Op-ed sees 2015 as possibly “the year we confirm both the virtues and the limits of general relativity”
DOI: 10.1063/PT.5.8098
In a 5 February op-ed in the International New York Times , the physicist, science writer, and former Nature editor Philip Ball speculates that 2015, besides being general relativity’s centennial, could also be its “big year.”
“You might think that physicists would be satisfied by now,” he begins, citing the theory’s durability and resilience. “But they are still investigating its predictions to the nth decimal place, and this centenary year should see some particularly stringent tests. Perhaps one will uncover the first tiny flaw in this awesome mathematical edifice.”
Ball explains what might seem counterintuitive to some readers: that physicists “would doubtless react with joy if it is proved to fail,” since failure might point the way beyond general relativity and quantum theory to a theory of quantum gravity.
After some layman’s history of general relativity—including mention of the 1919 Eddington experiment confirming that strong gravitational fields bend light rays, together with some summarizing discussion of pulsars and black holes—Ball reaches his passage about 2015:
While Newton’s theory of gravity is mostly good enough to describe the motions of the solar system, it is around very dense objects like pulsars and black holes that general relativity becomes indispensable. That’s also where it might be possible to test the limits of the theory with astronomical investigations. Last year, astronomers at the National Radio Astronomy Observatory in Charlottesville, Virginia, discovered the first pulsar orbited by two other shrunken stars, called white dwarfs. This situation, with two bodies moving in the gravitational field of a third, should allow one of the central pillars of general relativity, called the strong equivalence principle, to be put to the test by making very detailed measurements of the effects of the white dwarfs on the pulsar’s metronome flashes as they circulate. The team hopes to carry out that study this year.
But the highest-profile test of general relativity is the search for gravitational waves. The theory predicts that some astrophysical processes involving very massive bodies, such as supernovae (exploding stars) or pulsars orbited by another star (binary pulsars), should excite ripples in space-time that radiate outwards as waves. The first binary pulsar was discovered in 1974, and we now know the two bodies are getting slowly closer at just the rate expected if they are losing energy by radiating gravitational waves.
The real goal, though, is to see such waves directly from the tiny distortions of space that they induce as they ripple past our planet. Gravitational-wave detectors use lasers bouncing off mirrors in two-kilometer-long arms at right angles, like an L, to measure such minuscule contractions or stretches. Two of the several gravitational-wave detectors currently built—the American LIGO, with two observatories in Louisiana and Washington, and the European VIRGO in Italy—have just been upgraded to boost their sensitivity, and both will start searching in 2015. The European Space Agency is also launching a pilot mission for a space-based detector, called LISA Pathfinder, this September.
“Anyone working on quantum gravity,” declares Ball at the end, knows that general relativity “is a very hard act to follow.”
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Steven T. Corneliussen, a media analyst for the American Institute of Physics, monitors three national newspapers, the weeklies Nature and Science, and occasionally other publications. He has published op-eds in the Washington Post and other newspapers, has written for NASA’s history program, and is a science writer at a particle-accelerator laboratory.