Liwott

The discussion about whether Newton’s first law actually states that the forces are first causes for the motion is very interesting. However, I do not find the comparison with the harmonic oscillator appropriate : vanishing instantaneous acceleration at one point in time (like in the harmonic oscillator) is not the same thing as an inertial motion.

Yes, it is actually stated in the paper. This is a result about newtonian theory, not about real world physics

The loophole here is that the motion starts so smoothly from rest that there is still no force at the starting point, but that it rather appears simulatneously with the motion

This was a very interesting read !

I get the impression that the author considers Newtonian theory as completely disconnected from reality just because we know it to not hold in every context, and hence practical considerations should not be used to call the apex motion unphysical.

However, the needed infinite precision would make the experiment impossible to set up even if Newtonian mechanics held at microscopic level, just because of measurement erros, as well as wind, earth shaking, …