String Theory Put to the Test

secretsather writes to mention that scientists have come up with a definitive test that could prove or disprove string theory. The project is described as "Similar to the well known U.S. particle collider at Fermi Lab, the Large Hadron Collider, scheduled for November 2007, is expected to be the largest, and highest energy particle accelerator in existence; it will use liquid helium cooled superconducting magnets to produce electric fields that will propel particles to near light speeds in a 16.7 mile circular tunnel. They then introduce a new particle into the accelerator, which collides with the existing ones, scattering many other mysterious subatomic particles about."

You can't prove a theory

[hypnagogue]

Welcome to slashdot; here's your junk science for the day.

You can't prove string theory through experimentation, all you can do is attempt to disprove it.

Re:You can't prove a theory

[stevesliva]

Welcome to slashdot; here's your junk science for the day.

Welcome to Slashdot; here's your whining about semantics for the day. Pretty soon you're going to tell me that "subatomic particles" aren't actually particles, per se.

Proofs are for mathematics

[rumblin'rabbit]

I don't think it's whining. The public's confusion about science surely stems in part from sloppy reporting.

How often have we heard someone claim that we shouldn't allow something because it has never been proven to be safe? Such comments show serious misunderstanding about the nature of knowledge.

Re:

[stevesliva]

How often have we heard someone claim that we shouldn't allow something because it has never been proven to be safe?

Indeed, especially with regard to GMOs. Safety is a testable theory though, and "proven safe" is generally the third option of "lies, damn lies, and statistics."

Re:

[cwm9]

This is more than just "can't prove" in the "you can't prove you're alive" sense. It's more in line with the "you can't prove God exists" sense.

If you think gravity causes objects to attract one another, you can test the theory by putting two objects near each other and measuring their force upon one another. A big part of your experiment is showing that it isn't an electrical or magnetic field that is causing the attraction. You show that the two objects attract one another in some new way outside of th

Re:

[gstoddart]

How often have we heard someone claim that we shouldn't allow something because it has never been proven to be safe? Such comments show serious misunderstanding about the nature of knowledge.

OK, then disallow them until they have rigorously been established as not being dangerous. We'll grant you your metaphysical wiggling and make it nice and obfuscated (but logically and epistomoligically correct).

Way too many things have been released where the person says "it's perfectly safe" and has no evidence to ba

Re:

[rumblin'rabbit]

OK, then disallow them until they have rigorously been established as not being dangerous. We'll grant you your metaphysical wiggling and make it nice and obfuscated (but logically and epistomoligically correct).

It's not "metaphysical wiggling". It goes right to the heart of how we make decisions as a society. We ignore a deep understanding of the nature of risk at our peril. And this peril takes at least two forms: (1) avoiding beneficial practices because we mistakenly assume them to be too risky, a

Re:

[Ithika]

Well, have you ever tried splitting one?

Last time I took a knife to an atom the damn thing blew up in my face! Got a nice head on my beer though....

Re:You can't prove a theory

[Bastian]

I wouldn't call that junk science so much as failure to make a pedantic distinction.

If experiment can show that string theory makes predictions more accurately than current models, I'd say that proven is a good enough word to describe what has happened. Not in the sense that it's been shown to be an absolutely correct description of the machinations of the universe. Proven in the way that General Relativity was proven - decades before all of its predictions had been tested. Proven as in "it's been shown to be a better model," i.e., proven in about the same sense a person can "prove himself."

Re:

[PCM2]

If experiment can show that string theory makes predictions more accurately than current models, I'd say that proven is a good enough word to describe what has happened.

Part of the problem with string theory is that it makes no testable predictions at all. The experiment mentioned is intended to test some of the assumptions upon which string theory rests. Disprove those, and expecting string theory to produce meaningful predictions starts to sound a little silly.

Re:

[Bastian]

No.

Doggedly insisting on using one sense of a polysemous word for no apparent reason (other, maybe, than the apparent desire to show off) and in the face of the obvious fact that the word is perfectly reasonable to use in the given context if we allow other senses to be used is pedantic.

Re:You can't prove a theory

[giminy]

Thank you.

Please vote to give this article the scientificmethodcantproveonlydisprove tag :).

Cheers,
Reid

Re:

[truthsearch]

Please vote to give this comment the concatenated-words-need-hyphens-to-be-readable mod :).

Re:You can't prove a theory

[kripkenstein]

Welcome to slashdot; here's your junk science for the day.

You can't prove string theory through experimentation, all you can do is attempt to disprove it.

Depends on what philosophy of science you subscribe to:

1. According to the 'old consensus' (e.g. the Logical Positivists, early 20th century), you can prove scientific theories.
2. According to Karl Popper, you cannot prove theories, you can only disprove them. It appears that you follow this approach.
3. According to W. V. Quine, you cannot prove or disprove theories, strictly speaking; evidence is taken along with previous information in order to arrive at conclusions.
4. And if you listen to Thomas Kuhn, you get a really different picture from all of these (which I won't go into).

Note that both Popper and Quine are among the most influential philosophers of the 20th century. It is of course legitimate that you are presenting the views of one of them. However, Slashdot readers should be aware of the existence of other views, both in science and in philosophy.

Bah

[Phanatic1a]

It can't prove string theory. It can *support* it, or it can disprove it, falsify it, contradict it. But it can't confirm it. All the experimental data in the universe can't do that.

Re:Bah

[Bluesman]

Actually, ALL of the experimental data in the universe could do that.

Re:

[Sunburnt]

Actually, ALL of the experimental data in the universe could do that.

Of course, how would one know when they got there?

Re:

[gomoX]

There is a "dead end" sign there.

Re:

[the_bard17]

Nah... there's a restaurant.

Re:Bah

[Dragonslicer]

Of course, how would one know when they got there?

They'd see the sign for the restaurant. It's pretty tough to miss.

Re:Bah

[alienmole]

Not so fast -- for a start, you'd need all data from the universe's future, too. But even then, you still won't have proved your theory, unless you count all possible parallel universes too. Even if every event in the history of the universe fails to falsify a theory, it is still possible that you just got lucky, and nothing ever happened in such a way as to disprove the theory. Of course, I'll concede that in that situation, you've got a pretty useful theory and the errors it contains are moot for someone living in the universe in question.

Data that contains itself

[rumblin'rabbit]

Unfortunately that collection of data would have to part of the data itself, since it's part of the universe. And the part of the collection of data that represented the thing that collected data would have to be part of both the original collection, and part of the collection that represented the collection of data. And so on.

Enough to give Bertrand Russell a splitting headache, who's memory would also be part of the collection.

Re:Bah

[radtea]

The tests proposed would not "prove" string theory. They are only testing some of the fundemental assumptions on which string theory is based.

The assumptions are:

1) Lorentz invariance
2) Analyticity
3) Unitarity

The problem is that these are not exactly assumptions but rather desirable characteristics of any good theory in this domain, period. If anyone comes up with an alternative to string theory that is even remotely within the bounds of conventional physics, it will also have these chracteristics.

Lorentz invariance means that the theory is consistent with special relativity. Since our universe is manifestly correctly described by SR to a very high degree of accuracy, this is a desirable property of any theory of everything.

Analyticity (am I spelling that right?) means that the theory is mathematically continuous, which is again something that seems to be highly desirable as our universe contains very few (probably no) formal sigularities. One major goal for theories of everything is to show that the singularities in general relativity are smoothed away at small enough scales.

Unitarity means that the propogator conserves what is being propogated, so spontaneous creation or destruction of stuff doesn't just happen. Again, this is considered a generally desirable property, to the extent that any theory that lacked any of these three properties would be considered a very bad theory. The creator of such a theory would have to give some account as to why it was ok for their theory to not be Lorentz invariant, analytic or unitary.

So this is not so much "testing string theory" as "testing some very basic assumptions about the constraints any good theory should fulfill." This is a good and worthy goal, but it is a very weird bit of marketing to advertise it as "testing string theory" rather than putting it in its more fundamental context.

Re:

[Ambitwistor]

Again, string theory says that space is absolutely not continuous, it's discrete. You can not *infinitely* subdivide an interval, and particles are not perfect, literally *zero size* mathematical points.

String theory does have continuous space, and it says that strings are perfect curves of zero thickness.

String theory places limits on how small you can measure something, however, since you have to use strings to do it; esssentially, you can't measure something that is smaller than the strings you're using to probe it. So there is sort of a "fuzzy" minimum effective distance, even though space itself is continuous.

Somewhat innaccurate title

[ThinkFr33ly]

The tests proposed would not "prove" string theory. They are only testing some of the fundemental assumptions on which string theory is based.

If the test shows that one or more of these assumptions is incorrect, however, then it would probably force a very fundamental rethinking of string theory... essentially disproving it.

Life, The Universe, and Everything

[eviloverlordx]

42.

Did anyone honestly think that the answer would be different?

Re:

[iggymanz]

no, of course not, but the question might be different

XKCD Has a great take on this...

[Acy James Stapp]

http://www.xkcd.com/c171.html [xkcd.com]

Large what collider?

[elliott666]

Oh...Large Hadron Collider. If it was in the Castro district I would really be suspicious.

Hmm...

[rewt66]

Grinstein also noted that if their test does not substantiate what the theory predicts, one of the key mathematical assumptions about the current string theory would be incorrect.

As opposed to the whole idea being bogus? The difference is whether you go for the New, Improved String Theory, Now With Fewer Bogus Assumptions(TM), or whether you throw the whole thing out. Sounds like the physicists want to try to tweak it rather than junk it, even if it fails the experiment.

Note that "starting over with

Epicycles redux?

[sjbe]

I'm by no means an expert in string theory. I barely grasp the basic concepts. However I am an engineer who has taken a LOT of physics classes over the years and I'm not completely ignorant either.

String theory has always struck me as a modern day version of epicycles before it was realized that planets follow ellipses instead of circles. It just seems like we're trying to fit the math to the model instead of modifying the model so that the math makes sense. Add in the fact that it makes no testable predictions (not yet anyway) and it's bordering on not being science anymore. Maybe technology advances will change that but then again maybe not.

Maybe string theory is right, I don't honestly know. But it seems like a lot of group think is going on and little progress is being made.

Re:

[stevesliva]

String theory has always struck me as a modern day version of epicycles before it was realized that planets follow ellipses instead of circles

Epicycles were a way to explain why planets that were orbiting the earth apparently reversed their direction in our sky for certain periods of time.

Re:Epicycles redux?

[Ambitwistor]

Everyone always seems eager to compare to epicycles any modern physics theory they don't care for. String theory, dark matter, what have you...

Physicists were led to string theory in a search for a consistent theory of quantum gravity, not in a search to make up the most complicated theory possible to fudge arbitrary data. For more on why string theory should be taken seriously as a solution to this problem, you can read a long analysis in a previous post of mine here [slashdot.org]. String theory itself cannot be modified to "fit" to a model; it is a unique theory with no adjustable parameters or interactions. However, you can construct various string models to fit observations, as you can presently using quantum field theory models like the Standard Model.

It is also not correct that string theory doesn't make testable predictions. This whole story is about testing predictions of certain string models. However, we can't presently test predictions of all string models at once, and thus rule out all of string theory. But then, the same is true of quantum field theory models as well; there are infinitely many such models that could be true but which we can't yet test.

Re:Epicycles redux?

[Ambitwistor]

This whole story is about testing predictions of certain string models. However, we can't presently test predictions of all string models at once, and thus rule out all of string theory.

Shame on me for not RTFA. The story is about testing all string models at once. However, the tests of are a very general sort (e.g., "do probabilities add up to 1") so, with the possible exception of Lorentz invariance (obeying special relativity at all scales), even non-string theorists would not bet highly on violations being seen.

Re:Epicycles redux?

[alienmole]

I think you're quite right. The problem, though, is that we really don't know how else to do this kind of science at this point. We've reached the edges of our ability to test theories, not just for want of bigger particle accelerators, but also because of more fundamental issues -- we're inside the universe, and there's no fundamental reason that we should be able to figure out exactly how it universe works, from the inside, any more than a creature inhabiting the two-dimensional surface of a balloon can figure out that the balloon's surface is supported by air pressure in a three-dimensional space.

So in a sense, string theory is just the cover story that scientists use to continue conducting research. It's something to focus energy around, like the space program was for 1960's America. Eventually maybe we'll hit on some experimental data or a less unconstrained idea which gives us a clue as to how to proceed.

The LHC is at CERN

[Anonymous Coward]

I think it's funny how the article forgets to mention that the LH collider is located at the CERN (the European nuclear physics institute). As a matter of fact, it is not only in Switzerland, but extends to France as well. The article only mentions it is similar to the U.S. Fermilab accelerator, but then forgets to add that there are many kinds of accelerators world wide.

Funny, ain't it?

Re:

[GrayCalx]

Funny? Funny how? Funny as in it personally offends you that its specific location isn't mentioned?

Funny like, you naturally assuming the editor purposefully left out the location because it was not an American location?

Or funny like "Hahahah that old woman slipped on some ice and broke her hip" funny? Cuuuuz I gotta tell you, I didn't laugh as hard as I did at that woman this morning.

Nothing new

[forand]

The tests being proposed by the physicists in this blog would not test string theory, in that it does not test any prediction of string theory but the underlying assumptions. The write up is very misleading since Lorentz invariance has been tested throughout the past 80 years and always stood up to the tests. I suspect that someone wants to get more funding and mentioned testing string theory to a funding agency.

No Crying In Baseball / No Proof In Science

[localman]

All the tests in the world can only do one thing with string theory: show that we haven't found a way to disprove it yet. All scientific theories are open to being disproven, that is the beauty of science, that is why it is not a religion, as much as religious types would like it to be, and despite the fact that many so-called scientists actually use it as a religion. The best one can hope for is that observation continues to bear out the predictive abilities of the theory. And you can consider a well te

Black holes?

[egrinake]

I remember hearing about plans to use the LHC to produce and study miniature black holes. These are supposed to evaporate nearly instantanously due to Hawking radiation, but such radiation is only a theory without any experimental verification, and apparantly quite a few scientists are concerned it will just go ahead and gobble up the earth.

At least it will be quick :)

Why we musn't fear microscopic black holes

[benhocking]

The energies that will be created in the LHC happen on a daily basis in our upper atmosphere. The only difference is that we will have detectors in the immediate vicinity.

Re:

[Ambitwistor]

A centimeter-sized black hole would be as massive as the Earth itself. (The Earth's Schwarzschild radius is 0.5 cm.)

Re:

[David_Shultz]

I remember hearing about plans to use the LHC to produce and study miniature black holes. These are supposed to evaporate nearly instantanously due to Hawking radiation, but such radiation is only a theory without any experimental verification, and apparantly quite a few scientists are concerned it will just go ahead and gobble up the earth. At least it will be quick :)

First of all the black holes being created by the LHC are not intentionally being created -they are a predicted (by some) consequence o

Re:Black holes?

[vondo]

Second of all, a miniature black hole, even if it didn't dissipate due to Hawking radiation, wouldn't gobble up the Earth. It would still have the gravity of a mere two protons, since that is what constitutes its mass.

Not quite. The theorized micro-black-holes would have masses of about 1000 protons, the amount of energy available in the collision.

Re:

[David_Shultz]

The theorized micro-black-holes would have masses of about 1000 protons, the amount of energy available in the collision. That's a neat trick -but it makes sense. Thanks.

IANA Theoretical Physisist, but....

[hhr]

"The canonical forms of string theory include three mathematical assumptions--Lorentz invariance, analyticity and unitarity. Our test sets bounds on these assumptions." --Benjamin Grinstein

Don't quantum mechanics and GRT also include the above? Meaning if the experements don't confirm the above then more than just string theory is in trouble.

Of course analyticity probably has some very subtle meaning in string theory. Any one here in the know?

Re:IANA Theoretical Physisist, but....

[Ambitwistor]

Yes, those assumptions are also shared by standard quantum field theory. (You can write down Lorentz-violating quantum field theories though.) So you're right, if those turn out to be wrong it's a bigger deal than just ruining string theory.

Bye, everyone!

[Rob T Firefly]

November 2007? Sure, what the hell, I've had a good life.

So, who wants to loan me large sums of money? Pay you back in December?

Oh, lighten up.

[Quiet_Desperation]

We can have a raffle! How will the LHC destroy us? Check one: [ ] Microscopic black holes [ ] Trigger collapse of the false vacuum [ ] Strange matter [ ] Magnetic monopoles [ ] Disruption of the Wigner observer cascade causes a universal system reset [ ] God notices and stuffs us all into Carlsbad Caverns

Doubting Thomas

[Quantam]

Oh ye of little faith

debate still rages?

[mugnyte]

  It thought this was cleared up years ago:

  Scanning/Copying based on a terminator byte pattern is fraught with error and is definitely not secure.

  Buffer sizes are terribly problematic when left tot he caller to check on overflow. It must be in the methods, and thus part of the data structure. (see point above).

  Strings these days are UTF-7 or 8, which makes them an even better candidate for a object-based construct rather than a memory map.

I'd like to point out the....oh, wait...

Wrong--Not About String Theory at All

[adavies42]

If this is the same story referenced here [ucsd.edu], it's bogus [columbia.edu]. To quote Not Even Wrong [columbia.edu],

It is based on a paper which has nothing to with string theory and doesn't do a string theory calculation at all. The paper first appeared on the arXiv last April with the title Falsifying String Theory Through WW Scattering, and was extensively discussed here. In October a new version of the paper was put on the arXiv, with a changed title Falsifying Models of New Physics via WW Scattering (and this was discussed here). I'm gu

Link to Paper

[LotsOfPhil]

Here is the pdf of the paper on arXiv for those interested. [arxiv.org]

High-energy physics - fun, fun, fun!

[TheWoozle]

In what other endeavor can you persuade people to spend hundreds of millions of dollars to build complicated machinery and pay you a salary based on the following (roughly paraphrased) prospectus:

"You see, what we'll do is accelerate some shit up to within a hairs-breadth of the speed of light then smash it into some other shit and see what happens."

Gotta love those wacky physicists! ;-)

Re:

[Quiet_Desperation]

"You see, what we'll do is accelerate some shit up to within a hairs-breadth of the speed of light then smash it into some other shit and see what happens."

Other than the speed of light part, most anyone who ever worked on a military weapons contract.

Re:

[The_Wilschon]

Not actually. There were quite a large number of particles around before Gell-mann came up with the Eightfold Way or Path or whatever. They didn't even have much of any way of classifying them (which is why the nomenclature for hadrons is so screwy today). There were certainly not any models predicting the nucleus before Rutherford hit on it, at least not any that carried much weight. Quantum mechanics kind of grew weirdly from various models like the Bohr model of the atom which were entirely based on

arXiv link

[flawedconceptions]

http://arxiv.org/abs/hep-ph/0604255 [arxiv.org]

old prediction, new way to prove it?

[krotkruton]

In Brian Greene's book The Elegant Universe (1999), he claimed that the LHC would be able to find the existence of superparticles that were predicted by string theory. I'm unable to explain a lot of the details there, but this new article seems pretty similar. 8 years ago we were waiting for the LHC to come along and have a chance of confirming string theory, and now some scientists tell us to wait for the LHC to be able to prove string theory. It's not like we ran out of ways to prove/disprove string th

Proven String Theory

[WED Fan]

String Theory was proven on July 16, 2003, and confirmed after peer review and over 20 separate duplicated efforts, including a lab in Dallas, Texas.

Proven: When you need a piece of string to tie something up, and you find a piece of string in a junk drawer, it will always be too short for use, or too long and when cut to the appropriate length, the remaining piece will be too short for further use.

A similar, but as yet unproven theory is in testing: When you have a piece of string and measure it by "eyeballing" it will always be too short for actual use.

Some questions:

[Quiet_Desperation]

1. Which string theory? There's a few. Anyone who says "M-Theory" will get slapped.

2. What predictions does the string theory in question make?

3. Are the predictions unique to string theory?

 

Re:Some questions:

[Ambitwistor]

Which string theory? There's a few. Anyone who says "M-Theory" will get slapped.

All of them. (And "M-theory" is a perfectly legitimate answer; you can't escape the fact that all the string "theories" are really just different regions of solution space of the same theory.)

What predictions does the string theory in question make?

In this case, unitarity, analyticity, Lorentz invariance, and crossing. (Or rather, that all those properties are obeyed to arbitrarily high energies.)

Are the predictions unique to string theory?

No, they're also axioms of standard relativistic quantum field theories.

Re:

[Quiet_Desperation]

Thanks, although define "arbitrarily high". ;-)

From the author

[Ambitwistor]

If anyone cares to read a highly technical discussion of the paper by its first author (Jacques Distler), you can read his blog entries and the accompanying comments here [utexas.edu] and here [utexas.edu].

Mythbusters

[Cervantes]

it will use liquid helium cooled superconducting magnets to produce electric fields that will propel particles to near light speeds in a 16.7 mile circular tunnel. They then introduce a new particle into the accelerator, which collides with the existing ones, scattering many other mysterious subatomic particles about.

This is why the Mythbusters should not be allowed to design scientific equipment. I can picture Adam dancing about in girlish glee even now...

String Theory was Already Disproved

[rdmiller3]

Back when folks were still trying to figure out the Periodic Table of Elements, there was a promising idea which came out of the field of topology. It was based on the topology of knots, such as one could visualize as closed loops of string. It seemed to "predict" chemical properties for elements as heavy as Calcium but broke down beyond that. The similarity of the two patterns turned out to be only a coincidence, so the theory was discarded.

I predict that this new incarnation of "string theory" will b

Re:

[Ambitwistor]

Wow, a theory totally unrelated to modern string theory was once disproved, and you "predict" that string theory will also be disproved for similar reasons.

News at 11: phlogiston disproved, therefore string theory is wrong.

Re:Flipping Philosophies?

[skoaldipper]

I say, kill all the particles and let science sort 'em out...

Re:Flipping Burgers?

[Martin Blank]

The number of dimensions isn't that high. When all of the string theories are combined into M-theory, the total number of dimensions is eleven, IIRC. Harder to understand? Yes. Impossible to visualize? Yep. But not abhorrently high.

Why not use ten dimensions but make them bigger?

[spun]

Nigel: As you can see, our theories all go to eleven, right across the board. Look: eleven, eleven, eleven.
Marty: Does that mean it's better? Is it any better?
Nigel, well, it's one more, isn't it? Most blokes, their theories only use ten dimensions. They're at ten, where do they have to go from there? When we need that extra push over the cliff, you know what we do?
Marty: Put it up to eleven?
Nigel: Eleven. Exactly. One more!

Re:

[Frank Battaglia]

woosh

The trick is projection

[benhocking]

Impossible to visualize? Yep.

Not at all. You merely have to project one of the dimensions down so that you're only considering a 10-dimensional space.

Re:The trick is projection

[cain]

Impossible to visualize? Yep.

Not at all. You merely have to project one of the dimensions down so that you're only considering a 10-dimensional space.

Then just project that down so you're only considering a 9-dimensional space. Easy.

Then just project that down so you're only considering a 8-dimensional space. Easy.

Then just project that down so you're only considering a 7-dimensional space. Easy.

Then just project that down so you're only considering a 6-dimensional space. Easy.

Then just project that down so you're only considering a 5-dimensional space. Easy.

Then just project that down so you're only considering a 4-dimensional space. Easy.

Then just project that down so you're only considering a 3-dimensional space. Easy.

Then just project that down so you're only considering a 2-dimensional space. Easy.

Then just project that down so you're only considering a 1-dimensional space and you get this --> .

So where's my freakin' Nobel?

Re:

[DragonWriter]

Then just project that down so you're only considering a 1-dimensional space and you get this --> .

No, assuming that's meant to represent a point, you skipped a reduction; a point is zero dimensional.

Re:

[Ambitwistor]

It's not a great description. Its branching thing isn't really a 2D surface, it constantly appeals to lower dimensions as things that need to be embedded in higher dimensions in order to curve (not true), and it starts going badly wrong from there on (e.g., the fifth dimension in string theory is just a spatial dimension, not some set of personal quantum histories; likewise the sixth dimension is not a set of disconnected personal histories, it's just yet another a spatial dimension). I stopped watching a

Re:

[scoopr]

Harder to understand? Yes. Impossible to visualize? Yep.

Quite. Found some help for understanding from here [tenthdimension.com].

Re:Flipping Burgers?

[nebosuke]

Unfortunately, that site is totally bogus. Interesting, but it's entirely unrelated to string theory, which the author seems to mention just to lend his ideas some credibility.

Re:

[blincoln]

Unfortunately, that site is totally bogus.

Mod parent up. I've seen tons of people pass that link around and it has nothing to do with 10 dimensions in the string theory sense at least.

Re:

[Ambitwistor]

You can have the weird little string theories in 6 dimensions, and non-critical strings in less than 10. Critical superstring theory lives in 10 dimensions, and M-theory lives in 11 dimensions. Critical bosonic string theory lives in 26 dimensions, although that doesn't contain any fermion particles and hence doesn't describe our universe, unless it turns out to be related nonperturbatively to M-theory in some unknown way.

Re:Flipping Burgers?

[jaweekes]

Thou shalt have four dimensions. No more, no less. Four shall be the number of thy dimensions, and the number of the dimensions shall be four. Five shalt thou not have, neither thou have three, excepting that thou then proceed to four. Six is right out.

Re:Flipping Burgers?

[indifferent children]

ELEVEN DIMENSIONS?? You must be joking.

THE EARTH REVOLVES AROUND THE SUN?? You must be joking. I can clearly see the sun rising and setting. Any theory that interferes with the perceptions that I am comfortable with, is obviously bollocks. Last time I checked I couldn't see any evidence for the earth revolving around the sun, even when looking under the sofa.

Re:

[maxwell demon]

Of course you can project down 4D objects to 3D in several ways, and thus get some feeling about them. But our perception always keeps those images at 3D, so in our brain it's just a 3D image with mentally attached info, unlike in the 3D->2D projected case, where or brain manages to re-create the 3d image without problems. You simply cannot visualize four straight lines staying perpendicular to each other, no matter how hard you try. You can visualize four lines in 3D-space, and can mentally attach the i

Re:

[kfg]

String theory always seemed to be the most complicated mathematical way you could "force" a unified field theory into existence by adding as many dimensions and undefinable, physically meaningless constants as possible.

And the essential problem in trying to falsify it is that it's so bad it's not even wrong.

KFG

Re:

[turbidostato]

"And the essential problem in trying to falsify it is that it's so bad it's not even wrong."

Well, while this is funny, I find the Slashdot' news is "funny" too: "scientists have come up with a definitive test that could prove or disprove string theory". Last I checked, Mr Popper was a bit of a stubborn about how an experiment can disprove a theory, but it never can prove it!

Re:Flipping Burgers?

[Ambitwistor]

String theory always seemed to be the most complicated mathematical way you could "force" a unified field theory into existence by adding as many dimensions and undefinable, physically meaningless constants as possible.

Actually, it's the simplest known way of creating a unified field theory.

It's been known since the 1920s that adding extra spacetime dimensions allows you to unify forces; Kaluza and Klein successfully unified classical electromagnetism and gravity that way, with a theory in 5 spacetime dimensions. Unfortunately, this idea can't be readily extended to all the forces in the Standard Model, and the unified theory is at least as difficult to quantize as gravity alone.

From a different perspective, leaving gravity out of it, there are the grand unified theories. They too have "extra dimensions", except that the extra dimensions are not of spacetime, but of an internal "gauge" symmetry space. (Kaluza-Klein theory basically turns these internal gauge dimensions into true space dimensions, paving the way to a gravitational theory.)

String theory also does not add as many "undefinable, physically meaningless constants as possible". Indeed, it has fewer constants than the Standard Model. In fact, it has only one constant, which is certaintly definable: it is the string tension. Furthermore, the dynamics of string theory are unique, unlike the quantum field theories. (You can write down infinitely many different particle physics theories with different particle content and interactions, but all of the string theories are part of the same theory, and all the strings obey the same fundamental laws of interaction.)

In short, string theory is not a totally contrived fudge; pretty much all of the ideas that led to semi-successful unified field theories found their way into string theory in a natural and uniquely determined way.

Re:

[ColdWetDog]

Thanks, but my head still asplode.

Re:But OTOH Lee Smolin says that...

[Ambitwistor]

It's not a theory but a collection of theories. The original five different-but-possibly-dual theories and handwaved 'M-theory', plus different flavours with added restrictions or extensions?

No, it's one theory, with a collection of solutions that can be grouped by their behavior.

It's not by any means finished: for instance, finiteness hasn't been proven, and there is no explicit background independent formulation which yields GR spacetime?

Finiteness hasn't been proven, but then, that hasn't been proven in realistic quantum field theory either, and nobody complains about that. (You can win a million dollars for proving it.)

There are background independent formulations of string theory, but none that give (4D, non-supersymmetric) GR in an obvious way. However, formal background independence is a matter of philosophical preference, not physical necessity.

The basic idea may seem simple, but is overlaid by a lot of kludges such as supersymmetry to eliminate tachyons and fluxes to get a positive cosmological constant?

I wouldn't call adding supersymmetry to eliminate tachyons a "kludge", anymore than, say, adding gauge invariance in QFT to eliminate non-renormalizability. As for the positive cosmological constant, I'm not up to date on what is necessary to get that to work out in string theory, but all quantum theories have had notable problems explaining any realistic value of the cosmological constant.

Re:

[Ambitwistor]

I forgot to reply to the rest of your post:

But on the other hand, the topological variations on extra dimensions and fluxes add up to 10^500 different theories with different predictions. How does that make an improvement over the twenty variables of the standard model?

There are infinitely many different quantum field theories. The Standard Model is a particular theory, with a finite and relatively small number of free parameters. You can pick out specific models within string theory as well, with a finite and relatively small number of free parameters, including ones with the Standard Model embedded inside them. (They do tend to have more parameters than the Standard Model; they're more comparable to the Minimal Supersymmet

Re:Flipping Burgers?

[exp(pi*sqrt(163))]

String theory always seemed to be the most complicated mathematical way you could "force" a unified field theory into existence...

On the contrary, it is the simplest. The standard model has an arbitrary set if particles with few principles guiding how they should be chosen, and an arbitrary set of interactions that can take place between particles. It doesn't even single out 4 dimensions as special in any way - the choice of 4D is completely arbitrary. The choice of 30 or so constants defining the interaction strengths is also arbitrary.

String theory has one particle - the string. It has one force which emerges from the very simple dynamics put into it at the outset. A wide spectrum of particles and interactions emerges from it in a natural way. There is little choice for the dimension of spacetime - the theory locks it down from the beginning. Gravity emerges from it naturally - something that doesn't even get mentioned in the standard model. There are close to zero arbitrary constants. And at bottom, the initial assumptions of String Theory are really simple. Simpler than other quantum field theories.

The problem with String Theory is that taken at surface value it doesn't match the universe we see. We don't see a 10-dimensional universe, we don't see the predicted spectrum of particles and so on. The publicised problems we see with String theory are from all the attempts to make our 4D universe emerge from it - and the incredible freedom we have in doing so (eg. by folding up dimensions in various ways). At core, String theory is simple, beautiful and as far from arbitrary as you can imagine. There are all kinds of things wrong with String theory. But they have nothing to do with "adding as many dimensions and undefinable, physically meaningless constants as possible", which sounds more like the ramblings of someone who doesn't have a clue what String Theory is about.

Note that I am neither for nor against String Theory, which makes me part of a tiny minority in the physics world. I certainly doubt it's the ultimate theory of anything, but I also think that there is a lot of uninformed criticism of it. I'm just telling it like it is without my own ax to grind.

Truthiness comes to physics, on both sides.

[Kadin2048]

String theory has one particle - the string. It has one force which emerges from the very simple dynamics put into it at the outset. A wide spectrum of particles and interactions emerges from it in a natural way. There is little choice for the dimension of spacetime - the theory locks it down from the beginning. Gravity emerges from it naturally - something that doesn't even get mentioned in the standard model. There are close to zero arbitrary constants. And at bottom, the initial assumptions of String The

Re:

[exp(pi*sqrt(163))]

I think much of the debate over string theory is, at heart, irrational.

Totally. It's hard to talk about String Theory without people sizing you up to see if you're pro or con and then launching an attack. Whatever anyone says, String Theory includes some incredibly beautiful mathematics and and has some applications to other branches of physics, so I found it worthy of study. I've never felt any need to decide whether or not I think it's 'true' and don't understand the need for other people to take sides

Re:Truthiness comes to physics, on both sides.

[The_Wilschon]

IAAPhysicist, an experimental high energy physicist to be more precise, and I don't like string theory much. I am not opposed to its study, I do not campaign to have funding removed from its proponents, in short, I do not hate it. I just don't care for it, and rather hope that it turns out to be wrong. OTOH, I don't really like the Standard Model (and extensions to it) much either. I think that something different from either is what is needed. Not being a theorist, I am not working on an alternative myself, but I have seen one or two things at various conferences, and thought (just gut reaction) that they looked very promising. One in particular that I found myself unaccountably fond of was a neat little statistical approach from a guy at tamu.

Anyway, my reason for disliking string theory is not at all that I find it "too elegant" or "too cute". You have most of the experimental hep people I know, including myself, pegged quite wrong there. In my opinion, and that of most of my colleagues that I have discussed it with (not a large percentage of all my colleagues), the problem with string theory is that it is not as cute or elegant as it thinks it is. It has precious few free parameters (contrast the standard model), and its first principles are strikingly simple. That ought to be elegance. However, the fact remains, as the GP said, that getting our observable (3,1) universe to appear, even just at low energies, from string theory is quite difficult. Why is this? Primarily because string theory does not tell us how the small extra dimensions are wrapped up around each other. The topology of space presents a huge theory space to search around in.

The standard model is criticised because it does not nail down the values of its free parameters (tautology), and if you don't have the right values of those parameters, then the theory does not describe our universe. However, we can perform experiments which measure various values which depend upon those parameters, and by so doing, obtain values for those parameters with ever increasing precision. Thus, we can find the values such that the standard model describes our universe. Furthermore, the standard model is not chaotic. If you are just a little bit off in the values of your parameters, then your theory describes a universe which is very like ours.

Now, take string theory. The topology of space winds up acting very much like free parameters. However, we can't do experiments to measure the "value" of the topology of space, so finding the right topology is, as I understand it, a huge trial and error process. Furthermore, as I understand it, even if you managed to define some notion of "closeness" to the correct topology, one topology which was "closer" to right than another one would not produce a universe which was necessarily any "closer" in its various properties to correct than the other one. In that sense, string theory is chaotic. So, for all its apparent elegance, it seems to me that string theory is a great deal uglier in the end that QFT and the standard model. This is why I and many others do not like string theory.

Re:

[techno-vampire]

As a minor nitpick, I think you meant Occam's razor. More important, you clearly don't understand it. Occam's razor [wikipedia.org] simply says that you shouldn't add more assumptions than you need. To pick a real-world example, don't assume there's a Vast Conspiracy behind the War in Iraq if everything can be explained without it. Yes, atheists use Occam's razor to show that you can explain the universe without assuming the existence of God, but that's not all it's good for by any means.

Occam's Razor

[David Gould]

As I always like to point out, the most important thing to remember about Occam's Razor is that it's a rule of thumb, not a Law of Nature. If two proposed theories otherwise seem to work similarly well, but one introduces fewer assumptions than the other, Occam's Razor suggests that the former is probably better than the latter, but you can't take this as "proof" -- at best, it lets you make a better educated guess about which avenue is likely to be more fruitful to continue exploring.

Re:

[alienmole]

I haven't RTFA (site is returning a database error), but the biggest criticism of string theory so far has been that there aren't many good ways to falsify it, i.e. disprove it, which makes it somewhat suspect as a scientific theory. Having a way to do a test that could disprove it is, in a sense, very good news for the theory. (Besides, you can't ever prove a scientific theory, you can only support it with evidence and fail to disprove it with tests.)

OTOH, a test that actually does disprove string theory

Re:Don't they want string theory to succeed?

[kfg]

From the wording in the article it sounds like they actually want string theory to fail. . .

A test in which a theory fails is the most useful sort of test.

. . .despite the fact that we have few alternatives so far.

I cannot accept a theory simply because I don't know what to replace it with. Make the tests, generate failures; and then new theories which take the failures into account. That's how the alternatives come into being in the first place. That's why the "failures" are the most useful.

"Successes" only make us complacent with the state of our knowledge, which might well be wrong anyway. "Failures" let us know where we lack knowledge. Science is not done where we know, but where "here there be dragons." It's about exploring the dark corners of the map, not sitting in our offices diddling with ourselves.

We leave that sort of thing to the engineers.

And think about this:

Who says we need an alternative? The quest for a Unified Field Theory is an asthetic desire on the part of physicists. The universe is well known for taking our asthetic desires and shoving them up our collective arses.

Perhaps there can be only two.

KFG

Re:

[terrymr]

That's what experiments are for, you disprove a current theory and then start work on the new theory that fits the observations from the experiment.

Re:Damn, what a useless blurb

[frankie]

And furthermore, now that I have read the "article", it turns out to be a freaking BLOG POST containing nine whole sentences. NINE! Sheesh. Secretsather, you deserve some serious downmods for your laziness and obvious lack of subject knowledge.

A quick news search [google.com] reveals much more informative articles [physorg.com], which allows one to find the original journal article [aip.org]. Here's the abstract...

We show that the coefficients of operators in the electroweak chiral Lagrangian can be bounded if the underlying theory obeys the usual assumptions of Lorentz invariance, analyticity, unitarity, and crossing to arbitrarily short distances. Violations of these bounds can be explained by either the existence of new physics below the naive cutoff of the effective theory, or by the breakdown of one of these assumptions in the short distance theory. As a corollary, if no light resonances are found, then a measured violation of the bound would falsify generic models of string theory.

...most of which is beyond grasp of what I remember from 200-level college physics. Would a domain expert care to jump in now?

Re:

[exp(pi*sqrt(163))]

String theory describes very neatly and elegantly, using complex multidimensional mathematics, an imaginary universe.

Just for the record I thought I'd add that the classical mechanics of Newton (as well as Quantum Mechanics, Quantum Field Theory, Special Relativity, General Relativity, and just about every other physical theory) also "describes very neatly and elegantly, using complex multidimensional mathematics, an imaginary universe", so your statement has a fairly low information content.

Inventing

Re:

[Stanistani]

>waffle hinting

That's actually one of my hobbies...

Re:Stringtheory, plingdeory

[The_Wilschon]

String theory has not been "adjusted" to meet experiment. I'm not really quite sure where this notion comes from. For that matter, I'm not sure where the notion that this is entirely a bad thing comes from.

The standard model is "adjusted" all the time by experimental data. That is, our knowledge of the values of the free parameters in the standard model is changed every time someone gets a new analysis finished. Generally, we just get slightly better precision, but an adjustment is made nonetheless. If we claimed particular values for these parameters that turned out to be wrong, then the standard model would not describe our universe. So, the particulars of the theory are constantly adjusted, but the foundation of the theory is not.

String theory is quite similar, except that you replace free parameters with the topology of space. Now, using topology of space as your degrees of freedom presents a particularly nasty problem because topologies are not continuous like real numbers, so we can't just measure and get a good approximation. We're either quite right or quite wrong if we claim that "x is the topology of space". With the standard model, we can be almost right, and the closer we get to the correct parameter values, the closer our theory gets to right. With string theory, as I understand it, it is all or nothing. However, choosing different topologies, although it does count as an "adjustment" based on data, is not at all an adjustment to the fundamentals of the theory.

In other words, your comparison between theories of fundamental physics and theories describing the solar system is way off base. If anything, the standard model is more like the circles and epicycles than string theory is. The standard model is very ad hoc, and was never intended to be a comprehensive theory, merely a stopgap which described all our experimental data until we could get a better theory. Furthermore, the standard model has been disproven already! Neutrinos have been experimentally demonstrated to have mass, a direct contradiction of one of the first assumptions of the standard model.

Now, I am not in favor of string theory. I hope it does turn out to be wrong. But, at the same time, I am very much more opposed to extremely poor and misinformed "criticism" of string theory. If you don't know what you're talking about, shut up.

Disclaimer: I AM a physicist. I am not a theorist, however, but an experimental high energy physicist. There is a quite good chance that I will be working at the LHC in the next few years.