What is 4D spacetime?

4D spacetime is like a big, stretchy map that shows where and when everything happens.

Imagine you're playing with building blocks. You can move them left or right (that’s width), forward or backward (that’s depth), and up or down (that’s height). Those are the three directions of space, like a 3D puzzle.

Now, add something new: time. Time is like another direction you can move through. If you're playing with blocks at noon, then later in the afternoon, you're moving through time. So instead of just having where things are, you also have when they happen. That’s why we call it spacetime, because it mixes space and time together.

Think of spacetime like a video. Each frame is a moment in time, like one second of the video. If you watch the whole video, you can see how things move from one place to another over time. In 4D spacetime, all those moments are there at once, like having every frame of the video on a giant screen.

So when we talk about 4D spacetime, it's just space (3 directions) and time (1 direction), all working together to show where and when everything happens, like a super-detailed map for the whole universe!