That was the scene a few days ago in front of a packed auditorium at the Perimeter Institute, in Waterloo, Canada, when a panel of physicists was asked to respond to a single question: "What keeps you awake at night?"
The discussion was part of "Quantum to Cosmos", a 10-day physics extravaganza, which ends on Sunday.
While most panelists professed to sleep very soundly, here are seven key conundrums that emerged during the session, which can be viewed here.
