In 1916 Albert Einstein predicted the existence of a peculiar phenomenon called gravitational waves. Now 100 years later, the LIGO Scientific Collaboration (LSC) involving over a thousand physicists from all over the world (including the University of Sheffield), has finally detected and verified the very last of Einstein’s unconfirmed theories – the existence of gravitational waves.
(An artist's depiction of the destruction of binary star system J0806 generating gravitational waves as they lose energy. Photo: DANA BERRY/NASA)
There is a huge level of excitement and publicity surrounding this discovery, but what exactly makes it so “huge” and significant? To fully appreciate the great hype behind this finding, let us first understand what gravitational waves actually are.
According to Einstein, gravitational waves are “ripples” in the fabric of space and time, which can be imagined as actual “stretching” and “squeezing” of spacetime itself. (See this Piled Higher and Deeper comic strip for a slightly more detailed description of gravitational waves).
Logically, to prove that gravitational waves do in fact exist, one must first detect them, but from where, and how? According to Einstein’s General Theory of Relativity, any object associated with mass that moves through spacetime will “stretch” and “squeeze” spacetime and consequently form gravitational waves.
Hence the whole team of LSC cast their minds both into building an advanced twin detector, called the Laser Interferometer Gravitational-Wave Observatory (LIGO), and the densest objects in the Universe, black holes.
The two gravitational-wave observatories have a distinctive L-shape that involves two 2.5 mile (around four km) long “arms”. At the end of each tunnel lie gravitational-potential sensitive mirrors, which means that those mirrors can oscillate by incredibly miniscule, yet detectable distances (less than a thousandth the size of a single proton) in the presence of the “ripples” in spacetime.
Very fortunately, just as both LIGOs were still working in the test-mode on September 14th 2015, both observatories simultaneously detected the aftermath of GW150914 – the cataclysmic collision of two black holes 13 billion light-years away that was powerful enough to create “ripples” in the fabric of spacetime itself.
It took scientists five months to analyse the incredibly tiny movements of LIGO mirrors to examine the credibility of their results.
But how will this discovery impact the advancement of science and our understanding of the Universe?
If you are going to learn anything from this article, then it should be the appreciation towards the fact that discovering gravitational waves is a fundamentally new astronomical breakthrough. We are not talking about the detection of electromagnetic waves such as light; we are talking about a whole new and alternative way of extracting more information about the cosmic events within the observable Universe.
Dr Ed Daw from the department of Physics and Astronomy at University of Sheffield, one of the over 1000 researchers who have contributed towards LSC’s gravitational wave discovery, tells that “gravitational waves are so completely different from light, we’re probably only just beginning to understand how they reflect and shape our universe”. (Click here for Dr Ed Daw’s more detailed explanation of the gravitational wave discovery).
As for the actual implications, the most obvious ones apparently include the potential to advance the study of interiors of black holes, galactic collisions and even dark matter. It is also important to note that LIGO is not the only project focused on gravity research; ESA’s aspiring eLISA is one example of such alternative projects; it involves a three-satellite system that has the potential to detect and understand other types of gravitational waves.
In the end, I could not agree more wholeheartedly with Professor Sir Keith Burnett’s (the Vice-Chancellor of the University of Sheffield) response to the contributions and efforts laid into this major discovery; “the courage to work for many decades, with such profound technical challenges, guided only by Einstein's theory, deserves the greatest of scientific accolades.”