Is there more than one of you?
BIOLOGICALLY speaking, there is definitively only one you (see “How likely are you?”). Physics might give you pause for thought, however. The most bewildering argument against your uniqueness comes from quantum mechanics, the fundamental theory that describes the often counter-intuitive behaviour of subatomic particles. It might imply not only that there are multiple, identical versions of you, but even that there are an infinite number of yous out there.
The quantum realm is notoriously fuzzy: quantum objects such as particles are described in terms of probabilities, encoded in mathematical widgets called wave functions that give you the odds on any number of different states the object might be in. Only when you observe or measure it does the object take on one of those states, at least from your perspective.
“Quantum theory might imply there are an infinite number of yous out there”
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The truth of what happens at this point – and indeed what, if anything, the wave function itself is trying to tell us about reality – divides physicists. Many stick with a cop-out known as the Copenhagen interpretation: essentially, that we can never know what is happening in this fuzzy pre-measurement realm. In other words, quantum theory makes predictions about reality, but says nothing about what goes on under the hood.
That isn’t good enough for some. Physicists who subscribe to the rival “many worlds” interpretation insist that all the possibilities encoded in the wave function are real, and that they continue to exist in different universes that split off from ours every time a quantum measurement is made. The startling upshot of this view is that there are potentially squillions of versions of you going about their (your?) business in parallel universes.
Well, sort of. Those other versions of you aren’t really copies, says , a physicist at the California Institute of Technology: they are individuals who used to be you, but at some point split off and became separate. “You are not spread out over worlds,” says Carroll. “You are here in this world, and there are a lot of other people in other worlds who are closely related to you.”
As to how many other-worldly relations you have, it is impossible to say. “The number could be infinite or there could be a continuum of worlds rather than a discrete set,” says Carroll. “But the number might also be finite. We’re not sure.”
What we do know is that we can never observe these doppelgängers. Their worlds exist only in mathematical space; they have no physical connection to our own. Ultimately, the possible existence of as many worlds as you like doesn’t detract from your individuality in this one. Physics, like a doting parent, still says you are special.
All of the “You: Special issue” features
- You are stardust: The long view of when your existence really began
- How nature, nurture and sheer randomness combine to make a unique you
- Think your sense of self is located in your brain? Think again
- You are not one person: Why your sense of self must be an illusion
- Why it’s the aliens living inside you that create your sense of you
- Do we have free will or are all our decisions predetermined?
- If we can’t change the world, does anything we do matter?
- Why we’re in tune with our emotions – but suck at judging our smarts
- If the multiverse exists, are there infinite copies of me?
