This morning I was casting about for topics for Skeptophilia and happened upon one that kind of made my brain explode. Part of this was I came across it prior to my first cup of coffee, but even now that I'm reasonably well caffeinated it still leaves me in a superposition of "Okay, I get it" and "... wait, what?"
I use the "superposition" metaphor deliberately because this, like yesterday's post about Quantum Weeping Angels, is about the weirdness of quantum physics. To frame this, let's start with a refresher on two concepts that will be familiar to most of you -- Schrödinger's Cat and the Many-Worlds Interpretation.
Schrödinger's Cat -- a thought experiment dreamed up by the brilliant physicist Erwin Schrödinger -- looked at the bizarre prediction that with a quantum process, the phenomenon exists in the form of a wave function describing the probabilities of various outcomes. Until observed or measured, the wave function is the reality; it's not that the outcome is already decided, and we simply don't know at the moment which option is true (as in a classical situation like flipping a coin, prior to looking to see whether heads or tails came up). Here, the physics seemed to indicate that in a quantum process, the outcome exists in a superposition of all possible outcomes, but when it's observed, the wave function collapses into one of them, and the probabilities of the others drop to zero.
Schrödinger thought this couldn't possibly be correct, even though the mathematics was impeccable and agreed with all the experimental data (and, in fact, still stands today). His thought experiment locked a cat in a box with a flask of poison; the flask could be broken by a remote-controlled hammer triggered by detection of a particle by a Geiger counter (particle decay and radioactivity are inherently quantum probabilistic processes). So, is the cat dead or alive? It was ridiculous to think it could be both (until you open the box), but that was the inevitable outcome of the quantum model.
As a way around this, another brilliant physicist, Hugh Everett, turned the whole thing on its head by saying maybe measurement or observation doesn't collapse the wave function, it splits it -- bifurcating the universe into two branches, one in which (for example) the cat dies, and the other in which it survives. This idea -- which gave rise to hundreds of episodes on Star Trek alone, as well as my own novel Lock & Key -- pleased some people but massively pissed off others, because it results in staggering numbers of alternate universes which then are forever walled off from each other. The Many-Worlds Interpretation, as it has come to be called, thus appears to be intrinsically unverifiable, and another example of Wolfgang Pauli's acerbic quip, "This isn't even wrong."
Okay, so far that's just background, and probably you already knew most or all of it. But what the article I came across this morning did was to ask a simple question:
If Many-Worlds is correct, what is it like from the point of view of Schrödinger's Cat?
Or, since people might differ on whether a cat qualifies as an observer, suppose a human is inside the box, and within any given minute, the probability of surviving is exactly one-half. According to Many-Worlds, at every moment there is a non-zero chance of surviving and a non-zero chance of dying. What this implies is that in one branch of the universe, you survive every time.
In other words, the Many-Worlds Interpretation seems to guarantee immortality.
Peter Byrne, who wrote a biography of Hugh Everett, danced around the issue. "It is unlikely, however, that Everett subscribed to this [quantum immortality] view," Byrne wrote, "as the only sure thing it guarantees is that the majority of your copies will die, hardly a rational goal." Which may well be true, but the goal isn't the issue, is it? The reality is the issue. Philosopher David Lewis summed it up in a lecture, in a passage that if it doesn't give you the chills, you're made of sterner stuff than I am:
As all causes of death are ultimately quantum-mechanical in nature, on the Many-Worlds Interpretation, an observer should subjectively expect with certainty to go on forever surviving whatever dangers [he or she] may encounter, as there will always be possibilities of survival, no matter how unlikely; faced with branching events of survival and death, an observer should not equally expect to experience life and death, as there is no such thing as experiencing death, and should thus divide his or her expectations only among branches where they survive.
Which brings up a rather alarming question: if some version of me survives in at least one branch of the universe, whose consciousness does that "me" represent? The usual approach is that the "me" in some other branch is unaware of the "me" in this branch, and goes on his merry way making different decisions than I'm making; but how can there be more than just a singular "me"? If this is true, what does "me" even mean?
And the quantum immortality argument makes this infinitely worse. Physicist and deep thinker Max Tegmark points out that while the overall probability of your being in the "surviving branch" drops by half every minute -- and therefore, eventually becomes a really small number -- from the point of view of the "you" that has survived every branch thus far, it will still always be fifty-fifty.
Tegmark writes:
Quantum immortality posits that no one ever dies, they only appear to. Whenever I might die, there will be another universe in which I still live, some quantum event (however remotely unlikely) which saves me from death. Hence, it is argued, I will never actually experience my own death, but from my own perspective will live forever, even as countless others will witness me die countless times. Life however will get very lonely, since everyone I know will eventually die (from my perspective), and it will seem I am the only one who is living forever — in fact, everyone else is living forever also, but in different universes from me.
It's not all that I'm all that fond of the idea of kicking the bucket. I'm like my dad, who was once asked by a family friend what he wanted written on his gravestone, and he deadpanned back, "He's Not Here Yet."
But even so, can we all agree that this is a ghastly thought?
Tegmark agrees, although his objection to it -- based on the either/or nature of the thought experiment, as compared to the gradual process of many deaths -- strikes me as fairly weak. "The fading of consciousness is a continuous process," he writes. "Although I cannot experience a world line in which I am altogether absent, I can enter one in which my speed of thought is diminishing, my memories and other faculties fading... I am confident that even if [a person] cannot die all at once, he can gently fade away."
All righty, but I still want to know why the physics demonstrates that this can't be true.
So that's our unsettling journey through the deep waters of quantum physics for today. And you thought yesterday's post about "there's no such thing as local realism" was bad. Me, I think I need to have another cup of coffee and then go play with my puppy. He never worries about physics and philosophy. He never worries about much of anything, far as I can tell.
What an enviable quantum state to be in.
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