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Parallel Worlds Probably Exist. Here’s Why
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Norton 360 classical mechanics is great
if you know the state of a system say
the position and velocity of a particle
then you can use an equation Newton's
second law to calculate what that
particle will do in the future in
quantum mechanics if you know the
quantum state of a particle that is its
wave function you can use the
Schrodinger equation to calculate what
that particle will do in the future
usually it spreads out over time as it
is doing here note to make this
animation we really solved the
Schrodinger equation so there's a
beautiful symmetry here if you know the
initial state you can use an equation to
evolve that state smoothly and
continuously into the future the problem
is in quantum mechanics we never
actually observe the wave function like
this instead when we measure it we find
the particle at a single point in space
so how are we to reconcile the
spread-out wavefunction evolving
smoothly under the Schrodinger equation
with this point like particle detection
now I think it's understandable that
when the founders of quantum theory
approached this problem they considered
the measurement more real than the
wavefunction after all the measurement
was something we had actually observed
and it matches our experience of a world
of matter particles it was harder to say
what the wavefunction was exactly
Schrodinger formulated his wave equation
because scientists notably debroglie
suspected that matter has wave-like
properties but it took a third physicist
Max Born to propose how we should
interpret the wave function at each
point in space the wave function has a
complex amplitude essentially just a
real number plus an imaginary number Max
Born suggested if you take that
amplitude and square it you get the
probability of finding the particle
there the fact that you have to square
the amplitude actually appears as a last
minute footnote in boran's paper but
that is how probability was introduced
into the core of our picture of reality
that's a pretty big philosophical leap I
mean no longer is the universe
deterministic
this made a lot of scientists especially
Einstein uncomfortable but the born rule
as it is now called remains at the heart
of quantum mechanics because it is
spectacularly successful at predicting
the outcomes of experiments so the way
quantum mechanics came to be understood
and the way I learned it is that there
are two sets of rules when you're not
looking the wave function simply evolves
according to the Schrodinger equation
but when you are looking when you make a
measurement the wavefunction collapses
suddenly and irreversibly and the
probability of measuring any particular
outcome is given by the amplitude of the
wave function associated with that
outcome squared now Schrodinger himself
hated this formulation which is actually
why he invented the famous Schrodinger's
cat thought experiment put a cat in a
box with a radioactive atom add a
radiation detector that triggers the
release of poisonous cyanide gas now
although it was only meant as a thought
experiment Schrodinger helpfully notes
this device must be secured against
direct interference by the cat anyway
the whole point of the experiment is to
magnify the state of the atom up to the
state of something macroscopic and
tangible he could have picked anything
it didn't have to be alive but
Schrodinger selected a cat if the atom
decays the detector detects radiation
releases the poison and the cat dies if
the atom doesn't decay the detector
doesn't detect radiation poison is not
released and the cat remains alive since
the state of the cat and detector
apparatus are directly tied to the state
of the atom we say they are entangled
where things get weird is that according
to quantum mechanics the state of the
atom does not have to be either decayed
or not decayed generally it's in a
superposition of both decayed and not
decayed at the same time assuming no
measurements have been made this
superposition state of the atom gets
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