As you’ve probably seen, everyone has been going gaga on your Facebook feed about this new scientific discovery of ‘gravitational waves’, discussing what it is and its implications on future research in astronomy etc. You’re embarrassed to admit it, but you simply have no clue what’s so special about this discovery that has everybody talking (even the most reticent people on your friends list). Poor you!
So, without further adieu, let’s equip you with all the knowledge you need to understand gravitational waves comprehensively and impressively!
First of all, the idea of gravitational waves originates from Einstein, the same man of “Energy Mass Equivalence” fame, who is also associated with two-thirds of the quotes on the Internet. The guy became famous in the first half of the 20th century when he destroyed the established foundation of physics by saying that the speed of light is the universal constant, not time or space, which provided the world with his famous E = mc2 formula.
The basic idea was that space and time bend around an object with mass, and when heavy objects move really fast through space, they create ripples in it. This is something like the waves generated in water. If you’re wondering how waves can exist in space, considering that space is empty and waves need a medium to propagate, then unfortunately, you are incorrect on both counts and need some basic lessons in both quantum physics and astrophysics. You can catch up on the quantum level here, while I take the lead on the “medium to propagate” end.
The medium here is the entirety of space itself; to better understand this idea, imagine the distance between two points on a paper graph. Then, start pushing the paper inwards from the edges which will create a fold; then, imagine pulling back at the edges, which will flatten it back out. When you fold the paper, the imaginary single line that passes through the points will become shorter, as it would go straight through the paper, rather than folding with it.
If these expansions and contractions of space are generated by huge objects, are these movements huge too?
No! They’re actually really tiny. So tiny, in fact, that the instruments used to detect these waves were made sensitive enough to measure a change smaller than one-ten-thousandth of the diameter of a proton (10-19 meter).
Scientists at the Laser interferometer Gravitational-Wave Observatory (LIGO) faculty have something called an interferometer, which is basically a combination of lasers, some mirrors, and a detector. These are arranged so that the beam emitted from the laser is split in two at a 90o degree angle. Each beam then moves in its own separate tunnel and is reflected back from mirrors at the end. The returning waves are recombined to analyze the changes.
If there is no change or no gravitational waves passing through, then the waves cancel each other out. However, if there is a gravitational wave passing through, then the moment the two waves hit each other will be different than normal, and the alignment of the recombined beams will create a different realignment pattern.
For some idea of scale, the distance between the beam-splitting mirror and the reflective mirror is 4 km and the entire chamber is a high vacuum for noise reduction. There are two such functional laboratories, another under construction, and a proposed fourth. The first two are located in the United States – one in Louisiana and the other in Washington. The third lab is under construction in Europe – a collaboration between France and Italy – and the final lab is proposed for construction in India. The reason there are multiple labs is because they are used in combination to triangulate the source of the wave and verify each other’s findings for false positives.
So, what huge object caused these ripples in space? Well, according to the director of LIGO, the waves were produced by the merging of two black holes into a single one. The larger of the two was about 36 times the mass of our sun, and the other was 29 times as massive. Here’s something to help you get a better perspective of that scale. This event occurred about 1.3 billion years ago, but since the waves travel at the speed of light, they were detected on Earth as they passed the planet on September 14, 2015 at 5:51 a.m. They were detected within a 20-millisecond data recording. The delay between the detection of the waves at the two labs was about 7 milliseconds. This implied that the source was in the direction of the southern hemisphere of the planet.
The other questions that follow include why are these gravitational waves relevant? Why should you care about them? The simple answer is that these gravitational waves can tell us a lot more about our universe than we knew. Before this discovery, the only tools to see into the depths of the universe were radio and electromagnetic waves. To put this in perspective, it’s like upgrading from telegrams (less information constrained by distance) to mobile phones (huge data over huge distances). This new method can tell us about the mass of the objects and the speed of their movements, along with information about those things that do not emit any electromagnetic radiation, such as the mysterious “dark matter”. The best part is that these signals can be converted to sound waves. Essentially, it’s like hearing the universe talk back from the other end of the line. Here’s a recording of our first-ever conversation.