From Aristotle to classical physics

​What is everything made of? Why is the sky blue? Will the sun ever go out? What is it that happens when lightning strikes? How come light travels so much faster than sound?

Why does an apple fall down from a tree and not straight up? And how can that apple turn into energy that can be used to climb that tree? These are questions that all belong in physics. Questions about matter, light, electricity, movement, energy. Questions about time, space, about cause and effect.

Throughout history, people have tried to figure out how nature works. Based on experiences from daily life, we have formed an understanding of the laws and principles underlying it. Even if you never studied physics at school, you'll have a feel for how things work. We all have an intuitive sense for the laws that govern nature. For example, that it takes more effort to lift up a large rock than a smaller one, and if you drop something, it will fall to the ground.

And that light and heat have something in common. ​But this intuitive physics has some problems. Firstly, it sometimes leads us astray. It's simply not always correct. And secondly, there are plenty of questions that we don't get an answer to just by experiencing our daily lives, and when people didn't get any good answers, they made up their own answers. Heaven - people thought - must be a gigantic bowl, and the stars being small holes in it where the light gets through.

Earth, that's a large plane resting on four elephants. Why won't the elephants fall down? Well, they're standing on a giant tortoise, of course. When something happens that wasn't the direct action of a human being, people would conclude that it must be demons, gods, or spirits involved. In ancient Greece, where so much of today's philosophy and mathematics has its origin, people thought a lot about these questions.

The questions we see as part of physics. ​One of the greatest of the time, Aristotle, observed just like anyone could do, that a rock falls to the ground when being dropped. His explanation was that the rock is part of nature, and therefore, yearns to be reconnected to the ground. In much the same way, Aristotle thought that the moon and the planets had an innate desire to move in circular orbits. Most of Aristotle's ideas were considered to be true for another 2,000 years or so. The Aristotelian physics was pretty well suited to how people spontaneously perceived how stuff works.

It had a good fit with our intuitive understanding of physics. Most people's intuition says, for example, that a heavy object will fall faster than a lighter one. Even though a simple experiment is enough to show that this is wrong, it took until the late 16th century before the Italian scientist Galileo Galilei showed what actually happens. A heavy ball of iron falls just as fast as a light one made of wood. ​This was the beginning of a new era in science. No longer was intuition, dogma, tradition, or religion allowed to determined what is true and not.

A new way of reasoning spread based on experimentation, logic, and the questioning of old truths. But this was, of course, not appreciated by everyone. ​When Galileo Galilei explained that the Earth revolves around the sun and not the other way around - as Aristotle believed - he was attacked by the Pope and the Catholic Church. Galileo was forced to deny his scientific conclusions, threatened with torture, and was put under house arrest. But the measurements, calculations, and arguments spread by Galileo were so convincing that the Catholic Church didn't manage to stop the new insights from spreading. The era that had now begun was one where scientists started to question the old truths, and where many of the mysteries of physics got new and better explanations.