Question

Why is the speed of light used to define the metre?

Options

• Light is the fastest thing we can see

• The speed of light in a vacuum is constant everywhere

• Light travels exactly 1 metre per second in a vacuum

• It is easier to measure than other quantities

Answer 1

The speed of light in a vacuum is constant everywhere

Explanation:

The constancy of the speed of light (c = 299,792,458 m/s) makes it an ideal reference, it does not change with time, location, or observer, giving us an invariant and precise standard.