Happy New Year. This is when we celebrate the passage of time. The concept of time is fascinating. According to theoretical physicist Carlo Rovelli, time is an illusion: our naive perception of its flow doesn't correspond to physical reality. ... Reality is just a complex network of events onto which we project sequences of past, present and future. There's no such thing as "now" as far as physics is concerned. Space and time are fluid, affected by gravity and your speed. Einstein put it like this: "For us physicists, the distinction between past, present and future is only an illusion, however persistent.