## 0171: "String Theory"

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SpitValve
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SpitValve, that's really interesting. You say testable, which presumably means they might be able to one day but haven't yet. Have they figured out a method? What do they need to do to perform the tests?

They have been testing it. What you do it you get several tonnes of water. Each H20 molecule has like 10 protons or something, and there are like 6*10^23 molecules of H20 per 18 grams or so. Once you get something the size of a swimming pool (tonnes of water), you've actually got so many protons you can surround the pool with a crapload of detectors and start getting decent measurements.

Although as Air Gear points out, you can always adjust String Theory a little bit to make everything still consistent...

rlo
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SpitValve wrote:Although as Air Gear points out, you can always adjust String Theory a little bit to make everything still consistent...

Is this always true for string theory? Can string theory always be adjusted to make anything consistent? What are the limits on that? Are there any limits ?

Verysillyman
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That'd be pretty neat. Evetually it will say something completely different to what it does now, but it'll explain things better that way.

Peshmerga
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String theory is, was, and always will be.

There, you've covered every theoretical relative and quantum unmeasurable quantity.

Just like saying, Reeces Puffs for Breakfast is, was, and always will be..

I fail to see the practicality of even trying to learn about something that has almost no base to it. Is there not some standard agreement of even a few dimensions?
i hurd u liek mudkips???

rlo
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Peshmerga wrote:String theory is, was, and always will be.

There, you've covered every theoretical relative and quantum unmeasurable quantity.

If what you're saying is true, that string theory covers every possible theoretical universe, then yes, it would seem to be not worth all that much. Unless there was some test that could be devised that could show that it's true. Or if there are possible universes that can't be described by string theory.

But I'm not sure about our level of knowledge here - are we all sort of speculating? I'd have to rank my knowledge of string theory, on a 1 to 9 scale, at 2, maybe 3. I know enough about relativity and quantum physics to understand what string theory proposes, but I don't know enough to actually make a judgement myself without referring to those who are more expert. And my calculus sucks; I don't think I could follow the math behind it.

Is there anyone reading this who would rank themselves as a 7 or higher?

rlo
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I wrote:But I'm not sure about our level of knowledge here - are we all sort of speculating? I'd have to rank my knowledge of string theory, on a 1 to 9 scale, at 2, maybe 3....
Is there anyone reading this who would rank themselves as a 7 or higher?

If there's anyone here who's read both Brian Green books, then for purposes of this discussion you can call yourself a 6. If you've seen the three-part TV series all the way through, you're a 5. Brian Green books and either of the two new books criticizing string theory - you're a 7!

Yes, I am the judge and my decisions are arbitrary.

Air Gear
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rlo wrote:
SpitValve wrote:Although as Air Gear points out, you can always adjust String Theory a little bit to make everything still consistent...

Is this always true for string theory? Can string theory always be adjusted to make anything consistent? What are the limits on that? Are there any limits ?

I'm not sure if there are limits to it. There's a pretty wide area which it can be stretched to fit, but everything...no idea. I do recall, however, that there are something like 10^500 distinct vacua which the theory CAN describe; I'm not sure how far the process of elimination would take us at this point.

...huh, evidently there's some group that wants to search through the 10^500 somehow to find what could be real and what couldn't be. Even though string theory isn't my thing, if they somehow automate that and turn it into a distributed computing project, that could be kinda cool.

...though looking at what their group is doing, it sounds like they're doing it in a really dumb way that won't look anything like a sensible search through an unsensible space...

Ephphatha
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rlo wrote:
I wrote:But I'm not sure about our level of knowledge here - are we all sort of speculating? I'd have to rank my knowledge of string theory, on a 1 to 9 scale, at 2, maybe 3....
Is there anyone reading this who would rank themselves as a 7 or higher?

If there's anyone here who's read both Brian Green books, then for purposes of this discussion you can call yourself a 6. If you've seen the three-part TV series all the way through, you're a 5. Brian Green books and either of the two new books criticizing string theory - you're a 7!

Yes, I am the judge and my decisions are arbitrary.
I've seen the tv series. Twice. I'd rate myself a 3 at best.
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Pathway
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ÃœmlÃ¤Ã¼t wrote:The fun thing about today's theoretical physicists is that it's almost impossible to tell them from cranks, aside from the sort of journals that publish their work.

I mean, really. Eleven-dimensional vibrating strings? Time Cube? Unless you're a theoretical physicist yourself, how do you decide which to believe?

How do you decide? Why, you become a theoretical physicist.

No one ever gave a guarantee that there was an easy answer out there. The answer to questions involving expert knowledge, in the absence of someone you think is credible, is always to attempt to master the subject yourself, or admit defeat.

dogmeatstew
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this is very true, without extensive study of the topic there's no way you can decide on anything to believe.

Peshmerga
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dogmeatstew wrote:this is very true, without extensive study of the topic there's no way you can decide on anything to believe.

I disagree. I can believe that the Marshmellow man visits my bed everynight and tucks me in when I'm cold.

Maybe you meant to say, without extensive study of the topic, there's no way to create a scientific conclusion that has evidence supporting the claim.
i hurd u liek mudkips???

rlo
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Brian Greene defends string theory in the light of recent criticisms: http://www.nytimes.com/2006/10/20/opini ... nehed.html

MostlyHarmless
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If you read Brian Greene's books (particularly The Elegant Universe) carefully, you'll probably understand the subject as well as you can without actually studying theoretical physics.

Without extensive study of the topic there is no reasonable way to decide to believe it. The problem is, you can't be expected to study everything extensively. Instead you should figure out who is a trustworthy source and believe their knowledge, since hopefully it is based in extensive study.

Bluebottle
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"An intruiging little theory, and actually quite plausible for a universe of five or seven dimensions - if only we lived in one."
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Jesse
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I managed to get through The Elegant Universe quite well. It's a fantastic book and hopefully your local library would have one. Defintiely worth reading.

theY4Kman
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String theory? Bah! It's all about the jazzercise theory.
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Jesse
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And step and step and step and particle physics......

And step.

ly_yng
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People like to make fun of the "multiple dimensions" part of string theory, but that's actually a testable hypothesis that we'll have data on in two years or so as the LHC (Large Hadron Collider) goes online at CERN in Switzerland. There are a bunch of variations of the Standard Model that discuss some implications of multiple dimensions, and we can verify them by the data we get with the new collider. It's not as important for string theory as supersymmetry (which is currently the leading canidate for "beyond the Standard Model" type physics, mostly because it's a really nice starting point for explaining dark matter) but unlike a lot of other things in the theory, it's actually testable.

Pathway
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MostlyHarmless wrote:...Without extensive study of the topic there is no reasonable way to decide to believe it.

Exactly my point.

MostlyHarmless wrote:The problem is, you can't be expected to study everything extensively. Instead you should figure out who is a trustworthy source and believe their knowledge, since hopefully it is based in extensive study.

I disagree because although that method often applies in practice, it's still very far from optimal. It breaks down at "figure out who is a trustworthy source," which itself requires rather more than a passing knowledge. Furthermore, if there are trustworthy-seeming arguments on both sides then the layperson is left to make snap-judgments without any real basis in hard fact.

Air Gear
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Having not checked the individual comic threads forum in awhile, it never occured to me that this could STILL be going...

...but basically, to reply to some previous thoughts...I personally have no problems with how many dimensions a theory has, but the fact that string theory's following is almost cultist in its devotion to that one possibility and so far there's nothing to test that can result in more than parameters being altered...that's something else entirely.

theY4Kman
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Air Gear wrote:...but the fact that string theory's following is almost cultist in its devotion to that one possibility and so far there's nothing to test that can result in more than parameters being altered...that's something else entirely.

Aye, amen!
I am one who believes in your right to have beliefs of your own scientific dogma, but even though science is not anything quite like religion, the string theory closely ties in with beliefs in God, because there is no way to test His/Her/It (Hell, why not "their"?) existence, just like the string theory.

I'm still going with my jazzercise theory
Jesster wrote:And step and step and step and particle physics......

And step.

hahahahhahahaha! ha!
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Air Gear
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theY4Kman wrote:
Air Gear wrote:...but the fact that string theory's following is almost cultist in its devotion to that one possibility and so far there's nothing to test that can result in more than parameters being altered...that's something else entirely.

Aye, amen!
I am one who believes in your right to have beliefs of your own scientific dogma, but even though science is not anything quite like religion, the string theory closely ties in with beliefs in God, because there is no way to test His/Her/It (Hell, why not "their"?) existence, just like the string theory.

I'm still going with my jazzercise theory
Jesster wrote:And step and step and step and particle physics......

And step.

hahahahhahahaha! ha!

The cultist part I'm talking about isn't even whatever faith issue, but damn it, when it gets to "NO STRING THEORY IS IT AND PEOPLE WHO ARE LOOKING INTO ALTERNATIVES ARE WRONG"...that's completely against the entire damn way of science.

theY4Kman
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Oh, my speaking about faith and religion was just a metaphor: "There is no way to prove God WELL, and there is no way to prove the String Theory WELL."

And I didn't mean to sway any believers of String Theory in the wrong way...
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Iluvatar
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Just something interesting I found:
Theoretical Physicists Develop Test For String Theory.

So, it might actually imply something.
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Air Gear
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Iluvatar wrote:Just something interesting I found:
Theoretical Physicists Develop Test For String Theory.

So, it might actually imply something.

If the way she's saying it is right, it's testing Lorentz invariance, analycity, and unitarity...which doesn't seem to be a strong test.

Pathway
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There's an article that references this comic on PhysicsWeb: http://physicsweb.org/articles/review/20/2/1/1 , and Arts & Letters Daily (http://www.aldaily.com) referenced it.

More evidence that xkcd is big.

bippy
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There's been some experimental testing of string theory (and I'm debating whether to say "despite researchers' best efforts" here). The results weren't noticed unless you subscribe to Nature, mostly cause careful claims aren't sexy:

http://www.nature.com/nature/journal/v4 ... 01432.html

SpitValve
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bippy wrote:There's been some experimental testing of string theory (and I'm debating whether to say "despite researchers' best efforts" here). The results weren't noticed unless you subscribe to Nature, mostly cause careful claims aren't sexy:

http://www.nature.com/nature/journal/v4 ... 01432.html

Ok I read the abstract... Basically there are extra forces predicted by string theory. They tried to detect these forces. They didn't find them. So they must be quite weak, (or not exist).

Didn't prove anything really. Their findings are consistent with or without string theory - they just showed that if string theory is correct, certain parameters need to have a certain upper limit to agree with reality.

bippy
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That's very true but I think you're underselling the importance. String theory, as a purely mathematical work so far, has made scant few predictions about things that might actually be measured. This is an example of a prediction that was made by theorists -- look for a modification to Newtonian gravity on the 100 um scale -- and it turns out that there isn't one, within the detection limit of the experiment.

There are two reasons this is bigger news than you might think. First, like it says in the abstract, the potential parameter space is drastically reduced. That's just like what you said. However, for a purely mathematical theory, that's a big thing. I mean, all you HAVE is parameter space. But, constructively, perhaps results like this will help winnow down the infinite options and focus researchers, leading to a more rapid development and proving once and for all that string theory is the big kahuna.

But I think it's also important because we have had zero experimental evidence to believe string theory corresponds to this universe and we still don't. Further, when there is finally made a prediction of a real-world, measurable phenomenon, it doesn't pan out. After hearing for decades that the work is still a little too immature to make physical predictions, this isn't an auspicious outting.

I'm not sufficiently dorky/smart to have really staked out a position on the loop quantum gravity vs. string theory, but at least LQG has predictions and experiments going for it.

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I'm not sufficiently dorky/smart to have really staked out any idea of what loop quantum gravity might be. or string theory. my approach to most new science is tl;dr. even old science is only on my radar becasue i did it at school.
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Yakk
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So, physics has a problem.

Currently, the models of General Relativity and Quantum Mechanics are not consistent with each other. In situations where scales are small enough for QM to happen, and gravity is strong enough for GR to happen, the standard models go "frumph" and fail.

So that is why String Theory is "useful" -- it doesn't seem to go "frumph" and fail in those situations.

String Theory is a mathematical modelling technique that seems to be consistent with General Relativity and Q-M and Gravity.

Now, you get some nice results sometimes. For example, the predicted enthropy of a black hole agrees with a completely different approach that also predicts the enthropy of a black hole. The approaches are utterly different, yet they don't disagree.

It also puts forward as consistent a bunch of strange cosmological arrangements of space-time.

But the problem is, the framework is loose. A "universe made out of strings" happens to describe many more universes than just the one we live in.

Like, lots more.

So now the problem is, can one actually find experimental evidence that restricts the parameter space? If get lucky and you can restrict it enough, you might be able to rule out string theory entirely. If you get really lucky, you could experimentally find something completely unexpected.

Now, it is possible that String Theory says nothing -- if you could show that any set of observations has a String Theory explaination, then String Theory really says nothing. But I haven't seen such a claim put forward.

It does make possible predictions that are not produced by the standard particle model or by Q-M. But these are almost always "weak predictions", not strong ones.

The game is "can we come up with a different model that is consistent with QM, GR and Gravity, that makes strong predictions"?

TheSquirrel
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Yakk wrote:The game is "can we come up with a different model that is consistent with QM, GR and Gravity, that makes strong predictions"?

Hmmm ... I'd love to take up that challenge ... but I'm only an amateur Mathematician and Physicist. I've had a few post-secondary courses, but not enough to be worth anything on this.

But, I think I'll do a little research on String Theory myself ... it's interesting, at least.

bippy
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Yakk wrote:The game is "can we come up with a different model that is consistent with QM, GR and Gravity, that makes strong predictions"?

GR already explains gravity. In terms of the four fundamental forces, GR explains gravity and QFT explains the other three. So the task is just to unite the two theories, or rather, discover a quantum theory of gravitation. It's been pretty hard for the last 60 or so years.

Yakk
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bippy wrote:
Yakk wrote:The game is "can we come up with a different model that is consistent with QM, GR and Gravity, that makes strong predictions"?

GR already explains gravity. In terms of the four fundamental forces, GR explains gravity and QFT explains the other three. So the task is just to unite the two theories, or rather, discover a quantum theory of gravitation. It's been pretty hard for the last 60 or so years.

If B implies C, then A and B and C is equivilent to A and B. :p

GR consistently explains the long-range forces (EM/Gravity).
QM consistently explains the short-range forces (EM/Weak/Strong).

When Gravity gets short-ranged, we got nothin'. Mentioning gravity was intended to stress that it is the real bugger of a problem.

When your gravity warps spacetime itself, and your warping of spacetime has to obey uncertainty, it turns out that things get screwed up. String theory, IIRC, was the brain wave "what if we made the fundamental building blocks 1 dimensional instead of two -- a bunch of inconsistencies might go away!"

aldimond
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Quantum mechanics.

Relativity.

String theory.

They're all wrong.

It's turtles, all the way down.
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bippy
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Yakk wrote:If B implies C, then A and B and C is equivilent to A and B. :p

GR consistently explains the long-range forces (EM/Gravity).
QM consistently explains the short-range forces (EM/Weak/Strong).

When Gravity gets short-ranged, we got nothin'. Mentioning gravity was intended to stress that it is the real bugger of a problem.

When your gravity warps spacetime itself, and your warping of spacetime has to obey uncertainty, it turns out that things get screwed up. String theory, IIRC, was the brain wave "what if we made the fundamental building blocks 1 dimensional instead of two -- a bunch of inconsistencies might go away!"

I supposed when you said you needed to reconcile QM, GR and Gravity that I took that to mean you thought we needed to reconcile QM, GR, and Gravity as three independent things. In any event, I would still object because two of the things you listed were theories and one is a natural phenomenon; it's hard to unite a jaguar with a Jaguar in a way that doesn't involve bloody, furry bits stuck in the grill and an increased insurance premium. But I see your point -- gravity certainly is the odd man out, and the classical nature of GR seems to make it the more wrong-headed of the explanations.

flarets
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is anyone ELSE praying for 2008 to come sooner so the large hadron collider will open and this thread will end? it'll be cool to find out if our universe is fundamentally either a digital or an analogue system, that's about all.

william
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The universe isn't a truck.

It's a series of tubes.
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This cartoon appeared in the February issue of Physics World. I should know, I put it there

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The LHC will, at best, tell us that String Theory is wack. At worst...it won't tell us anything about String Theory.

As far as I am aware, while String Theory DOES make testable predictions, the problem is that none of these predictions, in part or as aggregate, can prove String Theory feasible.

In fact, in its current form, String Theory is quite flexible and can be modified to fit a vast amount of distinct observable states.

No theory is 100% sacred, nor should we enjoy that...I wouldn't have a job otherwise. But the utility of theories is really the discerning edge that science uses...Newton's theory of gravitation predicted the motion of heavenly bodies for a couple hundred years before any discrepency became noticable...and a Newtonian knowledge of gravity provides us with powerful tools...with it, for instance, we were able to navigate space well enough to land men on the moon; a feat that would have been considerably harder without mechanics and gravitational theory under our belts.

The problem, then, of String Theory is that...it does nothing.

Good ole' Max made a shot in the dark and said energy might be quantized in special cases, Einstein said it always is and confirmed it...and in less than fifty years, we had more quantum devices than we could shake a stick at, not least of which is the laser and, later down the road, the semiconductor transistor.

Oersted suggested that electricity and magnetism might be unified phenomena, and within a year Faraday had designed a simple, homopolar induction motor.

String Theory, in contrast, not only hasn't been confirmed or verified in the least...but it's not even clear what we would gain from such a verification. Hence, "Okay, what would that imply?"

I'm not trying to bash the theory, of course...even if it fails outright, the progress made in other branches by simply trying to validate String Theory is worth the failure. And perhaps, in time, we will find uses for it.

Perhaps I can shed some light on WHY String Theory is so ridiculous, however...Edward Witten, the leader of the so-called "second superstring revolution" (physicists need a better naming schema) is, probably, the most brilliant mathematician alive today. And, if I know anything about mathematicians (and I should, I'm quite a mathophile myself), it's that we enjoy abstracting everything to the extreme. Which is perhaps why String Theory is so polarizing, and so slow to be verified or utilized...because to even consider working with it, you need to be a brilliant mathematician...but if you're a brilliant mathematician, you'll probably care more about the abstract beauty of the theory than the gross, practical applications of it.

By the way, I absolutely love this comic. Great job.