Eli5: why is time considered to be the fourth dimension
In: Physics
We began looking at time as a fourth dimension because we observed a relationship between time and space. That means that we realized that space can affect time and the two are linked. This theory that time and space are linked which is called relativity, is the reason Albert Einstein is famous. It’s a refinement of the old-school Newtonian physics you might have learned in school. Einstein realized that physics models did not explain certain things observed in space, and realized that time and space are linked. Things moving very quickly experience time more slowly. They also appear to be shorter in length. If two observers are traveling at different speeds, they may not observe the same thing at the same time. He predicted this but did not prove it with evidence. However, all future experiments so far have fit this theory.
This theory is called the theory of relativity, and it is considered the biggest advancement of the century when it comes to physics. There’s so much to read but I’d start with [Wikipedia](https://en.m.wikipedia.org/wiki/Theory_of_relativity)
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