Explain how neutrinos can travel at speeds faster than light and still have mass?

Question

What is the force they experience which would cause such tremendous momentum?

Answer 1

Neutrinos do not travel faster than light.

Either neutrinos are massless or they have very little rest-mass (the latest limit I've seen is 0.3 eV -- by comparison the mass of an electron is 510,999 eV (electron-Volts).

If they are massless, then, just like photons, they can only exist at the speed of light. Using F = m a, we see that any force, however small, that is applied to a body of mass = 0 will give an unbounded acceleration (the neutrino will therefore go at the maximum speed allowed by the universe). Or, in other words, once they reach the speed of light, they are everywhere at once (the Lorentz gamma factor is infinite at a speed of c, so that the elapsed time for any length of travel is exactly zero, when viewed from the massless neutrino's frame of reference).

If neutrinos have mass, then:
a) they will travel (ever so slightly) slower than light, and
b) it should be possible, in theory, to slow them down and even stop them.

a is often tested by checking the time difference between photons and neutrinos arriving from supernova explosions. The difference is so small that it is difficult to measure.

b is being tried in various labs. The problem is that a neutrino only interacts with the Weak Force, felt only inside atomic nuclei. If a neutrino is stopped, it is most probably inside the nucleus of an atom, where the Weak Force is strongest: the neutrino will interact (and be changed), preventing its observation.

The fact that neutrinos are able to subtly change their nature (they change their "flavor"), is taken as a strong indication that their rest-mass is not zero. Because it takes time to change along the way, the elapsed time cannot be zero, therefore the mass cannot be zero. Other than this feature, there is still no accurate value for the neutrino mass (and some people still think of zero as a possibility).

Answer 2

I actually asked this same question on a different forum before. neutrinos don't actually exceed the speed of light. They travel very near the speed of light. They have such a small mass and zero charge that they very rarely ever interact with ordinary matter. They can pass straight through the earth without any resistance.

Answer 3

Click on this site for a lot more.


http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino.html