When viewing the light coming from distant galaxies, it is my understanding that there are 2 redshifts occurring, the doppler effect from the galaxies' peculiar motions, and the cosmological redshift from space itself expanding. For the cosmological redshift, I visualize a square of space, say 1 meter long, and a light wave sitting inside with a wavelength of 1 meter. When space stretches, lets say by a factor of 2, then the light wave sitting inside also gets stretched, and so now its wavelength is 2 meters long. I imagine space stretching and compressing due to gravitational waves is similar, and it is this stretching and compressing that will allow http://lisa.nasa.gov/" [Broken] to detect gravitational waves due to the changes in the wavelengths of the light waves hitting the LISA detectors, causing a change in the constructive/destructive interference. But lets say we have a square of space the same length as the distance between 2 of the LISA detectors/transmitters. If they are setup so the laser light is in perfect constructive interference, and a gravitational wave passes by, wont they stay in perfect constructive interference? The space will get stretched and then compressed, depending on the direction of the wave as I understand it, but so will the light waves sitting inside the space by the same factor, so there wouldn't be a change in the interference. The way I see it the detectors get moved say 1 meter farther from each other, but at the same time the wavelength of light gets stretched by 1 meter (if the distance between the detectors were 1 wavelength). So I'm obviously missing something. If I have 2 protons being held a certain distance apart so they are exerting a force of 1 newton on each other, and a gravitational wave passes through them in such a way that space compresses, do they move closer together, so I would then momentarily detect a force larger than 1 newton? Or do they somehow stay the same distance apart, even when the space between them is being compressed?