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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."
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. This is stuff for the likes of Dr. Charlie Eppes from the TV show Numb3rs. Maybe that's why Peter MacNicol aka Dr. Larry Fleinhardt bailed to be a heavy on 24?
Anyway, we may see some very smart guys flipping burgers next Christmas...
Who do you get to be an expert to tell you something's not obvious? The least insightful person you can find? -J Roberts
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?
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 :)
"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?
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. 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.
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 back that up. Then they put the onus on somsone else to prove it unsafe. In the cases of DDT, Thalidomide, asbestos insulation, and a whole bunch of things -- if someone had spent some time trying to provide evidence to support the claim these things were prefectly safe, we would have realized they weren't.
Fine, we can never prove that something doesn't pose a risk -- but, deciding to not even try to see if it does pose a risk is assinine. Let's assume it's perfectly safe, and once people start dropping like flies, then we'll check and see if there aren't issues.
So many of the things we make nowadays are really anything but safe -- we just don't know until long after everyone has assumed it was safe until any evidence to the contrary can be provided. It's like genetically modified food -- we haven't proven it's safe, but we don't have enoug evidence to support the belief that it's not harmful either. But, in the long run, we have NO evidence to support the claim it's perfectly safe to eat; we have a lack of evidence either way.
Cheers
Lost at C:>. Found at C.
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.
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.
SIGSEGV caught, terminating
wait... not that kind of sig.
While many people use it in your useage, I don't think it's really with merit as most theories nowadays are extremely complex and since our simplest observation tools are among the first discounted (matter is mostly empty space, yet it looks and feels pretty solid to my eyes and hands) so the simplest theories are seldom the right ones anymore; there's tremendous complexity to our theorizing.
I prefer to look at it this way: it isn't about two competing theories so much as one theory that encompasses each other. So, for example, a theory says "If I do a little dance and then pull the trigger, the bullet will fire." while an experiment shows "If I pull the trigger, the bullet will fire." We can use Occam's Razor to cut away the theory and we can pretty confidently say that dancing had almost nothing to do with the bullet firing. (Unless he was breakdancing--then he needs to be shot.)
This approach makes two different changes: for one thing, by the end, I stopped talking about being "right" and changed it to "useful", partially because simplicity makes things easier to use and partially because two competing models may be equally accurate. For example, while we like Galileo's model nowadays, Tycho Brahe accepted that the planets circled the sun, but he also held that the sun circled the earth. From a certain perspective, they both were "right" but the math involved with Brahe's model was much more complex. Galileo won out because it's just easier to think his way; but the reality is that it's equally valid to compute from the perspective of a still earth with a circling sun. Still, in the Brahe vs. Galileo fight, we used Occam's Razor to cut off those brancehs of Brahe's more complex theory that the earth didn't behave as a planet. (As an aside, at the time there were good reasons to prefer Brahe back then. For one, the problem of parallax. Also, if you drop something from a moving platform like a ship it falls directly down while the ship moves forward but if the platform of the earth moves around the sun then items dropped should similarly drop away from us but this doesn't happen--Galileo's response to these problems were never satisfactory to many of the best scholars of his day).
However, the second change in my formulation is to stengthen the cutting power of the razor almost purely on logical grounds alone. It is in vain to use more when less will do. It becomes a deductive tool rather than a rule of thumb and I can guarantee you that the cuts I make with my razor are never wrong while the cuts made with the "simplicity is best" razor might cut out science and leave only God given the right butcher.
FOR IMMEDIATE RELEASE
THE PHYSICS TIMES
Princeton, NJ
Ed Witten was seen reading Woit's THE NOT EVEN WRONG while simultaneuosly walking down Nassau Street in an inertial frame, followed by his 137 postdocs, who were chanting in unison, as measured by a stationy observer standing outside of PJ's Pancakes.
Some towards the front of the line started crying first (in the lab frame), as they realized it was the end of a free ride for blind obedience, and that for health benefits, trips to exotic conferences, and summers off, they were going to have to start thinking on their own.
The news spread far and wide. Up in Cambridge Lubos Motl changed his snarky one star amazon review for NEW to a laudatory five star review, so as to secure future NSF funding. And Michio Kaku added Woit as a friend on his myspace page, after a call from his media team.
"I've seen darker days than this," Brian Greene smiled, recalling the bar scene with the hot chick in his PBS mini-series. "I already got my two string theory coffee table books out and am set. I know that I have secured the Nobel--in literature."
Witten said, "It is time to make peace. The most important thing that we ST, LQGers, and Not Even Wrongers must do is continue to oppose physical theories, which unify disparate physical phenomena in the same physical framework. Otherwise mathematical masturbation will fall out of favor, and we will have to join the proletariat in working for a living and taking what they're giving."
I wish Woit would have talked more about his views on the future of physics. For it is not enough to criticize, and I would hate to see the future of physics dominated by those untying the knots of String Theory.
ST hath failed. Utterly and completely. It could not have failed more with twice as much NSF fundining.
String Theory was the only game in town, and now there are two--ST & deconstructing ST.
But there is another that actually unifies QM & SR & GR with a physical model: MDT--it's physics!
Moving Dimensions Theory is in complete agreement with all experimental tests and phenomena associated with special and general relativity. MDT is in complete agreement with all physical phenomena as predicted by quantum mechanics and demonstrated in extensive experiments. The genius and novelty of MDT is that it presents a common physical model which shows that phenomena from both relativity and quantum mechanics derive from the same fundamental physical reality.
Nowhere does String Theory nor Loop Quantum Gravity account for quantum entanglement nor relativistic time dilation. MDT shows these derive from the same underlying physical reality. Nowhere does ST nor LQG account for wave-particle duality nor relativistic length contraction. MDT shows these derive from the same underlying physical reality. Nowhere does ST nor LQG account for the constant speed of light, nor the independence of the speed of light on the velocity of the source, nor entropy, nor time's arrow. MDT shows these derive from the same underlying physical reality. Nowhere does String Theory nor Loop Quantum Gravity resolve the paradox of Godel's Block Universe which troubled Eisntein. MDT resolves this paradox.
Simply put, MDT replaces the contemporary none-theories with a physical theory, complete with a simple postulate that unifies formerly disparate phenomena within a simple context.
THE GENERAL POSTULATE
OF DYNAMIC DIMENSIONS THEORY
The fourth dimension is expanding relative to the three spatial dimensions.
If at first the idea is not absurd, then there is no hope for it.
-Albert Einstein
But after thirty years of the absurdity of String Theory, millions of dollars from the NSF, and billions of complementary dollars from tax and tuition and endowments spent on killing physics and indie physicists, perhaps it's time for something that makes sense-for a physical theory that actually accounts for a deeper reality from which both Relativity and Quantum Mechanics, from wh