It's been a couple of months since the news came out that the OPERA experiment at CERN got results which indicated that some neutrinos were moving faster than the speed of light.
Why the Speed of Light Limit?
This result was certainly surprising, because Einstein's theory of relativity - a theory which has been confirmed over and over again - places a speed limit on the universe, and that limit is the speed of light. As I've explained before, the equations of relativity indicate that it's impossible to accelerate to the speed of light. And if you take a speed that's greater than the speed of light and plug it into the equations, the results give you nonsensical answers, like imaginary energy! (An imaginary number is when you take a square root of a negative number.)
In other words, if the speed of light can be broken, then one of the fundamental principles that we thought we understood about the universe is clearly incomplete or invalid.
It's a very exciting time for physicists!
However, physicists are appropriately skeptical about such a claim. To overturn a century of consistent experimental evidence in support of the theory, it'll take more than just one anomalous result. That's how things work in science, after all. A theory is in place, confirmed by evidence, but there can be a gradual accumulation of data that refutes the theory. Scientists then have to revise or refine the theory in order to explain the new data. This is exactly how Albert Einstein originally developed his theory of relativity, in fact, to resolve holes in the previous theories of gravitation and electrodynamics.
Experimentalists have examined the results to see if they could find a flaw in the experiment, to show that these results are incorrect. Meanwhile, theorists have been trying to figure how they could explain the result if it turns out to be true. So far, there's been little success, because each proposed explanation runs into various problems by contradicting other known properties of the universe.
Refining the Test
The experiment works because a bunch of neutrinos created at CERN travel 730 kilometers to the Gran Sasso National Laboratory in Italy. These neutrinos are created by collisions back at CERN, so one of the possible sources of error could be that the physicists don't exactly know which neutrino came from which collision. There are statistical methods that physicists use in these cases, and they're generally considered accurate enough, but in this case it is one point of "fuzziness" that may have resulted in the unusual results.
Physicists like to tackle these challenges head on, though, so they worked to eliminate the fuzziness. Instead of having a more continuous collision (and thus a more continuous beam of neutrinos), they broke the beam up into short, 3-nanosecond pulses. Each tiny pulse underwent a collision, and then the neutrinos traveled to the Italian detector.
The results were consistent with the earlier findings - the neutrinos arrived approximately 60 nanoseconds before they should have been able to. The neutrinos still seem to be moving faster than the speed of light.
However, one problem of this new approach is that they got a lot fewer results. They were only able to conduct this test about 20 times. Further tests will need to be run, both at CERN and in other laboratories. If this is a result which only shows up in the OPERA experiment, there will continue to be the possibility that it's some sort of equipment issue rather than an actual violation of a basic law of physics. Confirming results carried out somewhere else would make this claim a lot more solid and go a long way toward convincing the physics community that it's correct.
If the experimentalists are able to replicate the results, then the race will really be on for the theoretical physicists to come up with an explanation that works.
- Symmetry Breaking - Scientists still seek explanation for faster-than-light neutrino result, Oct. 28
- Symmetry Breaking - Faster-than-light neutrino measurement withstands new test, Nov. 17
- Interactions.org - New Test Confirms the Results of OPERA on Neutrino Velocity, But It Is Not the Final Confirmation, Nov. 18
- New Scientist - New results show neutrinos still faster than light, Nov. 18
- Wired - How Many Neutrinos Does It Take to Screw Up Einstein?, Nov. 18
- IEEE Spectrum - Neutrinos Pass Retest, But Performance Still Under Review, Nov. 21
- Big Think - The Noose Around Relativity is Tightening, Nov. 22