Albert Einstein realized over 100 years ago, that space and time are one thing and are not independent parts of the universe. You can move only one direction at anytime only at the speed of light, your momentum always shared between space and time. It is similar to being able to head North East on a map, your momentum shared between going a little North and going a little bit to the East. I always imagine space time as a flowing net, like a spider’s web. This photograph is a close shot of two layers of crossing fishing line.