on s.p.r, for example.

It just seems to have fallen into a black hole. Even Smolin, in his recent essays, doesn't seem to refer to it.

Leonard Susskind (wellknown as String founding father) has been addressing the CC issue a lot

here is a December 2003 quote (from the edge interview) that is really just tip of iceberg

"String theory has a very large number of vacuum solutions. Some are supersymmetric but these do not support ordinary chemistry. In addition there appear to be a huge number of non-supersymmetric vacua with non zero cosmological constant. As Gerard says, the numbers could be as large as 10 to the 500 power or bigger. The evidence for this is mathematical but not rigorous..."

This is near the conclusion of the discussion on
http://www.edge.org/discourse/landscape.html
scroll down to right before the end where Maria Spiropulu comments.

On SPR (usenet sci.physics.research in case newbies are reading this) there was a flap "The String Theory Crackup" during September and October 2003 that had partly to do with the CC (getting it to be small and positive in Stringy theories) and partly was a backwash from Susskind's pronouncements. There was some tearing of hair over this "just one number": why does it come out negative when it is supposed to be positive etc etc. I assume you remember, being an SPR regular IIRC.

----------
selfAdjoint I think you are right about the preeminent String authorities (David Gross, Vafa, other greats) being strangely quiet about the CC. It is a pressing trouble that needs authoritative resolution, so one might expect one of the big guys to step up to the plate.

As for Smolin, he HAS been writing about CC in quantum gravity, only not in the string context. Not uncommonly he includes a small positive CC in his Loop Gravity papers. Several other authors have been including small positive CC in Loop/Foam analysis where it seems to overcome some difficulties and fit in ok.
Karim Noui, Roche, Livine, Girelli, Buffenoir, Kowalski-Glikman are names that come to mind. So Smolin is not alone in incorporating CC into LQG.

 

[marcus]

Originally posted by notevenwrong
The problem with string theory is not that
"all they have is the math formulas".
M-theory/non-perturbative string theory is
a purely conjectural theory, it is not known
what the dynamical degrees of freedom or
equations governing them are.

There are no predictions of string theory,
astrophysical or otherwise, since there
is no theory. Anyone who claims otherwise
doesn't know what they are talking about,
or is using a non-standard definition of
"prediction" (as in "string theory
predicts that X may happen, but then
again maybe it won't")

You're not going to find string theorists who
know what they are talking about claiming
predictions of the theory. People like Ed
Witten and David Gross are quite explicit
that the present state of the theory is such
that it can't predict anything. They hope
this will change and they will find a
way to make predictions. They have been
hoping this without success for 20 years.

this statement by notevenwrong, back in mid-January on
this thread
continues to go unchallenged
and I have been hoping that someone will make a
serious effort to refute it by pointing us to
proposed experiments

The gist of what notevenwrong is saying seems to be that,
at least for the present,
string theory is scientifically meaningless.

(According to scientific convention, theories only have meaning to the extent that they are falsifiable: to the extent that some experiment could cause their rejection. There is no meaning without risk. If you ask a theorist "What experimental result would cause you to discard your theory?" and he cannot think of one, then the theory is empty.

A theory is scientifically empty if it can conform to any experimental outcome. If it can be molded so as to successfully accommodate any experimental result, then it has no predictive power.)

It is possible that some type of string theory IS predictive
and notevenwrong is mistaken. In which case perhaps some poster can point this out. selfAdjoint may already have done so but I wasnt sure about this and if so it could do with a bit more emphasis I think.
Or it may be that the stringy theories are not, as yet, predictive but this is because they are still developing---still conjectural---and when more work is done on them they will become real testable theories.

Urs, do you have some comment you could give us as regards
notevenwrong's statement?

 

[Nereid]

Does it not 'predict' gravity? True that's a 'post-diction' (as Greene calls it), but a powerful result none the less.

Perhaps some of the observations from LIGO, VIRGO, etc (when they get a few years' of solid data under their collective belts) will cause S(M)T to choke? From this perspective, S(M)T - like all theories - is at the mercy of the experimenters, especially the Monty Python kind ('and now for something completely different').

 

[Haelfix]

Yes String Theory can output a small, nonzero CC. However it is highly fine tuned, and it exists only in toy models. So called Kachru Vacuua.

Worse, it is not unique, there is a huge landscape of such posibilities (see Susskind and Dines paper, etc) that all interact with each other in principle.

As for predictions made by String Theory. The theorists understand the theory kinda/sorta well in highly supersymetric 10 dimensional space. Its getting 4 dimensions that's hard, since there is in principle almost an infinite amount of different ways to compactify, and you end up with a large amount of parameters (added to the already enormous amount of degrees of freedom inherent in the theory).

If the LHC doesn't find SUSY, it becomes very hard for String Theory to continue in all innocence. Part of SUSY's original aim was to remove the fine tuning, and the most reasonable models put it firmly in the LHC's range. If it doesn't find the lightest superpartner there, unfortunately it doesn't falsify SuSY (it just breaks at a different scale the enthusiast will say). However much of the original niceness goes away.

If we do find SUSY at the LHC, String theorists will jump up and down and proclaim victory. However, the two theoriest are sufficiently disjoint, such that one need not imply the other. We could live in a world with SUSY, but no ST.

Brian Greene, and others are looking for ways to get a cosmological constraint on ST. There is some debate over whether Planck could in principle see a trace of quantum gravity. If it does find something interesting, it would be wonderful of course (it would say hey QG is in fact important), however that too won't falsify st. From what I gather, it will however add a few much needed constraints to the parameter space.

 

[IooqXpooI]

No, but it will never be proved true...At least not in this century, unless I can get around to a decent particle accelerator...

 

[Nereid]

Originally posted by IooqXpooI
*SNIP ...At least not in this century, unless I can get around to a decent particle accelerator...

PSR B1706-44, M87, NGC 253, BL Lac, Mrk421, GRB04mmdd, ... goodness, even M1 (the Crab Nebula)! All of them better than the most souped-up LHC you could ever dream of.

 

[pessimist]

As far as proof is concerned, it can't even be proven right. All they have is the math formulas, that's why some physicians consider it a metaphysics theory rather than physics theory.

Can you prove General Relativity or Special Relativity? Or Quantum Mechanics? No theory of physics can ever be proven. It can only be experimentally verified and checked for self consistency. The argument you propose doesn't really fit. BTW its physicist and not physician

 

[pessimist]

Yes, it can be proven wrong. If they're not able to find the supersymmetric particles (gravitino, gluino, etc), the theory will collapse like a house of cards

If they( I assume you mean particle physicists) are not able to find super symmetric particles, string theorists can simply claim or re-modify their theories to claim that they occur at higher energies not accessible by today's particle accelerators!

 

[zetafunction]

STRING theory is FALSE , is not even falsable :( so how can it be considered even right ??

in any case there ares some regularization methods for divergent integrals without using String theory (dimensional regularization, zeta regularization of integrals and so on ..)

 

[suprised]

If they( I assume you mean particle physicists) are not able to find super symmetric particles, string theorists can simply claim or re-modify their theories to claim that they occur at higher energies not accessible by today's particle accelerators!

As if string theory and supersymmetry would be as closely connected as many claim ... unfortunately this issue is seriously fogged by statements of non-stringers like Gordy Kane, etc.

 

[pessimist]

Supersymmetry is independent. But String theory depends on the existence of supersymmetric particles.

 

[suprised]

But String theory depends on the existence of supersymmetric particles.

Not at all! The only must is world-sheet supersymmetry, if one wants to have fermions in space-time. But this does not imply spacetime supersymmetry.

 

[erkokite]

I think it's an ill-posed question. String is more of a theory of theories. There is no one unified string theory. There are many stringy models with different properties. This is like asking if gauge theory or quantum field theory is wrong or disprovable.

As for the dynamical degrees of freedom question- aren't the worldsheet coordinates and their corresponding momenta the DOF?

 

[suprised]

As has been discussed again and again, here and at other places, the hallmark of string theory are stringy resonances, and (roughly speaking) finding them or not proves or disproves string theory. Though this is mostly a matter of principle and most likely not of practice (unless the string scale is very low, which is not excluded).

As if string theory would be a completely random and structureless theory. Just the opposite is true!

 

[Lost in Space]

If it's impossible to either prove or disprove string theory, won't the theory survive because it is impossible to prove? Can standard models as well as those theories beyond them ever be ditched because we will always lack the means to prove them outright, or do we continue to search for the evidence they predict which may or may not exist or be possible to find to support them?

 

[marcus]

If it's impossible to either prove or disprove string theory, won't the theory survive because it is impossible to prove? Can standard models as well as those theories beyond them ever be ditched because we will always lack the means to prove them outright, or do we continue to search for the evidence they predict which may or may not exist or be possible to find to support them?

Lost, as I understand it, science is not about Truth with a capital T.

It is more practical and easier to define than that. It is an evolutionary process tending towards the best fit to data with the simplest model.

What you are looking for is the simplest model that gives the best fit. You don't BELIEVE in the model, you USE the model to make predictions about future observations and you keep on testing.

The faith and hope of the scientist is that the prevailing model is wrong, and that he/she will be surprised by nature at some point and allowed the privilege of discarding that model and devising an improved one.

You may begin to provisonally trust a model if it passes lots and lots of different tests over a long time. But this only means that it is approximately right within the domain/range that you are using it to make predictions. You still hope that someday it will prove inadequate.

So the game is not about Belief in some ultimate Truth.
=======================

No theory is ever proven True. No physics theory I mean.

So that is not the issue as regards String either----the collection of various related theories studied in the String program.

I think the important issue regarding String is whether and how USEFUL it is. (e.g. in predicting new physical phenomena that we can look for, and explaining what we already see.)

The question would be, I guess, are there other more useful approaches to unification and quantum geometry?

Simpler? More predictive of accessible new phenomena? Having more to say about the early universe? More specific in how they say nature should be? Less ambiguous? Less already developed (so there are more genuinely interesting research problems in evidence)?

If not, then the present situation might continue. On the other hand if yes, then one can expect some research talent to move into alternative lines and the String program to contract and retrench slightly, perhaps become more mediocre talentwise, or less full of enthusiasm. Will this happen? We don't know.

In any case IMHO the issue is not so much about proving or disproving absolute Truth.

 

[suprised]

Let's take some heat out of this eternal discussion whether strings will ever be provable or falsifiable, and take the position of a pragmatic physicist and not of a philosopher of logic.

So imagine a hypothetical scenario where the string scale is very low, say 1TeV, and strings are moderately weakly coupled. This is not yet excluded, though very unlikely the case; but for the sake of argument let's assume it. Then a firm prediction of string theory are stringy resonances, essentially at multiples of 1TeV. Assume that with a 10 TeV accelerator finds such resonances at 1,2,3,4,5,6,7,8,9,10 TeV. Woulnd't any reasonable physicist call this a proof, or at least very strong evidence, of string theory? Surely it is not a strict, logical proof, as it is not excluded that all resonances from the 11th are missing. Perhaps wait for another 30 years when it will be found that the pattern continues to at least 100TeV. Woulnd't this be a good enough physics "proof" beyond any reasonable doubt?

Of course, the notorious critic would continue jumping up and down and shouting: I, the arm chair expert, demand a real proof! But who would care about Popper this point?

 

[eiyaz]

Isn't the discovery of a spherical EDM electron and lack of SUSY particles disproving SUSY and there by falsifying string theory?

Also the lack of extra dimension, and things of such nature.