Thursday, February 11, 2016

Hearing a sound from a billion years ago!

Today is a day for cheering. After many years gravitational waves have been finally reported to have been detected. In two separate detectors, in west and east coasts of the US, almost simultaneously it was detected that earth got shrunk a tiny bit from a gravitational curving pulse. Many researchers have been sweating for decades to make these detectors happen.

Let me explain what has been discovered. An early approval for the theory of general relativity in 60's was based on the following fact: the presence of a heavy object, like our sun, will causes its surrounding spacetime to be curved. This has been observed from the following experiment: the straight path on which light travels in the universe from A to B, if passes adjacent to a heavy object, will bend a bit toward the object, thus the path will not remain a straight path anymore.

Now, consider two heavy objects crazily rotate around one another with a crazy speed (a half of speed of light). Right before they merge they make a lot of ups and downs in the spacetime in between. This turbulence in the very spacetime fibres propagate to others places, similar to how tsunami waves propagate in the ocean. In other words, gravitational field is self-interacting; this means that it sources itself. It curves the space around itself because it carries mass/energy by itself much like a star does.

If the objects are many light years away, the waves passing through the Earth today makes a bit of stretches and squeezes in the radius of earth, something of the size of less than the radius of proton! This has been detected last year at LIGO detectors and today was reported, and peer reviewed already in the PRL.

From what they received we assume that the waves came from two 30-solar-mass black holes curling up around one another in a death spiral, a billion light-years away from us. This is a better-than-expected source for LIGO and sometimes the universe is nice to us!  In fact a billion years ago two heavy stars fell in love with one another and played hand in hand like kids, and today we got a bit of their happy sound!  Doing such an amazing science is similar walking a tightrope between surly curmudgeon and starry-eyed cheerleader. 
The last thing to notice: If you are sad you do not get cited more often, apparently Einstein’s prediction of gravitational waves has been cited only a few times!

By: Mohammad H. Ansari

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