Galileo: an old history lesson

Paul Arveson (
Fri, 12 Dec 1997 16:32:53 -0400

Don Page wrote:

> Glenn, the same observation would have been made if the earth were
>not rotating but the sun were going around the earth, since in that case the
>ship would have gone around the earth in the same direction as the sun and
>thus seen one fewer sunrise than the islanders who stayed fixed. Given
>enough people considering this question, and enough time (which I realize
>that you would not have had on this particular issue, since you write so
>prolifically), I'm sure that those in the 16th century (particularly those
>who really believed that the sun went around the earth) would have realized
>that this datum was consistent both with rotation of the earth and a fixed
>sun, and with a fixed earth and rotation of the sun around the earth.
> So I am curious as to what the evidence from the voyage of
>Magellan's surviving crew did convince the church authorities. On what
>issue and how did they change their minds?


The scriptures about the fixity of the earth referred to above might
include, for example:

"Yea, the world is established; it shall never be moved; thy throne is
established from of old; thou art from everlasting." - Psalm 93:2 RSV


"Say among the nations, 'The Lord reigns! Yea, the world is established,
it shall never be moved; he will judge the peoples with equity." - Psa. 96:10

But there are also verses in this section of Psalms that say the opposite:

"His lightnings lighten the world; the earth sees and trembles." - Psa. 97:4


"The crash of thy thunder was in the whirlwind; thy lightnings lighted up
the world; the earth trembled and shook." - Psa. 77:18

What are we to make of this? Galileo and Francis Bacon both explained the
problem as due to misinterpretation of Scripture. I think we would agree
that these verses really aren't talking about geophysics -- they are
talking about terra firma as a metaphor for the security and justice and
faithfulness of God, and the trembling earth as a metaphor for the judgment
and power of God. Both are true. But the point is that the Psalms are
writing about theology, not geology.

So the link between the Bible and geocentricity cannot be derived from pure
Bible study, because if the verses are interpreted 'scientifically' we get
an inconsistency. What happened historically is that the philosophy of
Aristotle had taken hold on science in the 17th century, and Aristotle
taught geocentrism -- rocks fall because they are made of the element
'earth', and they move toward their natural place. So the earth must be
the stable center of the universe.

It was Greek physics, not the Bible, that created the problem.

On the other hand, some church leaders like Cardinal Bellarmine were open
minded to science, and they asked Galileo for an experimental demonstration
of the rotation of the earth to settle the issue. Galileo worked on that
for many years, considering especially the tides. But as you note above,
even the travels of Magellan could not in principle demonstrate the motion
of the earth. In fact, Galileo never did produce a convincing

Such a visible experimental demonstration had to wait another 240 years,
until Michel Foucault's pendulum swung in a cathedral in France. Long
after Newton, and long after everyone had accepted the Copernican view --
and even after the French Revolution. One of the ironies of history.

(I'm not sure of all the details, but I recommend Charlie Hummel's book The
Galileo Connection as a description of this episode).

Paul Arveson, Code 724, Research Physicist, Signatures Directorate
Naval Surface Warfare Center, Carderock Division
9500 MacArthur Blvd., West Bethesda, MD 20817-5700
(301) 227-3831 (301) 227-4511 (FAX)