Topic 4.2 Notes – The Scientific Revolution

What Changed in the Scientific Revolution

This topic is less about a pile of discoveries and more about a new way of proving things. Europeans had long relied on Aristotle, Ptolemy, and Galen, but their ideas stopped being untouchable.

• People in this period usually called their work natural philosophy, not modern science.
• Authority shifted toward observation, experiment, mathematics, and reasoning.
• Ancient texts still mattered, but now they could be corrected.
• This was not a clean break from religion. Many thinkers were Christian and still accepted astrology, alchemy, or spiritual forces.

A few background changes made this possible:

• Printing press spread ideas and criticism faster.
• Renaissance humanism recovered old texts and encouraged comparing versions instead of blindly trusting them.
• Exploration exposed Europeans to new plants, animals, and maps that challenged old knowledge.
• Better tools like the telescope and microscope let people see what earlier writers could not.

How Astronomy Replaced the Old Cosmos

Before the new astronomy, Europeans pictured a geocentric universe. Earth sat still at the center. The heavens were thought to be perfect, unchanging, and moving in circles. Ptolemy used epicycles to explain strange planetary motion.

Ptolemaic geocentric model

Copernicus

In On the Revolutions of the Heavenly Spheres (1543), Copernicus proposed heliocentrism. Earth rotates daily and revolves around the Sun.

• This explained retrograde motion more simply. Planets only seem to move backward because Earth passes them.
• He still kept circular orbits and epicycles, so he did not fully break with older ideas.

Tycho Brahe

Brahe mattered because he produced the best observations before the telescope.

• His 1572 new star and 1577 comet showed the heavens changed.
• He proposed a geoheliocentric model, a compromise with Earth still central.
• His precise data later let Kepler fix Copernicus’s model.

Johannes Kepler

Using Brahe’s data, Kepler created the three laws of planetary motion in New Astronomy (1609) and The Harmony of the World (1619).

• Planets move in ellipses, not circles.
• They sweep out equal areas in equal times.
• Planets farther from the Sun take longer to orbit.

Kepler is a classic continuity example because he also practiced astrology.

Galileo Galilei

Galileo gave heliocentrism visible evidence in The Starry Messenger (1610).

• Mountains on the Moon and sunspots challenged perfect heavens.
• Moons of Jupiter proved not everything orbited Earth.
• Phases of Venus supported a Sun-centered arrangement.
• His inclined-plane experiments challenged Aristotle’s ideas about motion.

Church conflict matters here because it shows the stakes of changing knowledge:

• 1616 warning not to defend heliocentrism as truth
• 1632 Dialogue Concerning the Two Chief World Systems
• 1633 trial and house arrest

Isaac Newton

In the Principia (1687), Newton pulled the whole story together.

• Three laws of motion
• Universal gravitation with $F = G \frac{m_1 m_2}{r^2}$
• Same laws govern heaven and Earth

The famous apple story is more legend than proof, but it captures the big idea that gravity works on ordinary objects and on planets too.

Newton and the apple legend

This created a mechanical universe ruled by universal laws. Newton also studied alchemy, which is another key continuity.

How Medicine and Anatomy Challenged Galen

In medicine, the old model came from Galen. He taught humoral theory with four humors, and disease meant imbalance. Treatments included bloodletting and purging.

Andreas Vesalius

In On the Fabric of the Human Body (1543), Vesalius used human dissection to correct Galen’s animal-based mistakes.

• The method shift matters most. Look at the body itself, not just the book.

Vesalius, On the Fabric of the Human Body

Paracelsus

Paracelsus rejected much traditional university medicine.

• Diseases could have specific causes
• Favored chemical and mineral remedies
• Still mixed medicine with alchemy, astrology, and religion

William Harvey

In On the Motion of the Heart and Blood (1628), Harvey argued that the heart is a pump and blood circulates.

1. He observed valves in veins.
2. He used ligatures to show blood moved in one direction.
3. He estimated blood flow and showed the body could not constantly create that much new blood.

Marcello Malpighi later saw capillaries with a microscope in 1661, filling the missing link.

Bacon, Descartes, and the New Way of Knowing

Francis Bacon

In Novum Organum (1620), Bacon pushed empiricism and inductive reasoning.

• Start with repeated observations
• Build toward general conclusions
• Do not trust authority without evidence

René Descartes

In Discourse on Method (1637), Descartes emphasized rationalism and deductive reasoning.

• Begin with doubt
• Use logic and mathematics
• “I think, therefore I am”
• Cartesian dualism separated mind from matter

Together, Bacon and Descartes helped shape the scientific method, though there was no single fixed version. On the exam, evidence usually supports, modifies, or refutes a claim rather than merely repeating authority.

Change, Continuity, and Why It Matters

The biggest change was epistemological. People increasingly asked, What evidence proves this?

• Changes included heliocentrism, laws of motion, universal gravitation, improved anatomy, and circulation of blood.
• Continuities included religion, providence, astrology, alchemy, and gradual acceptance of new ideas.
• Named continuity examples you should know are Kepler and astrology and Newton and alchemy.

This matters because success in finding laws of nature encouraged later thinkers to look for laws of society, politics, and economics, which leads straight into the Enlightenment.