system
Given the following post, respond as if you're commenting on Reddit:
human
Is there a smallest unit of time, in the same way the planck length is the smallest possible length, and a photon is the smallest possible amount of energy?

Do any of the current models and of the universe explore this? And what is the explanation of why we have this minimum quanta of energy, length etc. ?
gpt
The Planck length is not the smallest possible length. It's the characteristic length scale at which gravitational effects are comparable to quantum effects, where our current understanding stops making sense. Maybe there will be meaningful lengths all the way down to zero, but we can't say for sure.

The Planck time is the Planck length divided by *c*, the speed of light, it served a similar purpose to the Planck length.

The photon is not "the smallest possible amount of energy". Energy can be arbitrarily small; a photon has an energy *E* = *h f* where *h* is Planck's constant and *f* is the frequency, so a sufficiently low frequency photon would have an arbitrarily small energy. 

It's better to think of the photon as being a smallest possible wave that can exist in the electromagnetic field, like a tiny little ripple. The best understanding we have of the universe is called quantum field theory, the key idea is that *everything* (forces and matter) is made up of *fields*, and these obey the laws of quantum mechanics. What we normally call particles are *quanta* of these fields, which means the smallest possible ripples that can exist.

As to *why* we have this quantization, that's really a philosophical question and it depends what type of answer you want; it's basically just the way the universe is.