The gravitational waves theory is a hypothesis that is a hundred years in the making. A couple of weeks ago, some scientists observed the warping of space-time generated by the collision of two black holes more than a billion light-years from Earth. The international team says the first detection of these gravitational waves will usher in a new era for astronomy. It is the culmination of decades of searching and could ultimately offer a window on the Big Bang.
According to Einstein’s theory of General Relativity, any accelerating mass should produce a ripple in the fabric of space time. However these effects are very weak. But if the mass is big enough and is moving at a high enough speed they are expected to wrap their surroundings to any appreciable degree. All these events should radiate gravity at the speed of light,
When gravitational waves pass through the Earth, the time and space it occupies should alternately stretch and squeeze. Think of a pair of stockings, not when you stretch them they elongate and become narrower. Scientists at the LIGO laboratory have been searching for this stretching and squeezing for a long time gradually improving the sensitivity of their equipment. All it had to do was detect disturbances the bigger than the width of a proton.
The idea is to split high-powered laser beams and send separate light paths through long vacuum tunnels arranged in an L shaped manner. There are mirrors placed inside so that these beams bounce back and forth and return to it’s original point. Now, the beam is reconstructed and sent through some detectors. If by any chance the gravitational waves did pass though the labs, the path of light will be slightly offset, this will be evident in the data analysis. This method is commonly known as Laser Interferometry.
Consider for the moments the black hole part of the story. The discovery of black holes made by humans is actually very indirect. We already know that black holes have such a strong gravitational pull that even light cannot escape it. They also don’t shine on out telescopes, but we know them to be out there as we can detect the light coming from the objects as it is bring torn apart because of the acceleration. Gravitational waves, on the other hand, are a signal that comes right from these objects themselves and carries information about them. In this sense, you can argue that we have just made the first direct detection of black holes as well.
As ever, the debate will be about the recipients and their place in the chain of discovery. Who will be regarded as having made the most significant contribution? Will the recipients be theorists or experimentalists in that chain? One thing is clear: it is in the nature of science today that the really big questions tend to be answered with the aid of really big machines. And without the LIGO Collaboration’s many hundreds of participants, who work across diverse fields on a range of complex technologies, this moment would never have come.