Messier 82

Messier 82
Beautiful Hubble shot of a starburst galaxy, M82

Tuesday, November 25, 2008

Science Basics: How Theories are Made, Part 1

There's a lot of confusion going around when it comes to scientific theories. The very first comment I got on my very first substantive blog entry serves to illustrate that fact. While the folks talking about things like climate change or evolution bear the brunt of the confused people, even such seemingly neutral subjects as particle physics attract people who believe that pseudoscience is somehow morally equivalent to science.

It's therefore necessary, every now and then, to have a basic discussion of what science is and isn't, and specifically what a theory is and isn't. While we all (hopefully) get a basic introduction to the scientific method in grade school, the hypothesis -> experiment -> analysis -> conclusion is a very simplified description of an extremely complex process, one that gets more and more complex as we deal with larger, smaller, or more complex systems.

The Beginning: Conjectures
Most scientific theories are born as conjectures of some sort. A conjecture is, essentially, a guess; it's an exercise in what's called "inductive reasoning," or making a generalization about a process or property based on observation of a specific aspect of it. There are a lot of ways of forming conjectures:
  • You can observe an object or event and make a conjecture about its nature, structure, or identity. For instance, I could observe that the moon is pale and lumpy and propose that it is made of green cheese.
  • You can make a prediction about the behavior of some general class of things, based on the behavior of a single member of that class. For instance, I could observe the behavior of helium balloons and propose that objects are repelled by gravitational fields.
  • You can make a prediction based on purely logical or mathematical reasoning from a known theory. For instance, I could propose that all objects in the universe obey Newton's laws of motion.
  • You can find an inconsistency in a known theory and postulate an explanation for it. For instance, I could propose that the Arctic ice cap is melting faster than predicted because magma is leaking into the Arctic ocean.
  • You can run a computer model or simulation and make a prediction of the behavior of the system it models.
  • And there are probably dozens of other ways to come up with your conjecture. There isn't really an invalid way to do this; whatever works for the specific problem you're trying to solve is fine.
The key feature of a conjecture is that it's formulated as a possibility. It may or may not conform to observed reality; it may or may not have any supporting data; it may or may not be contradicted by some existing data. Conjectures are probably the closest thing in science to the meaning of the word "theory" in common speech. If you ever hear the phrase "I have a theory that," chances are you're dealing with a conjecture. UFO claims, predictions based on religious texts, and all the myriad claims of ESP, magic, time travel, extra dimensions, and the like all fall under this umbrella. So do many proposals by scientists, including (at this stage) the mathematical-physics construct called string theory, which is a perfectly good theory in the field of mathematics but rises only to the level of conjecture in the world of science. It's a big umbrella.

Once you've got your conjecture, the first thing you must do is ensure that it conforms with what you have already observed. All of the ones I proposed in the bullet list would fail this test. However, it's not terribly difficult to come up with ideas that might pass it, if you tweak them a little bit.

Next up: Part 2, Hypotheses and Testability.

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