We normally think of the space we live in as having three dimensions. So a room has width, length and height. We can move backwards and forwards in each of these dimensions, so we can move from any point in the room to any other point and then back again.
Our experience of time is very different. We cannot move backwards and forwards in time at will. Instead we find time moves forward only.
But to describe things with very high energy we need to think of space and time as four different aspects of the same thing. The part of science called Relativity studies this subject. It shows that there is no real difference between space and time.
The theory called General Relativity shows that when an object moves or a force acts it affects the curvature of space-time. So the great mass of a star like the Sun will bend space-time, so that light from other stars does not travel in a straight line as it passes near the Sun. This has been proven to happen by watching eclipses.
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