Quantum Computing – The Foundation of Everything – Extra History – #1
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Quantum Computing – The Foundation of Everything – Extra History – #1

The year is 1927 29 people gather in Brussels
to discuss physics 17 of those people
will eventually win a Nobel Prize and for a few short days in the middle of Leopold Park They will wrestle
with the smallest question or perhaps the biggest one to ever face mankind The question at the foundation
of everything. [intro song] For those few days those 29 physicists wrestled
with the question of the quantum determinancy and whether our world
at the minutest level operates
as a fixed system or merely as a group
of probabilities Their question stemmed from one
of the oldest problems in modern physics, the problem of light For nearly three centuries since Newton wrote
his famous treatise on optics Physicists had debated
whether light was a particle or a wave in 1803 this argument was thought
to be put to rest by one of the most beautiful
and simple experiments ever created the double slit experiment Okay, think of two buoys
bobbing up and down in the water as the waves spreading out
from these buoys hit each other and overlap They interfere
with each other if the peak of one wave hits the peak of another they’ll amplify
and become a bigger wave Same with the troughs but if a peak of one wave
hits the trough of the other they’ll just flatten out they’ll combined
back down to nothing. A man named
Thomas Young said, Let’s take that principle
and apply it to light And so he did
the simplest thing imaginable he took
a monochromatic light, to make sure that all the light
had the same wavelength and he shone it on a partition
with two small slits cut into it If light acted
like a particle he should simply see two columns
of light on the wall on the other side But if light was a wave then the waves coming
through each of the slits should interfere
with each other amplifying and cancelling
each other out in places And he would instead see a weird pattern
of bright and dark lines as a result And as he expected he did indeed see
that funky pattern and that was that. The particle theory of light
was done and dusted he’d solved
the dang thing Now everyone could finally move on
to talking about just how smart he was But then physicists
in other labs found something strange
in their own experiments They found that when light strikes
a material it can force electrons
to spew out of it this wasn’t that startling but the way it happened
was all wrong and definitely not how it should have happened if light was the continuous wave they’d believed it to be Then in 1900 a man
named Max Planck came up
with an equation that fit it made sense
of what was happening But as Planck himself
would later say it was an act
of desperation It went against everything
he thought he knew The only way he could get
all of the math to work was by treating energy as something that could
only be absorbed or released in discrete units How could this be?
He thought. How could energy
not be continuous? How could it not be a flow? He had no idea, but then this fellow named Einstein took
Planck’s act of desperation and ran with it He declared that light itself
was quantized That
in many ways we can think of it as a particle
of zero mass always moving at well,
the speed of light And it is for this theory, not for special
or general relativity, that Einstein was awarded
his Nobel Prize Because this concept,
which we now call the photon solved a number
of lingering issues with how light interacted
with the world But the photon brings us right back to the problem
of Thomas Young’s double-slit experiment Because if light has
both the properties of a wave and a particle What happens if you fire
those particles through the slits one at a time? Well, here is where this becomes
the most astonishing and humble experiment ever devised Because if you shoot one photon at the slits
and detect where it hits on the other side You’ll find that it impacts some arbitrary point just the way
you think it should And if you fire
a second photon through, you’ll find that it too shows up at some
other arbitrary point on the other side But if you do this enough times, you’ll eventually see
the same interference pattern build up that we got back in
Thomas’s original experiments. That is madness each individual photon, which should
be completely independent of the rest shows up at some seemingly
random point on your wall And exactly where
they show up will be different each time
you run the experiments And! Knowing where the previous photon appeared in
no way allows you to predict where the next one
will show up yet when taken as a group it’s as if they’re affected
by how they Should interfere
with each other This feels impossible and yet it is experimental fact And the reason for this phenomenon
is one of the most hotly debated mysteries in physics Because the only way to conceptualize this is that each photon passes
through both slits as a wave, interferes with itself and then resolves down to a photon
when it actually hits the wall What is going on here? What is this? No, no, no, this is magic. This is magic ! [sine wave] [meow] No, you’re right Zoe. I should calm down because
we are not done yet because here is where it gets really freaky Remember how when Thomas
was first doing his experiment? We said that if light
were really a particle we should just see two columns
of light on the other side of his double slit paper? Well, if you put a detector on the slits, so that you can determine which slit
the photon you fired passes through That is exactly what you get. That’s all you have to do You don’t have to change the experiment
in any way or interfere directly with the photon You simply have to measure
which slit the photon passes through. Why does it do this? Because a photon is a particle and a wave but it can’t be both simultaneously The mere act of measuring
which path the photon took Forces it to resolve the wave-like nature
of the photon into a particle And this may be the hardest thing to wrap
your head around in all of quantum physics because the most common
way to view this is that the photon
when acting like a wave isn’t a real wave at all but rather a wave
of possibilities That wave represents
where the photon could be but not
where it is It’s only when something acts
to detect the photon whether it be
your measuring device or the wall on the opposite side of your double slit experiment That the photon is forced to, for lack of a better term, decide on where it will actually be and in doing so becomes a particle More unsettling still, is the fact that
these waves of possibility interfere with each other
just like normal waves The interference pattern
we see from firing particles one at a time through the double slit experiment is caused by peaks
and troughs of possibility cancelling each other out When you fire that photon and the wave
of possibility hits your double slit paper It is funneled through
as two possibility waves Just in the way that any regular physical wave
would be and just like
those regular waves waves of possibility interfere with each other Essentially making it so there are places where it is
more or less likely for a photon to land when detected Thus when you fire a lot of photons one at a time through
your double slit experiment The bands you see are simply
the high probability lines playing out But if you think
we’re done getting weird, think again, we’re only on episode one so join us next time as we get serious about
this idea that energy only comes in discrete packets and begin our journey
on what this means for the future
of quantum computing. We’ll see you next time or will we just perceive you next time because
would that mean we’d have to watch you watching us to know the oh boy [outro song]


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