It's 2146 and you're commuting to your retail job on Mars from one of Elon Musk's fancy new teleportation machines on Earth. You're put to sleep; the machine scans the position and other properties of every subatomic particle in your body and brain, and beams the information to Mars, where an identical new body and brain is created, while the original is dematerialised in a flash of light. You wake up on Mars and order a Cybercab to the depressing, hermetically sealed mall. Hey ho, another day.
It took people a while to get used to the idea of teleportation, but now it's routine. One day, however, there's a glitch. You wake up in the machine, but you're still on Earth. A soothing female AI voice explains that, while there's now an identical copy of you going to work on Mars, the machine failed to vaporise your original body as usual. Of course, the voice says, we can't have two identical citizens wandering around at any one time, or society would cease to function. The Teslaportation Company regrets to inform you, therefore, that you must now report to an assisted-death pod to be killed.
Is this fair? And which of these identical humans is the real you? Most normal people would reply that I am still the person on Earth, and that the copy on Mars, despite waking up with all my memories, my personality, and exactly the same body, is not me. The idea that he will go on to live his life just as I would is no consolation for my own impending execution. Indeed, all those times the teleportation process worked normally, wasn't I already being murdered time and time again?
A version of this sci-fi thought experiment was originally devised by the celebrated English philosopher Derek Parfit and reappears in The Future Loves You, a new book about "abolishing death" by the young neuroscientist Ariel Zeleznikow-Johnston. His argument is that the version on Mars is really me, too: any system that can fully recreate the workings of your brain, in all its electrochemical complexity, is you. This view has the advantage, he explains, of implying that we might be able to defeat death, even if it does offend ordinary intuitions about what makes us who we are.
For Zeleznikow-Johnston, this recreation of your brain could happen via a high-powered computer, or by growing a new one in a vat with stem cells, or any kind of cyborg combination of the two. Philosophers call this "the assumption of substrate independence", a notion that is, like many of Zeleznikow-Johnston's premises in this book, controversial - after all, no one has yet made a consciousness out of any material other than biological neurons.
But if he's right, and it were possible to perfectly record the "connectome" of a person - a high-resolution map of all their brain connections - before they died, then it would follow that we might one day be able to revive them with advanced technology, and reboot their consciousness inside a robot. This is a more Matrix-like vision of immortality than the one offered by cryonics, whereby rich people currently pay to have their whole bodies - or, if they're penny-pinching, just their heads - deep-frozen at death in the hope that future generations will figure out how to revive them.
None of what Zeleznikow-Johnston describes is possible at the moment. But he does spend many interesting pages on the current state of neuroscientific recording and the preservation of tissues. It turns out that, with a combination of chemical "vitrification" and low temperatures, we could already preserve a person's brain in such a state that, at least in principle, future technology would be able to read its connectome perfectly and recreate it, so waking it up into a baffling future.
The author pursues these implications with admirable doggedness. If it's possible to preserve people's brain-identities in such a way now, then, he says, we ought to be doing it. Remarkably, according to his calculations, it should cost only about $13,000 (£10,300) per person for the preservation procedure and a further $1,300 per year in cold storage - or, as he works out for us, only about an extra 4 per cent of the total annual NHS budget. Now there's something for Rachel Reeves to think about.
How seriously should we take all of this? Well, aside from all the tech-utopian speculation - which depends on the future invention of impressive technologies, as well as the willingness of our descendants to resuscitate lots of dead people, and, indeed, the survival of the human race itself - there are some excellent, concrete chapters. These focus on what we currently know about how memory, ageing and awareness work, making this book, additionally, an engaging description of modern brain science.
And then there might even be some readers who agree with Zeleznikow-Johnston's desire to "abolish involuntary death". As for all those poets and philosophers who have argued that death is what makes life meaningful, Zeleznikow-Johnston proposes that they've simply succumbed to a state of "learned helplessness" in the face of calamity. (The scientific journal The Lancet's "Commission on the Value of Death" in 2022 even claimed, with a straight face, that "it is healthy to die".) Even so, if you would hesitate to step into the teleportation machine, this book will not convince you that any kind of happy immortality awaits.
The Future Loves You is published by Allen Lane at £25. To order your copy for £19.99, call 0330 173 0523 or visit Telegraph Books