There’s a mood of excitement and anticipation among the scientists trying to answer the biggest questions about our existence: how did our universe start? What is it made of? How will it end? “In the course of the history of science there are occasionally really big changes in our understanding,” says Frank Close, professor of theoretical physics at Oxford University. “Looking back from 100 years in the future, I think this may be one of those big changes.”
Close’s Oxford colleague Brian Foster, professor of particle physics, shares this enthusiasm. “We are on the verge of making a wide range of breakthroughs,” he says, predicting that this will be the most fertile decade of discovery since his research career began in the 1970s.
The new ferment in physics and cosmology follows a relatively quiet decade of consolidation, after some big advances during the 1990s. These included the first images of the afterglow of the Big Bang that created the universe 13.7 billion years ago, and the discovery – quite out of the blue – that mysterious “dark energy” is still blowing the universe apart today.
Also during the 1990s, some of the world’s best-known cosmologists, such as Martin Rees and Stephen Hawking of Cambridge University, began to discuss seriously the theory that our universe is not alone but part of a “multiverse” containing an almost infinite number of other universes. (A signal that we have entered another exciting time for cosmology is that Hawking has co-written a book, The Grand Design – sub-titled New Answers to the Ultimate Questions of Life. It will be published later this week.)
The coming wave of breakthroughs will be driven by new data from space observatories, atom smashers and underground laboratories. Over the next few years, these experiments could reveal previously unseen fundamental forces and subatomic particles, hint at hidden dimensions wrapped up in space – and even suggest how the laws of physics might differ in other universes. The first source of optimism is the $8bn Large Hadron Collider at Cern, the European particle physics centre near Geneva. Following an embarrassing year-long shutdown, while engineers repaired the damage done by an electromagnetic failure shortly after the LHC’s original switch-on, the machine has been running at high power since March, smashing protons together at close to the speed of light.
As LHC collision data pour into Cern’s computer grid and on to the world’s physics labs, at a rate equivalent to 100,000 DVDs per year, scientists are analysing the myriad subatomic particles produced when protons annihilate each other in miniature re-creations of the original Big Bang.
The discovery of a fundamental particle does not come as a “eureka” moment, when physicists suddenly see something new and wonderful in one of the LHC’s 25m-high detectors. It arises from painstaking computer analysis of billions of collisions – a search for a statistical pattern that could not be explained by existing physics. Indeed just such an analysis of collisions at the veteran US Tevatron near Chicago, the world’s most powerful machine before the LHC, is beginning to show hints of the existence of the famous Higgs boson. This particle – a key target of the LHC – would explain how matter acquires its most basic property: mass.
Although individual LHC collisions produce almost four times more energy than Tevatron collisions, extra energy is sometimes less important for detecting rare subatomic processes than accumulating a gigantic database of collisions for analysis. “With the Tevatron cranking out more and more collisions, we have a good chance of catching a glimpse of the Higgs boson,” says senior Tevatron researcher Giovanni Punzi, of the University of Pisa. (Punzi is an illustration of the international character of particle physics, with hundreds of non-American scientists working on Tevatron while even more US scientists are working on the LHC.)
Atom smashers such as the LHC and Tevatron produce experimental evidence for cosmologists by actively reproducing on a microscopic scale the conditions of the early universe. The complementary approach is to observe what is already happening in nature.
Astronomers are the archetypal observers. Many telescopes, on earth and in space, have contributed to our understanding of the universe. The latest is the European Space Agency’s €700m Planck observatory, whose first spectacular view of the cosmos was released in July. Planck is the third and much the most sensitive satellite designed to observe the “cosmic microwave background”, the oldest light in the universe. This radiation was released about 400,000 years after the Big Bang, at the moment when the universe cooled enough for atoms to form and light to spread through space.
The very slight unevenness in the microwave background represents the seeds from which today’s galaxies and other celestial objects were later to form under the influence of gravity. But cosmologists are most interested in using Planck to look backward in time to the first moments of the universe, which are not discernible by direct observation. They hope that, by extrapolating back from the irregularities in the microwave background, they will learn about the primordial period of “inflation”.
Cosmic inflation, first proposed in 1980 by Alan Guth of the Massachusetts Institute of Technology, has become a key feature of most current models of the universe. It was an infinitesimally short period of unimaginably rapid expansion, which started a trillion trillion trillion trillionth of a second after the moment of creation in the Big Bang – and lasted for perhaps one trillion trillion trillionth of a second. Under the influence of a mysterious negative pressure or repulsive gravity, the universe blew up far faster than the speed of light.
“Inflation, as a concept, is beautiful and incredibly powerful,” says George Efstathiou, astrophysics professor at Cambridge University. It provides the best available explanation for the distribution of matter through the universe. “The principal drawback,” he adds, “is that we have not found a compelling mechanism for inflation from fundamental physics.”
If observations from atom smashers and space observatories lead to a better understanding of inflation, then physicists will be able to narrow down some of the mind-numbing complexities of “string theory”. This regards the basic units of energy and matter not as points but as minuscule vibrating loops or strings, no more than a millionth of a billionth of a billionth of a billionth of a centimetre long. The theory proposes a universe with nine or 10 spatial dimensions, compared with the three with which we are familiar. The extra “hidden” dimensions can be wrapped up in any number of complex geometric configurations.
String theory in its various manifestations – such as the M-theory espoused by Stephen Hawking – is the most promising prospect for a “theory of everything”, unifying all fundamental forces and particles. It reconciles the currently contradictory views of space-time proposed by quantum theory and Einstein’s theory of relativity.
The myriad possibilities of string theory “might seem problematic if we are trying to find a unique physical theory”, Efstathiou says. But for multiverse enthusiasts it offers endless options for varying laws of physics in different universes.
“The extra dimensions of string theory, far from being a problem, become an asset,” says Efstathiou. “All configurations exist physically and some of these can produce inflation. We live in the comfortable little corner of a ‘multiverse’ that has inflated to produce a big and old universe (necessary for stars to form) and that has just the right low-energy characteristics to allow life to form.”
Without invoking a deity, multiple universes provide an explanation of the “anthropic principle”, the astonishing series of coincidences that have fine-tuned physical laws to make our universe suitable for intelligent life. If there are an almost infinite number of other universes with different rules, as some forms of string theory suggest, then some of them must by chance have the right conditions. And, being alive ourselves, we must live on one of these.
Although the multiverse concept is winning wide acceptance in science, it is not rigorous enough to convince everyone. “I need to have some reason to accept that the multiverse idea is not just a cop-out,” says Frank Close of Oxford. “Until we have some experimental evidence, it’s just a sophisticated form of poetry or art.”
Nor is there any evidence yet for hidden dimensions: it is conceivable, though unlikely, that Cern’s LHC will have enough energy to reveal them. There is a much better prospect, however, that the LHC will prove the theory known as supersymmetry – a necessary ingredient in most forms of string theory. Supersymmetry holds that every conventional subatomic particle is partnered by a far heavier “superparticle”.
“There’s about a 50:50 split between particle physicists who believe in supersymmetry and those who don’t,” says Brian Cox, a physics professor at Manchester University, whose secondary role as a television science presenter has made him a celebrity scientist. The argument may be settled within a couple of years, if LHC collisions generate what theorists predict will be the most accessible superparticle, the neutralino. As well as bolstering the theoretical framework of forces and particles, discovery of the neutralino might also help solve one of the mysteries about what our universe is made of.
Astronomers have concluded over the past decade or so that ordinary, visible matter – the stuff that makes up stars, planets, dust, quasars and all the more exotic objects that can be seen through telescopes – makes up only about 4 per cent of our universe. They know this by observing the movements of distant galaxies and deducing the impact of gravity on them. The remaining constituents are “dark matter” (23 per cent) and “dark energy” (73 per cent). Dark matter is probably on the brink of explanation, says Martin Rees, the Cambridge cosmologist who is currently both Astronomer Royal and president of the Royal Society.
The neutralino is many scientists’ leading candidate to make up dark matter. According to this view, while neutralinos pervade the universe and shape it with their gravitational pull, they are invisible because they interact so weakly with light or ordinary matter.
However, neutralinos cannot live a totally isolated existence and must in principle be detectable. The best chance of finding neutralinos and other dark matter candidates – known collectively as weakly interacting massive particles, or Wimps – is to put detectors as far underground as possible. Several are installed in some of the world’s deepest mines, well shielded from the cosmic rays that blitz Earth with particles of ordinary matter and would otherwise swamp the detectors. Despite some hints, there has been no unequivocal detection of dark matter particles. But many scientists expect them to turn up soon, either in a deep mine or in the subatomic debris of LHC collisions at Cern.
Dark energy presents a far greater mystery. “It looks as though empty space itself has a certain energy and pressure,” says Rees. “The evidence we have for this is that the expansion of the universe is accelerating, rather than decelerating under the influence of gravity.” This acceleration seals the fate of the universe. The expansion will continue for ever, until the universe eventually becomes cold, dead, infinitely large wasteland. What was once seen as an alternative future – gravity eventually pulling everything back together into a Big Crunch – is ruled out by the discovery of dark energy.
“I don’t think anyone is even close yet to explaining dark energy,” says Brian Cox. “It is presumably similar to cosmic inflation after the Big Bang, but much weaker.”
By now you may be feeling confused by all the possibilities and uncertainties. So are many physicists – confused and excited. “Historically, these periods of confusion come before real breakthroughs in scientific understanding,” says Cox. Why then should we care enough about the origin and fate of the universe to spend many billions of dollars in public money on facilities to study it?
For George Efstathiou the answer lies in the human goldfish bowl. “We are a bit like goldfish, circling round in our little bowl,” he says. “We breed, eat and pollute our environment. Some of us lead happy lives, some of us less so. It would be a tragedy if none of us ever attempted to peer outside our bowl unless there was a direct economic benefit to our fellow fish to do so. We live in a fascinating universe, but we know very little about it, where it came from or why it exists. It is our moral duty, as a species, to spend some small fraction of our wealth to peer outside our bowl.”
Our human minds may not be equipped fully to comprehend the multiverse, any more than fish can understand the world beyond water, but we can at least try.
Clive Cookson is the FT’s science editor
Particle physics, also known as high-energy physics, studies the fundamental particles and forces that make up the universe.
Cosmology is the scientific study of the universe as a whole: its origin, evolution, current state and ultimate fate.
Big Bang is the idea that the universe started with an unimaginably rapid expansion of concentrated energy and space from a point-like beginning, which current thinking puts at about 13.7 billion years ago.
Cosmic inflation is an infinitesimally short period of exponential expansion, immediately after the Big Bang, during which the universe blew up far faster than the speed of light.
Supersymmetry is the theory that every conventional subatomic particle is paired with a far heavier partner or “superparticle”. It would iron out several inconsistencies in the Standard Model.
String theory regards the basic units of matter and energy as minuscule vibrating loops or strings, no more than a millionth of a billionth of a billionth of a billionth of a centimetre long. It proposes a universe with 10 or 11 dimensions of space and time.
Dark energy, which contributes 70 per cent of the mass-energy in the universe, is a mysterious property of empty space. It is driving continued cosmic expansion.
Dark matter, which makes up an estimated 25 per cent of the universe, is felt through gravity but does not normally interact with ordinary matter.
The neutralino is a particle predicted by supersymmetry, which is a leading candidate to make up most of dark matter. Scientists hope to find neutralinos either in special detectors shielded from cosmic rays in deep mines or in the debris of high-energy collisions in an atom smasher.