With the sci-fi prospect of a time machine comes the inevitable question: can we go back in time? But how do we know traveling to the past is in fact going back? This is because humans perceive time as one-directional. We think time only moves forward and nothing in the past can be changed or experienced again. Surprisingly, the common perception of time as having a direction has been confirmed by physicists. Furthermore, physicists discovered that our perception of time changes depending on when an event occurred. The distortion in our perception of time is named the temporal Doppler Effect.