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categories: ["minds"]categories: ["minds"]tags: ["identity", "parfit", "thought experiment", "survival", "uploading", "philosophy of mind"]tags: ["identity", "parfit", "thought experiment", "survival", "uploading", "philosophy of mind"]summary: "A thought experiment in which a person is scanned, destroyed, and rebuilt elsewhere, used to test whether survival requires physical continuity or only psychological continuity."summary: "A thought experiment in which a person is scanned, destroyed, and rebuilt elsewhere, used to test whether survival requires physical continuity or only psychological continuity."updated: "2026-08-23"updated: "2026-10-29"issues: ["Four-dimensionalism and non-branching accounts are described without citing a source."]issues: ["Four-dimensionalism and non-branching accounts are described without citing a source."]------ lines 45–58 → 45–5831 unchanged lines not shown
destroying. The original survives on Earth with fatal cardiac damage and a few days to live, whiledestroying. The original survives on Earth with fatal cardiac damage and a few days to live, whilethe replica walks around on Mars. Now the original can talk to the replica by radio. Very few peoplethe replica walks around on Mars. Now the original can talk to the replica by radio. Very few peopleare willing to say the original should be indifferent to their imminent death because the replicaare willing to say the original should be indifferent to their imminent death because the replicaexists — yet the replica's relation to the original is exactly the relation that, in the simpleexists, yet the replica's relation to the original is exactly the relation that, in the simplecase, was supposed to constitute survival. Nothing about the replica changed. Only the presence of acase, was supposed to constitute survival. The replica is the same in both cases; the onlycompetitor did.difference is that it now has a competitor. > [!key] Why the variant does the work> [!key] Why the variant does the work> If identity depended only on the intrinsic relation between two people, the branch-line replica> If identity depended only on the intrinsic relation between two people, the branch-line replica> would be the original whether or not the original survives. That it apparently is not shows the> would be the original whether or not the original survives. That it apparently is not shows the> criterion has an extrinsic component — whether anyone else has an equal claim — which is a strange> criterion has an extrinsic component (whether anyone else has an equal claim), which is a strange> feature for a fact about a person to have.> feature for a fact about a person to have. ## The intuition split## The intuition splitlines 75–84 → 75–8416 unchanged lines not shown
whether a rebuilt club is really the same club.whether a rebuilt club is really the same club. > [!debate] Williams's standing objection> [!debate] Williams's standing objection> Bernard Williams argued in 1970, a decade before Parfit's book, that the split cannot be blamed> Bernard Williams argued in 1970, a decade before Parfit's book, that the split cannot be blamed on> on exotic technology. Told he will be tortured after his memories and character are erased and> exotic technology. Told he will be tortured after his memories and character are erased and> replaced with another person's, a person's fear does not diminish, because "undergoing physical> replaced with another person's, a person's fear does not diminish, because "undergoing physical> pain in the future is not excluded by any psychological state I may be in at the time" — yet the> pain in the future is not excluded by any psychological state I may be in at the time"; yet the> same case, presented as a body-swap between two people, pulls most readers toward the> same case, presented as a body-swap between two people, pulls most readers toward the> psychological criterion, and Williams closed by admitting he did not know which verdict to> psychological criterion, and Williams closed by admitting he did not know which verdict to> accept.[^williams1970] The two presentations remain the cleanest statement of why no experiment> accept.[^williams1970] The two presentations remain the cleanest statement of why no experimentlines 99–107 → 99–10714 unchanged lines not shown
intuition, on this account, is a failure of imagination rather than a discovery.intuition, on this account, is a failure of imagination rather than a discovery. **Closest continuer.** Robert Nozick's theory makes the duplicate the original when no better**Closest continuer.** Robert Nozick's theory makes the duplicate the original when no bettercandidate exists, and not the original when the biological body survives.[^nozick1981] This delivers thecandidate exists, and not the original when the biological body survives.[^nozick1981] This deliversintuitive verdict in both cases at the cost of making survival depend on facts about other people —the intuitive verdict in both cases at the cost of making survival depend on facts about otherso whether one survives can be changed by an event elsewhere, after the fact.people, so that whether one survives can be changed by an event elsewhere, after the fact. **Four-dimensionalism.** Treating persons as extended in time, with momentary stages as parts, lets**Four-dimensionalism.** Treating persons as extended in time, with momentary stages as parts, letsone say that two person-worms overlapped before the scan. This resolves the logic of branching butone say that two person-worms overlapped before the scan. This resolves the logic of branching butlines 116–133 → 116–1338 unchanged lines not shown
The most influential practical response is to change the case. Instead of scanning and rebuilding,The most influential practical response is to change the case. Instead of scanning and rebuilding,replace the brain's components one at a time, each substitute reproducing the function of what itreplace the brain's components one at a time, each substitute reproducing the function of what itdisplaces, while the person remains awake. There is never a moment of destruction, never twodisplaces, while the person remains awake. There is never a moment of destruction, never twoclaimants, and never a gap in the running process — so all three camps can agree that the personclaimants, and never a gap in the running process, so all three camps can agree that the personsurvives, provided each replacement genuinely preserves function. Weaker versions of the same movesurvives, provided each replacement genuinely preserves function. Weaker versions of the same moveunderlie incremental framings of [[human-ai-merger]] and of the [[posthuman]] condition: a personunderlie incremental framings of [[human-ai-merger]] and of the [[posthuman]] condition: a personaugmented in small steps never confronts a moment of transfer.augmented in small steps never confronts a moment of transfer. This is why gradual routes dominate serious discussion of substrate change, and it is the identityThis is why gradual routes dominate serious discussion of substrate change, and it is the identityhalf of the argument for [[substrate-independence]]. David Chalmers, who defends the functionalisthalf of the argument for [[substrate-independence]]. David Chalmers, who defends the functionalistpremise, is notably more confident about gradual uploading than about the destructive kind.[^chalmers2022]premise, is markedly more confident about gradual uploading than about the destructiveThe catch is engineering: the required devices would have to reproduce a single neuron'skind.[^chalmers2022] The catch is engineering: the required devices would have to reproduce a singlecomputation, including dendritic nonlinearity and neuromodulatory response, inside living tissue —neuron's computation, including dendritic nonlinearity and neuromodulatory response, inside livingfar beyond anything achieved in [[neuroprosthetics]] or contemplated under [[medical-nanorobots]].tissue, far beyond anything achieved in [[neuroprosthetics]] or contemplated underThe philosophically comfortable route is the technically hopeless one.[[medical-nanorobots]]. The philosophically comfortable route is the technically hopeless one. ## What a real teleporter would do## What a real teleporter would do lines 135–159 → 135–1591 unchanged line not shown
laboratories since, transfers an unknown quantum state from one system to another using entanglementlaboratories since, transfers an unknown quantum state from one system to another using entanglementand a classical channel.[^bennett1993] It necessarily destroys the state at the origin, because theand a classical channel.[^bennett1993] It necessarily destroys the state at the origin, because theno-cloning theorem forbids copying an unknown quantum state.[^wootters1982] It is closer to Parfit'sno-cloning theorem forbids copying an unknown quantum state.[^wootters1982] It is closer to Parfit'ssimple case thansimple case than to the branch line, and it says nothing about identity, since the relevant questionto the branch line, and it says nothing about identity, since the relevant question is whether brainsis whether brains require quantum-state fidelity at all. Most neuroscientists think they do not:require quantum-state fidelity at all. Most neuroscientists think they do not: synaptic transmissionsynaptic transmission is a thermally noisy chemical process, and proposals that quantum coherence isis a thermally noisy chemical process, and proposals that quantum coherence is functionallyfunctionally important remain a minority position.important remain a minority position. ## Bearing on real technologies## Bearing on real technologies The problem is not idle. Destructive scanning for [[whole-brain-emulation]] has the teleporter'sThe problem has practical consequences. Destructive scanning for [[whole-brain-emulation]] has theexact structure, minus the reassembly of a body. [[brain-preservation]] and [[cryonics]] raise ateleporter's exact structure, minus the reassembly of a body. [[brain-preservation]] andmilder version: the process is not obviously destructive, but it does stop, and whether restarting[[cryonics]] raise a milder version: the process is not obviously destructive, but it does stop, andcounts as continuation depends on the same disagreement. The weaker products sold aswhether restarting counts as continuation depends on the same disagreement. The weaker products sold[[digital-immortality]] do not raise the problem at all, since a model trained on someone's messagesas [[digital-immortality]] do not raise the problem at all, since a model trained on someone'shas no continuity claim of any kind — a distinction the marketing tends to blur.messages has no continuity claim of any kind, a distinction the marketing tends to blur. Nothing in [[connectomics]], [[neural-correlates-of-consciousness]] research, orNothing in [[connectomics]], [[neural-correlates-of-consciousness]] research, or[[machine-consciousness]] work settles it, and no one has described a result that could. The[[machine-consciousness]] work settles it, and no one has described a result that could. Thephysical facts in the teleporter case are stipulated and complete. What remains is a decision about which description of those facts to accept,physical facts in the teleporter case are stipulated and complete. What remains is a decision aboutand the practical question of who gets to make that decision when a real procedure is on offer.which description of those facts to accept, and the practical question of who gets to make thatdecision when a real procedure is on offer. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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