It's 1887
Physics is almost complete
We almost know enough to see the clockwork of the universe
Only one last great question remains
The question of the aether wind
The question of the way that light travels
*Intro Music*
Two men are setting up a series of mirrors deep in a stone basement of a dorm in Case Western
Their strange apparatus sits on a monumental block of sandstone resting on top of a pool of mercury
They are about to perform one of the most important experiments of all time
The Michelson-Morley Experiments
They are looking for proof of the great invisible fluid
through which light flows
See, this was the central mystery stuck in the craw of physics
By the end of the 19th century,
this problem of how light moves
was becoming impossible to ignore
Because at the time light was largely assumed to be a wave,
just like sound, or waves of water
But the thing about those types of waves is that they have to travel through stuff.
A wave is just a motion,
and to have motion you have to have something being moved
Waves of water are simply motion propagated through the molecules of water
Waves of sound work the same way,
travelling by rippling through the air
But light travels through a vacuum,
and that's a problem
Experiment after experiment had been done where a complete vacuum was created
Where the air and other matter was pumped out of a container
and then waves were pushed through
Sound died.
The wave couldn't travel through nothing
But light.
Light travelled across the void
How did it do that?
The theory at the time was that there was some giant, invisible,
incompressible fluid that permeated all things
They called it the aether
It filled the dark between the stars,
and subsumed the void between worlds
And it was through this fluid
that waves of light moved.
The only problem was that,
well as physics got more and more advanced
We started to have to assign wilder
and wilder properties to this aether
It had to be fluid, but
totally rigid also
And it had to be incompressible, but also totally massless
It had to be utterly transparent, and yet also be a medium for light
Still, there was no better explanation
So, even as serious questions were raised about it,
the idea of the aether served as the working theorem for most of the scientific world.
But as the 19th century began to draw to a close
People were finally starting to figure out ways to build a contraption sensitive enough to test for the aether
Those people were Michelson and Morley
They had created a device so precise
that it should be able to detect the effect of speed of the earth on the speed of light
What does this mean?
Well, imagine that you've got two sets of people playing catch
One set of people are on a moving train
One set of people are on the ground next to the train
They both throw the ball at the same speed
But, relative to the people on the ground the ball thrown on the train either moves much faster or much slower
Depending on whether it was thrown with or against the motion of the train
By this point in history,
we had already worked out a speed for light against the fixed reference of the aether
Which in our previous analogy is basically like the people on the ground throwing the ball
What Michelson and Morely set out to do was work out the case for the people on the train
How did being on the planet earth,
hurtling through space affect the speed of light?
Unfortunately, the earth doesn't move very fast compared to the speed of light
Which made this a pretty challenging thing to test
Instead of throwing a ball on top of a train
This was sort of like
trying to measure the effect of throwing a ball from on top of the worlds
biggest slowest sloth
Hence them burying the experiment underground
resting it on mercury,
and placing limestone on that mercury
They would need to measure something so small
they couldn't have any wayward tremors messing up their results
Even as they adjusted their experiment and spun it around
But, and this is one of the triumphs of experimental physics
They did it!
Their experiment was so exact,
that it was hard to dispute that it should be able to pick up the affects of the aether wind
Only....
It didn't
There was none.
They got no effect at all.
Light moved at the same speed, no matter how they turned their device,
no matter when they took their readings
It was astonishing.
Countless times, people would refine this experiment hoping for a different result
And countless times it would just confirm
There was no aether.
Aether was not a thing
This threw science into chaos.
What could the explanation possibly be?
How could we make sense of this?
Well, in 1905
a young man named Einstein would propose a solution
Inspired by the Michelson-Morley experiments,
he would offer us special relativity
Which is called relativity because it does away with the concept of an absolute
frame of reference in physics
By which I mean "the aether"
This lead to a number of other conclusions
Such as, proposing that the speed of light in a vacuum was constant
That it wasn't actually affected by frame of reference.
And that we would have to see space and time as one contiguous thing
Rather than two completely separate ideas
But it's called special relativity for a reason
This paper pointed to something else
Something even stranger than the idea that space and time were one
And that was the idea that space-time might be curved
And that the curvature of space-time
might be affected by gravity
The special version of relativity only dealt with physics where gravitational distortion wasn't really present
But in 1915 Einstein would give the world the far more complex theory
of General Relativity
One that was applicable even where stars or black holes bent and warped the fabric of space-time
And it's that curvature of space-time, and the way that those curves get warped and changed
that we are interested in here, in this series
Because one of the most frightening things about accepting this new way of thinking
Of accepting relativity
Is that it also means that we have to accept
that we live in a non-Euclidean universe
Postulate 5 really isn't true in any higher sense
It doesn't represent the world as it actually is
In fact the strange geometries of Bolyai, Lobachevsky, and Riemann
were much closer to the truth
They're a far more accurate representation of the universe as we now understand it
And it is those geometries that we now use for much of modern physics
So the geometry that we built
all of mathematics on
That we built all of our calculus and our Cartesian coordinate system out of
That gave us Newtonian physics,
in the end,
it wasn't in any way real
It was and is,
simply a useful tool created by humankind
It was a way of thinking and a way of reasoning that turned out to be profoundly valuable
But that only mimicked the real world on a very terrestrial scale
When we look at the vastly large, or the imperceptibly small,
we find that Euclidean geometry only offers us an approximation
A short hand for the world as it really is
Now, does this mean that Riemann was right and Euclid was wrong?
Well, no. It just means that our knowledge is always evolving
It means that it might be the wrong idea to think of mathematics as
true or not true
Rather, it might be more useful to simply ask:
Is it well reasoned?
This frees us from the trap of having to prove the unproveable
And allows us to find reason in the unreasonable
Because, if the history of non-Euclidean geometry teaches us one thing it's that:
There is always more out there to learn and discover.
So welcome to a world where straight lines might not exist
And where parallels may not function the way you thought they functioned
It's not a frightening place really
You've actually lived there all your life
And when you think about it, it's pretty exciting, because there are limitless mysteries for us to unravel
And it is at this point I would like to announce a surprise follow up to this series
Sponsored by one of you who wanted to see us go even further
And explore Quantum Mechanics and Quantum Computing
We're going to have a multi-part series on quantum computing coming to this channel soon
And if you thought this math was wild... just you wait!
We will see you then
*Outro Music*