The graphic above represents two stars circling each other, their gravity ensuring that they will end each other’s existence in a collision that will release three times the mass of our Sun in a few seconds.
LIGO (the Laser Interferometer Gravitational-Wave Observatory) announced this week that it had detected the gravity waves of such a collision. Einstein predicted the existence of gravity waves in 1915 but until this week they had never been observed.
Gravity waves occur when the mass of two objects combine. The resulting entity has less mass and therefore “sits” on the fabric of space-time differently. The space-time fabric adjusts to the lesser mass and the adjustment ripples out from the new object through the fabric. The folds in the graphic represent those ripples.
LIGO’s detection mechanism is based on the fact that changes in the space-time fabric will affect the distance between objects. If those objects are mirrors then light will take longer to move between those two mirrors than it usually would.
Scientific America has a great description of LIGO’s process:
This observation is important for several reasons.
Firstly, gravity is one of what we believe to be the four fundamental forces at work in the universe. Up until now, the existence of gravitational waves has only been known in theory. It’s a little humbling to think something so basic and so important as this has just been observed for the first time. How primitive we are in some respects!
Secondly what happens when it becomes possible to experiment with gravitational waves? Can their energy be harnessed? We are a long way from being able to do anything like that.
Finally, its important to understand if gravitational waves can effect us negatively. Is a space tsunami possible?
As incredible as LIGO’s find is, LIGO’s detection method has a limitation. The gravity wave detected by LIGO was a high frequency wave meaning that its wavelengths were short. LIGO’s system doesn’t provide a wide enough net to capture lower energy longer wave lengths.
The only place to create a big enough net is in space and that’s the solution the European Space Agency has pursued. Whereas LIGO’s detection system was four kilometres long, ESA’s detection system will be one million kilometres long. Size matters.
ESA’s program is titled LISA (Laser Interferometer Space Antenna ) and will use lasers to measure changes in the distance between objects as they are effected by gravity waves. ESA’s test of this concept launched in December 2015 and will begin its work in March 2016.
Since gravity waves are energy they produce sound. Here’s a link to the sound of the wave LIGO captured:
Here’s a link to a great explanation of gravity waves by Janna Levin, Professor of Astronomy and Physics at Columbia University.