Whats the big deal about gravitational waves?

I recently went to really nice talk by Daniel Holz who explained at a very high level what gravitational waves are, how they are created and how they were observed with the complex LIGO interference setup. Here are the key things that I learnt. Note that some of these may not be accurate since these are just a reproduction of the notes I took during the lecture.

  1. We still don’t know why gravity pulls
  2. Gravitation wave affect time and space. They stretch and compress matter. Higher mass sees higher effect.
  3. They are created by events such as black holes colliding in each other, big bang or a neutron star crashing into a black hole. We are surrounded by these waves all the time. Why would these events occur? For example: 2 black holes rotating around each other will to loose energy (these lost energy waves are gravitation waves) over time and start coming closer. As they rotate around each other tighter they go faster and emit even more waves (observed as higher amplitude in the data below). Finally they come so close that they collapse in each other.
  4. Gravitation waves can loose energy. And this is a big deal!! Einstein predicted this 100 years ago but technology caught up to show this only now.
  5. To detect such a wave one would need to measure a change in distance between two or more free floating objects. A loud wave would only change the distance between earth and its nearest star (Alpha centurion) by the distance of one hair! The experiment to detect this is thus very sophisticated.
  6. LIGO is the most sophisticated experiment ever constructed by mankind. It is two fancy Michelson interferometers. It is sensing the change in distance of 1/1000 of a proton over a distance over 4km. Below is some of the slides from the talk.

Fig1: (Right) The small amplitude rise (1/100th of a second, strain ~ 10^-21) was the detected occurrence of the black hole collision. (Left) The various curves shows how the data collection quality improved over time.

Below is a brief introduction video.


I also found a more technical explanation of the LIGO experiment by PhD comics.




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