What Can Frogs See That We Can’t?

What would you see if you were drifting through space, looking back at the sun? Well its light intensity would decrease as the inverse square of distance from the sun. And you would imagine the intensity would decrease smoothly, asymptotically approaching zero.

But this is not what happens.

If you had sensitive enough eyes, like frogs’ eyes, you would find that at some point the sun would start to flicker. You would see flashes of light separated by complete darkness. And as you drift further from the sun, what’s strange is that these flashes do not decrease in brightness, but they do become less frequent. That’s because light comes in lumps, called quanta or photons, which are indivisible. So if you try to spread light out very thinly, you reach a point where there are only single bits of light reaching an observer’s eye at any given time.

I should acknowledge the book “The Fabric of Reality” by David Deutsch, which contains a similar story about a frog and a torch. It inspired me to make this film. Thanks also to MinutePhysics for reviewing earlier drafts and suggesting I make it more ridiculous.

by Veritasium.

Clarifications on frogs and single photons

This is a good article for starters:
http://physicsworld.com/cws/article/news/2012/sep/13/frog-photoreceptor-counts-photons

by Veritasium.