The first few moments of the Big Bang — according to most theories of how it actually worked — should have produced gravitational waves in the fabric of space-time that are still rippling through all of space today. But by now they should be extremely weak, and no detector has had the capability to detect them at any plausible predicted level.

LIGO consists to two L-shaped interferometers, one in Hanford, Washington (shown here) and one Livingston, Louisiana. Each arm of each L is 2½ miles (4 km) long. Lasers can measure changes in each arm's length as small as a thousandth the diameter of an atomic nucleus. Passing gravitational waves might distort space-time by that much.

LIGO Laboratory

Now that's changing. Scientists working with LIGO, the Laser Interferometer Gravitational-wave Observatory, are about to release two years of data that set a meaningful upper limit on certain frequencies of these waves from the start of everything. The limits are good enough to rule out some versions of inflation theory, the current basis for how and why the Big Bang happened.

Gravitational waves, according to Einstein's general relativity, are produced by any large masses violently changing speed. A "gravitational-wave backgound" is expected from the violent early moments of the Big Bang, rather like the cosmic microwave background that fills the sky with radio waves from the early universe. In recent years the microwave background has yielded the universe's age, density, composition, and much else to high precision.

The tunnel for one of the LIGO arms in Livingston, Louisiana. Having two units nearly 2,000 miles apart provides essential error checking and would help show the incoming direction of any gravitational waves.

LIGO Laboratory

But while the microwave background originated about 380,000 years after the Big Bang, the gravitational-wave background should come directly from events in the first one minute. The waves' strength, spectrum of frequencies, and other details should tell about the behavior of the universe during that brief, critical time.

The researchers' results, published in Nature for August 20th, set an upper limit on the gravitational-wave background by combining data from LIGO and a similar detector in Europe named Virgo. The limit also puts constraints on the existence of "cosmic strings": immensely long, line-like flaws in space-time that, theorists have proposed, might also be left over from the universe's very beginning.

The meeting of the arms

The interferometer arms and the equipment in their ends (seen here) are kept in an ultrahigh vacuum.

LIGO Laboratory

"Since we have not observed the stochastic [random] background, some of these early-universe models that predict a relatively large stochastic background have been ruled out," says Vuk Mandi, assistant professor at the University of Minnesota, in a Caltech press release about the results. "We now know a bit more about parameters that describe the evolution of the universe when it was less than one minute old."

Mandic adds, "We also know that if cosmic strings or superstrings exist, their properties must conform with the measurements we made — that is, their properties, such as string tension, are more constrained than before." This is interesting, Mandic continues, "because such strings could also be so-called fundamental strings, appearing in string-theory models" (inflated from microscopic size by the early expansion of space). "So our measurement also offers a way of probing string-theory models, which is very rare today."

Workers install a testing mirror for the laser beam during construction.

LIGO Laboratory

LIGO is still ramping up. Due to come online in 2014 is Advanced LIGO, which will have upgraded lasers, detectors, and test-mass isolation systems. These should increase the sensitivity by at least a factor of 10, vastly enlarging the volume of space in which LIGO should be able to sense such things as chaotic supernova cores imploding and neutron-star pairs spiraling together and merging. No such events have yet been observed, but the upgrade is expected to bring them within reach.


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Justin S

August 19, 2009 at 2:29 pm

The absence of evidence is very unconvincing to me. Has LIGO ditected ANYthing?

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michael farmer

August 20, 2009 at 7:09 am

Lack of evidence can be very useful. It can eliminate a lot of places where it is no longer worth-while to look. Remember the Sherlock Holmes story about the dog that did not bark.

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August 20, 2009 at 12:45 pm

If you are interested in Gravity waves you will be interested in the Origin of Gravity. As an alternative to Quantum Theory there is a new theory that describes and
explains the mysteries of physical reality. While not disrespecting the value of Quantum Mechanics as a tool to explain the role of quanta in our universe. This theory states that there is also a classical explanation for the paradoxes such as EPR and the Wave-Particle Duality. The Theory is called the Theory of Super Relativity and is located at: This theory is a philosophical attempt to reconnect the physical universe to realism and deterministic concepts. It explains the mysterious.

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lawrence Cain

August 20, 2009 at 5:45 pm

Peaked my interest, go LIGO

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lawrence Cain

August 20, 2009 at 5:45 pm

Peaked my interest, go LIGO

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August 20, 2009 at 11:57 pm

In any scientific research or experiment, a zero result is still a result. It can both prove a theory right or wrong.

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August 21, 2009 at 5:20 am

We as a society are spending billions on research to check where we came from. This is a mystery to me, since the bringing of social justice is more important than research on the fabric of space-time. Where we came from is where we came from, but the NOW is where we need to live in. We will never entirely be able to seek out the origin of our beings, simply because what made is, is bigger than us. Get alive!

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August 21, 2009 at 3:22 pm

>We as a society are spending billions on research to check where we came from......

Billions? Actually the NSF is only contributing something like $32 million per year for 7 or 8 years to upgrade LIGO. That’s a pretty tiny amount from the US national budget. The Army probably loses more toilet paper in a month than that. Much of the funding is from the universities involved. While bettering the lot of mankind is a great and noble thing, a part of what makes us human is a desire to understand the nature of the universe. Researching the laws of nature *is* a part of ‘the now’, and is a great and noble human enterprise that has done more for the benefit of humans than any form of social engineering. There’s more money spent on sci-fi movies and alien abduction stuff each year than there is on basic astronomical research.

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Derrick Hankel

August 21, 2009 at 4:49 pm

They said Einstein's theory of relativity would be interesting but worthless. And here we are today using it with GPS and dozens of other sophisticated instruments that better society. Apollo went to the moon for political as well as scientific study but today we really know as a race how small we are in the cosmos as a result of that endevour.

If we just concentrated exclusively on social issues we'd still be in the stone age. There will always be poor people, war's and social unrest but solving any of those things will not make us a greater race because we'd be too stupid to do anything else. Arts and sciences MUST advance so all those social issues can also. Yes, LIGO is worth every penny.

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Emanuel VonAnkh

August 21, 2009 at 6:22 pm

Regardless of what many scientists say, gravity is NOT understood. We don't know how it works or even how to uniquely define energy in gravitational fields. We do know that it DOES work. Therefore a zero result from LIGO, would not tell you anything more, than that we still do not understand gravity. As this is so, it should not come as a great surprise, if LIGO (or any other GW detectors) come out with a null result. However, LIGO like experiments may put new and interesting limits on quantum effects (spacetime foam) and extra dimensions.

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Allan Holmgren

August 21, 2009 at 8:31 pm

Can anyone tell me if the advanced LIGO is the space based system I have read about. I hope it is because one of the problems with gravitational wave detection is that we really don't know what wavelengths we will eventually encounter. When in doubt about wavelength, it is usually helpful to have a very long antenna so to speak.

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Larry Robinson

August 21, 2009 at 10:55 pm

Inflation is a fictitious attempt to explain an observation that was really a relativity effect. The universe WAS small when the cosmic background was radiated.

Since gravity is caused by the expansion of the universe, it can't brake it.

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Phil E. Drifter

August 22, 2009 at 12:28 am

"I have not failed. I've just found 10,000 ways that won't work." -Thomas Edison

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August 22, 2009 at 11:40 pm

About 850 Billion $ is spent yearly by the US for ALL things military. This is about 8% of its yearly 10,500 Billion $ GNP. The GNP of a poor country such as Bolivia is about 9 Billion $ per year. If developed countries gave away a part of their military budgets in a concerted effort to develop poor countries, say, one by one, things would probably get better fast.
Most developed countries use about 3% of their GNP for research, but this may include military-related and funded research. However, a lot of this research will be almost immediately useful, and other parts will be useful in the future. Whether they will be harmful or not depends on us. I'd rather reduce the military than the research budget. In the end, doing so would reduce our need for military spending as a more peaceful world ensues.

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