# Quantum Suicide: How to Prove the Multiverse Exists, in the Most Violent Way Possible

Quantum
mechanics says objective reality doesn't exist, that instead all we see
are probabilities collapsing into one particular configuration... and
all other possible realities might just exist together in a quantum
multiverse. Here's the deadly experiment that could help you to test
that very idea.

First,
let's take a look at two major interpretations for the nature of quantum
reality. The older and somewhat more preferred option is the Copenhagen
interpretation, which was devised by legendary scientists like Niels
Bohr and Werner Heisenberg in the 1920s. At its most basic, this
interpretation says that all the subatomic particles that make up the
universe can and should be thought of as wavefunctions, which are
probabilistic representations of a particle's location and velocity at
any given time. Measuring or observing these particles is what causes
them to collapse into only one of all possible values, and that's how we
get the universe that surrounds us.

The

*other*idea was first put forward by Hugh Everett in 1957. He kept most of the Copenhagen interpretation but removed one crucial part: the wavefunction collapse. Without it, all probabilistic values for every subatomic particle would exist in superposition, all at once. In theory, this meant that was a very large and quite probably infinite number of universes in parallel existence.
The obvious question then is why we only seem to observe one universe, and why it

*looks*for all the world as though wavefunction collapse is happening all the time. As Everett and those who followed him explained, the answer is another phenomenon called quantum decoherence. Basically, for all possible states of a particle to remain in superposition — to be coherent, in other words — their system needs to be isolated.
Being hit by even a single photon is enough to break that coherence, and what we see as wavefunction collapse is

*actually*just one of the many realities that describe the possible states of the particle. Add it all together, and you get the quite possibly infinite universes of the many worlds interpretation.
There are
certain theoretical advantages to this theory. The Copenhagen
interpretation relies on the presence of an observer - not necessarily a
sentient observer, just something capable of initiating wavefunction
collapse — and a lot of the apparent paradoxes of quantum mechanics are
eliminated if an observer is no longer necessary. For a start, it neatly
solves the legendary problem of Erwin SchrÃ¶dinger's cat, in which a cat
is placed in quantum superposition inside a box so that is

*both*dead and alive. The Many Worlds Interpretation has no issue with the cat being simultaneously dead and alive — it just spins the two results into different universes.
Despite
these potential benefits, the Many Worlds Interpretation has always
faced two seemingly insurmountable challenges. For one thing, there's no
way to test it experimentally, which makes it unfalsifiable and
arguably more a question for philosophy than for science. And, for a
second thing, it's completely, utterly bonkers. It roars against every
last shred of intuition we have about the world around us, violently
disagreeing with

*everything*we think must be true about the world. That doesn't mean it's*wrong*, of course, but that fact still does it no favors in the courts of popular and scientific opinion.
Actually, there is

*one*way to prove the existence of a quantum multiverse, but if anything it only makes the bonkers problem even worse. For now — and probably for the indefinite future — it's just a thought experiment, but it's not totally out of the question that this test could one day be attempted. If successful, it would prove that the multiverse exists — but only to one person.
The twin
notions of quantum suicide and immortality were first proposed by Hans
Moravec in 1987 and independently a year later by Bruno Marchal, but the
most work on the idea has been done by MIT's Max Tegmark. The most
common version of this experiment goes like this — place the
experimenter in a chamber with a life-terminating device, such as a
high-powered rifle pointed at her head. Every ten seconds, the spin
value of photons will be measured. Depending on the result — and there's
a 50/50 chance of either measurement — the device will either fire and
kill the experimenter or make an "all clear" noise that tells the
experimenter she is safe.

What
we've done here is tie the survival of the experimenter to a quantum
state, meaning she now exists in a superposition of being both alive and
dead. There's a 50% chance she survived the initial round, and she has
the same chance for every subsequent repetition of the experiment. No
matter how many times she repeats the experiment, half the time, she
survives.

Of course,
her overall survival chances are way less than 50%. The version of her
that died in the initial experiment doesn't have a 50% chance of coming
back to life in the next experiment. But each living version of the
experimenter retains that chance at survival, even if the overall chance
of survival keeps falling to 25%, then 12.5%, then 6.25%, and so on.
Let's say that in one universe, an experimenter eventually emerges
having survived 50 such tests in a row — something she has less than a
one in

*quadrillion*chance of surviving, which is way more than is needed to meet the 5-sigma level of certainty needed for an official discovery.
The
experimenter can then distinguish between the Copenhagen and Many World
interpretations — while there's less than a one in quadrillion chance of
her being there in the former interpretation, there's a 100% chance in
the latter, because

*some*version of her must be around to observe this particular superposition, and all the other versions of her are dead. Thus, the Many Worlds Interpretation has been proven and this particular experimenter has tasted quantum immortality.
The only
small hitch, of course, is that the interpretation has only been proven
to the experimenter. No other observers will be choosing between 1 in a
quadrillion and 100% chances — to them, the chances of the
experimenter's survival will be equally unlikely no matter which
interpretation one chooses. To be sure, the ridiculously low probability
— 1 in a quadrillion is essentially impossible — might convince the
experimenter's peers to accept the Many Worlds Interpretation as
correct, but that still leaves countless more universes where the
experimenter died. At best, Many Worlds is only going to be proven in a
tiny sliver of all possible universes, because everywhere else the
results just aren't unlikely enough.

For his
part, Max Tegmark once said — probably with his tongue planted firmly in
his cheek — that he might someday try the experiment, but only once
he's old and crazy, and thus his death in most of the universe wouldn't
be quite so hard for others bear. He also points out on his website
that the experiment could potentially be expanded so that both you and a
friend are either killed or spared in each round of the experiment,
which at least would give you someone else to share your knowledge of
the multiverse with.

I suppose one of sufficiently grandiose persuasion might imagine designing an experiment where

*everyone*on Earth is placed in one colossal chamber, and so*everyone*is a participant in this exploration of quantum immortality. Of course, you'd better be damn sure the Many Worlds Interpretation is correct before risking the entire population of Earth on proving it once and for all, and besides — much as I'm a firm believer in the search for scientific truth, I'm not totally sure it's worth killing off the populations of countless Earths just so that*one*surviving world can have its answer. Although, ask me that same question in another universe, and I might just feel differently...