From MSM

*''…So what’s this about quantum physics? Oh, right. Well, I kind of
identify the branching-paths effect in the video with the
Everett-Wheeler “Many Worlds Interpretation” of quantum physics.
Quantum physics does this weird thing where instead of things being in
one knowable place or one knowable state, something that is quantum
(like, say, an electron) exists in sort of this cloud of potentials,
where there’s this mathematical object called a wavefunction that
describes the probabilities of the places the electron **might be
at a given moment. Quantum physics is really all about the way this
wavefunction behaves. There’s this thing that happens though where when
a quantum thing interacts with something else, the wavefunction
“collapses” to a single state vector and the (say) electron suddenly
goes from being this potential cloud to being one single thing in a
single place, with that one single thing randomly selected from the
different probabilities in the wavefunction. Then the wavefunction
takes back over and the cloud of potentials starts spreading out again
from that randomly selected point.*

*A lot of scientists really don’t like this “collapse” thing, because
they’re uncomfortable with the idea of nature doing something “at
random”. Physics was used to dealing with randomness before quantum
physics came along– the physics of gases are all about the statistics
of randomly moving gas particles, for example– but those kinds of
randomness aren’t assumed to be actually **random, just
“effectively random” because the interactions of air molecules are so
chaotic and complicated that they’re too unpredictable for humans to
track. Think about what happens when you roll a die: the number that
comes up when the die lands isn’t strictly speaking “random”, it’s
absolutely determined by the physics of motion and the velocity at
which you let go of the die and so forth. The “randomness” of a die
roll isn’t about actual indeterminacy, but rather just a way of talking
about your ignorance of how the deterministic processes that control
the die operate. Quantum physics, on the other hand, has things that as
far as anyone can tell are really, objectively random, with no
mechanism producing that randomness and nowhere apparent to stick one. *

*Since this makes some physicists uncomfortable, they came up with a
sort of a philosophical trick: they interpret quantum physics in such a
way that they say when there’s more than one possible random outcome of
some quantum process, then the different possibilities **all
happen, in alternate universes. They can’t prove or disprove that this
idea is true– from the perspective of someone inside one of these
universes, everything behaves exactly the same as if the “wavefunction
collapse” really was just picking a random option. But it’s one way of
looking at the equations of quantum mechanics, and as far as the
mathematics cares it’s as valid as any other. Looking at things this
way, if there’s a 3/4 chance of a quantum process doing one thing and a
1/4 chance of it doing the other, then we get three universes where the
one thing happens and one universe where the other one does. This does
mean that there’s some universe where two seconds ago all of the atoms
in your heart spontaneously decided to quantum-tunnel two feet to the
left, but in **almost every universe this doesn’t happen so we don’t worry about that.*

*Science fiction authors **love this. There’s a bunch of stories
out there exploring this idea of a multiverse of infinite possibilities
all occurring side by side (the best of these I’ve ever read being
Robert Anton Wilson’s Schrödinger’s Cat).
Most of these stories get things totally wrong. Science fiction authors
like to look at many-worlds like, this morning you could either take
the bus to work or walk, so the universe splits in two and there’s one
universe where you decided to walk and one universe where you decided
to take the bus. This is great for purposes of telling a story, but it
doesn’t really work like that. The many-worlds interpretation is all
about the behavior of **quantum things– like, when does this atom
decay, or what angle is this photon emitted at. Whereas human brains
are big wet sloppy macroscopic things whose behavior is mostly governed
by lots of non-quantum processes like neurotransmitters releasing
chemicals.*

*This said, tiny quantum events **can create ripples that have
big effects on non-quantum systems. One good example of this is the
Quantum Suicide “experiment” that some proponents of the Many-Worlds
Interpretation claim (I think jokingly) could actually be used to test
the MWI. The way it works is, you basically run the Schrödinger’s Cat
thought experiment on yourself– you set up an apparatus whereby an atom
has a 50% chance of decaying each second, and there’s a detector which
waits for the atom to decay. When the detector goes off, it triggers a
gun, which shoots you in the head and kills you. So all you have to do
is set up this experiment, and sit in front of it for awhile. If after
sixty seconds you find you are still alive, then the many-worlds
interpretation is true, because there is only about a one in 10 ^{18}
chance of surviving in front of the Quantum Suicide machine for a full
minute, so the only plausible explanation for your survival is that the
MWI is true and you just happen to be the one universe where the atom’s
50% chance of decay turned up “no” sixty times in a row. Now, given, in
order to do this, you had to create about 10^{18} universes where the Quantum Suicide machine *

*did kill you, or copies of you, and your one surviving consciousness doesn’t have any way of telling the people in the other 10*

^{18}universes that you survived and MWI is true. This is, of course, roughly as silly as the thing about there being a universe where all the atoms in your heart randomly decided to tunnel out of your body.*But, we can kind of think of the multi-playthrough Kaizo Mario World
video as a silly, sci-fi style demonstration of the Quantum Suicide
experiment. At each moment of the playthrough there’s a lot of
different things Mario could have done, and almost all of them lead to
horrible death. The anthropic principle, in the form of the emulator’s
save/restore feature, postselects
for the possibilities where Mario actually survives and ensures that
although a lot of possible paths have to get discarded, the camera
remains fixed on the one path where after one minute and fifty-six
seconds some observer still exists.''*