The .gif shows the basic principles of how the Laser Interferometer Gravitational-Wave Observatory ([LIGO](https://en.wikipedia.org/wiki/LIGO)) detected gravitational waves. In reality, the legs are 4km in length (as can be seen [here](http://www.ligo.org/science/GW-Overview/images/LLO.jpg)). The distortion by gravitational waves is massively exaggerated, as in reality, it is only 1/1000 of the diameter of a proton (which is also why gravitational waves were so difficult to detect).
The .gif shows the basic principles of how the Laser Interferometer Gravitational-Wave Observatory ([LIGO](https://en.wikipedia.org/wiki/LIGO)) detected gravitational waves. In reality, the legs are 4km in length (as can be seen [here](http://www.ligo.org/science/GW-Overview/images/LLO.jpg)). The distortion by gravitational waves is massively exaggerated, as in reality, it is only 1/1000 of the diameter of a proton (which is also why gravitational waves were so difficult to detect).
This is the source video: https://www.ligo.caltech.edu/system/video_items/files/21/Einsteins_messengers_hi_res_Nov_17_MPEG720p.mp4?1447873693.
Given that the change they’re measuring is tiny, how can they be sure it isn’t caused by some kind of minute physical shift of the equipment/ground?
[I made a different version with slightly more legible text](http://i.imgur.com/uGz7NBs.gifv)
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Isn’t this similar to the Michelson-Morley experimental set-up?