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You might be unkillable, impossible to delete
out of existence – if one of the most exciting
ideas about physics, quantum immortality, is
true. To test this idea, we will put a nuclear
bomb in your living room. But more on that
later. This is real science happening around
one of the most successful theories of physics.
To understand why, we need to tell you a story.
The story of the smallest parts in the universe,
atoms and fundamental particles.
With everyday objects things intuitively
make sense – if you kick a marble ten
times with the same force and at the same
angle, it always lands in the same spot.
But if you kick an electron ten times exactly
the same way, it shows up in different places.
On the most fundamental
level of reality, randomness is the rule.
The story that solves this is called quantum
mechanics. Simplified it goes something like this:
A particle like an electron is not like a tiny
marble but like a shapeshifter – a diffuse thing
we call a wave, that ebbs and flows. But to make
it much weirder: It’s not a wave of matter or energy,
but a wave of probability – an immaterial
essence that has values between 0% and 100%.
What does this even mean?
Quantum mechanics doesn't really
tell us much about the electron.
It only tells us how this entity that
we call an electron behaves on average.
Say you shoot an electron gun at your
apartment. You shoot it 100 times –
80 times the electron shows up in your living
room, and 20 times in your kitchen.
So the probability wave of our electron is 80%
in the living room and 20% in the kitchen.
What is deeply annoying is that this story of
probability waves works insanely well in reality.
It's not just some brainchild
that only works on paper.
Scientists have tested it in countless
experiments and it works every single time.
It explains how a lot of real things
work, from information passing through
microchips to the atoms fusing in the center of
stars. And yet how can this story make sense?
All of our other scientific stories give us a
mental picture of the things they are describing –
a sphere of iron at the center of
earth, an elastic fabric of space.
But a wave of probability?
What’s that even supposed to look like?
Quantum mechanics doesn’t tell us
anything about the electron itself –
what it looks like, how it moves, or how it tastes.
But if our story doesn’t describe the electrons
themselves, what does it describe
and how does it potentially make you immortal?
What Is the Quantum Story Really About?
Scientists have been debating this for a
century. They’ve come up with tons of ideas
we can’t cover here, but there are two popular
schools of thought. We’ll call them
linguists and literary critics.
They are screaming and arguing
over what the quantum story really means.
The position of the linguists is “shut up and
calculate”. They basically claim that quantum
mechanics is not a story about reality, but
just a kind of grammar for the theoretical
language of the universe. With this language
we can predict experiments. Nothing else.
If there is no story, there is no point in
asking what the story says about the electron.
Whether electrons are tiny marbles or
clouds, waves of negative charge or Detective
Pikachu is missing the point. Quantum mechanics
doesn’t enable you to visualize any electrons.
All you can do is to run experiments.
And physics is all about experiments,
not about creating mental pictures for us.
So shut up, stop imagining fairy tales,
and just use the probability wave to calculate
things. Follow the grammar, ignore the plot.
“Nooooo!” scream the literary critics: Read
between the lines, there’s a hidden meaning here!
They are “many-worldians” and they
are convinced that quantum mechanics
is a story about reality.
And they want to interpret the story.
The many-worlds interpretation of quantum
mechanics is not the same as the multiverse by the way,
which is a whole different can of worms,
but we’ll get to that another time.
The many-worldians think that the universe
is an infinitely complex quantum state,
where all physically possible outcomes
coexist simultaneously. If the probability
wave of your electron is split 80% to 20%
between your living room and the kitchen,
that means that the electron is split in
a similar way. That there are 5 versions
of the electron – 4 of them are going to
the living room, and 1 to the kitchen.
But it isn’t just the electron that
splits. You are observing the electron,
so there are five versions of you, too!
Four of them see the electron in
the living room, and one in the kitchen.
Each of these different versions of you
and the electron are equally real, equally true.
And all of them exist at this moment,
in your house. But they can’t communicate
or interact in any way, so they are totally
invisible to each other. Which means that,
whoever “you” are right now, you
are just one of your versions,
experiencing just one thing – either seeing the
electron in the living room, or in the kitchen.
Many-worlds means that all physically possible
worlds are coexisting right here, right now,
but independently of each other, like the
branches of a tree. And there are a lot of them.
Every possible quantum process
means there are other possible worlds.
A radioactive atom decays? Another world exists
where it didn’t. A cosmic ray hits one of your cells?
Another world exists where
the ray just passed through.
Each second, bazillions upon bazillions of
new worlds exist on top of each other.
“Stop it!”, shout the linguists. “If these
worlds can’t interact with each other,
we can't check whether they exist! This is
not science. So please shut up and calculate…”
Wait! There is a way to find out.
But to do it, you’ll have to die a few hundred times.
And maybe prove that you are immortal!
The Ultimate Experiment
All we need are two electron detectors
connected to a nuclear bomb in your living room.
If the detector in your living room
is activated the nuke explodes. If the one
in the kitchen is activated you are safe.
Now sit on the nuke and have your brave
assistant shoot the electron gun. There are
two ways this can go. There is a 20% chance
the electron lands in the kitchen and
you survive, and an 80% chance you die.
Ok, let’s shoot!
Beep.
Oh, lucky you! The electron landed
in the kitchen. Let’s try once more:
Beep.
And once again:
Beep.
And another 100 times!
Beep, Beep, Beep, Beep, Beep, Beep, Beep…
If there is only one universe, you’ll die fairly soon.
Sooner rather than later the electron will trigger
the nuke and you’ll be instantly vaporized.
But if the many worlds interpretation is true,
then every time your assistant shoots the gun,
there are five versions of you and four
instantly die. Only one of your versions
is alive and there’s only one thing
you can experience – your survival.
It doesn’t matter how many times you try. From
your perspective, you will survive every time.
At first it will seem like luck. But at some
point your “luck” will become near-impossible.
In a universe with just one reality,
your odds of surviving 100 times in a row
are about 1 in ten duovigintillion
– a 1 followed by 70 zeroes.
So if you did the experiment 100 times and you
are still here, the universe just whispered
its deepest secret to you. Yes, you killed
hundreds of versions of yourself. But you
now know for sure that the many worlds are true.
Because you are still here experiencing things.
And that you are kind of immortal!
Okay, well, all that might be a bit
overwhelming - let’s break it down again.
The Cosmic Secret
If every possible quantum process
always happens in some branch,
then this doesn’t only mean that
there are almost, but not quite,
infinite versions of you – but there
is always a “you” that gets insanely lucky.
A tumor starts, but a cosmic ray kills it before
it spreads. A bolt of lightning strikes at you,
but a quantum fluke makes it miss
by a meter. A washing machine falls
from a roof, but all its atoms
quantum-tunnel through your body.
No matter how extremely high the
likelihood is that you will die,
there may always be a branch in which you survive.
So should you start wingsuit-flying today?
Well, not so fast. For every version of you that
survives, bazillions don’t. And all those versions
of you are just as real as you are right now,
watching this video. So if you care about the
current version of yourself, you should care
just as much about all the versions still waiting
to be and their loved ones. In other words – if
you see a washing machine falling, better move
away and save as many of your versions as you can.
The more universes exist with you in them the
better, your existence makes the universe richer.
And there is another good reason to move.
While the many-worlds interpretation of
quantum mechanics feels beautiful and elegant,
that doesn’t make it true. We don’t know if
it’s true and so far no literary critic sat
on a nuke to risk being wrong. If the “shut
up and calculate” people are right, there is
just one world. Just one version of you. And if
the washing machine hits you, you are done for.
But wouldn’t this be nice to know?
If the many worlds idea is true,
then no matter how unlucky you get,
you will always know that
somewhere, you are lucky.
Quantum mechanics is an amazing tool to explore
different realities. But what about this reality?
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