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."

A Lot of 'Theoreticals'

[eldavojohn]

How many micro-black holes have we measured in a lab?

None.

How many micro-black holes have we even seen?

None, as it turns out [wikipedia.org].

This is a story of hope and speculation--much like the story of super string theory.

Hell, do we even have the capabilities to smash two high energy protons together?

To be fair, Bosonic Super string theory has room for 25 [wikipedia.org] dimensions but it's flawed with tachyon, the so called imaginary mass.

I'd be interested to know how they intend to measure the micro-black holes.

Re:String?

[inexion]

check this out video [aspweb.cz]

Re:It depends upon what the definition of a theory

[Anonymous Coward]

Theories are testable. The problem is that until now, the "String Theory" people insisted their theory was testable, we just lacked the technology to test it. Thus, other scientists told them to get their heads out of the clouds and work on something serious.

Now that this technology is on the horizon, the scientists are developing tests that will prove string theory to be "incomplete" (aka, wrong) by generating scenarios that do not match the predictions made by String Theory (in this case, that they can generate more dimensions than String Theory allows for). If the correct number of dimensions appear every time the micro blackhole is created, then we know that String Theory has the number of dimensions correct, to the best of our ability to measure dimensions (perhaps our understanding of these equations is incorrect, or our measurement equipment is missing something). This doesn't make it "right", it merely makes it "less likely to be wrong". So the scientists will think up some other way to challenge the theory.

String Theory question

[MSBob]

Question for the theoretical physicists in the slashdot crowd:

If one day string theory is validated by an actual experiment what consequences will it have for the various interpretations of Quantum Mechanics? Is it going to give more credibility to any one of the interpretations of QM? Or is this a completely orthogonal issue?

Disclaimer: I know nothing about String Theory but methinks that a true Theory of Everything must provide us with an unambiguous answer for the nature of the collapse of a wavefunction, no?

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:The actual scientific paper...

[bcrowell]

From a brief perusal of the paper, it looks to me like:

1. It's talking about highly hypothetical experiments that they imagine could be done at the energies the LHC can reach, not experiments that have actually been done.
2. It's talking about tests of an unusual version of string theory, in which the extra dimensions aren't curled up as tightly as the Planck scale, and string theory starts to show effects at energies on the order of 1 TeV.
3. They say the experiment could only disprove string theory, not prove it, and then only if the production of microscopic black holes occurred.

This all seems pretty unexciting to me as a nonspecialist. I mean, heck, if the LHC starts producing microscopic black holes, then obviously quantum gravity becomes a much more reasonable thing to work on, regardless of whether string theory is right or wrong.

In addition to string theory's problems with non-uniqueness you refer to, it seems to me that there's also a problem with string theory as a theory of quantum gravity, because it assumes a smooth background spacetime with the 3+1 ordinary dimensions being flat. But that's just not a reasonable way for a theory of quantum gravity to work. In particular, there are strong model-independent reasons [wikipedia.org] for believing that spacetime must be discrete, not continuous, at the Planck scale. So even if string theory could have all its other problems taken care of, it would still not be a good candidate for a fundamental theory of quantum gravity.

Re:The universe is safe.

[blamanj]

Slightly off-topic question. Does vacuum pair production have anything to do with inflation? I've never understood what drives the rapid expansion right after the big bang.

Re:A Lot of 'Theoreticals'

[Jerf]

What ultimately put my mind at ease with regard to all of these "what ifs" is the recognition that cosmic rays routinely smash into the Earth with energies that we can still only dream of; for instance, see the Oh-My-God particle [fourmilab.ch], an impact event still several orders of magnitude in energy above what we can produce in a lab. If an impact event could produce a black hole that could swallow a planet, the Solar System and indeed the entire universe would be nothing but a bunch of black holes of various sizes orbiting each other, as every massive body has long since been hit with at least one particle sufficient to start the black-hole or strangelet putative chain reaction.

Seeing as how every massive body in the universe has been hit with umpteen bajillion of these impacts, yet massive bodies remain, it would seem the probability of this occurring is effectively 0.

A priori, it's not necessarily a wrong idea. But the evidence is pretty clear that it's not a problem.

Re:The universe is safe.

[ArbitraryConstant]

"Of course, we also don't have Large Hadron Colliders all over the universe, smashing particles together with enormous speed and accuracy, do we?"

The universe can easily put our best efforts to shame. For example, the Oh My God particle [fourmilab.ch]. If constant bombardment by these sorts of particles hasn't yet destroyed us, it's doubtful anything we do will make it worse.

Re:The actual scientific paper...

[moreentropy]

The paper is interesting because, although speculative in many regards, the mechanisms they present would possibly give the dimension of spacetime independent of the validity of string theory. String theorists have never quite looked reality squarely in the eye: you can only derive predictions (in the form of a spectrum) in 1, 2, 4, and 8 dimensions due to some complicated issues in harmonic analysis (it is only in those dimensions that a resolvent exists--associated with the real numbers, complex numbers, quaternions and octonians--and the spectrum is given by the poles of the resolvent). One of the interesting issues here is that if the universe is of one of the "off" dimensions, then there is no possibility of a predictive theory fully descriptive of nature. There can be no "final theory" in such a case, due to fundamental incapacity of our present mathematics. This strikes me as a big deal issue, that ought to be of intense intense interest to other physicists, except the math is really unpleasant. (I am a mathematical physicist to whom this was pointed out and, although the point is easy to see would be a monster to put in publishable form and I didn't have 2 years to spare on it.)

Re:Missed the asterisk

[joahewett]

Hello - this is my work. It has been misrepresented and blown out of proportion and I am quite upset about this. The asterisk means that there are many technical if's, and's, or but's of our analysis which are not explained in the news story. It means that our analysis applies to models of extra dimensions where micro-blackholes can be formed with a size less than the curvature of the additional dimensions and where the fundamental particles which make up our universe do not reside in the extra dimensions. These micro-blackholes must also exist at an energy scale which can be probed at the Large Hadron Collider. Under those, very specific, conditions our test holds. These conditions are possible within string theory, but need not be present.