I understood that the basic idea of the interferometric detectors is the michelson interferometer experiment, in which the change in the position of the mirrors will cause the interferometer ( constructive or destructive)which causes the changin the detected wave's intensity.the question is how do the gravitational waves cause the change in the arm length? here is the sentence I can't understand
"Gravitational waves lead to rhythmic distortions of space. This distortion influences the time it takes a light signal to travel back and forth between two freely falling test masses. As the distance the light signal has to travel is stretched or squeezed, it takes the light a little more or a little less time to travel from one test mass to the other." from EISTEIN ONLINE site Catching the wave with light
I think the reason that I can't understand this because I can't imagine how these distortion in space take place and how does the distance is stretched or squeezed.I hope someone can help!