This is a really cute little Fermi calculation, and so I hesitate to say this... (I also hesitate because it will kick off a storm of People on the Internet Ar

This is a really cute little Fermi calculation, and so I hesitate to say this... (I also hesitate because it will kick off a storm of People on the Internet Arguing about Physics...) but this is just wrong. It is irreparably wrong. The idea that a given oxygen molecule (or an oxygen atom, or an electron) in BCE 44 can be identified with an oxygen molecule (etc.) in the present day runs fundamentally counter to the way the universe works. Put it this way. In python, we have mutable variables, which have identity. so we can say >>> a=b=[] >>> c=[] >>> a is b True >>> a is c False >>> a.append(5) >>> a, b, c ([5],[5],[]) Starting out, a and b are the same empty list, and c is a different empty list. It seems naively that we could say the same of particles or atoms. That though we couldn't see it, or hope to trace its history, there existed some electron in 44 BCE that "was the same electron as" some electron today. But that is not how the universe is implemented. Every electron is the same as every other electron. Think immutable, not mutable variables. The state in 44 BCE is not "electron #4892489 is here, and electron #4892490 is there", it is "there exist electrons here, here, here (etc.)" (and they have thus-and-such spins, momenta, etc. etc.) Edit: http://lesswrong.com/lw/pl/no_individual_particles/ http://lesswrong.com/lw/pl/no_individual_particles/