This guy.
You've heard of him.
For many reasons perhaps
but for this video
we're going to look at his contributions to
physics
or in other words
why he won the Nobel Prize for Physics in
1967.
Now, according to the Nobel Committee,
Feynman and his colleagues won the award because,
for their fundamental work in
quantum electrodynamics
with deep ploughing consequences
for the physics of elementary particles
For the uninitiated,
Quantum Electrodynamics is
the unholy child born out of wedlock
between quantum mechanics
and special relativity
Specifically, for electrons and photons and
this...
...was Feynman's contribution.
If you've been around the pop-physics block,
you know this to be Feynman diagrams.
Diagrams that famously simplify a lot of
complicated equations that describe two electrons
bumping into each other.
It's not that hard to understand what this
diagram means,
there's a vertical time axis
and a horizontal space or position axis.
The lines represent the electrons and the
arrows denote how the electrons are moving.
The wiggly line represents the particle that
carries the electric force that repels the
two electrons.
The arrows are interesting,
because if they point in the same direction
as time, then it is _the_ particle
but if it is pointing in the opposite direction
then it is the... anti-particle?
Don't ask why.
The simplicity of Feynman Diagrams is
what makes it really useful.
This equation...
...becomes this diagram.
Pretty neat, huh?
Speaking of neat,
there's a really quick and dirty way to look
at graphs
and animate them, so to speak.
Say you've got a graph describing
the motion of a ball being thrown up.
You have distance from the ground on the y-axis
and time on the x-axis.
All you have to do, is make a rectangular
slit,
orient it like so...
and move it along the time axis.
And voila!
You see this red blob (that represents the
ball)
moving up and down.
Except it's not just moving up and down
This is scientifically accurate!
[TAKE THAT NOLAN]
Similarly, in our Feynman Diagram, the time
axis
is also upward so you have to move it along
the time axis.
Then you get this...
Two electrons moving towards each other
and one electron 'tells' the other electron
to move away.
Amazing, right?
NO!
Because this is wrong!
It's wrong for a lot of reasons, and explaining
these reasons require explaining quantum electrodynamics
which I'm not sufficiently qualified to do...
...so I'll explain the one big reason why
it's wrong.
For starters while it _looks_ like one, a
Feynman Diagram is not a graph.
Because you could take this diagram,
stretch these lines, and none of the underlying
math would change.
But the animation is completely different.
The truth is, even if your quick and dirty
animation does not agree
all of these diagrams are identical.
This is because the actual lines are not the
important
part of a Feynman diagram.
Sure, they are for "bookkeeping" reasons.
All that matters (mathematically, at least)
is
how many of what kind of lines go into and
come out of each vertex.
But the truth is a Feynman diagram is actually...
...a graph.
And when I say graph,
I mean one that looks like this.
You've probably heard of,
Euler's Konigsberg bridges, the puzzle where
you have a bunch of islands with bridges connecting
them.
And you need to walk through all the bridges
such that
you would cross each bridge only once.
You can simplify this problem by removing
all
the unnecessary details, and distilling it
to the most
important information.
Here, the bridges can be straight, bendy and
the
vertices themselves can be wherever.
But it doesn't really affect the final answer.
Because the information regarding the vertices
are the only things that matter.
Same thing
over here.
However, the idea of using graph to simplify
or keep track of the math is not a new idea
in physics.
If you've done physics in high school then
you've drawn or at least seen circuit diagrams.
Take this circuit for example.
You could draw it this way,
or this way,
or this way.
It doesn't matter
all the values that _you_ care about,
potential difference, current, resistances
they remain unchanged
despite how you prefer to represent the real
circuit.
That's because this is only notationally showing
you
all the complicated physics hiding behind
these junctions
and resistors and whatnot.
Think about it.
If current is electrons moving through the
wires
(it isn't)
and these wires suddenly bend then imagine
all
kinds of complicated bumping and whatnot must
happen
that you need to care about.
Well, you don't have to.
Because most of the time,
for the values that you care about,
how you bend the wire doesn't really matter.
Feynman diagrams aren't some direct representation
of the Universe.
Like your graph of a ball being thrown.
It's like a circuit diagram.
Except instead of electrons moving in wires
you have electrons bumping against each other.
Kind of.
Not really.
It's complicated.
But these diagrams were extremely important
because while it did not represent nature
at least not in the way we expect diagrams
to...
...they revealed something deeper.
But that is a video for another day.
Of course, you wouldn't know when this video
is coming out
not because of some quantum anomaly.
But because my upload schedule is crazy.
So if you want to know more, why not
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DFLVNWRKLSNTS
Anyway, thanks for watching.
