Did the Great Galileo Galilei Get Everything Right?

From the Lecture Series: What Einstein Got Wrong

By Dan Hooper Ph.D., University of Chicago

Galileo Galilei is regarded as the father of modern science by acclaimed scientists such as Newton, and he changed the world of science. His various scientific achievements included the invention of the telescope for studying the night sky and famous laws. However, he made mistakes on his path as well.

Statue of Galileo Galilei in Florence, Italy
Galileo was the father of modern science as he used experiment and observation to prove his theories, but he still made scientific mistakes. (Image: ArTono/Shutterstock)

Galileo’s Telescope

In 1608, the first telescope was invented in the Netherlands as a merchant tool. Traders used it to see the ships coming into the harbor. The early telescope also had military uses. None of the applications attracted Galileo Galilei, but he decided to use the tool for his studies. Later, he built telescopes that were significantly stronger than the early models, to study the night sky. Thus, he saw things in the sky never seen before.

He discovered thousands of stars, the structure of the Moon’s surface, sunspots on the surface of the Sun, the rings of Saturn, and the four largest moons of Jupiter. He also observed for the first time that Venus goes through a full set of phases. All these discoveries were groundbreaking at his time.

What Galileo Corrected: The Ptolemaic Theory

A representation of Galileo Galilei standing by his telescope under the night sky.
Galileo’s telescope was the foundation
of his groundbreaking findings
in astronomy.
(Image: delcarmat/Shutterstock)

The Ptolemaic theory was around for a long time and stated that all astronomical bodies orbited the Earth in perfect circles. When Galileo discovered Venus’s phases and Jupiter’s moons, it became clear that at least some of the planets orbited the Sun, not the Earth. If both the Sun and Venus orbited the Earth, Venus’s phases would have been very different. His findings in astronomy drastically changed the view of the universe, but they were not the most important things he did.

His studies also had an important impact on people’s understanding of sound, temperature, and light. Furthermore, he studied the motion of bodies and gravity. Perhaps the most important aspect of Galileo’s scientific work was his approach of experiment and observation.

Learn more about Einstein’s famous saying: “God does not play dice”.

Scientific Approach of Galileo’s Time

Even though experiment and observation are now definite parts of science, in Galileo’s time, they were not deemed necessary in natural philosophy. Acceptability of a scientific theory lies in how much it can accurately predict and explain. For example, the theory of general relativity is accepted over the Newtonian theory of gravity because it correctly predicts things like the orbit of Mercury and the deflection of light.

Aristotle was perhaps the highest-ranked thinker of the Middle Ages. However, many of his conclusions were wrong. For instance, he believed that women have fewer teeth than men. Galileo, on the other hand, tried to learn facts through experiments, which makes him the first true scientist. He did not make the mistake of guessing facts.

This is a transcript from the video series What Einstein Got Wrong. Watch it now, on Wondrium.

Galileo’s Mistake: The Theory of the Tides

Although there was no substantial evidence to prove how tides were made, many natural philosophers since the ancient Greeks believed they were related to the Moon. In 1609, Kepler argued that the gravity of the Moon caused the tides. Nevertheless, Galileo thought it too impossible for an object that far away to pull the water on the Earth upward. He explained tides differently.

Galileo believed the motion of the Earth causes the tides. The theory was based on the notion of inertia. For example, walking with a bucket full of water will make the water move and splash around due to inertia. Galileo thought the same thing happened to the oceans when the Earth orbited and rotated.

The mistake was rooted in Galileo’s wrong understanding of inertia. The speed of the Earth’s rotation and orbit does not create any time-varying force acting on the waters. However, Galileo was sure that he was right and even used it in another argument.

Learn more about general relativity.

A Dialogue Concerning Two Chief World Systems

Galileo published a book entitled A Dialogue Concerning Two Chief World Systems‌ to explain his findings. The findings regarding how the Earth and all planets orbit around the Sun were supported by his observations and experiments. Jupiter’s moons and Venus’s phases were among the arguments to support his theory.

Picture showing the trial of Galileo in Rome, 1633.
Galileo paid a high price for going against the stream, and the Inquisition was about to sentence him to death. (Image: Everett Historical/Shutterstock)

On the other hand, his ill-founded theory of the tides created more mistakes in his other theories and arguments. Regardless of how right or wrong they were, they had painful consequences for him.

The Inquisition that was supposed to detect heresy and ‘clean’ it accused Galileo of being a heretic. They threatened him with torture and death to make him recant his views. To escape death, he admitted that his views were wrong, but he spent the rest of his life under house arrest, with all his writings being banned.

 What we see today as Galileo Galilei’s greatest discoveries were regarded as heretical beliefs and mistakes at his own time.

Common Questions about Galileo Galilei

Q: What is Galileo Galilei famous for?

Galileo Galilei is the father of modern science. He discovered that the planets in the solar system orbit the Sun, not the Earth. His other grand discovery was how gravity works.

Q: What three things did Galileo discover?

Galileo Galilei made many scientific discoveries, but three were very significant. He discovered that the planets and other astronomical bodies did not orbit the Earth, they mainly orbited the Sun, and the moons of each planet orbited the planet itself. Next, Galileo discovered the phases of Venus.

Q: What did Galileo invent?

Galileo Galilei invented the telescope used for observing the sky and astronomical bodies. Before that, telescopes were not as strong and were used by traders to spot ships coming to the harbor.

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