A Washington-based search for gravity waves from deep outer space recently went into a five-year hiatus.
The world's largest gravity wave observatory -- based at the Hanford Nuclear Reservation -- completed a 16-month search of the reachable universe on Oct. 20.
Now it has begun an expected five-year overhaul.
"We'll be in the dark for a while," said Fred Raab, a California Institute of Technology physicist who is director of Hanford-based gravity-wave search.
The overhaul's goal: Make the observatory's equipment 1,000 times more sensitive. That means the observatory can detect infinitesimally smaller gravity waves -- as well as waves from much farther out in space by a factor of hundreds of millions of light years..
The observatory is the Laster Interferometer Gravity-Wave Observatory -- or "LIGO" -- which has been trying to find gravity waves in six long search periods since 2002.
Think of gravity waves as a type of sound wave. And think of southern Hanford's LIGO as the a microphone -- capturing those waves and turning them into electronic signals.
Picking up from Einstein
No one has ever caught nor looked at a gravity wave.
But Albert Einstein said they exist. And modern physicists believe him.
In 1916, Einstein mathematically wove space and time together to theorize that massive objects can warp and curve "space-time." The theory also makes gravity a property of space-time. All this leads to the idea that space-time can vibrate, something like a rock landing in a pond with its splash sending out ripples.
In outer space, those "rocks" could be stellar explosions. Or dying stars collapsing. Or black holes and neutron stars circling each other. Or black holes being created. Or even ripples from the "Big Bang" -- the cosmic explosion that theoretically created our universe.
"The existence of gravity waves are on a firm foundation. The problem is detecting them," Raab said.
So how do you catch a gravity wave and look at it?
That takes a device called an interferometer.
In the late 1980s, Cal Tech and the Massachusetts Institute of Technology huddled and decided to build the world's biggest and most sensitive interferometer network.
And $372 million in National Science Foundation funds later, Cal Tech and MIT have built a two-LIGO network, with massive interferometers at Hanford and at Livingston, La.
The LIGO's interferometer shoots a laser beam about the diameter of a flashlight at an angled piece of polished glass that splits it in two directions 90 degrees from each other.
Then the split laser beams are further reflected to go down two huge vacuum tubes 4 kilometers long -- that's about 2 1/2 miles -- to hit more mirrors to bounce back.
If everything is perfect, every bit of light returns to the laser. But if one mirror is slightly off, some light goes in another direction to be caught and studied.
Theoretically, gravity waves should jiggle the mirrors enough to send some light in that new direction.
Gravity waves reaching Earth are expected to be very, very faint.
So faint that when one hits one of the LIGO's mirrors, it is expected to move that mirror by one-thousandth of the diameter of an atom's nucleus. It would take 10 trillion such moves to equal the width of a human hair
The reason for one LIGO at Hanford and a second in Louisiana is locate the deep space source of any captured gravity waves through triangulation.
After eight years, the LIGO network and its smaller and less sensitive counterparts in Germany, Japan and Australia have caught nothing.
Actually, scientist are not surprised at finding nothing so far.
And finding "nothing" actually means something.
Raab pointed a key part of the old Sherlock Holmes story "Silver Blaze" -- a dog that did not bark at night when a murder occurred.
"The fact that the dog didn't bark is relevant," Raab said.
The non-barking dog is the absence of detectable gravity waves from some phenomena -- such as pulsars.
Pulsars are rotating neutron stars -- dramatically denser than our Sun -- that emit radiation visible to the Earth only when the beam-emitting side faces our planet and are supposedly prime sources for gravity waves.
The nearest pulsars are hundreds of light years to tens of thousands of light years away -- well with the LIGO's current range of many millions of light years.
The absence of detectable gravity waves from pulsars in the neighborhood of our solar system means that they are perfectly round, Raab said, since any bumps or distortions would create such a wave.
The absence of of detectable gravity waves does not mean the absence of gravity waves, Raab said. He said the physics and math postulating the existence of gravity waves are overwhelmingly accepted by physics and astronomy communities.
But, "we have no idea how strong gravity waves are," Raab said.
In 2008, the National Science Board allocated $205 million to upgrade the LIGOs at Hanford and Louisiana to improve their sensitivities by 1,000-fold -- the overhaul that has just begun.
This overhaul had been long anticipated when the LIGOs first went online in 2002.
The upgrade will include new mirrors, better lasers, improved electronics, more sensitive measurement equipment and motion isolation systems. The LIGO is so sensitive to outside motion that the vibrations of traffic at Hanford has to be neutralized.
Raab expects the equipment replacement to take three years with another two years allocated to fine-tuning the new LIGO.
"It's just a very complicated system," Raab said.
"This ups the odds of detecting gravity waves by a factor of 1,000. ... (The basic) LIGO got us into the ballpark, but didn't hit a home run. The advanced LIGO will let us hit a home run."
