String Theory and the various interpretations of QM

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String Theory and the various interpretations of QM

Postby jules.LT » Wed Jun 04, 2014 9:40 pm UTC

What is the relationship between String Theory and the various interpretations of quantum mechanics?
From what I understood, ST combines QM and General Relativity into one single mathematical AND interpretative model.
To me, the maths part seems to imply that you're looking for an underlying framework that explains both models... Doesn't that require "hidden variables"?
And the interpretative part, well, since it covers QM too, then surely it conflicts with some of the interpretations of QM?

The other night, I snapped at a guy who was mixing up ST and the existence of a multiverse . Shocking, right? Right? :?
I need to be a bit more sure about that stuff :oops:
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Re: String Theory and the various interpretations of QM

Postby stoppedcaring » Wed Jun 04, 2014 9:54 pm UTC

Most simply put:

Quantum mechanics is a series of observations about reality which we have been able to consistently model with some equations.

General and special relativity are a series of observations about reality which we have been able to consistently model with some equations.

Unfortunately, the equations for quantum mechanics and the equations for relativity look nothing alike.

String theory is a set of equations that seems to connect quantum mechanics and relativity, but we have not yet been able to find any evidence that these equations can be used to consistently model anything we didn't already know about.
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Re: String Theory and the various interpretations of QM

Postby cyanyoshi » Wed Jun 04, 2014 11:02 pm UTC

stoppedcaring wrote:String theory is a set of equations that seems to connect quantum mechanics and relativity, but we have not yet been able to find any evidence that these equations can be used to consistently model anything we didn't already know about.

This statement got me wondering. Is there any kind of test that can be done that disproves all of the string theories, or is string theory flexible enough that it is unprovable? I think ST requires that the universe have exactly 26 or so dimensions. Would discovering there are more dimensions be enough to disprove the variants of string theory?
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Re: String Theory and the various interpretations of QM

Postby Frenetic Pony » Thu Jun 05, 2014 1:31 am UTC

cyanyoshi wrote:
stoppedcaring wrote:String theory is a set of equations that seems to connect quantum mechanics and relativity, but we have not yet been able to find any evidence that these equations can be used to consistently model anything we didn't already know about.

This statement got me wondering. Is there any kind of test that can be done that disproves all of the string theories, or is string theory flexible enough that it is unprovable? I think ST requires that the universe have exactly 26 or so dimensions. Would discovering there are more dimensions be enough to disprove the variants of string theory?


Well the LHC can get to the lower bounds of hypothesized Supersymmetry particles, most of which have already been shown to not exist and the rest of the range should either be discovered or discounted soon enough. And there's an entire set of string theory that bases itself on supersymmetry (superstring theory). So if those ranges are eliminated, then so is supersymmetry and superstring theory. Unfortunately for string theory superstring theory is its kind of modern interpretation, and so that may indeed be a huge nail in the coffin for THAT specific and particular set of "string theory".

Of course there's always "it's just higher energy!" if you move numbers around enough. But eventually you could get to "it's just more energy than is actually available in the entire universe!" So practical tests may never "entirely" eliminate it, but then they'll never "entirely" eliminate anything. And that's the wonderful thing with string theory in general, there's always some way in which you're going to figure out how it might still apply, making it not very useful for actual predictions or tests.
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Re: String Theory and the various interpretations of QM

Postby BlazeOrangeDeer » Thu Jun 05, 2014 8:15 am UTC

Interpretations of Quantum Mechanics are usually ways of solving the measurement problem, more or less. String theory doesn't change that situation. It doesn't change the fundamentals of quantum theory, but rather describes a certain kind of quantum universe.
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Re: String Theory and the various interpretations of QM

Postby doogly » Thu Jun 05, 2014 1:54 pm UTC

Yeah, string theory has nothing to do with interpretations of qm.

It does have to do with the multiverse that is of the anthropic and eternal inflation type.
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Re: String Theory and the various interpretations of QM

Postby stoppedcaring » Thu Jun 05, 2014 3:03 pm UTC

cyanyoshi wrote:
stoppedcaring wrote:String theory is a set of equations that seems to connect quantum mechanics and relativity, but we have not yet been able to find any evidence that these equations can be used to consistently model anything we didn't already know about.

This statement got me wondering. Is there any kind of test that can be done that disproves all of the string theories, or is string theory flexible enough that it is unprovable? I think ST requires that the universe have exactly 26 or so dimensions. Would discovering there are more dimensions be enough to disprove the variants of string theory?

Yeah, unfortunately string theory is flexible -- hehe -- enough to render it more-or-less unfalsifiable. Now, if we managed to actually confirm some of its predictions, then we'd have something.
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Re: String Theory and the various interpretations of QM

Postby jules.LT » Thu Jun 05, 2014 4:49 pm UTC

Thanks for your answers, guys.
BlazeOrangeDeer wrote:Interpretations of Quantum Mechanics are usually ways of solving the measurement problem, more or less. String theory doesn't change that situation. It doesn't change the fundamentals of quantum theory, but rather describes a certain kind of quantum universe.

Since the measurement problem has to do with the limit between where QM and General Relativity apply, how does a theory that unifies them manage to avoid the subject? :shock:

doogly wrote:It does have to do with the multiverse that is of the anthropic and eternal inflation type.
How so?
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Re: String Theory and the various interpretations of QM

Postby doogly » Thu Jun 05, 2014 6:01 pm UTC

That is not the measurement problem.

ST doesn't change anything about QM. It does nothing to change foundations / interpretations, so if you do Bohm or Everett or Decoherence or what not it wouldn't effect it. Some theories (not st) which model wave function collapse as gravitational would effect quantum gravity more directly, but usually they are completely orthogonal questions.

As for multiverse,
http://en.wikipedia.org/wiki/String_theory_landscape
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Re: String Theory and the various interpretations of QM

Postby stoppedcaring » Thu Jun 05, 2014 6:09 pm UTC

jules.LT wrote:Thanks for your answers, guys.
BlazeOrangeDeer wrote:Interpretations of Quantum Mechanics are usually ways of solving the measurement problem, more or less. String theory doesn't change that situation. It doesn't change the fundamentals of quantum theory, but rather describes a certain kind of quantum universe.

Since the measurement problem has to do with the limit between where QM and General Relativity apply, how does a theory that unifies them manage to avoid the subject? :shock:

Unless you're talking about different sorts of measurements than I'm thinking of, the measurement problem has nothing to do with the limits between QM and relativity. It's an apparent paradox/puzzle in the equations of QM itself.
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Re: String Theory and the various interpretations of QM

Postby jules.LT » Thu Jun 05, 2014 7:06 pm UTC

doogly wrote:That is not the measurement problem.
stoppedcaring wrote:Unless you're talking about different sorts of measurements than I'm thinking of, the measurement problem has nothing to do with the limits between QM and relativity.

I was referring to this measurement problem, is there another?
The wiki says that it's about if/how Wavefunction collapse occurs, where I read:
"collapse is merely a black box for thermodynamically irreversible interaction [of a quantum system] with a classical environment"
and "Niels Bohr postulated wave function collapse to cut the quantum world from the classical".

What am I not getting?

String Theory admits many possible universes, so the best explanation for this universe's fine-tuning is the anthropic principle, which kinda requires for a large number of universes to be generated?
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Re: String Theory and the various interpretations of QM

Postby stoppedcaring » Thu Jun 05, 2014 8:05 pm UTC

jules.LT wrote:
doogly wrote:That is not the measurement problem.
stoppedcaring wrote:Unless you're talking about different sorts of measurements than I'm thinking of, the measurement problem has nothing to do with the limits between QM and relativity.

I was referring to this measurement problem, is there another?
The wiki says that it's about if/how Wavefunction collapse occurs, where I read:
"collapse is merely a black box for thermodynamically irreversible interaction [of a quantum system] with a classical environment"
and "Niels Bohr postulated wave function collapse to cut the quantum world from the classical".

No, that's the one. Only, it has nothing to do with general or special relativity at all.
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Re: String Theory and the various interpretations of QM

Postby jules.LT » Thu Jun 05, 2014 9:25 pm UTC

Don't the "classical environment" mentions mean "when you use General relativity instead of QM"?
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Re: String Theory and the various interpretations of QM

Postby stoppedcaring » Thu Jun 05, 2014 9:34 pm UTC

jules.LT wrote:Don't the "classical environment" mentions mean "when you use General relativity instead of QM"?

No, the "classical environment" is the non-quantum interpretation of electromagnetism, particle interactions, etc.

And GR isn't classical either; classical mechanics is Newtonian.
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Re: String Theory and the various interpretations of QM

Postby doogly » Thu Jun 05, 2014 9:35 pm UTC

Some circles will also call GR classical though; most of them that I know. But it is, in any case, a subset, and not what is meant when that page talks about 'classical.'
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Re: String Theory and the various interpretations of QM

Postby SU3SU2U1 » Fri Jun 06, 2014 4:13 am UTC

All right, I'm going to get a tad technical. Generally we get to string theory by extending quantum field theory, which is itself a theoretical framework that you get by sticking special relativity together with quantum mechanics.

Unfortunately, quantum field theory is "weird" in that a lot of the mathematical constructs don't stand on particularly firm footing. Only the absolute simplest quantum field theories (which unfortunately don't look like reality) are on firm foundations. This COULD have effects on interpretations of quantum mechanics, depending on your interpretation. Bohmian mechanics, for instance, does not look like its compatible with field theories, though the occasional researcher publishes a paper pushing towards a solution. The Everett/Many-Worlds interpretation in the context of quantum field theories is hard to pin down (its not fully formalized even in the case of non-relativistic quantum mechanics), in the simplest hand-wavey approaches we are left with the odd situation that the majority of "worlds" don't have well defined particles at all, which forces us into messy anthropic arguments.

Basically, quantum field theories are messy, and while they should inform the way we interpret quantum mechanics most of the people working on interpretations (philosophers not physicists mostly) don't know much beyond undergrad level quantum mechanics.
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Re: String Theory and the various interpretations of QM

Postby eSOANEM » Fri Jun 06, 2014 11:45 am UTC

doogly wrote:Some circles will also call GR classical though; most of them that I know. But it is, in any case, a subset, and not what is meant when that page talks about 'classical.'


This is more or less how my university uses classical. They would definitely say GR was classical in that it is a classical field theory.

They would probably not count it as part of classical mechanics though (which would be Newtonian mechanics and the Analytic formalisms thereof).
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Re: String Theory and the various interpretations of QM

Postby drachefly » Thu Jul 10, 2014 5:37 pm UTC

stoppedcaring wrote:Yeah, unfortunately string theory is flexible -- hehe -- enough to render it more-or-less unfalsifiable. Now, if we managed to actually confirm some of its predictions, then we'd have something.


From what I recall, the most significant result in String Theory is that non-supersymmetric string theory can't have interactions. So, no supersymmetry -> String Theory gets a biscuit for being falsifiable, but no bone on account of its not actually being right.
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Re: String Theory and the various interpretations of QM

Postby Frenetic Pony » Thu Jul 10, 2014 11:05 pm UTC

drachefly wrote:
stoppedcaring wrote:Yeah, unfortunately string theory is flexible -- hehe -- enough to render it more-or-less unfalsifiable. Now, if we managed to actually confirm some of its predictions, then we'd have something.


From what I recall, the most significant result in String Theory is that non-supersymmetric string theory can't have interactions. So, no supersymmetry -> String Theory gets a biscuit for being falsifiable, but no bone on account of its not actually being right.


I said that :!:

Regardless, I've never understood the argument for and about "classical mechanics". The definition always seemed to be "the universe works on some combination of/close enough to/GR and Quantum Mechanics together... except at some undefined scale something or other happens and then it doesn't somehow."

You always see Schrodinger's Cat brought up in arguments about it. Then you see something about measuring superpositions being measured in macroscopic objects and someone saying that means the cat could be alive and dead at the same time. Which has always seemed to me a misinterpretation of Schrodingers Cat to being with. I always took it as a more of the idea that we don't quite know what to make of superpositions, (EPR paradox and whatnot) and not that they don't exist.
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Re: String Theory and the various interpretations of QM

Postby Tchebu » Fri Jul 11, 2014 4:07 am UTC

From what I recall, the most significant result in String Theory is that non-supersymmetric string theory can't have interactions. So, no supersymmetry -> String Theory gets a biscuit for being falsifiable, but no bone on account of its not actually being right.

Unlike SUSY extensions to the standard model, string theory doesn't specify an energy scale at which supersymmetry should be broken, so it doesn't really get the biscuit unless we have measurements up to planck scale (in which case we'd all have a much better idea of what we're doing to begin with)... I suppose the "upside" is that it doesn't quite get denied the bone either...
Our universe is most certainly unique... it's the only one that string theory doesn't describe.
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Re: String Theory and the various interpretations of QM

Postby andyisagod » Fri Jul 11, 2014 7:07 am UTC

Tchebu wrote:Unlike SUSY extensions to the standard model, string theory doesn't specify an energy scale at which supersymmetry should be broken, so it doesn't really get the biscuit unless we have measurements up to planck scale (in which case we'd all have a much better idea of what we're doing to begin with)... I suppose the "upside" is that it doesn't quite get denied the bone either...


This is true for SUSY in general as well though since we don't know what the SUSY breaking scale is. As you increase the scale you reintroduce the hierarchy problem and the gauge couplings won't unify anymore but there's no rule that says SUSY can't be broken at a very high scale. In fact some string theorists would actually prefer a very high scale of SUSY breaking so discovering low energy SUSY might actually make things difficult for them.
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Re: String Theory and the various interpretations of QM

Postby drachefly » Mon Jul 14, 2014 3:07 pm UTC

Frenetic Pony wrote:
drachefly wrote:
stoppedcaring wrote:Yeah, unfortunately string theory is flexible -- hehe -- enough to render it more-or-less unfalsifiable. Now, if we managed to actually confirm some of its predictions, then we'd have something.


From what I recall, the most significant result in String Theory is that non-supersymmetric string theory can't have interactions. So, no supersymmetry -> String Theory gets a biscuit for being falsifiable, but no bone on account of its not actually being right.


I said that :!:


No, you said
Frenetic Pony wrote: And there's an entire set of string theory that bases itself on supersymmetry (superstring theory). So if those ranges are eliminated, then so is supersymmetry and superstring theory.

which doesn't tell people that superstring theory happens to be the only string theory worth talking about.


As for 'classical mechanics', it's just a set of approximations. Often, they're valid. Sometimes, they're not. It's not in-principle any different from approximating the force law at the bottom of a pendulum potential as a simple harmonic oscillator.
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