My book on gravitational waves states that, in an interferometer like LIGO, the armlength of either arm shouldn't be bigger than the wavelength of a gravitational wave in order for the detector to pick up the signal.
I'm not sure on why the detector wouldn't be able to pick up the signal if the armlength would be bigger than $\lambda_{\mathrm{gw}}$. Could anyone provide an intuitive explanation?
