Gravity: Making waves

Just like last week, there was a momentous press conference that began with these words: 'Ladies and gentlemen - we have discovered gravitational waves. We did it!' - Einstein has been proved right - again. Exactly 100 years ago, he predicted the existence of gravitational waves through his Theory of General Relativity.

Having found success with concepts such as spacetime and black holes, most scientists suspected that gravitational waves too could exist. Einstein predicted that it is possible for anything with mass to ripple spacetime - in other words, expand and relax like a speedboat's wake as it accelerates across a lake. He called these ripples 'gravitational waves'. This was the last prediction of Einstein that had not been proved until now, although theories that colliding black holes would generate gravitational waves were first written in the 1970s.

The concept of gravity itself was defined by Isaac Newton who apparently got inspired to develop that now-famous theory (or rather legend) after seeing an apple fall to the ground in his garden. Gravity holds everything together in space and here on Earth. Gravity is what keeps the Earth and the Moon apart, for instance. Now, scientists have detected gravitational waves for the first time, 100 years after Einstein predicted them in his seminal work.

Discovery

This a groundbreaking discovery that has many implications for a range of subjects from astronomy to future space travel. This is perhaps one of the most significant scientific discoveries in the past 10 years, along with the discovery of the so-called God Particle some time back.

The first direct detection of gravitational waves by the two Advanced LIGO (Laser Interferometer Gravitational Wave Observatory) interferometers in the US, from the merger of two massive black holes more than a billion light years from Earth, has been a global media phenomenon, with blanket coverage on newspaper front pages, news bulletins and websites worldwide. The discovery was the result of a US$ 1 billion, 34-year worldwide collaboration featuring 1,000 scientists in hundreds of laboratories and institutions based in 15 countries, which proves that worldwide collaboration is essential for high-end science research. According to scientists, LIGO's level of sensitivity is "like being able to tell that a stick 1,000,000,000,000,000,000,000 meters long has shrunk by 5mm." To put it another way, detecting a gravitational wave is like noticing the Milky Way - which is about 100,000 light-years wide - has stretched or shrunk by the width of a pencil eraser.

Faint

The discovery is even more significant because gravitational waves are very hard to detect as they are incredibly faint. They move the Earth by less than the width of an atom's nucleus. But you can "hear" them if you have the right equipment and data. "We can hear these gravitational waves, we can hear the universe," LIGO spokesperson Gabriela Gonzalez said during the press conference announcing their discovery.

Here's how they officially explained it: "As the two black holes rotate around each other, their orbital distances decrease and their speeds increase, much like a spinning figure skater who draws his or her arms in close to their body. This causes the frequency of the gravitational waves to increase until the moment of coalescence. The sound these gravitational waves would produce is a chirp sound (much like when increasing the pitch rapidly on a slide whistle) since the binary system's orbital frequency is increasing (any increase in frequency corresponds to an increase in pitch)." While that explanation sounds complex, what is important is that a great Nobel-worthy discovery has been made.

With his new discovery, we finally have an opportunity to see how the universe works. We have not even properly scratched the surface of the universe and our knowledge - even about our own Solar System and galaxy - is still rudimentary. Black holes, literally at the very centre of this discovery, are very mysterious in themselves. They are a favourite of science fiction authors who sometimes use them as "worm holes" - portals that can transport space travellers to the other side of the universe without the conventional trappings of slower-than-light space travel. (Incidentally, there have been many movies that explored this concept brilliantly - most recently Christopher Nolan's Interstellar).

Supernovas

Gravitational waves could help us understand more about black holes. Another application of gravitational waves is to reveal supernovas - huge, exploding stars that seed the universe with elements like carbon, nitrogen, and oxygen as well as platinum and gold - hours before they are visible to any telescope. ("Hours" is used strictly in a relative sense here - these events could take millions of years).

Gravitational waves will also allow astronomers to get close to celestial events that are simply inaccessible in another way because they can pass through any intervening matter without being scattered significantly. Whereas light from distant stars may be blocked out by interstellar dust, gravitational waves will pass through unimpeded. Gravitational waves can apparently also reveal what is going on inside a dying star. Death comes to every star - even our Sun will meet this fate five billion years from now. The good news is that space-based equipment on the lines of the Hubble Space Telescope is being developed to detect gravitational waves. These will be much more sensitive than ground-based interferometers prone to various disturbances.

There are those who criticise the allocation of vast resources for astronomy and space exploration, in this case US$ 1 billion. True, many things could have been done on Earth with that kind of money such as providing drinking water to much of Africa. But the study of astronomy and space is a long term project ultimately aimed at Man's survival beyond the confines of Home Planet Earth. The Earth has a limited lifespan - around five billion more years - but at the rate Man is altering the planet, Earth's actual habitable lifespan may be much less. Hence the need to venture beyond Earth step by step from now onwards, using robotic probes and space telescopes etc. Research on seemingly esoteric subjects such as gravitational waves could boost that drive to warp speed.