Thursday, 11 February 2016

Scientists Detect Gravitational Waves, Proving Einstein Right

A team of physicists who can now count themselves as astronomers announced on Thursday that they had heard and recorded the sound of two black holes colliding a billion light-years away, a fleeting chirp that fulfilled the last prophecy of Einstein’s general theory of relativity.
That faint rising tone, physicists say, is the first direct evidence of gravitational waves, the ripples in the fabric of space-time that Einstein predicted a century ago. And it is a ringing (pun intended) confirmation of the nature of black holes, the bottomless gravitational pits from which not even light can escape, which were the most foreboding (and unwelcome) part of his theory.
More generally, it means that scientists have finally tapped into the deepest register of physical reality, where the weirdest and wildest implications of Einstein’s universe become manifest.
Conveyed by these gravitational waves, an energy 50 times greater than that of all the stars in the universe put together vibrated a pair of L-shaped antennas in Washington State and Louisiana known as LIGO on Sept. 14.
If replicated by future experiments, that simple chirp, which rose to the note of middle C before abruptly stopping, seems destined to take its place among the great sound bites of science, ranking with Alexander Graham Bell’s “Mr. Watson — come here” and Sputnik’s first beeps from orbit.
“We are all over the moon and back,” said Gabriela González of Louisiana State University, a spokeswoman for the LIGO Scientific Collaboration, short for Laser Interferometer Gravitational-Wave Observatory. “Einstein would be very happy, I think.”
Members of the LIGO group, a worldwide team of scientists, along with scientists from a European team known as the Virgo Collaboration, published a report in Physical Review Letters on Thursday with more than 1,000 authors.
“I think this will be one of the major breakthroughs in physics for a long time,” said Szabolcs Marka, a Columbia University professor who is one of the LIGO scientists.
“Everything else in astronomy is like the eye,” he said, referring to the panoply of telescopes that have given stargazers access to more and more of the electromagnetic spectrum and the ability to peer deeper and deeper into space and time. “Finally, astronomy grew ears. We never had ears before.”

Long-Awaited Triumph

The discovery is a great triumph for three physicists — Kip Thorne of the California Institute of Technology, Rainer Weiss of the Massachusetts Institute of Technology and Ronald Drever, formerly of Caltech and now retired in Scotland — who bet their careers on the dream of measuring the most ineffable of Einstein’s notions.
Important players in the LIGO project, from left to right: Kip Thorne of the California Institute of Technology, France A. Córdova of the National Science Foundation, Rainer Weiss of the Massachusetts Institute of Technology, David Reitze of Caltech and Gabriela González of Louisiana State University. Credit Lexey Swall for The New York Times
“Until now, we scientists have only seen warped space-time when it’s calm,” Dr. Thorne said in an email. “It’s as though we had only seen the ocean’s surface on a calm day but had never seen it roiled in a storm, with crashing waves.”
The black holes that LIGO observed created a storm “in which the flow of time speeded, then slowed, then speeded,” he said. “A storm with space bending this way, then that.”
The chirp is also sweet vindication for the National Science Foundation, which spent about $1.1 billion over more than 40 years to build a new hotline to nature, facing down criticism that sources of gravitational waves were not plentiful or loud enough to justify the cost.
“It’s been decades, through a lot of different technological innovations,” France Córdova, the foundation’s director, said in an interview, recalling how, in the early years, the foundation’s advisory board had “really scratched their heads on this one.”
Word of LIGO’s success was met by hosannas in the scientific community, albeit with the requisite admonishments of the need for confirmation or replication.
“I was freaking out,” said Janna Levin, a theorist at Barnard College at Columbia who was not part of LIGO but was granted an early look at the results for her warts-and-all book about the project, “Black Hole Blues,” to be published this spring.
Robert Garisto, the editor of Physical Review Letters, said he had gotten goose bumps while reading the LIGO paper.
A pair of L-shaped antennas, known as LIGO, in Hanford, Wash., left, and Livingston, La., detected the gravitational waves on Sept. 14. Credit Caltech-M.I.T.-LIGO Lab

Elusive Disturbances

When Einstein announced his theory in 1915, he rewrote the rules for space and time that had prevailed for more than 200 years, since the time of Newton, stipulating a static and fixed framework for the universe. Instead, Einstein said, matter and energy distort the geometry of the universe in the way a heavy sleeper causes a mattress to sag, producing the effect we call gravity.
A disturbance in the cosmos could cause space-time to stretch, collapse and even jiggle, like a mattress shaking when that sleeper rolls over, producing ripples of gravity: gravitational waves.
Einstein was not quite sure about these waves. In 1916, he told Karl Schwarzschild, the discoverer of black holes, that gravitational waves did not exist, then said they did. In 1936, he and his assistant Nathan Rosen set out to publish a paper debunking the idea before doing the same flip-flop again.
According to the equations physicists have settled on, gravitational waves would compress space in one direction and stretch it in another as they traveled outward.
In 1969, Joseph Weber, a physicist at the University of Maryland, made headlines when he claimed to have detected gravitational waves using a six-foot-long aluminum cylinder as an antenna. Waves of the right frequency would make the cylinder ring like a tuning fork, he said.
Others could not duplicate his result, but few doubted that gravitational waves were real. Dr. Weber’s experiment inspired a generation of scientists to look harder for Einsteinian marks on the universe.
An engineer upgrading a component of the LIGO system. The team had barely finished calibrating its equipment when a loud signal was first detected. Credit Caltech-M.I.T.-LIGO Lab
In 1978, the radio astronomers Joseph H. Taylor Jr. and Russell A. Hulse, then at the University of Massachusetts Amherst, discovered a pair of neutron stars, superdense remnants of dead stars, orbiting each other. One of them was a pulsar, emitting a periodic beam of electromagnetic radiation. By timing its pulses, the astronomers determined that the stars were losing energy and falling closer together at precisely the rate that would be expected if they were radiating gravitational waves.
Dr. Hulse and Dr. Taylor won the Nobel Prize in Physics in 1993.
Another group of astronomers who go by the name Bicep made headlines in 2014 when they claimed to have detected gravitational waves from the beginning of the Big Bang, using a telescope at the South Pole. They later acknowledged that their observations had probably been contaminated by interstellar stardust.

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