Question: I saw this question somewhere in the Internet(I forgot the source) and I think this forum is a good place to ask it.

According to what I know, the atoms in a persons body are replaced every certain amount of years:
<https://skeptics.stackexchange.com/questions/18427/are-all-the-atoms-in-our-bodies-replaced-on-a-regular-basis>

Then, if a persons body atoms are replaced every x years, should the person be prosecuted today for a crime that he/she committed x years ago, when today that person is physically another person(different atoms)? 

And lets say hypothetically that 0.00001% of atoms are never replaced, should 0.99999% of the sentence in years be eliminated (the person is 0.00001% responsible for the crime) ?

This is a related question in the forum:
[Am I still the same person as I was yesterday?](https://philosophy.stackexchange.com/questions/2747/am-i-still-the-same-person-as-i-was-yesterday)

Answer: 
Atoms do not contain little tags that say "I am part of user63152", and whose unique properties determine the actions of user63152. Indeed, aside from differences in isotopes, and a handful of observables like nuclear spin, atoms of the same type are indistinguishable from each other.

Thus, we needn't care whether the atoms are replaced every minute, every decade, or never. That ongoing entity which is you is you by virtue of emergent properties (like thought) which are robust to changes in which atoms you are made from. So while time may have *some* bearing on how we choose to prosecute crime, it should *not* be because there has been some swapping around of functionally equivalent parts.
What is the purpose of punishment? If it is to link consequences to decisions, then the question is whether that old collection of molecules should have predicted the damage it would cause any better than this new collection of molecules.

Our notions of learning imply that behavior is a feedback loop and the consistency of personality is unrelated to the set of molecules that embody it, but related to the information that flows through them. So by and large, the prediction of recidivism remains good over long periods of time. Our morality gets no better with time, and the corresponding replacement of molecules, unless something else changes.

The better question is whether you should incarcerate, for instance, an amnesiac, or an addict who has just undergone something like ibogaine therapy, a rapist subject to chemical castration, or a terrorist who has undergone a religious conversion: a person who really feels like a 'new person' and has had a real part of their personality deactivated or removed in a way that has statistically proven likely to change current and future decision making.