Read more: 50 ideas to change science forever
Are you ready for the massive hidden reality promised by supersymmetry? Or the evolution of quantum mechanics? How about a black hole in your tool shed?
The window to a new reality
The standard model of particle physics is both wildly successful and manifestly incomplete. When we consider what might extend and deepen our understanding of nature’s most basic workings, there is often a one-word answer: supersymmetry.
Supersymmetry is like a wonder drug. It helps to unify the various fundamental interactions of nature. It plays a pivotal part in quantum theories of gravity based on string theory. It could even explain what the dark matter that fills the universe is made of.
At its heart is a simple idea: that all known particles have a heavier “superparticle” partner with a different quantum-mechanical spin. Particles and superparticles are mathematically linked through a “superspace” whose dimensions – and this is where things become a little hard to envisage – are the square roots of dimensions in our normal space.
Physics, technology and even philosophy were revolutionised when Einstein’s relativity taught us to regard time as a fourth dimension. Could the idea that the familiar dimensions of space-time have square roots be as revolutionary? As the Large Hadron Collider at CERN, near Geneva, Switzerland, searches for the first traces of supersymmetry, we are about to find out. John Ellis
John Ellis is a theoretical physicist at CERN and King’s College London
The AdS/CFT correspondence
Superconductors from black holes
Of all things in physics, black holes have possibly the most appeal. Mind-bogglingly extreme, they are abundant in the universe. In fact, there’s probably one in a lab near you – although you will need one of the weirdest insights of recent physics to notice it.
This is the grandly titled “anti-de-Sitter/conformal field theory correspondence”, or AdS/CFT for short. A result derived from string theory, it says that gravitational objects such as black holes are encoded in a very precise, albeit indirect, manner in the properties of exotic quantum matter probed in many physics labs worldwide.
Why does this matter? Because while quantum matter is largely a mystery even to the initiated, we have a pretty extensive tool kit for dealing with black holes and the like. With AdS/CFT, we can use the one to explain the other.
That might allow us, for example, to crack the 24-year-old riddle of high-temperature superconductors, materials whose quantum workings allow them to conduct electricity without resistance at temperatures well above absolute zero. If through that we can realise the dream of superconductivity at room temperature, we would rewrite the terms of the energy debate.
The grandest dreams of physicists, however, lie with what the AdS/CFT correspondence might deliver in another direction: could quantum-matter experiments be mobilised to obtain a deeper understanding of gravity, perhaps leading to a theory of quantum gravity that could unify all of physics? This promise captivates me and many others. Jan Zaanen
Jan Zaanen is professor of theoretical condensed-matter physics at Leiden University in the Netherlands
The end of space-time
Since Einstein published his general theory of relativity in 1915, space and time have been one: space-time. Almost a century on, they may be getting divorced.
General relativity provides an explanation for the force we call gravity. But it is not a quantum theory, unlike the theories describing the other three forces of nature. Last year, though, the Czech physicist Petr Horˇava worked out that by allowing space and time to change independently of one another, gravity becomes susceptible to quantum theory’s advances.
A marriage of the two would represent the greatest breakthrough of physics – a “theory of everything” to answer questions such as what happened at the big bang, when microscopic volumes met intense gravity. More complex proposals such as string theory are already attempting the same coup, and are equally unverified by experiment. Time alone will tell which approach is right.
“The marriage of relativity and quantum theory would be the greatest breakthrough of physics – a ‘theory of everything’”
The fittest of all possible worlds
It has bluffed the best minds since quantum theory’s inception. Quantum stuff can exist in several places at once, or spin clockwise and anticlockwise simultaneously. But when we make a measurement, we always get just one answer. Why?
Perhaps because of a Darwinian-style struggle for survival: quantum states compete with each other for our attention, with us only seeing the “fittest” state that influences its surroundings the most.
Experiments this year probing minuscule assemblages of electrons held in quantum dots seem to confirm some predictions of this “quantum Darwinism” (Physical Review Letters, vol 104, p 176801). If the idea proves right, it will confirm our suspicions that experiments can only probe a quantum system’s impact on its environment, never the system itself.
Random matrix theory
Not all randomness is equal
Randomness often does not seem random. In a lottery such as the UK’s National Lottery, in which six balls are plucked from 49, numbers clump: half the possible draws contain two consecutive numbers.
That’s traditional randomness. But a new, non-clumping form of randomness now seems to be cropping up in data all over mathematics and science, the signature of a mathematical curiosity called random matrix theory.
A matrix is a rectangular array of numbers that can be used to encode spatial transformations. The stretching or shrinking produced by a matrix in key directions of space is given by the matrix’s associated “eigenvalue“. Random matrices are matrices filled with randomly chosen numbers, and it is the patterns of their eigenvalues – which are randomly distributed, yet without clumping – that we now see everywhere.
They pop up in the distribution of energy levels in the nuclei of heavy elements like uranium, in the distribution of the zero values of the “Riemann zeta function”, which determine how the prime numbers are distributed, and even in the arrival times of buses in a town in Mexico where drivers determine their own timetables. Investigating why will be a fruitful new direction for mathematics and science. Marcus du Sautoy
Marcus du Sautoy is professor of mathematics and the public understanding of science at the University of Oxford