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."

Comments

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

[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

[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.

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.

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.

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.

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: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 reveals much more informative articles, which allows one to find the original journal article. 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: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.

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: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: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.