I Is there an experimental proof that an Earth/Moon barycenter exists?

[Nugatory]

Yet again, my only question was whether anyone reading this thread was aware of experimental proof that an EM barycenter exists instead of just the theory that an EM barycenter exists which does not appear to exist to the knowledge of anyone who has read this thread.

Huh? Various posters in this thread have mentioned lunar ranging, spacecraft navigation, and that planets appear where ephemerides calculations say they should be. All of these are observations showing that the barycenter exists. (There are also observations of double stars, which clearly orbit their common barycenter - it would be a strange universe indeed if gravity between stars worked differently than gravity between planets).

But even if none of that experimental evidence existed it would be mistaken to say, as you do in the first post and later, that the existence of the barycenter would be “just assumed”. The scientific claim about the barycenter is “If our current theories about gravity accurately describe the universe, then there is a barycenter”, and the existence of the barycenter is not an assumption, it is a deduction as solid as “if Euclid’s axioms are valid, then the interior angles of a triangle add to 180 degrees” - the conclusion follows inevitably from the premise.

Thus, any challenge to the notion of the barycenter is actually a challenge to the premise “our current theories about gravity accurately describe the universe”. That is, are there observations that disagree with the predictions made by our current theories about gravity? In the absence of such observations , I don’t need observational confirmation of the barycenter (although as noted above, there is an abundance of these) to conclude that it exists. It’s as valid a claim as the (completely untested) proposition that the next time I drop an object, it will fall just like the last time.

 

[PeterDonis]

The OP question has been thoroughly answered. Thread closed.