The Nature of Scientific Progress

Without having had a lesson, I don’t exactly have much to “reflect” on, but I definitely have things that I want to say about the future! The falling object experiment, which I plan to do for my first lesson, is one of my favorites. It’s not as exciting as making an explosion with some chemicals or having the kids build something that they can take home to show their parents, but to me it’s one of the most important experiments ever performed.

For centuries, people debated with each other about whether a heavy object or a light object would hit the ground if both were to be dropped from the same height. Aristotle reasoned that since heavier objects feel a stronger downward pull, they should hit the ground first. Others argued that lighter since objects are easier to move, the downward force they feel has an easier time pulling them to the ground despite being weaker, allowing lighter objects to win the race.

The issue was laid to rest when Galileo (the same one who famously defended the then-controversial heliocentric model of the solar system) decided to see for himself what the result would be by dropping to objects of differing weights. The answer he found was (C), none of the above! Any two objects, regardless of weight, will hit the ground at the same time when dropped from the same height! Although Galileo obtained this result through experiment, it wouldn’t be until the time of Isaac Newton that scientists began to understand why.

To put it simply, both arguments were in fact correct, just not individually—the correct explanation requires the effects of both arguments to be taken into account at the same time. It is through Isaac Newton’s 2^nd Law of Motion and his Law of Universal Gravitation that we can understand how to incorporate both arguments. Through the Law of Universal Gravitation, Newton stated mathematically something we already know: if object A has twice the mass of object B, A must then feel twice the gravitational force that B feels (i.e., A is twice as heavy). His 2^nd Law says that if A is twice as massive as B, then it is in fact twice as hard to push A as it is to push B (i.e., starting from rest, it is twice as hard to push A until it is moving at some speed as it would be to push B to the same speed). We can see both of the original arguments captured in these 2 statements. The incredible insight here is that the two different effects turn out to exactly balance each other out! Object A might be twice as heavy as B and is therefore pulled twice as hard by gravity, but it is also twice as hard to move A as it is to move B!

I think this simple experiment and the history behind it captures much of the philosophy of science. Regardless of how nice an argument sounds or who made it, it is still doomed if it fails to account for experimental results.

It also speaks about how science moves forward. Neither of the two arguments was wrong, but each failed to see the bigger picture. Scientific progress is ultimately about making our picture of the world ever so slightly bigger. Thus, the goal of science is not to find replacements for our current theories, but rather to expand upon them and make them more complete.

Today, Newton’s theory of gravity is known to be inconsistent with experiment when dealing with environments that have extreme gravitational fields. Our current understanding of gravity comes from Einstein’s General Theory of Relativity. Einstein’s theory is in complete agreement with Newton’s here on earth, and this was in fact used as an important test of the validity of General Relativity. What this test tells us is that Einstein’s theory explains at least as much as Newton’s. When it was confirmed that Einstein’s theory can also account for additional scenarios in which Newton’s fails, physicists knew this was the right theory to expand the horizon of our understanding of gravity. In non-extreme conditions, Newton's law of gravitation is a fine approximation of Einstein's (and also much simpler)—in fact, it was all we needed to go to the moon!