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for the most part
physics is a pretty straightforward
discipline
while the math might be complicated
physics is often about quantifying such
things as what goes up must come down
and
don't play chicken with a train
statements like those are intuitive
and pretty much everyone can get their
head around them
but over the last century or so physics
has explored some very unfamiliar realms
like what happens when objects go
incredibly quickly
or what rules govern the universe for
objects
of the size of an atom or smaller
that last one the one involving the
super small
has generated an entire field of physics
called quantum mechanics
now if you've heard anything at all
about quantum mechanics
there's a good chance you've heard about
such things about how it means that
cats are alive and dead at the same time
or that nothing is real until we see it
because we generate reality using only
our mind
and of course none of these things are
even remotely true
there are a series of outdated ideas
that were invoked
in the early years of quantum mechanics
in attempts to explain the subject
in simple ways each idea has burrowed
its way
into the subconscious of people who are
interested in science
but aren't quantum experts so what is
quantum mechanics
all about really to understand that in
any accurate detail takes a ton of study
but i thought i'd try to boil it down to
its essence in a single video
perhaps we should start with a name the
word
quantum implies a discrete quantity of
something
for instance the sahara desert can go on
seemingly forever with dune
following dune but as infinite as the
sea of sand
seems it has a quantum side the quantum
of a desert
is a single grain of sand alternatively
the ocean is majestic liquid and in
constant motion
there the quantum is a single molecule
of water
so that's what quantum means it means
that we're talking about the smallest
bit of something
the term mechanics is much easier it
just means the behavior and motion of
something
for instance celestial mechanics means
the motion of the planets
and other heavenly bodies thus quantum
mechanics
is the motion and interaction of
individual objects of a bigger
collection
by that definition the motion of an
individual car on a freeway could be
described as being governed by
quantum mechanics and of course that's
not quite what we mean
in order to experience the
counterintuitive bits of quantum
mechanics
we have to look at individual things
that are very small
generally smaller than an atom this is
because quantum theory uses the planck
constant which is a tiny number it's
this tininess that keeps the quantum
weirdness constrained
to the subatomic realm when physicists
first learn quantum mechanics as part of
our training
we are studying the behavior of
individual electrons surrounding atoms
or individual photons of light
by and large that is the realm of
academic quantum mechanics
in a subsequent video i'll talk about
how the weirdnesses of quantum mechanics
can manifest themselves on larger scales
but for now let's talk about this world
of the ultra small
where we're talking about individual
subatomic objects
okay so now i need to introduce a key
idea
called the wave function at the
subatomic level
a wave function is a mathematical
function that describes what is going on
it is called a wave function in part
because for individual photons or
electrons that aren't connected to an
atom
the wave function looks like a familiar
sine wave
there are other wave function shapes
when electrons are near a nucleus
but the big ideas aren't dependent on
the details of their shape
for simplicity you can simply think of
wave functions as
sine waves now that is the first
curiosity
the sand grain or water molecule is a
distinct and discrete object
what scientists call a particle waves
don't seem to be relevant
however in the world of the super tiny
the wave function
is the only way to explain what's going
on now exactly what the wave function
actually means is a lot trickier than
you'd think
i'll get to that in a little bit
answering that question is a big part of
the reason why
conversations about quantum mechanics
are so mind-blowing
however there are ways we can think
about the wave function
that are easier to understand if we take
the wave function and square it
which means to multiply it by itself the
squared wave function
tells you where a particle can be found
where the wave function is large there
is a large probability of finding the
particle there and where it's zero
the probability of finding the particle
there is 0.
so that's not too bad the wave function
squared gives you the probability of
where you can
find the particle the wave function is
describing
that's the first big quantum idea
now when we detect the particle say the
electron or photon
we don't find it everywhere we find it
in one location
at the moment of detection the location
of the particle is determined
scientists call this moment of detection
the collapse
of the wave function there's a reason
for that particular phrase
and it's because of a quantum weirdness
when you roll a fair die
there is a probability that each side
will come up
it's difficult to predict which side
we'll see when it starts rolling
but if we knew the cube's original
velocity and the details of the surface
of
that it's rolling on we could reliably
predict
the top face of the die in quantum
mechanics
it's different in quantum mechanics the
electron or photon
is actually in all locations allowed by
the square
of the wave function and it is at the
moment at which the particle's location
is detected
that the wave function changes from
being in many locations
to the one location where the particle
is found
the wave function collapsed from being
in many locations
to just one so those are the two
key components of quantum mechanics now
before we get into just
why quantum mechanics still seems so
mysterious
it's worth stating the things on which
most scientists agree
there is a mathematical function called
a wave function that
when you square it tells you the
locations that you can find the
subatomic particle and
with what probability the subatomic
particle is simultaneously everywhere
the wave function
says it can be kind of like the electron
or photon
being spread out and then when the
particle is detected
the wave function collapses and then we
know with a hundred percent certainty
where the subatomic particle is there's
nearly universal agreement that this
way of thinking about things gives
accurate predictions
so just what is so confusing about
quantum mechanics
well it boils down to the very simple
fact that nobody really knows what the
wave function
really is i mean we know how to use it
to make predictions
that's what's been called the shut up
and calculate school of thought
but the true nature of the wave function
is perplexing
the simple and honest fact is that
despite a century of thinking about it
nobody knows what it is there are
philosophers who argue about whether the
wave function is an
ontological or epistemological construct
and those are big words because well you
know philosophers
then there are some people who claim
that the waves are actually things that
just
push other things around they say that
the electrons are particles getting
pushed by the waves like
surfers on a gnarly curl at oahu
the technical term in quantum mechanics
for this idea is
pilot waves another school of thought
says that the wave function predicts
what can happen and when you collapse
the wave function you literally create
several universes
in which each one one of the possible
outcomes occurs
this is called the mini world's
interpretation
so which one of these ideas is right
nobody knows
it's truly a head scratcher and because
science hasn't figured it out yet
that opens up the conversation to weird
ideas like the mind body
problem of traditional philosophy
because it's been said that nothing is
real
until it's observed those things really
aren't connected to quantum mechanics at
all
this is the bottom line we know how to
use the wave function to make accurate
predictions of the subatomic world
and yet we don't have a fundamental
understanding of the wave function
and what happens when it collapses this
is a
not so secret secret of physics
and it's not for lack of trying many
people have mowed things over and
generated tons of ideas
but none of them have resulted in a
definitive conclusion
it's a dissatisfying state of affairs to
be sure but it is what it is and it's
going to take a genius
to move us forward for the time being
we'll just have to wait and see
and hopefully you now know enough to
dismiss
any explanation that invokes zombie cats
that generate reality
by looking at it so i hope that this
video was eye-opening
in that it kind of gave you a sense of
the key ideas of quantum mechanics
and hopefully you can see why books
written for the public about quantum
mechanics can
be kind of sketchy physicists can use
quantum mechanics but
don't understand this underpinnings very
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