On this day in physics: 11 February 2016- New York Times publishes an article reporting that LIGO (Laser Interferometer Gravitational-Wave Observatory) has confirmed gravitational waves from the collision of two black holes, confirming the last of Einstein's predictions of General Relativity. [Source]
Word of the Day: Gravitational Waves are a prediction made by Einstein's General Theory of Relativity which were heretofore unobserved before last September. As we've talked about in a previous word of the day, Any mass causes a gravitational warping of the fabric of spacetime, letting the rest of the universe "know" how to move. Now this is where things get interesting. In physics, generally when we visualize the universe, everything is stationary. But that's not usually the case. The universe is a dynamic and changing place. So when you have something with a phenomenal amount of gravity, like a neutron star or black hole, which is MOVING, how does this warping in spacetime, the information of the gravity of this object, transmit to the rest of the universe? The answer is that this information ripples through spacetime at the speed of light. So, if we have two orbiting massive objects, say two orbiting neutron stars, even light years away, their gravity affects our spacetime fabric, and their motion will in a very small way, slightly change our spacetime, which should measurably change when massive objects drastically change.
Enter LIGO, a facility built to measure these changes. It is in the shape of an L, so it can check for waves in two dimensions, and each arm of the L is a long tunnel (like 2.5 miles long) which is created to be a vacuum, i.e. no air whatsoever. The purpose of the observatory is to measure the distance of each of these tunnels with extreme precision. As an example, gravity waves from neutron stars millions of light years away would change the length of something like LIGO less than one thousandth the diameter of a proton. This is the type of fluctuations the scientists are LIGO are looking for. The hope was that Neutron Stars "close" to us, i.e. 10^26 light years (HUGE distance btw), would do something colossal that could be measured at LIGO. For ten years, they listened for fluctuations. Nothing. Whatsoever. How hard do you think it would be to secure funding for a 200 million dollar facility for 10 years with no reportable findings? Then something happened. Two black holes, spiraled together, forming an even bigger black hole, creating a predictable pattern of gravitational waves, which were observed by both arms at LIGO. The findings were announced on 11 February 2016.
The reason that this is such a big deal is that gravitational waves were not observable, not unlike the Higgs Boson. A major theory of physics, General Relativity, had one lingering facet which had yet to be observed. Without observation, we cannot say for sure that it is correct. So observing a gravitational wave is a monster boost for general relativity, and physics in general. Plus we were able to detect two black holes colliding into a bigger black hole. How cool is that.
Quote of the Day: "If you ask me whether there are gravitational waves or not, I must answer that I do not know. But it is a highly interesting problem." - Albert Einstein [Source]
Keywords: Gravitational Waves, Einstein, Relativity, Black Hole
