tl;dr: The side of rationality during Galileo’s time would be to recognise one’s confusion and recognise that the models did not yet cash out in terms of a difference in expected experiences. That situation arguably holds until Newton’s Principia; prior to that no one has a working physics for the heavens.
The initial heliocentric models weren’t more accurate by virtue of being heliocentric; they were better by virtue of having had their parameters updated with an additional 400 years of observational data over the previous best-fit model (the Alfonsine tables from the 1250s). The geometry was similarly complicated; there was still a strong claim that only circular motions could be maintained indefinitely, and so you have to toss 60 or so circular motions in to get the full solar system on either model.
Basically everyone was already using the newer tables as calculational tools, and it had been known from ancient times that you could fix any point you wanted in an epicyclic model and get the same observational results. The dispute was about which object was in fact fixed. Kepler dates to the same time, and will talk about ellipses (and dozens of other potential curves) in place of circular motion from 1610, but he cannot predict where a planet will be efficiently. He’s also not exactly a paragon of rationality; astrology and numerology drive most of his system, and he quite literally ascribes his algebraic slips to god.
A brief but important digression into Aristotle is needed; he saw as key that was made was that the motion of the planets is unceasing but changes, whereas all terrestrial motions ceased eventually. He held that circular motions were the only kind of motion that could be sustained indefinitely, and even then, only by a certain special kind of perfect matter. The physics of this matter fundamentally differed from the physics of normal stuff in Aristotle. Roughly and crudely, if it can change then it has to have some kind of dissipative / frictional physics and so will run down.
Against that backdrop, Galileo’s key work wasn’t the Dialogue, but the Siderius Nuncius. There had been two novae observed in the 40 years prior, and this had been awkward because a whole bunch of (mostly neo-Platonists) were arguing that this showed the heavens changed, which is a problem for Aristotle. Now Galileo shows up and using a device which distorts his vision, he claims to be able to deduce:
There are Mountains on the moon (so that it is not a sphere contra Aristotle)
There are Invisible objects orbiting Jupiter
That the planets show disks
That the Sun has spots, which move across the face and separately change with time
That Venus has phases (which essentially require that it orbit the Sun)
That Saturn has lumps on it (and thus not a sphere—he’s seeing the rings)
As an observational program, this is picked up with and deeply explored by loads of people (inc. Jesuits like Riccioli). But to emphasise: Galileo is using a device which distorts his vision and which can only be tested on terrestrial objects and claiming to use it to find out stuff about the heavens, which contemporary physics says is grossly different. Every natural philosopher who’s read Aristotle recognises that this kind of procedure hasn’t historically been useful.
From a viewpoint which sees a single unified material physics, these observations kill Aristotelian cosmology. You’ve got at least three centers of circular-ish motion, which means you can’t mount the planets on transparent spheres to actually move them around. You have an indication that the Sun might be rotating, and is certainly dynamic. If you kill Aristotle’s cosmology, you have to kill most of his physics, and thus a good chunk of his philosophy. That’s a problem, because since Aquinas the Catholic church had been deriving theology as a natural consequence of Aristotle in order to secure themselves against various heresies. And now some engineer with pretensions is turning up, distorting his vision and claiming to upend the cart.
What Galileo does not have is a coherent alternative package of physics and cosmology. He claims to be able to show a form of circular inertia from first principles. He claims that this yields a form of relativity in motion which makes it difficult to discern your true motion without reference to the fixed stars. He claims that physics is kinda-sorta universal, based on his experience with cannon (which Aristotelian physics would dismiss because [using modern terminology] experiments where you apply forces yourself are not reproducible and so cannot yield knowledge). This means his physics has real issues explaining dissipative effects. He doesn’t have action at a distance, so he can’t explain why the planets do their thing (whereas there are physical models of Aristotelian / Ptolemaic models).
He gets into some pro forma trouble over the book, because he doesn’t put a disclaimer on it saying that he’ll retract it if it’s found to be heretical. Which is silly and it gets his knuckles rapped over it. The book is “banned”, which means two things, for there are two lists of banned books. One is “burn before reading” and the other is more akin to being in the Restricted Section; Galileo’s work is the latter.
Then he’s an ass in the Dialogue. Even that would not have been an issue, but at the time he’s the court philosopher of the Grand Duke of Tuscany, Cosimo I de’ Medici. This guy is a secular problem for the Pope; he has an army, he’s not toeing the line, there’s a worry that he’ll annex the Papal states. So there’s a need to pin his ears back, and Galileo is a sufficiently senior member of the court that Cosimo won’t ignore his arrest nor will he go to war over it.
So the Inquisition cooks up a charge for political purposes, has him “tortured” (which is supposed to mean they /show/ him the instruments of torture, but they actually forget to), get him to recant (in particular get Cosimo to come beg for his release), and release him to “house arrest” (where he is free to come, go, see whoever, write, etc). The drama is politics, rather than anything epistemological.
As to the disputes you mention, some had been argued through by the ancient Greeks. For example, everyone knew that measurements were imprecise, and so moving the earth merely required that the stars were distant. It was also plain that if you accepted Galileo’s observations as being indicative of truth, then Aristotelian gravity was totally dead, because some stuff did not strive to fall (cometary tails were also known to be… problematic).
Now, Riccioli is writing 20 years later, in an environment where heliocentrism has become a definite thing with political and religious connotations, associated to neo-Platonism, anti-Aristotelean, anti-Papal thinking. This is troublesome because it strikes at the foundational philosophy underpinning the Church, and secular rulers in Europe are trying to strategically leverage this. Much like Aquinas, Riccioli’s bottom line is /written/ already. He has to mesh this new stack of observational data with something which looks at least somewhat like Aristotle. Descartes is contracted at about the same time to attempt to rederive Catholicism from a new mixed Aristotilean / Platonist basis.
As a corollary, he’s being quite careful to list every argument which anyone has made, and every refutation (there’s a comparatively short summary here). Most of the arguments presented have counterpoints from the other side, however strained they might seem from a modern view. It’s more akin to having 126 phenomena which need to be explained than anything else. They don’t touch on the apparently changing nature of the planets (by this point cloud bands on Jupiter could be seen) and restrict themselves mostly to the physics of motion. There’s a lot of duplication of the same fundamental point, and it’s not a quantitative discussion. There are some “in principle” experiments discussed, but a fair few had been considered by Galileo and calculated to be infeasible (eg. observing 1 inch deflections in cannon shot at 500 yards, when the accuracy is more like a yard).
Obviously Newton basically puts a stop to the whole thing, because (modulo a lack of mechanism) he can give you a calculational tool which spits out Kepler and naturally fixes the center of mass. There are still huge problems; the largest is that even point-like stars appear to have small disks from diffraction, and until you know this you end up thinking every other star has to be larger than the entire solar system. And the apparent madness of a universal law is almost impossible to understate. It’s really ahistorical to think that a very modern notion of parsimony in physics could have been applied to Galileo and his contemporaries.
Thank you for that informed account of the history.
You mention three times, without attributing it to any contemporary of Galileo, that the telescope “distorted the vision”, which is a tendentious description. Given that the military application of the telescope was grasped as soon as the instrument became known, who at the time made this criticism? Did they similarly eschew its terrestrial use for the improvement of vision?
The precise phrasing is deliberately a little tendentious, but the issue of the epistemological status of the telescope was raised by loads of people at the time. For a modern review with heavy footnotes, see eg
Galileo, Courtier: The Practice of Science in the Culture of Absolutism, pp 95-100,
(though the whole chapter is good)
For example, the first anti-Galilean tract is by Horky in 1610 and focussed mostly on the lack of reliability of the telescope. For another, Magini’s letters (confirmed in Kepler and Galileo) write of a “star party” in 1610 where Galileo attempted to convince a number of astronomers of the discovery of the Medician (now Galilean) moons; noone else could see the moons and additionally the telescope produced doubled images of everything more distant than the moon.
There wasn’t much dispute about terrestial applications. Under Aristotle’s physics everything above the moon is made of different stuff with different physics anyway, so any amount of accuracy when looking at stuff of the four elements doesn’t allow one to induct to accuracy in observations of the heavens.
For a modern review with heavy footnotes, see eg Galileo, Courtier: The Practice of Science in the Culture of Absolutism, pp 95-100, (though the whole chapter is good)
I think these words are rather telling (emphasis in the original, p.96):
...Galileo began to be attacked for the Copernican implications of his discoveries only after the reliability of his telescope began to be accepted. In a sense, attacks on his Copernicanism were a sure sign of his enemies’ taking his telescope and discoveries seriously.
And it goes on to show how the dispute was conducted on both sides in terms of status, Galileo getting princes on side by sending them telescopes, and his opponents attacking him because he was succeeding.
Under Aristotle’s physics everything above the moon is made of different stuff with different physics anyway, so any amount of accuracy when looking at stuff of the four elements doesn’t allow one to induct to accuracy in observations of the heavens.
That sounds a rather odd argument to make, even at the time. Astronomy from antiquity was founded on accurate observations. Galileo’s contemporaries could argue that the telescope wasn’t good enough, but hardly that getting a better view of the heavens could reveal nothing new. They were arguing over what could be seen, not that seeing was the wrong thing to do.
That sounds a rather odd argument to make, even at the time. Astronomy from antiquity was founded on accurate observations.
Astronomy and epistemology aren’t quite the same. Predicting where Saturn would be on a given date requires accurate observation, and nobody objected to Coperniucus as a calculational tool. For example, the Jesuits are teaching Copernicus in China in Chinese about 2 years after he publishes, which implies they translated and shipped it with some alacrity.
The heavens were classically held to be made of different stuff; quintessense (later called aether) was not like regular matter—this is obvious from the inside, because it maintains perpetual motion where normal matter does not. A lot of optical phenomena (eg. twinkling stars, the surface of the moon) were not seen as properties of the objects in question but properties of regular 4-elements matter between us and them.
By a modern standard, the physics is weird and disjointed… but that is historically how it was seen.
Jesuits are teaching Copernicus in China in Chinese about 2 years after he publishes
Do you have a citation for that?
Added: No, this is false. The Jesuits were founded in 1540; Copernicus published in 1542. Francis Xavier proposed sending astronomers to Asia while in Japan in 1552. In the same year he died trying to reach China. I don’t think Jesuits learned Chinese until about 1580. One of the first to do so, Matteo Ricci, again asked for astronomers in 1605, which suggests to me that he was not, himself, teaching Copernicus.
I’d lay my money on their both being recognizable, but QM coming through cleaner than GR. They both pull a lot of weight—a lot more than 16th century physics did.
Epicycles are sort of like Fourier analysis. Just like you can break down a non-sine function into sine waves, you can break down a non-circular orbit into a combination of circles.
But if you’re going to use epicycles anyway, why prefer Copernicus to Ptolemy?
Fewer epicycles means easier calculations. Still, it isn’t clear why you should prefer the Copernican system to the Tychonic (the other major contender in Galileo’s time) when evaluating based on some mix of accuracy and ease of calculation (if your goal is to know “where Saturn would be on a given date”).
Whoops, you’re right. It seems as though Copernicus dropped an equant at the cost of adding even more epicycles. Hardly an unambiguously preferable trade-off.
tl;dr: The side of rationality during Galileo’s time would be to recognise one’s confusion and recognise that the models did not yet cash out in terms of a difference in expected experiences. That situation arguably holds until Newton’s Principia; prior to that no one has a working physics for the heavens.
The initial heliocentric models weren’t more accurate by virtue of being heliocentric; they were better by virtue of having had their parameters updated with an additional 400 years of observational data over the previous best-fit model (the Alfonsine tables from the 1250s). The geometry was similarly complicated; there was still a strong claim that only circular motions could be maintained indefinitely, and so you have to toss 60 or so circular motions in to get the full solar system on either model.
Basically everyone was already using the newer tables as calculational tools, and it had been known from ancient times that you could fix any point you wanted in an epicyclic model and get the same observational results. The dispute was about which object was in fact fixed. Kepler dates to the same time, and will talk about ellipses (and dozens of other potential curves) in place of circular motion from 1610, but he cannot predict where a planet will be efficiently. He’s also not exactly a paragon of rationality; astrology and numerology drive most of his system, and he quite literally ascribes his algebraic slips to god.
A brief but important digression into Aristotle is needed; he saw as key that was made was that the motion of the planets is unceasing but changes, whereas all terrestrial motions ceased eventually. He held that circular motions were the only kind of motion that could be sustained indefinitely, and even then, only by a certain special kind of perfect matter. The physics of this matter fundamentally differed from the physics of normal stuff in Aristotle. Roughly and crudely, if it can change then it has to have some kind of dissipative / frictional physics and so will run down.
Against that backdrop, Galileo’s key work wasn’t the Dialogue, but the Siderius Nuncius. There had been two novae observed in the 40 years prior, and this had been awkward because a whole bunch of (mostly neo-Platonists) were arguing that this showed the heavens changed, which is a problem for Aristotle. Now Galileo shows up and using a device which distorts his vision, he claims to be able to deduce:
There are Mountains on the moon (so that it is not a sphere contra Aristotle)
There are Invisible objects orbiting Jupiter
That the planets show disks
That the Sun has spots, which move across the face and separately change with time
That Venus has phases (which essentially require that it orbit the Sun)
That Saturn has lumps on it (and thus not a sphere—he’s seeing the rings) As an observational program, this is picked up with and deeply explored by loads of people (inc. Jesuits like Riccioli). But to emphasise: Galileo is using a device which distorts his vision and which can only be tested on terrestrial objects and claiming to use it to find out stuff about the heavens, which contemporary physics says is grossly different. Every natural philosopher who’s read Aristotle recognises that this kind of procedure hasn’t historically been useful.
From a viewpoint which sees a single unified material physics, these observations kill Aristotelian cosmology. You’ve got at least three centers of circular-ish motion, which means you can’t mount the planets on transparent spheres to actually move them around. You have an indication that the Sun might be rotating, and is certainly dynamic. If you kill Aristotle’s cosmology, you have to kill most of his physics, and thus a good chunk of his philosophy. That’s a problem, because since Aquinas the Catholic church had been deriving theology as a natural consequence of Aristotle in order to secure themselves against various heresies. And now some engineer with pretensions is turning up, distorting his vision and claiming to upend the cart.
What Galileo does not have is a coherent alternative package of physics and cosmology. He claims to be able to show a form of circular inertia from first principles. He claims that this yields a form of relativity in motion which makes it difficult to discern your true motion without reference to the fixed stars. He claims that physics is kinda-sorta universal, based on his experience with cannon (which Aristotelian physics would dismiss because [using modern terminology] experiments where you apply forces yourself are not reproducible and so cannot yield knowledge). This means his physics has real issues explaining dissipative effects. He doesn’t have action at a distance, so he can’t explain why the planets do their thing (whereas there are physical models of Aristotelian / Ptolemaic models).
He gets into some pro forma trouble over the book, because he doesn’t put a disclaimer on it saying that he’ll retract it if it’s found to be heretical. Which is silly and it gets his knuckles rapped over it. The book is “banned”, which means two things, for there are two lists of banned books. One is “burn before reading” and the other is more akin to being in the Restricted Section; Galileo’s work is the latter.
Then he’s an ass in the Dialogue. Even that would not have been an issue, but at the time he’s the court philosopher of the Grand Duke of Tuscany, Cosimo I de’ Medici. This guy is a secular problem for the Pope; he has an army, he’s not toeing the line, there’s a worry that he’ll annex the Papal states. So there’s a need to pin his ears back, and Galileo is a sufficiently senior member of the court that Cosimo won’t ignore his arrest nor will he go to war over it.
So the Inquisition cooks up a charge for political purposes, has him “tortured” (which is supposed to mean they /show/ him the instruments of torture, but they actually forget to), get him to recant (in particular get Cosimo to come beg for his release), and release him to “house arrest” (where he is free to come, go, see whoever, write, etc). The drama is politics, rather than anything epistemological.
As to the disputes you mention, some had been argued through by the ancient Greeks. For example, everyone knew that measurements were imprecise, and so moving the earth merely required that the stars were distant. It was also plain that if you accepted Galileo’s observations as being indicative of truth, then Aristotelian gravity was totally dead, because some stuff did not strive to fall (cometary tails were also known to be… problematic).
Now, Riccioli is writing 20 years later, in an environment where heliocentrism has become a definite thing with political and religious connotations, associated to neo-Platonism, anti-Aristotelean, anti-Papal thinking. This is troublesome because it strikes at the foundational philosophy underpinning the Church, and secular rulers in Europe are trying to strategically leverage this. Much like Aquinas, Riccioli’s bottom line is /written/ already. He has to mesh this new stack of observational data with something which looks at least somewhat like Aristotle. Descartes is contracted at about the same time to attempt to rederive Catholicism from a new mixed Aristotilean / Platonist basis.
As a corollary, he’s being quite careful to list every argument which anyone has made, and every refutation (there’s a comparatively short summary here). Most of the arguments presented have counterpoints from the other side, however strained they might seem from a modern view. It’s more akin to having 126 phenomena which need to be explained than anything else. They don’t touch on the apparently changing nature of the planets (by this point cloud bands on Jupiter could be seen) and restrict themselves mostly to the physics of motion. There’s a lot of duplication of the same fundamental point, and it’s not a quantitative discussion. There are some “in principle” experiments discussed, but a fair few had been considered by Galileo and calculated to be infeasible (eg. observing 1 inch deflections in cannon shot at 500 yards, when the accuracy is more like a yard).
Obviously Newton basically puts a stop to the whole thing, because (modulo a lack of mechanism) he can give you a calculational tool which spits out Kepler and naturally fixes the center of mass. There are still huge problems; the largest is that even point-like stars appear to have small disks from diffraction, and until you know this you end up thinking every other star has to be larger than the entire solar system. And the apparent madness of a universal law is almost impossible to understate. It’s really ahistorical to think that a very modern notion of parsimony in physics could have been applied to Galileo and his contemporaries.
Thank you for that informed account of the history.
You mention three times, without attributing it to any contemporary of Galileo, that the telescope “distorted the vision”, which is a tendentious description. Given that the military application of the telescope was grasped as soon as the instrument became known, who at the time made this criticism? Did they similarly eschew its terrestrial use for the improvement of vision?
The precise phrasing is deliberately a little tendentious, but the issue of the epistemological status of the telescope was raised by loads of people at the time. For a modern review with heavy footnotes, see eg Galileo, Courtier: The Practice of Science in the Culture of Absolutism, pp 95-100, (though the whole chapter is good)
For example, the first anti-Galilean tract is by Horky in 1610 and focussed mostly on the lack of reliability of the telescope. For another, Magini’s letters (confirmed in Kepler and Galileo) write of a “star party” in 1610 where Galileo attempted to convince a number of astronomers of the discovery of the Medician (now Galilean) moons; noone else could see the moons and additionally the telescope produced doubled images of everything more distant than the moon.
There wasn’t much dispute about terrestial applications. Under Aristotle’s physics everything above the moon is made of different stuff with different physics anyway, so any amount of accuracy when looking at stuff of the four elements doesn’t allow one to induct to accuracy in observations of the heavens.
I think these words are rather telling (emphasis in the original, p.96):
And it goes on to show how the dispute was conducted on both sides in terms of status, Galileo getting princes on side by sending them telescopes, and his opponents attacking him because he was succeeding.
That sounds a rather odd argument to make, even at the time. Astronomy from antiquity was founded on accurate observations. Galileo’s contemporaries could argue that the telescope wasn’t good enough, but hardly that getting a better view of the heavens could reveal nothing new. They were arguing over what could be seen, not that seeing was the wrong thing to do.
Astronomy and epistemology aren’t quite the same. Predicting where Saturn would be on a given date requires accurate observation, and nobody objected to Coperniucus as a calculational tool. For example, the Jesuits are teaching Copernicus in China in Chinese about 2 years after he publishes, which implies they translated and shipped it with some alacrity.
The heavens were classically held to be made of different stuff; quintessense (later called aether) was not like regular matter—this is obvious from the inside, because it maintains perpetual motion where normal matter does not. A lot of optical phenomena (eg. twinkling stars, the surface of the moon) were not seen as properties of the objects in question but properties of regular 4-elements matter between us and them.
By a modern standard, the physics is weird and disjointed… but that is historically how it was seen.
Do you have a citation for that?
Added: No, this is false. The Jesuits were founded in 1540; Copernicus published in 1542. Francis Xavier proposed sending astronomers to Asia while in Japan in 1552. In the same year he died trying to reach China. I don’t think Jesuits learned Chinese until about 1580. One of the first to do so, Matteo Ricci, again asked for astronomers in 1605, which suggests to me that he was not, himself, teaching Copernicus.
I wonder how current physics will look like if/when GR and QM will be finally unified...
I’d lay my money on their both being recognizable, but QM coming through cleaner than GR. They both pull a lot of weight—a lot more than 16th century physics did.
It’s worth noting that Copernicus’ use of circular orbits required the use of epicycles to make the theory fit the observations.
Epicycles are sort of like Fourier analysis. Just like you can break down a non-sine function into sine waves, you can break down a non-circular orbit into a combination of circles.
But if you’re going to use epicycles anyway, why prefer Copernicus to Ptolemy?
Fewer epicycles means easier calculations. Still, it isn’t clear why you should prefer the Copernican system to the Tychonic (the other major contender in Galileo’s time) when evaluating based on some mix of accuracy and ease of calculation (if your goal is to know “where Saturn would be on a given date”).
Going by wiki, Copernicus’ system had more epicycles.
Whoops, you’re right. It seems as though Copernicus dropped an equant at the cost of adding even more epicycles. Hardly an unambiguously preferable trade-off.
According to Koestler (The Sleepwalkers) Copernicus just hated Ptolemy’s “eccentrics” because a good Platonist God does not do ugly assymetrical work like that. http://en.wikipedia.org/wiki/Deferent_and_epicycle