Just what are Einstein’s Gravitational Waves?

February 14 20:00 2016

As the world reacts to the massive discovery, India is readying itself to host the world’s third Laser Interferometer Gravitational Observatory (LIGO-India). By looking at the time of arrival of the signals-the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford-scientists can say that the source was located in the Southern Hemisphere.

“Four hundred years ago Galileo turned a telescope to the sky and opened the era of modern observatory astronomy”, said David Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatory (LIGO) laboratory at Caltech, southern California, where part of the experiment was based. In fact, two of the pioneers here are Prof. But global scientific collaborations made it possible in 2007 to bring together LIGO and VIRGO teams which agreed to share data.

One may be tempted to fancy that this discovery has suddenly elevated Einstein’s General Theory of Relativity (GTR) from the status of being a mere “electrostatic” effect to that of dynamic “electromagnetism” where the effect propagates like a wave with a finite speed (of light). This introduces tiny ripples in space-time, that is to say that the space (and all that is in it) is slightly distorted by the passage of these waves is elongated in one direction and compressed in another sense.

In February of 1916, Einstein predicted that if space and time could have lumps and bumps, then perhaps those bumps could move, said Kennefick.

This has to do with complex non-linear nature of GTR vis-a-vis simple linear nature of electromagnetism. So when a big object moves and accelerates, you have two objects, orbiting around one another, it’s creating these ripples that travel outward, and that’s what a gravitational wave is. One needs to make various tacit assumptions or simplifications. This week, however, we’ve come a long way in understanding gravity and its impact on the universe, and gained further appreciation for modern science and the incredible gifts of a legendary scientist. The surprising slowing down of the neutron star was attributed to gravitational radiation. Fans of the 2014 movie “Interstellar” know that gravitational anomalies and black holes were employed to enable exploration of the universe. The level of certainty in this result is given, in physics terms, as a 5.1 sigma event. This collision of two black holes had been predicted but never observed. But before Einstein could reject his gravitational waves in that journal, Robertson indirectly nudged him to change his mind back again. Only a black hole can pack so much mass into such a small space – making this the first time that black holes have been detected.

A gravitational wave generated by a different kind of event would produce a different “chirp”. These super faint stellar objects form after a star dies, just as some black holes do. The site of mass energy in a black hole is the central singularity.

By 1919, solar eclipses were sufficiently well-understood and documented that normal circumstances would not have warranted an expedition to such a far-flung place just to take a few pictures. Also during the “ring down” stage, can any energy come out of the trembling horizon of the dynamic black hole? They’re more like atom-sized distortions. Gravity as an idea, and even a name, predates Newton.

“Tianqin will likely collect more information about the phenomenon, as a larger black hole may be detected in space compared with one detected on the ground”, said Chen. Black holes, for example, do not emit light, radio waves and the like, but can be studied via gravitational waves. “Those should explode and leave behind black holes”.

Coalescence of two neutron stars are expected to generate not only bursts of gravitational waves but also bursts of gamma rays. The lasers could then indicate if a gravitational wave has altered the position of objects inside spacecraft. In contrast, the coalescence of true singular black holes need not give rise to strong electromagnetic counterparts.

Such questions apart, it’s a moment for celebration for astronomy and in particular for Einstein’s theory of general relativity which just completed its centennial. The views expressed are personal.

The original documents related to Albert Einstein's prediction of the existence of gravitational waves are are at Hebrew university in Jerusalem. AP

Just what are Einstein’s Gravitational Waves?
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