[darkwater]

Being exact doesn't mean it is not an approximation, which was the initial topic. Being exact in science means that 2+2=4 and that can be demonstrated following a logical chain. But that doesn't make our knowledge of the universe exact. It is still an approximation. What it can be "exact" is how we obtain and reproduce the current knowledge we have of it.

[squidbeak]

The speed of light, or plank's constant - are these approximations?

[darkwater]

To our current knowledge, no. But maybe we are missing something, we cannot know. Did infrared light or ultrasound start to exist only when we realized there are things our senses cannot feel?