Slashdot Mirror
Test for String Theory Developed
inexion writes "PhyOrg is reporting that SLAC (Stanford Linear Accelerator Center) scientists have found a way to test the revolutionary theory, which posits that there are 10 or 11 dimensions in our universe. This past December, Joanne Hewett, Thomas Rizzo, and student Ben Lillie published an article in Physical Review Letters which shows theoretically how to measure the number of dimensions that comprise the universe. By determining how many dimensions exist, Hewett and Rizzo hope to either confirm or repudiate string theory under specific conditions which would consist of creating and examining 'micro-black holes', which could be formed by smashing two high energy protons together. Using the predicted decay properties of the emitted neutrinos, Hewett and Rizzo solved equations to find that our universe may have more than 10 or 11 dimensions -- too many dimensions to be explained by string theory."
"Black Holes in Many Dimensions at the CERN Large Hadron Collider: Testing Critical String Theory" JoAnne L. Hewett, Ben Lillie, and Thomas G. Rizzo Phys. Rev. Lett. 95, 261603 (2005)
For those with access to PRL, the doi for the paper is: 10.1103/PhysRevLett.95.261603
This is the abstract: For those without access to PRL, you can view a different version of the manuscript on arXiv.
My comments (with the usual disclaimer: while I am a scientist, I'm not a particle physicist/string theorist, so I would appreciate any corrections to what I say): This work appears significant. String theory is incredibly elegant and fits in very well with other (experimentally verified) theories (quantum field theory, etc.). However, what string theory has always lacked, is experimental backup. The fact that there may be a way to experimentally test one of its predictions/requirements (that of extra dimensions) is truly significant, and will allow these fundamental theories to be advanced way beyond their current speculative nature.
As I understand it, one of the current "problems" in string theory is an over-abundance of theories. There are millions (perhaps even an infinite number) of theory-variants that are all consistent with the current string-theory formalism. Of course only one (or possibly zero) of the theories is right. An experimental test would (I hope!) help pick out which theory variant is the right one... or perhaps tell us that string theory is completely wrong! Either way it's a good thing for science and I look forward to this test being performed at the LHC.
Hell, do we even have the capabilities to smash two high energy protons together?
... not yet, anyways. But that's why the Large Hadron Collider is being built! This is the frontier of particle physics.
Well particle accelerators have been smashing high-energy protons together for a long time... but can we smash them hard enough to create micro-black-holes? No.
I'd be interested to know how they intend to measure the micro-black holes.
The LHC has been in the works for a long time, and should come online sometime in 2007. This instrument will be able to probe these questions, and set limits on the possibility of micro-black hole production, as well as extra dimensions.
All black holes emit Hawking radiation, which is essentially black-body radiation (the object is trying to come into thermal equilibrium with the rest of the universe, so is emitting/absorbing radiation to do so). The origin of Hawking radiation is vacuum pair production, if anyone is interested. This radiation causes the black-hole to slowly "evaporate." The temperature (hence rate of evaporation) is inversely proportional to the black-hole mass (hence size).
Micro-black-holes are (obviously) very small. Thus, they evaporate very, very quickly. In fact, they are well below the sustainable threshold, and will evaporate much faster than they accumulate new mass. Also note that these micro-black-holes have quite low mass, hence their graviational attraction is pretty much nill. They are "black holes" because their mass density is infinite, and they are thus a singularity, but nothing about "black holes" definitely implies "consumes matter indefinitely" (this only happens for black holes of sufficient size).
So, no, there is no danger with micro-black-holes eating up the entire Earth. Yes, our current theories may be incorrent (you never know), but if micro-black-holes were able to grow without bound, then you'd expect the universe to be littered with black holes all over the place (which is not the case). Thus there's no reason to worry: the LHC will not gobble up the Earth.
From Wikipedia: "String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics..."
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Here is the article:http://en.wikipedia.org/wiki/String_theor
Sun and Fun
Peter Woit, a critic of string theory, points out some of the misleading bits in this article on his blog, "Not Even Wrong: http://www.math.columbia.edu/~woit/wordpress (scroll down for it). A brief discussion of why this isn't quite as exciting as it may sound.
JoAnne Hewett (one of the original authors) also comments in the blog, saying that the journalists tried to make the work a little more accessible by suppressing important details: As for the headline that is blazened on the SLAC home page - I saw it for the first time when someone drew my attention to it. I knew it was going to cause headaches...
So while this may be solid work, it doesn't seem quite so sexy as it has been made out to be...
They have indeed studied this intensely, although happily for us in this case it boils down to one entirely comprehensible sentence:
The accelerator won't be doing anything that hasn't already happened many, many more times in the interaction with cosmic rays (natural accelerated particles) in our atmosphere, therefore we're not going to destroy the Earth.
And as an environmentalist, I have to come out as being against destroying the Earth.
Most string theorists do not believe that string theory will resolve any of the interpretational questions of quantum mechanics. The term "theory of everything" merely means that it incorporates all the known forces, not that it answers all foundational questions in physics. String theory applies standard quantization methods, just to strings instead of particles. As such, it has all of the interpretational problems of ordinary quantum mechanics. It's possible that string theory will teach us new about quantum theory, but as of yet, there is no strong indication that it will.
The main point is that there are many "ifs", "ands", and "buts" in the paper that did not make it into the news release. Essentially what we showed was that, in a very special set of circumstances it is possible to make a measurement at the LHC which will could possibly determine the number of extra dimensions. If that can be done, then the result will be very important to understanding string theory, since the number of dimensions plays an important role in that theory. It certainly can not rule out string theory. We think it's an important and interesting piece of work, but it isn't a definitive "test" of string theory, as the headline suggests.
Here is a comment JoAnne left on Peter Woit's blog when this showed up there, and the complaint was raised that the story sounded over-hyped:
I've also replaced the arxive version with the published version: http://arxiv.org/abs/hep-ph/0503178, so both versions should now be the same.
Ben Lillie
He's the paper's author, and he's modded at one right now.
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