Scientists are getting ready to begin a new search for one of the most elusive mysteries of the universe: gravitational waves.
Gravitational waves are predicted to be ripples in the fabric of space-time that occur after an energetic event of monumental size. For example, the collision and merging of two black holes, or the final death throes of a colossal star exploding to dispel its unimaginable build up of energy. The aftershock of this event (like the ripples around an object in a pond) takes the form of gravitational waves.
The Laser Interferometer Gravitational-Wave Observatory (LIGO) has been upgraded to greater sensitivity than ever before in an effort to detect the tiny effects of gravitational waves. There are two LIGO bases; one in Livingston and one in Hanford. The LIGO machines are long pipes in an L shape. A beam of light is shot down each branch of the L and bounced back to the source with a mirror. When the beams meet again, a laboratory reconstructs the data held in the beam.
A promising result would be if there were tiny alterations in the returning beam: this would indicate that the beams of light were being altered by gravitational waves. The effect would be miniscule, however: even the vibration of the atoms that make up the mirrors off which the rays of light bounce distorts the delicate signal. The data that the lab receives have to go through a lot of refinement to extract the gravitational wave signal.
LIGO experiment via BBC
"Every time we open a new window on the Universe, we make surprising discoveries," said Professor Ken Strain, Institute for Gravitational Research. "That was true for example with radio astronomy, which led quickly to the discovery of pulsars. And we expect the same with gravitational wave astronomy.
"Gravitational waves are produced by the bulk moving mass of an object. In the case of a supernova, this is the very core of the exploding star. And while today we can view a supernova optically with telescopes – we see the flash – we don't really know how it is produced. But if we can detect the gravitational waves from that supernova, we'll gain information directly about the underlying mechanisms."
There is room for LIGO to be even more refined than it is at the moment; the laser light is very susceptible to noise or random fluctuations that look a lot like gravitational waves but aren't. Instead of splitting a laser beam, scientists want to aim for splitting an atom and sending a "half" down each laser arm.
In fact, vibrations in the Earth are sometimes too distracting to see a gravitational wave signal: the experiment works best up in the vacuum of space. A sister experiment, LISA (Laser Interferometer Space Antenna) would have taken this experiment to space but was cancelled in 2011 due to a lack of funding.
The theory of general relativity predicts the existence of gravitational waves; they seem to be inevitable. So it's teeth-grittingly frustrating that no one seems to be able to see them.