By Jesse Velay-Vitow
On the 11th of February, the Laser Interferometry Gravitational-Wave Observatory (LIGO) released confirmation that they had direct detection of gravitational waves. What followed was a lot of phycisists cheering excitedly and many people knowing that something important had obviously happened, but not quite sure about its relevance. Hopefully this blog post will shed some light on why everyone should be excited about this.
First, a bit of history. Back in 1915 a guy named Albert Einstein (you may have heard of him) published his work on General Relativity (GR), which simply put, is a correction to the Newtonian theory of gravitational attraction. GR explains how spacetime influences how objects move. This theory led to a number of predictions, one of which was that the closer you are to a heavy object, the slower time would move. This has been proven numerous times, and in fact, the GPS in your phone wouldn’t work without the satellites making corrections based on GR. GR also predicted that light should bend around heavy objects (this too has been observed). Observing gravitational waves is so exciting, because they were one of the last predictions of GR yet to be observed.
So what are gravitational waves? Ripples in spacetime itself. Trippy, I know. LIGO detected them by setting up a big L shaped laser beam. One beam travels in one direction, and the other beam travels in a direction 90 degrees to the direction of the first beam. Both beams bounce off a very reflective mirror and return to the origin. When a gravitational wave of sufficient size passes through the laser beams it causes an observable lag, and then pulse. These waves were not detected sooner, because our instruments have not been sensitive enough, and the gravitational waves not large enough. The problem being that large gravitaitonal waves are very rare, so they aren’t likely to occur close to us. And as the universe is expanding, if the source of the waves is distant, by the time they arrive they will have been stretched out to the point that they are too small to observe.
I promised you reasons for why you should care, and I promise I will deliver. First and foremost, it’s satisfying to have observational proof of a process we were pretty sure was happening. We’ve observed the orbits of stars decaying, and as energy is conserved, there must be some mechanism for it to leave the system. Gravitational waves are this mechanism. Secondly, it’s a bench mark of how far we’ve come, we’re able to detect the “sound” of two black holes colliding 1.3 billion light years from earth. That’s crazy, so crazy I don’t really have an apt metaphor to make it more relatable. Finally, you should care because it’s interesting, and the more excitement and press there is around scientific achievements like this, the more people will become interested. You never know where the next revolutionary answer will come from, but it will never come from someone who doesn’t know the question even exists.
When Jesse isn’t busy trying to finish up his never-ending degree in Mathematical Physics, he’s helping run the Science Undergraduate Society (into the ground). In his free time, he likes to drink beer, play music and argue with people about politics.