Wednesday, October 10, 2007

Nobel Week Continues...

Today, the Nobel Prize in Chemistry went to Gerhard Ertl of Germany, who provided insight in to understanding how chemical reactions take place on surfaces. I am not a chemist, nor do I study materials science, so I cannot say much about Ertl's work that was not stated in the various online news stories about the award.

Today is the first day of talks here at the University of Texas by John Mather, last year's winner of the Nobel Prize in Physics. Dr. Mather will be speaking on topics other than his Nobel-winning work, but I'm going to talk a bit about the science that resulted in the Nobel because (a) I almost understand it, and (b) it is an ideal illustration of the way science should work.

The whole story begins with the Big Bang. The Big Bang theory was proposed back in the 1930s to explain the observation that all galaxies in the Universe appear to be moving away from one another. If you run the clock backward far enough, all of those galaxies should have started in the same spot. So, a giant explosion of some sort about 14 billion years ago might explain why all the galaxies appear to be moving away from one another.

This is a nice idea, but to become an accepted theory, an idea has to make testable predictions that pan out. In the late 1940s, the Big Bang theory was developed further, and it made two major predictions. One, it predicted that the universe should be about 75% hydrogen and 25% helium. Two, it predicted that the universe should be glowing in microwaves, and "echo" of the Big Bang still visible today. Both predictions were found to be true! This is why the Big Bang theory is widely held to be correct. Not only did it explain what we already knew, but it made testable predictions that proved true.

Yet another prediction was then made. In order for galaxies, stars, and people to form in only 14 billion years, the Universe had to be slightly lumpy after the Big Bang. Not too lumpy, or everything would collapse into a black hole, and not too smooth, or gravity would not have had time to pull things together. Therefore, predictions were made that the echo of the Big Bang, called the "cosmic microwave background," should show lumpiness at a very small, but detectable level. This level would be one part in one hundred thousand. Such a measurement is hard, but quite possibe -- like trying to determine how many people live in New York City and not be off by more than 75 people, and then repeating the same measurement for forty thousand other cities, all within three years.

So, anyway, the lumpiness was predicted, but had not been seen. John Mather was lead scientist on the project that built a satellite, the COsmic Background Explorer (COBE) to measure the lumpiness. And, they detected the lumpiness, at just the right level that theories predicted! This was an amazing feat, and also another amazing confirmation of the Big Bang theory. Since that time, the WMAP satellite has made even more precise measurements of this lumpiness that have confirmed even more aspects of the theory.

Lots of people (though only a few professional astronomers, who can be counted on the fingers of two hands) claim not to believe in the Big Bang theory. Yet when push comes to shove, the Big Bang theory has made several testable predictions that have been proven true. No other theory can claim that. It is also true that the Big Bang theory is not the whole story -- it cannot explain some details in what we observe. Expanded versions of the Big Bang theory (using things such as "cosmic inflation" and dark energy) do seem to be able to explain these details, but these ideas are still in development and being tested. I think they will be right to some degree, but time will tell. Yet all of these expanded theories include the Big Bang, because the Big Bang theory works. No other theory does.

It's a point I bring up on here many times, because it is crucial to understanding why scientists believe certain theories. An idea is suggested to explain observations. The idea makes predictions. If the predictions are right, the idea will become an accepted theory. If the predictions fail, the idea has to be changed or discarded. And, in the case of the Big Bang theory, it has predicted several things that have since been discovered. And each of those is worthy of a Nobel Prize.

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