Scientists are putting Einstein's claim that the speed of light is constant to the test. While researchers found no evidence that light's speed changes with energy, this null result dramatically tightens the constraints on quantum-gravity theories that predict even the tiniest violations. ScienceDai...

Scientists are putting Einstein's claim that the speed of light is constant to the test. While researchers found no evidence that light's speed changes with energy, this null result dramatically tightens the constraints on quantum-gravity theories that predict even the tiniest violations. ScienceDai...

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 behave slightly differently at extreme energies. By tracking ultra-powerful gamma rays from distant cosmic sources, researchers searched for tiny timing differences that could reveal new physics. They found none, but their results tighten the limits by a huge margin.

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 behave slightly differently at extreme energies. By tracking ultra-powerful gamma rays from distant cosmic sources, researchers searched for tiny timing differences that could reveal new physics. They found none, but their results tighten the limits by a huge margin.