Question: how does space time work

David Pyle answered on 25 Mar 2011:

We are used to thinking of space (distance) and time being separate and independent things that we can measure, and add together or subtract from each other. Once we are dealing with things travelling at or close to the speed of light, we have to into account effects that arise from Einstein’s theories of relativity. Lets thinks of an easy example of this: if we have two cars which start at rest and move away from each other at 30 mph, then the apparent speed of any one car from the viewpoint of the other car is 60 mph. Now, let’s take Einsteins idea that the speed of light is everywhere a contstant. Lets imagine that the two cars are photons, travelling in opposite directions at the speed of light. Special relativity then says that from the viewpoint of either of the photons, the other photon is moving away at the speed of light (because it can’t be moving faster); and the way that this can happen is because time passes slower from the viewpoint of the photon..

So, we need to have a new coordinate system that includes both space and time! This coordinate system is hard to imagine in four dimensions, and becomes even harder to imagine when we find out that it can be ‘bent’ by massive objects, for example!