It's not your average confession show: a panel of leading physicists spilling the beans about what keeps them tossing and turning in the wee hours.
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.
Why this universe?
In their pursuit of nature's fundamental laws, physicists have essentially been working under a long standing paradigm: demonstrating why the universe must be as we see it. But if other laws can be thought of, why can't the universes they describe exist in some other place? "Maybe we'll find there's no other alternative to the universe we know," says Sean Carroll of Caltech. "But I suspect that's not right." Carroll finds it easy to imagine that nature allows for different kinds of universes with different laws. "So in our universe, the question becomes why these laws and not some other laws?"
What is everything made of?
It's now clear that ordinary matter – atoms, stars and galaxies – accounts for a paltry 4 per cent of the universe's total energy budget. It's the other 96 per cent that keeps University of Michigan physicist Katherine Freese engaged. Freese is excited that one part of the problem, the nature of dark matter, may be nearing resolution. She points to new data from experiments like NASA's Fermi satellite that are consistent with the notion that dark matter particles in our own galaxy are annihilating with one another at a measurable rate, which in turn could reveal their properties. But the discovery of dark energy, which appears to be speeding up the expansion of the universe, has created a vast new set of puzzles for which there are no immediate answers in sight. This includes the nature of the dark energy itself and the question of why it has a value that is so extraordinarily small, allowing for the formation of galaxies, stars and the emergence of life.
How does complexity happen?
From the unpredictable behaviour of financial markets to the rise of life from inert matter, Leo Kadananoff, physicist and applied mathematician at the University of Chicago, finds the most engaging questions deal with the rise of complex systems. Kadanoff worries that particle physicists and cosmologists are missing an important trick if they only focus on the very small and the very large. "We still don't know how ordinary window glass works and keeps it shape," says Kadanoff. "The investigation of familiar things is just as important in the search for understanding." Life itself, he says, will only be truly understood by decoding how simple constituents with simple interactions can lead to complex phenomena.
Will string theory ever be proved correct?
Cambridge physicist David Tong is passionate about the mathematical beauty of string theory – the idea that the fundamental particles we observe are not point-like dots, but rather tiny strings. But he admits it once brought him to a philosophical crisis when he realised he might live his entire life not knowing whether it actually constitutes a description of all reality. Even experiments such as the Large Hadron Collider and the Planck satellite, while well positioned to reveal new physics, are unlikely to say anything definitive about strings. Tong finds solace in knowing that the methods of string theory can be brought to bear on less fundamental problems, such as the behaviour of quarks and exotic metals. "It is a useful theory," he says, "so I'm trying to concentrate on that."
For the rest go to New Scientist