Friday, October 12, 2007

When to keep or discard a theory

I've been blogging a lot recently about how wonderfully simple science is -- you come up with an idea, make predictions based on the idea, if the predictions hold true, then your new theory lives to fight another day; if the prediction fails, you discard the theory.

But this is a greatly simplified view. If a theory fails, we don't always toss it out, because even wrong theories can be mostly correct, and with a little re-tooling, the theory can be saved. Imagine, for example, that a friend tells you she can identify any type of car based solely on the engine noise, long before she can see the car. So, you go to a spot where you can here cars before seeing them and you test her abilities. She gets the first ten cars right, but for the eleventh car she predicts a Chevy Tahoe truck, and then a Ford F-150 comes into sight.

Is your friend's theory that she can predict the cars wrong? Obviously not completely, because she is 10 for 11, much better than chance. Maybe the Ford needed a new engine, and the owner stuck a Chevy engine in. Maybe those two particular engines are just a little too similar to tell apart. Or, maybe your friend is a very lucky guesser.

In science, there are theories that we know are not the full story. For example, Isaac Newton's Law of Gravitation are a theory of gravity. We use these laws to send space probes to the far corners of the Solar System. You can use Newtonian gravity to predict precisely where the planets will appear in the sky ten thousand years from now. Except for one pesky problem -- the planet Mercury doesn't follow Newtonian gravity exactly. It's very, very close, but not quite right. Does this mean that Newton was all wet, and his theory is complete hogwash? NO!

Newton's Law of Gravity is not completely wrong, but it is incomplete. It took Einstein to realize how Newtonian gravity was incomplete, do to a complex relationship between space, time, and mass. Einstein's Theory of General Relativity makes the necessary corrections, and it has worked in every situation it's ever tested! But if you take Einstein's General Relativity and look hard at the equations for the Moon going around the Earth, they look almost exactly like Newton's gravitational equations. They have to, because Newton's gravity works for the moon!

More yet, we know that Einstein's General Relativity and another major physics theory, quantum mechanics, cannot both be true. One, or both, must be incomplete. This doesn't mean that relativity and quantum mechanics are hogwash -- GPS satellites use relativity to determine your position, and many parts of the satellites' electronics use quantum mechanics to do those relativity calculations. For what we ask the theories to do, they are good enough, though of course we are looking for the full answers.

Today, the Nobel Peace Prize was awarded to Al Gore and to the United Nations' Intergovernmental Panel on Climate Change (IPCC) for their work in alerting the public to the imminent dangers of global warming. Al Gore has worked tirelessly to spread the message; the IPCC is a body trying to put together all the pieces of the science. A number of vocal people are claiming, though, that global warming does not exist. I've already blogged about how, among scientists, the reality of global warming is not debated, though, amazingly, some non-scientists still claim there is a debate. It is true, though, that the climate theories differ on the predictions of exactly what will happen, though all of these theories predict global warming will continue and accelerate. Obviously, these theories are incomplete. But, just because of that, it would be wrong to completely throw climate theory out the window! We joke about how the weathermen never can predict the weather, but they are right quite often (Click here to see how accurate your weatherman has been -- all of the cities I've tried are above 70%). So, like Newton's Law of gravity useful for a lot of things, we clearly know something about weather and the climate and can make good use of that knowledge.

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