Earlier this year, the LIGO collaboration announced the first-ever detection of gravitational waves, ripples in space-time that were predicted by Einstein a century ago. The announcement was greeted with cheers, celebration and front-page headlines around the world.

Now they are getting ready for the sequel.

Although the Laser Interferometer Gravitational-Wave Observatory recently had a massive upgrade to become Advanced LIGO, the experiment isn’t running at full strength yet. The aim is for it to be able to measure changes in distance as small as 10-21 metres – one-ten-thousandth the width of a proton.

But there are several hurdles to overcome before it gets there, and researchers may be stymied by the fundamental laws of physics. At this week’s American Physical Society meeting in Salt Lake City, Utah, they met to discuss a plan of attack.

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