Galileo and observational "proof" for Copernicus

Ted Davis (
Mon, 16 Mar 1998 10:10:20 -0500

I respond to Inge Frette's missive:

Galileo could not give empirical evidence that were strong enough to
convince aristotelian thinkers to give up the geocentric view.
Venus did the same ), he concluded that it should be possible to
see the phases of Venus. Which he also observed. But from logic we know that

if A, then B
B, therefore A
is a logical fallacy so observing the phases of Venus does not establish
the fact that the earth revolves around the sun.

EBD: Yes, this is correct. Owen Gingerich points this out with much
eloquence and force in "The Galileo Affair," Sci Amer (Aug 1982), 133-43.
George Murphy's comments on Tycho are also correct. Galileo conveniently
and, no doubt, deliberately, ignored Tycho's cosmology in his polemics
against the traditional cosmology. He was frankly an arrogant SOB who
didn't want people to have an alternative between his Copernican views and
the Aristotelianism of his opponents.

Well, my question is this. When did we get empirical support for the thesis
that the earth revolves around the sun? With empirical support I think here
of experimental
confirmation that is so strong that it would have convinced the aristotelian
thinkers of Galileos time? And how was the experiment performed that
confirmed the heliocentric theory?

EBD: Inge, the type of evidence you call for was not found until the
mid-18th century, when the aberration of starlight was observed. Stronger
evidence -- the type Galileo would have loved -- did not come until the
1830s with the discovery of stellar parallax. (The aberration evidence is
subtler, which I why I say this.)

However not even that sort of evidence is sufficient to convince some today,
such as contemporary geocentrists (yes, there are some). There is today a
Bulletin of the Tychonian Society, and there are webpages on which one can
read about geocentrism by advocates of the view. LOGICALLY, one can still
understand all known evidence in terms of geocentrism, as long as one is
prepared to find alternative explanations for such things as aberration,
parallax, and the Corilois force. Scientific theories, by and large, are
incapable of "PROOF" in the sense in which one can prove a theorem in
mathematics. Indeed, a famous essay by Tarski, written about 50 years ago
(Caution: I'm going from memory here), makes the point of distinguishing
between scientific "truth" that is empirically verified and mathematical
"proof" which is not. The one is certain, the other less certain; the one
is "true" in that it conforms to nature, the other is true only
analytically, which is actually much less interesting and may not be true at
all in scientific sense.

Ted Davis