2.1 Nobody expects the Italian inquisition
Galileo got into deep trouble with the Vatican for publicising the proof, based on his observations of the movement of Jupiter’s moons, that not all heavenly motion is centred on the Earth. The video presents a reconstruction of some of the arguments at the time.
Download this video clip.Video player: moons_1_vid030.mp4
Transcript
SIMPLICIO
Your thoughts, signor, are heresy.
GALILEO
The truth is the truth. Is the Mother Church so fearful of science? Our Earth behaves as do all the wandering stars. I have observed that there are four moons that circle Jupiter in orbits of their own. So does our Moon the Earth as the Earth describes her orbit around the sun.
SIMPLICIO
No. You are deranged. If the Earth were truly spinning round the Sun, surely we would feel this ceaseless motion. The very air we breathe would be snatched away from our lips and a ball thrown upwards would vanish over the horizon.
GALILEO
No! It would not. I have explained, and I have proven--
SIMPLICIO
Proven, signor?
GALILEO
Where do I begin? A ball falling from a great height will fall faster and faster until it reaches the ground.
SIMPLICIO
Why faster and faster?
GALILEO
It is a gravity which pulls the ball downwards. The speed of its fall increases in proportion to the duration of the fall. In my experiments, I have shown that all bodies fall at the same increasing rate. That is vertical motion. But I can also make a ball move horizontally.
SIMPLICIO
Sideways motions?
GALILEO
Sideways motion. Give me a plank of infinite length, smooth and horizontal. And could I but
remove all impediments, this marble could roll along that plank at a uniform speed forever.
SIMPLICIO
Without an external force to keep it in motion? Oh, come now! Nothing is eternal but the maker of all things.
GALILEO
You have been sent to trap me.
SIMPLICIO
Oh, Galileo.
GALILEO
I have suffered enough. I have recanted ...
SIMPLICIO
It’s not true ...
GALILEO
... that which I know ...
SIMPLICIO
I have told you ...
GALILEO
... to be the truth! The Earth moves around the Sun.
SIMPLICIO
A dangerous contention.
Yet.
GALILEO
Yet?
SIMPLICIO
The heavenly bodies, Jupiter and his moons, and why does our Moon not fall downwards? Hmm?
GALILEO
If I understood the nature of gravity and the role of forces ... I have drawn her in detail. I have measured her mountains, but what keeps her there? And the stars in the heavens, forever out of reach. I cannot say, but gravity must be the key.
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