I’m sure I’m not really understanding gravity theory, but I have in mind the illustration of marbles on a bedsheet. If that bedsheet is space-time, why isn’t there some sort of universal up and down as objects relate to each other?
In: Planetary Science
Here is a very ELI5 visual:
Imagine you are pointing “down” at the same time as someelse on the exact other side of the earth. You are both pointing down, but technically, you are pointing at each other in opposite physical directions. For you to point the same physical direction as them, you’d have to point “up”.
Gravity gives you a point of reference that is pulling you relatively down on the surface of a sphere. In space, you don’t have that single point of reference, but many of varying shapes and sizes.
Another easy visual, tides. From our perspective, the tide comes in and out. We see that as moving “front to back”. But if you could ask the water, it’s just moving down towards the moon. It’s not moving to and fro, but constantly towards the moon (barring the resistance of land and the lack of force from the moon compared to Earth, but this is ELI5, not explain like in in Jr high).
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