One-way speed of light

Since 1983 the metre has been defined as the distance traveled by light in vacuum in 1⁄299,792,458 second. This means that the speed of light can no longer be experimentally measured in SI units, but the length of a meter can be compared experimentally against some other standard of length.

1. What is the speed of light in one direction?
2. Is it possible to measure the one way speed of light?
3. Is the speed of light the same in all directions?
4. Is there only one speed of light?

What is the speed of light in one direction?

The speed of light has never been measured in one direction but always using a reflected media. Thus c is constant in that method.

Is it possible to measure the one way speed of light?

We just cannot measure the speed of light in one direction because relativity prevents us from maintaining synchronised clocks. The result is that the speed of light c is really the average speed over a round-trip journey, and that we cannot be certain that the speed is the same in both directions.

Is the speed of light the same in all directions?

Light does not travel at the same speed in all directions under the effect of an electromagnetic field. ... In an absolute vacuum, light travels at a constant velocity of 299,792,458 m/s. It seems natural that it should propagate at the same speed in all directions.

Is there only one speed of light?

Light traveling through a vacuum moves at exactly 299,792,458 meters (983,571,056 feet) per second. That's about 186,282 miles per second — a universal constant known in equations and in shorthand as "c," or the speed of light. ... That means the speed of light functions as a speed limit on the whole universe.