String theory in one sentence please

[Entropee]

My teacher told me that in my essay I need to briefly describe string theory (because I'm talking about how the LHC is a good test for string theory) and by briefly she told me 1 sentence.

If anyone could tell me how THEY would describe string theory in 1 sentence that would be much appreciated!

-Gavin

 

[tom.stoer]

I'll try it:

String theory tries to construct a supersymmetric framework in 10 (11) dimensions from which all known elementary particles and interactions including gravity emerge (uniquely) from the modes of an one-dimensional, vibrating string.

The "trial" is bold bevcause up to now they did not succeed; "uniquely" is in brackets because there are indications that the theory is by no means unique; some string theorists try to find a selection principe, some others simpy believe in the anthropic principle; "11" is in brackets because there are indications that the theory has a dual description in 11 dimensions; I leave out certain subtleties like higher-dimensional objects, p-branes etc.

Let's discuss it ...

 

[Entropee]

Heh, thanks Tom, the only problem with yours is it's too complicated for my class. I have been coming up with things along those lines but I realize I have to "dumb it down" a lot, considering it's english class, not physics class haha.

Thanks though, I might use the part about particles and interactions emerging from different dimensions.

 

[Demystifier]

Let me try:

According to string theory, elementary particles are not really pointlike, but have a shape of a short string, too short to be visible with present technology.

Is that dumb enough?

 

[Bob_for_short]

String theory is another failed attempt to describe everything without any experimental background.

 

[Borek]

My teacher told me that in my essay I need to briefly describe string theory (...) and by briefly she told me 1 sentence.

I realize I have to "dumb it down" a lot, considering it's english class, not physics class haha.

Don't we love humanists?

 

[BigFairy]

String theory is another failed attempt to describe everything without any experimental background.

Thats a bold statement.

 

[MathematicalPhysicist]

Thats a bold statement.

And as time passes by, it seems more plausible.

Besides, every physical theory is a failed attmept to describe phenomena eventually.

 

[Bob_for_short]

...Besides, every physical theory is a failed attmept to describe phenomena eventually.

Not to that extent.

Let us look at the Newton's second law: ma = F. It is a generalization of many experimental data. Look at the Hook's law: F = -kx. It is also an experimental fact for elastic bodies. Remember PV=NT, I=U/R, q=-λ∇T (for heat flux), etc. Each physical law has its domain of application where all involved letters are physically meaningfull. Another matter these laws are not universal, they all have limited ranges of validity.

The usual geometry is a generalization of experimental facts too.

It is a big mistake to think that one can start from ungrounded postulates or axioms and obtain some reality. What is obtained in this way is mathematical sequences of mathematical postulates, nothing else. String theory is just a mathematical exercise with big but unfounded claims. No wonder it resulted in nothing physical.

 

[Dmitry67]

1 Each physical law has its domain of application where all involved letters are physically meaningfull. Another matter these laws are not universal, they all have limited ranges of validity.

2 It is a big mistake to think that one can start from ungrounded postulates or axioms and obtain some reality.

3 What is obtained in this way is a mathematical sequences of mathematical postulats, nothing else

1 Yes, if we look retrospectively.
But TOE, by definition, should not be limited to any domain

2 It is an exact program of MUH, called "physics from scratch"

3 mathematics IS physics!

 

[Bob_for_short]

...mathematics IS physics!

So let us force the Nature to obey our mathematical fantasies ?

 

[Dmitry67]

I don't want to touch (again) the MUH, but at least agree that when we talk about TOE we must be ready that it will be a very final step in a sequence of the infinite reduction.

 

[Bob_for_short]

...agree that when we talk about TOE we must be ready that it will be a very final step in a sequence of the infinite reduction.

So we observe a rush of geniuses: who first will guess the TOE. It is very near! One more patch and here it is!

 

[Dmitry67]

YES
I don't share your sarcasm.

 

[Bob_for_short]

And I do not like to fool myself.

 

[Chronos]

String is a purely mathematical attempt to model reality. It is not provably wrong [and may never be], but, empirically unsatisfying thus far. It explains some observations, mostly at the quantum level, but otherwise has no compelling observational support.

 

[suprised]

String is a purely mathematical attempt to model reality.

What a nonsense. Of course string theory is built on physical principles. Only because most people don't understand the mathematical language in terms of which these physical principles are formulated, they confuse it with "pure" mathematics. Such comments just reveal ignorance.

 

[Galteeth]

String Theory Summarized:

http://xkcd.com/171/

 

[Demystifier]

String is a purely mathematical attempt to model reality.

It is not more "purely mathematical" than, e.g., general relativity.

 

[MathematicalPhysicist]

Not to that extent.

Let us look at the Newton's second law: ma = F. It is a generalization of many experimental data. Look at the Hook's law: F = -kx. It is also an experimental fact for elastic bodies. Remember PV=NT, I=U/R, q=-λ∇T (for heat flux), etc. Each physical law has its domain of application where all involved letters are physically meaningfull. Another matter these laws are not universal, they all have limited ranges of validity.

The usual geometry is a generalization of experimental facts too.

It is a big mistake to think that one can start from ungrounded postulates or axioms and obtain some reality. What is obtained in this way is mathematical sequences of mathematical postulates, nothing else. String theory is just a mathematical exercise with big but unfounded claims. No wonder it resulted in nothing physical.

That's what I meant, we first were accustomed to the notion that Newton's laws describes everything, but with time we've seen that it's limited in scope, and then it was substitued with Einstein's GR, and thus only mathematical theories are timeless as opposed to physical theories which change with time.

 

[BigFairy]

I think Chronos sums it up well.

 

[Demystifier]

It is a big mistake to think that one can start from ungrounded postulates or axioms and obtain some reality. What is obtained in this way is mathematical sequences of mathematical postulates, nothing else. String theory is just a mathematical exercise with big but unfounded claims. No wonder it resulted in nothing physical.

There are counter-examples to your claim.
For example, Yang-Mills theories (non-abelian gauge theories generalizing quantum electrodynamics) were postulated merely by mathematical beauty. Later it turned out that they describe something physical - strong and electroweak interactions.

 

[Demystifier]

I think Chronos sums it up well.

Chronos does not sum up the string theory at all. His "explanation" can be applied to at least a dozen of theories that have nothing to do with string theory. He said absolutely nothing that refers specifically to string theory and not to some other theory.

Likewise, if your homework in the history class is to explain who Hitler was, you may say:
"He was a very bad guy who made a lot of bad stuff.",
but it will not explain Hitler at all. This explanation can be applied to many other people as well.

 

[Bob_for_short]

It is not more "purely mathematical" than, e.g., general relativity.

And GR experience is, of course, a perfect model for following, isn't it?

You know, transition to an accelerated reference frame does not change the geometry, in particular, the space or space-time curvature R. It is true in both Galilean and Minkowski space-times. Introduction of the space-time curvature (i.e. a Riemann space-time) was not necessary to describe the gravity in the relativistic theory.

Rejection of the plane (Minkowski) space-time in GR means at least:

1) Rejection of additive conservation laws,

2) Describing the gravitational filed as a geometrical feature of space-time rather than as a physical field, for example, carrying the energy-momentum when radiated.

At the same time the theory can be formulated in the Minkowski space-time without loosing the conservation laws and with describing the gravity as a physical field (RTG of A. Logunov’s). Do you feel a difference? Is there any experiment contradicting the additive conservation laws? So the GR is a bright example of how far one can be misled with non-physical principles implemented in the theory.

That's what I meant, we first were accustomed to the notion that Newton's laws describes everything, but with time we've seen that it's limited in scope, and then it was substituted with Einstein's GR, and thus only mathematical theories are timeless as opposed to physical theories which change with time.

You forgot to underline why the "mathematical theories" are timeless - there is no motivation to change them because they are not supposed to describe the experimental data. As soon as you compare a "mathematical theory" with experiments, you are obliged to modify some principles in order to take into account correctly the experimental data.

There are counter-examples to your claim.
For example, Yang-Mills theories (non-abelian gauge theories generalizing quantum electrodynamics) were postulated merely by mathematical beauty. Later it turned out that they describe something physical - strong and electroweak interactions.

Another bright example of postulating or axiomatization of something physically non-motivated. Indeed QED has conceptual and mathematical difficulties. It does not work without renormalizations. The local gauge invariance principle leads exactly to these difficulties. Yet one generalizes it to other symmetries, and why? In order to introduce interaction. But there are other ways of introducing interaction and the "gauge" way is not the only one.

Now, we have to live with those singularities, worm holes, and rotten apples as if it is something inevitable.

Briefly, there are good and bad examples to follow in the physics history.

 

[arivero]

Don't we love humanists?

Nope, a humanist would try a more complicated kafkakantiesque approach. Something on the line of "in string theory spatial extension is incorporated in the concept of particle, while in particle theory space is dual to the elementary entity"

 

[marcus]

... (because I'm talking about how the LHC is a good test for string theory) ...

That's the main trouble with your paper, Entropee. String theorists have not made any concrete quantitative prediction which the LHC can test---and thereby test the theory. So you are basing your whole paper on a false assumption. I'll explain with some examples:

Major issues are, for example, the existence of extra dimensions and the existence of partner particles---socalled "supersymmetric" particles which have never been detected but are like shadow partners of those we know about.
Unfortunately, string theorists are not on record predicting that the LHC will detect any definite partner particles, or on the other hand predicting that the LHC will NOT. They don't predict either way. So LHC finding or not finding would not prove anything.

Unfortunately too, they do not make any definite prediction about LHC finding evidence of extra dimensions. They don't say it will and they don't say it won't. So nothing LHC is expected to be able to do, when they get it working, can actually test the validity of string thinking.

Tom Stoer gave you a good brief summary at the very start of your thread:

...

String theory tries to construct a supersymmetric framework in 10 (11) dimensions from which all known elementary particles and interactions including gravity emerge (uniquely) from the modes of an one-dimensional, vibrating string.

The [word "tries" is in bold letters] because up to now they did not succeed; "uniquely" is in brackets because there are indications that the theory is by no means unique...
...

...thanks Tom, the only problem with yours is it's too complicated for my class. I have been coming up with things along those lines but I realize I have to "dumb it down" a lot, considering it's english class...

Tom's description is already as simple as it can be. You don't want to "dumb it down". You want to unpack it and make it understandable. That means put it in the context of two other sentences, so that the sentence about string can be simple. Set up the context first.

"The aim of particle physics is to explain the list of fundamental particles and describe their interactions---construct a theoretical framework where you can so-to-speak "turn the crank" and out will come the list of known particles together with formulas describing them (masses, charges) and their interactions (forces, how they decay, how they react with each other)."

So far you have not used up your sentence about string theory because this sentence only sets the scene. It is not about string theory. It is a general statement that applies to all theoretical particle physics, whatever the approach. Now you can say what string is, in one sentence.

"String is an approach which tries to do this by representing particles as small flexible objects instead of points."

Now you have given a simple one-sentence definition and you can, if you want, say something about the string theoretical framework. This is not definition, it is discussion of something you just defined. So the onesentence limit does not apply. You could, for example, say this:

"So far ST does not boil down to one single theory making definite quantitative predictions about future experiments. There are a number of different ST versions. But theorists have found that to make any version work they need to assume two things which the LHC can look for: socalled "supersymmetry" (abbr SUSY) and extra dimensions. SUSY just means that the known particles have some number of partners, in a definite pattern---these suspected partners have not yet shown up in the couple of decades they have been looked for. It would be a help for ST if evidence of either SUSY or extra dimensions showed up at LHC. But ST does not predict that LHC will find either, because so far it has been unable to say at what collision energy evidence might show up. So if LHC does not find evidence of SUSY or XD it wouldn't prove anything---the expected effects might still be waiting to appear at some higher collision energies which LHC cannot achieve."

Don't use any abbreviations besides "LHC" with an English teacher. I'm using abbreviations like ST, SUSY, XD to talk to you because I don't like typing and it makes it easier to read. But I advise you to write everything out, and if you give a talk, say everything: say "string theory" instead of ST, say "supersymmetry" instead of SUSY.

 

[tom.stoer]

And feel free to ask again if you like.

My position is quite similar to Marcus'. But I think it's fair to start with a basic explanation of the idea and then try to figure out what went wrong. You should be prepared for the question why string theory SEEMS to FAIL, but you must not skip the explanation what the original INTENTION was!

We had a discussion which theory could repace string theory. There are a couple of interesting programs, but as far as I can see their claims are not as broad as strings.

 

[Dox]

String theory is another failed attempt to describe everything without any experimental background.

Ha ha ha... Impressively accurate!

 

[BigFairy]

Chronos does not sum up the string theory at all. His "explanation" can be applied to at least a dozen of theories that have nothing to do with string theory. He said absolutely nothing that refers specifically to string theory and not to some other theory.

Likewise, if your homework in the history class is to explain who Hitler was, you may say:
"He was a very bad guy who made a lot of bad stuff.",
but it will not explain Hitler at all. This explanation can be applied to many other people as well.

Yes but it was all that was necessary. Maybe you misread the context of the posts.

 

[Demystifier]

Yes but it was all that was necessary. Maybe you misread the context of the posts.

Maybe we are not talking about the same posts. I am talking about the first one on this thread.

Anyway, if the homework is not to explain what string theory is, but to explain why string theory is bad, then I agree that the mentioned summary was good.

 

[Bob_for_short]

Maybe we are not talking about the same posts. I am talking about the first one on this thread.

Anyway, if the homework is not to explain what string theory is, but to explain why string theory is bad, then I agree that the mentioned summary was good.

There two aspects of the OP: what is a string in the string theory and does it work?

 

[Demystifier]

And GR experience is, of course, a perfect model for following, isn't it?

Exactly!

You know, transition to an accelerated reference frame does not change the geometry, in particular, the space or space-time curvature R. It is true in both Galilean and Minkowski space-times. Introduction of the space-time curvature (i.e. a Riemann space-time) was not necessary to describe the gravity in the relativistic theory.

Agree.

Rejection of the plane (Minkowski) space-time in GR means at least:

1) Rejection of additive conservation laws,

2) Describing the gravitational filed as a geometrical feature of space-time rather than as a physical field, for example, carrying the energy-momentum when radiated.

Agree.

At the same time the theory can be formulated in the Minkowski space-time without loosing the conservation laws and with describing the gravity as a physical field (RTG of A. Logunov’s). Do you feel a difference?

Yes I do. Still, I prefer GR because it is simpler.

Is there any experiment contradicting the additive conservation laws?

Is there any experiment contradicting GR?

Another bright example of postulating or axiomatization of something physically non-motivated. Indeed QED has conceptual and mathematical difficulties. It does not work without renormalizations. The local gauge invariance principle leads exactly to these difficulties. Yet one generalizes it to other symmetries, and why? In order to introduce interaction. But there are other ways of introducing interaction and the "gauge" way is not the only one.

Do you know an example of another way of introducing interaction that agrees with experiments in particle physics?

Now, we have to live with those singularities, worm holes, and rotten apples as if it is something inevitable.

No we don't. The mainstream view is that GR is only an approximation. True, we still do not know the exact theory without singularities and other pathologies. Perhaps it is something like Logunov theory. Or perhaps it is something more similar to GR. Or perhaps it is something completely different.

 

[Demystifier]

There two aspects of the OP: what is a string in the string theory and does it work?

The question "does it work" is too vague. You may say that it doesn't work because it does not yet lead to a quantitative prediction testable with current technology. Or you may say that it works because it avoids ultraviolet divergences, qualitatively predicts the observed gravitational and gauge interactions, and is not in contradiction with existing experiments. The truth is somewhere in between.

 

[Bob_for_short]

...Still, I prefer GR because it is simpler.

You yourself mention "singularities and other pathologies" that are absent in RGT. How can we count on a theory with pathologies? How can we compare the gravitational effects if they belong to different geometries? Do you like a geometry varying with time?

Do you know an example of another way of introducing interaction that agrees with experiments in particle physics?

In QED, yes, see my publications where I outlined such a way. It is quite physical.

 

[Demystifier]

You yourself mention "singularities and other pathologies" that are absent in RGT. How can we count on a theory with pathologies?

We can use it for weak fields where pathologies are absent.

How can we compare the gravitational effects if they belong to different geometries? Do you like a geometry varying with time?

I don't quite understand what are you pointing out here.

In QED, yes, see my publications where I outlined such a way. It is quite physical.

Have you calculated g-2 in your theory? Have you also achieved an agreement with experiments up to 10 decimals (as QED has)?

 

[suprised]

So here a single-sentence characterization:

String theory is a physical model based on tiny strings that incorporates both quantum mechanics and general relativity and attempts to unify gravity with particle physics.

 

[Bob_for_short]

We can use it for weak fields where pathologies are absent.

Only weak field effects are not sufficient to "prove" or prefer the entire GR.

Have you calculated g-2 in your theory? Have you also achieved an agreement with experiments up to 10 decimals (as QED has)?

Not yet. No one can fulfil the forth order QED calculations in one article.

By the way, agreement "up to 10 decimals" and even better can be obtained for any normal function developed in Taylor series up to the fourth order with the small parameter of about 0.001 ( ≈ α/2π ). There is too much exaggeration about predictive force of QED in this respect.

 

[Demystifier]

Only weak field effects are not sufficient to "prove" or prefer the entire GR.

With that I agree.

Not yet. No one can fulfil the forth order QED calculations in one article.

I wish you a good luck.

By the way, agreement "up to 10 decimals" and even better can be obtained for any normal function developed in Taylor series up to the fourth order with the small parameter of about 0.001 ( ≈ α/2π ). There is too much exaggeration about predictive force of QED in this respect.

But the problem is that in QED you do not know this "normal function" explicitly.

 

[Bob_for_short]

I wish you a good luck.

Thanks. You know, for some Lagrangians it is sufficient to prove renormalizability to start working with them seriously. In my case the theory is divergence-free which is much better than renormalizability.

...the problem is that in QED you do not know this "normal function" explicitly.

That's right. QED has tought us many wonderful things and I really hope it's not finished yet.

By the way, I encountered a case (not in QED) when the exact function is known explicitly but its Taylor series does not coincide with the perturbation theory expansion! See formula (A3.5) and page 16 in arXiv:0906.3504.

 

[Galteeth]

So here a single-sentence characterization:

String theory is a physical model based on tiny strings that incorporates both quantum mechanics and general relativity and attempts to unify gravity with particle physics.

String theory is an attempt to mathematically unify quantum mechanics and general relativity by using strings vibrating in multiple spatial dimensions as the fundamental building blocks of the universe.

 

[Demystifier]

The question remains: why strings? Screws are much better for unifying.

Screws do not predict gravity and gauge interactions.
Screws do not avoid UV singularities.

 

[Finbar]

String is a purely mathematical attempt to model reality. It is not provably wrong [and may never be], but, empirically unsatisfying thus far. It explains some observations, mostly at the quantum level, but otherwise has no compelling observational support.

Edit

String is a purely mathematical attempt to model reality. It is not provably wrong [and may never be], but, empirically unsatisfying thus far. It has no observational support.

 

[Entropee]

Thanks Marcus, It's an essay that nobody in my class will understand so i won't be graded down on it, but I am very interested in knowing more about the subject and where I went wrong. I was under the impression that when they smashed the particles together, there might be a loss in mass, and the mass had to go somewhere, so into another dimension? I am not sure I am only 17 so you guys obviously know way more about it than I do, any more info would be appreciated, and thanks again Tom for your summary. (Thanks to everyone else also contributing to the post too).

 

[tom.stoer]

Congratulations to you for keeping with us and surviving all these discussions.

I would still propose my explanation as a starting point

"String theory tries to construct a supersymmetric framework in 10 dimensions from which all known elementary particles and interactions including gravity should emerge from the modes of an one-dimensional, vibrating string."

but of course I agree with many aspects mentioned by others, especially (some changes from my side to achieve the one-sentence goal)

"It is a purely mathematical attempt to model reality which is not provably wrong [and may never be], but, empirically unsatisfying thus far and w/o any observational support."

I think those two statement could be the core of your talk or small paper or whatever. Then you have to explain a bit what it means ...

 

[suprised]

"String theory tries to construct a supersymmetric framework in 10 dimensions.."

In four dimensions as well, of course... ever heard about that ?

" purely mathematical attempt "

What means "purely" mathematical? Of course there are physical principles built in, like quantum mechanics, actions, scattering amplitudes etc... in particular it is based on the physical picture of a string, and the action is a manifestation of that. How can one call this pure mathematics? Are other theories of quantum gravity (I should say much less founded attempts) any less "mathematical"?

I suspect "purely mathematical" simply needs to be translated "incomprehensible to me".

Why people who have no idea about this subject confuse the discussion with second hand opinions and misleading, if not outright incorrect statements. No wonder why any expert in this field is driven out from this forum here. Good bye.

 

[Fredrik]

Tom, I think your sentence would be much better, at least for "normal" people, if you just replaced the word "supersymmetric" with "mathematical".

I'm not crazy about Finbar's sentence. I think it's pretty misleading actually.

a) it's misleading to call it "purely mathematical"
b) words like "unsatisfying" are very subjective shouldn't be included in a brief explanation of what the theory says
c) the fact that you're not floating away from the chair you're sitting on is experimental support for string theory, so you should find a better way to express your thoughts about the experimental situation.

A few comments about a): There's no such thing as a purely mathematical theory, and a mathematical model is always purely mathematical. A theory consists of a mathematical model and a set of axioms that tells us how to interpret the mathematics as predictions of results of experiments. It's OK to say that string theorists are trying to find an appropriate mathematical model, and that their work at this time is therefore "purely mathematical", but if they don't ever do anything more than that, it won't ever be a theory. So it's wrong, or at least misleading, to talk about string theory as a "purely mathematical attempt". What they're attempting to do is certainly more ambitious than to just find some cool mathematics.

 

[Bob_for_short]

The problem is that the UV divergence of QG is managed with some cut-off (string size) and a great deal of physical meaning is given to it without experimental evidence whereas a cut-off is just an awkward stop-gap.

 

[tom.stoer]

"In four dimensions as well, of course... ever heard about that ?

The space in which strings move is 10-dim. Everything else is refinement, solving the equations, constructing vacua etc. The starting point and one of the core problems is that it's 10-dim. One does not know how to select the "correct" vacuum = our universe in 4 dim. And one does not even know why 6 dims are compactified; why not less or more?

What means "purely" mathematical?

It's quite simple. w/o suport from experiments it is a mathematical excercise, not phsics. It will become a physical theory if it either post-dicts some already know particles, masses, coupling constants etc., or if it makes at least one falsifiable prediction.

Are other theories of quantum gravity (I should say much less founded attempts) any less "mathematical"?

As long as physical predictions atre missing they suffer from the same problems.

No wonder why any expert in this field is driven out from this forum here. Good bye.

If they are not willing to participate it's not my problem. The problem is neither that we are talking about weaknesses of the theory nor that the theory has weaknesses. The problem is that the experts are partially not willing to even accept that these issues exist. Best example is the finiteness of the theory: there's the claim that ST is finite in all orders PT. The problem is that beyond 2 loops there is not even a definition of the amplitude!

 

[Coin]

I think the problem with describing string theory in one sentence is there isn't exactly just one "string theory". 1990s string theory is somewhat different from modern M-theory is different from AdS/CFT. I'd attempt something like:

"String theory" refers to a group of related research programs, which share the starting point of suggesting things that appear to be particles can be thought of as a side-effect emerging from the vibrations of one-dimensional strings.

And then explain what this has to do with the LHC.

Researchers believe that if string theory is real and not just a quirk of mathematics, particles must be "supersymmetric": this means every type of particle has a rare "superpartner" which has so far never been seen, but which the LHC would probably be able to find.

That sound about reasonable?

 

[tom.stoer]

I agree with the first sentence; its focus is slightly different, so if it could me merged with mine it would be OK.

Regrading the LHC there's a problem: if the LHC finds SUSY this is a hint for a support of strings, NOT a proof (SUSY / SUGRA could exist even if ST does not); if the LHC does not find SUSY it simply may be there at even higher energies. So either way ST could survive by making the right turn - and that's the core roblem with it: anything goes ...