eli5: If every frame of reference is valid, why do people say the earth spins around the sun instead of the opposite, wouldn’t both views be equally valid?
In: Physics
No.
Although many of the other comments are right that we can make the math work (with difficulty), that doesn’t mean all frames are equally valid.
In particular, the statement you’re talking about is usually about relativity. All velocities are relative so it doesn’t matter who you pick as “0 speed”.
But *acceleration* isn’t relative, it’s absolute. In that sense, the earth and sun reference frames are not the same. The earth is constantly accelerating (going in a circle) around the sun. We can directly measure that effect. The sun is *not* constantly going in a circle around the earth. We can force the math to model the motion that way but there’s no physics to back that up. There is no force out there causing the sun to move in a circle around the earth. There is a force causing the earth to go in a circle around the sun. Or at least a spacetime distortion that acts like a force (general relativity).
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