In 1994, French artist Jean-Marc Philippe conceived of a spacetime capsule named KEO. This satellite would launch into space and orbit the Earth while carrying samples of our dirt, air, and water.

Can we turn back time? Ask a savvy physicist, and the answer will be “it depends.” Schemes for retrograde time travel abound but usually involve irreconcilable paradoxes and rely on outlandish ...

What makes any person’s Notes app so revealing is that its contents have no audience. Unlike social media, it’s not intended for public consumption; unlike a text, it’s not even intended for one other ...