[Physicist]

I was specifically thinking of the fact that particles would be getting smaller, atomic nuclei would be smaller, reactions would occur over smaller distances, thus they'd occur faster (the speed of light wouldn't change).

Good thought, but I did specify that rulers would shrink, and the speed of light is, in the deepest sense, merely a ruler. It relates physical distance scales to physical time durations. We aren't changing the time scale, but we are changing the length scale, so the speed of light will be compelled to shrink right along with everything else.

[PatrickHenry]

We aren't changing the time scale, but we are changing the length scale, so the speed of light will be compelled to shrink right along with everything else.

Tenacious fellow, aren't you? If you're going to defend the equivalency of math and reality by taking away my one big clue, then okay ... I can't distinguish between cosmic expansion and shrinkage. If we were unknowingly living in a shrinking universe it wouldn't change my plans for the weekend.