“The Character of Physical Law” started off as a series of lectures by Richard Feynman. They were targeted at the first year physics students, who had chosen to enter physics out of a desire to learn about and contribute to the cutting edge research, only to be told they first have to learn about pulleys and balls rolling down hills.
In these lectures he talks about general principles in physics, not as much the physics itself as useful ways a physicist approaches his subject. For instance in the first chapter/lecture he defends what he calls “Babylonian” mathematics over “Greek” mathematics, wherein the Babylonians did tons of calculations and saw what fit, whereas the Greeks derived things in a logical manner. His argument was that you don’t always know where the next innovation will come from, so trying the calculations in all sorts of ways and seeing what fits can show you something that you might not have been able to deduce from whatever starting point you have on hand. Here are 10 things I learned from “The Character of Physical Law”:
1) You could derive torque from the definition of energy and it’s law of conservation of energy.
So torque is what allows you to multiply your force using a lever. The definition of energy is F*x, or a force applied over a distance (also called the capacity to do work). My old physics teacher used to joke that the reason waiters got paid so little was all the work they did was when they lifted the plates up and down, and since most of their job (taking orders and running back and forth from the kitchen) was not technically work. Shut up, it’s funny!
Anyway, the amount of energy involved in moving a lever a little distance vs moving a lever a large distance depends on how much force you have to apply. The long lever travels more distance, and due to the law of conservation of energy, the short lever has to have proportionately more force. As it turns out a number of concepts early students of physics are taught can be later disregarded, since you can derive it using the conservation laws alone. This makes the laws of conservation enormously powerful tools.
2) Conservation laws have to be local.
This is best understood by considering the alternative. Suppose energy could be borrowed randomly from other ends of the universe, where a book in your room might suddenly fly off the shelf while a planet on some foreign galaxy loses a trivial amount of momentum. Since the planet can’t be observed, this would have the appearance of there being no law of conservation of energy at all. In experiments the presence of a non-local conservation law and the total absence of conservation are indistinguishable.
3) Feynman reads all his mail — doesn’t appreciate the all the toilet-bowl suggestions.
I have a confession, “toilet-bowl suggestions” is my phrase. It comes from an experience I had back in college. When passers-by or new acquaintances found out that me and my friend where into computers, they would proceed to inundate us with “revelations” they had (presumably when on the toilet, when else do such people think?) about business ideas or inventions that we could build for them for free that would totally make us all rich, I swear!
What Feynman was specifically complaining about was that people who had no expertise in that branch of physics would send in letters making suggestions, and the suggestions they make would always be the most obvious things that him and colleagues have ruled out ten times over. Had they studied they would have known this. But Dr. Feynman continues to read his mail in the hopes of a good suggestion.
4) The nature of discoveries is that you couldn’t have predicted it from just the knowledge/logic behind past discoveries.
This is a perspective that Feynman has, that the thought processes of Newton that produced Newtonian mechanics was insufficient to discover relativity. For instance, for hundreds of years there were experts in Newton’s mechanics that failed to discover relativity. He then argues that the logic that produced relativity was insufficient to produce quantum mechanics. For these reasons he’s pessimistic about those endeavoring to discover the next great leap by using the approaches of the past. It will require something truly original. For this reason also it will be impossible to predict what such a leap would be like.
5) There are a lot of basic particles, like 40-70.
So there’s six different types of quarks, then three types of neutrinos, other leptons such as the muon or tauon, and different types of bosons. Then, multiply that by two to account for antiparticles. Now imagine that in 1900 there were plenty of physicists who were rather skeptical of the “atom hypothesis.” We’ve come a long way.
6) Symmetry is best thought of as constancy across some transformation.
Symmetry is a favored term in physics. In addition to regular “symmetries” they will also talk about an idealized “super symmetry” that some hope to discover. They borrow the symmetry analogy from a mathematician who defined it as constancy across a transformation. For instance, the ordinary symmetry that we see is if you reverse the sides of an object, that it appears the same. Within physics you have something like translational symmetry, which is that if you do an experiment on, let’s say gravity, the fundamental gravitational constants and equations hold just as well here as in a galaxy far away. In other words, if you moved our solar system a million miles in one direction, as long as the earth/moon/sun and other planets/debris in our system moved in exactly the same way, then we would get the exact same results. Obviously translational symmetry is not kept as you move across a field, for instance if you move further from the earth the effect of gravity on you would lessen. So in that particular way the symmetry is broken.
7) The bending of light in sugar-water is asymmetric.
Apparently, if you change the direction of the light, or switch around the entire, apparatus, it still passes through water the same way. Freaking weird!
8) The decay of Beta particles is only one-handed. You could use that to tell aliens right from left.
In a similar vein, Feynman plays this game of suppose we met aliens and started talking, how could we describe our world to them in terms they can understand (i.e. things observable in their experience). We don’t know how tall they are so lengths like “foot” or “meter” don’t work, but thankfully the radius of a hydrogen atom is the same here as it is anywhere else, and Hydrogen is the most abundant element in the universe. So we could say I am 5.2*10^29 hydrogen atoms tall, or whatever stack of hydrogen atoms equals 5’10”.
The bigger question is one of handedness. Suppose those creatures have radial symmetry, how would they understand right from left? It might first occur to you to use the sugar water as an example, but where would they get the sugar? More likely they are able to observe the decay of Beta particles, since those are right handed, we can define right from left in terms of the orientation/spin of the particle as it decays. What a wild conversation to have!
9) If an alien then reaches out to shake your hand with it’s left tentacle, RUN FOR THE WIND!
The above example fails if the aliens are made of anti-particles. The decay of anti-Beta particles is left-handed. Aliens that observe this phenomena are likely to live in a world/be made of anti particles. Matter and anti-matter turn to pure energy on contact. In other words, DON’T TOUCH the left-handed alien! If you do, your death will be instant.
Hell, you won’t have much to complain about after. Imagine the asshole astronaut who tells the alien ahead of time that “yeah back on Earth we greeted each other with our right hands, but now in space, we use our left, it’s what makes us different”, just to see the terror on his friends’ faces over what turned out to be minor social confusion.
10) A good theoretical physicist knows at least 7 different conceptual frameworks that describe the same thing.
This is Feynman’s answer to the problem “How do you discover something new, if it requires thinking that’s never been done before in your field?” You learn every possible way of representing the information in your field, as different conceptual frameworks (the universe is strings, the universe is membranes, the universe is tiny loops, etc) offer different possibilities and predictions you could make. They also allow you more ways to filter and interpret new information, and increase your chances of making the next most useful analogy. (Note that some of this is my interpretation of what Feynman is saying, and that i’m getting some of this from Surfaces and Essences by Douglas Hofstadter)
“The Character of Physical Law” was an enjoyable and enlightening book that gave me a window into how a physicist thinks. If you take the time to check it out, you will not regret it.