I think one way to prove that would be to observe electromagnetic activity of the sun and neutrinos originating from it. If you manage to find correlation that

I think one way to prove that would be to observe electromagnetic activity of the sun and neutrinos originating from it. If you manage to find correlation that looks like neutrinos and photons arrive at roughly the same time it would indicate that neutrinos are affected by gravity. I think it was done but I'm not sure.