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I am trying to understand why physicists consider a neutrino beam not to be light.

Here's the research that I did to find the answer:


According to the reasoning in that research neutrino beam must be light beam. I am looking for answers from experts explaining why this is not the case and where I go wrong in my reasoning.

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As a first step, you should not use Matt Strassler's web-site as the basis for research. At the very least, you should get yourself to a point where you are able to use a standard textbook on quantum field theory as a starting point. Understanding the difference between the massless spin-1/2 representation of the Lorentz group and the massless spin-1 representation of the Lorentz group, which is a mathematical way of saying that neutrinos and light are different, is arguably a life-long endeavor. –  Peter Morgan Apr 9 '12 at 13:35
You are trying to reinvent the wheel, starting from linguistics of wheel. If you are really interested in physics start with a physics course and learn how the current physics knowledge is tabulated and described. The simple answer is that neutrino does not have an electromagnetic field and thus cannot be light even if we were wrong in assigning it a spin 1/2. Light by definition is a time varying electromagnetic field. –  anna v Apr 9 '12 at 13:50
A neutrino beam isn't light because it doesn't shine. When it hits, directly or reflected, the human eye, we still see darkness. At most, a large enough number of neutrinos - larger than we can produce - may induce cancer in the eye but we still don't see the culprit. ;-) That was by the old definition of light, something that looks light through the eye. Using a more modern definition of light, light is a beam of electromagnetic waves and/or photons and neutrinos are not photons and/or electromagnetic waves. It's that simple. –  Luboš Motl Apr 9 '12 at 14:03
You won't find any light beams that happily shine through 700 km of rock, the the CERN to Gran Sasso neutrino beam does. –  dmckee Apr 9 '12 at 15:24
Naturally I don't know (or care) what exactly did prompt 4 people to downvote this, but part of the reason one might downvote this question is because it asks about a rather far-fetched idea without presenting any evidence in the question itself. Just as answers should contain the essential information in the answer itself, so that you aren't required to follow external links to make sense of it, the same applies to questions: the essential points of a question should be in the question itself, and should not require us to look at an external link (unless it's really too much to include). –  David Z Apr 9 '12 at 15:38
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First I think you should post the full question here rather than a link to google docs, as not all of us have the time to go pursuing external links.

Anyhow, I did look at your Google doc, and a proton beam is not a laser beam. You can use lasers to create a proton beam by heating matter to very high temperatures, but all you are doing is ionising atoms to create a beam from the protons in their nuclei. If you direct the protons onto a suitable target they will create pions when they collide with the target, and the result is a pion beam. The pions decay to (amongst other things) neutrinos, so you end up with a beam of neutrinos. There is no sense in which the neutrinos are the same as the original laser beam.

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