[Geezer]

Ladies and Gentlemen,

We seem to be on a tangential trajectory regarding the merits or otherwise of String Theory. I'm sure there are many interesting points being made, but that's well beyond the scope of the original question. Not only that, but those points are going to get lost, and it's unlikely that anyone tuning in on this thread will learn much at all.

Soooo, we are going to insist you stick to the original question. If the thread keeps getting lost in the delta, we'll have to split or lock this topic.

If you do want to initiate a discussions about the finer points of String Theory, please frame an appropriate question and post it as a new topic.

Thanking you in advance for your cooperation!

[yor_on]

I'm confused by what this debate is actually about. 

Is the question whether or not string theory makes testable predictions?  I don't think anyone's arguing that it currently does. 

Is the question whether or not string theory should be considered science?  That depends on how strictly you define scientific theories to require immediately testable results.  Many accepted scientific theories require a lot of effort before they make testable predictions.  Would Einstein have been working for years in philosophy, rather than science, because his general theory of relativity took a long time to complete?  If so, is there some immediate transformation from philosophy to science when the first testable prediction is made?  Does the attempt to work towards mathematically towards a testable theory count as science?  I think that you could argue this all day and not come to an answer.  The goal of string theory seems to be to eventually yield testable results and to make sure it agrees with current observations, so I would say that yes, it is a scientific field of research.  I'd probably stop short of labeling it a scientific theory, however--maybe it's a theory-in-progress.

Or is the question whether or not string theory should be attracting funding or scientific talent, since it may or may not yield practical results?  I suspect the mathematics behind the theory will turn out to be useful in other areas, even if the theory is eventually discarded, so that funding it is probably worthwhile.

You are perfectly correct JP.
Einstein took philosophy extremely seriously as I've understood it. He went a far way to philosophically anchor his ideas before verifying them mathematically. Not that I understand string theory, it seems to be one of the most esoteric mathematics there is today. But even if it was proved to be all wrong for this universe we have no guarantee that it will be wrong for some other. That is, if mathematics is the language of the Gods. Because that is the unsaid truth mathematics seems to rest on, that everything can, and will, be expressed correctly if you just find the correct mathematical concepts and equations. I have great hope for our mathematics to become even weirder before we get to the truth

[abacus9900]

The original question was: "What experiment can validate string theory?"

I was under the impression this was what was being discussed.

[abacus9900]

Yes, I am labouring under that misapprehension - even the most beautifully self-consistent theory must be able to be tied to lumpen reality.  The experimental evidence for many areas of truly unbelievable and deeply profound physics is astounding.  The LHC is trying, amongst other things, to recreate the conditions of the universe just after the big bang to search for the higgs boson, quantum mechanics in all its wondrous variety is eminently testable, and gr and sr make the world go round. 

The LHC may or may not support M-theory. Again, you are missing the point.

And the point you are missing is why should M-theory rather than any other be a starting point for new ideas? Few ideas have had more intellectual weight thrown at them for decades, and yet it is becoming more complex and rarefied rather than concrete and applicable.

Once again, because it is the 'best fit' to date.

Science would be exactly where it is now - because that is, to an extent, how we did behave.  However, String theory is a question that has been asked - almost ad infinitum - and is yet to yield greater physical understanding.  The mathematics is awesome, the complexity breath-taking, but the results...

...will have to wait for future generations to grapple with. One often has to be patient in science

[Geezer]

The original question was: "What experiment can validate string theory?"

I was under the impression this was what was being discussed.

That's the problem. There were multiple questions. If we don't know what the question was, it's unlikely the debate will be fruitful.

I will start a topic on validation and we can debate that question there.

EDIT: I have also modified the topic title to be a bit more specific. Please try to avoid turning this thread into  a general discussion about any aspects of String Theory. We would prefer not to lock this thread, but if it becomes impossible to moderate, we will have no choice.

If you think additional topics are appropriate, please start them.

[abacus9900]

So much for a free exchange of views.

[abacus9900]

That's the problem. There were multiple questions. If we don't know what the question was, it's unlikely the debate will be fruitful.

I'm sorry, but most questions raise many more; that is the nature of debate.

[Geezer]

That's the problem. There were multiple questions. If we don't know what the question was, it's unlikely the debate will be fruitful.

I'm sorry, but most questions raise many more; that is the nature of debate.

Quite so, but I was referring to the original post. The object of this forum is to try to answer specific questions. I'm sorry if that is a problem for you.

If you have recommendations on how we can improve the site, rather than posting them in-line, please post them in the Feedback section, or send me, or another moderator a PM.

Thanks!

[melodysquare (OP)]

Ladies and Gentlemen,

We seem to be on a tangential trajectory regarding the merits or otherwise of String Theory. I'm sure there are many interesting points being made, but that's well beyond the scope of the original question. Not only that, but those points are going to get lost, and it's unlikely that anyone tuning in on this thread will learn much at all.

Soooo, we are going to insist you stick to the original question. If the thread keeps getting lost in the delta, we'll have to split or lock this topic.

If you do want to initiate a discussions about the finer points of String Theory, please frame an appropriate question and post it as a new topic.

Thanking you in advance for your cooperation!

I think their discussion on the merits of string theory applies directly to the question of "is string theory science or philosophy?". In a sense I am discovering that answer, and now I got a new book to read thanks to this thread, "The Trouble with Physics". On the flipside, I own the elegant universe, so the balance is fair.

[melodysquare (OP)]

The original question was: "What experiment can validate string theory?"

I was under the impression this was what was being discussed.

That's the problem. There were multiple questions. If we don't know what the question was, it's unlikely the debate will be fruitful.

I will start a topic on validation and we can debate that question there.

EDIT: I have also modified the topic title to be a bit more specific. Please try to avoid turning this thread into  a general discussion about any aspects of String Theory. We would prefer not to lock this thread, but if it becomes impossible to moderate, we will have no choice.

If you think additional topics are appropriate, please start them.

Did you? I can't find it. If you want this thread to die that fine, i just want to see this discussed further no matter where.

[Geezer]

Sure did. It's right here.

http://www.thenakedscientists.com/forum/index.php?topic=34188.0

BTW - We certainly do not want this thread to die. We just want to be able to answer a question, so any supporting information that helps to answer the question is quite appropriate.

The idea behind one question per topic is that it helps to focus the discussion so that the topic does not turn into a broad general discussion with no particular conclusions. It also helps prevent misunderstandings. It's quite easy for two posters to be in violent agreement because they are trying to answer two different questions  []

[yor_on]

I think string theory is doing what it can to model our universe. But the math becomes so extremely complicated and esoteric that people like me get a headache after just reading a couple of sentences. And I'm talking about the math now.

" In the late 70s and very early 80s bosonic string theory had been constructed, initially with the hope it might explain the interaction between quarks. This was because the force between two quarks seemed to act like a string or tube between them, if you pulled them further apart the force attracting them increased, as if connected by a bit of elastic string.

Eventually QCD won out, using the notion of colour confinement and gluons to construct 'flux tubes'. String theory then entered a bit of a lull because bosonic string theory had problems with tachyons, as well as being totally unphysical because it lacked fermions. Someone then realised that if you put in fermions, a number of amazing things happened. The tachyons disappeared and the theory was supersymmetric. Previously, supersymmetry (which had been developed for usual QFT around the same time as bosonic string theory) had to be tagged on by hand, you could have unequal numbers of fermions and bosons. In string theory, if you had both kinds of particles, you had to have equal numbers!

However, there are varying degrees of supersymmetry. N=0 means 'no supersymmetry'. N=1 means 'a little bit' (in very non-technical terms) and it goes all the way up to N=8, "that's ****loads of supersymmetry!". The bigger the value of N, the more extra particles there were predicted, as if the particles we can currently see are a smaller and smaller tip of an iceberg. N=0, we can see all the iceberg, N=1 we see about half of it, N=8 we only see the very edge of it. The value of N also alters the particle content. N>1 is excluded by experiments because it doesn't account for the left/right handed nature of the Weak force (known as 'chirality'). Usual constructions of superstring theory had N=2. A bit of a problem.

Another problem was that superstring theory had lots of dimensions, 10 of them (9 space, 1 time). But we only see 4 (3+1) so the only way that makes sense is if 6 of them are too small for us to see with experiments. In QFT (and relativity in general), energy and length are inversely proportional (if you set c=G=1, your units are such that units of mass = 1/(units of length)), so that in order to access smaller and smaller length interactions, you need more and more energy. This makes sense if you think about how we need bigger and bigger accelerators to probe smaller and smaller objects. So if these dimensions hadn't appeared yet, they must be very small. Experiments say smaller than 10^(-15) metres, theory says as small as 10^(-35) metres! We'd need an accelerator larger than the universe to get that kind of energy!

So how to get past these two problems? Well one problem fixes the other. We have to make 6 of the dimensions small, 'compactified'. But how we do that affects the symmetry of our theory and so alters the amount of supersymmetry. If you compactify your 6 extra dimensions in the simplest way, onto 6 circles (ie a 6d torus, T^6), then you quadruple the amount of supersymmetry your theory has. So a 10d string theory with N=2 goes to a 4+6d string theory with N=8. Bugger, that didn't help.

Well perhaps our ideas about compactification need to be refined a little? Perhaps we need to make the small dimensions a little more complicated. This is where holonomy comes in. We want a theory with N=1 supersymmetry. This is akin to saying that we want a unique spinor in our theory under parallel transport around a closed loop in our space-time. In n dimensions, parallel transport around a closed loop acts like an operator on the spinor, specifically like a membler of a subgroup, G, of SO(n). In flat space-time G=SO(n). However, in complicated spaces you get G < SO(n). It turns out that in order to get a working theory, you need an even number of dimensions in your compact space, so n=2m, and to get the right kind of supersymmetry you need an holonomy group G = SU(m).

Through some rather unpleasant differential geometry (see Joyce), you can prove that a manifold with SU(m) holonomy is Kahler and Ricci flat and has vanishing 1st Chern Class and that's known as a Calabi-Yau space (since Calabi predicted and Yau proved those properties are equivalent). Thus 3 dimensional (3 complex dimensions) Calabi Yau spaces form the core of string theory interest in compact dimensions. Orbifolded and orientifolded tori are a kind of step in the right direction. A general Calabi Yau doesn't have anywhere near the nice description that tori do and you'd have to work through a huge number of cases. At present the orbi/orientifold constructions allow us to see the kind of problems which will arise in full Calabi Yau models and learn how to solve some of them in a nicer environment.

The difference between an orbifold and an orientifold is that an orientifold has had an extra quotienting process applied to it. Rather than just an orbifold group G, an orientifold also have the group (-1)^(F_L)Os quotiented out. (-1)^(F_L) is the 'left fermionic oscillation counter'. It's +1 if there's even numbers of fermionic oscillators going 'to the left' and -1 if odd. O is the worldsheet parity operator and s is an involution (ie a Z_2 map). Sometimes orbifolding isn't enough or you want to have additional structure."

On a 'a quick history of compactification' by AlphaNumeric, who actually works in this field.

And just reading this makes me realize how easily one can lose oneself in this type of advanced mathematics. But as I said, I have great hope and faith in mathematics and I think they are on to something. Another thing I wonder on is how they see it, as a linear field of study, or as a non-linear.
Simply expressed, how do we expect non-linearity to come out of linearity?

[graham.d]

I like the concept of being in "violent agreement", Geezer :-)

[Geezer]

I like the concept of being in "violent agreement", Geezer :-)

I can't remember where I first heard that one, but it is a goodie.

Anyhoo, in this month's SciAm, Stephen Hawking and Leonard Mlodinov question if any single theory will ever emerge as the "Theory of Everything". They seem to be of the opinion that it's quite likely that we will have to continue using the most appropriate theory for particular situations.

If they are right, String Theory, or M-Theory, or whatever it morphs into, may turn out to be a bust.

As an aside, in the same article, they point out that Copernicus didn't prove that Ptolemy was wrong about the center of things, he just made the math a lot simpler! (I'm paraphrasing a bit, but it's a very interesting point.)

[yor_on]

Yep, it's about Occam's razor, we use it and we hope that the universe agrees If it have another view on it it at least have to be 'simple' too me thinks. Maybe a 'super position' is the 'simplest thing' there is as seen from the universe's view, that and entanglements?

Why, if that is so Occam's razor still stands
So we get the best of two worlds, QM and Relativity.