At number 3 in The Guardian’s list of the ten best physicists is Galileo Galilei.
Galileo is often thought of as the founder of experimental science, although there were others before him. But there is no doubting his huge contribution in our early understanding of what we now call physics. He made important observations of the Solar System, including discovering four moons orbiting Jupiter, and showing that Venus must be orbiting the Sun. He showed that a pendulum keeps the same period irrespective of amplitude, and that the period depends on the length of the pendulum. He introduced the concept of inertia, the tendency of bodies to remain at rest or to keep moving.
Galileo’s brief biography
Galileo was born in 1564 in Pisa, Italy. He was the first of six children; his father Vincenzo Galilei was a famous musician. Galileo initially studied for a medical degree at the University of Pisa. But, in 1581, whilst doing his medical studies, he noticed that a swinging chandelier’s period was not dependent on how large the swings were but rather on the length of the pendulum. This changed the course of his life, he persuaded his father to let him abandon his medical studies and instead he switched to studying mathematics and “natural philosophy” (as physics was commonly known at the time).
In 1589 he was appointed Chair of mathematics at the University of Pisa. In 1592 he moved to the University of Padua, where he taught mathematics, geometry and astronomy. He stayed in this position until 1610. In 1609 Galileo built a telescope and was soon making important discoveries, including proof that Venus orbited the Sun. He published this and other findings, bringing him into conflict with the Catholic Church.
In 1616 Galileo was summoned to Rome and told to stop promoting the idea of a Heliocentric Universe, the idea that the Sun and not the Earth was at the centre of everything. Initially Galileo obeyed, but by 1623 he revived his project of working on a book to argue in favour of the Heliocentric model. This was finally published in 1632, under the title “Dialogue Concerning the Two Chief World Systems”. This book some him placed under house arrest by the Church, under which he lived for the rest of his life. In In 1638 he published “The Two Sciences”, which summarised much of his life’s work. It is for the work in this book that Galileo is often referred to as the “father of Physics”. He died in 1642, and is buried in the Sante Croce in Florence.
Galileo’s contributions to Physics
Galileo’s title as “the father of Physics” comes about because of his laying the foundations of much of mechanics, which Isaac Newton later formalised in a more mathematical framework. Whilst he was still training for a Medical degree, he noticed in 1581, that the period of oscillation of a chandelier did not depend on how large the swings were, but only on the length of the pendulum. The story is that this observation was made in Pisa Cathedral, where a chandelier was being blown by the wind to swing with different amplitudes. Galileo used his pulse to measure the periods and saw that they were all the same, irrespective of the amplitude of the swing.
After building his own telescope in 1609, based on the design of one built in The Netherlands about which he heard, Galileo made some crucial observations which helped show that the Earth and the other planets orbit the Sun, contrary to the popular view of the time. Key to showing the veracity of the Heliocentric model were Galileo’s discovery of four moons orbiting Jupiter, and his observations of Venus.
Once Galileo had showed that Jupiter had moons orbiting it, it strengthened the argument that not everything went around the Earth. However, Jupiter’s moons still allowed for the planets, the Moon and the Sun to be orbiting the Earth (the Geocentric model), but with Jupiter having its family of moons. However, when Galileo turned his telescope on Venus he was able to see that the planet exhibited all phases, from crescent to full, just like our Moon. Not only this, but the size of Venus when full was smaller than when it was crescent. It is impossible to explain these observations if both the Sun and Venus are orbiting the Earth. If one has a model where Venus is orbiting the Sun and both orbit the Earth it is possible to explain the observations, but the size difference between the crescent and full phases of Venus argues against this interpretation. In a model where Venus orbits the Sun inside of Earth’s orbit about the Sun the observations are explained perfectly in the most simple fashion.
Galileo argued against Aristotle’s view that heavier objects fell more rapidly towards the ground. It is not clear whether he actually conducted the experiment, but he argued that two objects of different weights would fall at the same rate. He introduced the concept of inertia, which is the tendency a body has to either stay at rest or keep moving once it is set in motion. Galileo’s Principle of Inertia stated: “A body moving on a level surface will continue in the same direction at constant speed unless disturbed”. Newton’s first law of motion is essentially a statement of the concept of inertia.
Galileo also made many other contributions to Physics including attempts to measure the speed of light using lanterns, and developing thermometers and better compasses. He was one of the first scientists to realise that much of physics can be explained mathematically.
Personally I think there is little doubt that this pioneer of experimental physics deserves to be in this list of the ten best physicists. What do you think?
You can read more about Galileo and the other physicists in this “10 best” list in our book 10 Physicists Who Transformed Our Understanding of the Universe. Click here for more details and to read some reviews.