Quora Question: How did LIGO validate the signal they detected?

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Answer from Peter Graham, Stanford Physics Professor and Gravitational Wave Researcher:

This is a very important question, and also very complicated. In fact, for the real answer I recommend reading the papers that LIGO put out. Here I can just give some of the basic ideas of how it is done. When looking for such a small signal, it is absolutely crucial not to fool yourself because there is always a lot of noise in such a precise measurement. The LIGO collaboration worked very hard for a long time to make sure that they could claim a detection with confidence when it occurred. There are many possible problems with making such a detection and so LIGO applies many different strategies for dealing with these problems. A few of these are as follows. First they built two detectors, one in Washington and one in Louisiana, and required that both detectors see the same signal at (almost) exactly the same time. This greatly cuts down on the chance that the signal is just coming from random noise. There are very few things besides a gravitational wave that are going to hit both detectors at basically the same time with the same signal. They also work very hard to make sure that each detector has as little noise as possible, and that the level of the noise is well understood. For example, the earth vibrates all the time at a small level and this is a noise source for LIGO so they use impressive mechanical systems, a bit like shock absorbers, to keep their mirrors from feeling these vibrations as much as possible. Even the best laser is not perfect, and will have some noise in it. So they build two baselines in each detector to allow them to subtract off the laser noise that will be comment to both baselines. This is just a small fraction of the number of different noise sources they have considered, calculated carefully, and worked hard to understand and reduce as much as possible. They also use blind analysis techniques to help them make sure that they are not fooling themselves and are estimating their uncertainties correctly. And they spend a long time understanding their detector and the noise in it after they turn it on.

The real answer is much longer than this, and is also crucial for truly being certain that gravitational waves were detected and not just noise. The LIGO collaboration has done a very impressive job on a very difficult measurement. It is their impressive work that has most physicists convinced that we have in fact detected gravitational waves. It is truly an amazing experiment.

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