A team of engineers and scientists has shown for the first time that a hard-X-ray cavity can provide net X-ray gain, with ...

Scientists at the X-ray free-electron laser SwissFEL have realized a long-pursued experimental goal in physics: to show how ...

There's an ultimate speed limit in the Universe: the speed of light in a vacuum, c. If you don't have any mass — whether you're a light wave (a photon), a gluon, or even a gravitational wave — that's ...

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 ...