by Ashley Hay
Smolin’s starting point is a reformulation of general relativity known as shape dynamics, developed by the independent physicist Julian Barbour and others. Whereas in relativity space and time stretch and condense for observers travelling at different speeds, in shape dynamics only sizes change. Two distant observers will always agree on what’s happening ‘now’ in a galaxy regardless of their relative motions; they just won’t be able to agree how big things in that galaxy are.
That might seem like a zero-sum game, replacing one uncomfortable principle with another. For Smolin, though, bending only space, rather than space and time, neatly recreates a conception of time of the sort quantum physics uses, one in which a single external clock provides a beat that distinguishes one moment from the next. The great prize on offer is the possibility of unifying our understanding of quantum theory with that of gravity, the only one of the fundamental forces of nature to have no quantum description. The route to a ‘theory of everything’, Smolin thinks, is through a better understanding of time.
* * * * *
Once simultaneity is regained, it becomes possible to describe the entire universe as a series of layered moments – a succession of objectively identified times in which all events are simultaneous. ‘All that exists is this moment,’ says Smolin. This is unlike the block universe, where past, present and future are equally real, or Ellis’s conception, where only the past and the present are. Instead, the only things that are real about the past or future in Smolin’s world are signs of them in the present: records of the past and indicators of what is to come in the future. Smolin is working with Marina Cortes from the University of Edinburgh to flesh out the idea with mathematics, and to explore which of the many theoretical approaches to quantum gravity it is compatible with.
Price is unmoved. Even if Smolin’s or Ellis’s approach can provide an objective way of defining the present, he says, there is still a big logical hole. On the one hand, such arguments demand that the present moment be unique; on the other, they demand that every other moment also acquire that unique property. ‘The whole idea of a privileged present moment is incoherent,’ he says.
Tim Maudlin, a philosopher and mathematician at New York University, has a different objection. Even if Ellis’s or Smolin’s theory provides a physical basis for our intuitive conception of here and now, neither explains the fact that we see time flowing, whereas physics suggests it is stationary. This is a fundamental omission, says Maudlin. ‘The notion that time passes is absolutely commonplace; it is not a bit of technical jargon invented by philosophers.’ Without flowing time, he says, nothing would move at all. Things like rivers appear to flow in space, but ‘it’s the fundamental direction in time that underlies all of these other directionalities.’
For the past five years, Maudlin has been working on what he calls the theory of linear structures, which he hopes will allow him to reincorporate a flowing time into physics. The idea is rooted in mathematics rather than physics: unlike shape dynamics, it doesn’t provide a rival physical basis for the warped space–time geometry introduced by relativity. ‘It is the language in which to write a physical theory, not a physical theory itself,’ says Maudlin, who is aiming to publish the details in a book.
The principal addition to this language’s vocabulary is an object called a directed line. In any conventional geometry, lines between two points in space and time do not come with a natural direction: we have to define a line in terms of a coordinate system, specifying that it passes from me to you rather than you to me, or drawing an arrowhead on the line to make things clear. In Maudlin’s geometrical language, however, that arrowhead is implicit in the definition of any line. Once this is built into the fundamental language of geometry, time can naturally acquire a direction.
Ellis thinks Maudlin’s work is interesting, and also compatible with his growing block picture, explaining in more detail how the flow of time can be fundamental to physics. ‘In the end, you have to base your theories on some fundamental givens. Time, it’s just kind of a given, which everything else flows around,’ he says.
Carroll is more sceptical. Rather than attempting to change the block universe to explain our experience of time flowing, he says we should concentrate on explaining human experience in light of what our very successful physics tells us about the block universe. That task, he says, is quite achievable. ‘That doesn’t mean that we’ve done it yet, but I see no obstacle to doing it.’
* * * * *
Craig Callender, a philosopher from the University of California, San Diego, agrees. Explaining our apparently aberrant perception of time does not mean we have to overturn physics or invent a whole new way of doing geometry. When, he says, we ‘embed critters like us’ in a universe like ours, it makes sense that we should see a flowing time and distinguish past, present and future – even when the reality is something different.
To explain why, we can return to that vantage point gazing down on the entire block universe, and zoom in on that tiny human speck: the four-dimensional worm with a baby at one end and a corpse at the other. This worm’s perception of time differs from ‘reality’ first in that it remembers the past but does not see the future. That can be explained as a consequence of thermodynamics. The universe started off in a highly ordered, taut state after the big bang, and has been expanding into an ever more disordered, flaccid state ever since. There is an infinitude of paths in which the universe can evolve forward in time, but only one path back into its history. Why the universe works like that is another, fundamentally unanswered question – but it means that, purely statistically, we are only ever likely to have a clear view backwards in time.
Even then, you would expect we worms to feel as if we are stationary in time with a view in only one direction, rather than what we experience: moving backwards into the future with no clear view of where we are heading. For Callender, the key to this illusion is an important psychological fact about ourselves: we have a sense of identity. According to physics, your life is described by a series of slices of your worm – you as a baby, you as you ate breakfast this morning, you as you started reading this sentence and so on, with each slice existing motionless in its respective time. We generate time’s flow by thinking that the same self that ate breakfast this morning also started reading this sentence. ‘Really there’s all these different mes at all these different times,’ says Callender. ‘But because I think that I’m identical over time, that’s why time seems to flow, even though it doesn’t.’
So do we really need to mourn time’s passing? Einstein, for one, drew solace from the view of the timeless universe he had helped to create, consoling the family of a recently deceased friend: ‘Now he has departed from this strange world a little ahead of me. That means nothing. People like us, who believe in physics, know that the distinction between past, present and future is only a stubbornly persistent illusion.’ So it goes.
* * * * *
Postscript: Tim Maudlin’s book, New Foundations for Physical Geometry, was published in May 2014.
The oldest known star
The quantum spinmeister
Reached by committee, nineteen eighty-three
Paul Magee
A metre is the length travelled by a ray of light
in a
vacuum
over
299,792,458ths
of a second.
They used to count
one million six hundred and fifty thousand
seven hundred and sixty-three point seventy-three
wave
lengths
of the radiation between the levels two p ten and five d five
of the Krypton eighty-six atom in the dark, old
seconds prior to accurate measurement, before we embraced
the light.
The now delusion
Liner notes, Voyager Golden Record
Material of the future: Sticky tape, honey and graphene
Lisa Clausen
; Three clear bottles stand like trophies on an otherwise empty shelf in Professor Dan Li’s office at Melbourne’s Monash University. Two are filled with powder the colour of midnight, while the third contains a lump of silver-grey rock. They’re all forms of graphite, a type of coal we all rely on somehow, whether it’s in brake lining, batteries or pencils. But that’s not why Li has the bottles displayed behind his desk. Among scientists like Li, graphite is now celebrated as the source of graphene, the phenomenal new material that researchers, governments and corporations the world over are betting could transform a multitude of industries, from electronics to renewable energy.
Scientists had long suspected graphite contained something interesting. But while they knew this smudgy, light rock was composed of stacks of graphene sheets, none of the brilliant minds working on it could figure out how to isolate a single sheet, let alone manipulate it. Then in 2004, University of Manchester physicists Andre Geim and Konstantin Novoselov had an inspired idea. Taking a block of graphite, the pair simply began stripping off flakes with sticky tape. They ended up with micro flakes of a completely new material, each too thin to be seen by the naked eye, its carbon atoms arranged in a dazzlingly perfect honeycomb pattern. Their playfulness won them, just six years later, the Nobel Prize in Physics. ‘No one really thought [releasing graphene] was possible,’ said the Royal Swedish Academy of Sciences. ‘Carbon, the basis of all known life on earth, has surprised us once again.’
Since then, the surprises have kept coming, as graphene continues to show just how much it may be capable of. For starters, it’s the world’s thinnest material – with a sheet of graphene just an atom thick, it’s a two-dimensional material. You’d need three million sheets to make a stack 1 millimetre high. It’s very flexible, yet harder than diamond and 200 times stronger than steel; it is so strong, Columbia University researchers once calculated it would take an elephant balanced on a pencil to break through a layer of graphene as thick as plastic food wrap. It is practically transparent, so dense that not even the smallest gas atoms can penetrate it, and it conducts electricity and heat beautifully. While other commonly used materials such as silicon can match graphene in maybe one or two ways, what makes graphene so special is that it brings so many desirable qualities together in one package. In short, it seems to have it all.
* * * * *
So what might this marvellous material give us? Some say transparent, super-thin computer and TV display screens that can be rolled up and put away. Slimmer, faster phones that recharge in seconds. Smaller, speedier computer chips. ‘It’s beyond our comprehension of what is possible,’ says Cathy Foley, chief of the CSIRO’s Materials Science and Engineering Division. ‘There will be changes that will blow us away.’ Graphene also has researchers fascinated with its potential for biomedical tools, optics and plastics reinforcement (such as building lighter, hardier aircraft or satellites), as well as creating high-performing solar cells and electric vehicles, and next-generation filters for water purification and desalination. Defence industries are pursuing graphene-based ultra-sensitive gas and chemical sensors, while Bill Gates recently funded a University of Manchester project using graphene to make stronger, thinner condoms.
With such prizes on offer, scrutiny of graphene is intense. In 2004, the year Geim and Novoselov had their Eureka moment, fewer than 500 scientific papers on graphene were published. In 2012, there were almost 9000. Thousands of patents have been issued, and while few graphene-based devices are yet a reality, corporations such as Samsung are racing to control the market. The European Union last year committed €1 billion ($1.5 billion) to its multi-nation research efforts.
In such a busy crowd, Australia’s researchers must find ways to stand out. ‘Our funding pool in Australia is much more limited,’ says Dan Li, who leads a team of ten, ‘but that doesn’t mean we can’t do something unique’. A cheerful man with the rapid-fire speech of the very bright, Li is one of Australia’s leading researchers in graphene, a field he entered after arriving in Australia on a fellowship from the US in 2006. ‘I wasn’t that optimistic about graphene at first,’ he admits. ‘A lot of promising materials never make it to market.’
While most researchers have focused on individual graphene sheets, Li is on a quest to use these sheets as molecular ‘bricks’, assembling them in different ways to create new materials and devices infused with graphene’s talents. He likens graphene to a world-beating athlete – extraordinary on its own and capable of as yet unimagined feats when teamed up with other materials. But as an engineer he knows that architecture is everything. ‘You could have the strongest bricks, but that doesn’t necessarily mean you’ll end up with the strongest building – it depends on how all the components interact.’
Having already come up with a groundbreaking and deceptively simple technique which uses water and a series of chemical reactions to separate sheets of graphene and keep them from restacking, Li’s team’s latest success has been in the area of supercapacitors, specialised batteries already used in, for example, digital camera flashes, laptops and hybrid electric vehicles. Their flaw has always been their bulky size and regular need for recharging; using a graphene-based gel they invented at Monash, Li and his team have been able to produce supercapacitors in the lab that can store triple the amount of energy in a much smaller, and hence cheaper, package. ‘It’s a kind of an impossible thing to do, but now we can do it,’ says Li. Since publishing results in August 2013, they’ve been swamped with enquiries from around the world.
Li and his team are also working with Australian and Chinese researchers to use graphene in bone and tissue regeneration, harnessing its superconductivity to deliver electrical stimulation for cell growth. They’ve also patented a graphene-based foam which, by mimicking the natural structure of cork, is super elastic and lighter than air but able to support objects up to 50 000 times its own weight. Blended with other materials, such as plastics, it could vastly improve toughness and heat resistance. Li, who has received several fellowships for his work and is now looking to the private sector for commercialisation partners, has a preference for graphene projects with a social dividend. ‘I want to get something useful out there into the real world. I’m grateful to Australia for giving me these opportunities and I’d like to make sure Australia gets something in return.’
* * * * *
University of Wollongong researchers also have high hopes. By placing two sheets of graphene – 25 000 times thinner than a human hair – on a biopolymer (a naturally produced molecule such as a protein), they hope to create a device to implant in the brains of people with epilepsy. The plan is that its graphene electrodes could detect an impending seizure and trigger the release of anti-seizure medication. Researchers last year also devised a way of using textile techniques to spin nano-fibres of graphene, designed to give super strength to materials used in bullet-proof vests and aircraft fuselages. They’re working, too, in collaboration with Australian colleagues on applying graphene in nerve regeneration for damaged limbs.
Professor Gordon Wallace, executive research director of the Australian Research Council Centre of Excellence for Electromaterials Science, says while the scientific community is taking a wait-and-see approach, the excitement around graphene is more than hype. ‘The question is whether we, as scientists, technologists and engineers, can take its amazing properties from the nanomaterial world to the level of macroscopic devices,’ he says. ‘And that’s not graphene’s challenge – it’s ours.’
Graphene is not giving up all its secrets easily. Its amazing properties, for instance, mean that electrons surge through it at a constant speed of a million metres per second – yet it’s not fully understood how they can be guided. Moving from the nanoscale to the commercial scale remains hugely complex. Making enough of it is still tricky. ‘We want to be able to press a button and have kilometres of the stuff come out,’ says the CSIRO’s Cathy Foley. At the moment, complex chemical and thermal processes are used to obtain graphene, but most t
ake hours or days, involve toxic ingredients or only produce small amounts, not the mass quantities consumer products would need.
One group of CSIRO researchers thinks they’ve solved that conundrum, in part thanks to a bad cold. In 2011, PhD student Donghan Seo was at home in Sydney nursing a cold with lemon and honey tea and reading the Bible. When he came to ‘Exodus’, which talks of ‘a land flowing with milk and honey’, he had his own epiphany. ‘I suddenly thought, why wouldn’t honey work in making graphene? I had a strong religious feeling that it would work, and from a scientific point of view it made sense.’ The next day, he took some honey to the lab, where he subjected less than a gram to plasma testing, pelting it with highly charged ions to purify it down to its basic carbon structure. The CSIRO Plasma Nanoscience team he’s part of can now create a 1 centimetre × 1 centimetre sheet of graphene in nine minutes – ‘while I go and get a coffee,’ he says. The team claims they have already used honey-derived graphene in a gas sensor and butter-derived graphene in a battery. ‘We know it works in the lab,’ Seo says.
In the meantime, Australia has graphite deposits, and several companies keen to begin mining. Adelaide-based Archer Exploration Ltd hopes to fire up its new mine on South Australia’s remote Eyre Peninsula within two years. With world graphite prices rising, high-quality deposits ‘are ripe for development,’ says Archer’s managing director Gerard Anderson. Back at the University of Wollongong, Gordon Wallace says he’d love to use local graphite. It’s one way, he says, in which Australia has the chance to help shape the era of graphene.
