Newsroom Tokyo S2015E146 - Putting Einstein to the Test

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.