Ligo works by destructively interfering light from a laser using an interferometer. Its said that no light enters the photo detector when all mirrors are the same distance. However,based on my research,the light would just create an interference pattern and never completely destructively interfere. How exactly does ligo do this? Can I get it done on a smaller scale?

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    $\begingroup$ Yes, it creates an interference pattern with a null on the detector. $\endgroup$
    – Jon Custer
    Oct 15, 2023 at 15:48
  • $\begingroup$ what research ? $\endgroup$ Oct 15, 2023 at 15:53
  • $\begingroup$ @ZeroTheHero research as in researching the topic through reading. Not actual scientific research. $\endgroup$ Oct 15, 2023 at 18:14
  • $\begingroup$ what readings? It would be much easier to have the source. $\endgroup$ Oct 15, 2023 at 18:18
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    $\begingroup$ A Michaelson interferometer with equal arms can be set up so that the beam splitter sends all the light out of one port and none out of the other. Nothing mysterious in that. $\endgroup$
    – mike stone
    Oct 15, 2023 at 18:31

1 Answer 1


I suspect you have read a simplified explanation of LIGO. The LIGO detector works by looking at one single point in the interference pattern between the two beams. The beam optics are actively adjusted to minimise the intensity of light at this point - I imagine it is not possible to achieve zero intensity (which would require an infinitely long measuring time anyway) but they get as close as they can. Any change in light intensity at that point - or, equivalently, any change in the adjustment required to minimise light intensity - indicates a change in the beam length in one or both arms. Much of the engineering complexity of LIGO and similar detectors lies in reducing the level of noise in the apparatus to the point where gravitational waves are detectable.

  • $\begingroup$ I think the instrument is deliberately adjusted to be just off the null point. I would also be surprised if laser light was wasted by only measuring the intensity at a point in a Michelson-like interference pattern. Isn't the measured signal collected from the entire beam width? $\endgroup$
    – ProfRob
    Oct 16, 2023 at 6:37

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