Einstein’s claim that the speed of light is constant has survived more than a century of scrutiny—but scientists are still daring to test it. Some theories of quantum gravity suggest light might ...

So, you’re driving a car at half the speed of light. (Both hands on the wheel, please.) You turn on the headlights. How fast would you see this light traveling? What about a person standing by the ...

In 1887, one of the most important experiments in the history of physics took place. American scientists Michelson and Morley failed to measure the speed of Earth by comparing the speed of light in ...