Time is the strange dimension: Unlike its spatial siblings, it is a one-way street as the clock only ever ticks forward and never backward. Scientists have long been aware of time's quirks, with the ...

Space and time looked settled, at least in broad outline. Einstein’s special relativity gave physics a durable framework for describing motion, and for more than a century one boundary seemed firm: ...

We all know we live in three-dimensional space. But what does it mean when people talk about four dimensions? Is it just a bigger kind of space? Is it “space-time”, the popular idea which emerged from ...