Are neutrinos affected by gravity?
If not, could that be a plausible reason for a neutrino taking a shorter path than light, since light is affected by gravity?
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asked Sep 30, 2011 at 16:47
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2 Answers
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Everything is affected by gravity. Gravity warps of space-time according to the Einstein Field Equations, and traveling on "geodesics" (shortest path curves) on that curved surface is how gravity is manifested.
Thinking as though there is some sort of euclidean space underneath the non-euclidean space-time in which neutrinos can take a more direct "straight line" between the points is not at all supported. Everything we know of travels on this curved spacetime.
Also, speaking more Newtonianly, neutrinos do seem to have mass in the more classic sense.
answered Sep 30, 2011 at 17:24
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2$\begingroup$ Actually, it's interesting to ask what is the level of precision that the equivalence principle has been tested for neutrinos. The classic Eötvös experiments clearly puts some pretty strong bounds on essentially everything, since protons and neutrons are almost entirely "virtual" so gets contributions to its energy-momentum tensor from all sorts of fields. But what exactly is the contribution from the neutrino field (i.e. the part of the electroweak doublet)? How does this translate into actual bounds on the physical particle? I think this is a good and well-motivated question. $\endgroup$– gennethCommented Sep 30, 2011 at 17:55
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1$\begingroup$ @genneth: I wonder if anyone has done the equivalent of the semi-famous neutron potential shift experiment with neutrinos. $\endgroup$ Commented Sep 30, 2011 at 18:42
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Both neutrinos and anti-neutrinos are affected by gravity (same magnitudes and direction).
The 1987 Supernova event was the first instance of neutrino and anti-neutrino detection of a source outside of our solar system. Not only were they detected, but the neutrino event recorded occurred a short interval of time AFTER the visible light and gamma ray burst arrived from the same supernova. This was the first hint that neutrinos might actually have mass. Formerly, they had been considered to be massless particles.
The arrival times of the anti-neutrinos for this event were close enough to the time for the neutrinos that any curvature of the path lengths by gravity had to be the of the same magnitudes and directions. This has been cited as proof of the idea that particles of antimatter are affected by ordinary gravitation in the same manner and direction as matter.
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1$\begingroup$ " This was the first hint that neutrinos might actually have mass." Aside from the solar neutrino deficit... And for that matter having mass is not a prerequisite for being affected by gravity. $\endgroup$ Commented Mar 10, 2014 at 0:28
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2$\begingroup$ The neutrinos arrived before the light pulse. $\endgroup$– ProfRobCommented Apr 7, 2016 at 20:34