Galileo did not only overthrow Aristotle’s physics of motion, he destroyed the whole myth of the ordered cosmos, he most painfully disturbed the intellectual and the emotional  securities it had sustained and threatened the very stability of societies which saw themselves as ordered by it.  You begin to see why the Church got so upset.  Through his telescope he was claiming to see a moon made not of some heavenly crystalline substance but of stone, which far from seeking to fall to the centre of the earth was floating up in the air, with mountains on it to boot.  It was beginning to look as if the earth and the heavens were made of the same kind of stuff. It was not so much that his discovery that Jupiter has moons could not be fitted into the pattern of the heavenly spheres, although it was hard to see how – but then again the myth of cosmic harmony had taken  planets moving backwards in its stride by inventing epicycles so why not Jupiter and his moons? – as the unsettling uncertainty of what next Galileo might see through his telescope.  Fixed stars that moved? New planets?  Even that the heavenly bodies did not go round in perfect circles but in some sort of ellipse, all of which in time of course did turn out to be the case.  But the real revolution wrought by Galileo was even more unsettling.  For the ordered cosmos of Aristotle he substituted the abstract space of mathematics.                                                                                                                                  


No longer are mathematics irrelevant to physical motions, they are the very cause and condition of them.  The default condition of things is no longer rest but movement.  For efficient causes that you can see happening – well maybe not air, you can’t see air, but you almost can – he substitutes mathematical relationships that you can’t see at all.  Air doesn’t now cause projectiles to move, it stops them doing it.  According to his principle of inertia once a thing is set in motion it will keep going for ever in a straight line, unless impeded.  For ever?  You can’t imagine it.  It is very unsettling indeed to find yourself living in a world that you can’t imagine any more.  And in a straight line?   What happened to the perfectly circular motions of the heavenly spheres?  You can see the stars up there doing it for heavens sake. What nonsense all this new physics is.  But what was really annoying was that military engineers who followed Galileo’s parabolic physics, rather than Aristotle’s, were  knocking down the walls of fortresses much, much more efficiently.  It is because Galileo’s destruction of the whole Medieval myth of cosmic harmony was so total that his discoveries are so often seen as the beginning of the modern world, and as the origin of that process whereby fabulous, immaterial and supernatural causes of things were replaced by rationally ascertained material ones.  This is to misread him completely.  Far from seeing himself as destroying a supernatural mystical order he saw himself as strengthening it by showing it was true and actually working in the world.  Far from seeing himself as overthrowing Aristotle he thinks he is fulfilling his work. It is Aristotelians, not Aristotle, he can’t bear.  The very last thing Galileo thought was that the world can be explained in terms of material causes. He was not the first Baconian, he was the last Platonist.   


In 1588 Galileo gave a lecture to the Academy of Florence on the dimensions of hell. Taking much of his information from Dante, he estimated that hell is a cone taking up one twelfth of the earth’s mass with its vortex at the earth’s centre.[1]  We might well wonder how the first great scientist came to be indulging these delusions and how he could compromise his principles to this extent.  We assume, precisely because he was the first great scientist, that he is on our side of the great watershed that divides Medieval imaginary fantasy from modern rationally established certainty.  But we forget that he was not a man of our time but his own, and he did not make his discoveries against the background  assumptions that a twenty-first century scientist would make, but in the thought world of the late Renaissance in which he actually lived.  He no more thought ‘Amazing. I am the first great scientist inaugurating the modern era’ than people woke up on January 1st 1485 and said ‘Hello. It’s the end of the Middle Ages.  Happy 1485 to 1689’.  What was the Academy of Florence and why was Galileo addressing it?

[1] Michael White 2007 Galileo Antichrist.London Weidenfeld and Nicolson.  Penguin ed. 2009 pp 55-56.


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