First things first, what is time? “Time is what keeps everything from happening at once,” as Ray Cummings put it. Funny, but not very useful. If you ask Wikipedia, time is what clocks measure. Which brings up the question, what is a clock. According to Wikipedia, a clock is what measures time. Huh. That seems a little circular.
Luckily, Albert Einstein gets us out of this conundrum. Yes, this guy again. According to Einstein, time is a dimension. This idea goes back originally to Minkowski, but it was Einstein who used it in his theories of special and general relativity to arrive at testable predictions that have since been confirmed countless times.
Time is a dimension, similar to the three dimensions of space, but with a very important difference that I’m sure you have noticed. We can stand still in space, but we cannot stand still in time. So time is not the same as space. But that time is a dimension means you can rotate into the time-direction, like you can rotate into a direction of space. In space, if you are moving in, say, the forward direction, you can turn forty-five degrees and then you’ll instead move into a direction that’s a mixture of forward and sideways.
You can do the same with a time and a space direction. And it’s not even all that difficult. The only thing you need to do is change your velocity. If you are standing still and then begin to walk, that does not only change your position in space, it also changes which direction you are going in space-time. You are now moving into a direction that is a combination of both time and space.Sabine Hossenfelder, “Is Time Real?” at BackRe(Action) (January 2, 2021)
We think time is real but that it has never been convenient.