Consider a teleportation booth which exactly replicates ones body and mind in Mars, whilst destroying that on Earth; as in Parfits Reasons and Persons.

There is only one you at any one time; so where you are is easily tracked - at one point you were on the Earth, and at another later time, and suddenly you were on Mars.

But, suppose at a critical moment the machine breaks down and so there are two yous, one on Earth and the other on Mars. Which one is really you? Of course they both behave differently, after all one is on Mars and the other is on Earth; and thus faced with different circumstances that are immediately present; still each responds to the same name, claims the same woman as his wife (and another as his mistress); has the same memories of college, and of playing football on a field by a stony beach that ran out to a cold sea; and though they wear different clothes; they wear recognisably similar fashion choices; and their mannerisms would be familiar to their friends.

So which is the real you?

The conclusion to Descartes cogito is 'I am'; this sense of inner awareness; how can this be at different places separately?

One could for example, consider a conscious AI who had an avatar here on the earth and another on Mars; but his conscious would be unitary; his avatars, in a sense are mechanisms for perceptions and acts.

But we have two quite distinct persons, who are also the same.

If consciousness is unitary - perhaps this means that, in fact, no such machine is possible - and it is in fact just science fiction, whose fictional ontology is just that - fictional.

Is this a sensible conclusion to take?

  • So, in this case, is there enough air for the replicated one to breath in? I mean, your question is sometimes too analogous-imaginary so there could be any answers from even belief-based side, I thought.
    – user13955
    Commented Apr 28, 2015 at 3:30
  • So when the duplicator-the-machine puts another you on Mars, whatever environment currently the widely held view is, he or she can breath, drink, there is enough gravity, so on and so forth?
    – user13955
    Commented Apr 28, 2015 at 3:40
  • I'm sorry, -1, For the reason, too imaginary, the first part of the sentence, I thought, could reside in your brain only.
    – user13955
    Commented Apr 28, 2015 at 3:43
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    It's a matter of using ones imagination; if it troubles you then suppose one booth is in Japan and the other on Korea; but if you are going to accept the possibility of a teleportation booth - then one may as well go the whole distance and accept a colony on Mars too. Commented Apr 28, 2015 at 4:05
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    So far we have only dealt with conscious beings on scales small enough that signals travelling at the speed of light is effectively instantaneous from the point of view of the observer (observing itself). What happens when an single conscious entity stretches over distances such that the time lag of mental signals travelling between its different constituent parts is no longer negligible? Is such an entity possible at all? Maybe the speed of light puts an upper bound on the spatial size that a conscious entity can have? Commented Apr 28, 2015 at 18:46

3 Answers 3


If memory serves, in the context of Reasons and Persons "which is the real you" would be an empty question. There would be no answer to this question and e.g. the claim "we have two distinct persons" would be neither true nor false. You could still decide on a specific answer, but this would not add anything non-trivial to what is already known on a reductionist level. Also in that context, the premise "consciousness is unitary" would not hold.

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    In other words: The tag "parfit" may not be warranted :)
    – Drux
    Commented Apr 28, 2015 at 7:51
  • I gathered that Parfit had out-Humed Hume ;). Commented Apr 28, 2015 at 8:03
  • Is it eliding too much to say that Parfits view is 'I think, therefore I am not'? Commented Apr 28, 2015 at 20:06
  • @MoziburUllah I think he suggests something like "It is thought: thinking is going on."
    – Drux
    Commented Apr 28, 2015 at 23:48
  • Drux:Ok, it sounds like a process theory of mind. Commented Apr 29, 2015 at 13:58

There are at least 3 answers to this:

  • Per DesCartes: the “I” of the cogito is made of something other than material substances (per Cartesian substance dualism). A teleportation device using physical principles would not be able to transport the mind stuff the way it did the body stuff, and so the real you would have never made it to Mars via teleportation in the first place and the problem is dissolved.
  • Per Buddha, Hume, and Russell: There is no “I” or “You”. What we perceive as the self is not a distinct entity (physical or otherwise), it is just the amalgam of thoughts and experiences which your body has accumulated over the years. Since there was no real you to start with, again the problem is dissolved.
  • Per Hofstadter: The teleportation process has created two copies of the strange loop that constitutes yourself, both of them are you and both of them are real. In the same way that a corporate entity can be split into two, so it is with the self, it can be split into two entities. This would be the case if someone were able to upload a copy of your strange loop to a larger server as well. The self definitely exists, but it is not unitary (and BTW, unless you agree with substance dualism, why should it be?)
  • Can you please provide a specific quote by Russell in this context?
    – Drux
    Commented Apr 28, 2015 at 23:48
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    @Drux from Russell's "Analysis of the Mind" - lecture 1: "We say: "I think so-and-so," and this word "I" suggests that thinking is the act of a person. Meinong's "act" is the ghost of the subject, or what once was the full-blooded soul. It is supposed that thoughts cannot just come and go, but need a person to think them. Now, of course it is true that thoughts can be collected into bundles, so that one bundle is my thoughts, another is your thoughts, and a third is the thoughts of Mr. Jones." (Continued in the next comment) Commented Apr 29, 2015 at 1:01
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    " But I think the person is not an ingredient in the single thought: he is rather constituted by relations of the thoughts to each other and to the body. This is a large question, which need not, in its entirety, concern us at present. All that I am concerned with for the moment is that the grammatical forms "I think," "you think," and "Mr. Jones thinks," are misleading if regarded as indicating an analysis of a single thought. It would be better to say "it thinks in me," like "it rains here"; or better still, "there is a thought in me." " Commented Apr 29, 2015 at 1:01

One possible stance referred to by Drux is that with perfect copying none of the resulting instances are more real than the others (Parfit). This is rational and OK as far as it goes. But it's only an observation about the immediate reality, and does not go into consequences.

Two other answers referred to by Alexander S. King are that mind is supernatural (Descartes, nonsense), and that there is no "I" or "you" (Buddha, Hume, Russel, again nonsense, as, for example, I can attest that I exist). Alexander also referred to Hofstadter giving essentially the realistic view of Parfit. Out of the five philosophers mentioned in the answers before this, then, two have apparently had reasonable rational views on the matter.

Going one step further then Perfit/Hostadter, or at least beyond what's been referred from them so far, we can imagine the copy on Mars doing some criminal act immediately after the copying. It could for example be fraud, but to make it interesting let's say that it's murder. Then there are two questions that at least springs readily to my mind:

  • Is the instance on Earth legally responsible for the Mars actions?
    There's almost no difference between the two minds at the time of the murder. So what one of them would do, the other would also do, placed in the same situation. Therefore the one on Earth would have committed the murder if he (or she) just were placed in the appropriate situation. If the purpose of punishment is to some degree correction of a mind that's otherwise prone to criminal behavior, then it stands to reason to apply that to the instance on Earth. But this involves punishing someone who's done nothing wrong.

  • Is the instance on Earth responsible if the Mars one murders and suicides?
    Someone is bound to hit on the idea of creating a body+mind clone via teleportation, where that clone murders someone and then commits suicide. Having planned and executed this, can the original be punished? After all, one probably can't prove that it was planned, that he/she was an accessory or used the clone merely as an instrument to commit the murder.

Since much of the purpose of law is to protect society, I guess that if this hypothetical situation were ever to develop then the law would view the person on Earth as responsible, at least for some time after copying. But that does not necessarily imply a view where the one on Earth is viewed as the same person (or to a large degree the same) as the one on Mars. Rather, it might just mean that the law would hold anyone responsible for making a criminal act much more likely by doing the teleportation without being very sure that one would never do anything really criminal within such and such a short timespan.

I think these considerations might appear to extremely far-fetched, due to the OP's choice of mechanism for mind cloning. But it's worth noting that any reasonable calculation places an upper limit of about 40 years on the appearance of computational power sufficient to do a real time human brain simulation, which indicates that machine intelligences (although possibly not very mature) will appear well before that. And with a machine intelligence cloning the mind might be a practical proposition, rather then science-fiction-ish.

Then there will be a need for suitable legislation. E.g., one would need legal mechanisms to deal with ownership and responsibility.

  • Why would a clone commit suicide? What is the rational? Like you pull the trigger believing that you kind of jump back into the mind of the "original"? I don't get it. Can you explain?
    – nir
    Commented Jun 16, 2015 at 19:26
  • @nir: If I (devious criminal mind that I am) planned to do such a thing, then I would probably ensure the suicide via e.g. an implant that could only be disarmed via information on Earth. Or, hypnotic command. Or something. Commented Jun 16, 2015 at 19:30
  • how does that change anything? From the point of view of the "clone" it still practically commits suicide. to try to clarify the problem, what if the "original" and the "clone" didn't know which is which and had to draw a straw to decide who gets to commit suicide? Would you agree to such a plan? suppose you draw the bad straw; would the idea still seem attractive to you? Or would you feel it was nonsense and refuse to carry it out?
    – nir
    Commented Jun 16, 2015 at 19:39
  • 2nd bullet: person has conspired to commit a crime; I don't see proving this form of conspiracy more difficult than any other.
    – Dave
    Commented Jun 16, 2015 at 20:31
  • @Dave: Re conspiracy of one as “not … more difficult”, there's no external communication to use as evidence, for one, and there's no imperfect knowledge of what others have said and done, for you to exploit in questioning. Still, I think the detective angle misses the point here. ;-) Commented Jun 16, 2015 at 23:17

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