Gravitational waves: breakthrough discovery after two centuries of expectation


From today’s* Guardian*:

Physicists have announced the discovery of gravitational waves, ripples in spacetime first anticipated by Albert Einstein a century ago.

“We have detected gravitational waves. We did it,” said David Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatory (Ligo), at a press conference in Washington.

The announcement is the climax of a century of speculation, 50 years of trial and error, and 25 years perfecting a set of instruments so sensitive they could identify a distortion in spacetime a thousandth the diameter of one atomic nucleus across a 4km strip of laser beam and mirror.

The phenomenon was detected by the collision of two black holes. Using the world’s most sophisticated detector, 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.


Heady stuff. I’m not sure I completely understand it. How did they know what they were registering was the collision of two black holes?


I could be mistaken, but it sounds like the early experiments that fine-tuned our understanding of the chemistry of air.

We could see the effects on matter (or organisms) in a controlled environment, and knew something was going that had to be in the air.

It sounds like they are drawing the bulk of this from the length of those rods, but I’m not sure if they can actually see the wave or the wave patterns themselves.

He reasoned that something must cross space to transmit the force of gravity. Faraday’s reasoning inspired the great British mathematician James Clerk Maxwell to think about how an electric force travelled, and arrive at an understanding of light and a prediction of radio waves.

The graviton? :smiley:

Now THAT would be another whopping find!


From my understanding, the wave is actually propagating through spacetime itself, and what was measured were the expected distortions seen from outside the distorted metric as the wave passed through the rods.


They detected a signal which is like a chirp, which is predicted by Einstein’s theory of General Relativity. The signal was detected at two different labs. Because it matches the theory, and they don’t know of anything else that could produce such a signal, they are confident that it is from the merging of two black holes.

Here are a couple of links about the chirp signal:
LIGO (Laser Interferometer Gravitational-Wave Observatory) Chirp Graphs

LIGO (Laser Interferometer Gravitational-Wave Observatory) Chirp Sound
The sound recording first plays the original waveform, which sounds like a faint bass drum beat, then plays it again at an artificially elevated frequency (higher pitch) which is easier to hear.


I saw this story earlier…AMAZING!!!

I bet we learn some incredible new things in the near future due to this.


That’s what I took from it as well.


Gives us something more to study. Great stuff.


As far as I know, it’s other stuff happening in the vicinity of the black holes that tells them that.


I found this to be especially enlightening.

It basically explains how the lasers were used to deduce the existence of gravitational waves.



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