Laws of Nature
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[edit] Definition
A law of nature is a statement of an observed regularity in nature with no known exceptions.
[edit] Yes, but what is a law of nature?
The most common mistake people make about the laws of nature is to reify them: that is, to treat them as things. This leads to questions such as "where are they", and "what do they look like" and "how do they control nature".
This is a mistake. Under most circumstances it is a harmless mistake, because, after all, you can do physics (for example) perfectly well if you imagine that the Law of Conservation of Angular Momentum (for example) is some sort of little omnipresent demon cracking a little cosmic whip to make sure that no particles get out of line. It would still be the same law with the same practical consequences, and your calculations would give you the same answer.
The problem with this reification comes when you start thinking about the demon and the whip as objects of enquiry in themselves. How does the demon know how the particles are meant to move? How, in fact, does it interact with them? Do we not now need another law specifying how demons interact with particles? And where did the demon come from?
Clearly, a different view is needed. We shall illustrate this with a very simple law:
- Law of Cyanide Poisoning : If a person eats (a sufficient quantity of) potassium cyanide, that person will die.
This does not have the profound significance of most laws that you find in science textbooks, but it is an observed regularity in the universe that no-one has broken, and is therefore, by the definition we have given, a law of nature.
Now, the reader should be able to see that the reason that this law holds is not that there is some thing, some entity, some Demon of Cyanide Poisoning, which enforces it. The law holds because all humans have a respiratory mechanism involving cytochrome c oxidase, and all potassium cyanide inhibits the correct operation of cytochrome c oxidase.
The law exists, then, because all humans have something in common, and likewise so do all molecules of potassium cyanide; and what the law is, is a description of an observed regularity, not a causal factor in that regularity.
In the same way, we can have laws of fluid dynamics, for example, because all fluids have certain properties in common; we can have laws about electricity because all electrons are exactly the same; we can have laws of chemistry because the chemical properties of one sodium atom (for example) are much like those of another. And, by contrast, we have such a difficult time laying down laws for human psychology because people are so diverse in the ways that they think.
It follows from this that the fundamental reason why there are laws of nature at all is that the Universe is, at the smallest level, made up only of a few types of things, with each member of each type being identical with the other members of its own type: zillions of electrons, each exactly like all the other electrons; zillions of protons, each just like all the other protons, and so on with the neutrons and the photons and so forth.
[edit] Laws are breakable; laws have been broken
We have said that a law of nature is an observed regularity with no known exceptions. But tomorrow, exceptions might be found to our favorite law, in which case we would have to abandon or revise it. The fact that something is called a "law" does not really give it a higher status as knowledge than other facts that we know, or think we know, empirically: like anything else in science, laws must be subject to revision in the light of new evidence.
No law, then, can ever offer us 100% certainty of the sort dreamed of by philosophers: but if we have tested a law under a wide range of circumstances, and always found it to be valid, then it is reasonable to act on the conviction that it will operate the same way in the future, and did operate the same way in the past, especially under circumstances similar to those under which we have tested it.
By convention, a rule that does have known exceptions may be referred to as a law for historical reasons: for example, Mendel's "law" of independent assortment is not true when it is applied to genes on the same chromosome; Boyle's "law" of gasses breaks down when the gas is very dense, and so forth.
Usually this should cause no confusion: if you come across such a "law" in a science textbook, the scope of its validity will almost always be pointed out. However, you should be aware that just because something is called a law, even by a respectable scientist, doesn't mean that it is one.
