It's difficult to say what I disagree with. No, no ghostly self. But there is something it is like to be you, and something it is like to be me. Exactly how that comes about is still a mystery. It is certainly dependent on the physical body, although we haven't figured out how it works. But something not explained by the properties of particles and laws of physics, none of which suggest things like subjective experience or teleology. Yet we have subjective experience and teleology. As Terrence Deacon says in Incomplete Nature: How Mind Emerged From Matter, when speaking about the existence of computers:

No non-cognitive spontaneous physical process anywhere in the universe could have produced such a vastly improbable combination of materials, much less millions of nearly identical replicas in just a few short years of one another. These sorts of commonplace human examples typify the radical discontinuity separating the physics of the spontaneously probable from the deviant probabilities that organisms and minds introduce into the world. — Terrence Deacon

Such things come about because of our consciousness. We may use physical features to identify people in various situations. But my identity is my consciousness. We don't care what Bach or Beethoven looked like, or their fingerprints. Their identities are not about their physical characteristics.

Just as my physical body has continuity throughout the changes it undergoes throughout my life, so, too, does my consciousness/identity.

Like I said, I'm not sure how much we disagree. I assume at least on whether or not anything other than the interactions of particles, which everything physical ultimately reduces to, is at play.

Just wanted to note that the Thomas Riker situation only implies body-soul dualism, not the often associated ideas of the immortality and immutability of the soul (or some aspects of it).

Because as we know from another beaming mishap on the USS Voyager, it is possible for two souls to be combined into a novel, composite soul (sharing a composite body). This was, of course, Tuvix.

Unfortunately, they were somehow able to undo this fusion, both killing Tuvix and forcing Voyager to continue on for several more seasons in the Delta Quadrant with Nelix, the most annoying member of the cast.

I don't think the Rikers or Tuvix imply body-soul dualism. Quite the contrary.

I do not believe the transporter would be capable of transporting, duplicating, or doing anything else with, an immaterial soul.

I do not think the Riker soul was split in two, each duplicate having half a soul from then on. nor do I think the soul was duplicated, Will and Thomas each getting a copy. I think the body was duplicated, and a living human body produces consciousness. (Through whatever means.)

I do not think Tuvix possessed two souls. I think he got quite a bit of physical traits from each. Including memories of each. And, as that is yet another example of a living (sorta) human body, it was conscious. And it drew on the memories of each, while having its own identity, which was becoming less and less a combination of the two, and more its own unique consciousness, as time went by.

I believe killing Tuvix was, indeed, murder. And it was done for nothing. Tuvok and Neelix had already died when they were dematerialized. Replicating them may have given the ship people to fill those rolls again, but they were newly created life, with the total memories of those who had died. Tuvix, regardless of how he came to be, was a conscious being, and should've been allowed to remain so.

We may use physical features to identify people in various situations. But my identity is my consciousness. We don't care what Bach or Beethoven looked like, or their fingerprints. Their identities are not about their physical characteristics. — Patterner

It depends on context. Casual acquaintances might identify Bach by his appearance and mannerisms. The police, by his fingerprints. Us, viewing him as a historical figure, by his works and influence. But only Bach might identify himself by his own internal state.

Back to the OP. Would you survive a teleportation? I'm still torn on this, I go back and forth on it in my mind. On the one hand, the new body, and brain, is perfectly continuous with the old. The new body certainly thinks it survived. But did the original survive? Or is teleportation equivalent to the death of the original body?

@Christoffer wrote a story where it turned out that sleep was actually death. Consciousness doesn't survive, a new one is born every morning, with memory intact. This bothered me, I think because if seems like a distinction without a difference. So what if I "die" every night? What if every hour, or every second, I "die". What would be the observable consequence? There would be none at all. And so if there is no observable consequence from this distinction, shouldn't we discard the distinction?

Can this same reasoning apply to teleportation? If the original did or didn't "survive", there is no consequence, since the new one feels it survived either way. And so, does the question even mean anything?

we could easily set up the transporter as a Prestige scenario. Supposedly, it deconstructs the body, mapping out every particle exactly, and reconstructs a duplicate of the body elsewhere. So let's just make it slightly better at its job, and say it can map every particle exactly without deconstructing the body. Now when it makes a duplicate elsewhere, the duplicate is in no way different from a duplicate that would have resulted from the original technology. However, we still have the original. Well, we don't need two of the same person, and sometimes we really don't want two of the same person. Since we must've had a reason for wanting the duplicate where we put it, killing the original is the logical choice. And we're not really killing anybody, because the duplicate is still at the other location, right?

It depends on context. Casual acquaintances might identify Bach by his appearance and mannerisms. The police, by his fingerprints. Us, viewing him as a historical figure, by his works and influence. But only Bach might identify himself by his own internal state. — hypericin

The context i'm concerned with, and what I believe the OP is concerned with, is the internal state. We are not posting here about how tall we are, what our hair color is, the shape of our fingerprints, etc. Our discussions here or concerning our consciousness, desires, intentions, etc. Bach's compositions are not expressions of the former. They are expressions of the latter. you

No. Kirk wasn't also split. Kirk was split. Riker was not. Two entirely different scenarios.

Kirk was, indeed, split in two. His yin and yang halves were separated.

Riker was duplicated. — Patterner

Are you sure duplicating doesn't entail splitting?

If you duplicate a man without simultaneously splitting him, in the Newtonian scenario you have identical copies synchronized. Has any human seen this in 3D?

If you duplicate a man without simultaneously splitting him, in the QM scenario you have upwardly energized that man into superposition. In that situation, meeting one or the other duplicate means being in one or the other of two alternate realities. Moreover, these alternate realities, with respect to the duplicates (whatever that is) are indistinguishable. So, when one duplicate is met, the other duplicate collapses, and vice-versa. Now you have branching trajectories of multiple witnesses who are necessarily paradoxically lying about the simultaneous identical yet differential circumstances of meeting one or the other duplicates, both equally and identically yet differentially true.

If you duplicate the man and simultaneously split him, one man being in one place and moving about out of sync with the other man being in another place and also moving about out of sync with the first it's clear they are extremely similar in form and content but not duplicates. As they continue to be in different places having different experiences, even as the same man they, like twins, will continue to grow apart.

And we're not really killing anybody, because the duplicate is still at the other location, right? — Patterner

This is the crux of the problem. From one perspective, the fact that there is a duplicate of you somewhere else in the world seems to have no bearing on your own self interests, and on whether you consent to being killed. In that moment, that duplicate, even if qualitatively identical to you, is numerically distinct. Therefore, that someone else gets to live your life is slim comfort in the face of the fact that you will be killed.

In that moment, that duplicate, even if qualitatively identical to you, is numerically distinct. Therefore, that someone else gets to live your life is slim comfort in the face of the fact that you will be killed. — hypericin

Yes. It seems to me that duplication entails splitting.

And we're not really killing anybody, because the duplicate is still at the other location, right?
— Patterner

This is the crux of the problem. From one perspective, the fact that there is a duplicate of you somewhere else in the world seems to have no bearing on your own self interests, and on whether you consent to being killed. In that moment, that duplicate, even if qualitatively identical to you, is numerically distinct. Therefore, that someone else gets to live your life is slim comfort in the face of the fact that you will be killed. — hypericin

Right. And it's the same whether the transporter kills the original before the duplicate is created, or after.

Right. And it's the same whether the transporter kills the original before the duplicate is created, or after. — Patterner

I think the illusion of teleportation's safety relies on the transporter killing the original before, or exactly as, the duplicate is created. If it kills the original after, then it is pretty clear there are two distinct individuals at that time, and that killing the original is murder.

But logically yes it doesn't matter.

Star Trek's transporter is riddled with issues. :lol: We can argue it does very different things, and back it up with what happened in one episode or another.

Maybe Descartes himself could explain all that. (After having been briefed on Start Trek material.)
But I'm afraid he would rather say that you have misinterpteted his writings and would suggest you to study them. :smile:

Where have I misinterpreted Descartes' writings? I haven't even mentioned Descartes.

It was a pun on body-soul dualism! :smile:

@Christoffer wrote a story where it turned out that sleep was actually death. Consciousness doesn't survive, a new one is born every morning, with memory intact. This bothered me, I think because if seems like a distinction without a difference. So what if I "die" every night? What if every hour, or every second, I "die". What would be the observable consequence? There would be none at all. And so if there is no observable consequence from this distinction, shouldn't we discard the distinction? — hypericin

There may be no observable consequence for you, but it isn't a distinction without a difference. If sleep brings death, and the next day brings a new, replacement self, then you won't "'die' every night".

Far from it. You'll only die once - tonight. Today will be the first day of "your" life, and also the last day. Today will be the day you die, and bedtime (assuming you don't take a nap in the meantime) will be the date and time of your permadeath. Yes, you may not know any difference since "you" won't be around to reflect on the matter at a later stage, but then that's true of normal death (assuming for the sake of argument that death equals oblivion).

It's a distinction with a pretty big difference to me!

If you create an identical body with an identical
brain in exactly the same condition as the original, you would have 2 identical conscious people, both with identical memories and emotions about those memories.
Going forward , their experience would diverge creating different memories and experiences.

Currently writing for University on this topic under one of Parfit and Williams PhD students.

Interesting thread

If you create an identical body with an identical
brain in exactly the same condition as the original, you would have 2 identical conscious people, both with identical memories and emotions about those memories.
Going forward , their experience would diverge creating different memories and experiences. — Fess

This has been my solution to the Branch-line case. There is no numerical identity, and qualitatively, after any, even infintesimal, span of time after the 'event' of branching, the two 'people' have different mental quality. So, there is no issue. There are two people, on any account other than an Immaterial Soul-type of account.

So, there is no issue. — AmadeusD

Tell that to the spouse of the duplicated person. :wink:

No issue for them either. All the relevant memories were conserved heh. But i see your point

No issue for them either. — AmadeusD

As a hobby SF writer (in the past), I disagree. In fact, there are issues to figure out that more pressing than body-soul dualism. For example, here: Could the spouse be tried for bigamy? Multiple spouses suggests yes. Only one marriage certificate suggests no.

Wait, only one marriage certificate? Two individuals sharing the same certificate? After all, both of them have the same history, so that one certificate is valid for them both.

So what about... oh, I don't know... debt? You borrow a dollar on Monday, get duplicated on Tuesday, and now what? Do I get two dollars on Wednsday? After all, no matter who pays me, the other didn't pay me and still owes me a dollar.

If it's a freak accident, people will figure things out, but in the Star Trek case... it's a transporter malfunction. You know what that suggests to anyone even remotely familiar with the history of invention? That's right: human duplication technology. You can *try* to make it illegal, I suppose, but... black markets and rich guys with silly philosophies... (In the Star Trek Universe, the prime suspect would be Ferenghi, no?)

Now you have a social problem. While we talk about body-soul dualism, several legislators die of aneurisms while trying to solve very real problems. So here's the question: solve those legal problems and see whether your approach tells you something about your instinctive attitude towards the problem at issue. Maybe?

As a hobby SF writer (in the past), I disagree. In fact, there are issues to figure out that more pressing than body-soul dualism. For example, here: Could the spouse be tried for bigamy? Multiple spouses suggests yes. Only one marriage certificate suggests no. — Dawnstorm

These relate to whether you're a legal positivist or not. Yes? Then the cert. does it's job and there is no problem.
No? You need to figure out your own intuition about who is who - but that's not really pertinent here. The law runs according to the above.
Ignoring that the two people are qualitatively, AND numerically different after any span of time isn't really the fault of the facts, if you see what I mean.

Wait, only one marriage certificate? Two individuals sharing the same certificate? After all, both of them have the same history, so that one certificate is valid for them both. — Dawnstorm

As I said, they are not the same person on ANY conception except Immaterial Soul (and that's assuming the soul jumped to Mars.. you may hold the view, and think that's not happening). There is no problem.

So what about... oh, I don't know... debt? You borrow a dollar on Monday, get duplicated on Tuesday, and now what? Do I get two dollars on Wednsday? After all, no matter who pays me, the other didn't pay me and still owes me a dollar. — Dawnstorm

Who are you referring to? There are two different people. It is not possible the person on Mars is party to the contract in question (on this account). Problem solved (in all three cases you've mentioned). Though, all of this assumes legal positivism.

If it's a freak accident, people will figure things out, but in the Star Trek case... it's a transporter malfunction. You know what that suggests to anyone even remotely familiar with the history of invention? That's right: human duplication technology. — Dawnstorm

I'm unsure what you're driving at here, so my response might seem off-kilter. A transporter malfunction is exactly what the Branchline case is. So, I cannot see that this is an issue of any kind. Thought, you could make the argument that this presents an issue for them because they don't legally exist. But again, not relevant to the discussion as it could be solved by generating a birth certificate (see the NB below for why that might make sense).

So here's the question: solve those legal problems and see whether your approach tells you something about your instinctive attitude towards the problem at issue. Maybe? — Dawnstorm

There was no problem to solve. Well, to be more accurate, my conception removed the problem. So, it seems unhelpful to restate a problem which this account removes. Person B is not analogous to person A beyond the exact moment of creation. In that moment, all of these issues arise. But they die away just as quickly.

NB: probably worth realizing that in a world that this machine exists, the Law knows about it and has anticipated these problems. In any case, these are legal issues, not metaphysical ones. The two people are distinct in all meaningful ways. Their mentality is different, their personality is different (as a result of their mentality), their body is now different from being in a different environment, subject to different forces and chemical interactions, their thoughts are divergent, their emotions are divergent etc.. etc.. etc.. Sharing an extremely similar physical and mental make-up does not an identity make.

If there's something meaningful that remains between teh two, fire it at me :)

If there's something meaningful that remains between teh two, fire it at me — AmadeusD

They share a history. This is something no legal system is equipped to handle.

If I do something, I'm liable for it, no? I'm not legal expert.

Person P(t1) did deed D(t1), therfore Person P(t2) is responsible for D(t1). That works for many things: marriage, debt, murder... Legal responsibility assumes that the Person who did the thing at t1 is responsible for it at t2.

Now, if we have a branching point, what we get is

P(t1) --Duplication event--> P1(t2) and P2(t2). There is no P1(t1)/P2(t1). There's only P(t1).

So what's your intuition here? Mine is that P1(t2) and P2(t2) are P at t1. That's where biographical continuity leads for both of them. It would then, maybe, follow that they both are responsible for D(t1), because there is no distinction between P1 and P2 at t1. That can lead to absurdities, though, like in the situation of debt collection.

Obviously, the problem disappears for all deeds that occur at t2 or later. The branching point creates a situation where two people are identical with one person before a certain event. This is a fundamental change. We need to adapt to this: legally, morally, economically, pscho-socially...

For example: Is it more economic to train 1000 employees, or to train 10 and then duplicate the best one 1000 times? And if the latter is more efficient on paper, what about a working environment where you only work with versions of yourself (not twins, but people who know everything about you that you know, too, before the branching point).

I don't think any of our current intuitions can prepare us for this type of technology. We need to go through a period of chaos and see which way it settles.

As for specific points:

These relate to whether you're a legal positivist or not. Yes? — AmadeusD

What any one person believes is besides the point. How likely is it that all relevant personage agrees? And what about effects and implications of their decisions that they didn't anticipate?

As I said, they are not the same person on ANY conception except Immaterial Soul — AmadeusD

As per the above, they are not the same person now. They were the same person before the splitting event, which is when the certificate was issued. Legally, I see three possibilities:

a) The certificate is invalid for both (because neither P1 nor P2 are uniquely continuous with P)
b) The certificate is valid for both (because both P1 and P2 are continuous with P)
c) The certificate is valid for one of them, and invalid for the other (no idea how to argue for this; my least favourite)

On top of that, a/b/c might apply differently in different contexts. For example, in the case of marriage, I could see annulling the marriage with a possibity of remarriage with one of them as a plausible solution. In the case of ownership of property, though, joint ownership might be a better solution.

Of course:

NB: probably worth realizing that in a world that this machine exists, the Law knows about it and has anticipated these problems. — AmadeusD

Yes: if the tech's been around for a while. I'm talking about the transition period. You're not going to predict all the problems that'll arise from the introduction of such a fundamental novelty.

For example: when I wrote about joint ownership above, I wondered how that would look like. Pre-arrangements would be likely, if the duplication is voluntary (and not an accident or forced). But what would that pre-arrangement entail? My immediate intuition went to "contract", but that wouldn't work, since the potentially disagreeing parties are at that time still one person. A type of "will"? I will let this to P1 and this to P2?

Obviously, after the first few generations this is all going to be the new normal. But for the people who have to figure out how to deal with non-unique personal continuity as a novelty, these are going to be... interesting times.

Nice, good, thank you for the thorough response.

They share a history. — Dawnstorm

This is not a meaningful thing, unless you're restricting the discussion to the exact moment of duplication - at which time its extremely important. But, in the TE, the destruction of P1 happens before P2 comes into existence. So, it's even less of a problem than I had put forward. If you want to plum say "Ok, well then P2 clearly takes on P1s past and constitutes P1s future", fine that's a very practical and likely the most workable version, wihch (in reference to your closing portion) would influence policy and law I'd think.

But in the branchline case, that's not possible. There are two people. Two different people. The one which came into existence five seconds ago(P2) did not do and is not responsible for anything at all that P1 did and as soon as the exact moment of their creation passes, they are no longer analogous, identical to, or able to be understood as P1. So, the fact they share a hsitory is not meaningful. It is not, as far as I can tell, even true viz. they share memory, not history. The body of P2 simply did not do anything the body of P1 did. Nor did their brain. Or their intention. Or anything else. They didn't exist at the relevant time. You can here think about false memories, influenced memories, implanted memories etc.. etc... We cannot use memory as an accountant, in this discussion. The biggest problem is how its possible that P2 (in the original case) can be conferred the rights and responsibilities of P1, which they are not constitutive of. Is this just basically a rights transference by Deed? Could be. But nothing logical allows it.

P(t1) --Duplication event--> P1(t2) and P2(t2). There is no P1(t1)/P2(t1). There's only P(t1). — Dawnstorm

Sort of, and would agree on that arrangement but I would arrange it this way

P(t1) ->Duplication event is t2 and here we have P1 and P2 at t2-> any infintesimal period of time later is t3 and then we have P1(t3) and P2(t3):

separated, not even confusable as identical due to the sheer difference in body, mentality and situation (again, rejecting an immaterial soul concept) and anything but superficial appearance (as their actual bodily make up will be difference after any infintesimal amount of time.
There is absolutely a single moment of convergence where there is no notable (in this sense, I mean, it wouldn't be detectable by any means even if its logically there) difference between the two Ps. However, this moment is so faint and insignificant I can't rightly give it much at all.

I don't think any of our current intuitions can prepare us for this type of technology. — Dawnstorm

Definitely agree, and have fun with these things rather than 'care' to much of a degree. We're no where near this type of tech, if it's even possible.

What any one person believes is besides the point. — Dawnstorm

This (and the rest of the para) isn't quite groking what I"m saying. You're making an argument based on legal positivism. It's a practical argument, based on the fact you believe the law is a legitimate system for regulating technology. If you didn't believe this, your arguments would be different (this is an assumption, i'm just aclarifying my point because it's been missed). It's not a philosophical argument.

They were the same person before the splitting event, which is when the certificate was issued. — Dawnstorm

I'm sorry, because I don't want to sound so incredulous given how reasonable you are - but what the heck? There s no P2 to be discussed before the event. This is a complete nonsense. There was only P1 before the splitting even - regardless of Classic or Branchline version. There simply is nothing to be discussed, unless the split has taken place. You cannot read from P2 backwards to before the splitting event. They did not exist at that time. They share absolutely nothing but memory. And even this is divergent, immediately P2 gains awareness. P1 doesn't ahve that memory, and P2 doesn't have the memory of hte machine(and anything after that) post-button-pressing.

c) The certificate is valid for one of them, and invalid for the other (no idea how to argue for this; my least favourite) — Dawnstorm

This is the only reasonable item from your list to me, and i've made the argument. Hopefully it hits. The other two are clearly not true, in any sense of that word, in the TE.

My immediate intuition went to "contract", but that wouldn't work, since the potentially disagreeing parties are at that time still one person. A type of "will"? I will let this to P1 and this to P2? — Dawnstorm

I would (as a legal professional) posit that you would need two things:

A deed conferring your rights on P2 assuming the machine works; and
A clause within the Deed that allows you to retain all rights and responsibilities in the event you do not predecease P2 (which is the expected outcome). All that needs to happen is that 'ideally' when a person is created on Mars (and the branch occurs) they receive a (futuristic) birth certificate (or creation certificate). In the Classic case, no one would care. Its just impractical to care, unless there's a significant amount of time that they both exist.

I would imagine this would go hand-in-hand with a (futuristic) Will in the sense that, what if both die? Or the split doesn't happen, yet you're destroyed. In this way, the problem is entirely avoided. P2 needs to come up with his/her own life after the Branching, if it happens. It's not P1s fault, and P2 is an accident, essentially. Though, in the original Branchline P1 dies three days later, so by the time P1 dies, P2 is an entirely different person with nothing shared between them except superficial appearance. I see no issue. The problem here, would be that all P1s significant relations knows someone who looks exactly like the deceased is out there, not being the deceased. And that would hurt.

I have digressed way too far from my points of interest here though - The legal ramifications appear extremely easy to deal with for me. It does assume a certain level of understanding in any P1 going into the machine, but we can't assume the worst if we want the future to rise above it. My points of interest are in establishing Identity, or why/why not.

I don't think identity can be established. And I don't think it matters. It's very uncomfortable, and I'd like to be wrong.

There was only P1 before the splitting even - regardless of Classic or Branchline version. — AmadeusD

This is where I think we're talking past each other.

First, this is not how I used P1 and P2. Before the duplication event there was one person P. After the duplication event, there were two people P1 and P2. P1 and P2 exist simultaneously as separate existances. P exists only in a past where neither P1 nor P2 existed.

How do you connect P1 and P2 to P? Who's responsible for acts that P did? Nobody? P1? P2? Both?

Second, I don't know what you mean by branchline vs. Classic version. For me, there's a branching point in the personal history of P, such that at some point History(P) split into Histoy(P1) and History(P2). This is a novel situation. There is no Classic version I can see.

I'll re-read your post later. Maybe I'll get it some time.

I've re-read your post, and I now think our differences might be this:

A transporter accident results in:

You: an original and a copy

Me: Two copies of the original (which is destroyed).

Thus, I think during normal operation a transporter creates a copy of a body, and the beam contains the information for re-assembly. The information can be used multiple times.

As for souls; I don't find the concept useful, so I don't worry about that.

Me: Two copies of the original (which is destroyed). — Dawnstorm

This is not the case in the TE. The branch line case results in the original and one duplicate; not two duplicates. Perhaps that’s the issue? If it were the case that P in the machine is also duplicated and die, leaving P1 to walk out of the machine and P2 to pop up on Mars, I can start from your premise - and it gets murky. That would be difficult intuitively, but I think my account applies there too. They are two different duplicates immediately qualitatively discernible from one another (and obviously numerically so).

However, that’s not the case we’re discussing and not the start point I’ve used.

In Parfit’s branchline, there is either P at t1 who dies, then P(2) wt t2 who do not exist simultaneously OR P and P(2) existing simultaneously at t3 (as in my previous comment) They don’t require a discussion of whether they are the same person. One is X years old (I assume 18 or more) and one is seconds old - there is no comparison.

This is not the case in the TE. The branch line case results in the original and one duplicate; not two duplicates. Perhaps that’s the issue — AmadeusD

Ah, yeah, I was talking Star Trek transporter as per the OP. I missed the two-line post about Parfit. I've never heard of that case, and am unfamiliar of the specifics. I'm not sure I'd change my mind, but I might. What's "TE"?

So after reading up on Parfit's branchline scenario, that's definitely a case with an original and a copy, based on physical continuity. Consider the difference to the Star Trek transporter technology with the following example:

I kill a person, then duplicate myself. Then two identical people show up at the police station, saying "One of us killed X."

Under the Parfit model, the guilty party would be the one who walked out of the scanner; and it would be a matter of proving who that was. At the very least the original and copy would know who is who.

Under the Star Trek teleporter model, there's nothing meaningful to distinguish the resulting individuals, since the original (who committed the killing) got taken apart, and both versions were assembled using the same information. There'd be no practical way to tell them apart, so any ruling (if you hold only one responsible) would have to be of a theoretical nature. Not even the people themselves would have a clue.

So, yes, I'd say there's at least a theoretical difference here; but the simple existence of such a duplication technology might have effects that need to be dealt with one way or another.

For example, consider a religious fanatic who thinks he must kill unbelievers but since killing is a crime, he must also atone for it. He could use this technology to first kill someone, then duplicate himself, then turn himself in, expecting his duplicate to do the same (which he probably will if it is possible, since he is an identical copy of the original).

If comparable cases are relatively rare, this could probably be accommodated somehow under existing legal models. But if it becomes a common pattern, we might be looking at a new legal concept. A new type of legal person (defined as a natural person and all its copies)? A reframing of responsibility? And so on.

This is not primarily a philosophical problem; it's not about truth. It's about how to efficiently get things done, and how to accommodate the new social-psychological configuration of the public, all of which is hard to predict.

And since I think our ideas are based on our experiences, I think such technology might have rather radical effect on what ideas we can even think about.

Ah, yeah, I was talking Star Trek transporter as per the OP. I missed the two-line post about Parfit. I've never heard of that case, and am unfamiliar of the specifics. I'm not sure I'd change my mind, but I might. What's "TE"? — Dawnstorm

Totally fair enoguh - I may have missed that that was the case, and if so, apologies. I could've done much better to have a constructive exchange.

TE=thought experiment.

At the very least the original and copy would know who is who. — Dawnstorm

I think that's true, yes. There memories would differ in "cogito"-type ways that ensure knowledge of which they are.

Under the Star Trek teleporter model, there's nothing meaningful to distinguish the resulting individuals, since the original (who committed the killing) got taken apart, and both versions were assembled using the same information. — Dawnstorm

I agree, but only to a point. The exact point of duplication. After that, they are numerical and qualitatively different people. Otherwise, there would be nothing to tease apart any sufficiently similar people (in terms of trying to figure out a 'rule') without even trying to invoke identity.

Not even the people themselves would have a clue. — Dawnstorm

This is absolutely the weirdness of that case. Metaphysically, I don't think we have any issue. But they would both, until the critical moment after duplication (say five seconds) have absolutely no way to tell each other apart. But after about five seconds, in practical terms, it could be done. They have either seen each other, or are aware another of 'them' exists - ensuring it is not 'them' from each other's perspective. I think you're inadvertently invoking a situation in which they couldn't tell which person they were. I think that's not really ever going to happen, sans serious mentall aberration of schizo-affective type. They would know they weren't the other person, for sure.

but the simple existence of such a duplication technology might have effects that need to be dealt with one way or another. — Dawnstorm

100%.

For example, consider a religious fanatic who thinks he must kill unbelievers but since killing is a crime, he must also atone for it. He could use this technology to first kill someone, then duplicate himself, then turn himself in, expecting his duplicate to do the same (which he probably will if it is possible, since he is an identical copy of the original). — Dawnstorm

This appears to me to be praying with your finger's crossed and isn't a move open to a religious fanatic. But, you're right that the general problem obtains. Typically, a religious fanatic would run into the immaterial identity concept, anyway, making this a moot point for them.

I think such technology might have rather radical effect on what ideas we can even think about. — Dawnstorm

I am not convinced, But i look forward to finding out i'm wrong :)

TE=thought experiment. — AmadeusD

Ah, thanks. I could have figured that out, but didn't.

I think that's true, yes. There memories would differ in "cogito"-type ways that ensure knowledge of which they are. — AmadeusD

Actually, I think I made some assumptions when I said this, so it's not necessarily true. For example, if the "original" were duped into thinking it was just going to be a transportation, then the person popping out on Mars would think he's the original, and the person walking out of the transporter would think the transportation failed. What really matters, I think is this:

There's a difference in bodily continuity between the person not "transported" and the person on Mars, and that difference is susceptible to ordinal description: one body is more continuous than the other.

That is not the case under the Star Trek model. Even non-duplicative transporter usage creates a copy of a body that's been destroyed. So is the person who steps into the transporter the same person that steps out of the transporter, even though the body that stepped into the transporter has been taken apart and re-assembled?

And if the answer to that is "yes," then what changes when you assemble a copy more than once?

Personally, I think: not much. (And I think the answer is "yes", not because of any philosophical position, but because that's how I think people treat each other in Star Trek stories.)