This article tries to explain: https://www.forbes.com/sites/startswithabang/2018/09/15/ask-ethan-if-light-contracts-and-expands-with-space-how-do-we-detect-gra

This article tries to explain: https://www.forbes.com/sites/startswithabang/2018/09/15/ask-ethan-if-light-contracts-and-expands-with-space-how-do-we-detect-gravitational-waves/ https://www.forbes.com/sites/startswithabang/2018/09/15/ask-... "Ask Ethan: If Light Contracts And Expands With Space, How Do We Detect Gravitational Waves?" It also links to the FAQ at LIGO: https://www.ligo.caltech.edu/page/faq https://www.ligo.caltech.edu/page/faq which for this question ends with: "This varying pattern of misaligned laser beams, observed and recorded over the time it takes for the gravitational wave to pass tells us two things: 1. How much the arms changed length during the light-beams' journeys and, 2. the frequency at which, or how quickly the arms changed lengths (longer then shorter then longer, etc.) in response to the gravitational wave. This information can tell us what generated the gravitational wave in the first place. In this scenario, the actual wavelengths of the beams of light have no bearing on the much more important interference pattern. The effects of the length changes in the arms far outweigh any change in the wavelength of the laser, so we can virtually ignore it altogether."