It was 100 years ago when an obscure 26-year-old office worker in a Swiss patent office submitted five papers that would radically change the way people think about the universe.
In fact, Albert Einstein's ideas, devised entirely from thought, were so advanced that scientists are still trying to prove some of them.
To find evidence for the brilliant physicist's ideas, researchers are using the latest in technology and a century of research -- neither of which Einstein had when he devised such profound concepts as the General Theory of Relativity.
"It's amazing Einstein came up with his theories just by thinking about the situation," said Peter Shawhan, a staff scientist at the California Institute of Technology.
Catching a Wave
Shawhan is part of a large team of researchers who operate LIGO, a set of two giant, L-shaped experiments in Louisiana marshland and Washington state forestland. The facilities each feature two 2.5-mile-long steel tubes built in perfectly straight lines that are designed to detect one of the faintest and most rare signals in the universe -- gravitational waves.
According to Einstein's General Theory of Relativity, gravitational waves are sent out by any object that undergoes acceleration. The waves are so faint, however, that only those emanating from huge events -- such as colliding neutron stars or two black holes smashing together -- can be detected.
Even waves from these events are so faint that by the time they reach Earth, they will be recorded by a difference of timing in the instruments amounting to just 0.0000000000000000000000001th of a second.
"This is one of the hardest parts of his theory to prove because the waves we hope to see are just so incredibly weak," said Shawhan. "It's a tiny effect."
So far, the crew of scientists has no direct evidence the waves are there. But a century ago Einstein proposed their existence, and so they're confident they'll prove him right. It's just a matter of when.
An instrument at the joint of the two passageways sends light beams down each arm. The light travels down the tubes and hits mirrors at the near and far ends of each tunnel and then bounces back and forth 100 times.
If no gravitational wave has been detected, then both light beams arrive back at the source at exactly the same time. But if a gravitational wave has struck Earth, then it will ever so slightly alter the path of the beams so one will arrive fractions of a second before the other.
The problem is, to measure something so slight, every aspect of the experiment has to be extremely precise. And although LIGO is extremely precise, it isn't as precise as it could be, says Shawhan.
"If there is a storm, it shakes the ground. High winds can shake the buildings, which affect the readings, as does general traffic in the area," he said.
A Waiting Game
To buffer the skewing affect of local vibrations, engineers are in the process of installing a feedback control system that will eliminate such outside "noise." They're also fine-tuning the instruments' mirrors to prevent warping by heat from the lasers.
By 2013, LIGO is due to be ramped up even further so it can detect gravitational waves emanating from even further out in space. That should improve the experiment's chances since researchers suspect that events large enough to emit a gravitational wave big enough to detect are few and far between.
"We'll be able to detect events 10 times farther away with the improvements," said Shawhan. "By then, there's a good chance we'll see something. Otherwise, we might have to wait 10 to 100 years for a big event."
Three other similar facilities in Italy, Japan and Germany are also waiting for a big wave. With so much money, work and time invested, some may wonder if all the effort might be in vain. But they're not just banking on Einstein's brilliance.
In 1993, two Princeton University scientists won a Nobel Prize for demonstrating that the increasing speed of two spiraling neutron stars fits exactly with Einstein's theory of relativity and gravitational waves.
"They've been tracking this for some 20 years and the change in orbit agrees exactly with the general theory of relativity," said Shawhan. "It looks like great confirmation, but it's not a direct one."
What Did Einstein Miss?
While the LIGO team is eager to find direct confirmation of gravitational waves and prove Einstein right, other groups are scanning space for evidence that the physicist's theory might be slightly off.
Why search for chinks in Einstein's armor? As his theory now stands, the ideas don't mesh completely with another major field of physics -- quantum theory. Quantum theory examines all matter and motion in terms of particles. As the theories now stand, Einstein's General Theory of Relativity doesn't incorporate all the concepts within quantum theory. So scientists have yet to discover a "Theory of Everything" -- something Einstein spent the last 30 years of his life pursuing -- in vain.
"Einstein's theory of gravity is not a complete theory," said Michael Salamon, a physicist at NASA headquarters in Washington, D.C. "In order to probe gravity fully, we believe there are deviations from Einstein's classical theory. Our mission is designed to find those deviations."
Salamon is part of NASA's Gravity Probe B mission, which has launched four gyroscopes into orbit around Earth. The sensitive instruments were designed to detect whether or not a large spinning object in space (in this case, Earth) drags space-time -- the fabric of space -- with it, as Einstein's theory predicts.
"It's like twirling a spoon in a jar of honey," explains Salamon. "You see the honey dragging along with the spoon. It's analogous to what happens in space."
Scientists with the Gravity Probe B mission announced last fall that the instruments have indeed proven that space-time is dragged by large spinning objects, as Einstein predicted. But as more data streams in, they hope to also reveal aspects of gravity that Einstein didn't predict. It's this information that could point to an all-encompassing theory that includes both Einstein's thinking and the more recent concepts of quantum theory.
Even if scientists find evidence for new explanations of the universe, Salamon stresses that Einstein's theories will still play a central role.
"Whatever new theory we come up with," he said, "it will ultimately contain Einstein's original thinking. There is no doubt about that."