Is teleportation travel or death?
Does the person who steps out on Mars survive, or replace you?
I
It is travel
The person on Mars is you. Psychological continuity, with the right cause, is what personal identity consists in.
- Best argument
- Everything that makes you you, your memories, personality, intentions and relationships, continues uninterrupted. Physical continuity matters only because it normally carries psychological continuity. Here the information is carried another way. Refusing to step in is like refusing to send a letter by email because the paper is not physically transported.
- Strongest objection
- The branch-line case: suppose the machine malfunctions and fails to destroy your body on Earth. Now there is a you on Earth and a you on Mars. Both are psychologically continuous with the person who stepped in. They cannot both be you, since they are two people. So psychological continuity cannot be what identity is.
- The reply
- Some say identity holds only when there is no competitor (a 'non-branching' condition). Parfit thought this showed that identity is not what matters: in the branching case, you get everything that matters in survival, twice.
- Defended by
- Derek Parfit, John Locke, Sydney Shoemaker
II
It is death
You die in the booth. The person on Mars is a new person who is exactly like you.
- Best argument
- Your body, including your brain, is destroyed. A different body is built from different atoms. That the new person has your memories does not make them you, any more than a perfect forgery of a painting is the original. The branch-line case shows this: when the original survives, everyone agrees the person on Mars is a copy. Why should destroying the original turn a copy into the original?
- Strongest objection
- If physical continuity is what matters, then gradual replacement of your atoms, which happens anyway, should worry you as well. And the view makes your survival depend on something you could never notice from the inside.
- Defended by
- Eric Olson, Bernard Williams
III
Identity does not matter
There is no deep fact about whether the person on Mars is you. What matters, psychological continuity, is fully preserved, so teleportation is about as good as ordinary survival.
- Best argument
- Parfit argued that once you know all the facts about bodies, brains and psychological connections, there is no further fact about identity to discover. The question 'is it really me?' is empty. And what you care about in survival, that someone will carry on your life, love your family and finish your projects, is all there on Mars.
- Strongest objection
- Most people cannot shake the feeling that there is a further question: will I experience Mars, or will everything go black? Parfit's answer seems to deny the most pressing question of all.
- The reply
- Parfit admitted that he could not fully believe his own view at an emotional level, but found that when he did, he felt less afraid of death.
- Defended by
- Derek Parfit
Where you stand
Would you step into the teleporter?
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For the full background, variations and open questions, read the entry: Would you step into the teleporter?.