Mysterious Universe

Everyone can travel in time(opens in new tab). You do it whether you want to or not, at a steady rate of one second per second. You may think there's no similarity to traveling in one of the three spatial dimensions at, say, one foot per second. But according to Einstein(opens in new tab)'s theory of relativity(opens in new tab), we live in a four-dimensional continuum — space-time — in which space and time are interchangeable.