This question already has an answer here:
A friend and I were having a discussion about the LIGO experiments and were wondering if there is any issue with the laser light undergoing a wavelength shift as a result of the gravitational wave? Akin to the red/blue shift we see in the galactic sense but on a much smaller level.
Wouldn't this make it "impossible" to measure the length contraction since the "ruler" itself contracts within the space also?
Feel free to go into detail, but we are just looking for a simple explanation.