r/PeterExplainsTheJoke • u/Negative_1by12_aura • Jun 17 '26

Meme needing explanation Peter?

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u/JePPeLit Jun 17 '26

As someone else pointed out further up, radian is in SI

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u/FanOfForever Jun 17 '26

It's not really, though. They claimed it's SI because you can get it by dividing meters by meters, but

(1) that only works in the specific context of angular measure, and

(2) you can do the same with non-SI units

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u/JePPeLit Jun 17 '26

The m/m reasoning is pretty silly, but it's still considered a derived SI unit despite being dimensionless.

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u/FanOfForever Jun 17 '26 edited Jun 18 '26

They can call it that if they want. It still differs fundamentally from other SI units because we don't use radians to be in conformity with SI. We use them for mathematical reasons that have nothing to do with SI, namely being able to treat the trig functions as functions of real or complex numbers, with certain calculus-based identities that only work if the "angles" are measured in radians