World Science Festival: Waiting for Einstein's Gravity Waves

By Joseph Calamia | June 7, 2010 6:35 pm

LIGO-04Some picture gravity as a rubber sheet–stretched taut like a trampoline. If the Sun is a bowling ball, its heft will form a bowl-shaped valley on that sheet. In its stable orbit, the Earth rolls along the edges of the Sun’s valley. But if gravity is like a rubber sheet with weights on top, what happens when those weights misbehave? What if they collide or explode, sending ripples along the rubber surface?

In 1916, Einstein predicted the existence of these gravity waves: ripples not in rubber, but in space-time, the surface of our universe. Today, almost 100 years later, gravity waves remain the last piece of his theory of general relativity that no scientist has observed directly. But a series of detectors, including two in the United States, are looking for these waves.

Rainer “Rai” Weiss is the father of LIGO, the Laser Interferometer Gravitational Wave Observatory. He first devised the instrument as a homework assignment for some of his MIT students, and it started operating in 2001. Weiss spoke last Friday night as part of a World Science Festival event in New York.

Light waves, like any waves, can interfere with one another. Two peaks can build to make even brighter light and a wave and a trough can cancel one another out to leave only darkness.  Weiss and colleagues have designed and built a large interferometer, an L-shaped device with a series of lenses and mirrors. Laser light is split at the L’s joint and travels along each of the L’s two legs. At the end of each, the light reflects off a mirror, travels back along the leg, and recombines at the joint before going to a detector.

By adjusting the length of the two 2.5 mile-long arms, scientists can change the interference pattern formed by the two beams’ recombination so that the light beams just cancel one another out. If a gravity wave comes along, for example from two pulsars colliding or even two black holes, scientists can measure gravity waves as these space-time ripples change the arms’ lengths and thus the pattern formed by the light’s combination.

Their current system can detect changes in the arms as small as 10-16 centimeters, or one-hundred-millionth the diameter of a hydrogen atom. With two such interferometers, as are currently operating in Livingston, Louisiana, and Hanford, Washington, the scientists can rule out other changes in the interference pattern such as “micro-earthquakes.” Other detectors are operating across the globe, so that if scientists find a wave, they can map out where in the universe it came from.

As you might guess, the changes in the pattern are so small that seeing them will be difficult, requiring a computer to sort out the change from other “noise.” The metaphor with sound is intentional since scientists map the signal onto audio frequencies we can hear and will listen for a what they predict will be a “whooop” as two massive objects collide.

“That’s the whole challenge, to dig that sound out,” Weiss said, after asking his audience to listen for two massive objects, like black holes, spiraling around one another and then colliding. “Your ear is a very good detector. It takes a lot of computing power to get that–what you heard–out of that noise.”

Related content:
Cosmic Variance: Catching the waves
Cosmic Variance: Einstein’s cosmic messengers
80beats: Gravity-Wave Hunters Find Nothing—and Make a Big Discovery
DISCOVER: Works in Progress

Image: Interferometer lens on display as part of the World Science Festival

  • Louis Savain

    There are no gravity waves simply because there is no such thing as spacetime. Several requirements of Einstein’s physics such as a time dimension and continuous structures are not even wrong. For one, a time dimension makes motion/change impossible (surprise!) and second, continuous structures lead to an infinite regress.

    Einstein’s physics has retarded progress in our understanding of nature by at least a century. Physicists still have no clue as to the real cause of gravity. They can blame it on Einstein and his cheerleaders.

    This is the beginning of the end of Einstein’s era in physics, i.e., the end of Star-trek voodoo physics, time travel and the like. Google “How Einstein Shot Physics in the Foot” to find out more.

  • Rob R.

    Gettin an Error 404 – Not Found from the 80beats: Gravity-Wave Hunters Find Nothing—and Make a Big Discovery link.

    Found this link for it via Google.

  • Eliza Strickland

    Sorry about that broken link, Rob — fixed it!

    – Eliza, DISCOVER online news editor

  • Chad Roberts

    @ Louis Savain

    I have spent some time reading about your perspective, and although interesting, I find it rather unfounded and blasphemous.

    You (and the article you quote) say that a time dimension can not exist because it wouldn’t allow motion. This makes absolutely no sense to me. I think you missunderstand what a dimension really is. The artical mentions opposition towards relativistic theories because it supports time travel… but if you take the time to understand the whole point of classifying time as a dimension, you would understand that this is not the case. A forward march of time is supported by the theory of relativity… time is described as a dimension because it’s value can be altered. However, just like the 3 spacial dimensions, you cannot have a negative number for time because it simply doesn’t make sense. In other words, having a negative value for the x-axis would completely throw off our whole existance. This is the same for time. You can not have a negative value for time, because it simply doesn’t make sense. You can approach zero, you can approach infinity, but a negative number doesn’t work.

    How does a time dimension stop motion/change? I consider myself open minded, so if you wish to further discuss the theory you support please e-mail me at

  • Brian Too

    Isn’t it interesting that the LIGO experiments just keep going on, and on, producing negative results? Of course a negative result in science still has a lot of value but… ultimately, these detectors were built to detect gravity waves. Where are the gravity waves?

    I’m sure I was reading about the LIGO proposal 15 years ago.

    You have to think that eventually these experiments are going to wind down unless they detect something.

  • valentine s. goroshko

    I guarantee ,my friends, the next generation of telescopes will not see Mythical Big Bang emerging soup Broth nor will it capture Gravity Waves-the whole approach is Wrong-I will send to each of you a symbolic 1$ if I am Wrong, & you will send me 1$ if I am Right, each one of you. The Reason is Very Simple, We give to the Very Basic Spatial Propagational Concepts from 0 to C & Constant E=C so many Linguistic Frameworks , frankly scientists are Lost in that Jungle. Scientists will also not find in Particles/Smashers the Ultimate Particle. We should re-think Our Traditional Concepts.

  • kate s

    I agree that there is so much fragmented info and we are as far from a unified understanding as ever. Fractals imply a small to large understanding as does EM so why the dogged determination to do gravity waves? Chasing the Higgs down a dark alley seems counter intuitive.
    Now LIGO enthusiasts seem focused on the current compression of Sol’s heliosphere which both myth and they claim. When the compression releases suddenly at 2013 this will create a wave in the local field which even tho there is no massive nova or two BH circling each other next door will be the new discovery of the long sought truly mythical gravity waves.
    I predict explanations that rationalize the appearance without the instigators will be non-stop.


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