Galileo (Leaving Cert Religious Education): Revision Notes
Galileo
Who was Galileo?
Galileo Galilei (1564-1642) is widely recognised as the "father of modern science." This Italian mathematician and astronomer revolutionised our understanding of the universe by combining mathematics with careful observation and experimentation. His work laid the foundations for modern physics and marked the beginning of the scientific method as we know it today.
Galileo's significance extends beyond science - his conflict with the Roman Catholic Church became known as "The Galileo Affair," representing a crucial turning point in the relationship between religious authority and scientific discovery.
The world Galileo challenged
The mediaeval worldview
When Galileo lived, European thought was dominated by two main sources of authority:
- The Roman Catholic Church's interpretation of the Bible (often taken literally)
- Ancient Greek philosophy, particularly the writings of Aristotle
This mediaeval worldview had remained largely unchanged for over 1,300 years and presented a very specific picture of the universe that would prove extremely difficult to challenge.
The geocentric model
The accepted model of the universe was geocentric (Earth-centred), based on the work of:
- Aristotle - who divided the cosmos into two distinct regions:
- Earth (sublunary) - changeable, imperfect, heavy, and stationary at the centre
- Heavens (superlunary) - perfect, unchanging, made of "ether," moving in perfect circular motion around Earth
- Ptolemy (2nd Century CE) - who created a complex system of "epicycles" (circles upon circles) to explain planetary movements whilst keeping Earth at the centre
Religious significance
For Christians, Earth being at the centre wasn't just scientific theory - it had theological importance. Earth was seen as:
- The centre of God's creation
- The stage where human salvation was being played out
- Proof of humanity's special place in God's plan
The Church used biblical passages like Joshua 10:13 ("the sun stands still") and Psalms 93:1 ("the world is firmly established and cannot be moved") to support this view.
The Copernican Revolution
A radical new theory
In 1543, Nicholas Copernicus, a Polish priest and mathematician, published "On the Revolution of the Heavenly Spheres." His revolutionary idea proposed that:
- The Sun, not Earth, was at the centre of the universe (heliocentric model)
- Earth was just another planet that rotated daily on its axis and revolved annually around the Sun
Initial reception
Copernicus was reluctant to publish his theory, fearing ridicule from both the Church and academic scholars. Many people initially dismissed the idea as laughable - the thought that Earth was spinning at tremendous speed seemed absurd.
The Catholic Church initially tolerated the theory when presented as mathematical speculation rather than physical reality. However, this tolerance would not last when Galileo began providing evidence for its truth.
Galileo's revolutionary methods
The scientific method
Galileo pioneered what became known as the scientific method, which involved:
- Observation - carefully watching natural phenomena
- Measurement - quantifying what was observed
- Experimentation - testing ideas through controlled investigation
Inductive reasoning
Unlike mediaeval scholars who worked from accepted authorities downward, Galileo used inductive method:
- Started with concrete observations and data
- Built up to general patterns and theories
- Moved from specific evidence to broader conclusions
Practical Application of Galileo's Method
Traditional approach: "Aristotle says heavy objects fall faster, therefore it must be true."
Galileo's approach:
- Observe: Drop objects of different weights from the same height
- Measure: Time how long each takes to fall
- Experiment: Repeat under controlled conditions
- Conclude: Objects fall at the same rate regardless of weight (ignoring air resistance)
Thought experiments
Galileo created "thought experiments" - combining mathematical reasoning with empirical observation. This created constant interaction between theoretical ideas and experimental evidence, making the physical world understandable through mathematics rather than mystical explanations.
Galileo's groundbreaking discoveries
The telescope revolution
In 1609, Galileo modified his telescope to achieve 9x magnification. Through this instrument, he made observations that would shatter the mediaeval worldview:
Key discoveries
- The Moon's surface was pockmarked with mountains and valleys - not the perfect, smooth sphere Aristotle had claimed
- Jupiter had four moons orbiting around it - proving not everything revolved around Earth
- Venus showed phases like our Moon - this could only be explained if Venus orbited the Sun, not Earth
- The Milky Way contained countless individual stars at enormous distances - suggesting the universe was far larger than previously imagined
Revolutionary implications
These discoveries directly contradicted the Aristotelian-Ptolemaic worldview and supported Copernican theory. They proved that:
- Celestial objects were not perfect and unchanging
- Earth was not unique - other planets had moons too
- The heliocentric model better explained observed phenomena
The conflict with the Church
Initial acceptance
At first, the Roman Catholic Church was sympathetic to Galileo's work. Pope Paul V welcomed him, and many Church officials were impressed by his discoveries. However, the Church grew cautious about the theological implications of a heliocentric universe.
Growing tension
The situation deteriorated when:
- Galileo published "The Starry Messenger" (1610), revolutionising astronomy
- He began arguing that Copernican theory was physical fact, not just mathematical speculation
- Cardinal Bellarmine warned Galileo not to teach Copernicanism as fact
The trial of 1633
In 1632, Galileo published "Dialogue of the Two Chief World Systems," which strongly defended Copernican theory while mocking the Aristotelian-Ptolemaic view. This brought him into direct confrontation with Church authority.
The Charges Against Galileo
The Holy Office accused Galileo of:
- Breaking his 1616 promise not to hold or teach Copernican views
- Heresy (false teaching)
- Challenging biblical interpretation and Church authority
Under threat of imprisonment and torture, Galileo was forced to deny his Copernican views four times under oath. He was condemned and placed under house arrest for the remainder of his life until his death in 1642.
Galileo's attempt at reconciliation
The "two books" metaphor
Despite the conflict, Galileo remained a devout Catholic who wanted to reconcile science and religion. In a 1619 letter, he used Francis Bacon's "two books" metaphor:
- The Book of Scripture (the Bible) - written in poetry and symbolism, teaching "how one goes to heaven"
- The Book of Nature (the physical universe) - written in the language of mathematics, showing how the heavens go
Key principle
Galileo argued that both books came from God, so they couldn't contradict each other. He believed caution was needed when trying to read scientific truths directly from Scripture, since the Bible's primary purpose was spiritual guidance, not scientific instruction.
This idea, summarised by Cardinal Baronius, stated that the Bible teaches "not how the heavens go but how one goes to heaven."
Historical significance
Paradigm shift
Galileo's work marked what historians call a "paradigm shift" - a fundamental change in how people understood the universe. It represented:
- The separation of mediaeval science and philosophy from religion
- The beginning of the scientific age
- A new way of understanding humanity's place in the cosmos
Long-term impact
Although Galileo was forced to recant, his work laid the foundation for:
- Modern physics and astronomy
- The scientific method still used today
- A new relationship between science and religion
- Recognition that both scientific and religious truth have their proper domains
Key Points to Remember:
- Galileo combined mathematics with observation - creating the foundation of modern scientific method
- His telescope discoveries proved the heliocentric model - the Moon had craters, Jupiter had moons, and Venus showed phases
- The Church initially tolerated but later condemned Galileo's support for Copernican theory as physical fact
- He attempted reconciliation through the "two books" metaphor - Scripture teaches how to go to heaven, while nature teaches how the heavens go
- His work marked the beginning of the scientific revolution - separating scientific inquiry from religious authority while maintaining both had valid domains