Originally published 30 May 2000
In 1905, Albert Einstein published a paper in which he proposed that all observers will measure the same velocity for light, regardless of any motion of the observer or the source of light.
It’s as if a bullet were to strike you with the same velocity whether you were speeding toward the gunman or standing still.
This radical idea was a kick in the teeth to conventional physics, but physicists gave it a look because it neatly explained a few troubling experimental observations, and because Einstein was known to be a clever fellow.
The new theory was called relativity, and it made some wild and indeed almost unbelievable assertions about the nature of matter, energy, space, and time.
For example, consider the famous “twin paradox.” According to Einstein’s theory, if a twin went off on a journey in a space ship, traveling at a significant fraction of the speed of light, and returned, less time would have elapsed for the traveler than for the stay-at-home twin. The traveler would return and find herself younger than the twin she left behind.
A bizarre prediction. But, of course, the twin paradox has now been tested many times, not with actual human twins, but with atomic “clocks” of one sort or another. The results precisely confirm Einstein’s intuition. Many other tests of the theory have been equally successful.
Relativity has become a pillar of contemporary physics. What was once “unbelievable” has become commonplace.
Now along comes astronomer Kenneth Brecher of Boston University to put the screws ever more tightly to relativity. He has devised a test of a central tenet of relativity — that the speed of light is independent of the velocity of the source — that is accurate to 20 decimal places.
He does it by studying distant gamma ray bursts, powerful explosions of radiation from the edge of the observable universe. If the explosions fling particles out in every direction, then the particles must be moving at different velocities with respect to the Earth, and — if the velocity of light depends on the source — the radiation the particles emit would smear out during the long journey our way. But the observed bursts are tight; light from all the particles arrives at the same time. Einstein rules to one part in 100 quintillion.
Why bother testing a theory to such precision when everyone already believes it to be true? Here’s the kicker. Astronomer Bradley Schaefer of Yale University says: “We push as hard as we can, hoping that something breaks.”
On the face of it, this seems admirable. One of the reasons we have confidence in scientific ideas is because scientists hold the feet of their theories to the fire of experience.
Furthermore, what Brecher is doing fits nicely into Thomas Kuhn’s famous ideas about science, expressed in his 1962 book, The Structure of Scientific Revolutions.
According to Kuhn, scientists generally work within the confines of a “paradigm,” a commonly held set of assumptions about how the world works. The questions scientists pose, and the answers they get are shaped by the paradigm. This is Kuhn’s stage of “normal” science.
Within normal science, the few things that don’t fit are generally ignored. Eventually, however, difficulties within a paradigm can become unsustainable, and a revolution occurs. A new paradigm is established, and work goes on.
It was a Kuhnian shift of paradigms took us from Newtonian (absolutist) physics to Einsteinian (relativistic) physics.
By this account, Brecher’s gamma-burst test of relativity is an example of normal science: Playing the game of science within the confines of the Einsteinian paradigm. Pushing the theory to see if it breaks.
But not everyone would applaud Brecher’s preoccupation with that 20th decimal place.
Many sociologists of science see the normalization of science within a paradigm as conservative and self-serving. Alternate versions of the “truth” are delegitimized, and established science, with its consumerist-military preoccupations, becomes the only game in town.
Young scientists are acculturated within a paradigm, say these critics of science, and spend the rest of their careers tweaking theories. Dissent is frowned upon. The real problems of society are ignored in the pursuit of that extra decimal place.
I happen to disagree with the critics. Science may be the only knowledge-building game in town, but so far no one has proposed a better one. And, yes, science has often allied itself with the so-called military-industrial complex, and made some egregious blunders on behalf of prejudice, but I think history will show that, in the long haul, science has advanced the cause of human freedom and equality.
At the same time, scientists might concern themselves more fully with how research within an established paradigm might best serve society. Those 20 decimal places begin to look a tad self-indulgent in the face of such manifest problems as the AIDS epidemic in Africa or growing inequalities of rich and poor.
