A gravity well also distorts lengths, as best I understand (which is not very well, to be honest; take everything I&#x27;m saying here with a big grain of salt).<p>The difference in terms of detection is that the wave does this in a time-varying, periodic fashion.<p>For something like LIGO, we&#x27;re trying to measure length changes on the order of 1e-18 meters.  We&#x27;re not actually measuring the lengths of LIGO&#x27;s arms to that accuracy, though.  What we&#x27;re measuring is the difference between the times light takes to travel down those arms.  And even that&#x27;s hard to measure on an absolute scale, so what we really measure is how that difference changes in time.<p>Or put another way, the effect of Earth&#x27;s gravitational well is not really distinguishable from inaccuracies in making the two legs of the interferometer equal length to start with, and is a much smaller effect than those inaccuracies.  Again, if I understand this right...