In a happy example of interdisciplinary synchronicity, both SciTech Daily and Arts and Letters Daily have links to a Scientific American article about tests of Special Relativity. With both artists and techies recommending it, how can I pass it up as blog fodder?
The article describes a couple of different experiments designed to look for hints of exotic physics beyond our current models of the Universe, by looking for places where Einstein's most famous theory breaks down. Not the "E equals m c squared" bit (though that's the graphic they chose to illustrate the piece), but rather the bits about Lorentz invariance. This is the mind-bending stuff about time slowing down and objects changing size when you travel at speeds close to the speed of light-- it's provided the material for countless pop-science books and tv shows, and made many a dazed undergraduate say "whoa" in a Keanu Reeves sort of way.
The experiments in question are fascinating, and each is a technical tour de force in its own right. Happily, some of the experiments also happen to be carried out by friends and colleagues-- in this case, Nathan Lundblad works in the Laser Cooling Group at NASA's Jet Propulsion Laboratory (JPL), with Bill Klipstein and Rob Thompson, who I worked with at NIST, back in the day. (The group also happens to be headed by the brother of a current colleague... Small world...). As one would hope from the involvement with JPL, the ultimate goal of the experiments is to propel some things with jets, specifically to put sensitive atomic clocks into orbit on the International Space Station. There are two main experiments, outlined nicely by NASA to save me a bunch of typing: one involves comparing clocks in space to clocks on the ground (it goes by the acronym PARCS), the other involves putting a laser-cooled rubidium atomic clock in space, to see if it runs at the same rate as a microwave frequency standard which should be orbiting at the same time.
The article also highlights the work of a group at Konstanz in Germany, where they've performed fundamental tests by comparing the frequencies of two atomic clocks over a long period of time, and by repeating the famous Michelson-Morely Experiment (famous, of course, because Morely was a Williams grad...). These experiments are a little less speculative (they don't require blasting the apparatus into space, for one thing), and have already produced results.
One of the most interesting things about these experiments, and the thing that made this article particularly attractive as blog fodder, is that these are all essentially recapitulating classic experiments of physics. The Konstanz group is explicitly repeating (and updating) Michelson-Morely, and NASA's description of the RACE experiment highlights that aspect of it as well. Other experiments mentioned in the article are just re-checking the previously observed relativistic effects on rapidly moving bodies, and re-confirming the fact that gravity affects all masses equally. This sort of thing tends to be somewhat surprising to non-scientists-- after all, if we've done the experiment once, why repeat it?
It's a question I get asked a lot when friends and relatives ask about my work, and it's the same sort of question that leads to the faintly surprised tone of the links to the article (and the opening paragraph of the article), and answering it is the main point of the whole thing:
After a century, Einstein's special theory of relativity, which describes the motion of particles moving at close to the speed of light, has held up remarkably well. But as scientists probe the edges of the current knowledge of physics with new tests, they may find effects that require modifications on the venerable theory.
Several current theories, designed to encompass the behavior of black holes, the big bang and the fabric of the universe itself, could lead to violations of special relativity. So far, recent, updated versions of century-old experiments show no signs that Einstein's vision is reaching its limits. Various tests are ongoing, however, and a new generation of ultraprecise, space-based experiments is set to launch in the next few years, offering some chance, however slim, of observing signs of the laws that will eventually supersede relativity.
It should come as no surprise that people continue to test Einstein's theories after a whole century, because people continue to test Newton's Law of Gravitation three centuries after Newton more or less started the whole field of physics. A group at the University of Washington has done an absolutely astounding series of experiments, demonstrating that the basic expression of the force of gravity (proportional to the product of the two masses, and inversely proportional to the square of the distance between them) holds on scales from the cosmological (attraction between distant galaxies), to the nearly microscopic (separations of less than a millimeter).
The point of testing Einstein's theories is the same as the point of testing the theories he overthrew. It's not exceptionally likely that you'll find a deviation from the accepted theory, but if you do, it's big news. And in a very fundamental way, science extends only as far as our best measurements. This isn't another statement of uncertainty-- just a statement of fact. There's always some theorist, whether a respected member of the scientific community, or just some wing-nut cranking out mimeographed copies of his Theory of Everything in a basement in Kansas, who will boldly predict that Newton and Einstein were wrong, and the proof of the Theory of Everything lies just beyond the scientific lands we know. Relativity will break down when you go at just the right speed, or gravity will change its behavior when the masses are a hundredth of a millimeter apart, or Invisible Pink Unicorns will suddenly become visible and cavort about the lab if you do some experiment that you can't quite do just yet. Until and unless you make the measurement, you'll never know for sure.
When I was an undergrad, I did some semi-official tutoring for some friends who were taking the stereotypical "Physics for Poets" class, taught by a wonderful professor, a slightly absent-minded theoretical physicist who lacks only a German accent and a white lab coat to be the very image of the popular idea of a physicist. He introduced the lecture on gravity, they told me, by saying "The great thing about gravity, is that every time you drop something, it falls," and dropping a piece of chalk into his hand. "At least," he went on, "you think that every time you drop something, it's going to fall." And dropped the chalk into his hand a few more times, as if waiting for it to take off an rocket through the ceiling.
It got a big laugh from the students (in a slightly nervous, "my-professor's-a-lunatic" sort of way), but it makes a very valuable point. Until you actually do the measurement, you never really know. That's why, as scientists, we keep repeating old experiments, testing venerable theories, and dropping pieces of chalk. Most of the time (every time so far), you get exactly what you expect-- the results are the same, the theory is upheld, the chalk hits the floor-- but until you do it, you never know. And the one time the chalk flies off through the ceiling will stand the whole world of physics on its head.
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