From classical to modern physics

​ ​During the 17th century, scientists started to ask themselves, Are we really sure that this is how stuff works? Galileo Galilei, the Italian astronomer and mathematician, wasn't satisfied with explanations like, Because the Pope says so, or, That's how we've done things since Aristotle. In France, the philosopher René Descartes went so far in his questioning of what can be known for certain that eventually, the only thing he was sure of was his own existence. I think, therefore I am, or in Latin, Cogito ergo sum. The Englishman, Francis Bacon, was also interested in the principles of how we can gain knowledge about the world.

He laid the foundation to a way of working that we still call the scientific method. The method is based on making predictions and then systematically testing them through experiments. And when reality doesn't behave according to the predictions, the ideas behind them are discarded and new ones are generated and tested again. The same year that Galileo Galilei died, 1642, another man, Isaac Newton, was born in England. Isaac Newton has challenged the traditional and intuitive ideas in physics, possibly more so than anyone else in history.

Through experiments and an entirely new kind of calculations, he uncovered the laws of nature in a range of different areas. Today, Isaac Newton is probably best known for his explanation of gravity - that's the force of attraction which makes an apple fall downwards and keeps the moon in its orbit around the Earth. Isaac Newton was also the first one to properly explain how forces, mass, and motion all fit together. The physics that was developed during this period is called Classical Physics, or in honor of old Isaac, Newtonian Physics. Classical Physics still works very well today when it comes to explaining most of the everyday stuff that we encounter.

We still use Newton's laws of motion to calculate how an object falls and when sending up satellites into space. As long as we stick to sizes and to speeds that we are used to, Newton's calculations are impressively precise. But when we study very small things, like individual atoms or even smaller, then something peculiar happens. In this world of the teeny-tiny, among protons, neutrons, and electrons, the laws of nature are entirely different from those of Newtonian Physics. This is where quantum mechanics takes over.

Quantum mechanics is an odd field of physics, to say the least. In quantum mechanics, a particle can exist but at the same not be present in any particular place. An electron, for instance, is a particle whose position can only be described using probability but not as an exact location. Quantum mechanics often contradicts our intuitive understanding of physics. It can be just as fascinating and mind-boggling to attempt to grasp.

Just as classical physics doesn't apply at very small distances, it also breaks down when considering things travelling at very high speed. A train is travelling at 100 kilometers per hour and someone's running on its roof in the same direction as the train at 10 kilometers per hour. Relative to the ground, he is now travelling at 110 kilometers per hour since 100 plus 10 is 110. Nothing weird so far, but if he stands on the roof of that train and he turns on a flashlight pointing it forward, then the light will not travel any faster than it would have if he stood still on the ground. Now that's bewildering, isn't it?

To deal with velocities near the speed of light, you will need Einstein's special theory of relativity, and that theory, just like quantum mechanics, is something that doesn't go well with our everyday intuitive understanding of physics. So if you wish, here is a rough sorting of physics into three categories. First, you have the pre-classical physics. We can call it Aristotelian physics. It's largely shaped by intuition, and then carried by tradition and religion.

Later, during the 17th century, people like Galileo, Newton, and others turned the Aristotelian physics on its head. With the help of structured experiments and mathematics, the classical physics took form. Then, 300 years later, in the beginning of the 20th century, classical physics was itself challenged and the door was opened to the modern physics, including quantum mechanics and the theory of relativity. Now that can make your head spin. There's a good reason to be grateful for the many discoveries made throughout the winding history of physics.

Because without them, you wouldn't be able to stream music at your party. In fact, we don't have to go back very far in time for you to start missing all the useful things physics has brought you.