system
Given the following post, respond as if you're commenting on Reddit:
human
Is space continuous? And if is it then why do we have Planck Length?

I have always wondered if space can be quantized or not. We have always been told that space is continuous. But if that is the case then why does Planck Length exist?
gpt
It's a common misconception that the Planck length is the "smallest possible distance" or any similar property related to the quantization of space. The physical significance of the Planck length is still a matter of theoretical study and it's not excluded that it has some significance, but this is as of yet unknown.

Anyway, where then does this Planck length come from and why is it relevant? Well, the Planck length is part of a system of units called Planck units (or natural units). You're probably familiar with different unit systems already, since the most famous example is the distinction between the imperial system used in the US (with miles, feet, pounds, etc...) and the metric/SI system used pretty much everywhere else (with meters, grams, liters, etc...). Both systems express the same things, just rescaled. You rescale both measurements, but also some constants of nature. For example, the speed of light has a different value in km per hour than it does in miles per hour.

Planck units are another way to rescale things like distance, mass, etc... The scale is chosen in such a way that some important natural constants (including the speed of light and gravitational constant) are exactly 1. This is very convenient for a lot of physics, since it makes the equations much simpler. An additional argument in favour of this system is that it is more "natural" as the scale is based directly on natural constants, rather than the somewhat arbitrary definitions of things like meter, gram, foot and pound.

The Planck length is simply the unit of length in this system. Instead of meters or feet, distances are measured in Planck lengths when using Planck/natural units.

Finally, there is no evidence either way regarding the quantization of space (or time). There are various hypotheses, but the question of whether space is discrete or continuous is still open. But if it turns out that space is indeed discrete, then it isn't necessarily linked to the Planck length. Though it might. Who knows?