Is String Theory the Monopolistic Theory in Modern Physics?

[julian]

Just to quote Smolin's - `appealing to authority' -sorry - "The case for background independence" http://fr.arxiv.org/pdf/hep-th/0507235

"Some string theorists have also claimed that string theory does not need a background independent formulation, because the fact that string perturbation theory is, in principle, defined on many different backgrounds is sufficient. This assertion rests on exaggeration and misunderstanding. First, string perturbation theory is so far only defined on stationary backgrounds that have timelike killing fields. But this is a measure zero of solutions to the Einstein equations. It is, however, difficult to believe that a consistent string perturbation theory can be defined on generic solutions to the Einstein equations because, in the absence of timelike killing fields, one cannot have spacetime supersymmetry, without which the spectrum will generally contain a tachyon21."

He then goes on to say:

"More generally, this assertion misses completely the key point that general relativity is itself a background independent theory. Although we sometimes use the Einstein’s equations as if they were a machine for generating solutions, within which we then study the motion of particles of fields, this way of seeing the theory is inadequate as soon as we want to ask questions about the gravitational degrees of freedom, themselves. Once we ask about the actual local dynamics of the gravitational field, we have to adopt the viewpoint which understands general relativity to be a background independent theory within which the geometry is completely dynamical, on an equal footing with the other degrees of freedom. The correct arena for this physics is not a particular spacetime, or even the linearized perturbations of a particular spacetime. It is the infinite dimensional phase space of gravitational degrees of freedom. From this viewpoint, individual spacetimes are just trajectories in the infinite dimensional phase or configuration space; they can play no more of a role in a quantization of spacetime than a particular classical orbit can play in the quantization of an electron."

 

[Ilja]

I really don't think this is true. There are, for example, a lot of people doing LQG, higher spin field theory, etc. In my department, we have people working on "2 time physics", which is highly speculative and probably only a handful of people do it. And outside of quantum gravity, you also have people working on all kinds of beyond-SM stuff.

Maybe the situation has already changed a little bit, given that the failure of string theory has been already recognized more widely. That would be nice.

As someone about to apply for my first postdoc, and thus intimately aware of the job-insecurity game, I have to disagree with the notion that this shuts out new ideas. A new idea is not generally developed in the fashion of Einstein (working on something alone for years and then publishing it). A new idea is developed a little bit at a time, shared with the community, improved upon, etc. And if any new idea looks promising (or even just interesting), I guarantee a lot of people will jump into it and publish a flurry of papers, potentially making the originator(s) of the idea famous and important. This is what has happened in the last year and a half over black hole firewalls, for example.

This is possible if the new idea is sufficiently close to the mainstream. My approach was too far away from it - I have used a preferred frame, and that's almost forbidden. But, even worse, once there was a preferred frame, I have continued to move into this direction and tried for a condensed matter interpretation of the GR and SM fields. That was already far too much, an ether theory. So my experience was that I was completely alone. And even after I have succeeded to publish the results in Foundations of Physics, there was almost no reaction.

Quite surprising, if you look at the results. The particular quite simple model gives all the SM fermions, exactly three generations, and the SM gauge group with its action on the fermions. Together with a lot of massive scalar fields, so I'm yet not afraid of the Higgs observation. Imagine something similar reached by string theory, there would be thousands of papers about it. I have also needed a lot of time to complete the model, but I was unable to publish any intermediate results. That I was able to publish the final paper arXiv:0908.0591 was also only a happy accident: I have been able to solve a final large problem - to include weak interactions appropriately - weeks after receiving a review which required major revisions - because the model was yet unable to include weak interactions. Without this accidental coincidence, I guess the final paper would have been rejected because the Higgs sector is not handled appropriately.

Up to now, I haven't seen any reaction in form of people jumping in or papers about it. An ether theory is, obviously, even if published in Foundations of Physics and considering relativistic gravity and the standard model, too far away from the mainstream, too much anathema.

 

[atyy]

Just to quote Smolin's - `appealing to authority' -sorry - "The case for background independence" http://fr.arxiv.org/pdf/hep-th/0507235

"Some string theorists have also claimed that string theory does not need a background independent formulation, because the fact that string perturbation theory is, in principle, defined on many different backgrounds is sufficient. This assertion rests on exaggeration and misunderstanding. First, string perturbation theory is so far only defined on stationary backgrounds that have timelike killing fields. But this is a measure zero of solutions to the Einstein equations. It is, however, difficult to believe that a consistent string perturbation theory can be defined on generic solutions to the Einstein equations because, in the absence of timelike killing fields, one cannot have spacetime supersymmetry, without which the spectrum will generally contain a tachyon21."

He then goes on to say:

"More generally, this assertion misses completely the key point that general relativity is itself a background independent theory. Although we sometimes use the Einstein’s equations as if they were a machine for generating solutions, within which we then study the motion of particles of fields, this way of seeing the theory is inadequate as soon as we want to ask questions about the gravitational degrees of freedom, themselves. Once we ask about the actual local dynamics of the gravitational field, we have to adopt the viewpoint which understands general relativity to be a background independent theory within which the geometry is completely dynamical, on an equal footing with the other degrees of freedom. The correct arena for this physics is not a particular spacetime, or even the linearized perturbations of a particular spacetime. It is the infinite dimensional phase space of gravitational degrees of freedom. From this viewpoint, individual spacetimes are just trajectories in the infinite dimensional phase or configuration space; they can play no more of a role in a quantization of spacetime than a particular classical orbit can play in the quantization of an electron."

Smolin did not argue that string theory was worthless. He argued that string theory had been oversold by some string theorists, and that approaches other than string theory are also valuable.

In fact, Smolin had worked on possible relationships between LQG and string theory, which indicates he considered it worthwhile. I suggest reading these 3 papers that indicate the relationship between LQG and string theory is still worth studying.

http://arxiv.org/abs/0905.3627
http://arxiv.org/abs/0907.2994
http://arxiv.org/abs/1212.5183

The link between LQG and strings in the second is indirect, but tensor networks were recently used by Hartmann and Maldacena, both of whom are stringists. The last is a collaboration between an LQGer and a stringist.

 

[atyy]

I am. Did I say something to give myself away? ;)

Well, I saw you had lots of posts in the squalid state section:)

My discipline (living organisms) is even more squalid than yours, but may I suggest why condensed matterists should consider string theory their Trojan horse?

Two condensed matter viewpoints I've heard are:
1) No theory of everything!
2) Everything is emergent!

With the string landscape, string theory has taught HEP people that there will be multiple vacua - just like condensed matter is in large part a study of the multiple low energy "vacua" that correspond to different materials, ie. string theory is the apotheosis of squalidity. (John McGreevy makes a similar analogy: Monovacuist (n): One who believes that a theory of quantum gravity should have a unique groundstate (in spite of the fact that we know many examples of much simpler systems which have many groundstates, and in spite of all the evidence to the contrary)).

Then with AdS/CFT presently providing the only non-perturbative definition of string theory, that means that string theory is defined by QFT, which perhaps can be emergent from a condensed matter type of lattice model. (A string theorist who's said something like this is Raman Sundrum: Let us ask whether the pre-requisite CFT can itself emerge from something even more basic and less symmetric. It is common for equilibrium condensed matter systems, which may be discrete lattice theories at short distances, to approach conformal field theories in the IR, at second order phase transitions. Because time is out of the picture at equilibrium, these are Euclidean CFTs. However, in real-time systems even the approach to emergent special relativity, let alone Lorentzian conformal invariance, is subtler.)

So secretly, condensed matter rules the "TOE". OK, I'm half kidding, but just half;)

 

[Ben Niehoff]

By world-sheet theory do you mean perturbative string theory cus this is not background independent because basic structures - Hilbert space, algebra of observable operators, etc depend on the background spacetime chosen.

By world-sheet theory, I mean the CFT defined on the worldsheet. I.e., it is a 2d CFT with various fields living on some Riemann surface with punctures. Specifically it is a kind of nonlinear sigma model.

There is no background spacetime.

You need to remove cartoony pictures in which a "string" propagates on some "background" from your head. That is not how string theory is understood today.

To be background-independent the Hilbert space etc must simultaneously accommodate all backgrounds.

GR doesn't even do that. I guess GR is not background independent.

Of course, really we're talking nonsense here, because GR is a classical theory and there is no notion of Hilbert spaces in the first place. If "background independence" is a quality we say GR should have, then certainly it is not a notion that is defined by referring to Hilbert spaces.

But I have yet to see a clear, precise definition of what "background independent" is actually supposed to mean except "a property we want LQG to have but string theory not". I have occasionally seen it paraphrased as "no prior geometry", but as you see here, when I explain how string theory has no prior geometry, the definition of "background independent" weasels its way into something else.

Perturbative string theory can't even be defined time-dependent spacetime without getting Tachyons.

Patently false. Worldsheet SUSY is enough to kill the tachyons. Low-energy solutions to supergravity need not be supersymmetric.

Think about that for a moment. If a theory has a certain symmetry, must all solutions of that theory have the same symmetry? For example, Newton's law of gravity is rotationally invariant. Is the motion of the solar system rotationally invariant?

Just to quote Smolin's - `appealing to authority' -sorry - "The case for background independence" http://fr.arxiv.org/pdf/hep-th/0507235

I don't know why Smolin appears to believe that string perturbation theory requires us to choose, by hand, a spacetime in which the string propagates. Maybe it's because he hasn't done string theory in a long time, and his understanding of it is not up to date. (Nor would I expect his understanding to be up to date; despite his being a very smart guy, he does, after all, work in an entirely different field now.)

 

[carlgrace]

Well, I saw you had lots of posts in the squalid state section:)

My discipline (living organisms) is even more squalid than yours, but may I suggest why condensed matterists should consider string theory their Trojan horse?

Two condensed matter viewpoints I've heard are:
1) No theory of everything!
2) Everything is emergent!

With the string landscape, string theory has taught HEP people that there will be multiple vacua - just like condensed matter is in large part a study of the multiple low energy "vacua" that correspond to different materials, ie. string theory is the apotheosis of squalidity. (John McGreevy makes a similar analogy: Monovacuist (n): One who believes that a theory of quantum gravity should have a unique groundstate (in spite of the fact that we know many examples of much simpler systems which have many groundstates, and in spite of all the evidence to the contrary)).

Then with AdS/CFT presently providing the only non-perturbative definition of string theory, that means that string theory is defined by QFT, which perhaps can be emergent from a condensed matter type of lattice model. (A string theorist who's said something like this is Raman Sundrum: Let us ask whether the pre-requisite CFT can itself emerge from something even more basic and less symmetric. It is common for equilibrium condensed matter systems, which may be discrete lattice theories at short distances, to approach conformal field theories in the IR, at second order phase transitions. Because time is out of the picture at equilibrium, these are Euclidean CFTs. However, in real-time systems even the approach to emergent special relativity, let alone Lorentzian conformal invariance, is subtler.)

So secretly, condensed matter rules the "TOE". OK, I'm half kidding, but just half;)

Wow that's a fascinating article! Thanks for sharing it. You know, the level of discourse between my colleagues and me regarding string theory is pretty much at the level of Brian Greene and Lee Smolin books, but I would agree with you about the idea we are quite suspicious of even the idea of a theory of everything (even if, as you imply condensed matter *is* the theory of everything haha). Also, the concept of everything is emergent sure resonates with us.

Thanks for the link!

 

[tom.stoer]

I'll think we need to start a new thread - https://www.physicsforums.com/showthread.php?t=700495

 

[Demystifier]

To all who say they wish to become a String Theorist (but may not have even graduated from college yet), I ask a serious question:

Why would you want to do such a thing?

Because string theory is the theory of everything, and who doesn't want to know everything?

 

[schema]

I am deeply rooted in relativistic physics. I reject string theory on all levels due to my bias. This is basically what I conclude from hours and hours of Michio Kaku pontification: " Our entire, long standing, anomaly riddled theory is hinged apon the existence of gravitons, for which there is -and probably never will be- proof of. But we are right, trust us."
Everyone is out searching for a unified theory, and I hate to say it, but string theory is the best game in town right now. I heard conjecture somewhere about string theory and how the theorists are abandoning the idea of the strings in favor of variations of M-theory. I am not sure if that is true or not, but I concure none-the-less. I never understood the significance of 7 smaller dimensions. I can't fathom the dimenions suggested in M-theory. I guess they have to make the math make sense somehow.

 

[friend]

Everyone is out searching for a unified theory, and I hate to say it, but string theory is the best game in town right now. ...

"unified theory..." I strongly suspect that we are not going to know how to unified all the quantum fields until we know where quantum theory comes from to begin with. And String theory doesn't even start to address this.

 

[schema]

"unified theory..." I strongly suspect that we are not going to know how to unified all the quantum fields until we know where quantum theory comes from to begin with. And String theory doesn't even start to address this.

Before we can understand QM, we have to have a complete working standard model. One of the problems with the model now is that is being challenged by particles that aren't predicted by the model. Take for instance the "2nd" higgs that was discovered some months back. It wasn't heavy enough to be an accurate model prediction, yet the theorists ignored the fact and gladly announced it. That is the problem with string theory to being with- it is centralized around a "theorized" model that is only complete in theory (sparticles, gravitons).

String theory or not, our biggest problem is the model itself. It is polarizing. Some theorists wish to describe reality as it SHOULD be (according to the model) instead of how it actually is.

 

[schema]

I think we will find symmetry in the future. I think the secret lay somewhere in the higgs field. I can't wait to see what kind of exotic particles CERN is going to discover in the next decade.

 

[mitchell porter]

schema - it seems like part of your problem with string theory is actually a problem with the very idea of gravitons, because you are thinking of "gravity caused by gravitons" as logically incompatible with "gravity caused by curved space"?

 

[schema]

schema - it seems like part of your problem with string theory is actually a problem with the very idea of gravitons, because you are thinking of "gravity caused by gravitons" as logically incompatible with "gravity caused by curved space"?

What evidence is there of string theory? I don't think there is enough to warrant revisions to General Relativity. The idea seems more like meta-physics, or philosophy to me. But I am open minded and willing to debate the facts without being biased.

At the moment, Einstien's theory holds true which is evidenced by detectable gravity waves.

 

[mitchell porter]

String theory grew out of particle physics, and one of its attractions is that it has the potential to explain numbers that quantum field theory can't - I mean numbers like the parameters of the standard model. In a field-theoretic framework, they are necessarily freely adjustable parameters, but in a string theory, given a particular topology (etc) for the extra dimensions, they are potentially calculable.

I mentioned "gravitons vs curved space" because it seems to be a factor in your thinking - you seem to think it's an either/or choice. But in an advanced theory of quantum gravity, a graviton should be a "quantum of curved space". It's not throwing out general relativity, it's combining it with quantum mechanics.

 

[Mandelbroth]

Is string theory worthwhile?

I usually don't poke my head too much into this part of physics forums. I typically stay with the mathematical portion of the forum, so perhaps "mathematically elegant" means something different to me than to you.

Is string theory worthwhile? This is an odd question for a scientist, particularly because it says, to me, that the person asking has no interest in science.

Is it worthwhile to spend millions upon millions of dollars constructing a 27 kilometer ring for firing really small particles at each other in the hopes of proving the existence of a theoretical particle that explains the phenomenon of mass? Surely this money could have been spent on providing food to starving children or finding a cure for cancer?

Of course it's worthwhile! If you think it isn't, then you should seriously reconsider if you'd be better off with a career in underwater basket weaving. Science is about discovery. It's not about whether or not we spend an almost ridiculous amount of our resources attempting to understand an idea that could very well be false. It's about understanding the intricate workings of the universe. If string theory is wrong, then it's wrong, but we shouldn't stop working on it until we figure out a way to prove whether it IS right or wrong.

As for mathematically elegant, physics is often inelegant on its own. It doesn't particularly help that you guys use that disgusting prefix notation for integrals. It hurts my eyes. I'd really appreciate a mathematically elegant part of physics.

 

[DiracPool]

At the moment, Einstien's theory holds true which is evidenced by detectable gravity waves.

Ummm, have gravity waves been detected yet? If so, you better tell these guys before they blow a lot of dough on that detector they're planning on building...

http://lisa.nasa.gov/

 

[DiracPool]

It's not about whether or not we spend an almost ridiculous amount of our resources attempting to understand an idea that could very well be false. It's about understanding the intricate workings of the universe. If string theory is wrong, then it's wrong, but we shouldn't stop working on it until we figure out a way to prove whether it IS right or wrong.

I think that hits at the heart of the issue. In my opinion, of course string theory research should continue with spirit and vigor. The issue is how much of the public resource should be devoted to research that can't be tested and, accordingly, which collegiate department should the study fall under (math or physics), which will also determine the allocation of funding to some degree.

 

[friend]

which collegiate department should the study fall under (math or physics), which will also determine the allocation of funding to some degree.

I think that it should be considered math until it makes predictions.

 

[schema]

Ummm, have gravity waves been detected yet? If so, you better tell these guys before they blow a lot of dough on that detector they're planning on building...

http://lisa.nasa.gov/

detetcing gravity waves with QM. How apropos.

they are simply programming a satellite to confirm for themselves previously recorded obesrvations:

http://www.universetoday.com/97107/effects-of-einsteins-elusive-gravity-waves-observed/

they plan to study the same binary system.

 

[WannabeNewton]

You know, there was a time when general relativity was seen to be largely in the domain of mathematics, as a theory wielded primarily by mathematicians (e.g. Choquet-Bruhat) until John Archibald Wheeler came along. It wasn't always seen the way it is seen today by physicists.

 

[ShayanJ]

What evidence is there of string theory? I don't think there is enough to warrant revisions to General Relativity. The idea seems more like meta-physics, or philosophy to me. But I am open minded and willing to debate the facts without being biased.

At the moment, Einstien's theory holds true which is evidenced by detectable gravity waves.

mmmm...I think you're missing some points.

At first...physicists aren't revising GR,they're just trying to extend it to the quantum realm!

And second...its not all about string theory.One day,physicists realized that they can't use GR in the quantum world,so they started a search for an extension to it.and then,as a result of that need,some of them grabbed string theory.
Its not because of string theory that they're trying to extend GR,string theory as it is now,is a result of the need to extend GR!

I usually don't poke my head too much into this part of physics forums. I typically stay with the mathematical portion of the forum, so perhaps "mathematically elegant" means something different to me than to you.

Is string theory worthwhile? This is an odd question for a scientist, particularly because it says, to me, that the person asking has no interest in science.

Is it worthwhile to spend millions upon millions of dollars constructing a 27 kilometer ring for firing really small particles at each other in the hopes of proving the existence of a theoretical particle that explains the phenomenon of mass? Surely this money could have been spent on providing food to starving children or finding a cure for cancer?

Of course it's worthwhile! If you think it isn't, then you should seriously reconsider if you'd be better off with a career in underwater basket weaving. Science is about discovery. It's not about whether or not we spend an almost ridiculous amount of our resources attempting to understand an idea that could very well be false. It's about understanding the intricate workings of the universe. If string theory is wrong, then it's wrong, but we shouldn't stop working on it until we figure out a way to prove whether it IS right or wrong.

As for mathematically elegant, physics is often inelegant on its own. It doesn't particularly help that you guys use that disgusting prefix notation for integrals. It hurts my eyes. I'd really appreciate a mathematically elegant part of physics.

Thanks...So good for a mathematician! :D
In fact,we need a theory of Quantum Gravity and now we have some candidates.It is just a matter of taste that we choose which of them first for investigations.Well,the one that is chosen first,may be proved to be wrong,but that doesn't mean we have wasted time.We did learn some physics in that process!
And about the last paragraph...I personally will welcome every mathematician who wants to make physical theories mathematically rigorous and elegant!

 

[GODISMYSHADOW]

I am not capable of really understanding the math behind string theory, but what little I can understand is quite beautiful. I can see why it's adherents are so dedicated to it... it's incredible to have such an otherwordly frame work and have general relativity pop out of it. If I'm not mistaken Witten has said at some point that that is equivalent to empirical verification.

As for dark matter, if you define it as "there is something going on we don't understand, and we will label it dark matter while we investigate" then I would disagree that dark matter hypotheses are BS. I'm tangentially involved with a high-pressure liquid Xenon detector project that will be able to detect WIMPs (one of the proposed dark matter particles). So, at least dark matter physics so far makes falsify-able predictions, right? ;)

I looked over two books; The Little Book of String Theory, and also the critical book Not Even Wrong. String theory math is too much for me and I don't understand it. I personally believe that string theory is a collaborative effort with many brilliant minds making contributions and tinkering with it, yet no one, not one person anywhere, understands it.

 

[Ilja]

... it's incredible to have such an otherwordly frame work and have general relativity pop out of it. If I'm not mistaken Witten has said at some point that that is equivalent to empirical verification.

If he said this he was clearly wrong. General relativity, despite looking complex for a newcomer, follows from quite simple symmetry principles. So if it somehow pops up out of other theories this is fine but clearly not decisive, and is far away from empirical verification.

If you doubt, for my own ether theory http://arxiv.org/abs/gr-qc/0205035 I can make a similar claim. The Einstein equations of GR appear in a natural limit \Xi, \Upsilon\to 0, which is AFAIU a much simpler limit in comparison with the way string theory has to use to get rid of tachyons.

 

[Ilja]

In fact,we need a theory of Quantum Gravity and now we have some candidates.It is just a matter of taste that we choose which of them first for investigations. Well,the one that is chosen first,may be proved to be wrong,but that doesn't mean we have wasted time.We did learn some physics in that process!

The problem with string theory is another one: It presents itself as it is the only game in town. Not just as one of many wildly speculative approaches which has reached some minor points.

And the actual way science is organized supports this unjustified monopolistic position. Young scientists, those who should start developing alternative approaches, have to think about their next job after the two years of their actual job. So they have to write papers about something where one can get many job offers, thus, for a mainstream direction.

Give young scientists a badly paid but safe job. This would give them the freedom to develop something different, an alternative to string theory. And maybe publish about this a single paper after 15 years, maybe never. If only one of a hundred guys succeeds with proposing such an alternative, this would be much better than a thousand new papers about string theory.

And after this, other, less successful scientists would be free to try out the new direction. Today it is impossible. Even if an alternative theory is published, it will be ignored, because nobody can risk to work in a new direction with only a single guy working in it.

You doubt? Look at http://arxiv.org/abs/0908.0591. A published alternative, the results would be a wet dream for string theory (predicting all fermions of the SM, together with the gauge group and its action on fermions, compatible with gravity), but no reaction.

 

[ShayanJ]

The problem with string theory is another one: It presents itself as it is the only game in town. Not just as one of many wildly speculative approaches which has reached some minor points.

And the actual way science is organized supports this unjustified monopolistic position. Young scientists, those who should start developing alternative approaches, have to think about their next job after the two years of their actual job. So they have to write papers about something where one can get many job offers, thus, for a mainstream direction.

Give young scientists a badly paid but safe job. This would give them the freedom to develop something different, an alternative to string theory. And maybe publish about this a single paper after 15 years, maybe never. If only one of a hundred guys succeeds with proposing such an alternative, this would be much better than a thousand new papers about string theory.

And after this, other, less successful scientists would be free to try out the new direction. Today it is impossible. Even if an alternative theory is published, it will be ignored, because nobody can risk to work in a new direction with only a single guy working in it.

You doubt? Look at http://arxiv.org/abs/0908.0591. A published alternative, the results would be a wet dream for string theory (predicting all fermions of the SM, together with the gauge group and its action on fermions, compatible with gravity), but no reaction.

Yeah...you're mostly right!
But «It presents itself as it is the only game in town.» is a little...weird!String theory is only a theory,it can't "present" itself!
Its just that Its supporters seem to have great faith in it and I think that's because string theory isn't only a quantum gravity theory,but also a TOE.But other famous candidates of QG,are just QG theories!
But yes,I agree that some of the supporters of string theory may look at themselves as a cult believing a common thing which is completely out of scientific view.Although it is OK that when there is not enough evidence showing which theory is right,then every one has the right to choose a theory to work on,on non-physical grounds but NO theory should be ignored and all of them should be given equal chance and also the possibility should be considered that non of the existing theories are right!
Maybe some kind of Anti-Monopoly movement should be started among physicists which always tries to balance the chance given to competing theories!