8.8 — From Superstition to Science

For two thousand years, the way to settle a question about the natural world was to consult an authority. Does a heavy object fall faster than a light one? Aristotle says yes. Does blood pass through the wall of the heart? Galen says yes. Is the Earth at the centre? Ptolemy's system says yes and it predicts the planets accurately.

All three are wrong. Each was overturned in the same way: somebody checked.

That sentence is the scientific revolution. Everything else in this chapter is the machinery that made checking systematic, public, and cumulative.

What actually changed

Not curiosity, which is universal. Not observation, which the Babylonians, Chinese, Greeks, Indians and Arabs all did well.

Five things changed, and it is the combination that made the difference.

1. Controlled experiment as the arbiter. Not just observing what nature does, but arranging a situation so that one factor varies and the rest are held constant, and letting the result decide. Ibn al-Haytham did this in optics (Chapter 7.2); what changed in seventeenth-century Europe is that it became the normal method rather than an individual's practice.

2. Mathematics as the language of nature. Galileo's claim that the book of nature is written in mathematical characters. The move is from qualitative description — heavy things seek their natural place — to quantitative law: distance is proportional to the square of the time. A quantitative law makes predictions precise enough to be wrong, which is what makes it testable.

3. Instruments that extend the senses. The telescope, the microscope, the barometer, the air pump, the thermometer, the pendulum clock. Each opens a domain no argument from first principles could reach.

4. Publication and replication. A result that is not published does not exist. Leonardo's notebooks (Chapter 8.1) are the counter-example: brilliant, unpublished, and without influence.

5. Institutions that outlive individuals. The Royal Society (1660) and the French Académie des Sciences (1666), with journals — Philosophical Transactions, from 1665, the oldest continuously published scientific journal — which established the conventions of dated priority, peer scrutiny and citation that science still runs on.

Points 4 and 5 are the ones most often left out and they are the ones that make it cumulative. Chapter 8.2 supplied the technology; this chapter is the social machinery built on top of it.

Copernicus

Nicolaus Copernicus, a Polish canon and astronomer, published On the Revolutions of the Heavenly Spheres in 1543, the year he died.

The proposal: the Sun is at the centre and the Earth is a planet orbiting it and rotating daily.

Why he did it is not what most people assume. Ptolemy's Earth-centred system predicted planetary positions well. Its problem was aesthetic and philosophical: it required the equant, a device in which a planet moves uniformly as seen from a point that is not the centre of its circle, which violated the principle of uniform circular motion the whole system rested on. Copernicus's stated objection was to that inelegance.

And his system was not simpler in practice. He kept circular orbits, so he still needed epicycles to fit the data, and his model was not more accurate than Ptolemy's. Its virtue was that it explained naturally several things Ptolemy had to build in by hand — why Mercury and Venus never stray far from the Sun, and why the outer planets appear to loop backwards.

The Maragha connection should be noted (Chapter 7.2): Copernicus used geometrical devices identical to those developed by Islamic astronomers, and whether by transmission or independent invention is unresolved.

The book was not immediately controversial. It was dedicated to the Pope, and an unauthorised preface by the editor Osiander described the model as a calculating device rather than a claim about reality, which defused it. It was placed on the Index only in 1616, seventy years later, when Galileo made it a public argument.

Kepler

Johannes Kepler had the best data in the world and he took the model seriously enough to break it.

Tycho Brahe had spent decades making naked-eye observations of unprecedented accuracy — to about an arcminute — from an observatory funded by the Danish crown. Kepler inherited the data.

He spent years trying to fit Mars's orbit to a circle, and got it to within eight arcminutes — good enough that most astronomers of the period would have accepted it. He refused, on the grounds that Tycho's data were better than eight arcminutes, and eventually concluded the orbit is an ellipse.

Three laws. Orbits are ellipses with the Sun at one focus. A line from the Sun to a planet sweeps equal areas in equal times, so a planet moves faster when nearer. And the square of the orbital period is proportional to the cube of the semi-major axis — which relates the different planets to each other in a single formula.

Kepler is the pivotal figure and he is underrated. He gave up the circle, which had been an unquestioned assumption since Plato, because the data would not fit it. That is the method working exactly as it should, and Newton's gravitation is derived directly from Kepler's laws.

He also held that the planets were moved by a physical force from the Sun — the wrong force, and the correct instinct that celestial motions have physical causes.

Galileo

Galileo Galilei's contributions are three and each is substantial.

Mechanics. He established that all bodies fall with the same acceleration regardless of weight, contradicting Aristotle. The leaning tower experiment is probably a legend; what he actually did was roll balls down inclined planes, which slows the motion enough to time with the water clocks available, and showed that distance is proportional to the square of the time. He also formulated the principle of relativity — that mechanics inside a smoothly moving ship is indistinguishable from mechanics at rest — which answers the standard objection to a moving Earth and which Einstein built on.

Astronomy. He did not invent the telescope; he built better ones and pointed them at the sky and published. In 1610 he reported: mountains and craters on the Moon, so heavenly bodies are not perfect spheres; four moons orbiting Jupiter, so not everything orbits the Earth; innumerable stars in the Milky Way; and — the decisive one — that Venus shows a full set of phases like the Moon, which the Ptolemaic system cannot produce and which requires Venus to orbit the Sun.

And method. He wrote in Italian rather than Latin, deliberately, for a lay audience.

The affair, accurately

The popular version is a simple confrontation between science and religion. The actual sequence is more specific and more instructive.

The Church's position in 1616 was that heliocentrism could be taught as a hypothesis useful for calculation but not asserted as physically true without proof. That was, by the standards of evidence then available, not an unreasonable demand — the decisive proof, stellar parallax, was not observed until 1838, and the Church's own astronomers, the Jesuits, were competent and had confirmed Galileo's observations.

Galileo was told in 1616 not to hold or defend the position.

In 1632 he published the Dialogue Concerning the Two Chief World Systems, in which three characters debate. He had permission to present both sides. He put the Pope's own argument into the mouth of a character named Simplicio — the simpleton — who is defeated throughout. Urban VIII had been his patron and supporter.

He was tried in 1633, forced to abjure, and spent the rest of his life under house arrest, during which he wrote his best book, on mechanics, and had it smuggled out and published in the Netherlands. He was not tortured and not burned. The story that he muttered and yet it moves is a later invention.

The honest reading: a real conflict about authority, badly handled by the Church and handled with considerable arrogance by Galileo, in which the substantive question of evidence was genuinely open and the institutional question of who may decide was the actual issue. Chapter 16.4 uses it: the mechanism that matters is not whether an authority is religious, but whether any authority can settle a question that evidence should settle.

Newton

Isaac Newton's Principia Mathematica, 1687, is the single most consequential scientific book ever written.

The three laws of motion, and universal gravitation: every mass attracts every other with a force proportional to the product of the masses and inversely proportional to the square of the distance between them.

Why it is the turning point. It unified the heavens and the Earth. Aristotle's physics had two realms with two sets of rules — corruptible sublunary matter and perfect celestial spheres. Newton showed that the force that makes an apple fall is the force that holds the Moon in orbit, and gave one equation for both.

And it derived Kepler's laws. From the inverse-square law, elliptical orbits and the other two laws follow mathematically. A set of empirical regularities became consequences of a single principle.

It also predicted new things. The oblate shape of the Earth, the precession of the equinoxes, the tides (Chapter 1.2), and — the most spectacular — Halley applied Newton's method to comet observations, concluded that three recorded comets were one object on a 76-year orbit, and predicted its return in 1758. It returned. Halley had been dead for sixteen years.

Volume IV covers the physics. The point here is what a successful prediction of that kind does to a culture's confidence in a method.

Everything else

Vesalius (1543) dissected human bodies himself, rather than having a barber do it while a professor read Galen aloud, and published On the Fabric of the Human Body with illustrations of extraordinary quality — correcting Galen, whose anatomy had been based on animals, in dozens of places.

Harvey (1628) demonstrated that blood circulates, and the argument is quantitative and decisive: he measured the heart's output and showed that in half an hour it pumps more blood than the whole body contains, so the blood cannot be continuously manufactured and consumed as Galen held. It must go round.

Boyle established chemistry as distinct from alchemy and insisted on publishing failed experiments as well as successful ones.

Hooke and Leeuwenhoek opened the microscopic world — Hooke naming the cell, Leeuwenhoek describing bacteria and protozoa with lenses he ground himself and never explained to anyone.

And Bacon and Descartes wrote the method down. Bacon argued for systematic experiment and induction from many observations, and against reasoning from authority. Descartes argued for systematic doubt and for mathematical deduction from clear principles. They disagreed with each other, and science ended up using both, which is why the two-word summary "the scientific method" is a schoolroom simplification of something that is really a set of overlapping practices.

Why Europe

This is the question the whole Part has been building to, and the honest answer has several parts and no single cause.

Political fragmentation. Chapter 7.9 and 8.4 established it and here it does its most important work. Europe was a few dozen competing states with a shared learned language. A scholar or a book banned in one place moved to another — Galileo's last book was published in the Netherlands, Descartes lived and published there, and the Dutch presses printed what France and Rome prohibited. A single empire can shut down an inquiry with one decision. A continent of rivals cannot, and rivals also competed to attract talent, since a good astronomer or engineer was a strategic asset.

Printing. Chapter 8.2, and specifically the cumulative correction of texts and the exact reproduction of diagrams and tables.

The universities. Chapter 7.4's self-governing corporations, with a curriculum that already included natural philosophy and a scholastic habit of formal objection and reply.

The institutional separation of religious and political authority (Chapter 7.4), which left space that neither could fully control.

And the Reformation's indirect effects — literacy for scripture reading, the shattering of a single religious authority, and the discrediting of argument from authority in general once the highest authority in Europe had been publicly defied.

What is not the explanation: any difference in intelligence, curiosity or capability. Chapter 7.2's Islamic scholars practised experiment, mathematics and instrument-making at the highest level, and Chapter 7.9's China had better technology than Europe in 1400. The difference is in the institutional arrangements that let results accumulate, be corrected, and be protected from any single authority's veto.

Where this shows up in your life

Everything technological, because engineering is applied science and the compounding started here.

Peer review, journals, citation, replication and priority — the conventions of every research field, invented by the Royal Society in the 1660s.

And a habit you can use. The core move is: state the claim precisely enough that it could be wrong, then check, then publish the check so someone else can repeat it. That is available to anyone about anything, and Chapter 16.4 turns it into a practical tool for reading the news.

What the next page covers

Once a method for settling questions about nature had visibly worked, people asked whether it could settle questions about society — about government, rights, law, religion and how a person should live. Chapter 8.9 covers the Enlightenment: what its thinkers actually argued, the disagreements among them, the political ideas that went straight into the American and French revolutions, and the honest reckoning with the fact that several of its greatest advocates of universal rights owned slaves or defended empire.