1. The problem statement, all variables and given/known data The current limit on the proton’s lifetime is determined by observing a large body of water for a long time and noticing that no one of the hydrogen nuclei in H2O have decayed. Assuming that the experiment making this measurement has been going on for 10 years, how many tons of water are needed to set the constraint on the lifetime of the proton τ > 1034 years? 2. Relevant equations N = N0e-t/τ 3. The attempt at a solution For this I would think we would use this equation to then find the amount of protons needed to make -t/τ = -(10)/(1034 and then from that figure out the number of protons in H2O and then figure out how many molecules then multiply by the molecular weight. Am I on the right track?