Space is infinite or finite? : Newton's logic in 17th century
Updated: May 27, 2020
Let's imagine the general atmosphere in the scientific community in the 16th and 17th centuries. Galileo had just discovered moons of Jupiter, proving Copernicus' theory that all interstellar bodies like planets, sun, and moons, don't have to revolve around Earth. Planets can have their own, personal moons now! Kepler had showed that moons and planets don't revolve in circular orbits, but in elliptical orbits. Then Newton came in 17th century, mathematical guns blazing, and proved all of this true by his own-invented Calculus. He also gave Law of Gravitation, that explained why all this pushing-pulling and revolving is even happening in the first place. Secrets were out and things were good, as we knew much more about the world around us (I imagine big parties around that time, with champagne flying all over Flat Earth model).
Until someone asked, "But what about stars, you party heads?"
Till now, no one used to think much about these stars scientifically that adorned the night sky. Because of church, the general thinking was that they are just fixed bodies outside our solar system which don't affect us. It was very comfortable for church then, since this will allow a lot of room for heaven and hell, and hell was definitely being created by the church if someone tried to oppose this 'theory'.
But science was getting stronger now, specially after the Law of Gravitation came out. People started asking questions like how big is our universe, where does it end, or does it end at all? Are there infinite number of stars? And how far they are from each other? Won't gravity act between them and pull everything together at one place??
According to this law, yes, the gravity should pull everything together, but the higher the distance between 2 stars, the weaker is the gravitational force between them. So maybe the stars were too far away from each other and gravity was too weak between them?
They thought of this back then, which is actually true too, but had no mega telescopes or data to prove this. But there was still a flaw in this logic. Even if the gravity is weak, there is still some small force there. So the stars should still fall at the same point, even if it takes very very long time.
Thus, Newton entered, waved his amazing locks of hair aside and said, "Yes, that will happen, unless the universe is infinite, my dudes and dudettes!" See, if the universe is infinite, then there is no central point where all the stars can fall to. Any point in the universe can be a central point, and stars will stay at their own positions. Stars are all assumed to be of same sizes at same distances. Everything was very symmetrical, and all the gravitational forces were balanced with each other. "That's why you don't see a star coming to Earth, you see," Newton inferred.
People liked this theory, and it fits well with their comfort zones and peace that universe is static and unchanging. It may have existed forever like this, or maybe was created at some point in time, but it never changed after that, and will stay like this, whatever happens to us. And they stayed with this theory for next couple of centuries (Actually science was divided into 2 camps, with people giving arguments about finite and infinite universes, which is a very interesting read, but this post is only about Newton for now. Also, it was NEWTON, so his arguments were more favored at the time than any other scientists).
Now we know, that this is not true. Universe is a chaotic place with explosions, banging of stars and planets, black holes, and what not. It expands and contracts, so not static. And though it is very big, it's not infinite. Science evolved very much in this field in 20th century and proved all these, but it is very interesting to see how old philosophers and scientists used to wonder about our universe. Thanks to the groundwork they laid, we are where we are today.