• Question: The Icarus collaboration are refusing to believe the claims about neutrinos, saying that they would have lost energy if they had travelled faster than light. Why would they lose energy?

    Asked by sare13 to Ben, Jony, Katharine, Mark on 23 Nov 2011.
    • Photo: Jony Hudson

      Jony Hudson answered on 23 Nov 2011:

      This is a bit of a confusing one, so bear with me:

      You shouldn’t believe the ICARUS people! Their statement is based on a theoretical paper that says that if the neutrinos were going faster than the speed of light, then they would have to lose a lot of energy. But the problem with this logic is that if the neutrinos _were_ going faster than the speed of light then the theory that was used in the paper must be wrong! So the theorists are making a logical error, by making a prediction from a theory that relates to evidence that disproves that theory.

      The same logical error has been made by a lot of physicists when talking about causality. I’ve heard a lot of people in the news saying that if the neutrinos are going faster than light, then this would break causality/allow reverse signalling etc. But the reason people are saying this is because Einstein’s relativity predicts that if a particle goes faster than light, then causality is broken. This is silly, because if neutrinos do go faster than light, then Einstein’s relativity is wrong, so you shouldn’t be using it to make predictions! It’s the same logical error as above.

      So, while I think the ICARUS results are interesting and useful, I don’t think they prove anything.

    • Photo: Ben Still

      Ben Still answered on 23 Nov 2011:

      The Icarus statement is based on a theory paper by nobel prize winner Sheldon Glashow and his colleague Andrew Cohen: http://arxiv.org/abs/1109.6562 . I have to say that the OPERA result contradicts itself when talking about this paper as they see neutrinos with energy above the upper cut off limit (~12GeV) – so Icarus brings no new information to the debate.

      In the theory neutrinos lose energy because they emit weak force carrier particles which carry away energy, before then producing pairs of electrons and positrons. In short the reason for neutrinos emitting the weak force carriers is that even if the neutrino travels faster than light, the weak force cannot with current theory. I wrote a blog post on this paper shortly after it was published which goes over in a lot more detail http://neutrinoscience.blogspot.com/2011/10/weak-booom.html

      Essentially what the paper is saying is that either:

      A. The neutrinos are not travelling faster than light, or
      B. The model of the (electro-)weak force is wrong.

      With all the experimental evidence backing up the theory behind the (elctro-)weak force to amazing accuracy, what Glashow and Cohen are saying is that it must be reason A and not B. The fact that we only detect the neutrino via the weak force in the first place also adds to the argument of A over B.

    • Photo: Mark Basham

      Mark Basham answered on 23 Nov 2011:

      Hi sare13,

      Think the other guys have this pretty much covered. I guess we will only know with more experiments.