Thursday, April 17, 2014

Hey hey mama

It gladdens my heart to see Jimmy Page with his double-neck guitar on the pages of a science magazine, even in Italian. So it is with the March-April issue of Sapere, where the second of my “music instinct” columns has now appeared. Here it is.


Attempts to explain how music moves us generally have only one big idea on which to draw. But it’s a good one, and is surely a big part of the answer. When in 1956 the musicologist and composer Leonard Meyer published his book Meaning and Emotion in Music, he was one of the first people to move beyond the cool, formal analysis of musical structure and try to get at why music can make us dance, jump for joy, or break down in tears.

Meyer suggested that it’s all to do with setting up expectations and then violating or postponing their resolution. We think the music is going to do one thing, but it does another – or perhaps it does what we expect, but not quite when we expect it. The unexpected creates a feeling of tension, which might be experienced as excitement. And if that tension is then released, say by the final closing chord of a piece, we feel all the more satisfaction from the delayed gratification. Even the simple rallentando slowing at the end of a Chopin prelude will work that magic.

I’ll give several examples in the forthcoming columns of how this violation of expectation can be played with to raise the emotional temperature, sometimes with exquisite results. Here I want to look at rhythm. This is one of the easiest ways to set up an expectation, because we expect rhythm almost by definition to be repetitive and predictable.

So when it isn’t, we get a thrilling shock. The classic example is Stravinsky’s Rite of Spring, in particular the “Dance of the Adolescents” section. A repeated chord beats away in an insistent pulse – but with an emphasis that shifts with every bar, first on the second beat of the bar, then the first, first again, then second… We never guess when it is coming, so each time it delivers an electrifying jolt.

These unexpected emphases enliven all sorts of music – in jazz, they appear as syncopation, where the beat seems to jump in early and make the rhythm swing. But there are other ways of playing with rhythmic expectation too. Take Led Zeppelin’s song “Black Dog”, where the instrumental riff sounds easy until you try to play it. What’s going on – have they added an extra beat or something? But no, John Bonham’s drums are still ticking away four beats to the bar. The surprising complexity comes from the fact that the guitar riff doesn’t actually fit into this four-beat bar – it has an extra half note. So as it is repeated, it begins and ends in a different place in each bar. The result of these imperfectly overlapping rhythmic structures is disorientating where you think it should be simple. That way, it forces us to pay attention and gives the song a kind of coiled tension and urgency. Stravinsky, I like to think, would have approved.

Monday, April 14, 2014

Particle Fever is aptly named

Here’s the thing. Director and former particle physicist Mark Levinson has made a film, Particle Fever, about the finding of the Higgs particle by the LHC. That’s good news. And it sounds appealing – no omniscient narrator, just the scientists telling the tale. And there are plenty of female physicists in it. But… Here is Levinson on why his background was useful for doing this job: “In some senses, physics hadn’t changed that much since I got out of it in the 80s, because they didn’t have the LHC.” There’s a word missing in that sentence, Mark: “particle”. Particle physics hasn’t changed that much – and to say so is not a great endorsement of your former discipline. But this equating of “physics” with “particle physics” not only plays along with the media myth that the only thing worth noting in physics is what is going on at CERN, but also explains outbursts like this one I received from a (non-particle) physicist recently: “Perhaps the poster child for overselling science should be high-energy physics. They oversold the most expensive toys that physicists have ever produced: high-energy particle accelerators… their arrogance when they talk about ‘the god particle’ and ‘the most important problems’ is disappointing.” I’ve heard similar things from other frustrated physicists. Perhaps Levinson is not now a spokesperson for the particle-physics community, but he does it no favours in this remark.

And it’s evidently not a one-off slip. Later he suggests that there is some fundamental division (in physics) between theorists and experimentalists, along the following lines: “A theorist can wake up in the morning, suddenly erase an equation and rewrite it. An experimentalist, meanwhile, has been working on building a machine for 10 years to prove that theory.” This is not remotely true outside of particle physics – not only could most experimental physicists ill afford to spend 10 years working on building a machine (even if they had to) without having their funding dry up, but most physicists I know work on theory and experiment at the same time.

It is hard not to feel a churl if you express some reservations about the jamboree around the Higgs – but when you see that this circus has apparently convinced some outsiders that the discovery of the Higgs was the most important event in science in the past 100 years, it seems right to feel a twinge of concern. That’s part of the reason I wrote this article. CERN is a blast, the Higgs news was mighty fine, and Peter Higgs deserved the Nobel. But can we please keep a sense of proportion, both about the importance for physics and the whole issue of what physics is?

As for Levinson, he redeems himself by planning – if I read the signs right – to make a film about Denis Noble’s book The Music of Life. I look forward to that.

Friday, April 11, 2014

The physics of marathons

Here, just in time for the London Marathon, is my latest piece for BBC Future. And now I know where the cover of Critical Mass came from.


Around 40,000 people will run the London Marathon on 13 April this year. But if you’re a serious long-distance runner, don’t come with high expectations. “I have to admit to being completely frustrated by the congestion and for 18-19 miles was just dodging people and being held up”, one participant grumbled after the 2012 event. “I had to overtake a lot of people and ended up with bruised forearms from all the elbows”, said another. “People couldn't let you past for a lot of the way.”

There’s no getting away from it – mass running events like this are likely to be congested. But could the crowding problems be reduced, without restricting the number or calibre of participants? The issue here differs rather little from one that has received far more attention: how to optimize traffic flow on our roads. And while the stakes on the road are much higher – congestion comes at considerable cost in pollution, economic losses and personal inconvenience, while a collision could leave you with far worse than a bruised arm – nonetheless there can also be real dangers from bottlenecks and jams in marathons.

This is why Martin Treiber of the Technical University of Dresden has set out to devise computer models that can predict the flows of participants in marathons and mass cross-country skiing events. Treiber has previously developed models for understanding road traffic flows, and he says that these can be adapted in relatively straightforward ways to capture the essential details of how runners and skiers behave en masse.

One of the first attempts to model traffic flow was made in the 1950s by James Lighthill, an expert on fluid flow, and his collaborator Gerard Whitham of Manchester University. They considered the traffic as a kind of liquid flowing down a pipe, and looked at how the flow changes as the fluid gets denser. At first the flow rate – the amount of stuff you can pump through the pipe in a given time – increases as the density increases, since you simply get more stuff through in the same period of time. But if the density becomes too high, there’s a risk of blockages occurring, and then the flow rate plummets – you have a jam.

Treiber’s model of a marathon, described in a preprint, invokes this same principle that the flow rate first increases and then decreases as the density of runners increases, thanks to an abrupt switch from free to congested flow. He assumes that there is a range of different preferred speeds for different runners, which each sustains throughout the race. With just these ingredients, Treiber can calculate the flow rate of runners, knowing the ‘carrying capacity’ at each point on the route. For example, when the route narrows at bottlenecks, so that the maximum ‘free flow’ rate is lower, the model predicts how congestion might develop and spread elsewhere.

This allows Treiber to figure out how congestion might depend on the race conditions – for example, for different starting procedures. Some marathons start by letting all the runners set off at once (which means those at the back have to wait until those in front have moved forward). Others assign runners to various groups according to ability, and let them start in a series of waves.

Treiber has applied the model to the annual Rennsteig half-marathon along a hiking trail in the Th├╝ringian Forest of central Germany, which attracts around 6,000 participants. In 2013, because the police were no longer willing to close a road to ensure that runners could cross safely, the traditional route had to be altered. It could pass either over a 60m wooden hiking bridge or through a tunnel. Treiber used his model to predict the likely congestion incurred in the various options. If the bridge were to be used, it was important to ensure it did not get too overloaded with runners – a danger if bottlenecks ahead of the bridge spill back onto it. The model predicted that a mass start would certainly risk this, but so, to a lesser degree, would wave starts (which the Rennsteig uses). Only by moving the starting point further back from the bridge could the danger be avoided – and even then, if some of the numbers assumed in the model were only slightly inaccurate, there was still a risk of jams reaching the bridge.

Treiber and his coworkers found that no dangerous congestion seemed likely for the tunnel route. The run organizers consulted with Treiber’s team, and eventually chose this option. They also adopted the team’s recommendation for a wave start with delays of about 150 seconds between waves.

Treiber and his coworkers have adapted his model to describe mass skiing events such as the cross-country Vasaloppet hosted each year in Sweden, a 90-km race that draws around 15,000 participants. This is a more complicated situation to model. Partly that’s because the speed of the skiers can depend quite dramatically on the slope of the course, especially when it is uphill. Treiber built this explicitly into his model, deducing the gradient of the course from Google Maps and applying rules that describe how speed depends on slope. He also included lane-changing rules, since the entire course is divided into well-defined lanes. His computer simulations predicted that massive jams, delaying participants by up to 40 minutes, would form where the route has a steep uphill gradient – just as is seen in the real event. The Vasaloppet has a mass start – but Treiber says that if it could be persuaded to adopt a wave start, with 5-minute delays between waves, all the jams would disappear. Whether the organizers will accept this “wisdom for the crowd” remains to be seen.

Thursday, April 10, 2014

Sceptical hauntings

The aforementioned A Natural History of Ghosts by Roger Clarke (which I highly recommend) informs me that Einstein once wrote “Even if I saw a ghost, I wouldn’t believe it.” I know what he means. I once had an experience that can only reasonably be called paranormal, and I don’t believe it. The fact is, though, I don’t disbelieve it either. I don’t see how I can. It remains a mystery, and I can only say that I have almost no idea how to interpret it – which, to be honest, is something I rather like, even if it leaves me feeling a little like the protagonist in Alan Lightman’s novel Ghost.

As a teenager, Clarke went hunting for ghosts around the Isle of Wight, where he lived at what I suspect must have been much the same time as I did. But perhaps the grand manor houses where he seems to have spent his childhood were not the only or even the best places to search. I don’t actually recall the exact, or even the approximate location of the house in which, aged around 15, I had my weird experience, but I think it was in Shanklin, and I do know that it was an unremarkable terraced house probably dating from no further back than the 1950s. It belonged to a relative, maybe an aunt, of one of the friends with whom I had gone to a party, and who had bravely agreed to lend their floor to three teenaged boys after they had undoubtedly consumed more alcohol than was wise or even legal. It was around Christmas time, and I remember there was a decorated tree in the living room (definitely a “living room”, nothing as refined as a “sitting room”) where we laid out our sleeping bags.

So yes, we had been drinking, but not into a stupor, and I remember feeling fairly coherent when we turned out the lights in the early morning. There may well be a perfectly rational and natural explanation for all of this, but I won’t accept that it was simple inebriation.

This “haunting” was entirely within my own mind, which is why I am kind of happy to regard it as a mental phenomenon of some sort. But it was like none I have had before or since. As a child and young person I was plagued by nightmares, but I never knew any other occasion when I awoke from them doubting that this is all they were. What happened as I was sleeping was nothing like a nightmare. For a start, I was fully aware of where I was: lying in a sleeping bag next to my friends on a borrowed floor. But what I felt – and it came upon me quite suddenly – was that I was being taken over and possessed by an incredibly malign force. And it had the character of a personality, one that was raging wildly. I could hear a voice in my head, intoning words that I couldn’t recognize but which sounded to be spoken in something approaching a Scottish accent, and utterly fearsome and demonic. Here’s the worst thing: I could feel my whole body inside my sleeping bag, and it felt as though it was being emptied out, shrivelling up into a dry husk as this “thing” took it over.

Then I woke up, and in an almost parodic manner I sat bolt upright, eyes wide open, and said “Ah!”. I was terrified. But there were by friends, sleeping soundly next to me. I have not the slightest suspicion that this was any kind of prank played by them, and I don’t see how they could have created the mental effect anyway.

Well, I suppose I thought, that was a very scary experience indeed. But here I am, in this mundane little house, and there’s evidently nothing strange going on here. So after a time, I lay down and went back to sleep.

That was a mistake. I’d scarcely nodded off when the whole thing happened again: the same fury and sense of malevolence, the same feeling that I was being possessed and crushed within my own body. That’s the way to put it: as though any shred of my own self was to be pulverized out of existence.

And again I “awoke with a start”, in that phrase that children’s writers seem unable to do without. This time, sitting upright and seeing everything as before, I thought: sod it, I am not going to risk going back to sleep. I’ll sit the night out. But I couldn’t. At some point I drifted back into slumber.

This time it started differently: not with that sense of frantic raving and anger, but insidiously, as though this “thing” had decided this time that I would be more effectively eliminated by stealth. But I knew it was happening, just as I knew I was lying there helpless. Then I “heard” a distinct phrase in my head, and I can only suppose it was the voice of some part of me. It said this: “What do you think it wants?”

I have never forgotten those words, especially because they were evidently regarded as a provocation. The moment they “sounded”, the “thing” returned in full, furious force, and there I was again, becoming this shrivelled husk.

But I woke up again. And this time I’d really had enough. I was beside myself with fear. Why didn’t I wake up one of my friends? What, a teenager, admitting to his mates that he was scared he was being possessed? No, I wasn’t going to risk that. Instead I was determined that this time I’d stay awake until dawn. And I nearly did, because I remember that there was the first dim light starting to appear through the curtains, and the birds were starting to tweet, when I fell asleep again, this time into an untroubled slumber.

So there you have it. I was too confused, too shy and embarrassed, to say anything in the morning or to make any enquiries about the house or the people who lived there. I wish I had, but there you go.

All this ghost business comes from the research I have been doing for my next book, Invisible. And I remember reading somewhere in the course of that research about a well attested brain disturbance that can create the sensation of a weight pressing on the chest – purportedly an explanation for some nocturnal “manifestations” that have been described through the ages, perhaps like the one depicted so provocatively in Fuseli’s famous image. Mine is I suppose a little similar, although it went considerably beyond that. What really perplexes me is the triple repeat, with episodes of clear and even lucid waking in between. I have, once or twice, awoken only to slip back into something like the same dream – one can never be sure how “similar” it really is, given the way dreams leave odd imprints on the memory. But I’ve never known anything even remotely like this.

It’s why I like the fact that Clarke remains open-minded in his book and doesn’t try to explain everything away, even though he reports the known hoaxes, the possible role of ultrasound, and so forth. I think he probably believes in ghosts, in a way that I can’t – for one thing, each manifestation seems too attuned to the preconceptions and ethos of its times. But something very strange happened to me all those years ago, and I simply don’t know what it was.

Wednesday, April 09, 2014

Bleary-eyed in Madrid: on Catholicism, curiosity, and ghosts

There is probably some unwritten rule somewhere that you should never blog at 5 in the morning, but I see no real prospect that the Atletico Madrid fans celebrating their victory over Barcelona in the square outside are going to stop singing before dawn. Ah well, it is just one of those things you have to love about Spain. Also, I doubtless drunk too much coffee in this interview with El Pais during what is now yesterday. The headline (and ensuing comment) reminds me, as did a nice dinner with the folks at the Fundacion Telefonica discussing Franco and Catholicism, that some things are going to be perceived differently down here in the south.

Needless to say, I’m not sure that I will exactly be retiring from football in order to spend more time with the Internet… And it seems that there is no way now that I’m going to prevent people forever suggesting that I am/was the “editor of Nature”. But Javier was a very nice chap, and I’m not complaining. Anyway, this is all an excuse to mention the lovely quote that I found yesterday in Roger Clarke’s wonderful A Natural History of Ghosts. He says that the shade of the dead brother of Robert Boyle, Lord Orrery, once appeared to Boyle’s sister Lady Ranelagh. Boyle, one of the key figures in my book Curiosity, responded to this news in typical fashion by asking his sister to pose a series of metaphysical questions to the ghost when it next appeared. She duly did so, whereupon the ghost replied “I know these questions come from my brother. He is too curious.”

I was delighted to find that Roger Clarke, like me, grew up on the Isle of Wight, and so knows all about the local ghosts there. I have another one for him, of which more later.

Saturday, April 05, 2014

Ballard - always head of his time

My enjoyment of eulogies for J. G. Ballard, like this one in the Guardian on the 5th anniversary of his death, is always tempered by a sense of bitterness. For I can’t help feeling some resentment at the way the literary world now embraces this writer who was considered infra dig when I devoured everything he wrote 40 years ago. Even as a callow and barely literate teenager, I had a sense – which I could never then have articulated – that his works were far more relevant a window on the modern (by then almost postmodern, I suppose) age than the majority of works celebrated by what I now imagine was a literary community of a largely Leavisite mindset. Deborah Levy has it quite right in this article that the classification of Ballard as “science fiction” was really an attempt to tame and marginalize a writer who was too edgy, strange and visionary for that kind of sensibility. I think young Ballardians like me could intuit that writers like Michael Moorcock, Philip K. Dick, Kurt Vonnegut and most of all Ballard were working in a different kind of genre from Asimov and Clarke, and that the superficial sci-fi traits that some of them used from time to time were merely tools that suited their ulterior purpose. I surely read books like The Atrocity Exhibition with as threadbare a set of cultural references as I brought to my uncomprehending forays on Dostoevsky, having no real notion of who this Ralph Nader and Ronald Reagan were (that was the 1970s) and little idea of why Jackie Kennedy represented much more than a dead president’s wife (specifically, the harbinger of the modern age of celebrity). In short, a lot of it went right over my head. But I read on, feeling I suppose that this stuff was going to matter, that it was worth more than the values of the day seemed to allow.

What has changed, I suppose, is that the literary community is now populated by folks from a similar time and attitude as mine – Self, Kunzru, Mieville – for whom that kind of “speculative fiction” was as valid as the old, approved canon. I think this is progress. But it would be foolish to imagine that they too, we too, are not now overlooking and snobbishly dismissing writers who will turn out, in retrospect, to be the true prophets of our times.

Thursday, March 27, 2014

How the universe got blown up

No one particularly needs me to tell them about the BICEP2 results, given that so many others have already done so very nicely. But here is the way I put it in the latest issue of Prospect, where I wanted to try to put the findings within the broader picture of our unfolding cosmological view over the past century. That’s why I mention dark energy and the cosmological constant, even though one can perfectly well explain inflation without that. I’d contend that, if this work bears up, we’ll see the major landmarks as:
1912/1919: general relativity proposed and ‘confirmed’
1927/29: the Big Bang and cosmic expansion predicted and confirmed
1965: the CMB detected (and a minor landmark with the 1992 COBE results)
1998: the accelerating expansion of the universe
2014: inflation and gravitational waves ‘confirmed’ (?)
Who’s going to put money on Guth and Linde for the Nobel? Probably needs an independent confirmation first, though.

I feel like I spend a fair bit of time these days trying to bring a critical eye to the excesses of science boosterism. So how nice it is to be able for once to relish the sheer joy of how fab science can be. That was an exciting week. And if this piece is a little loose around the edges, forgive me – it had to be knocked out essentially overnight.


The discovery reported on 17 March by a US-led team of scientists will join the small collection of epochal moments that, at a stroke, changed our conception of what the universe is like. It offers evidence that, within an absurdly small fraction of a second after the universe was born in the Big Bang, it underwent a fleeting period of very rapid growth called inflation. This left the fabric of spacetime ringing with “gravitational waves”, which are predicted by Albert Einstein’s theory of general relativity but have never been seen before.

Finding evidence for either inflation or gravitational waves would each be a huge deal on its own. Confirming both together will leave cosmology reeling, and – barring some alternative explanation for the data, which looks unlikely – it is inconceivable that they will fail to win a Nobel prize in their own right and probably to motivate another for the theories they support. According to astrophysicist Sean Carroll of the California Institute of Technology in Pasadena, the results supply “experimental evidence of something that was happening right when our universe was being born”. That we can find this nearly fourteen billion years after the event is astonishing.

The discovery was made by a team led by John Kovac of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, using the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) telescope located at the South Pole. It’s the kind of milestone in observational cosmology that comes only once every few decades, and fits perfectly into the narrative created by the previous ones.

We might start in 1919, when the British astronomer Arthur Eddington observed, from the island of Principe, the bending of starlight passing by the sun during a total solar eclipse. This confirmed Einstein’s prediction that gravity distorts spacetime, forcing light to trace an apparently curved path. The discovery made Einstein internationally famous.

Because of this effect of gravity, general relativity predicts that violent astrophysical events involving very massive objects – an exploding star (supernova), say, or two black holes colliding – can excite waves in spacetime that travel like ripples in a pond: gravitational waves. Scientists were confident that these waves exist, but detecting them is immensely difficult because the distortions of spacetime are so small, changing the length of a kilometre by a fraction of the radius of an atom. Several gravitational-wave detectors have been built around the world to spot these distortions from a passing gravity wave via interference effects in laser beams shone along long, straight channels and bouncing off mirrors at the end. They haven’t yet revealed anything, but the hope is that gravitational waves might eventually be used just like radio waves or X-rays to detect and study distant astronomical events.

The BICEP2 findings unite gravitational waves and general relativity with the theory of the Big Bang, for which we need to go back to the second cosmological milestone. In 1929 American astronomer Edwin Hubble reported evidence that the universe is expanding: the further away galaxies are, he said, the faster they are receding from us. Hubble’s expanding universe is just what is expected from an origin in a Big Bang. In fact Einstein had already found that general relativity predicts this expansion, but before Hubble most people believed that the universe exists in a static steady state, and so Einstein added a term to his equations to impose that. Yet in 1927 a relatively obscure Belgian physicist, George Lema├«tre, dared to take the theory seriously enough to predict a Big Bang. Hubble’s data confirmed it.

Yet it wasn’t until 1965 that one of the key predictions of the Big Bang theory was verified. Such a violent event should have left an ‘afterglow’: radiation scattered all across the sky, by now dimmed to a haze of microwaves with a temperature of just a little less than three degrees above absolute zero. While setting up a large microwave receiver to conduct radio astronomy, Arno Penzias and Robert Wilson found that they were picking up noise that they couldn’t eliminate. Eventually they realised it was the fundamental noise of the universe itself: the cosmic microwave background (CMB) radiation of the Big Bang. That’s milestone number three.

Number four came in 1998. While observing very distant supernovae, two teams of astronomers discovered that these objects weren’t just receding from us: they were speeding up. That was a real shock, because most cosmologists thought that the gravitational pull of all the matter in the universe would be slowing down its expansion. If, on the contrary, it is speeding up, then some force or principle seems to be opposing gravity. We call it dark energy, but no one knows what it is.

Einstein had already unwittingly provided a formal answer with his balancing act for getting rid of cosmic expansion: he added to his equations a fudge factor now called the cosmological constant. This amounts to saying that the vacuum of empty space itself has an energy – and because this energy increases as space expands, it can in fact produce an acceleration.

BICEP2’s results now look like milestone number five, and they stitch all these ideas together. The telescope has made incredibly detailed measurements of the CMB, spotting temperature differences from place to place in the sky of just a ten-millionth of a degree. Hence the exotic location: the telescope sits at the Amundsen-Scott South Pole station, 2,800 up on an ice sheet, where the atmosphere is thin, dry and clear, and free of interference from light and radio signals.

For the fact is that the CMB isn’t simply a uniform glow: some parts of the universe are a tiny bit “hotter” than others. This was confirmed in 1992 by observations with the Cosmic Background Explorer (COBE) satellite, which provided the first map of these “anisotropies” (hot and cool spots) in the CMB – and thereby some of the best evidence for the Big Bang itself. Since then the maps have got considerably more detailed.

Yet the puzzle is not so much why the CMB isn’t entirely smooth but why it isn’t even more uneven. A simple theory of a Big Bang in which the universe expanded from a tiny primeval fireball predicts that it should be much more blotchy, consisting of patches that are receding too fast to affect one another. So space should be far less flat and uniform. In 1980 the American physicist Alan Guth proposed that very early in the Big Bang – about a trillion-trillion-trillionth of a second (10**-36 s) after it began – the universe underwent a burst of extremely rapid expansion, called inflation, which took it from much smaller than an atom to perhaps the size of a tennis ball – an expansion of around 10**60-10**80-fold. This would have smoothed away the unevenness. In effect, inflationary theory supposes that there was a short time when the vacuum energy was big enough to boost the universe’s expansion.

Inflation doesn’t smooth out space completely, though. Quantum mechanics insists on some randomness in the pre-inflation pinprick universe, and these quantum fluctuations would have been frozen into the inflated universe, imprinted for example on the CMB. In turn, those variations seeded the gravitational collapse of gas into stars and galaxies – a staggering idea really, that infinitesimal quantum randomness is now writ large and glowing across the heavens. It’s possible to calculate what pattern these quantum fluctuations out to give rise to, and observations of the CMB seem to match it.

All the same, there was no direct evidence for inflation – until now. The theory also predicts that the microwave background radiation should be polarized – its electromagnetic oscillations have a preferred orientation – with a characteristic pattern of twists, called the B-mode. This swirly polarization is what BICEP2 has detected, and there’s no obvious explanation for it except inflation. Cue a Nobel nomination for Guth, and other architects of inflationary theory, in October.

What’s all this got to do with gravitational waves? Cosmic inflation was rather like a shock wave that set the universe quaking with primordial gravitational waves. They have now, 13.8 billion years later, died away to undetectable levels. But they’ve left a fingerprint behind, in the form of the polarized swirls of the CMB, just as ocean waves leave ripples in sand. It seems the only way these swirls could have got there was via gravitational waves.

OK, but where does inflation itself come from? Physicists’ usual response to a question they can’t answer is to invent a particle that does the required job, and give it a snazzy name: neutrino, WIMP, graviton, whatever. Carroll, who now proudly records Kovac among his former students, admits that this is what they’ve done here. “We don’t know what field it is that drove inflation”, he says, “so we just call it the inflaton.”

In other words, just as the photon (a ‘particle of light’) is the agent of the force of electromagnetism, and the Higgs boson was initially postulated as the force field that gave some particles their mass, so the inflaton is the alleged particle behind the force that unleashed inflation. It’s just a name, but here’s the point: it’s a particle whose behaviour, like that of all fundamental particles, must be governed by quantum theory.

And that’s where we really hit the exciting stuff. Confirming these two astonishing ideas, inflation and gravitational waves, is terrific. But they always looked a pretty safe bet. It’s what lies behind them that could be truly revolutionary. For gravitational waves are a product of general relativity, the current theory of gravity. But here they get kicked into existence by an effect of quantum mechanics, orchestrated by the quantum inflaton. In other words, we’re looking at an effect that bridges the biggest mystery in contemporary physics: how to reconcile the ‘classical physics’ of relativity with quantum physics, and thus create a quantum theory of gravity. Sure, BICEP2’s results don’t yet show us how to do that. But how many simultaneous revolutions could you cope with?