scientists in different part of the world have conducted expirements to find the speed of light in vaccum. if the result of the expirement are identical they would most likely be valid, biased, unreliable, or non observable
the results will most likely be valid because the scientists kept getting the same results after REPEATED experiments. If they just conducted one experiment then they would not have been sure if what happened was a fluke or if another thing would happen after another experiment.
