Currently, the theories and projects physicists are working on are concepts that have always managed to elude humankind. What is reality? What is everything made of? In attempting to answer these questions, it has been suggested that physics may have reached the end of its usefulness and further knowledge will require an evolution in thought. Here are the 7 biggest questions facing physicists in the world:

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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 “”, 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 .

Why this universe?

In their pursuit of nature”s , 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 ? “Maybe we”ll find there”s no other alternative to the universe we know,” says 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 engaged. Freese is excited that one part of the problem, the nature of , may be nearing resolution. She points to new data from experiments like NASA”s 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 . But the discovery of , 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 of the dark energy itself and the question of , allowing for the formation of galaxies, stars and the emergence of life.

How does complexity happen?

From the unpredictable behaviour of to the rise of life from inert matter, , physicist and applied mathematician at the University of Chicago, finds the most engaging questions deal with the . 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 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 is passionate about the mathematical beauty of – the idea that the fundamental particles we observe are not point-like dots, but rather . 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 and the , while well positioned to reveal new physics, are unlikely to say anything definitive about strings. Tong finds solace in knowing that the methods of , such as the behaviour of quarks and exotic metals. “It is a useful theory,” he says, “so I”m trying to concentrate on that.”

What is the singularity?

For cosmologist and Perimeter Institute director , the biggest mystery is the one that started it all, the . Conventional theory points back to an infinitely hot and dense state at the beginning of the universe, where the known laws of physics break down. “We don”t know how to describe it,” says Turok. “How can anyone claim to have a theory of everything without that?” Turok is hopeful that string theory and a related development known as the “”, which shows that a singularity in three can be translated into a mathematically more manageable entity in two dimensions (which may imply that the third dimension and gravity itself are illusory). “These tools are giving us new ways of thinking about the problem, which are deeply satisfying in a mathematical sense,” he says.

What is reality really?

The material world may, at some level, lie beyond comprehension, but , professor of physics at the University of Vienna, is profoundly hopeful that physicists have merely scratched the surface of something . Zeilinger specialises in quantum experiments that demonstrate the apparent influence of observers in the shaping of reality. “Maybe the real breakthrough will come when we start to realise the connections between reality, knowledge and our actions,” he says. The concept is mind-bending, but it is well established in practice. Zeilinger and others have shown that , so that observing one affects the outcome of the other. No one has yet fathomed how the universe seems to know when it is being watched.

How far can physics take us?

Perhaps the biggest question of all is whether the process of inquiry that has revealed so much about the universe since the time of Galileo and Kepler is nearing the end of the line. “I worry whether we”ve come to the limits of empirical science,” says of Arizona State University. Specifically, Krauss wonders if it will require knowledge of other universes, such as those posed by Carroll, to understand why our universe is the way it is. If such knowledge is impossible to access, it may spell the end for deepening our understanding any further.

Turok says that”s exactly why the Perimeter Institute exists, to harness the thinking of the world”s brightest young minds in an unrestrained environment. By optimising conditions for creative thinking, it may be possible to avoid such an impasse.

“We”re used to thinking of theoretical physics as accidental,” says Turok. “We need to ask whether there”s a more strategic way to speed up understanding and discovery.”

Perhaps then all those troubled physicists can finally get some rest – or at least switch to more mundane worries.