Science

Einstein's gravitational waves heard for the first time

caltech-web-grab-grabwaves.jpgThe top of Caltech's website today.

The physical science world got to make a big, big announcement today. Last Sept. 14 at 2:51 in the morning, instruments picked up the sound of two black holes merging millions of years ago. The gravitational waves from such an event had been predicted by Albert Einstein, and studies had confirmed it should have happened, but until last September such waves had never been detected. Now they have, and physicists and astronomers say it's new day for what they know of the universe. There's a press conference being held in Washington and a gathering at Caltech to watch it. Select reporters had been prepped on the science of all this, but apparently sworn to secrecy, so the stories posted this morning are good with awesome graphics.

In short, it's the observation for the first time of ripples in the fabric of spacetime. Just as predicted a century ago.

grav-waves-grafic-caltech.jpgFirst, the announcement from Caltech in Pasadena, whose Kip Thorne has been part of the international effort to detect these waves for decades. When the school is able to include Richard Feynman in its news, you know this is kind of big.

For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window onto the cosmos.

LIGO was originally proposed as a means of detecting these gravitational waves in the 1980s by Rainer Weiss, professor of physics, emeritus, from MIT; Kip Thorne, Caltech's Richard P. Feynman Professor of Theoretical Physics, emeritus; and Ronald Drever, professor of physics, emeritus, also from Caltech.

IGO, the most ambitious project ever funded by the National Science Foundation, consists of two L-shaped interferometers with four-kilometer-long arms; at their ends hang mirrors whose motions are measured to within one-thousandth the diameter of a proton. Managed jointly by Caltech and MIT, Initial LIGO became operational in 2001; the second-generation Advanced LIGO was dedicated on May 19, 2015. On September 14 at 2:51 a.m. Pacific Daylight Time, both of the twin LIGO detectors, located in Livingston, Louisiana, and Hanford, Washington, nearly simultaneously detected the characteristic "chirp" of the black holes' fusion.

The New Yorker put up a great tick-tock piece by Nicola Twilley. The lede:

st over a billion years ago, many millions of galaxies from here, a pair of black holes collided. They had been circling each other for aeons, in a sort of mating dance, gathering pace with each orbit, hurtling closer and closer. By the time they were a few hundred miles apart, they were whipping around at nearly the speed of light, releasing great shudders of gravitational energy. Space and time became distorted, like water at a rolling boil. In the fraction of a second that it took for the black holes to finally merge, they radiated a hundred times more energy than all the stars in the universe combined. They formed a new black hole, sixty-two times as heavy as our sun and almost as wide across as the state of Maine. As it smoothed itself out, assuming the shape of a slightly flattened sphere, a few last quivers of energy escaped. Then space and time became silent again.


The waves rippled outward in every direction, weakening as they went. On Earth, dinosaurs arose, evolved, and went extinct. The waves kept going. About fifty thousand years ago, they entered our own Milky Way galaxy, just as Homo sapiens were beginning to replace our Neanderthal cousins as the planet’s dominant species of ape. A hundred years ago, Albert Einstein, one of the more advanced members of the species, predicted the waves’ existence, inspiring decades of speculation and fruitless searching. Twenty-two years ago, construction began on an enormous detector, the Laser Interferometer Gravitational-Wave Observatory (LIGO). Then, on September 14, 2015, at just before eleven in the morning, Central European Time, the waves reached Earth. Marco Drago, a thirty-two-year-old Italian postdoctoral student and a member of the LIGO Scientific Collaboration, was the first person to notice them. He was sitting in front of his computer at the Albert Einstein Institute, in Hannover, Germany, viewing the LIGO data remotely. The waves appeared on his screen as a compressed squiggle, but the most exquisite ears in the universe, attuned to vibrations of less than a trillionth of an inch, would have heard what astronomers call a chirp—a faint whooping from low to high. This morning, in a press conference in Washington, D.C., the LIGO team announced that the signal constitutes the first direct observation of gravitational waves.

Some of the quotes from scientists this morning:

"Until this moment, we had our eyes on the sky and we couldn't hear the music," said Columbia University astrophysicist Szabolcs Marka, a member of the discovery team. "The skies will never be the same."

"It's really comparable only to Galileo taking up the telescope and looking at the planets," said Penn State physics theorist Abhay Ashtekar, who wasn't part of the discovery team. "Our understanding of the heavens changed dramatically."

"It's one thing to know sound waves exist, but it's another to actually hear Beethoven's Fifth Symphony," said Marc Kamionkowski, a physicist at Johns Hopkins University who wasn't part of the discovery team. "In this case, we're actually getting to hear black holes merging."

“Einstein would be very happy, I think.” Gabriela González of Louisiana State University, a spokeswoman for the LIGO Scientific Collaboration, short for Laser Interferometer Gravitational-Wave Observatory.

Clifford V. Johnson, the USC cosmologist who blogs about science and Los Angeles, among other things, calls this What fantastic news!

This is an amazing day for humanity! Notice I said humanity, not science, not physics – humanity. The LIGO experiment has announced the discovery of a direct detection of gravitational waves (actual ripples in spacetime itself!!), opening a whole new window with which to see and understand the universe. This is equivalent to Galileo first pointing a telescope at the sky and beginning to see things like the moons of Jupiter and the phases of venus for the first time. Look how much we learned following from that… so we’ve a lot to look forward to. It is 100 years ago since gravitational waves were predicted, and we’ve now seen them directly for the first time!


Actually, more has been discovered in this announcement:- The signal came from the merger of two large (stellar) black holes, and so this is also the first direct confirmation of such black holes’ existence! (We’ve known about them indirectly and also about supermassive black holes in the cores of galaxies, but this is a real direct detection of stellar black holes – black holes that probably resulted from the collapse of stars…)

The other great thing is that there are several new wave detection experiments about to come on line around the world over the next few years, and the resulting network of detectors should allow us to begin to map out the events/objects in the sky as we detect the ripples from them. The prospects are fascinating.


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