The Philosophy Discussion Forum

Being a relatively greater novice at the physical sciences, compared to some novices, that I am, I have some questions:

If all movement is "relative" to the observer and there is no "fixed" frame of reference, does that mean that a spruced-up model of the movement of the planets in our solar system resembling Ptolemy's earth-centric configuration of orbits would be technically "equivalent" to the heliocentric model of our solar system if it could be made to perfectly match the physical observations of our heliocentric solar system?

So, for example, if I simply altered Ptolemy's physical model so that the planets made even crazier movements to make them match the movements of our planets precisely according to the observational data on their orbits that our telescopes currently gather, would that count as just as good a model of the movement of our solar system as the one we currently have with the Sun at the center? Can that be done, or is it not possible to do that? And if it can be done, does relativity tell us that such a "model" is "accurate"? Or does the theory of "relativity" still tell us that it is "inaccurate" as Newtonian physics does?

Well yeah, you could do that for the planets in the solar system (and comets and asteroids, which would make it insanely complicated), but you would have impose a limit on the size of the universe, because anything further away would be travelling faster than the speed of light. Which, of course, is impossible according to special relativity.

If all movement is "relative" to the observer and there is no "fixed" frame of reference, does that mean that a spruced-up model of the movement of the planets in our solar system resembling Ptolemy's earth-centric configuration of orbits would be technically "equivalent" to the heliocentric model of our solar system if it could be made to perfectly match the physical observations of our heliocentric solar system?

One can pick any frame of reference that one wants, even in Newtonian mechanics. It's not an Einstein thing.

One picks a frame of reference which makes the calculation easier or the visualization more clear.

For example, one can choose to model a billiard ball moving on the pool table with the frame of reference fixed to the ball. As a result, the ball is stationary and the table spins and slides around the ball.

When the Copernican heliocentric system was developed, it was not more accurate (or much simpler) than Ptolemy's geocentric system. Astronomers kept using the Ptolemy system.

The significant innovation was the discovery, by Kepler, that orbits are elliptical. Previously, it was believed that orbits were some complex combination of 'perfect' circles. (Because God likes circles.)

are we sure that elliptical orbits are not caused by wobbly planets?

oh sure, gravitational pull from all objects sounds more "scientific"...

-Imp

In relativity, you can choose any reference frame, so a Ptolemaic-style model could fit observations if made complex enough. However, it becomes far less simple and physically meaningful than heliocentric models fnaf, which better reflect underlying dynamics.