I can point out some instrumentation problems we had to overcome, but I won't do it justice. Each of these has had people dedicating their entire careers to solving them: * Laser stabilisation: a lot of work has gone in to calming down our lasers. Although lasers are monochromatic, the exact wavelength they produce will slightly fluctuate over time given external factors such as heat. Even though these fluctuations are slight, they are enough to "look like" a gravitational wave on our interferometer so we need to deal with them using special techniques and equipment. * Thermal noise: every atom in every bit of equipment in the interferometer is jiggling due to thermal excitation. This is a major problem on the mirrors which we bounce the laser light off of - a thermal jiggle of the surface of the mirror leads to a phase change in the laser light which again looks like a gravitational wave. We've pioneered low-noise coatings to deal with this problem, but it's a problem that keeps coming back with every bigger and better interferometer we build or plan to build. * Seismic isolation: the Earth is always shaking, and this vibration can move our mirrors and make it seem like there was a gravitational wave when there actually wasn't. We've designed exquisite suspension systems to isolate the test masses from the effects of ground motion, but this is a complicated problem to fix and requires a whole host of technologies. * Control: the interferometer isn't just made up of two arms. There are laser "cavities" which contain high light power in many places in the interferometer - five within the main interferometer - and the position of the mirrors in these cavities need to be controlled within picometres of precision. In most cases, the only tool we have available to us to sense the position of these mirrors is the laser light, and extracting information about the motion of individual mirrors from a beam of light is a complicated task that requires careful modelling. [SL, interferometry PhD student, Glasgow]