B Is string theory dead or still valid

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I agree, I'm working with group manifolds and the coolest thing happened, I reduced the possible manifolds that might allow dS vacua to 4 (compactification to D=6, trying to find a toy model).
It turns out I get almost exactly the same equations (unsolved for now) for each manifold. This suggests something deeper could be happening but I haven't seen it yet. (my advisor and his collaborators has a hunch but its far from conclusive)

That's the deal with string theory and supergravity, often we have a feeling and need to investigate more but going deeper takes time (which I no longer have).

I'd say the answer to the OP is that it's not dead but there are some issues we don't fully understand.

And my opinion wrt other candidates for a theory of quantum gravity is that we need some authorities that know two of the theories very well.
Who knows one could use ideas from other theories in whatever flavour they like best.
 
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Similar to my opinion. We need a 3rd and fourth revolution. I guess also, we will get these inspirations from complete different fields to string theory. We will see.
 

haushofer

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I agree, I'm working with group manifolds and the coolest thing happened, I reduced the possible manifolds that might allow dS vacua to 4 (compactification to D=6, trying to find a toy model).
It turns out I get almost exactly the same equations (unsolved for now) for each manifold. This suggests something deeper could be happening but I haven't seen it yet. (my advisor and his collaborators has a hunch but its far from conclusive)

That's the deal with string theory and supergravity, often we have a feeling and need to investigate more but going deeper takes time (which I no longer have).

I'd say the answer to the OP is that it's not dead but there are some issues we don't fully understand.

And my opinion wrt other candidates for a theory of quantum gravity is that we need some authorities that know two of the theories very well.
Who knows one could use ideas from other theories in whatever flavour they like best.
Then you surely must have seen this one,

https://arxiv.org/abs/1804.01120

We present a brief overview of attempts to construct de Sitter vacua in string theory and explain how the results of this 20-year endeavor could point to the fact that string theory harbors no de Sitter vacua at all. Making such a statement is often considered controversial and "bad news for string theory". We discuss how perhaps the opposite can be true
To me, it becomes a bit suspicious how every time something initially bad for string theory turns out to be good. Just sayin'.
 
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Is it true non-perturbative string theory or M-theory cannot be reduced to QFT except in some limits? Why?

What are the most complicated forces/new fields of nature that QFT can be valid and where it is not (then M-theory or something more complicated takes over)? Any reference of the limitations of our vintage QFT?
 

phyzguy

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We cannot currently detect the extra dimensions, but M-theory makes a lot of predictions that can be tested. At the moment, it is still valid.
Can you name any testable predictions made by M-theory and tell us how the results compare to observations? I would not consider it "valid" until it is an actual theory where one can do calculations and compare the results to observations. I do not think that this is yet the case.
 

Fra

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To me, it becomes a bit suspicious how every time something initially bad for string theory turns out to be good. Just sayin'.
I think this is another manifestation of "duality". There is no such thing as, good or bad, it is all just a matter of choice of background context ;-)

/Fredrik
 

phyzguy

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It seems to me that the name "string theory" is a misnomer. A theory in physics is a model where I can do calculations and compare the results of these calculations withe experiment. SInce this isn't (yet) the case in string theory, I think it would be more appropriate to call it the "string concept" or the "string idea".
 

PeroK

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It seems to me that the name "string theory" is a misnomer. A theory in physics is a model where I can do calculations and compare the results of these calculations withe experiment. SInce this isn't (yet) the case in string theory, I think it would be more appropriate to call it the "string concept" or the "string idea".
... or "string thing"?
 

haushofer

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It seems to me that the name "string theory" is a misnomer. A theory in physics is a model where I can do calculations and compare the results of these calculations withe experiment. SInce this isn't (yet) the case in string theory, I think it would be more appropriate to call it the "string concept" or the "string idea".
Well, string theory is a 2-dimensional (superconformal) quantum field theory. But quantum field theory in itself is a paradigm, not a theory. So I guess that's where the bad naming starts.

Regarding experiments: I think people doing AdS/CFT would disagree. String dualities are testable.
 

phyzguy

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Well, string theory is a 2-dimensional (superconformal) quantum field theory. But quantum field theory in itself is a paradigm, not a theory. So I guess that's where the bad naming starts.

Regarding experiments: I think people doing AdS/CFT would disagree. String dualities are testable.
Quantum Field Theory can do detailed calculations that can be compared to experiment in exquisite detail. Things like scattering amplitudes and the electron or muon magnetic moment. It's not at all like string theory in that respect.

Can you name a "string duality" that has been tested against observations?
 

ohwilleke

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Didn't someone invent a bunch of dimensions in order to make the theory compatible with other theories but are the extra dimensions right or correct.
String theory has never been established to be a valid description of the real world. But, it isn't dead. A plurality of theoretical physicists in the world are still working on it.
 
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String theory has never been established to be a valid description of the real world. But, it isn't dead. A plurality of theoretical physicists in the world are still working on it.
Well as Niels Bohr might say, ST —or any other theory for that matter— cannot describe the actual, real, underlying world of particle physics, it can only say something about it.

In that sense ST has said a lot, a whole whole lot over 40+ years now. Maybe too much for some people’s taste.

The day all that can be tied to a feasible experimental set-up, ST will explode. I would think cosmology is a better candidate to provide that experimental link one day than HEP/particle physics...maybe with the Webb space telescope and some high-resolution soundings of black holes?...


IH
 

Dr. Courtney

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Didn't someone invent a bunch of dimensions in order to make the theory compatible with other theories but are the extra dimensions right or correct.
The question, "Is string theory dead or still valid?" highlights a common failure of science education that instills (or allows) folks to frame scientific questions as false dichotomies when it comes to the validity of theories.

It is more complicated than "dead or still valid."

Scientific theories are never really proven, but given a long enough track record of making testable predictions that are later confirmed, one can say a theory is well supported and validated. String theory never came anywhere near this.

Scientific theories can also be disproven by experimental results that contradict their predictions. String theory has not really suffered this fate either, since there have not been many (or any) real predictions within the abilities of modern experiments to test them.

The ups and downs of string theory have been more like a scientific popularity contest falling in and out of favor (and funding) rather than really meeting the fundamental scientific tests of validity or testability.

https://blogs.scientificamerican.com/cross-check/why-string-theory-is-still-not-even-wrong/
 

FactChecker

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Can you name any testable predictions made by M-theory and tell us how the results compare to observations? I would not consider it "valid" until it is an actual theory where one can do calculations and compare the results to observations. I do not think that this is yet the case.
I have always thought that a statement like this deserved some discussion. Clearly the theory agrees with many facts that were already known. The difference between those earlier-known facts and later-confirmed predictions is just the timing of the development of the theory. Of course, one must be sceptical of theories that were rigged to agree with already known facts, but I think there should be better criteria applied than the simple timing of the development of a theory. Some theories fit very simply into earlier accepted theories while others seem like "Rube Goldberg" contraptions.
 
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phyzguy

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I have always thought that a statement like this deserved some discussion. Clearly the theory agrees with many facts that were already known.
Can you give an example of a known fact that is derivable from string theory and explain how it is derived from the set of string theory assumptions?
 

FactChecker

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Can you give an example of a known fact that is derivable from string theory and explain how it is derived from the set of string theory assumptions?
I have no expertise on this subject, so I can not. My question / comment is a general one that keeps occuring to me when the issue comes up. I just assumed that there were some constraints on the theory. If there are no constraints at all, either to fit facts already known or to predict results, then I don't know what the purpose of the theory is. It never occured to me, till you asked, that the theory may not fit any already known facts.
 

phyzguy

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I have no expertise on this subject, so I can not. My question / comment is a general one that keeps occuring to me when the issue comes up. I just assumed that there were some constraints on the theory. If there are no constraints at all, either to fit facts already known or to predict results, then I don't know what the purpose of the theory is. It never occured to me, till you asked, that the theory may not fit any already known facts.
You are the third person in this thread who has made the claim that string theory makes testable predictions, and the third person who has been unable to name one when I challenged them. I think, as I said in post #32, that string theory is not a "theory" in the sense that we usually mean. It is more a set of ideas that might some day be concise enough to allow predictions to be made.
 

FactChecker

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You are the third person in this thread who has made the claim that string theory makes testable predictions, and the third person who has been unable to name one when I challenged them. I think, as I said in post #32, that string theory is not a "theory" in the sense that we usually mean. It is more a set of ideas that might some day be concise enough to allow predictions to be made.
Sorry if I wasn't clear. Let me clarify my earlier post. Are you saying not only that it can not make predictions of new things to be verified, but also that it does not fit and support any already tested facts? That would be a strong statement that you are making and it leaves the obvious question: What motivated the theory if it can't explain anything we already know and can't predict anything new. The difference between the two cases is only the chronology of the facts being verified versus the development of the theory.
 
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phinds

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What motivated the theory if it can't explain anything we already know and can't predict anything new.
The early developers thought it eventually WOULD make testable predictions. Even after forty years of none such some of them apparently have still not changed their minds.
 
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String theories have not been shown to be either true or false.
A lot of things are like that.
 
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It looks pretty?

Cheers
That would seem to be one very big attraction. Despite the complex maths vs Occam’s razor, ST would seem to have some very elegant mathematics behind it.

String theorists are betting that it is a big, huge, comprehensive and immensely complex version of Dirac’s equation out of which anti-matter miraculously ‘plopped’ out, that its elegant maths predict boatloads of unsuspecting physics...that its mathematics are an Oracle...


IH
 
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