Re: [asa] geocentricity

Responding to Gordon, let me try some "predictions" that geocentricity made,
and that seemed to be correct at least to first order.

Ted (ASA Council Member)

>>> gordon brown <gbrown@Colorado.EDU> 7/5/2007 2:10 PM >>>
Since motion is relative, one could declare the earth to be fixed, center
one's coordinate system there, and, in theory, rewrite the laws of physics

using those coordinates. Then attribute to the rotation of the heavens
what is due to that of the earth. If you didn't want to do physics or
astronomy, you would see no reason to change, but if everyone had taken
this approach, many areas of physics would not have advanced since the
fifteenth century because it would look too complicated. Since not much
physics can be developed from it, we can't give many examples of what
geocentricity accurately predicts.

****

Under geocentrism, cannon balls fired east ought to go the same distance as
cannon balls fired west--all other things being equal. Balls dropped from
the tops of towers ought to land at the bottom, not a few hundred feet away
from the tower. Birds in flight ought to be able to do what they do,
without being left behind by the rapidly spinning earth beneath them. And,
there ought not to be any annual stellar parallax (though a diurnal parallax
was known to exist and was used sometimes to answer interesting questions).

Until the 1830s, all of these predictions were correct. True enough,
Galileo's idea of horizontal inertia (not identical to the
Cartesian/Newtonian notion of rectilinear inertia) could account nicely for
the moving objects, but only by denying the obvious: it's obvious that
objects in motion do not move forever, on the earth; they do come to rest.
Inertia is not true in the "real" world of ordinary experience, only in the
abstract world of Galileo's mind, in which the "hindrances of nature" (as he
called them) are abstracted away so that bodies move inertially in a pure
geometric space. It's quite a lot to swallow, to toss away experience so
readily. As Galileo himself said, he had much admiration for followers of
Copernicus, for allowing reason to overcome the evidence of their senses to
such a degree.

These "predictions" can, I believe, fairly be called that. They are all
found in Tycho Brahe's writings, to the best of my knowledge, in the context
of arguing against the earth's motion. He knew he couldn't find annual
parallax, and modest man that he was (not), he knew therefore that it didn't
exist. He also knew why: the earth just doesn't move, not at all. The fact
that it dovetailed with his Lutheran faith (according to which Copernicanism
was a useful hypothesis that could be taught, but not the actual truth) was
just one more reason to affirm that the earth is at rest.

ted

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Received on Thu Jul 5 14:44:12 2007