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It is usually said that Planck units have no scientific ground, yet they are useful indeed because many laws collapse, make no more sense at, say, Plancks length or time.

Can you mention a couple of laws that support this opinion and what makes no sense at a length less then $1.6 \times 10^{-35}$ m?

Qmechanic
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user157860
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1 Answers1

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We have, at yet, no specific evidence that any of our current laws of physics collapse at the Planck scale. However, we do expect that at or near the Planck scale quantum gravitational effects will become important. We don’t know which ones will break down nor do we know in what way they will fail.

None of this has anything to do with “justifying” Planck units. Units are just defined, their definitions do not need justification. Planck units are simply defined so as to make many constants equal to 1. No further justification is needed.

Dale
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  • How is your answer related to the question? units are the ones in the system considered ;KS, CGS etc. Most of all, why should the unit of length be the square root of anything? why c^3 and not c^2 or c^4 and so on? Is there any method in it all? – Why c^3 and not c^2 or c^4? if you combine the units in a different way you get different unit of length, why is 1.6x10^-35 more convenient then 1.6x10-36m? – user157860 Mar 17 '22 at 09:51
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    @user157860 the answer directly answers the question you asked. “Units don’t have or need any justification” directly answers the question in the title. And “we don’t know” answers the question in the body. If you wanted to know about $c^3$ and square roots then you should have asked that in the question. Nobody here is a mind-reader. Please ask a new question that describes what you actually want to know. Link to this question and explain in the new question how it differs from this one. – Dale Mar 17 '22 at 11:05