String Theory Put to the Test 407
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."
Somewhat innaccurate title (Score:4, Insightful)
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.
Epicycles redux? (Score:5, Insightful)
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:You can't prove a theory (Score:5, Insightful)
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."
Proofs are for mathematics (Score:5, Insightful)
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:Bah (Score:3, Insightful)
Of course, how would one know when they got there?
Re:Don't they want string theory to succeed? (Score:5, Insightful)
A test in which a theory fails is the most useful sort of test.
. .
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:Bah (Score:5, Insightful)
Re:Epicycles redux? (Score:5, Insightful)
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.
Re:Flipping Burgers? (Score:5, Insightful)
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.
Some questions: (Score:3, Insightful)
2. What predictions does the string theory in question make?
3. Are the predictions unique to string theory?
Re:Black holes? (Score:4, Insightful)
Wrong place, mate. (Score:1, Insightful)
Re:Epicycles redux? (Score:4, Insightful)
Re:Why not use ten dimensions but make them bigger (Score:2, Insightful)
Re:Flipping Burgers? (Score:3, Insightful)
Re:Proofs are for mathematics (Score:3, Insightful)
Who said we shouldn't test things? Who are you arguing with?And we can never rigorously establish anything as not being dangerous. The best we can do is show that the odds of suffering specific types of injury are probably small. Not very satisfactory, but the best we can do.
Re:Flipping Burgers? (Score:3, Insightful)
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:Flipping Burgers? (Score:5, Insightful)
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:The trick is projection (Score:1, Insightful)
Then just project that down so you're only considering a 9-dimensional space. Easy.
Occam's Razor (Score:5, Insightful)
Truthiness comes to physics, on both sides. (Score:3, Insightful)
I think much of the debate over string theory is, at heart, irrational. Some people are attracted to its beauty and elegance, while others find it so elegant that it is therefore suspect. (I.e., the subluminiferous aether was actually pretty beautiful as a theory in a certain way, too, as were epicycles, crystal spheres, and any number of now-disregarded theories; some people would hold that string theory is suspiciously similar to other elegant ideas which have ended up on the scrap heap.)
In some ways, the debate is less of a purely scientific one than an ideological battle between idealists and cynics; lacking experimental evidence, the community seems split mostly between idealists who support string theory, in all its theoretical elegance, while on the other side are cynics who think the whole thing is just too cute to be true, and that it owes itself more to wishful thinking than actual physics.
This is to be expected; until someone can come up with an experiment that will disprove part or all of string theory (or until the theoreticians can find some prediction made by string theory which differs materially from that made by a competing theory), it's an un-winnable argument. There really is little besides "gut reaction" (and other not-quite-rational factors, like the reputations of various people who have already taken sides) to pick sides based on.
Re:The trick is projection (Score:2, Insightful)
Then just project that down so you're only considering a 8-dimensional space. Easy.
Re:Bah (Score:2, Insightful)
I do not believe there is anyone today who can give us satisfactory answers.
Re:The trick is projection (Score:2, Insightful)
Then just project that down so you're only considering a 7-dimensional space. Easy.
Re:The trick is projection (Score:2, Insightful)
Then just project that down so you're only considering a 5-dimensional space. Easy.
It's about Boson scattering... (Score:2, Insightful)
Assuming I'm reading it correctly, if the Bosons don't bounce the right way, it means that string theory (as currently formulated) violates one of the fundamental assumptions (Lorenz invariance, analyticity or unitarity). If the string predicted scattering doesn't match the experimental observations, then string theory (in its current form) is "impossible" and at the very least "would have to be reshaped in a highly nontrivial way."
If the Bosons bounce within predicted limits, then string theory still isn't proven - it just survived this elimination round and moves on to next week's physical challenge...
Re:Flipping Burgers? (Score:3, Insightful)
Re:The trick is projection (Score:3, Insightful)
Re:Yeah..... (Score:3, Insightful)
Even string theory has experiment backing it up. No, really, it does. Everyone talks all the time about how string theory has no experimental evidence. Well, no, it has just does not have any predictions which are currently testable which differ from leading other non-string theories. But, think about it. Other, leading, non-string theories don't have any predictions which are currently testable which differ from string theory! That puts it in the same boat as the standard model and friends.
Furthermore, string theory in its original incarnation was motivated by experiment. It was first developed as a rival to QCD. I don't think that any theory ever (with any kind of success) has been just dreamed up in an experimental vaccuum. Certainly not quantum mechanics. Certainly not string theory. Certainly not thermodynamics, nor Newtonian mechanics. Certainly not relativity, either general or special. All have been motivated by some kind of observations. Later, many of them were found to have predictions that were more far-reaching than what had been observed so far.