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The last refuge of the Self, perhaps, is “physical continuity.” Despite the body’s mercurial nature, it feels like a badge of identity we have carried since the time of our earliest childhood memories. A thought experiment dreamed up in the 1980s by British philosopher Derek Parfit illustrates how important—yet deceiving—this sense of physical continuity is to us.15 He invites us to imagine a future in which the limitations of conventional space travel—of transporting the frail human body to another planet at relatively slow speeds—have been solved by beaming radio waves encoding all the data needed to assemble the passenger to their chosen destination. You step into a machine resembling a photo booth, called a teletransporter, which logs every atom in your body then sends the information at the speed of light to a replicator on Mars, say. This rebuilds your body atom by atom using local stocks of carbon, oxygen, hydrogen, and so on. Unfortunately, the high energies needed to scan your body with the required precision vaporize it—but that’s okay because the replicator on Mars faithfully reproduces the structure of your brain nerve by nerve, synapse by synapse. You step into the teletransporter, press the green button, and an instant later materialize on Mars and can continue your existence where you left off. The person who steps out of the machine at the other end not only looks just like you, but etched into his or her brain are all your personality traits and memories, right down to the memory of eating breakfast that morning and your last thought before you pressed the green button. If you are a fan of Star Trek, you may be perfectly happy to use this new mode of space travel, since this is more or less what the USS Enterprise’s transporter does when it beams its crew down to alien planets and back up again. But now Parfit asks us to imagine that a few years after you first use the teletransporter comes the announcement that it has been upgraded in such a way that your original body can be scanned without destroying it. You decide to give it a go. You pay the fare, step into the booth, and press the button. Nothing seems to happen, apart from a slight tingling sensation, but you wait patiently and sure enough, forty-five minutes later, an image of your new self pops up on the video link and you spend the next few minutes having a surreal conversation with yourself on Mars. Then comes some bad news. A technician cheerfully informs you that there have been some teething problems with the upgraded teletransporter. The scanning process has irreparably damaged your internal organs, so whereas your replica on Mars is absolutely fine and will carry on your life where you left off, this body here on Earth will die within a few hours. Would you care to accompany her to the mortuary? Now how do you feel? There is no difference in outcome between this scenario and what happened in the old scanner—there will still be one surviving “you”—but now it somehow feels as though it’s the real you facing the horror of imminent annihilation. Parfit nevertheless uses this thought experiment to argue that the only criterion that can rationally be used to judge whether a person has survived is not the physical continuity of a body but “psychological continuity”—having the same memories and personality traits as the most recent version of yourself. Buddhists
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James Kingsland (Siddhartha's Brain: Unlocking the Ancient Science of Enlightenment)