Laser beams in a physics laboratoryCallum Fraser / Alamy Stock PhotoA new way to gauge distance using lasers can measure lengths of more than 100 kilometres to within a thousandth of the width of a human hair, and could be used to make better space telescopes.In lab-settings, scientists can use lasers to measure distances with extreme precision, to within a few nanometres. But for longer distances of a kilometre or more, the precision of these techniques tends to be much lower, to within around a millimetre.