Putting Einstein to the Test
Nov. 19, 2015
Scientists are at work deep in the mountains of central Japan. They hope to prove a theory of Albert Einstein's. Two hundred meters underground, inside an abandoned zinc mine, the researchers have laid two pipes in tunnels at right angles, each three kilometers long. The tunnels are so long it's impossible to see light at the ends. The tunnels are also so long that on this job, the scientists move around by bicycle.
The project, called KAGRA, began three years ago. It is an initiative of the University of Tokyo. It is led by a team of researchers from Japan and other countries. They're preparing to start testing in March.
They aim to observe a cosmic phenomenon known as "gravitational waves" -- something that has never been detected before.
Experts say it will be worthy of a Nobel prize if and when scientists succeed in directly observing the phenomenon.
What exactly are gravitational waves?
Albert Einstein advanced his hypothesis in 1916 about the existence of gravitational waves. His theory on general relativity proposed a completely new concept of gravity.
Newton’s law of gravity states that the sun and the earth pull against one another. But Einstein believed that a heavenly body with a large mass strongly distorts time and space. He said the real cause of gravity is when something falls into a cavity of distorted time and space.
Heavenly bodies that circle the sun -- like the Earth -- move along the cavity, maintaining their balance through centrifugal force. Einstein suggested there were ripples in space-time -- called gravitational waves. He believed they are like springs, that can stretch or contract space.
He argued that the waves distort space. The problem is, nobody has ever been able to directly observe them. If they are affecting space-time, the distortions are too small to be measured with existing technology.
So now, researchers around the world are in a race to be first to observe the waves.
The KAGRA detector comprises a vacuum-sealed pipe inside an L-shaped tunnel. It stretches for three kilometers in each direction. Lasers continuously measure the length of the pipe in both directions.
If gravitational waves are distorting space, one path will expand while the other contracts. To put it simply, if the researchers can detect this change, they'll have proven that Einstein was right.
The scientists say each pipe has to be three kilometers long because the distortions are likely to be tiny. So, the longer the pipe, the greater the chance of detecting the discrepancy.
Heading the project is Nobel laureate Takaaki Kajita. The University of Tokyo professor won this year's Nobel physics prize for his research into the elementary particle called a neutrino.
"I definitely want to be the first to observe gravitational waves," he says. "And the next few years will be crucial, so I plan to work as hard as possible."
It may seem odd that the challenge of detecting waves from outer space needs to be conducted 200 meters underground. But this is because vibrations are the biggest obstacle to the job. Gravitational waves are very subtle. Even the tiniest vibration can make them difficult to detect. Other waves caused by things like traffic, human activities, even wind and rain, pose a hindrance.
And the depth isn't a problem because gravitational waves pass through everything.
The team's technical creativity has made KAGRA capable of observing a distortion in space as small as one billionth of a hydrogen atom.
Yoichi Aso is a member of the team. He is an Associate Professor at the National Astronomical Observatory of Japan. He had this to say: "These observations will enable us to solve various mysteries of the universe, such as how black holes are formed, and similar quandaries. Since no light is emitted, the phenomenon can’t be observed with an optical telescope, and it can’t be observed through magnetic waves, but we think it’s transmitted via gravitational waves. This experiment should give us information about the start of the universe, just after the Big Bang."
We asked Aso how confident he feels that KAGRA could be first to make the discovery.
“In terms of functionality, it can compete with foreign technologies," he says. "We want to be first. But it’s also necessary to take observations from more than one location in order to confirm the existence of gravitational waves. International cooperation is essential. I want to share our results.”
KAGRA is expected to be fully operational by 2018. The team believes that gravitational waves could be detected within a few years after this. So the near future may bring us even greater knowledge about the creation of the universe.