Galileo Galilei
Dialogo di Massimi Sistemi del Mondo
Dialogue on the Great World Systems
Defends Copernican model against Ptolemaic model.
- Observations alone do not decide between the two hypotheses, ``for
the same phenomena will appear in the one case as in the other.''
- But the Copernican system seemed to be simpler overall.
Used the Socratic method of the Platonic dialogues:
- Simplicio representing the Aristotelian/Ptolmaic view.
(= the Pope?)
- Salviati representing Galileo's view.
- Sagredo , uncommitted, willing to learn.
An example
Salviati: [In the earth centered system, all the stars have to
move around their giant sphere once per day, with the ones near the
celestial poles moving on little circles, the ones near the celestial
equator moving on big circles. In the sun centered system, only the
small earth has to rotate around it's axis once per day. That's simpler.]
Simplicio : ``It seems that you base all you say upon the
greater simplicity and facilty of producing the same effects. To this
I reply that I am also of the same opinion if I think in terms of my
own not only finite but feeble power; but, with respect to the strength
of the Mover, which is infinite, it is no less easy to move the
Universe than the Earth, yea, than a straw. And if his power be
infinite, why should he not rather exercise a great part of it than a
smaller? Therefore, I hold that your discourse in general is not
convincing.''
Salviati : ``If I had at any time said that the Universe did not
move for want of power in the Mover, I would have erred, and your
reproof would have been seasonable; and I grant you that to an infinite
power it is as easy to move a hundred thousand as one. ... [But]
a most true maxim of Aristotle teaches us that...`that is done in vain
by many means which may be done with fewer.' This renders it more
probable that the diurnal motion belongs to the Earth alone, rather
than to the whole Universe with the sole exception of the Earth.''
Galileo's abjuration, ordered to be read from pulpits throughout Italy:
`` ...I swear that in the future I will never again say or assert,
verbally or in writing, anything that might furnish occasion for a
similar suspician regarding me; but should I know any heretic or person
suspected of heresy, I will denounce him to this Holy Office, or the
the Inquisitor or Ordinary of the place where I may be. ...''
This successfully killed astromical heresy in Italy, but the church
had lost control of much of Europe...
ASTR 121 Home
Davison E. Soper, Institute of Theoretical Science,
University of Oregon, Eugene OR 97403 USA
soper@bovine.uoregon.edu