Everything posted by johnjoe
Thanks Andrew you are absolutely right. In GR you can choose either heliocentric or geocentric frame. But, if You choose the geocentric then you get pretty much Tycho Brahe's systems with lots of epicycles. You can work with this but it's much more complicated that Kepler's heliocentric. Ultimately, all we have are models and their predictions. When we have two or more models whose predictions all fit the data then science chooses the simplest. That, I believe, is key to what science does and why it is so successful.
thanks Michael. I agree with all you points but, as the historians do a circle count, i'd like to dismiss them on their own ground, if possible.. Surely someone somewhere drew both the Copernican and Ptolemaic system to the same scale?
Thank you Michael I believe that it was the phases of Venus that Galileo cited in his Dialogue as evidence for the heliocentric system. But, as you say, they were compatible with Tycho Brahe's system that still had the Earth at its centre. Galileo's other evidence was earthshine on the moon - but that didn't prove geocentricity, only that the Earth is another heavenly body. He also claimed that the earth's tides were caused by the Earth's annual rotation , but that was clearly erroneous. I agree that it was specific simplifications, such as a rational explanation for retrograde motion, that convinced these great astronomers. However, in loads of history of science books the authors claim that the simplicity argument - Ockham's razor - was erroneous because of the circle count criterion. I'd just like to knock it on the head as it kind of implies that some of the greatest scientists were deluded when they cited simplicity as their reason for supporting heliocentricity. i think that the relative simplicity of the Copernican would be obvious in a scaled diagram of the Ptolemaic vs Copernican because the Copernican circles are correcting for smaller errors. But i don't where there is one or how to make one. Anyone know?
Hi I am writing a book about the role of Ockham’s razor in science and one of the topics is the successive simplification of the solar system from the Ptolemaic system through Copernicus to Kepler. Both Copernicus and the young Kepler (before he worked out the correct system) and Galileo and Tycho Brahe claimed that the Copernican system was simpler than the Ptolemaic and simplicity was the reason for their preference for heliocentricity. It is well known that the heliocentric Copernican system provided no more accurate predictions than Ptolemy's geocentric system. So despite their lack of evidence, Copernicus, (the young) Kepler and Galileo were all convinced the heliocentric system was true solely on the simplicity criterion – Ockham’s razor. Galileo additionally gave erroneous proofs, such as the tides but, apart from these, the only argument the Copernicus, Kepler and Galileo could muster for heliocentricity was that the Copernican system was simpler than the Ptolemaic. Yet historians of science such as Thomas Kuhn and Arthur Koestler, who have counted the orbits and epicycles (circles) in both systems and come to roughly the same number, so they claim that Copernicus, Kepler and Galileo were deluded as both systems were equally complex. But then why had these great scientists been convinced by geocentricity without any other evidence? I find it hard to believe that they were deluded themselves. The reason i believe is that the Copernican system, despite having a similar number of circles, was actually simpler because it only had to correct for Copernicus' two errors: his insistence on perfect circles and uniform motion. The deviations of the actual planetary orbits from perfect circles to ellipses and uniform motion to variable motion is relatively minor compared to the deviation of a geocentric from a heliocentric system. So i am guessing that Copernicus' correcting epicycles are much smaller than Ptolemy's. But all the diagrams i can see online are not drawn to scale so i cannot compare them. Does anyone have scaled diagrams of the two system? Or is it possible to calculate the relative size of the circles in both systems?