If you can be copied, the copy will be just as sure it's you

Until recently, copying a mind sounded like pure science fiction. The recipe for what's called whole brain emulation goes roughly like this: preserve a brain, slice it, scan it, rebuild it in 3D, then simulate it. Anders Sandberg and Nick Bostrom's 2008 roadmap describes the goal plainly: "take a particular brain, scan its structure in detail, and construct a software model of it that is so faithful to the original that, when run on appropriate hardware, it will behave in essentially the same way as the original brain" 2.

The scanning part has moved fast since then. In 2024 scientists published the first complete wiring diagram of an adult fruit fly brain, 139,255 neurons joined by about 50 million connections 3. In 2025 a team mapped about a cubic millimeter of mouse brain, with more than 200,000 cells and 523 million connections, taking up 1.6 petabytes of data 4. And in 2026 a startup reported a simulated fruit fly brain driving a virtual body with "91% behavior accuracy," a company claim that still awaits peer review, from a model that can't form new memories 5.

A whole mouse brain hasn't been mapped yet, and one research group projects an optical method could do it in about five years 6. A human brain is vastly bigger again, but the direction is clear, and the question Parfit asked as a puzzle is slowly becoming one engineers will face.

Philosophers have argued about this for a long time, and there are roughly two camps. One camp says you are your body, or at least your brain, so the teleporter kills you and the replica is a new person with your memories. The other says you are the pattern, meaning your memories, personality and habits of mind, so as long as the pattern continues, you continue.

Parfit's own answer was more radical. He argued that what matters in survival is psychological continuity, the unbroken chain of memories and personality, and that the question "is it really me?" carries less weight than we feel it does 1. The Stanford Encyclopedia of Philosophy sums up his view in a single line: "Identity itself has no practical importance" 7.

There's a gentler version that I find harder to dismiss. Instead of copying your brain all at once, replace it one neuron at a time. David Chalmers imagined exactly this: "only a single neuron is replaced. Its replacement is a silicon chip that performs precisely the same local function as the neuron." Then another, and another, until "every neuron in the system has been replaced by a chip" 8.

Chalmers used this to argue that your experience would most likely carry on through the whole process, though he admits his reasoning doesn't "constitute conclusive proof" 8. It leaves open whether the person at the end is still you, yet it makes the gradual path feel very different from the teleporter, even though the end result is the same.