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A mind-being theory called quantum immortality suggests that your consciousness shifts to parallel universes after you die.The theory is an offshoot of several other hypotheses that rely on their being multiple universes.While some experts are skeptical of the idea, they agree that it still provides value to the field of quantum physics as a whole, whether or not our consciousness is actually immortal.
Our consciousness persists throughout our whole lives. From the moment we wake up to the moment we fall asleep, it’s the thing that is constantly with us, shaping our perception. So, when we die, what happens to our consciousness? While science doesn’t have a firm answer to that yet, quantum physics can produce an odd interpretation. It’s called quantum immortality—a theory that assumes we continue living in other universes after we die in this one.
Quantum immortality is an offshoot of the “Many-Worlds” theory, proposed by then-PhD student Hugh Everett III at Princeton University in 1957. Very simply put, Everett suggested the many-worlds theory when trying to conduct measurements in quantum mechanics. In a twist on the observer effect—a phenomenon where a system is disturbed by the very act of observation—he proposed that every observation of the quantum state (or wave function) of an object will split off a copy of our universe. And as observations pile up, so will alternate universes.
While not everyone agreed with the many-worlds notion (quantum pioneer Niels Bohr being one of them), studies on the theory continued—especially in the 1980s. For example, MIT physicist Max Tegmark, PhD, investigated a related notion known as “quantum suicide.” It ponders whether you would die in all universes, should you deliberately die in this one. Tegmark posed this as a thought experiment, however, which would be difficult or impossible to solve as we cannot access other universes.
By association with these theories, some proponents of quantum immortality say that our consciousness straddles many universes. This, of course, takes a broad leap, assuming there are multiple, parallel universes. So is it possible that when you die in one universe, your consciousness would shift to another universe? While we cannot access these other universes in our own living experience, the theory supposes, some part of your consciousness would persist forever, jumping from one lifetime to the next—whether or not you realize.
Peter Lewis, PhD, a philosophy professor at Dartmouth College who examines the philosophy of physics, argues the quantum-immortality theory has fallacies. The first issue, he explains, is that consciousness appears to be a physical phenomenon based on brain activity.
“The many-worlds interpretation of quantum mechanics is going to say that physical reality, like branches in time, moves forward into a number of copies,” he says. “But if consciousness is a physical phenomenon, it’s going to be embedded in one of those branches.” So in other words, there could be no consciousness-jumping between universes, because your physicality is stuck in this one.
What Happens After You Die?
Lewis continued with a counterargument: Maybe there is a process that collapses all universes, or all possibilities, into one. But even that idea is an issue. One reason (among a few) is considering what is physically possible against the “astronomically unlikely,” as Lewis put it.
For example, in 2004, philosopher David Lewis (who has no relation to Peter Lewis) published a peer-reviewed article in the Australasian Journal of Philosophy called “How Many Lives Has Schrödinger’s Cat?” Assuming many worlds exist, it talks about death in our world as a sort of “life-and-death branching” opportunity, in which you could be alive in some other worlds and dead in others. But both the researchers named Lewis (David and Peter) independently appear to come to the same conclusion: taken to its logical conclusion, a consciousness could persist forever—long past a human lifetime, naturally.
On that basis, Peter Lewis argues, a many-worlds hypothesis is absurd. “There’s some minuscule, absolutely tiny, probability of being alive for 1,000 years,” he explains. But by the same token, we don’t need a many-worlds hypothesis to come to that conclusion; we could also argue that in the lifetime of the human species, a particular human could have genetics allowing them to last 1,000 years, for example. “You don’t need quantum mechanics to explain that part,” he says.
While quantum immortality is unlikely, Peter Lewis explains that the notion illustrates other functions of the quantum universe that allow for a better understanding of quantum physics.
For example, other universes are experimentally inaccessible to each other because of a phenomenon called decoherence. That’s a complex topic of its own, but decoherence (a splitting of the quantum systems into states, upon measurement) can explain the observation effect and why quantum systems cannot be measured externally.
More simply put, decoherence shows “there’s absolutely no way, experimentally, to tell that this other branch exists,” Peter Lewis explains, because other branches would be indetectable by virtue of the measurement. And studies of the many-worlds theory, he says, have benefited from using parallel universes and decoherence together. “It helped fans of the many-worlds theory really clarify what their theory says, and what it doesn’t say.”
Unfortunately, it therefore appears to Peter Lewis that, if you happen to die in this universe, your consciousness will not persist into others. But more broadly, the many-worlds theory does illustrate the limitations of physical reality, as well as how to better understand the strangeness of quantum theory—although there will always be more to explore in the world of the very small.
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Elizabeth Howell (Ph.D., she/her) is one of a few space journalists in Canada. She has written five books, and was Space.com’s former staff reporter in spaceflight. As a freelancer, she has written or edited articles about astronomy and space exploration for outlets such as Payload Space, Air&Space Magazine, Sky & Telescope and Salon. Elizabeth holds university degrees in journalism, science and history and also teaches an astronomy course, with Indigenous content, at Canada’s Algonquin College. Aside from watching several astronaut missions launching from Florida and Kazakhstan, Elizabeth once lived like an astronaut at the Mars Society’s Mars Desert Research Station in Utah.