30
votes
8answers
6k views

Why does the speed of light have no uncertainty?

I could understand that the definition of a second wouldn't have an uncertainty when related to the transition of the Cs atom, so it doesn't have an error because it's an absolute reference and we ...
2
votes
2answers
252 views

The famous drop of $c$

In this, in my opinion, intriguing speech, Rupert Sheldrake, tells the story of the drop between the measured valued of $c$ in 1928 and 1945. When he goes to visit the Head of Metrology of the Physics ...
0
votes
1answer
111 views

Zero uncertainty constant and a unit change

So, we know the speed of light with zero uncertainty. We also know that values of $\epsilon_0$ (electric constant) and $\mu_0$ (magnetic constant) are known with zero uncertainty. My questions are ...
4
votes
4answers
1k views

Measuring the speed of light and defining the metre - absolute or relative?

If the metre is now defined as the distance light travels in vacuum in 1⁄299,792,458th of a second and the speed of light is accepted to be ...