A common question relating to the LIGO story by Barry Evans (Field Notes, Oct. 26) is "how can light beams detect gravity waves when light and matter are equally stretched and shrunk by passing gravity waves?"
The answer lies in the constancy of the speed of light, so that a stretched light wave has a lower frequency. The two light beams no longer cancel each other after traveling different lengths at the same speed (even though the lengths differ by way less than the diameter of a proton!). I urge Barry to follow his story with LIGO's fantastic detection of merging neutron stars.
Don Garlick, Fieldbrook