You might actually be immortal according to quantum mechanics.
Then again, maybe not.
In a previous post, I explained why quantum mechanics predicts that there are countless versions of you running around in what could be an infinite number of parallel universes.
This time, I’m going to introduce a controversial proposal by MIT physicist Max Tegmark, that uses these parallel universes to argue that you might actually be immortal.
But before you go about testing it empirically, be sure to read the rest of this article because many physicists don’t think “quantum immortality” is all it’s cracked up to be.
Ket yourself before you wreck yourself
As I’ve noted before, the vast majority of a quantum physicist’s job involves drawing mediocre doodles that represent the objects they’re interested in investigating.
But doodles don’t get you research grants, so physicists like to put their doodles inside funny-looking brackets called “kets” that look like this ⎜ 〉 to convince taxpayers that they’re doing something super complicated. All the ket means is that we’re talking about the object we’ve drawn inside in the context of quantum mechanics.
For example:
Draw the stick figure on the left, and you’re a fourth grader with a bad sense of proportions. But put that same stick figure into a ket, like I did on the right, and hey — you’re ready for grad school.
Killing yourself with kets
Let’s use kets to describe a strange experimental setup.
We’re going to take an electron — a tiny particle that can spin either clockwise or counterclockwise — and connect it to a gun that’s pointing at your head.
If the electron is spinning clockwise, a signal will be sent to the gun, and the gun will go off and kill you. If the electron spins counterclockwise, the gun won’t go off, and you’ll live.
With kets, here’s what this will look like if the electron is spinning clockwise, before the signal has reached the gun:
A moment later, the gun goes off, and things look like this:
The bullet flies through the air, and your experiment comes to an abrupt end:
If the electron had been spinning counterclockwise, the situation would have been a bit simpler. In fact, the before and after kets would all be identical, since the gun will never be triggered to fire:
Parallel universes and quantum suicide
It turns out that tiny particles like electrons have a weird superpower: they can actually spin both clockwise and counterclockwise at the same time.
As I mentioned in my last post, the best way to picture this is to imagine drawing an analogy with colours: if clockwise is white, and counterclockwise is black, then electrons can be grey.
Not white or black, but both at the same time.
To illustrate this, physicists like to use a plus “+” sign. With that notation, our “grey” electron then looks like this:
Now let’s look at our suicide experiment again, and see what happens if we start our electron off spinning in two directions at once:
What happens next? According to quantum mechanics, it turns out that the gun will get “split” into two versions of itself by our electron.
One version of it will get the signal from the clockwise spinning electron and go off, and the other won’t:
The bullet is now flying at top speed (and at the same time, not flying at all), heading straight at you.
So, what will happen to you?
Just like the gun, the laws of quantum mechanics say you’ll be split in two. One version of you gets killed, the other doesn’t:
What we’ve effectively got here are two parallel universes: one in which the electron was spinning clockwise, the gun went off and you were killed, and another in which the spin was counterclockwise, and you survived.
This whole setup — an electron spinning in two directions at the same time, connected to a gun which is aimed right at you — is known as a “quantum suicide” experiment.
And some have argued that understanding it is the key to proving that you’re already immortal.
Quantum immortality
How would it feel to be the stick figure in the kets we’ve drawn above? In one case, you’d feel perfectly fine, having, quite literally, dodged a bullet.
And in the other?
Well, you can’t possibly experience what it’s like to be the “dead you” in the quantum suicide experiment, since the dead you has no experience of the world at all.
There’s no mind to inhabit, since it’s been blown to bits — and no consciousness to experience.
In fact, the only universe you’ll ever be around to witness is the one in which you survive the experiment:
So the outcome you’re guaranteed to perceive when you run the quantum suicide experiment is the one where you survive.
Now imagine taking a new electron, and trying this experiment again. According to quantum immortality, you should also experience the survival outcome in this second round of the experiment.
In fact, if you repeat this experiment 100 times, you should experience the survival outcome each time. You’re destined to experience walking away unscathed against all odds (the odds in this case being 1 in 2¹⁰⁰, or about one in 1300000000000000000000000000000):
A cool consequence of this is that the quantum suicide experiment could actually allow you to prove to yourself that parallel universes exist.
Here’s how that would work:
- If there actually exists only one universe, you should expect to die with 50% probability after each experimental run. Repeat the quantum suicide experiment a dozen times, and you’re virtually guaranteed to die.
- But if there actually do exist universes with survival outcomes for every round of the experiment, the door for quantum immortality is left open. So surviving all the way through 100 or more rounds of the quantum suicide experiment would essentially prove to you that parallel universes are real.
Look mom! I’m immortal!
Ok, so you just read the beginning of this post, got excited about quantum immortality and secured the research grant you needed to build your quantum suicide gadget.
You hop inside, and run 100 rounds of the experiment, and come out ecstatic: you’ve proved that parallel universes exist, and now it’s time to tell the whole world and pick up your Nobel Prize!
Not so fast.
To other people — who weren’t in the quantum suicide device with you — you’ll certainly seem incredibly lucky.
But no matter how many times you survive the experiment, that’s all you’ll ever seem to them, because if you try to repeat it another hundred times, you’re almost guaranteed to die, from their point of view.
This becomes clearer if we re-draw our universe forking diagram, and include some onlookers in the picture:
From this new diagram, we can see that to everyone who isn’t you, the “dead you” outcomes will certainly seem every bit as real as the “living you” outcome. So although you’ll perceive that you survived every round of the experiment, everyone else will see you die in the vast majority of universes.
But what about the observers in the universe where you survive all the way through the 100 rounds of the experiment? Would they believe you?
Unfortunately not. Raising one eyebrow, they’d turn to you with skepticism and say, “I could believe you’re really, really lucky. But if you’re actually immortal, you’ll be able to repeat that experiment another 100 times.”
And if you did, the vast majority of their future experiences would involve staring smugly at your limp corpse, only wishing you were alive so they could say “I told you so” (physicists are assholes):
So even if quantum immortality is a thing, you’d only ever be able to prove it to yourself. To everyone else, you’ll either seem like one lucky bastard, or a very dead idiot.
Pushing it to the limit
Some people take quantum immortality even further: every heart attack, cancer, bullet wound, etc, that might spell the end of you is theoretically the product of a huge number of cellular — and ultimately, molecular and even subatomic — events.
An electron, nudged to the left or to the right, might cause a cancer gene that would otherwise have killed you to stay dormant, for example.
And because molecular and subatomic events are governed by the laws of quantum mechanics, those events will also lead to splitting universes in just the same way as our “grey” electron did, leaving the door open to the quantum immortality effect.
So hard-core fans of quantum immortality say that we’re all destined to experience eventually becoming the oldest person on earth — outliving our friends and family, and eventually even the human species and planet Earth as a whole.
Just imagine the arthritis.
What’s wrong with this picture
The quantum immortality party was getting a bit rowdy, so the skeptics decided to get out of bed, throw on their Schrodinger equation-tiled nightgowns, velcro up their sandals, and saunter on over to shut it all down.
What’s so hard to believe about parallel universes and quantum immortality, you ask?
One problem is that the case for quantum immortality depends entirely on the instantaneous death of the experimenter.
Think of the case where the gun goes off: for several hundred milliseconds after the gun is fired, you’re still alive and fully conscious. So there actually is something to experience in that timeline — even if it’s just a few fleeting moments of awareness. That’s enough to challenge the notion that that timeline is a complete nothingburger of subjective experience:
As a result, it’s argued, your subjective experience can absolutely fall into the “dead you” timeline, and once it has, there’s no escaping your ultimate fate.
But the quantum immortality diehards (sorry about that) shot back: “Fine, we just have to design an experiment that kills you instantly. No more Mr. Nice Guy: the next time we run this thought experiment, it’ll be with a laser beam and not a gun.”
Easier said than done.
Some say it’s also unclear whether the state of “being vaporized” is a valid state of human existence, too. You could certainly argue that there will be versions of you that will “experience” nothingness, whatever that feels like.
So it’s pretty unclear what kinds of guarantees can be made about your subjective experience of the quantum immortality experiment, at all.
The jury’s still out on the case for quantum immortality. And the only way to know if it’s true is to build a contraption that’s currently beyond the reach of modern technology (and which may even be impossible), and to put yourself directly in its line of fire.
Besides, as much as I’m curious about whether parallel universes exist, I definitely wouldn’t say I’m dying to find out.
My new book, Quantum Physics Made Me Do It, is now available at fine bookstores across the multiverse! You can also find it on Amazon here (Canada), here (U.S.) and here (U.K.).
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