Image: V. Altounian/Science
The gravitational wave signal was detected by physicists at LIGO on September 14 last year, and the historic announcement was made at a press conference this morning.
Gravitational waves are so exciting because they were the last major prediction of Einstein's general theory of relativity that had to be confirmed, and discovering them will help us understand how the Universe is shaped by mass.
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.
But by the time those ripples get to us on Earth, they're tiny (around a billionth of the diameter of an atom), which is why scientists have struggled for so many years to find them.
The phenomenon was detected by the collision of two black holes. Using the world’s most sophisticated detector, LIGO(Laser Interferometer Gravitational-wave Observatory) the scientists listened for 20 thousandths of a second as the two giant black holes, one 35 times the mass of the sun, the other slightly smaller, circled around each other.
At the beginning of the signal, their calculations told them how stars perish: the two objects had begun by circling each other 30 times a second. By the end of the 20 millisecond snatch of data, the two had accelerated to 250 times a second before the final collision and dark merger.
“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.”
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2) Why do measurements of the gravitational constant vary so much?