The speed of light and constancy.
When Albert Michelson and Edward Morley tried to measure the speed of light back in the 19th century, they found that no matter what they did to it, the speed remained almost exactly the same.
All right, philosophy, huh? Not physics at all. No, must be physics. Anyway, the speed of light can be affected by things like black holes, but it can’t be relative because if xms-2 + yms-2 adds up to some velocity greater than x or y individually, then things in the night’s sky would disappear if light behaved in the same way.
But I’m still not really seeing the philosophy. All right, I suppose this is like the natural philosophy of the Greeks, but if this section of the book was really going to work, it’d have to be some of their more absurd theories rather than things that have been established by scientific investigation.
Today it was the speed of light; tomorrow, the contrariness of the photon.