From what I've gathered, Planck length is the smallest measurable length, though we do not know whether it is the smallest length physically possible. The Planck temperature is called the theoretically highest temperature, meaning this theory assumes that the Planck length is the smallest possible length. Given that it is (presumably) a theory, that makes me wonder what reasons we have to think the Planck length is the smallest length. I get speculating that it is the smallest length, given that it is the smallest measurable length; but calling it a theory means there's actually some reasons, or even evidence. So, what are those reasons?
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Or are there only amateurs who think so?
Bingo :) The Planck units don’t give sharp limits on the existence of quantities like length, time, etc (or rather, there’s no reason to think that they do). Instead, they provide a scale at which a more complete theory of fundamental physics (which incorporates quantum gravity) will be relevant.
For example, when the mass of a black hole is equal to the Planck mass, then its Compton wavelength will be on the order of its Schwarzschild radius (which is also the order of the Planck length). The weird bits of quantum mechanics and gravity will intersect, and we just don’t know what happens in that scenario.
Albatross
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I'ts only a reference that came from the universal constants, as far as I know there is no theoretical limit
