The discussion centers around the concepts of heliocentrism and geocentrism, particularly questioning whether both perspectives can be considered correct due to the relativity of motion. Participants explore the implications of choosing different reference frames in modeling planetary motion, the historical context of these models, and the challenges associated with each approach.
Participants express differing views on the validity and utility of geocentric versus heliocentric models. There is no consensus on whether both models can be considered correct, as some argue for the superiority of heliocentrism based on predictive capabilities, while others maintain that relativity allows for both perspectives to hold validity under certain conditions.
The discussion reveals limitations in the assumptions made about reference frames and the definitions of models versus theories. The complexity of celestial mechanics and the historical context of astronomical models are also acknowledged but remain unresolved.
Someone correct me if I'm wrong, but I think the Aristotleans considered the Earth the to be the absolute centre of the the universe. I think till Hubble came along, something or the other was the absolute centre of the universe. First it was the Earth, then the Sun (Copenicus), and then the Milkyway(Herschel).Swapnil said:OK, so its harder to work with a Geo-centric model than a Helio-centric model. But that doesn't change the fact that they were both right, right?
No. AFAIK, no one was ever able to construct a geocentric model that actually worked to the point where it was difficult to distinguish the results from what Newton's theories (much less Einstein's) predicted. Ie, the basic reason for needing to move beyond Ptolmey is that his model didn't work very well. They just kept adding epicycles, but were never able to make the model work very well.Swapnil said:OK, so its harder to work with a Geo-centric model than a Helio-centric model. But that doesn't change the fact that they were both right, right?
That's a different issue (several, really). Until decent telescopes were invented, no one had a very good idea of the definition of "universe" anyway.neutrino said:Someone correct me if I'm wrong, but I think the Aristotleans considered the Earth the to be the absolute centre of the the universe. I think till Hubble came along, something or the other was the absolute centre of the universe. First it was the Earth, then the Sun (Copenicus), and then the Milkyway(Herschel).
russ_watters said:No. AFAIK, no one was ever able to construct a geocentric model that actually worked to the point where it was difficult to distinguish the results from what Newton's theories (much less Einstein's) predicted. Ie, the basic reason for needing to move beyond Ptolmey is that his model didn't work very well. They just kept adding epicycles, but were never able to make the model work very well.
There are still crackpots running around who have wacky ideas about Geocentrism, and you'll find some on BadAstronomy.com, but I remember some discussions where people put it to them to actually try to build some woking models and no one could. It isn't something to be taken seriously.
Geocentrism may be able to simulate motions planets (and roughly at that) I don't know if that counts as a model. They were never able to explain what caused the planets to follow those paths.Swapnil said:OK, so its harder to work with a Geo-centric model than a Helio-centric model. But that doesn't change the fact that they were both right, right?
You're pushing my math, but doesn't that just yield a potentially endless series of bandaid terms who'se overall length depends on how precise you want the model to be?selfAdjoint said:Their basic problem was not the epicycles per se. As has been noted elsewhere, a rigorous epicycle formalism is just Fourier analysis in disguise, and it should be able to reproduce any reasonable physics.
russ_watters said:You're pushing my math, but doesn't that just yield a potentially endless series of bandaid terms who'se overall length depends on how precise you want the model to be?
In the terrestrial frame employed by medieval astronomers, the trajectories of the planets are exceedingly complicated, their overall forward motions being frequently checked by phases of retrograde motion which insert loops into their paths; ... To explain such trajectories, the medieval astronomers (following Ptolemy) were compelled to develop a theory in which the planets were fixed to wheels, which rolled around the circumferences of other wheels, which in turn rolled around on a third set of wheels, and so on -- the theory of epicycles. By switching to the solar frame, Copernicus was able to demonstrate that the planetary paths become very nearly circular and, after a more precise determination of their orbits by Kepler, this opened the door to a theory of the planetary motions based on Newton's law of gravitation. Again, we are not to regard the Copernican description of the planetary motion as being the true account, whereas the Ptolemain one as invalid. Both are valid in their respective frames, but the Copernican point of view is overwhelmingly the more convenient and seminal.
Am I the only one remembering that rotational motion is NOT inertial motion? There is a measureable difference between the sun going around the Earth and the Earth rotating. Motion is only relative between two intertial frames. The sun and the Earth are not in inertial frames.Swapnil said:According to Einstein, in an inertial frame, if one sees a person "fly by," one cannot say if he/she is moving or that other person is moving because there is no universal rest frame.
All I am saying that if we apply the same concept to the motion of planets, then we can't really prove that if the all the planets (including the Earth) revolve around the Sun or if all the planets (excluding the Earth) and the Sun revolve around the Earth. Am I right?
According to Guillochon, the response seems to be yes.