every now and then i look at the wikipedia article "world line" and recall this incredible image with the words "hypersurface of the present" in it
it took me a minute to remember how to comprehend this image but i did and you can understand it too
here's a short explanation:
- a "surface" is a 2d flat region. a "hypersurface" is the 3d equivalent of that. this is the hypersurface of the present bc it has the 3 spatial dimensions but no 4th dimension (time)
- the light cone of a thing is the region of all space-times that the thing can be or has been. it's made by just drawing out all the spacetime paths of light from that thing, because to get outside of the light cone it would have to go faster than light, which is impossible
- for example, 10 feet behind you right now at this exact time is on the hypersurface of the present/outside your light cone, because you can't possibly reach that location in literally 0 seconds. however, 10 feet behind you at one fucktillionth of a microsecond from now1 is inside your light cone, because if you could move at near-lightspeed you could potentially be there
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not an exact measurement
