String Theory/M-Theory

[QED]

Colossal waste of time or the holy grail of the TOE?

I'm going for the former here. String theory is leading us to a mathematical dead end with no observable evidence. The Standard Model is made of particles - not waves of energy vibrating like strings. There are no ten or eleven dimensions... no parallel replica universes. Maybe the closest they can get to strings are the acoustic waves of electromagnetic energy that eventually polarized from the plasma energy surge during the big bang. Still, that energy is what caused the recombination of actual particles to form matter. I believe the Standard Model is the best picture we have of the subatomic world, but in no way do they have characteristics of "strings".

Correct me if I am wrong here, but it all seems like science fiction.

 

[neuvik]

It hasn't married Quantum Mechanics with General Relativity yet, nor has it produced any experimental predictions.

Who knows. Thats just one reason why we built the LHC.

 

[darkmatter4brains]

I've complained about String Theory on here many times. I personally think it's along the lines of Ptolemy's Epicycles - you can make the math say whatever you want, but that doesn't mean you're describing reality. More of a trick, if anything. I believe Feynman even thought along these lines about String Theory, but don't quote me on that.

I do, however, feel that higher dimensions will play some sort of role in the future of physics - just not the way String Theory is using them.

Also, as I understand it, the number of free tunable parameters, which are used to make the theory "work", have gone up by an order of magnitude from the Standard Model. Not exactly what you would expect from a theory of everything.

 

[KickLaBuka]

It is a very difficult discussion, particles vs. waves vs. "strings." Although I agree that no string theory is competitive, it's all about energy--whether we think about the particles creating the energy or just to understand the energy itself. The insult is when new causes are introduced with only mathematical backing. Math can never precede cause.

 

[ramparts]

How many people here are intimately familiar with the mathematics of string theory? I'm not. It's really disingenous to dismiss a theory which you only have a layman's understanding of.

As for the epicycle comment - well, that's why physicists use aesthetics. The epicycles were an ugly theory, to be replaced later by the much more elegant Keplerian theory. So far no more elegant alternative to string theory - a theory who's aesthetic beauty is, arguably, it's strongest feature - have been put out there, so surely string theory is worth a shot. There are very few examples in physics where an ugly theory replaced a beautiful one.

 

[QED]

What is so beautiful about a theory that cannot be tested?

 

[ramparts]

a) Mathematical elegance is independent of testability. In fact, any kind of elegance should be - a theory should be beautiful or ugly regardless of whether our technology happens to be able to verify its predictions, no?
b) Cannot be tested yet and cannot be tested period are two very different things. String theory is the former. General relativity couldn't be tested for the first few years after Einstein published the original paper, but that didn't make it any less valid (or elegant). The fact that a few years for GR might be a few decades or more for string theory doesn't invalidate the thing, it just means we need to get our act together technologically and start devising some really smart experiments.

 

[QED]

There are very few examples in physics where an ugly theory replaced a beautiful one.

Aesthetic value means phooey when it cannot even be actually tested and observed. It's not a complete theory. Not even close. To me, an aesthetically pleasing theory is when both the math and objective reality are in sync. This is also why the majority of physicists have a hard time accepting string theory as the only theory possible to finding the missing link to the TOE.

Some dimensions are curled up and invisible to us? Come on. The equations always call for more dimensions, more this more that... it's like running down the hallway in a nightmare that never ends. They make things way more complicated than they really are and are getting lost in their own mathematics. There ARE some alternatives to string theory that I've been looking into. String theory is like the leading franchise of physics as McDonald's is the leading franchise of fast food - tastes/looks good, but the after-effects are bad.

As far as ugly theories, the cosmological constant was put in place in order for Einstein to beautify his stable/static/unchanging universe. He eventually called it one of his biggest blunders, due to Hubble's discovery. Abandoning his own theory was one of the few ugly truths, but a pretty damn important one. However, the WMAP favors the cosmological constant, so that it actually has value once again - just in a different way. People also think God is aesthetically pleasing in the mechanics of our universe, but I'm not even going to go there.

 

[ramparts]

QED, I may be misinterpreting you but from what I can tell it seems like you're putting your epistemology ahead of your ontology - that is, you're making what we know more important than what exists (regardless of whether we know it). The math and objective reality of a theory can be "in sync" even if the theory is 100%, completely untestable.

I don't think you got the point of my analogy to GR: Einstein published the field equations, Schwarzschild solved them in a spherically symmetric vacuum, and all sorts of fun stuff happened with GR before it was actually testable. So in 1917, 1918, would you have said the same thing about GR? "Oh, it's all pretty math but it's untestable, what garbage"?

Let me try to simplify what I'm trying to get across a bit... string theory is either correct or incorrect (or, likely, some mixture), and that has nothing to do with how testable it is. The universe doesn't care whether or not we can test the theories which correctly describe its behavior, and it especially doesn't care whether or not our technology happens to be up to the point where we can test those theories. One day, string theory will be testable. It's hard to say when that day will be, but that's a day worth getting to because string theory is a viable theory. It doesn't become more viable when our technology improves, we just get better at figuring out how viable it is.

And in the meantime, of course, we should be looking at all sorts of alternatives. My impression has been that there aren't any very convincing ones, but I'm going to withhold judgement on that until I'm actually qualified to understand these theories.

 

[QED]

We can't test dimensions that we cannot observe. It will never be completely testable. Ever. That's why, and I am glad you can agree, that other theories should be looked into than string theory, but the depressing part is... they haven't been worked on nearly as much. This is probably why nothing else is convincing yet.

What we know now is the foundation of what could exist. String theory uses rationality and mathematics to describe the universe, however, what we know from the subatomic world (Standard Model), things are quite irrational... but it is both observably and mathematically true. From what I've gathered about string theory over time, is it seems to be the trickle-down economics of theoretical politics. What I mean by that is, it works from a macro scale, to a micro scale (unobservable energy)... instead of the micro to the macro (from subatomic, observable energy), which is the most obvious way to finding accurate answers. If you ask me, The Standard Model is and always has been the perfect start. It has pieces of the puzzles we are looking for. That's even if we find the HB, but I believe it's eventually possible (holy crap a lot of TeV it will take though). It's mass has already been configured. It doesn't decay like most other particles do, so that is why it is so tough to detect in a particle accelerator. All in all, tweaking those infinite values that the SM spits out is where we should be cracking away. Not up in another dimension, hanging from strings.

 

[ramparts]

That first claim is just a non-sequitur and you should know it; no theory is completely testable. Ever. But once you're at the point where a lot of its predictions have been verified and none have been falsified, some of the underlying architecture becomes a lot easier to accept, because it's hard to conceive of a way it could be otherwise. Every great, well-tested theory - GR, quantum field theory, and the like - is like that, and there are plenty of underlying assumptions you can't really test. It's just a question of when string theory will get to that same point (or will be sufficiently falsified).

Also - "Tweaking those infinite values that the SM spits out" is where people are cracking away, and they've been cracking away at it for the better part of the last half century. You make it sound a lot easier than it is, my friend.

Of course, if you're that dissatisfied with string theory, I would highly recommend you go get some physics degrees, go into academia, and work on those alternatives yourself Seriously.

 

[QED]

That first claim is just a non-sequitur and you should know it; no theory is completely testable. Ever. But once you're at the point where a lot of its predictions have been verified and none have been falsified, some of the underlying architecture becomes a lot easier to accept, because it's hard to conceive of a way it could be otherwise. Every great, well-tested theory - GR, quantum field theory, and the like - is like that, and there are plenty of underlying assumptions you can't really test. It's just a question of when string theory will get to that same point (or will be sufficiently falsified).

Also - "Tweaking those infinite values that the SM spits out" is where people are cracking away, and they've been cracking away at it for the better part of the last half century. You make it sound a lot easier than it is, my friend.

Of course, if you're that dissatisfied with string theory, I would highly recommend you go get some physics degrees, go into academia, and work on those alternatives yourself Seriously.

A non-sequitur? Not at all. Of course there have been theories that have been completely testable and confirmed... for the past several hundred years, in fact. In modern physics, there is are uncertainty/error margins included in theorem and they are usually so marginal it matters not. The triple-slit experiment, for example, had a error margin of about 2% from the Born equations.

Actually, I'm working to a physics major in order to crack away at those equations. I think that string theory just complicates things and is leading us into never-never land. Additionally, I didn't state that no one was cracking away at these equations from the SM... I stated "not enough". Big difference.

 

[ramparts]

A non-sequitur? Not at all. Of course there have been theories that have been completely testable and confirmed... for the past several hundred years, in fact.

Name them. GR? Can't prove the existence of a 4D spacetime manifold with a Riemannian metric, could just be a useful mathematical tool. Quantum mechanics? Prove the existence of the wavefunction. Same thing applies. I don't see how these are qualitatively different from the extra dimensions in string theory.

Actually, I'm working to a physics major in order to crack away at those equations. I think that string theory just complicates things and is leading us into never-never land.

Good!! But, keep an open mind as you do; consider that there may be a very good reason that the majority of physicists working on quantum gravity see string theory as the most promising avenue we know of. And I, in return, will consider the possibility that they're wrong as I work my way through grad school.

 

[darkmatter4brains]

How many people here are intimately familiar with the mathematics of string theory? I'm not. It's really disingenous to dismiss a theory which you only have a layman's understanding of.

As for the epicycle comment - well, that's why physicists use aesthetics. The epicycles were an ugly theory, to be replaced later by the much more elegant Keplerian theory. So far no more elegant alternative to string theory - a theory who's aesthetic beauty is, arguably, it's strongest feature - have been put out there, so surely string theory is worth a shot. There are very few examples in physics where an ugly theory replaced a beautiful one.

well , to be honest I am a bit torn on string theory. The reason being is that String Theory on a conceptual level is VERY aesthetically pleasing (to me). It also solves some of the problems of why general relativity and quantum mechanics don't jive up, in a very nice way, conceptually.

However, I have done a little bit of reading on the math and my opinion is that it gets downright disgusting. Mind you, I haven't actually done the math, just read how it works, from several books. And, there are several elements that make it sound more and more like Ptolemy's Epicycles, IMHO. Also, if you study the history of String Theory, there are professional physicists, who have done the math, and have shared this opinion about String Theory at different points in time - some of these were resolved, but others seem to be inherent to the structure of the theory at this point.

I would tend to think, that overall, if String Theory replaced GR and QM, that would be an ugly theory replacing two beautiful ones. The fact that I already have that opinion and have only touched the surface of String theory, more than likely isn't promising if I actually delved into it some more.

But, yeah, String Theory it is worth a shot - mainly, because it is the only thing we got going.

 

[darkmatter4brains]

Name them. GR? Can't prove the existence of a 4D spacetime manifold with a Riemannian metric, could just be a useful mathematical tool. Quantum mechanics? Prove the existence of the wavefunction. Same thing applies. I don't see how these are qualitatively different from the extra dimensions in string theory.

I think they are. I don't remember the details, but I do remember the substance of what I read about the extra dimensions and they remind one very much of Ptolemy's Epicycles or even Fourier Analysis.

You can make a bunch of sine waves look like a sawtooth function, or any other function under the Dirichlet conditions, if you add enough up together in just the right way. The impression I got, and it is shared by some professionals in the research fields, is that they are doing the same thing with the higher dimensionality of String Theory.

I don't see this in GR or in QM.

Let's face it - String Theory does have some controversy around it and suspicions for more reasons than one - one of those reasons, is the "ugliness" of the math.

 

[ramparts]

Again, I don't know much about this either (I'm really hoping to take the string theory course offered at my grad school this year), but one of the great things about extra dimensions is that they make it possible to unify forces in what can be a very elegant way. Are you familiar much with Kaluza-Klein theory? Add a spatial dimension, solve the Einstein field equations in five dimensions in vacuum, and get the 4D Einstein field equations coupled to an electromagnetic field that obeys Maxwell's equations. I mean, damn. If that ain't beauty, I don't know what is.

 

[yevaud]

Yep, simplicity itself. I truly don't think most people realize how stark and elegant a proper equation can be.

 

[darkmatter4brains]

Again, I don't know much about this either (I'm really hoping to take the string theory course offered at my grad school this year),

You're one brave soul

but one of the great things about extra dimensions is that they make it possible to unify forces in what can be a very elegant way. Are you familiar much with Kaluza-Klein theory? Add a spatial dimension, solve the Einstein field equations in five dimensions in vacuum, and get the 4D Einstein field equations coupled to an electromagnetic field that obeys Maxwell's equations. I mean, damn. If that ain't beauty, I don't know what is.

Yeah, I am familar with that and like I've said before, I am a major fan of higher dimensions. I even think they represent reality, and are not just a useful mathematical tool.. But, I'm not under the impression that that is all String Theory is doing. Anytime I see people making math (like in Fourier Analysis, Ptolemy, etc) say what they want it to say, rather than letting predictions fall out of it naturally, I get suspicious.

I mean, this is partially why people aren't fully comfortable with the Standard Model. It has free parameters which are tuned in order to make the theory work. Well, M-theory (the new String Theory) has many more than the Standard Model.

That's not simplicity - and that's just one example.

There is a lot of complex math that still needs to be worked out. Could be all this gets hashed out in the end and String Thoery will work great. But, till then, I'm personally suspicious of it.

 

[darkmatter4brains]

Again, I don't know much about this either (I'm really hoping to take the string theory course offered at my grad school this year),.

Ramparts, I take it you have done a bunch of QFT then? Just curious if you recommend a good text book.

I like Quantum Field Theory in a Nutshell and am starting Weinberg's book, but have still not found one that really jives up with me. It could just be that I find the subject very difficult ... but the books just don't seem as good as say a good QM or GR book.

 

[QED]

well , to be honest I am a bit torn on string theory. The reason being is that String Theory on a conceptual level is VERY aesthetically pleasing (to me). It also solves some of the problems of why general relativity and quantum mechanics don't jive up, in a very nice way, conceptually.

However, I have done a little bit of reading on the math and my opinion is that it gets downright disgusting. Mind you, I haven't actually done the math, just read how it works, from several books. And, there are several elements that make it sound more and more like Ptolemy's Epicycles, IMHO. Also, if you study the history of String Theory, there are professional physicists, who have done the math, and have shared this opinion about String Theory at different points in time - some of these were resolved, but others seem to be inherent to the structure of the theory at this point.

I would tend to think, that overall, if String Theory replaced GR and QM, that would be an ugly theory replacing two beautiful ones. The fact that I already have that opinion and have only touched the surface of String theory, more than likely isn't promising if I actually delved into it some more.

But, yeah, String Theory it is worth a shot - mainly, because it is the only thing we got going.

Pretty much this. ^ Except, other theories will arise. I'm pretty sure of it.

 

[QED]

Anytime I see people making math (like in Fourier Analysis, Ptolemy, etc) say what they want it to say, rather than letting predictions fall out of it naturally, I get suspicious.

I mean, this is partially why people aren't fully comfortable with the Standard Model. It has free parameters which are tuned in order to make the theory work. Well, M-theory (the new String Theory) has many more than the Standard Model.

And this, as well. Hence, my comment earlier about Einstein's cosmological constant and his blunder - all because he wanted that perfect universe.

However, the SM is the best picture we have of the subatomic world, despite it isn't a TOE, but I believe it is definitely part of it. The free parameters are the issue at hand, indeed, but I don't see anyone trying to rig the math. The three forces in the Standard Model (electromagnetic, weak and strong) have agreed with its predictions. Gravity is the only thing left out of the picture here. I bet those equations are doozies to work out. :shock:

 

[darkmatter4brains]

yeah I should probably clarify I don't necessarily think the Standard Model is rigged, so to speak. But, the free parameters are an issue. It's also been an astoundingly accurate theory. Also, I still remember a show with that young British guy that keeps showing up on the science shows these days. They showed Einsteins Equation (G=8*pi*T, with indices left out) and mention how that pretty much sums up GR, then they wade through a few pages of the Standard Model math and mention how that pretty much sums that up. Simplicity my a$$ :lol:

although, I've also been leaning towards the Higgs not being found and based on Yevaud's recent thread, maybe my opinions are best ignoored :lol:

 

[emperor_of_localgroup]

Good topic.

From what I've gathered about string theory over time, is it seems to be the trickle-down economics of theoretical politics. What I mean by that is, it works from a macro scale, to a micro scale (unobservable energy)... instead of the micro to the macro (from subatomic, observable energy), which is the most obvious way to finding accurate answers. If you ask me, The Standard Model is and always has been the perfect start. QED

I was also thinking along that line. Gravity (GR) is in macro world, QM is in micro world. I hope I'm wrong, but attempts to combine this two worlds with one single theory seem futile. This 2 worlds run on 2 different sets of natural laws. We are missing an 'adapter world' that joins this micro and macro world. This 'missing links' seem absent from physicist's existing thinking and theories.

I don't remember the details, but I do remember the substance of what I read about the extra dimensions and they remind one very much of Ptolemy's Epicycles or even Fourier Analysis.

You can make a bunch of sine waves look like a sawtooth function, or any other function under the Dirichlet conditions, if you add enough up together in just the right way. The impression I got, and it is shared by some professionals in the research fields, is that they are doing the same thing with the higher dimensionality of String Theory. darkmatter4brains

Use of Fourier analysis in explaining string theory is definitely interesting. But note that when we generate a sawtooth wave, we do not combine hundreds/thousands of sine waves to form the sawtooth. But to analyse the sawtooth wave we can break it down into its constituent waves, in other words, it is only theory. A particle is not probably formed by combining many strings, but we can theoretically split a particle into many strings, here the particle is real but the strings are theory. But there may be one use of string theory, which may be realizable in the far far future. Fourier analysis is useful if we want to eliminate certain frequency in the sawtooth by using filter, someday we may be able to 'filter out certain strings' to obtain a new particle. Even then string theory will be treated as only theory, like Fourier decompositions.

 

[ramparts]

Again, I don't know much about this either (I'm really hoping to take the string theory course offered at my grad school this year),.

Ramparts, I take it you have done a bunch of QFT then? Just curious if you recommend a good text book.

I like Quantum Field Theory in a Nutshell and am starting Weinberg's book, but have still not found one that really jives up with me. It could just be that I find the subject very difficult ... but the books just don't seem as good as say a good QM or GR book.

Actually, I haven't That's why I said I'm hoping! In theory I can do the prereqs by the time the string theory course rolls around, but given that I plan to take a bunch of GR-track courses as well, whether that happens in practice is completely up in the air.

Have you seen David Tong's excellent QFT lecture notes? http://www.damtp.cam.ac.uk/user/tong/qft.html

 

[ramparts]

Also, I still remember a show with that young British guy that keeps showing up on the science shows these days. They showed Einsteins Equation (G=8*pi*T, with indices left out) and mention how that pretty much sums up GR, then they wade through a few pages of the Standard Model math and mention how that pretty much sums that up. Simplicity my a$$ :lol:

This. I <3 GR.