September 14th, 2015, two pieces of LIGO (not the toy, check the link) separated by 3000 km were able to measure the small deformations created by gravitational waves generated by the fusion of two black holes of around 30 solar masses each... 1300 million light years away from us. February 11th, 2016, the world took a pause to listen to the press conference that told us about the end of a 100 year long story, and the beginning of a new phase in astrophysics.
This story starts back in 1916, when Einstein published an equation that describes the Universe in a large scale. In his General Relativity, he imagined that space and time are so interlaced that it makes no sense to speak about them separately, that is why we use both words, and always talk about space-time. Space-time has 4 dimension: 3 of space and one of time. The most important (and probably craziest) part is that this space-time is not always flat. Object's mass deforms, bends it, and this deformation is precisely what we know as gravity force. That equation, also, predicted that a force known as gravitational waves should exist.
So, last September two absolutely independent detectors identified something that Einstein proposed 100 years ago. Out of pure imagination, pencil and paper. ONE HUNDRED YEARS AGO; 100.
Then, it turns out that there's phenomena in the Universe that also deform space-time just as the presence of objects with mass do, but in a way gravitational waves are created. Massive, extremely accelerated objects (like the merging of two black holes or two collapsing stars) change the curvature of this space-time and produce gravitational waves. The Big Bang itself should've generated gravitational waves before they were so trendy.
What is a Gravitational Wave?
As gravitational wave propagates, we can think of it as a concentric wave that shrinks and grows the spider web that conforms space-time while it travels at the speed of light, totally understandable until you start thinking about it. Space-time is not only deformed by what it contains, but also by the ingormation of what happens at a point takes a non-instant time to reach another point. Just as a CNN reporter that talks to the studio with a slight delay, even the Universe itself has to wait to know what is happening elsewhere, always under that absolute limit: the speed of light.
What did we do?
Because it is a bit hard to abstract a 4 dimension Universe, lets suppose for a moment that there's only 2, like a pond full of water. Gravitational waves in this example would be simple ripples (yes, consider "time" to be able to observe them: A 3rd dimension; but... meh, I rather simplify). All objects with mass (all, every one of them: A grain of rice, a building, your dog, Jupiter or a neutron star) somehow disturb this surface, deforming it. Yet, some event not only do this, they also generate waves that travel along the surface. Now, the wave depends on how much is our 2D surface is perturbed, to be able to measure them, we need large events that create large waves (or at least, measurable events; large, within our limits). Then, what do we look for in this surface?, something subtle? No: We seek a huge boulder. A humongous rock getting in there would generate a wave that could propagate to the furthest edges of the pond; or, at least, as far as that buoy we call Earth is at, us, with our little measuring devices. In this case, the boulder we were able to measure was two black holes, dancing in spiral, falling into each other until they merge.
How do we measure that?
In our daily lives, we're constantly surrounded by waves; sound (air wave) electromagnetic ones like light or radio, X rays and Gamma rays, among others. Gravitational waves are not electromagnetic, but they propagate at the speed of light as if they were.
The question is if we can "see" these waves. And the answer is no, as we cannot see IR light or radio waves; yet, we can detect them. When these violent events occur in the Universe, they make the net that conforms space vibrate like a drum. Space-time undulations spread in all directions, travelling at the speed of light and physically distorting everything in their path. But the further they go from their origin the smaller they become. They lose amplitude. An initial distortion in space measuring several kilometers is reduced to a proton size once it reaches Earth.
"WAITAMINUTE! Are you telling me that a gravitational wave will pass right over us, deforming our space and also us? Effectively, yet, the distortion is so small, we do not even perceive it.
Now, returning to what I mentioned at the beginning of the article, the detection. It is VERY important because it gives us a new sense to observe the Universe. Until before that we only observed what we could perceive with our eyes, this is, electromagnetic waves. Now, it's like we have hearing aids to complement. And observe the Universe in a whole new way.
We developed a sense that allows us to detect, locate and study systems and events that appear in our Universe. We're still changing diapers to the Gravitational Astronomy era, and this implies a lot of joy for people that love to obsessively discover a bit more of "how does the Universe work?".
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