If you don't destroy the original body, then both copies have an equal claim to being "you" right after the teleportation, since both are psychologically continuous with the person who existed moments before. Over time, they will have different experiences and different memories and gradually become different people.

>What if the copy comes back to Earth via spaceship and shoots you? The end result is the same, but it sure looks like you're dead.

The end result is very different because the memories of the surviving copy will be very different. He will remember killing a copy of himself, which by that point is more like a close family member than an identical self.

> If you don't destroy the original body, then both copies have an equal claim to being "you" right after the teleportation

This doesn't seem like a good enough reason to kill one of you?

Not sure what you mean. Do you mean would it be ethical to kill one of them? In my opinion, once two people exist, it would be unethical to kill either of them.

Then the transporter should never destroy the source person, right? That's my whole problem with the idea. Imagine that the technology to destroy the person at the source didn't exist (this is fantasy tech for the purposes of philosophical naval-gazing, afterall), and the machine simply shot you to death after completing the upload to the source.

According to the psychological continuity theory, it shouldn't matter what happens to the original body, as long as the experience is the same. Whether your original body is vaporized or shot, you experience entering the teleporter on Earth and emerging from the teleporter on Mars a moment later. You weren't killed, you were transferred to a different body.

Of course, you don't have to agree with the premise that personal identity is psychological continuity. But I think there are other thought experiments that make the bodily continuity theory counter-intuitive. What if my brain was transplanted in such a way that I experienced going to sleep in my body and waking up in someone else's body, with my memory and personality otherwise unchanged? The bodily continuity theory says I would be a different person, but my intuition is that I would still be the same person, just with a different outward appearance.

Speaking as a potential original body, screw that - I'm not setting foot in a teleporter. But if other people want to try it, that's interesting too. Of course, it's hardly a new problem/paradox; if you haven't seen Christopher Nolan's "The Prestige", it's worth a watch and this is a plot point. And obviously the thought experiment goes back much farther. I'd hardly be surprised if some Greek dudes were arguing about it before the birth of Christ.

Yeah, I'm generally not an early adopter of technology -- I would probably let a few million people try it out before I put my own body in it. The Prestige is excellent. Christopher Nolan has a talent for taking a philosophical concept and turning it into a great action/thriller movie.

Not a philosophical point, but potentially a physical one.

The quantum no-cloning theorem says that it's physically imposible to make any copy of a quantum state, for example all of the state which comprises your body. But it is possible to transfer quantum state from one form to another. This is of course only true of the physical world if the assumptions of the no-cloning theorem are true. Let's assume they are.

Teleportation of your body including whatever quantum state you might consider important therefore must involves a process that appears, to an observer outside, to dissolve the state at one end simultaneous with recreating it at the other end. For some fuzzy definition of simultaneous; this is quantum state after all, and time is subject to the uncertainty principle just like position and momentum famously are.

The information transfer is analogous to transferring a box which the teleporter cannot look inside. You know it can't look as looking destroys the delicate contents. The teleporter cannot use non-quantum information to encode the contents. But the no-cloning theorem doesn't rule out translating quantum states to different forms, such as complex molecular states to light pulses and back. This is difficult, after all modest size quantum computers are difficult to build, maybe even impossible in practice, and they are much simpler than quantum teleportation of interesting size objects.

Squint a bit, and from a certain point of view, this is not destroying your body while creating a copy. It is an exotic form of physical movement, a bit like traversing a wormhole with your body retaining its integrity during the movement, except the wormwhole geometry is not spatial as we normally think of wormholes, it is instead a kind of complex state transformation analogous to geometry. But to you, it might appear that the universe around you is dissolved by the teleporter, then a new location of the universe is reformed around you, then you step out. No loss of physical continuity.