Planck's constant is a thing we all hear about in high school physics classes, but no one really talks about why it's cool.
Textbooks will talk dryly about "blah blah theories of quantum gravity" and teachers will repeat that "something something a photon's energy to its frequency. And sure, these things are true. But when people say stuff like that, they're really burying the lede.
Planck's constant is about the limits of what's physically possible in the Universe!
A Planck length is a unit of length which can be derived from Planck's constant. It is the smallest length which is possible in our Universe.
And it's unimaginably tiny. A hundredth of a billionth of a billionth of the size of a proton. But this is significant. Anything smaller than a Planck length cannot exist. It would not make physical sense.
Planck lengths are basically Universe pixels.
A Planck time is the time taken for light to travel one Planck length. As Einstein proved, it's impossible for anything to travel faster than light. That's the upper speed limit for anything travelling through the spacetime fabric of our Universe.
So the Planck time is arguably the smallest unit of time which can possibly exist and still have any meaning.
@InvaderXan oh shit, like the sampling rate of the universe
@InvaderXan wait does that mean there's a Planck frequency too?
@professor_stoke Yes, there would be a highest possible frequency which would make any physical sense in the Universe. I don't think I've heard it called a Planck frequency before, but that's totally what it is.