Hey Crazies.
It’s time for photons!
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I imagine a lot of you feel like you know what a photon is.
It’s just a packet of energy or whatever.
But you know what happens when you assume.
You make a mistake
sometimes.
Calling a photon a “packet of energy” isn’t wrong.
It’s just not very useful because everything is a packet of energy.
I have something in this box.
Can you guess what it is?
No?
Here’s a hint: It’s a collection of atoms.
Did that help?
Probably not.
Surprise!
It’s a squirrel!
My point is there’s a better way to describe photons.
Yes, it’s a packet of energy, but it’s the details about that energy that make it
a photon.
Hmmmm How should we tackle this?
I think the top-down approach is going to work best.
Reductionism
Basically, it’s the idea of starting with
something normal-sized and then breaking it up until you find the smallest pieces.
What you might call its elementary pieces.
Honestly, this is how we came up with quantum physics in the first place, so it seems like
a great place to start.
Elementary particles are like bite-sized pieces of something ordinary.
Kind of like how this video series comes in bite-sized pieces of quantum physics.
It’s almost like I planned this or something.
Anyway, a photon is the smallest piece of light.
Like you might find coming out of a flashlight like this.
Can I have the flashlight back now?
Do you remember what happened the last time I gave a flashlight to a clone?
I wonder what this button does.
Ah! Turn it off! Turn it off!
Behave!
What if I promise to behave?
Alright, we’ll try this one more time.
Ok, back to business!!
A beam of light is one of those normal-sized things I was talking about earlier.
It’s something we can see with our eyes.
Something the size of us.
But if we’re going to understand it like a quantum physicist.
Physicist?
Physicist.
We need to break that beam into smaller and smaller parts until we find something we can’t
break anymore.
Light beams are giant collections of many electromagnetic waves.
If we focus on one of those waves, we can see a repeating pattern.
One cycle of that pattern looks like this.
That’s one wavelength of that wave.
There really isn’t anything smaller than this for a wave.
Is that a photon then?
No.
We have a slight problem.
Light waves can be anywhere on the EM spectrum
including the low frequency end like radio waves.
A single radio wavelength can be as large as a small city.
I find it hard to believe a single photon could ever be that big.
Maybe we’re looking at this all wrong.
I seem to remember saying something important earlier.
Yes, it’s a packet of energy, but it’s the details about that energy that make it
a photon.
Right, this isn’t about the space something takes up.
Elementary particles like photons don’t really have size anyway.
This is about energy.
It’s the energy we have to break into pieces.
Let’s start with a standard incandescent light bulb.
This one is 60 watts.
That means it transforms 60 joules of electrical energy into heat and light every second.
Incandescent bulbs are terribly inefficient though
so only about 10% of that actually becomes light.
When you turn it on, 6 joules of light leaves the bulb every second
but that spreads out in all possible directions.
Eventually we’re going to see gaps between those pieces.
Those tiny pieces of light energy are called photons,
but the amount of energy they have is very small.
You can calculate it using E = h f.
The “h” is Planck’s constant, which is extremely small.
The "f" is frequency tells you what type of light it is
and, in the visible range, it tells you color.
So the energy of a photon is a constant times its color.
For that 60 watt light bulb, that’s 10 million trillion photons/second.
Huuuuu, that’s a lot of photons.
Because individual photons don’t have that much energy,
you have to get really far away to notice the gaps between them.
Let’s say you move away from the Sun at an unimaginable speed
and somehow manage to avoid any of Einstein’s relativity.
Eventually, way out in space you start to notice the Sun’s light flicker.
What you’re seeing are individual photons.
Actually, the human optic nerve doesn’t send a signal to the brain
unless at least 9 photons arrive within 100 milliseconds.
You have to ruin everything, don’t you?
I don’t ruining things.
I make them more accurate.
Alright, so humans can’t see individual photons, but that actually explains a few
things.
If you move away from the Sun like we did earlier
you can’t see the flicker of the photons, so at about 750 light years
the Sun’s light will just fade away into the blackness of space.
That’s why the night sky is mostly black lit by just a few nearby stars.
The rest of the photons are just too infrequent for us to see.
So, what the heck is photon?
Right! Right!
Stay focused, Nick!
There are a lot of little packets of energy floating around the universe.
What makes some of them photons is all in the details, my dear crazies.
Photons have a specific set of properties that make them photons.
A charge of zero, a spin of 1 with two possible orientations,
and, lastly, a rest mass of zero, which makes many things about photons possible.
Their speed of almost 300 million meters per second.
Their energy being proportional to their momentum
and their inability to experience time or space.
Any little packet of energy with those properties is, by definition, a photon.
So, got any questions?
Please ask in the comments.
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And, from one packet-of-energy to another, remember, it’s ok to be a little crazy.
Several people asked about the Red/Blue kind of 3D glasses.
One.
They’re not Red and Blue.
They’re Red and Cyan. because those are opposite colors.
Together, they make white.
Two. They use color filters to block one of the images instead of using polarizers
so they don’t really work on color images only black & white ones.
Anyway, crazies, thanks for watching!