The Crowd and the Cosmos: Adventures in the Zooniverse

by Lintott, Chris

  far beneath the cheering crowds, where planners have taken

  advantage of the stadium’s deep foundations to create a stable

  environment for the university’s world-leading mirror-making

  laboratory. This is the domain of Roger Angel, a now ageing hip-

  pie who combines the sharpest of scientific insight with a crafts-

  man’s flair and love of tools. In the 1990s, Roger realized and

  demonstrated how to make enormous mirrors which were

  nearly hollow, supported by a honeycomb structure and thus

  much lighter and easier to manoeuvre than would otherwise be

  the case. They’ve become the de facto standard for large mono-

  lithic mirror telescopes. The only alternative, utilized by the next

  generation of extremely large telescopes, is to use a mirror that

  comprises multiple, usually hexagonal, segments, but where

  possible the simple charms of a single mirror still hold sway.

  How Science iS Done 33

  When I first visited the mirror lab under the stadium, a typical

  example of its products was laid out on the floor. Like most of

  Roger’s large mirrors, it was 8.4 metres across, a size dictated

  not by scientific need or even by cost, but by the maximum size

  that can be easily transported on American highways. I got to

  scramble on top of it, and tried hard to imagine it at the heart of

  an enormous telescope swinging around the sky. Since I was

  there, that mirror has had its turn on the enormous polishing

  machine, which ground it slowly to the correct shape with

  almost unbelievable accuracy by the careful application of a

  black goo called pitch in a process that, degree of mechaniza-

  tion aside, hasn’t changed much since Newton’s day. The pro-

  cess took months, but at the end of it the main mirror for the

  telescope that will drive astronomy’s new data deluge was

  ready.

  The telescope in question is known, somewhat clumsily, as the

  Large Synoptic Survey Telescope (LSST). Large it certainly is;

  with its giant mirror, it can compete with the largest telescopes

  in the world today. The key word, though, is synoptic. The plan is

  for the telescope to complete a general survey, scanning the

  whole sky available to it on average once every three nights,

  making a movie of the sky. Among the thirty terabytes of data it

  will produce every night will be discoveries of asteroids whip-

  ping around the Solar System, the signs of stellar death in the

  form of supernovae, and the flickering of galaxies as material

  falls irretrievably down to their central black holes. Construction

  of the telescope is now underway, yet astronomers including

  myself are still struggling to get our heads around the sheer size

  of LSST data. Even if, for example, you decide you only care about

  things that change from night to night, you should expect a con-

  servative estimate of a million alerts a night. Filtering that list of events to find those worthy of our attention is essential for

  34 How Science iS Done

  LSST science, but understanding how to do that well requires a

  research programme of its own.

  The LSST telescope is just a few years away, but we can already

  see even greater challenges on the horizon. The next big inter-

  national project in astronomy is a radio telescope, known as the

  Square Kilometre Array (SKA). Rather than being a single mono-

  lithic structure, the SKA will span two continents, scattering sen-

  sitive radio receivers throughout the emptiest parts of southern

  Africa and western Australia. Away from the noisy trappings of

  civilization (and especially pleased to be free of interference from

  mobile phones), the SKA will listen to the cosmos with a sensitiv-

  ity never before achieved. The telescope will be so powerful that

  there are serious worries that attempts to observe nearby sources

  with it will be swamped by the presence of millions of previously

  undetected background galaxies, and serious consideration is

  being given to the feasibility of finding alien airport radar on

  nearby planets.*

  It’s the volume of data that matters, though, and here it’s hard

  to find a proper comparison. I could tell you that the SKA will

  provide as much information in its first week as exists in the five

  million million million words that have been uttered during the

  history of humanity. It is certainly an impressive statistic, with

  the additional advantage of being true, but I’m not sure it helps

  one really get a grip on what’s going on. Does it help to know

  that the total data rate flowing between dishes will amount to ten

  * Initially thought to be a promising source of signals for SKA-era SETI (the search for extraterrestrial intelligence), the consensus seems to be that the fact that we don’t know the rotation rate of the planets involved will stymie any serious search. It seems it may be simply too hard a task for us to expect to pick out an unknown signal without knowing when its host planet will be positioned just right for us on Earth to intercept a signal meant for the incoming space plane from Alpha Centauri. Still, the fact that this is even worth arguing about gives you an idea of quite how sensitive this new telescope will be.

  How Science iS Done 35

  times the current traffic on the internet? I’m not sure, but take

  my word for it: SKA is a project that will live and die on its ability to handle large data sets, and this vulnerability is not confined to

  astronomy. Whether you’re an oceanographer contemplating

  data flowing from a new generation of Earth-observation satel-

  lites or an ecologist carpeting your study area with motion sensi-

  tive cameras, you’re going to spend a large part of the next decade

  thinking about data processing.

  Of course, scientists have been here before. It’s the largest pro-

  jects, whether the Human Genome Project or the LHC at CERN,

  that have had to confront the data deluge first. The world wide

  web was built as a way of sharing information produced by the

  latter, but the real action happens deep underground in the

  experimental cavities within which precision engineering brings

  the beams of particles, travelling in opposite directions around the

  27-kilometre-long tunnel at much more than 99 per cent of the

  speed of light, together to collide.

  At the instant particles collide at these sorts of velocities a

  tremendous amount of energy is released, creating conditions

  not seen since the first tiny fraction of a second after the Big

  Bang.* Most of that energy quickly results in the formation of

  new particles which fly outwards from the point of collision.

  Many of the new particles are unstable, and so decay into fur-

  ther particles, creating a complicated cascade of debris. It’s this

  shower of particles, some created in the collision and some the

  * This statement of course ignores the possibility of alien particle physicists who may have built colliders greater than our own. This is perhaps unfair; any civilization which has grown to at least our puny technological civilization’s level has presumably its share of creatures with the same love of banging nature together to see what it’s made of that characterizes the Earthly experimental physicist. Still, if they are out there t
hey don’t publish in our journals, which is all that really counts.

  36 How Science iS Done

  result of subsequent decay, that crash into the successive layers

  of detectors wrapped around the collider beam and are picked

  up by the carefully calibrated instruments. One layer might be

  designed to deflect and thus measure the properties of particles

  with positive or negative charge, while a final layer might be a

  calorimeter designed to absorb the energy of particles that

  make it that far.

  By piecing together what each of these detectors find, the sci-

  entists can work out what happened in the short time after the

  collision. When, on 4 July 2012, researchers from two of the

  experiments at the LHC, ATLAS and CMS, announced that they

  had evidence for the elusive Higgs boson—what they had actu-

  ally seen was a repeating pattern of several different cascades of

  particles which corresponded to what was expected if the Higgs

  had (briefly) been created. There is no box of bosons in the CERN

  visitor centre, but the evidence for its existence had been piling

  up in collision after collision provided by the LHC’s collider team

  to the eager and waiting physicists.

  But how did they find those tell-tale signatures in the data?

  Most events do not produce Higgs bosons. Indeed, the produc-

  tion of such a particle is enormously rare, but luckily by 2012,

  over 300 trillion (300,000,000,000,000) collisions had been

  recorded. That breaks down to a rate of around 600 million col-

  lisions a second, or 300 gigabytes a second of data, the equivalent

  of having the entirety of English Wikipedia read to you seven

  times each and every second. Were you subject to such a cacoph-

  ony, I suspect you’d reach for the same solution as CERN’s

  scientists. They filter the data they receive from the collider’s

  experiments, throwing out much of it almost instantly and keep-

  ing only those events which match a predefined set of triggers.

  Anything corresponding to a Higgs event, for example, would be

  snarfled, saved for future Nobel Prize-winning analysis, but more

  How Science iS Done 37

  than 99.999 per cent of the data collected by the LHC is discarded

  within a second or so of being received.

  The LHC, though, has never been just a Higgs-seeking machine.

  Plenty of other experiments are underway, each with their own

  set of triggers to snatch information from the flow of live events.

  One of the most exciting for those of an astronomical bent is the

  search for dark matter, and this is a little different. Dark matter is, we think, the stuff the Universe is made of. All of these atoms, all

  of these protons, electrons, and neutrons, all of these neutrinos,

  muons, and more amount to only so much scum floating on a

  sea of dark matter. It accounts for about 80 per cent of the matter

  in the Universe, and the embarrassing fact is that we don’t know

  what it is.

  Help is, however, on hand. We have good evidence that what-

  ever dark matter is, it behaves as if it is composed of massive neu-

  tral particles. You might think of a sea of particles, each with the

  mass of the nucleus of a copper atom, but neutrally charged so

  that it can’t interact with light. (Such particles are known as

  WIMPs; weakly interacting massive particles.) If this explanation

  is accurate, then it seems possible that dark matter particles will

  be produced in some fraction of the collisions at the LHC. They

  would likely shun the embrace of both ATLAS and CMS detectors,

  fly straight through, and thus show up as a loss of energy in the

  experiment.

  That missing energy would be hugely exciting, for it would

  mean that an unexpected particle, whether or not it turns out to

  be responsible for dark matter, was being created within the col-

  lider. Knowing how much energy was missing (and thus the

  energy needed to create such a particle) would allow physicists

  to focus their search and start to pin down its properties. It’s pos-

  sible, though, that the LHC would already have the data that’s

  needed; if the particles sometimes weakly interact with the

  38 How Science iS Done

  detectors then in the morass of previously discarded data should

  be nuggets of gold.* More likely though, if the LHC is producing

  (as we all hope it will!) some truly unexpected physics, the years

  of prior experimental runs will count for nearly nothing. If the

  triggers weren’t set to collect the right type of data—if the evi-

  dence for dark matter interactions or whatever else has been

  thrown out with the junk—then there’s nothing for it than to

  reset the triggers and run the experiment again.

  This isn’t supposed to be a criticism of the LHC. The truth is

  that their data rate is so extreme, and our ability to capture, store, and sort data so puny in the face of such an onslaught, that they

  really have no choice but to throw out much of what is produced.

  They’ve also set triggers that might catch likely dark matter can-

  didates, but I like thinking about CERN’s struggles to do the right

  thing because they make clear the complexity of modern sci-

  ence, and the decisions that we have to confront when dealing

  with large data sets. We are a long way from simple experiments

  with one variable changed each time and into the realms of big

  computation—despite the hype, we have become reliant on big

  data.

  Yet not all responses to overwhelmingly large data sets need

  be so alien. Sometimes, the solution is not to reinvent the pro-

  cess of discovery, but instead to look at what scientists have been

  doing for years. It’s just that with more data, you need more sci-

  entists. And that, dear reader, is where you come in. You, and

  everyone you know.

  * I don’t mean that literally, although when the LHC is not colliding protons it collides lead nuclei, and this has probably produced a residue of gold, albeit not at an economically viable price. It’s still nice for modern physics to have fulfilled the dreams of alchemists through the ages, though.

  2

  THE CROWD AND

  THE COSMOS

  When did humanity become aware of the Universe? Not of

  outer space itself, and not only of the stars that speckle our

  local neighbourhood, but of the whole kit and caboodle, the

  potentially infinite realm that stretches out for billions of light

  years in every direction? You can make a case, I think, that it was

  when we first discovered galaxies, or rather when we found that

  these often enigmatic objects were in fact immense systems of

  hundreds of billions of stars.

  Look at a galaxy through a small telescope, and you won’t see

  any stars. You won’t, in fact, see much of anything, just a misty

  patch of diffuse light. Only when you realize that that light is

  generated by a vast number of stars, each too distant to be

  resolved, does the true distance to these objects become appar-

  ent. They are revealed as what used to be known as ‘island uni-

  verses’, individual travellers separated by vast oceans of empty

&
nbsp; space. A few centuries after being displaced from the centre of

  the Universe by the Copernican revolution, discovering that their

  galaxy, the Milky Way, was nothing special, dealt the denizens of

  Earth another blow to their collective ego.

  40 The Crowd and The Cosmos

  That might be depressing, or the vast scale of the stage on

  which the Universal drama is played out might inspire you. In

  either case, these discoveries were only the start of astronomers’

  attempts to understand the formation and evolution of the galax-

  ies. Our attempts to understand how we ended up with the

  Universe we see around us, and in particular how the galaxies we

  see got to be the way they are, are driving some of the most ambi-

  tious and exciting projects in astronomy. It’s been that way for a

  while, and back in July 2007 I found myself listening to the latest

  arguments at a conference in Piccadilly organized by the Royal

  Astronomical Society.

  I’m not sure what images the mention of a scientific confer-

  ence will conjure up. Maybe a bearded Russian theorist mum-

  bling nearly incomprehensibly at a chalky blackboard? Maybe

  a whole gamut of scruffy academics engaging in hand-waving

  debate about obscure and incomprehensible points? The latter’s

  about right, at least for the conferences I go to. Ignore any

  thoughts about calm and considered discussion; the atmosphere

  is often more febrile than you might imagine, but the rudest of all

  are not those indulging in backbiting and snark, but rather those

  of us who disappear into our laptops, barely conscious of being

  in a lecture hall at all. We’ll have fought for the few seats with

  power sockets, look up from our iDevices only occasionally, and

  will—at larger conferences—know to sit on the edges of vast

  hotel ballrooms so that we can plug in.

  To hide from the speaker and get on with work you could be

  doing at home is rude, and distracting, but I’m as bad, if not

  worse, than most, and on that sunny July morning you’d have

  found me prodding at a laptop, grumpy in the middle of the back

  row in a cramped and already sweltering lecture theatre. It must

  have taken almost two or three slides from the first speaker to set

  my mind wandering and the search for viable Wi-Fi to begin.