Gravitational waves are big.
I mean that in two different ways. Over the past week, they have gone from an obscure prediction resulting from the mathematics underlying the General Theory of Relativity to front page news. It is a rare day when obscure physics can knock Donald Trump from the headlines but last week's announcement sure did.
Everyone wants to know just what gravity waves are and why we should care. They are big news.
They are also big in the sense of being a very large phenomena created by an even larger event. The "explosion" which generated the waves detected at LIGO produced more than 50 times as much power as all of the stars in the known universe put together.
It was a massive rip in spacetime.
It echoed across the intervening space as if a massive bell had been rung. We are only catches the faintest of sounds because we are so far away.
Of course, it isn't really a sound that the astronomers were able to measure. Rather, it was a stretching and contraction of
spacetime which resulted in a distortion within an interferometer.
The device being used is actually very simple in design.
Interferometers depend on the principle of constructive and destructive interference in waves. If two waves are in synchronization with the same wavelength, then their peaks will occur at exactly the same time and place. The result will be reinforcement and the wave will be larger.
If, on the other hand, the two waves are not in perfect synchronization, then the peak of one will occur in the trough of another and the result will be cancellation. We can see this effect by simply holding up a CD (if you still have one) where the interference pattern results in the appearance of the rainbow of colors in the visible spectrum.
The idea behind the Advanced Laser Interferometer Gravitational-Wave Observatory (or LIGO for short) is to allow two laser beams to interfere with one another by reflecting light off of mirrors and recombining them to get an interference pattern. The trick with LIGO, though, is the laser beams are fired down two perfectly straight four-kilometre-long vacuum tubes oriented at a perfect 90 degrees before being reflected.
In essence, the instrument allows scientists to detect changes in the length of the two four-kilometre arms of the interferometer to within nanometers. And since a gravity wave alters spacetime, the distortions they cause show up as a change in the length and time for each arm separately.
The resulting distortion in the interference pattern is what the scientists were able to observe.
One might think that having two four-kilometre tubes waiting for a tiny vibration might lead to all sorts of false positive readings. After all, a hummingbird landing on one of the tubes would show up as a massive ripple at the level LIGO operates. That is why there are two of the devices. Both must receive the same signal at the same time, allowing for the time it takes the gravitational wave to travel between the two sites.
This is exactly what was observed. The same signal observed at the same time from two devices thousands of miles or seven millilightseconds apart is not an artifact. It is the real thing.
The result was obtained last September and the team in charge of LIGO has been all over the equipment checking to make sure it is real. Their conclusion was released on Feb. 11 with the announcement they had observed gravitational waves.
What does this all mean? Why spend billions of dollars searching for such obscure phenomena?
In part the answer should be inherent scientific curiosity. But mostly the search for gravitational waves has been driven by Einstein's General Theory of Relativity. Yes, the math predicted the presence of gravitational waves but for over a hundred years, physicists have asked "Where are they?"
The answer is they have been there all along. We just haven't had a sensitive enough method to detect them. Now that we do, there are any number of questions which might be answered. For example, gravitational waves will allow astronomers to better refine their models for the development and growth of black holes. We might even see the death of a black hole one day.
Indeed, gravitational waves might allow us to finally understand the big bang that started it all in the first place. They might also allow physicists to finally generate a Theory of Everything, uniting quantum mechanics and particle physics with gravitational attraction and interstellar space.
Who knows? Maybe a better understanding of gravitational waves will ultimately refine our understanding of gravity itself to the point where we can finally control it.
Maybe one day we might surf gravitational waves and travel amongst the stars themselves.
