This episode was supported by Brilliant.org
Hey Crazies.
We have a slight problem.
The world we live in. The one filled with things like people, animals, and cars
is described by something called “Classical Physics.”
It says the world is predictable.
But the tiny world of quantum particles is inherently random.
Quantum physics says the world is unpredictable.
Which leads to one question:
How can a world made of unpredictable things
be predictable?
Prepare to have your minds blown!
Before we get into particles though… let’s start with something random but familiar.
Like a penny.
Most people consider coins to be pretty random.
The reason I like them is they only have 2 states:
Heads or Tails.
Nice and simple.
If you give it a good flip, you’re not going to have any idea what state it’s in.
When I just flipped it, I got tails
but I could have just as easily gotten heads.
Let’s say I do it 10 times.
I could have end up with any number of either state.
Totally unpredictable, right?!?!
Well, maybe not.
While I could have gotten, say, 10 heads, that’s not very likely.
There’s only a 1 in 1024 chance that will happen.
The same goes for the possibility of all tails: a 1 in 1024 chance
or another way to say that: There’s a little less than a 0.1% chance.
That’s what we called a “Probability”
and that probability is much higher for mixed states,
which is exactly what we ended up with for 10 flips.
Even though each coin flip is unpredictable, we can make some predictions about a group
of flips.
Get a friend because this is going to take a while.
Flip your pennies a lot more than 10 times, say, 1000 times.
The more flips you do, the closer the group will tend toward 50/50.
For 1000 flips, that’s about 500 heads and about 500 tails.
Which is an extremely predictable result and probably
Eh? Eh? See what I did there?
probably not that surprising to most of you.
If you flipped the coin 1000 times again, it would probably happen again.
In fact, there’s only a 1 in 10.7 googol googol googol chance
you’ll get all heads or all tails, so that’s probably never going to happen.
These are things we develop instincts about.
It’s predictable.
No one ever expects to get 1000 heads in a row.
Except pennies aren’t actually random.
You’re right. You're right.
He’s right.
Real pennies are not random.
They’re just very complex.
They’re only unpredictable because there are a lot of variables to consider.
In fact, when my wife and I flipped our coin, we didn’t even get 50/50.
There was a slight bias toward tails.
Science experiments at home are the bomb, yo!!
But, here’s the thing. I’m not really talking about pennies.
Pennies are just an analogy for quantum particles.
Coins have two sides, two states.
If that coin is perfectly balanced and perfectly random,
well, then behaves exactly like a photon.
Photons have no rest mass, no electric charge, and no color charge.
Just a couple of spin orientations and that’s it.
They can spin forward, what we call counterclockwise or right-handed spin.
Or they can spin backward, what we call clockwise or left-handed spin.
Those are the only options available .
So does that mean circular-polarized light is more fundamental than linear-polarized light?
Yep. That’s exactly what this means.
The two linear orientations are quantum super-positions of left and right handed spin.
But spin is the fundamental property of the photon.
If you’ve got a light source like a light bulb, then there’s no built in preference.
You have a 50/50 chance of getting either spin state with each photon.
Just like our perfect penny.
Although, unlike a real penny, our quantum penny
I mean, photon, isn’t really in either state until we actually measure it.
It’s in one of those quantum super-positions with a 50% chance of collapsing into either
possibility when measured.
That’s what true randomness looks like.
In the penny experiment, we got to look each time to see what state the penny was in.
We can't actually see the spin of a photon,
so we have to send it through a circular polarizer
like these.
If you have a right-circular polarizer, it will pass all right-circular photons
and it will block all left-circular photons.
It’s either passed or it’s blocked.
No in-between!
Each measurement is individually random, but if you do it a bunch of times?
Like, say, the 10 million trillion photons coming out of this bulb every second?
Half of them will pass through and the other half will be blocked.
Each photon is random, but the whole group isn’t.
and this works for other photon interactions too.
We don’t know if any one photon will reflect off of a mirror or get absorbed.
But we do know about 84% of them will reflect and about 16% will get absorbed.
It’s not even limited to just photons.
It works for any quantum particles.
We call this the law of large numbers.
If you perform an experiment an enormously large number of times
the results will equal the expectation.
That’s exactly what happens with the universe.
Everything in it is made of an unimaginable number of quantum particles.
The Earth? About 10 to the 52 particles.
The human body?
About 10 to the 29 particles.
A single piece of dust?
About 1 million million million particles.
A virus?
About 100 million particles.
I think I’ve made my point.
No matter how random each individual particle is, the thing they’re a part of
will be predictable because of the sheer number of particles.
No! No! No! No! No! No!
Woooo, that was close.
As usual, if you have any questions, please ask in the comments.
Honestly, there was so much I wanted to talk about in this video,
I really had to rein myself in.
Thanks for liking and sharing this video.
Don’t forget to subscribe if you’d like to keep up with us.
And until next time, remember, it’s OK to be a little crazy.
Still feeling like you need some practice with probability?
Then check out Brilliant.org.
Brilliant is a problem solving website designed to train you to think like a scientist on
a wide variety of topics.
They even have a thorough course on probability that could really hone your skills.
There are questions about coin flips, dice rolls, and playing cards
all of which are all great analogies for quantum systems.
If you find yourself struggling, that’s OK.
Making mistakes is often the best way to learn.
Brilliant even has hints and solutions to get you into that critical frame of mind.
It’s a great way to practice without too much pressure.
Brilliant was nice enough to sponsor this video and crazy enough to offer you a discount.
The first 72 people to visit brilliant.org/ScienceAsylum will get 20% off an annual premium subscription.
It’s a really good offer if you’re interested in getting some extra practice.
The featured comment comes from Neuro Transmissions who asked:
How can the universe have no edge?
Well, there’s two possibilities:
One! The universe is infinite, so of course there’s no edge.
Two! The universe is finite, which is a little weirder.
If you traveled far enough you’d end up back where you started.
Anyway, thanks for watching!