« on: 09/01/2019 21:28:34 »
Einstein did not posit a train moving at light speed.
Wrong. Einstein noted that if his train moved faster, he would see the clock tower clock move more slowly and if it went at the speed of light, the clock would appear to slow to a halt.
Which is why I said 'even in principle'. One can communicate faster than light with such a rope. I can build an infinite energy engine with such material.
Wrong. If you learn how to set up relativistic thought experiments you'll learn that the only physical traits you are allowed to idealize are those that do not alter the outcome of the experiment. As I explained, the rope and mirror are metaphors to show the point of reflection of the light beam.
The answer is very dependent on how the light is observed down there, but you're not observing it at all.
Wrong. There needn't be an observer at the mirror. If you want to set up a different experiment and place an observer at the mirror, that's fine. I didn't do that because this setup is simpler and reveals the result I was trying to find.
It isn't infinite anything if the light doesn't reach the event horizon. If it does, nothing is reflected, so there is no light observed at all coming back, shifted or not.
This thought experiment uses what is called "reductio ad absurdum". I begin by assuming that a Schwarzschild black hole is possible and that it is possible for matter to travel to the event horizon. Then I show that this is impossible because it would require infinite time. Because anything that cannot happen in finite time is impossible, I conclude Einstein was correct that black hole event horizons are impossible.
You say the mirror motion is fixed and finite, and you measure it by counting winch revolutions of your hypothetical unstretchable rope. I can allow that I think, but I don't think you ever reach the black hole using such coordinates.
Correct. Nothing moving at a finite speed can travel to an event horizon in finite time. Not light and certainly not anything moving slower than light.
You have no observer specified, so I cannot accept this. Our observer is on the platform and any relativistic shift is undone by the return trip.
I don't really care if you understand it or can accept it. It is a fact of causality that the light beam cannot have an infinite sequence of light waves until after the source has generated the light waves. If you aren't able to apply conservation of energy (gravitational blueshift/redshift) and causality to solve a physics problem, I can't help you.