Teleporting persons and multiple "you's" are discussed in serious thought experiments in physics and philosophy.

I feel like most of the time these scenarios come up, I would not make the same assumptions I feel the experimenters do however. The problem is, most of the time they never explain their assumptions that allow them to make the claims they do.

When I think of the self, I can't picture how it can be teleported along with the rest of the body. This is due to how I picture the duplicator version of the thought experiment. In the duplicator, nothing happens to your original body. Instead of being decomposed and beamed then recomposed, your original body remains unaffected, and a duplicate is beamed instead. There are now two materially identical versions of you, each with their own conscious experiences. When the consciousness of the version of me on Mars feels pain, my consciousness on Earth does not. And vice versa.

Thus I would never take a transporter because I believe your self must die every time. If it did not die, I can't explain the duplicator version.

But then I hear other serious philosophers and physicists think no, you would wake up on Mars. Or in quantum immortality, you will live forever, instead of saying a version of something that branched from you lives forever.

So A) is my version of the self incompatible with quantum immortality and being able to say I woke up on Mars, and B) is this the minority opinion of the self within philosophy? How else can I explain serious philosophers and physicists not listing their assumptions when they talk about transporters and quantum immortality. Where can I go that discusses this within the example of teleporters and quantum immortality?

  • The thought experiments can always be done, but in reality, they can't. For a discussion about the self, they are useful though. That's why the only way for you to reappear on Mars, is to decompose you, transfer the particles to Mars, and compose them again there. In which case you could just as well could have gone there by the interplanetary subway. Beaming up information about your particles and make a new body with this information (with different particles) will not create another you since you stay behind on Earth.
    – user52804
    Commented Jun 14, 2021 at 8:28
  • @Methadont I still think you need to say why a decomposed you into particles can't be copied into another set of particles to say the first part then. Once decomposed we are implying they are just particles, and you are temporarily gone. Particles are all the same. If recombination is essentially "put this atom here and this atom here", I can just go get another set of atoms and do it twice. I think you maybe can make this first version (not beaming) work with some additional assumptions like only the particles that came from you can be used (why I don't know) and definitions, but not as is.
    – J Kusin
    Commented Jun 14, 2021 at 8:46
  • To reconstruct the particles from which I'm made (after, say my death) in a new me, you need the information of the whole universe. You have to do the same if you send my particles to Mars. The particles that you send is me being dead. You just can't wake me up while I'm dead. This involves knowing the whole history of my particles and all particles that have lead to the particles from which I'm made. This means knowing the history of the whole universe (or at least the particles in the past lightcone). Impossible.
    – user52804
    Commented Jun 14, 2021 at 8:50
  • The computer doing the calculation needs to know the whole history all particles in your past lightcone. But the computer is part of this past too. So it can't do the calculation, as the information about the particles that do the calculation isn't involved.
    – user52804
    Commented Jun 14, 2021 at 8:52
  • @Methadont I pretty much agree wholeheartedly, but I will say we don't seem to talk about particles in this way usually - describing a single electron in terms of the entire rest of the universe. And that no two electrons are really the same ever. I think we may ultimately have to do something like that for all of physics at some point, but most theories and conversations simplify from that picture.
    – J Kusin
    Commented Jun 14, 2021 at 8:53

3 Answers 3


Contemporary philosopher Derek Parfit discussed such a Earth-to-Mars teleportation in his book Reasons and Persons according to reference here:

At time 1, there is a person. At a later time 2, there is a person. These people seem to be the same person. Indeed, these people share memories and personality traits. But there are no further facts in the world that make them the same person. Parfit's argument for this position relies on our intuitions regarding thought experiments such as teleportation, the fission and fusion of persons, gradual replacement of the matter in one's brain, gradual alteration of one's psychology, and so on. For example, Parfit asks the reader to imagine entering a "teletransporter," a machine that puts you to sleep, then destroys you, breaking you down into atoms, copying the information and relaying it to Mars at the speed of light. On Mars, another machine re-creates you (from local stores of carbon, hydrogen, and so on), each atom in exactly the same relative position. Parfit poses the question of whether or not the teletransporter is a method of travel—is the person on Mars the same person as the person who entered the teletransporter on Earth? Certainly, when waking up on Mars, you would feel like being you, you would remember entering the teletransporter in order to travel to Mars, you would even feel the cut on your upper lip from shaving this morning. Then the teleporter is upgraded. The teletransporter on Earth is modified to not destroy the person who enters it, but instead it can simply make infinite replicas, all of whom would claim to remember entering the teletransporter on Earth in the first place. Using thought experiments such as these, Parfit argues that any criteria we attempt to use to determine sameness of person will be lacking, because there is no further fact. What matters, to Parfit, is simply "Relation R," psychological connectedness, including memory, personality, and so on.

Thus according to Parfit, we could know all the facts about a person's continued existence and not be able to say whether the person has survived after the perfect teleportation in principle. He concluded that we're mistaken in assuming that personal identity is what matters in survival; what matters is rather psychological connectedness (memory and character) and psychological continuity. Identity is not as determinate as we often suppose it is, but instead such determinacy arises mainly from the way we talk. People exist in the same way that nations or clubs exist. Following David Hume, Parfit argued that no unique entity, such as a self, unifies a person's experiences and dispositions over time. Therefore personal identity is not "what matters" in survival. A key Parfitian question is: given the choice between surviving without psychological continuity and dying but preserving psychological continuity through someone else's future existence, which would you choose? Parfit argues the latter is preferable.

So in this sense, there're 2 types of self, one is the appearance induced ego-like self which may not exist at all, another is soul-like self which correspond to one's memory, characters and psychological continuity...

  • Now I finally know to whom I talk at night... :) Commented Jun 13, 2021 at 23:27
  • Thank you for the very relevant post and quote. Could you explain "A key Parfitian question is: given the choice between surviving without psychological continuity and dying but preserving psychological continuity through someone else's future existence, which would you choose? Parfit argues the latter is preferable." What do you mean through someone else's future existence? Like allow yourself to die fully, and be content your good actions will be embodied by other people you connected with in life - instead trying and failing to be immortal, because we can't be?
    – J Kusin
    Commented Jun 14, 2021 at 5:27
  • @JKusin thx for your comment! Indeed you're certainly right your referred scenario is a clear example and one correct interpretation of Parfit's views, and he used this teleportation thought experiment to challenge the traditional self-interest rational theory with moral consequentialism in his book as referenced here (en.wikipedia.org/wiki/Derek_Parfit). Also this seems in line with most world religions' inheritance lineage in the spirit of immortality of their respective worldviews. Commented Jun 14, 2021 at 5:37
  • @DoubleKnot thanks so much for the resources and info. I was feeling a bit trapped that none of the philosophers I knew of touched on these issues.
    – J Kusin
    Commented Jun 14, 2021 at 5:54
  • This story still states that it is possible to teleport the particles (and their history) you are made up from to Mars. This si simply not possible. You can't make a copy of you or me in (in time or in space) this universe because of the simple fact that there would be two of you then! If a copy of me is made then all particles have to be the same (including their history). This can never be achieved. Maybe in a future universe, you can appear for a second time.
    – user52804
    Commented Jun 14, 2021 at 6:16

I think you can imagine wakening up on Mars after your body has been decomposed into its constituents (elementary particles) which are transported to Mars and subsequently composed back into the form had on Earth. You could just as well have traveled to Mars without the decomposing and composing but let's assume. If you are decomposed on Earth your consciousness obviously fades to zero (assuming it to be tied to matter). If the matter is composed again on Mars your consciousness will gradually wake up. Just as after an operation by a physician. You will wake up.
On the other hand, if the information about the composed elementary particles is sent to Mars (if this information can be acquired without disturbing the composition), and this information is used to compose your body out of a reservoir with elementary particles, you will not think that it is you who wakes up. The elementary particles you are composed of have to stay the same particles. A clone of you is made up of different particles, so the clone is not you.
The particles in your body when you were born are almost all replaced by new ones. By other particles. Are you a different person from who you were in childhood? No, of course not. The particles can be changed over time. If you replace each particle of your body with the same kind of particle the result will still be you. In the case of constructing another body on Mars, based on the information of your body on Earth, there are no particles of your body in earlier times involved. This is why the body on Mars doesn't wake as another you. If you built a person, say you, out of the same kinds of particles (with the right relation wrt each other) the result won't be you. It's another person.
The result can only be you if the same particles out of which your body (including your brain) consists are used for creating another you. This is obviously not possible if the creation means that there will be two of you. The created new "you" is a different person. A person identical in make-up to you, living in a parallel world will always be different from you, even if they live in different times, as the particles in both universes are always different from each other. In our universe it could be you in the future. If someone in the future would find all elementary particles you were made up when you were ten years old and if could manage to reconstruct you, it could be possible that you experience to be a new ten-year-old walking the streets.
If a new collection of elementary particles would emerge after a new big bang (assuming a sequence of big bangs) it depends on how you see the particles in the in-between-bangs universes. If you consider them as being the same particles you can be reborn again (if the particles evolve again as they did in a universe that gave birth to you). If you consider them as a whole new collection of particles (as in the Ekpyrotic universe, it's questionable but reasonable. According to the logic I used it would be impossible for you to reappear. Because different particles appear they will never give rise to the same you. But I'm not sure if this logic can be applied to two temporally disconnected universes instead of temporally disconnected regions in one universe. That is, if a whole new process of new particles (the process of evolution) gives birth to your body, as did a process taking place in an earlier universe (with different particles) it could be another you. You can't create another person in this way on Earth. For that, you would have to recreate the entire process of evolution. In fact, you would have to recreate the entire universe... Needless to say that that's impossible.

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    – Geoffrey Thomas
    Commented Jun 14, 2021 at 8:20

What we consider "the same person" is purely conventional. That's Parfit's point about there being nothing in the world that makes either answer to the question true or false. We often say things like this in everyday life: "He wasn't the same person after his traumatic brain injury." Another acquaintance of the person might protest that the same person they've always known is still there underneath all of the observable effects of the neurological damage. Who's right? Continuity of personal identity over time is a matter of degree. And the identity of the particles we're composed of is, in my view, a much less relevant factor than continuity of personality and memory. Others have different intuitions on that, but I can't see what considerations can possibly arbitrate between the conflicting intuitions, since sameness of self is purely conventional and a matter of degree.

In the duplicator version, both you and your duplicated self would share the same past self, while also presently being two different persons. One person became two people. What's incoherent about that? Your duplicated self would certainly consider your past self their past self too, because that's everything they remember and how they became who they are and came to believe, desire, and value all that they believe, desire, and value. Would they be wrong to consider that their past self?

  • But if everyone were watching me from afar walk up to a duplicator ray, get scanned, then go sit down while the new copy of me is shuttled to Mars, there would be no disagreement like you have above. Original me is on Earth and Copy me is on Mars and no one watching would disagree. I, Original me, would never have a doubt in my identity. Spectators neither. And Copy me would wake up and realize he is the copied one.
    – J Kusin
    Commented Aug 2, 2021 at 20:42
  • Yeah, I agree everyone would consider you Original You and copy you Copy You, as should the Copy You themselves. But I think Copy You also has a legitimate claim to consider your past self to be also their past self. Why can't two distinct present selves have one and the same past self?
    – Dayv87
    Commented Aug 2, 2021 at 20:48
  • My present sense of self is a product of my knowledge of my past and current awareness. My continually evolving-with-the-present sense of self has been growing and changing since I began to record memories. And it factors in things like knowing cells from each parent were grown in my mother, which lead to a fetus being birthed. Copy me's self knows its matter and cells came from disparate places, coming together mere moments ago using lasers and biochemical machines. These selves don't overlap. Until someone shows something with a sense of self can undergo mitosis I am not convinced by this.
    – J Kusin
    Commented Aug 2, 2021 at 21:04
  • That seems to beg the question. If we had one of these duplicators, wouldn't that be sufficiently functionally similar to mitosis? I also don't see why material continuity is a necessary condition of continuity of personal identity. If scientists discovered that neurons replace themselves every several years just like most other cells of the body do, would you then no longer consider your self of ten years ago to be your past self?
    – Dayv87
    Commented Aug 2, 2021 at 22:59
  • I'm not sure how to resolve this current line of inquiry tbh. But as for my original question, how does same past-self, distinct current selves resolve teletransportation (in this case sans duplicator version) or quantum immortality? When authors say you wake up on Mars or you always survive a game of Russian roulette, a person is still dying aren't they? It seems to reassure this present me very little even if there can be two persons with the same identity.
    – J Kusin
    Commented Aug 2, 2021 at 23:39

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