6/3/2023 0 Comments When you bust a neutrino![]() ![]() I rely for most of my science reporting on sites like Research Blogging. It also amazed me how many people referred to the detection of 20 or so neutrinos from SN1987a as proof that neutrinos travel at the same speed as photons, completely ignoring any possibility of difference between travel through rock rather than empty space. It would also alter our understanding of how neutron stars and black holes work. If cN is much greater than c it could remove the need to invent inflation as a solution to the horizon problem in the big bang. It would still be worth repeating the experiment with neutrino beams going right through the Earth. I estimated the size of such an effect if cN were infinite and unfortunately it would be less than that measured by OPERA. Passing through the rock between CERN and OPERA might have begun to show a small effect if the value of cN is much greater than c. That is extremely difficult to measure except by sending neutrinos through huge amounts of matter. What is not known is the maximum speed of information propagation inside nuclear matter (let’s call it cN). They only interact weakly and so can travel right through nuclei and rarely interact. With some modifications we can explain how that fits with the speed of photons through matter, even within atoms in the large space between electrons and nuclei. Photons, being massless, naturally travel at that speed in free space. It is the maximum speed of information propagation in free space. But that, according to Einstein, is not its primary function. We bias our thinking by always referring to c as the speed of light. It amazed me how everyone seemed to jump to the conclusion that if OPERA was right, Einstein must have been wrong. The two propositions you listed are not the only possibilities. The correct statement is that “neutrinos from the CERN beam to OPERA and ICARUS travel just below, and unmeasurably close to, the speed of light”. ![]() So when people say “neutrinos travel at the speed of light”, they are speaking loosely - and I make this error too sometimes, I’ve noticed. OPERA can detect early or late time arrival of a few nanoseconds, but if you could send both a photon and a 10 GeV neutrino from CERN to OPERA, they would arrive (according to Einstein) a few femtoseconds apart - and a femtosecond is one millionth of a nanosecond. That is too close to the speed of light for OPERA or ICARUS or any other existing experiment to detect the difference between the neutrino speed and light speed. However, a neutrino of mass 0.1 eV/c-squared (we don’t know neutrino masses yet, but they are smaller than 1 eV/c-squared) and with energy of 10 GeV (the typical energy of an OPERA neutrino) would have a speed of 99.999999995% of the speed of light. Neutrinos, since they are massive, travel below the speed of light, according to Einstein. ![]() I’ll answer to this one since it contains a physics misconception. But I still think it would be useful to hear what you have to say. Granted, since you’re reading this blog, you’re a member of a non-representative sample of the public. What’s your perspective on all of this? What surprised you most? What annoyed you or turned you off or excited you? Are you disappointed in or pleased with the scientific process as you saw it unfold? Are you more suspicious of or less suspicious of scientists and/or of science now that you’ve seen this happen? I think these are things that many scientists would be curious to learn. I would like to know how seeing this episode unfold changed (or did not change) your view of science, or physics, or particle physics. Now, with this backdrop, I would like to ask YOU a question or two. It is now pretty clear that possibility #2 was right first OPERA admitted it had found two mistakes which made its previous results invalid then its competitor down the lab, ICARUS, announced it had seen neutrinos arriving just as expected from the same CERN neutrino beam and finally OPERA itself revealed that it had managed to characterize its errors in detail and now, re-analyzing its data, finds (preliminarily) that neutrinos do in fact arrive as expected. The news media made a huge deal out of the first possibility, while the vast majority of professional physicists assumed, for various reasons we can discuss, that the second possibility was almost certainly correct. OPERA made a mistake, and their expectations were off.Einstein was wrong and neutrinos travel faster than light, or.Of course there were, from the beginning, two natural explanations: This is the one that found that neutrinos sent from the CERN lab near Geneva, Switzerland to the Gran Sasso lab in Italy (where OPERA is located) arrived earlier than they expected. So, many of you have probably been following, to a greater or lesser degree, the story of the OPERA experiment. ![]()
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