Passage: 1040 (10 duodecillion) yearsGiven our assumed half-life of the proton, nucleons (protons and bound neutrons) will have undergone roughly 1,000 half-lives by the time the universe is 1040 years old.  To put this into perspective, there are an estimated 1080 protons currently in the universe.  This means that the number of nucleons will be slashed in half 1,000 times by the time the universe is 1040 years old. Hence, there will be roughly 0.51,000 (approximately 10−301) as many nucleons remaining as there are today; that is, zero nucleons remaining in the universe at the end of the Degenerate Age. Effectively, all baryonic matter will have been changed into photons and leptons. Some models predict the formation of stable positronium atoms with a greater diameter than the observable universe's current diameter in 1085 years, and that these will in turn decay to gamma radiation in 10141 years.

Question: What is the theory behind how many protons there are in the universe?
1080 protons