What is a neutrino and how is it possible that it could travel faster than the speed of light?
A neutrino is one of the particles that according to our best theory of Nature (called the Standard Model) is elementary, that is, fundamental. There are three kinds of neutrinos. They have zero electric charge, and very small mass. We do not know exactly their masses, but we know they are not zero and the heaviest neutrino mass is roughly 10^-8 the mass of the electron. Neutrinos are produced naturally in radioactive decays (a banana produce about one neutrino per hour), in the sun, and by cosmic rays. They can also be produced in reactors and accelerators.
Can it travel faster than light? Well, according to the Standard model, it cannot. Yet, like anything else in physics, the question is not what the theory predicts but what we see in experiments. The reason we are very skeptical about the new result is the fact that it seems to contradict a lot of other results. In particular, there is one result that measure the neutrinos that came from a far away source, a supernova. A supernova is an event when a star dies. It is a big explosion that emit a lot of light and neutrinos. in 1987 there was a supernova called SN1987A, and we were able to see the light and detect the neutrinos from it. Because the neutrinos arrive almost at the same time as the light we know that neutrino travel very close to the speed of light. If the new claim from CERN is correct, these neutrinos should have arrived in 1983! – Prof. Yuval Grossman, Accelerator Physics
A neutrino is an elementary particle that is emitted in certain nuclear reactions, such as beta-decay (a form of radioactivity) or in reactions in particle accelerators. It reacts extremely weakly with matter: about 1 light-year of lead is required to stop a typical neutrino.
According to special relativity, only massless particles can travel at the speed of light. Neutrinos have a very tiny mass, so we expect their speed to be very close to, but slightly smaller than, the speed of light. – Prof. Saul Teukolsky, Astrophysics
With a margin of error of just 10nsec, are there any possible systematic points of error in this analysis that could have caused these results?
Yes, there are many very complicated things that went into the analysis. The production process is far from trivial, and it involves a lot of things that we may not understand. If I need to bet, I would bet that this is the reason for the result, that is, that there are some subtle effects that we do not yet identified. It is important to note that the people who did the experiment do not claim that they saw faster than light neutrinos. All they claim is that there is something they do not understand. –Prof. Yuval Grossman, Accelerator Physics
Systematic errors can always be underestimated. For example the experimenters assign little systematic error to the GPS overall distance scale inaccuracy mentioned above as a likely cause for the discrepancy. – Prof. Richard Talman, Accelerator Physics
What tests are further needed before these results are fully confirmed and widely accepted in the science community?
We first really have to understand all that enter into the simulation of the beam, which is far from trivial. second, one need to see an independent confirmation of the result. There is a similar experiment in the US that can check it, and they are working on it. – Prof. Yuval Grossman, Accelerator Physics
Besides checking this experiment, someone else will have to do an independent experiment. There are similar experiments in the works at Fermilab in the United States.– Prof. Saul Teukolsky, Astrophysics
Need to confirm the GPS accuracy or, if the above explanation is correct, decrease the radius of the earth by 159 meters. All manner of other things have to be checked as well.– Prof. Richard Talman, Accelerator Physics
If neutrinos do travel faster than the speed of light, what is the significance of this discovery for physics?
This would be a revolutionary discovery. Relativity is an extremely well-tested theory. A trivial example: GPS would stop working in about half an hour if the effect of relativity on the moving clocks in the satellites was not accounted for. Coming up with a new theory that explained everything we know but still allowed neutrinos to travel faster than light would be a big challenge. – Prof. Saul Teukolsky, Astrophysics
This would give a strong incentive to figure out what is wrong. Far more likely is that something other than relativity is what is wrong. For example, if the earth’s radius (as built into the GPS navigational system) is too great by 159 meters then the neutrinos would be travelling at exactly the speed of light. This does not necessarily contradict the usual contention that the GPS is accurate to 1 centimeter. The whole distance scale can be wrong in the GPS model, and this would have little effect on ordinary navigation using GPS. – Prof. Richard Talman, Accelerator Physics
In terms of Einstein’s theory of relativity, E=mc^2, did the neutrinos accelerate from a velocity less than c to a velocity greater than c? Or were they at a velocity greater than c to begin with?
In relativity, a particle with mass (like a neutrino) would require an infinite amount of energy to be accelerated up to the speed of light. That’s why its speed is always less than the speed of light. So presumably in this new theory one would have the neutrinos created with a speed greater than c. – Prof. Saul Teukolsky, Astrophysics
Do the findings from the CERN experiment disprove Einstein’s theory of relativity?
Yes and no. If they turn out to be correct, they imply that relativity, as we know it, is not correct. Yet, there are two remarks. First, it is far from clear that indeed neutrinos travel faster than light. Second, even if they do, it does not mean that relativity is wrong, it would imply that relativity is an approximation. And, basically like anything in physics, we keep on making better and better approximations to the true theory of Nature.– Prof. Yuval Grossman, Accelerator Physics
There is so much experimental evidence in favor of relativity that this experiment will need to be scrutinized very carefully before its findings are accepted. It is quite complicated to time how long it takes the neutrinos to travel from CERN to the Grand Sasso tunnel where the detector is, and it is possible there is a subtle error in how this was done.
The experiment is also in conflict with an experiment in 1987, which detected neutrinos from a supernova 170,000 light years away. The neutrinos in that experiment arrived as expected, close to the time the light arrived. If the current experiment were correct, those neutrinos should have arrived 4 years earlier.– Prof. Saul Teukolsky, Astrophysics
If their analysis is correct, that would require Einstein’s theory of relativity to be corrected.”Disproved” is a bit too strong. Einstein’s theory “corrected” Newton’s. – Prof. Richard Talman, Accelerator Physics
How does the neutrino discovery fit in with alternative theories of relativity?
According to my theory, it is light itself, which occupies all space, and not the relativity of time as postulated by Einstein’s Special Theory of Relativity that prevents a particle from moving faster than the speed of light. While it is certain that neutrinos do not have a charge, it is currently uncertain whether they have a magnetic moment that would allow them to interact with light or not. If they do not have a magnetic moment, according to my theory, they would not interact with the light through which they move, and consequently, they would not experience a counterforce, and they would not be constrained by the speed of light. Therefore, if they were ejected from the neutrino-producing reaction in CERN with a velocity greater than the speed of light, they would maintain that velocity. On the other hand, according to my theory, neutrinos should not be able to go faster than the speed of light if they do have a magnetic moment. – Prof. Randy Wayne, Plant Biology
Original Author: Nicholas St. Fleur