Time is something we all use throughout our lives, although many of us probably don’t think about how it work – we just get on with it!
Us humans divide time up into small chunks, like hours and minutes and seconds; or into bigger chunks, like days, weeks, months and years. And we measure time by looking at clocks or watches or calendars.
Animals and plants and other creatures also measure time but they don’t use clocks – they rely on the amount of light to tell if it’s day or night, and they sense more gradual changes in the seasons.
Time-travel, or the ability to move backwards or forwards through time, is an idea that pops up in stories and films. But could it actually happen?