What is space time, how can dimensions be fused, and how is time a dimension?
In: Physics
Spacetime is simply space and time together as one whole. In other words space is just spacetime in any given moment (which is usually “right now”). So you don’t think of space as something that changes, but space as it was in the past and how it will be. Basically the difference between “I’ll meet you in front of the school” and “I’ll meet you in front of the school next Thursday at 3 PM”. If you open up a movie on your computer there will probably be a timeline on the bottom where you can decide _when_ in the movie you want to jump. Imagine if someone looked at a complete recording of the universe and could rewind and fast forward with something like that.
“Dimension” is a term that’s used for very fancy sci-fi things but in practice it’s related to measurements. Grab a tape measure, lay it out flat. That’s one dimension (if you ignore its thickness or just think of its edge) and you can tell where you are on the tape measure with one number, the one that’s written on it.
On a flat sheet of paper you can do something similar with two tape measures laid down at the edges of the sheet so they meet in a corner at 0 – for any point on that sheet of paper you can read from one tape measure how far up/down you are (if you look at your point from that side of the paper) and the other tells you how far left/right you are. So it is said that the surface of a paper has two dimensions.
For space, add a third: how far above/below. For spacetime, add a fourth: how far into the past/future: when.
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