I am a PhD students in physics, and my father is a Math researcher. One time, I asked him
"Doesn't the fact that we can use math to explain things that happen in front of us, tell us that math is not a human invention but rather a discovery?"
My father said that in his opinion, no - we were just able to find a very useful language to describe physical phenomena.
But then, I learned about Fraunhoffer diffraction, which tells us that if a light wave passes through a slit of a given shape, on a screen really far away from the slit we actually see the Fourier transform of the slit! I was mind blown.
I then went to my father and told him, "look! nature does Fourier transform, so Fourier transform cannot be man made!". He disagreed, and stated the same thing he told me before.
Does my statement make sense? Can we say, based on Fraunhoffer diffraction, that Fourier transform is an act of nature rather than a human invention?