In-Place Teleportation And More: New Thought Experiments For Probing Personal Identity & Survival

In an era of shrinking science budgets, thought experiments remain affordable

Whether you know it or not, if you've consumed any science fiction in the past fifty years, then you've already wrestled with the big questions about personal identity. Are you your body? Your memories? Your continuous stream of consciousness? Maybe even your soul?

Some of the classics include:

1. Teleporter (e.g. Star Trek)
   Captain Kirk steps into the transporter on the Starship Enterprise. It scans every atom, disintegrates him, then rebuilds him perfectly on the planet below. Did Kirk just travel? Or did he die while a perfect copy took his place?

2. Gradual replacement (e.g. roughly like Learning To Be Me)
   Ndoli gets nanobots injected to combat his impending dementia. They gradually replace dying neurons—5% after ten years, 40% after thirty, eventually 100%. The process is imperceptible. Is the final Ndoli still Ndoli, or did the original slowly fade away while no one noticed?

3. Duplication (e.g. SOMA)
   Simon Jarrett's brain gets scanned and uploaded. Scientists boot up 1,000 digital Simons across various robotic bodies and virtual worlds. Which ones count as "real" Simon? All of them? None?

These are classics for a reason - they force us to pin down exactly what we mean by “survival” and “identity.” But after decades of debate, people have perhaps gotten too comfortable with contradictory answers. The same person who states “breaks in consciousness entail death” often still readily submits to anesthesia for surgery. Another might declare that “a teleporter would kill you, but gradual replacement would be fine”, while then struggle to articulate why teleportation isn’t equivalent to arbitrarily-sped-up gradual replacement.

Stepping back from sci-fi, philosophers have grappled with these questions for centuries, developing competing theories of personal identity in the process. Despite their efforts to make progress though, the familiar thought experiments may have become too comfortable, allowing us to hold contradictory intuitions without really noticing.

What might help reinvigorate fresh thinking is new situations that scramble our intuitions and expose the inconsistencies in our thinking about identity.¹ The following scenarios recombine the key elements - continuity of matter, mind, and consciousness - in ways designed to short-circuit pat answers.

If these make you realize your views on personal identity aren't as coherent as you thought, good! Better to find out now than before any of these technologies become personally relevant.

1. Long-term coma
   In some cases of severe epileptic attacks or traumatic brain injuries it can be necessary to place a patient into an induced coma. If an individual is provided deep anaesthesia they may enter a state of absolutely no electrical brain activity (i.e. ‘isoelectric EEG’).² In this circumstance unconsciousness is assured, and patients who emerge later have no sense of how much time has passed.
   
   Despite their unconsciousness, the body of a patient in an induced coma keeps doing its thing - replacing cells and recycling materials, with most material in their skin, blood, and brain replaced every few months. If a patient is maintained in deep anaesthesia while being provided adequate nutritional and nursing care, they will replace their entire body mass roughly every 1.5 years.³
   
   Imagine someone is kept in an induced coma for four years before they are awakened. During their break in consciousness, their entire body mass has been replaced several times, including almost all components of their brain.
   
   Is this functionally equivalent to the dematerialisation/rematerialisation of a teleporter? In both cases, the break in consciousness only ends once their body is constructed out of (almost) entirely new material.
   

2. In-place teleportation
   Ndoli's brother, Jean, also begins to suffer from the first signs of dementia. He’s offered the standard nanobot treatment, but the idea of synthetic neurons disturbs him. Instead, he opts for a newer procedure.
   
   The treatment works like this: doctors use a modified teleporter that targets just one cubic centimeter of brain tissue at a time. That tiny chunk gets scanned, disintegrated, and instantly rebuilt in the exact same spot - minus any disease proteins. Then they move to the next cubic centimeter. After approximately 1,400 small teleportations, his entire brain has been refreshed.
   

   Some patients get it all done in one three-hour session. Others spread it over months, getting a few chunks replaced each visit. Jean chooses the gradual approach - every week, another small piece of his brain vanishes and reappears, cleaned.
   

   Most people who reject teleportation accept gradual replacement. But what about this case? It’s gradual like the nanobot case - Jean walks around normally between sessions, slowly accumulating a brain made of new matter. But it’s also teleportation - each chunk is definitely destroyed and recreated, not repaired or replaced cell by cell.
   

   If regular teleportation is death, is Jean dying 1,400 tiny deaths? Or does breaking it into bite-sized pieces somehow make it acceptable?
   

3. Gradual psychology change
   Parkinson’s disease, a condition where patients suffer difficulties with initiating and controlling movements, is caused by the progressive death of dopamine-producing neurons in the brainstem. One potential treatment is to provide them with stem cells that replace the dead cells.
   
   Imagine that medical researchers succeed in getting such a treatment to work, but that in a small percentage of cases, the stem cells slowly proliferate out-of-control and cause widespread changes in brain plasticity. In this unfortunate circumstance, they even end up eventually wiping a person’s autobiographical memories and totally changing their personality, while leaving their language, motor, and reasoning skills intact.
   
   This progresses gradually over the course of ten years, so that the individual at the end is completely psychologically different from the person at the start. However, at each intermediate time-step, the individual only undergoes small changes in psychological properties, such as a change in musical tastes or the loss of a few childhood memories.⁴
   
   Is the individual at the end of this process the same person as the individual at the start?
   

4. Psychology reset⁵
   After a devastating breakup, Marcus opts for an experimental treatment. Fortunately, he’d had his brain scanned four years earlier as part of a research study - capturing the exact strength of every synaptic connection. Now, using sophisticated optogenetic and chemogenetic techniques, doctors offer to reset his neural connections to that earlier state. Yet while this will succeed in erasing his traumatic memories of his ex, the process will revert his entire psychology to the time before they met.⁶
   
   The procedure works perfectly. He doesn't remember meeting Sophie, the trip to Barcelona, moving in together, or the ugly final fight. Physically, his body has still aged and replaced most of its cells through normal biological processes. But psychologically, he's been restored to exactly who he was before.
   

   Is Marcus after the procedure the same person who entered the clinic? He has continuity of body and brain, but a four-year gap in experience and personality. Is this sophisticated amnesia, or did the heartbroken Marcus essentially commit suicide-by-reset, leaving behind a branch of an earlier version inhabiting his body?
   
   Is this equivalent to the teleportation case (Marcus’ psychology is the same but his physical materials have been totally changed)? Is it like duplicating him, and then four years later, destroying one of the branches? Or is it simply akin to amnesia?

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As we edge closer to technologies that can copy, pause, edit, and restore human minds, we'll need to make decisions based on how we answer these thought experiments. Indeed, for those considering preservation/cryonics/biostasis, these questions already have practical relevance: if forced to choose between optimally preserving the neural information underlying memories and personality versus maintaining biological viability, which matters more? While most treat these scenarios as discussion fodder for philosophy tutorials, they're rapidly becoming urgent questions - not for academic journals, but for medical consent forms and end-of-life directives.

1. I’m saying these are new, but in all probability someone has come up with at least some of these before. If you notice a case where I should be citing someone else, let me know in the comments and I’ll edit in the appropriate reference.

2. Such as with high doses of barbiturates.

3. The only material not replaced over time is some molecules in their eye lenses, some proteins in the nuclei of their brain cells, and the enamel of their teeth. The proteins that make up synapses are replaced every 1-2 weeks. Also, this really refers to the mass of cells - if we’re including extracellular fluids, the time to fully replace one’s body mass is actually much shorter.

4. This is related to Thomas Reid’s (1710-1796) criticisms of a Lockean theory of personal identity. People have been arguing about these ideas for a long time.

5. Credit to Andrew McKenzie for making me aware of this one.

6. This is somewhat related to the premise of the movie Eternal Sunshine of the Spotless Mind, although that movie is more about targeted memory erasure.