Day 10: Backwards Clock of the Isartor

Isartor's Backwards Clock

Since my visit to the Einstein Museum in Bern, the concept of time has been turning around in my head. While trying to find my way to the Deutsches Museum, I came across a clock that looked at first as if it were showing the wrong time. On closer inspection, I noticed that all of the numbers on the face of the clock were reversed. The clock was a mirror reflection of a real clock, its hands turned the other way; behind its face, all of the clockwork must have been meticulously designed to run in reverse. On the opposite side of the tower was an identical clock running "forwards" - i.e. the correct way.

I recalled seeing, in the Musee d'Histoire des Sciences in Geneva, an orrery. This machine, a clockwork model of the solar system, can be seen as a sort of metaphor for what is now termed "classical" mechanics - i.e. physics prior to relativity and quantum physics. The universe is governed by clearly identifiable and deterministic laws; it evolves in a perfectly predictable way as if it was driven by a sort of clockwork mechanism. This is an attractive prospect - it makes it seem as though the universe is really knowable, on the most fundamental level, through physics.

Seeing this clock on the Isartor turning backwards throws up some interesting philosophical questions. What if time really did run backwards? What if the mechanism behind the "clockwork universe" was reversed? How would our world look different?

The physics question for today: Imagine a world where time runs backwards. The world would look like a film played in reverse. What physics experiment could you do to determine that time was, indeed, running in reverse and not "forwards"?