what is the best estimates on the number of neutrinos in nature?
Some say about three times the number of photons, which is about 10 billion times the number of protons, which is about 10^80 in the observable universe out to about 14 billion light years. So you get about 3 x 10^90 neutrinos counting all three flavors.
A more sophisticated calculation depends on details of cosmology.
what do you mean by details of cosmology?
Isn't this the particle that Feymann suggested that there may be only 1 in the whole universe, it just has the ability to switch it's direction in time at random?
Or am I thinking electrons?
Yes, you are thinking of electrons, but the idea was not thought up by Feynman. Although he mentioned it in his Nobel Prize lecture, the idea actually came from John Wheeler.
Good to know. Thank you Cristo.
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