Look this is the old Greek philosophical question of The Ship of Theseus, or a Soroites paradox.

One explanation for who we are is that experience is a binary relation. In order for identity or anything else to be experienced by someone, they have to be operating.

There is an episode in Star Trek where a transporter accident didn't destroy the original copy. Obviously a copy of someone isn't that someone because identity is a transitive relation, and the two copies aren't each other!

So by simple logic, a copy of someone isn't that someone because you can have multiple copies. Of course the real issue is the question of someone's identity in the first place.

Because identity is a TRANSITIVE relation (meaning if A is related to B and B to C then A is related to C). And two copies of the same thing aren't each other.

Actually identity is an example of what's called an EQUIVALENCE RELATION which means it is reflexive (A is related to A), SYMMETRIC (If A related to B then B related to A) and transitive. Those 3 properties are necessary and sufficien for a relation to be an equivalence relation. An equivalence relation partitions a set into subsets called "equivalence classes" where all members are equivalent.

So the big question is, what is the relation here that would form equivalence classes between copies of a person? Perhaps it is that two people are the same if, in some sense, they arose as a natural continuous change from some previous biological thing.

That way we can acknowledge the vast complexity of what it's like to be human and alive, and still make a meaningful definition.

It just so happens that this definition is along the lines of hinduism - I've been listening to some Alan Watts lecture recently.

What if the copy is running while I'm still alive, would I experience what the copy experiences? No, right? So what gives? Why should I expect to live on in my software copy?

That's very strange logic. You don't experience future versions of yourself in the present either. But they are also you.

Really? Very strange logic? I experience future versions of myself in the future, and present version(s) of myself in the present. That seems normal. You say, "they [future versions] are also you." But your tense is wrong. Don't you mean... "will be also you"?

The fact that the software copy of me is in my present time frame and yet is obviously separate from me seems to force the conclusion that I am not it, generally, in all time frames. This does not fill me with confidence that I will live on in any sense in this software copy once my present conscious experience is snuffed out.

Why does the time "you" exist matter? Whether another version of you exists in the present time or 10 seconds in the future, it's still "you".

Is sentience made up of atoms? Is consciousness?

Is a computer program made up of atoms? The computer it's running on is. But you can make a copy of the information in a computer program and run it on a different computer.

Copies of the program itself are saved on a medium that is made up of atoms. Execution of the program is facilitated by the simple movement of electrons in a prescribed manner.

What is the physical nature of sentience? What are its mechanics? Does it consist of atoms?