String theory fails first major experimental test

Illustration for article titled String theory fails first major experimental test

String theory is one of the more popular candidates to combine quantum mechanics and relativity into a grand unified theory. But it had remained completely untestable until recent experiments at the Large Hadron Collider. The early results don't look good.

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A few years ago, a group of physicists came up with an ingenious way to test for the existence of hidden dimensions, a key aspect of many string theory models. Basically, the experiment rests upon the existence of micro black holes, objects tinier than an atomic nucleus that could theoretically be produced by smashing together a pair of protons at tremendously high velocities.

This micro black hole would be very unstable and quickly decay, releasing lots of different subatomic particles. The physicists figured out the specific combinations of particles that would be created if the universe has 10, 11, or even more dimensions. The hope was that the Large Hadron Collider would be able to produce the massive energies required to create these micro black holes.

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Well, they ran the experiment, and the results are less than encouraging. The LHC has completed an extensive search for these objects in high-energy proton collisions, and no evidence at all turned up for micro black holes between 3.5 and 4.5 tera-electron-volts. That's a massive energy level and pretty much the upper limit of what we can currently test. This more or less rules out versions of string theory that includes micro black holes at those energies.

Now, let's back up a bit. This isn't good news for string theorists, but it doesn't invalidate string theory either. The original idea for this experiment was always a bit of a long shot, more an attempt to come up with something - anything - that could be used to test aspects of string theory using today's technology.

Researchers hoped to find certain exotic phenomena that would likely exist in a world governed by string theory. Even a few small things can throw this off - the micro black holes might still exist, but they might be larger than the curvature of the hidden dimensions, which would mean they remain unaffected by the extra dimensions. Or it might be even simpler: the micro black holes just can't be found at these energy levels, and we need the next generation Hadron Collider - or even the one after that - to detect them.

String theory definitely lost this particular battle. But this setback isn't the end of the line - it just means the search for a grand unified theory won't be getting any easier. We probably shouldn't have expected anything else.

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[CERN via Slashdot]

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DISCUSSION

Badger_Crowley
Badger_Crowley

As an interested outsider (my film degree does not qualify me to have any opinion on string theory or general physics) which is why I usually don't participate in these conversations. I just read, learn and wonder.

But I am breaking my silence to ask a question: Does string theory remind anyone else of Ptolemy's earth-centric view of the orbits of celestial bodies?

Every scientist from the time of Aristotle until Copernicus believed the universe revolved around the earth and they created elaborate theories to reconcile observational data (retrograde orbits).

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Then Copernicus opened our eyes, changed the paradigm and the ridiculous complexity of the universe became simple, manageable and, most of all, believable.

Nothing about string theory strikes me as simple, manageable or believable. In fact, in my completely unqualified opinion , String Theory is the "retrograde orbits" of modern physics.

If you buy that comparison, then maybe, we should be asking ourselves what 21st century bias or world-view is preventing us from finding that simple and believable solution. In Copernicus' time it was the inability to see the earth (and humans) as not being the center of the universe. It was heresy (literally).