Article in the CERN newsletter "symmetry breaking" has the following statement: "Neutrinos are often the first particles to bring news of events in space to Earth, beating even light.". What does this mean?
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asked May 1, 2013 at 3:40
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7$\begingroup$ You could give us a link. What is the point of witholding the context that we would need in order to see, e.g., what kind of source is being referred to? Probably it means that the neutrinos are emitted first, so they get here first. $\endgroup$– user4552May 1, 2013 at 3:58
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$\begingroup$ Not a physicist, but my understanding is that the limit is the speed of light in a vacuum, so in the physical world you might have situations where something is faster then a photon in a medium. $\endgroup$– UncleZeivMay 1, 2013 at 8:35
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3 Answers
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They are probaby talking about supernovae, like how SN1987A was first detected by neutrinos before the light arrived. In that case neutrinos and photons are both produced in the core of the supernovae explosion, but they have dense clouds of gas to get through before they get to empty space and travel freely to us. Since the neutrinos are weakly interacting they can pass through the gas cloud much more easily than the photons and so break free earlier. In a fair race photons beat neutrinos (this was confirmed when the whole OPERA fiasco got sorted out).
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4$\begingroup$ A similar phenomenon occurs in our Sun. While "estimates of the 'photon travel time' (from the core of Sun to its surface) range from as much as 50 million years to as little as 17,000 years", neutrinos travel directly through Sun as it is basically transparent for them. $\endgroup$– PetrMay 1, 2013 at 6:30
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$\begingroup$ @MichaelBrown A fair race in vacuum, sure, but I think the interstellar medium has enough free electrons such that photons will be slowed down to speeds slower than that of a typical neutrino while traversing the galaxy, at least in certain frequencies. $\endgroup$– user10851May 1, 2013 at 8:08
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$\begingroup$ @ChrisWhite Really? Interesting. Would love to see a paper if you have the ref. $\endgroup$– MichaelMay 1, 2013 at 8:27
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1$\begingroup$ @MichaelBrown I've never seen this in a paper. I could work it out myself (preferably while not sleep deprived), but I think I'll let the community handle it ;) $\endgroup$– user10851May 2, 2013 at 1:59
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Here's the reported article on the neutrino detection which has the phrase. To answer your title, neutrinos have a very small mass. They don't carry charge which makes them invulnerable to EM radiation. But, they still interact with charged particles such as electrons, protons and muons. Fast neutrinos can interact with electrons in some medium (like water) and cause them to emit Cerenkov radiation (as a consequence of breaking the light barrier in water). Maybe that's why the neutrino observatories are placed in ice caps.
There are several Wiki articles addressing this early warning...
In the current model the neutrinos are emitted well before the light from the supernova peaks, so in principle neutrino detectors could give advance warning to astronomers that a supernova has occurred and may soon be visible. The neutrino pulse from supernova 1987A was detected 3 hours before the associated photons..!
answered May 1, 2013 at 4:09
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Because the neutrinos follow a straighter line.
The visible light that reaches your eye/telescope has been pulled back and forth by various influences such as gravitational pull along its long path to you. The neutrinos have taken a straighter route because they are much less influenced.
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3$\begingroup$ The gravitational effect on neutrinos is indiscernably different from that on photons of the same energy (since the mass of neutrinos is so small). BTW, I'm not one of the downvoters, but this is probably the reason for them. $\endgroup$– MichaelMay 1, 2013 at 13:30