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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."
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.
Liberty you never use is liberty you lose.
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.
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.
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.
You can never go home again... but I guess you can shop there.
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 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 could be very bad news for string theorists. But you can bet there'll be a lot of scrambling to rejigger the theory after a failed test...
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.
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.
Ben Hocking
Need a professional organizer?
http://arxiv.org/abs/hep-ph/0604255
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 reveals much more informative articles, which allows one to find the original journal article. Here's the abstract...
...most of which is beyond grasp of what I remember from 200-level college physics. Would a domain expert care to jump in now?
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.
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.
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 the other known mechanisms. You haven't exactly proven that gravity exists, but you've shown a property that is consistent with your theory and cannot be explained by other means.
This string theory experiment is more akin to saying you're going to test the theory of gravity by showing energy is conserved when the two objects approach each other. You know that your theory of gravity requires the conservation of energy, so you check to see if energy is conserved. If energy isn't conserved, you know your theory is wrong.
The problem is, even if it turns out energy is conserved, it didn't show your theory was right or can't be explained by some other theory. There are a other mechanisms that cause attraction which also exhibit conservation of energy, not just gravity.
This experiment just tests some key things that must be true in order for string theory to be true. It does not test any actual observable unique to the theory.
It's like trying to prove that God doesn't exist by showing that he doesn't make a personal appearance in the next hour. The fact that no bushes burn doesn't really disprove God -- it's just a precondition for him not to exist.
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.
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.
- 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?
- 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?
- 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?
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? Granted, string theory attempts to explain more, but... Really? Which? Does the mythical 'M-theory' exist other than as a big 'Maybe'? What does it look like? What predictions does it make? Substitute 'might be' for 'are' and add a 'conjectured' in front of 'theory'... Perhaps. But there seems to be a lot of contrivance in there.Holy crap I'm bored.
Actually, this website instructs you how to visualize the ten dimensions of string theory. Has anyone read the book that it's advertising?
No, assuming that's meant to represent a point, you skipped a reduction; a point is zero dimensional.
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.
SIGSEGV caught, terminating
wait... not that kind of sig.