110 years ago today, Albert Einstein published his General Theory of Relativity, which redefined the relationship between matter and gravity. Suddenly, our mysterious universe made a little more sense ...

Time travel has shifted from pure fantasy to a serious, if highly constrained, topic in modern physics. The equations that describe gravity, quantum fields and the structure of spacetime now allow ...

Even if it turns out that time loops never take shape, studying them provides key insights into the deepest rules of reality.