Has Recent Research Challenged the Validity of String Theory?

[Liger20]

I've been hearing a lot of talk lately regarding the validity of String Theory. There have been a lot of people that I have met that seem to think that the entire theory is completely wrong. Is there something I've been missing out on? I've always been under the impression that string theory is a valid way of describing the universe, apart from the fact that it can't really be proven directly. My argument is that just because we don't yet have the technology to verify it doesn't mean that it isn't accurate. So my question is this: has there been some kind of development in the past few years or so that has uncovered some kind of flaw in the theory?

Thanks.

 

[Sojourner01]

As my friend says "The problem with a theory of everything is that getting it to be a theory of anything is extremely difficult"

Essentially, it isn't finished. The validity of a theory is based on its ability to make testable predictions. It's not that string theory doesn't do this, merely that it doesn't do this yet. Essentially, it hasn't been shown that it probably won't work, so we must assume it probably will.

 

[marcus]

We had an earlier discussion about it in this poll thread
https://www.physicsforums.com/showthread.php?t=191373

... So my question is this: has there been some kind of development in the past few years or so that has uncovered some kind of flaw in the theory?

Well there was a major development in January 2003 with the appearance of the so-called KKLT paper----which indicated that string could not tell the difference between millions of alternative versions of physics. The number one hears estimated is usually 10⁵⁰⁰ alternative string vacua.

this paper had a major impact. It is the most highly cited string paper from then on (more references to it in subsequent research journal articles than to any paper written by string theorists since).

there was also a highly-cited followup paper by L Susskind trying to make the best of it by imagining that each one of this huge landscape of 10⁵⁰⁰ versions actually exists and we just happen to live in the one we do, which has conditions tolerable to us. The Susskind paper caused a lot of dissatisfaction and uncertainty. since those 2003 events, there has been a decline in string research output and a decline in the amount of citations string papers get.
(string theorists are writing less and they are finding less worth citing in each other's papers).

So there is internal evidence of a decline in the field, which may be temporary. It is not all traceable to KKLT. In fact several indices peaked around 2000-2001 and have been in decline since 2002. But the KKLT finding was kind of symbolic or symptomatic of the problem as a whole.

So you find that some leading figures, including very talented people, have gotten out of the string field----while others stay in the field but are noticeably less productive. This might have no longterm meaning---it might simply be a temporary doldrums or some kind of cyclic behavior---but it is observable.

It has very little to do with the books of Peter Woit and Lee Smolin, which did not appear until 2006. Whatever had been happening had been going on for several years before that.

Anyway in answer to your question, YES there has been "some kind of development" that can help to explain the impressions you have been getting. A simple way to designate it is to refer to the 2003 KKLT paper. The letters stand for four Stanford string physicists Kachru, Kallosh, Linde, Trivedi. Susskind is also a Stanford string thinker. So the whole thing is intimately associated with that one place. It's not a full explanation but it's something you can get your hands on.

 

[Cold Winter]

Well there was a major development in January 2003 with the appearance of the so-called KKLT paper----which indicated that string could not tell the difference between millions of alternative versions of physics. The number one hears estimated is usually 10⁵⁰⁰ alternative string vacua...

ThankYou for that.

String Theory is a very elegant mathematical "castle in the air". Its a bit like creating a word to describe this thing we call the "cosmos". We only need one word. The math crowd created one massive multi "option" algebra to do the same thing.

OTOH, it is precisely the fact that the "truth" is somewhere in that 10^500 options that is intriguing. This is where Lisi's Theory about E8 comes in. He has basically told us this E8 math looks like the probable option.

I've seen a lot of people pointing at these 26 dimension manifolds in E8. I believe those are the 26 un-normalized dimensions string theory started with. In effect, String could live on for a very long time as theory and experiment knock down the invalid options.

 

[marcus]

OTOH, it is precisely the fact that the "truth" is somewhere in that 10^500 options that is intriguing...

I don't think anyone can claim to know that the truth is somewhere in those particular options. It would be a leap of faith, based on personal rather than empirical grounds. But one can certainly imagine that it does, if one likes.

The most striking thing I see going on at the moment is some leading people that were in string research getting out and venturing into other areas of research. It's hard to know what will come of this, or if it is just temporary.

BTW, if you are a really enthusiastic spectator of the scene you might like to look at some of the YEAREND STATS, here
https://www.physicsforums.com/showthread.php?t=206174

 

[Fra]

I don't think anyone can claim to know that the truth is somewhere in those particular options. It would be a leap of faith, based on personal rather than empirical grounds.

I agree with this.

I've reflected over the formalism behind QM and QFT that also string theory builds on. My impression is that one problem is the general confusion between expectations and facts. a lot of these models are to simplifiy a bit, exploiting the concept of symmetries, and by "forcing symmetries" onto our mathematical models one can rule out a number of possible competitor theories by deduction.

But I personally think many of the symmetries are nothing but expected or emergent symmetries. This means that our inductive reasoning that assumes the symmetries to be carved in stone, rather than expectations, becomes speculative and it's equivalent to assigning too much confidence to the deductions themselves. And the final expectation may be crippled since along the way small deviations from our originally expected premise are hardly excluded. I call this speculative until someone can prove the symmetries, but it happens to be quite clear that this is impossible, we only have different degrees of support. And indeed a natural phenomenon is that when the degree of certainty becomes close enough to an _expected_ unity, it is assumed to be exact because this "simplification" of lowering the confidence level is sometimes favourable by the environment, since maintaining a high confidence level may take more resources than can be motivated by increasing the confidence a small relative amount.

But as humans scientists pondering about things, this i think can't be overseen in principle.

I think deductive reasoning should be replace by inductive inference where the premises are more honestly assigned a limited confidence. This balances against our limited brain capacity and resources. There is probably a limit to how many parallell working theories mankind can maintain until the overhead is too large. I think our capacity of social, economical and brain capacity limits is boundto limit our "open mindness". To always think about possible ways you can be wrong is clearly consuming resources, and you better make sure that that benefits are making up for these increased investments.

Edit: The implicit point of my ramblings is that this relates to the complexity scaling since I personally think is the physical basis for the implementation of the above. Even a human is a physical system as far as I am concerned.

A philosophical question I asked myself is, what would i do if I was a subatomic particle "exploring the world"? or more appropriately, what COULD I do? This isn't intended as a joke though, but as a teaser on how the complexity of the observer has major impacts on it's behaviour, and that non-trivial things are bound to happen as you scale the complexity.

I think there is a major difference in descrioptions how a subatomic particle experiences the world and how a human experiences how a subatomic partible seems to experience the world in the lab.

How do we parallelltransport these views by scaling information capacaity?

/Fredrik

 

[Cold Winter]

I don't think anyone can claim to know that the truth is somewhere in those particular options...

Perhaps I should have said "the truth may be" ...however taken in the context of my original post I don't think it matters.

I might also add, that we've known since the 1930s that mathematics is not necessarily linearly predictive. So I still stand by my basic policy. there's my lab bench. Show me something I can test.

 

[David_Harkin]

We had an earlier discussion about it in this poll thread
https://www.physicsforums.com/showthread.php?t=191373



Well there was a major development in January 2003 with the appearance of the so-called KKLT paper----which indicated that string could not tell the difference between millions of alternative versions of physics. The number one hears estimated is usually 10⁵⁰⁰ alternative string vacua.

The first article of the most recent new scientist talks about this...check it out.