Which Revolution was more Important?

The Reformation (1500)
The Scientific Revolution (1600)
The Industrial Revolution (1850)
The Green Revolution (1950)

The Laws of Physics

What Laws of Physics are and why we should pay attention to them.

What is a Law of Physics?

A Law of Physics (capitalized due to their Fundamental Importance) is an encapsulation of a basic empirical property of reality. They are based on collective observations made over long time periods (millennia for example) of the way things are. These observations are made by everyone, not just scientists, and in this sense we are all scientists. Laws are independent of theories, which are attempts to explain laws and fit them in a predictive framework. Good laws are more than a mere summary of observation; they cut to the core to arrive at something closer to a fundamental truth. Quite often this truth requires the introduction of new and very general concepts. Examples are energy, momentum, and entropy. For this reason many laws can seem quite obscure to non-scientists.

The Heads Law

Let's say that you are a physicist and have decided to flip a coin a thousand times. Every time it comes up heads. And say everyone you know who has flipped a coin also gets heads. And all your text books say heads, and that Sumerian script you discovered under your compost heap says heads, and the billion dollar experimental facility staffed with pencil-necked geeks says heads. You might publish a paper entitled,

The Heads Law of Coin Flipping -- in which it is postulated that flipping a coin always yields heads

and you would be perfectly justified. A few years later some brainiac may then publish a paper called

An Explanation of the Heads Law -- in which extra-dimensional superstring cohomologies cause persistent headedness

purporting to explain your law.

Your law will have joined the pantheon of fundamental laws of physics. The newspapers would call, you'd make appearances on Letterman and the Today Show, you'd be a guest voice on the Simpsons, and your grant money would be quadrupled.

A Law is Always Useful, and therefore Never Wrong

One hundred years later some kid is flipping a coin at your mausoleum on the Mall and it comes up tails! The world is thunderstruck. Another ten years and billions of dollars later it is realized that coins come up tails whenever the moons of Saturn are aligned with Amy Winehouse's hair, La Nina has caused an excess watermelon crop in Fiji, and the Cubs have won the World Series.

Strictly speaking, your law is no longer true. But is it wrong? For almost all purposes the law is correct, and in that sense the law is useful, and useful things aren't wrong.

Eventually someone may figure out what is going on:

An Explanation of the Heads Law Anomaly -- the interaction of extra-dimensional superstrings with Amy Winehouse's hair

Now you understand the exception to the Head Law, and it might be possible to come up with a Generalized Head Law, but the original law is so good, nobody but a few fusty academics would care. So in this sense, the original Head Law is not wrong.

Although goofy, this scenario is a good facsimile of the way things are. For example, we have never seen a violation of the Law of Conservation of Energy. Maybe in the distant future, in some obscure corner of the Universe, energy will not be conserved. But practically speaking, none of us will care. Energy is either strictly conserved or it is practically conserved. In either case we can rely on conservation of energy to guide us in examining every day phenomena.

Some Laws

Some fundamental laws that can provide guidance when examining controversial scientific issues are

Conservation of Momentum

Every object has a quantity called momentum associated with it (momentum is velocity × mass) and the sum of all momenta never changes. This law will not appear often in the discussions in this zine but it is relevant to everyday life. For example when you fire a gun, the momentum imparted to you is equal (but opposite) to that imparted to the target.

Conservation of Energy

Every object has a quantity called energy associated with it and the sum of all energy never changes. In other words there is no free lunch. There are two kinds of energy, one associated with the motion of an object and one associated with the forces acting on the object. Forms of energy can be converted into each other, but it can never be created or destroyed. The modern version of this Law stems from a book by Hermann von Helmholtz (Über die Erhaltung der Kraft; Hermann was my great-great-great-great-great-great-grand supervisor :-)

The Second Law of Thermodynamics

Every collection of objects has a quantity called entropy associated with it. The entropy of the universe is always increasing. This is often translated to You can't break even or The disorder in the universe is always increasing or Heat cannot flow from a lower temperature object to a higher temperature object. A practical application of the law is that perpetual motion machines are impossible.

As far as we know the first two laws are always true. The Second Law of Thermodynamics is an example of a law that is not strictly true, but is true for all practical situations (it need not hold when there are only a few particles in the system being considered.)

Often, there can be very deep underlying reasons for laws. For example, Conservation of Momentum arises because Nature seems to insist that the result of an experiment does not depend on where you perform it (assuming no external influences). Conservation of Energy arises because the results of experiments do not depend on when you perform them. The Second Law of Thermodynamics is commonly regarded as giving an explanation for Time's Arrow, namely why it appears that time always flows forward.

Finally, there are other laws, like Conservation of Total Electric Charge or Conservation of Total Lepton Number that are just as deep as our main three, but are less useful when it comes to discussing common scientific issues.

Why are there Laws?

Why are there laws at all? This is deep question that has perplexed the likes of Einstein, who said,

The most incomprehensible thing about the universe is that it is comprehensible

so don't expect an answer here! One thing we can do is appeal to the anthropic principle. Namely, if the universe were not orderly (ie, governed by laws), it would have been impossible for life to evolve.