What Can Frogs See That We Can't?

[Applause] Imagine you're in a space suit drifting away from the Sun. Rather than dwell on how you ended up here, open the P bay doors.

"How?"

"I'm sorry, Derek, I'm afraid I can't do that."

You decide to collect data for your Google science fair project. You notice that as you move further away from the Sun, the intensity of its light decreases. And this isn't due to the light dying away or being absorbed; it's simply due to the light energy being spread over more space.

Consider the light emitted by the Sun in a single second. It's enough energy to power the whole world for a million years, or to heat up 3,200 billion billion hot pockets. As all that light travels out through space, you can think of it spreading out over the surface of a growing sphere. Since the surface area of a sphere is 4πr², the intensity of light is inversely proportional to the square of the distance from the Sun.

So when you're twice as far away as where you started, the light will be a quarter as bright. This is known as the inverse square law. As you continue past Pluto, formerly known as a planet, the light becomes dimmer and dimmer until it is so faint that you can't even see the Sun. Well, that's not terribly surprising.

But what if you had really sensitive eyes, like the eyes of a frog? Well then, as you move further away from the Sun by the inverse square law, you would expect to see the light decreasing in brightness but never fading out completely. But that is not what you see. At some point, the Sun begins to flicker, so you see flashes of light separated by complete darkness.

And what's weirder: as you continue to move further away, the flashes would not decrease in brightness; instead, they merely become less frequent. If you took the average of the flashes in darkness, you would find it smoothly follows the curve of the inverse square law. But the light itself comes in lumps; they are indivisible, and so they can't get any less intense, only more spread out.

This dramatically demonstrates that light is quantized, meaning it always comes in multiples of a smallest quantity called a quantum. Is that incredible?

You're making the slit narrower, and yet the spot on the wall is getting wider. The narrower you make it, the wider that spot on the wall becomes. To understand this, we have to look at Heisenberg's uncertainty principle.

"Can you think of some other things that are quantized? Please put them in the comments and say what a single quantum of that thing is."

"I'm sorry, Derek, I'm afraid I can't do that."

For example, cash money is quantized, and a quantum of money is a penny. Unless you live in Australia, in which case we've got rid of pennies, so the smallest division is 5 cents. But now, a lot of machines won't even take 5 cents, so we should probably get rid of that too.

Okay, what other things can you think of?