Science has revolutionized the way we live thanks to its influence on technology, but it’s perhaps less well-known how science has utterly transformed the way we think about the world.
For example, in ancient times it was thought that the earthly realm was separate from the heavenly realm. God, or the gods (depending on belief) ruled differently in the heavenly realm, so that the sun, moon, planets, and stars moved at their whim. On earth, too, the gods were ultimately able to act if it pleased them, but if they did not intervene, then objects moved according to noted regularities (which we nowadays call physical laws).
One of Newton’s greatest achievements (building on the work of Galileo, Kepler, Copernicus, and Brahe, among others) was to argue that there is only one realm. Motions in the heavens, as well as on earth, can be described mathematically, and are not subject to the caprices of gods.
His decisive argument made use of his laws of motion and his newly created law of gravity. He supposed that the moon circled the earth because it is subject to the same force (albeit diminished in strength because of the moon’s great distance from the earth) that pulls an apple down from a tree: earth’s gravity. He tested this hypothesis by calculating what the period of the moon ought to be if it really could be described by his new law of gravity. His calculation agreed with the observed period of the moon “pretty nearly,” which gave him confidence that his theory was good. He went on to use the theory to explain tides and other celestial phenomena.
Three centuries of further testing and use have firmly established Newtonian mechanics. A spectacular use of the theory in the 19th century was the discovery of Neptune, which you can read about here or here. This was a dramatic application of the idea that the universe is one realm.
Newtonian mechanics has served us admirably, helping us to understand practically all every-day phenomena.The theory was created by Newton based on evidence (in the form of observations and experimental results) and reason. The theory has been verified countless times, and its fingerprints can be found on the bridges, skyscrapers, rockets, satellites, and machinery that make modern society what it is.
Newtonian mechanics is insufficient for understanding the very small (atoms and their innards) and the very fast (typically phenomena that also have their origin in the innards of atoms), but it remains the bedrock theory upon which modern physics is founded.