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 ...

“What is time? If no one asks me, I know what it is. If I wish to explain it… I do not know”, famously quipped Saint Augustine. Our modern understanding of time is more scientific than ever, and many ...

“This retroactive idea. It has to be that,” says Nobel Prize-winning mathematical physicist Sir Roger Penrose, reflecting on a problem about the building blocks of reality that has dogged physics for ...

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Contemporary physics has learned to describe the universe with unprecedented precision. Yet when it tries to say what time is, it stumbles again and ...

An advanced laser technique has allowed researchers to observe, in real-time, the decomposition of a pollutant into atmospheric nitrous acid, which plays a key role in the formation of ozone and ...