Since gravitational waves are the stretching of spacetime itself, they have the interesting property that the measured displacement between two reference objects scales with the original separation between those objects. In other words, if there is more spacetime to stretch, the total stretch is larger. LISA’s arms are roughly a million times longer than LIGO’s, which means that a gravitational wave of the same amplitude will produce displacements that are roughly a million times larger in LISA. The total displacement is still small, on the order of picometers (one picometer = one trillionth of a meter) but is well within the range of modern metrology techniques. From the metrology perspective, the LISA measurement challenge is “easier” than that of LIGO, which is important given that it has to be robust enough for spaceflight as well as be able to be operated from far away.