system
Given the following post, respond as if you're commenting on Reddit:
human
Why does plank length "exist?" why is there a lower bound to the amount of distance that can be measured? why can't we measure a shorter distance?
gpt
What you write is not accurate, though it is probably something you have often heard.

We do not know if the Planck length is the minimal distance, or even if there *is* a minimal distance.

What we do know is this: We have a classical (i.e., non-quantum) theory of gravity, called general relativity.  We do not know how to merge quantum mechanics and general relativity (things like string theory and M-theory and loop quantum gravity are attempts to do just that).  However, we can ask what is the distance at which using general relativity without quantum mechanics would no longer make sense; that is what the Planck length is.

So above the Planck length, general relativity is okay.  At the Planck length and below, we'd need a theory that combines general relativity and quantum mechanics into a quantum theory of gravity.  Whether the quantum theory of gravity would imply the existence of a minimal length is not yet known.