5.14. The Beginning of Physics#
When Galileo reached the conclusion that all objects fall to Earth with the same acceleration, he was going against what he — and Aristotle, and everyone else — actually observed. Let’s review the number of Galilean ideas that we’ve encountered…all of which were overthrows of the Aristotelean – and hence Catholic – dogma.
Pencils Out! 🖋 📓
To understand nature one must do experiments.
To understand nature, one may not defer to authority, like the Bible or Aristotle’s writings.
For a pendulum: the period of two pendulums of the same length, but started at different heights will have the same period.
For a pendulum: the period of two pendulums of the same length, but different materials will have the same period.
For a pendulum: the period of two pendulums of the same length, but different masses will have the same period.
In free-fall: two objects of different sizes but of the same material would reach the ground at the same time.
In free-fall: two objects of the same size but of the different mass would reach the ground at the same time.
An object already moving in a horizontal direction will never stop and will not require an active pusher.
Any object, regardless of material or mass, if thrown as a projectile will execute a parabolic path and will not require an active pusher.
A whole bunch of astronomical observations and conclusions that we’ll talk about later!
Each of these requires that there is no resistive medium affecting the motions. So each is a discovery that cannot be shown to be absolutely the case on earth. Yet each is a statement reflecting what we now know are fully-trustworthy rules about nature.
Let’s visit the Matrix.
5.14.1. The Red Pill, or the Blue Pill?#
This is very un-Aristotle. First of all, Aristotle would never have countenanced doing experiments. You can look at Nature, but don’t touch. But Galileo was all about constructing experiments and making quantitative measurements of what he observed. This was largely new and recognizably “modern.” But there’s more. To him Nature’s rules are hidden to us. We can get close to them by reducing marginal effects like friction but then we have to extrapolate from what we see in our rough and ready laboratory to the hidden rules of a more perfect world. The pendulum bob gets close when it swings back, but the actual rule driving the motion would instruct the pendulum bob to come all the way back to the original height. That’s what’s real.
I cannot over-emphasize how important this is. This is very much Plato’s view of nature, not Aristotle’s. For Plato, The Real was perfect and with our poor, corrupt visual tools we can only perceive inferior copies of the real things—Platonic Ideals. While there is much that’s wrong with Plato’s philosophy, the uncovering of nature’s hidden order — free of imperfection — is the goal of modern science.
5.14.2. The Father of Physics#
Nobody had ever done what Galileo did in all of history. Let’s summarize his strategies:
First, Galileo chose not to explain nature (motion in his case) on the basis of logical argument from within pre-conditioned philosophy (neither Aristotle’s nor the Church’s): Galileo confronted nature without precondition: he assumed that Authority did not dictate how the physical world behaves.
Second, rather than sit passively and observe, Galileo created artificial circumstances designed to explore particular questions: he assumed that Nature can be characterized by doing experiments.
Third, rather than report results as a narrative, Galileo made quantitative measurements under the assumption that arithmetical and geometrical constructions were the appropriate way to describe physical behavior. This idea that nature appears to behave according to mathematics is not new (going back to at least Pythagoras) and is the bedrock of modern physics. We don’t understand why the universe is so understandably mathematical!
The first three strategies alone would make Galileo one of the first, great scientists. But he went further, and his Physics Paternity comes from his Platonism.
Fourth, Galileo chose to interpret nature as consisting of rules that can only be discovered by going beyond the rough regularities that we always see in our observations. Nature is best assumed to be simple and mathematical, but all that we can observe is complicated by extraneous effects and the true nature…um, of nature is hidden, just out of grasp. Strip away complications like friction as best you can and through mathematical modeling and extrapolation we can uncover nature’s hidden rules.
Without this fourth strategy, physics would be impossible.
The rules of nature are often hidden from experiment and must be inferred by a combination of theoretical modeling and experimental confirmation.
Taken together, these four strategies form the modern-looking nature of physics.