The most distant galaxies in this deep field image from the James Webb Space Telescope appear as small, faint dots—and are receding from us faster than the speed of light due to cosmic expansion. If ...

Scientists pushed photons across the universe to test the speed of light—and found Einstein’s cosmic speed limit still holds ...

If there is an absolute law in the universe, it’s that nothing can travel faster than the speed of light. For science-fiction enthusiasts, that’s a bit depressing. Space is big, and while the speed of ...

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 ...

The speed of light varies in materials, impacting fiber optics, laser systems, and semiconductor lithography through complex electromagnetic interactions.