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Thursday, January 28, 2010

Mother, do you think they'll drop the Bomb?

I thought in this post I would touch on science and morality by means of the Manhattan Project.

The picture at the head of the page is of the very early stages of an atomic bomb going off. The roughly spherical fireball is approximately 20 metres across at this point. It was taken using a "rapatronic" camera, invented by Harold Egerton for just this purpose.  The exposure time for this camera can be as short as 1/500,000th of a second (2 microseconds). Cameras were fired sequentially at periods less than 1/1000th of a second (1 millisecond) after detonation, to produce a sequence of images of which this is just one. The camera is triggered by a photocell, which picks up the x-ray flash as the bomb goes off, and a delay circuit. The shutter contains no moving parts, it is a "Kerr cell" placed between two polarizers arranged such that they let through no light. When a current flows through the Kerr cell the polarisation of light is rotated and so can make it through both polarizers - no current and no light gets through. This is all done electronically so can happen really fast.

The bomb was detonated on a gantry tower supported by guy wires, the bright spikes beneath the round explosion are known as "rope tricks", they are where the metal guy wires have been vapourized by the light from the initial detonation. If you cover the guy wires in aluminium foil the rope tricks disappear because the light is reflected, paint them black and the spikes appear larger because more light is absorbed. The distorted shape of the fireball is a relic of irregularities in the bomb casing, and the small shed at the top of the gantry tower in which the bomb is placed.

To me the story of the making of the atomic bomb is fascinating and exciting. In the period of a few years from 1939-1945 methods were found to extract scarce isotopes of uranium in kilogram quantities; manufacture plutonium; the fundamental radioactive properties of the substance were discovered; calculations were done to work exactly how much uranium you needed for a bang, how quickly you had to get it together and the whole thing converted into a working device that could be carried in an aeroplane. And they did a lot of this work twice, since the bombs dropped on Hiroshima and Nagasaki are quite different in design.The story about the rapatronic camera shutter is just a relatively little-known footnote to the whole endeavour.

The Manhattan Project was served by a considerable number of scientists, including twenty Nobel Prize winners, amongst a staff of around 130,000. These scientists represent a large fraction of the most renowned scientists of the period. I think I can imagine how I would have felt to working on the bomb, I would have been keen to be part of the war effort, I'd have been thrilled by the intellectual firepower of my colleagues, I'd have been excited by the technical challenge of actually making a real thing.

And then there was the Trinity test firing, I think at this point I would have become really aware of the enormity of what I had been involved in. J. Robert Oppenheimer, who directed the Los Alamos site where the bomb was constructed, later said he thought of this line from the Bhagavad Gita:
Now I am become Death, the destroyer of worlds
Which always struck me as being a bit pretentious, but maybe that's a result of my ignorance. Whilst Kenneth Bainbridge, the director for the Trinity test, is reported to have said:
Now we are all sons of bitches
Which strikes me as a rather more plausible response. I have to say, with a little embarrassment, that I would have been thrilled by the size of the bang I had made.

Less than a month after the Trinity test an untried version of the atomic bomb was dropped on Hiroshima, instantly killing 80,000 people; then a few days later a second bomb, identical to the Trinity test bomb, was dropped on Nagasaki killing another 40,000. Subsequently many more people died of their injuries.

I'm not sure how I would have felt at this point I think I would have been a bit shocked, I struggle to conceive of that many people dying. The world was at war so I would have been familiar with the idea of people dying in, for example, the air raids in the UK. So maybe I would have thought this was justifiable, that the war against Japan couldn't have been won in any other way or at least any other way would have led to just as many deaths. Maybe it would have been clear to me at the time that the atomic bomb was as much about the Soviet Union as it was about the war with Japan.

After the war many scientists returned to normal life. Some didn't, Edward Teller enthusiastically promoted the thermonuclear bombs for just about any application imaginable. Joseph Rotblat left the Manhattan Project before the bomb was dropped, and whilst continuing scientific work, he helped found, and run, the Pugwash Organisation and spent the rest of his life campaigning for peaceful conflict resolution.

Do scientists have a special moral responsibility? They certainly took the initiative in terms of highlighting the potential of an atomic bomb before the war, but actually making the bomb and deploying it took far more than just a few scientists. As to the morality of killing people in war, then I don't think scientists can claim any special moral insight here.

Finishing in this way seems a bit trite, and it feels in some ways an abdication of responsibility. I think the point I'm trying to make is that scientists are just people, and we bear the same moral responsibilities as anyone else. The only difference is that scientists have the potential to open up new moral questions: "Is it more wrong to kill 100,000 people with one bomb, as opposed to many bombs?". Maybe we have the ability to close old moral questions through evidence.

Saturday, January 23, 2010

Caverns measureless to man

I thought this week I would talk about conferences, since they are something that is very much part of life as a scientist and which are perhaps are a little alien to people.

My first scientific conference was in Durham, where I did my PhD, I took the opportunity to find accommodation in the town before I moved up from Bristol. There was a problem with this: the conference supplied us all with name badges on which we were to write our names in our own fair hand. I was sitting opposite to an elderly academic at lunch who felt my name was somewhat small and indistinct. So I re-wrote it in large capitals with my biro, going over the letters repeatedly to get a "bold" effect. Now my handwriting isn't great at the best of times, doing large-size capitals freehand has the look of the scrawling on the lunatic asylum walls. Later I went off looking at rooms in houses, but felt I was getting funny looks when I asked for directions. Later I realised why: not only did I still have my lunatic-asylum name badge on, I had it on upside down!

In many ways that first conference set the pattern for future ones, accommodation was primitive: in Durham Castle, which is used as student accommodation during term time. I met an old chap who, on hearing what I was doing swore blind he had done it all 10 years ago (I checked, he hadn't, they never have). I learnt interesting things from esteemed academics in the bar.

For most the price of attending a conference is to present a poster, or a talk. This means I am accustomed to public speaking, just an odd sort of public speaking. In fact when I've had to speak at weddings, I've felt the lack of an overhead projector and had to resist the temptation to "thank the organisers for inviting me", this is nearly appropriate but needs rephrasing. Conferences have also given me ninja buffet skills, and an appreciation that if you march off confidently in any direction (in my case in search of lunch), then quite a few people will follow you for no better reason than it looks like you know what you're doing.

I'm not sure how widespread the idea of a poster presentation is outside of science, the idea is you convert your most recent work into.... a poster, a jumble of text boxes, figures and graphs (see below). If you're flash, and organised, you print it out as a single sheet on laminated paper at some central service and then carry it around in a special tube. Otherwise you print it out on a load of A3 sheets. Posters are typically viewed in an over-crowded hall whilst drinking warmish white wine and eating finger food, text on the posters is normally too small and you're too far away - the combination of these things always gave me a splitting headache. Supervisors attempt to get their students to defend their posters, that's to say chat to anyone who wanders up.

Conferences are where you learn all the interesting stuff that people don't write down, like how it took some poor PhD. student months to get an experiment to work once and they've never quite managed it again, or how a little fix is required to get a numerical simulation to work. You also learn lore from the more senior members of the community: how X has been doing Y or small variants thereof for the last 20 years. How Z has been wrong for all of living memory. How W, although publishes great work is not a very nice man. You may get some idea of what someone's master plan is (you're certainly not going to get it from journal articles), you'll get to appreciate that other academic groups work in radically different ways. I also learnt that science transcends barriers of language and culture, the scientists I meet on tour are my tribe, my closest relatives beyond my real family.

All these conferences mean I've done a fair amount of travelling, personally I don't consider this a great benefit. Business travel rarely gives you much time for sightseeing and the places you end up there may not be sights to see, and if there were I'd much prefer to go with my wife rather than a random collection of other scientists. I've visited Rhode Island, Boston, Sante Fe, Heidelberg, Sitges, Akron (Ohio), Philadelphia, Cancun and numerous towns around the UK. The only upsides of Cancun were the tropical fish just off the shore, the ever present iguanas and the Mayan ruins, otherwise it's an overpriced tourist hell-hole.

The best conferences I've been to have been the smaller ones, the invitation only ones, the ones where discussion is programmed into the schedule, the specialist meetings for young academics. The larger conferences tend to be soulless and confusing: which of the 10 parallel sessions should I attend? And is it physically possible to switch sessions? There is a fine conference in the UK for the polymer community, which used to be based near Moretonhampstead, but now lives in Pott Shrigley. The presence of the golf courses is significant here, the organisers liked their golf so we had a morning session, an evening session and an afternoon off for golf. The non-golf players went off for walks in the country, which was a fine bonding experience. I remember distinctly my future postdoc supervisor standing on a tussock in the middle of boggy ground suggesting to the rest of the group that we proceed no further. It turns out being a Fellow of the Royal Society does not guarantee good navigation skills!

Is there still a need for conferences, in these days of electronic communication? Although the prospects for online networking via various social media are great, currently uptake by scientists is pretty low in percentage terms and the bandwidth of the communication is low. The amount you learn about a person from just one face-to-face meeting is enormous compared to what you get through electronic media; electronic media are great as an introduction and for maintaining contact but there's nothing like meeting people.

The "caverns measureless to man" title is in homage to the SIGGRAPH conference I attended in Boston, there were somewhere in the region of 20,000 delegates. It was held in the vast Boston Convention and Exhibition Center.

Sunday, January 17, 2010

We are the angry mob

Once again it feels like I'm accused being a member of an angry mob of twitterers. This time by Catherine Bennett in The Observer, over the censure of Rod Liddle, stimulated by his potential appointment as editor of The Independent. As far as I can tell Rod Liddle is a rather unpleasant individual both in terms of his personal treatment of those close to him and in his public writing, actually looking down the first page of his Spectator articles I would appear to agree with him approximately 10% of the time.

Catherine Bennett raised this as an issue of free speech, implying that we are attempting to remove Rod Liddle's right to free speech and also the rights of those such as Jan Moir, whilst going easy on Islam4UK. As an articulate member of a mob, I'd like to say this is really not what I want to do. To my mind Rod Liddle, Islam4UK and the BNP should all have a right to let their views be known, I just don't believe they have a right to express that freedom anywhere or any time. However, the corollary of this is that I believe that I also have the right to point out that what they say is stupid, unpleasant and wrong. When given a public platform the BNP and Islam4UK seem to do a pretty good job at making themselves look risible, remove that platform and you risk people imagining that they are eloquent and right  for lack of any evidence to the contrary.

The intriguing question with people like Jan Moir and Rod Liddle is that they have liberal backgrounds of a sort, they are clearly pretty smart. So when they write something that sounds illiberal, offensive and pandering to the basest of instincts are they simply being "radical for pay"? Do they really believe what they write, or do they just write what they know will go down well with their employers and their readers, happy in the knowledge that all publicity is good publicity. Writing a blog brings these questions to the fore, because it's very obvious how frequently a post is read (or at least looked at). Should I write something worthy, but dull to most people and get a few hits or something that people are impassioned about which will get many hits and mentions?

What is it I want from complaint? In a way I want to shout that someone is wrong on an equal footing, I want access to the means of production (okay dissemination, but you have to turn a phrase when you can). In the past the right to provide public comment was a special privilege, available to the few who had a newspaper column or similar. What I have written here contains no more or less research than the Observer piece, I'd humbly suggest that my opinion is of equal value to Catherine Bennett's. I am happy to accept that her writing is somewhat superior to mine. Is this the message for mainstream media? Ill-informed rant is no longer viable, because anyone can do that - genuine insight, research, knowledge and good writing are valuable because they are hard.

Saturday, January 16, 2010

Follow Friday - a post for twitterers...

There is a tradition on Twitter, called Follow Friday in which, of a Friday, you mention people you follow who you think other people would be interested to follow. For me this is a cause of social stress for fear of forgetting someone I should remember, so I thought I'd try doing it in my own way. You can see all the people I follow here, and the people that mention me are here (I think you might need to login to twitter to follow those links).

And here, in alphabetical order to avoid accusations of favouritism, are my micro-biographies of people you should follow:

@alexconnor is an astrophysicist who now works on policy at the Institute of Physics. He shows his weekend DIY exploits to great acclaim.

@Allochthonous is a geologist, he writes the Highly Allochthonous blog. I mis-pronounce is name "allo-kan-thus", I believe it's a habit I cannot break.

@andromedababe Observer of shagging frogs, lover of shoosies. Blogs at AndromedaBabe's Blog on teaching and other stuff.

@BarbaraMaller a closet writer and chatter from California.

@BillyGottaJob originally @BillyNoJob took us on a journey at his now named At Long Last I've Got A Job blog.

@Carmenego is a very cheerful musical lady from old London town, who blogs skeptically at Carmen Gets Around (II)

@ChristineOttery a journalist, doing an MA in science journalism, her blog is Open Minds and Parachutes but she is also published in proper media like the Guardian's Comment is Free.

@Crafthole is a archeologist / historian person engaged married to @ladycrafthole. We share an interested in the scientists of the 18th and 19th centuries

@DaintyBallerina historian, and writer of the Fragments blog, is often the first with a #wine hashtag.

@DanielFurrUK is a libertarian Liberal Democrat, who blogs at

@deborahshelton is an interior designer, see here. She hangs around with the historians.

@doyle2718 - it's me mate from work: Doylie! The only one on twitter, the rest just think I'm odd...

@dr_andy_russell is an atmospheric physicist at Manchester University. Writes a blog. Handy for a knowledgeable opinion on climate change.

@DrEvanHarris is former LibDem MP for Oxford West and Abingdon, and was the party's Science spokesman. He joined twitter recently and immediately gained a massive following of nerds and geeks, he uses twitter like a pro and is responsive to queries. His website is here.

@Drop4three an enigma I have yet to crack, he blogs at dropped

@Duddy an author of several novels of a scientific bent, and Cestrian and Keeper of Snails blog. She has retired from Twitter, but the blog is still well worth visiting

@Essiefox a historian and the writer of the Virtual Victorian blog, we seem to share a taste in music.

@FyreFlye a chatty lady, who I always associate with the big sunflower in her avatar.

@Gelada is a mathematician and makes pretty sculptures with maths, his blog is Maxwell's Demon.

@GentlemanAdmn a gentleman and an administrator, he writes an eponymous history blog.

@graemearcher is a statistician and a relatively unpolitical politician who writes an occasional blog post on Conservative Home. He likes swimming, cats and Mr Keith.

@hangbitch always happy with an acerbic comment. She has a blog at Hang Bitch.

@HappyMouffetard is my wife, so I must mention her. Cruelly deprived of twitter at work, when she can she tweets on nature and gardening. Curator of The Inelegant Gardener

@iknowhim I always think of as mysterious, a cause de her avatar. She has a blog, Last Tango in Dulwich. And her twitter background is a very fine, if not sensible, shoe.

@Jackpot73 another friendly soul of the interwebs, who has been sharing my sense of humour, which may or may not be a good idea ;-)

@jme_c is many things including college lecturer at Somerville and MSc Science Communicator at Imperial College, he is suffering geek-envy for my HTC Desire. His website is here.

@jordancdarwin is a fellow code monkey, these things are important. He is also an enthusiastic atheist, as you can tell from his website.

@KateKatV is @PaoloViscardi's mum! I know this is an impolite way to introduce someone, she also has a blog here.

@laales is a split between Hong Kong and Dorset (which is where I come from), she is a member of the historical faction.

@LadyCrafthole is a photographer who blogs at Lady Crafthole's Blog. She makes little planet photos.

@lahossner is most mysterious, I believe she is a fan of books.

@langtry_girl was best able to finish the sentence: "Understanding the Periodic Table is very much like making love to a beautiful woman..." is an economist, so nearly a scientist ;-)

@Lesanto is a social media consultant with a difference, speak to him and he'll speak back: he tries interesting things on twitter. His company is media140.

@localbuilderuk Lover of snowboarding and wine, of which I approve - not so sure about the golf ;-)

@louwiseman joins me from the gardening faction, she seems obsessed with insects at the moment.

@LucyInglis historian and writer of the awarding winning Georgian London blog, she attracts the strangest blog search terms and seems to like cricket, or possibly cricketers...

@Margit11 was living in Edinburgh but is now living in Munich. Blogs at Intercultural Musings, on being a foreigner in the UK but things will change.

@markgfh science editor of the Times, and fellow science-politics geek.

@MarkReckons is a fellow LibDem, and political blogger - you can find him here. A moderate in all things.

@masticatingmanx is a fan of food, no indication as to how this has affected waist-line but his blog looks pretty healthy. An inhabitant of the Isle of Man, which I have only seen as a distant shadow.

@MentalIndigest a macho biologist, proud of his snowsocks, my main competition in the race to identify the Friday Mystery Object (see below). He writes the Mental Indigestion blog

@Morphosaurus a teacher who was able to recognise tunicates from my inept description, keeper of Bastard the Cycad and author of multiple blogs.

@nemski is that rare creature: the American Liberal he comes from just down the road from Malvern (Mrs SomeBeans comes from the UK version). Various sciencey tweets.

@Nora_Lumiere is an animator and writer, and a friend of food. She blogs at Animated Writing, where she has been kind enough to invite me over as a guest blogger.

@opheliacat a member of the historical faction, she is our woman in New York.

@PaoloViscardi biologist and proper curator at a museum. Also master of the Friday Mystery Object, on his blog Zygoma, which provides me with much distraction.

@PatrickBaty and @PapersPaints are one and the same, analyser of historic paints and one-time instructor of tank drivers. He blogs at News from Colourman, he's been on the TV but was upstaged by his cat, Caspar.

@philipmcdermott is a research associate and software engineer. He blogs at

@Quackwriter author of Kill-Grief and alumni of the Wirral, curator of the Quack Doctor blog, which reports on the wacky medical adverts of the past.

@rebekahthornton is local. She sometimes has a mathematical air about her and is fond of darts.

@ripplestone is from the gardening tendency, although her name makes me think of geology. She blogs at Ripplestone Review.

@robajackson chemistry lecturer, card-carrying red, and trombone player. He blogs on chemistry and politics.

@rosamundi I associate with a pair of purple shoes, which she used as an avatar for a long time. She is a lady of mystery, and is often found with the historians.

@rose_darling Writer. Editor. Poet. Dreamer. Music lover. Conversationalist. Gastronaut. Traveller. I love it when people write their own biographies! She has a blog here, which I don't think she pimps enough!

@sallybercow  I started following all sorts of people for the election. Sally, self described #1950shousewifebot with a familiar surname is by far the most fun

@Samiahurst Doctor, teacher, blogger, and sometimes apprentice chocolate maker.

@sarahsiddons seems to come to me from the historical faction, curator of the Weird, Ordinary, Wonderful blog.

@Schroedinger99 is a fellow skeptic, how did I manage not to add him sooner? He has a blog at Bad Reason.

@Sciorama a scientist I know from some time ago, a biological physicist with very red hair.

@Scisu interested in things sciencey, she blogs for BioData.

@smithatcity is a doctor and a Science Communicator in training at Imperial College, she blogs at in bed with medicine.

@Stephen_Curry a fellow scientist, who scatters x-rays from crystals. He blogs at Reciprocal Space.

@stephenemoss a biological scientist, his work was on the BBC website recently. We hang around together at virtual science policy gatherings. He blogs at a little bit at The Mad Professor.

@Steve_P_Knight is the king of lasers. I think we must have met over something sciencey, but I can't remember what!

@TiggerTherese is of the gardening tendency, her bio mentions being an ex-banker - but she doesn't like to talk about it.

@thecredo I think may have escaped from The Thick of It. Originally the owner a mad old bearded-man avatar, this is how I will always see him.

@ThetisMercurio is in her own words rationalist, humanist, satirical... Staunch opponent of Steiner-Waldorf schools, the homoeopathy of education.

...and now I find I have shifted my social stress to a different sphere. My plan is to keep updating this post, if you spot any factual errors, find my biography offensive, or feel left out then please let me know.

Added Saturday (16/1/10): @scisu @Stephen_Curry, @Sciorama, @Samiahurst, @Quackwriter, @PatrickBaty, @paperspaints, @PaoloViscardi, @Nora_lumiere, @morphosaurus, @mentalindigest, @lucyinglis, @lesanto, @jackpot73, @happymouffetard, @GentlemanAdmn, @Gelada, @FyreFlye, @duddy, @daintyballerina, @ChristineOttery, @Carmenego, @BillyGottaJob, @BarbaraMaller

Added Friday (22/1/10): @AlexConnor, @Allochthonous, @GraemeArcher, @Rosamundi, @StephenEMoss
Added Friday (29/1/10): @opheliacat, @ThetisMercurio, @rebekahthornton, @LadyCrafthole
Added Friday (5/2/10): @dr_andy_russell
Added Friday (26/2/10): @crafthole
Added Friday (6/4/10): @jme_c, @MarkReckons, @TiggerTherese, @smithatcity, @DrEvanHarris
Added Friday (30/4/10): @hangbitch @nemski @louwiseman @sarahsiddons
Added Friday (7/5/10): @sallybercow @jordancdarwin @rose_darling @markgfh, @Schroedinger99
Added Friday (5/6/10): @laales, @KateKatV, @iknowhim, @doyle2718
Added Friday (30/7/10): @masticatingmanx, @robajackson, @deborahshelton, @lahossner
Added Friday (27/8/10): @ripplestone, @Steve_P_Knight, @Margit11, @langtry_girl
Added Friday (3/9/10): @andromedababe @thecredo @localbuilderuk
Added Friday (17/9/10): @philipmcdermott

Thursday, January 14, 2010

Making Science and Engineering a Policy Issue

This is a post on the debate organised by the Campaign for Science and Engineering in the UK featuring the science spokesmen of the Conservatives (Adam Afriyie), Labour (Lord Drayson) and Liberal Democrat (Evan Harris) parties. The debate was structured around pre-selected questions presented to the panel. It was chaired by Roger Highfield, editor of New Scientist and hosted at the Institute of Engineering and Technology.

Lord Drayson benefited from not being on the end of another sustained assault regarding the Science and Technology Facilities Council funding difficulties which have been a centrepiece of most of his recent public outings in this type of forum. The consensus seemed to be that outside problems with the STFC, science and technology had done quite well under Labour. The concerns over impact, which I discussed in a previous post made a showing, my view is that Impact is important but so is the way you measure and use it and the current ideas don't seem to be going in the right direction. Lord Drayson was able to make a fair defence of recent government policy over stimulus which focuses on the shorter term when compared to stimulus packages in other countries, but he seemed shaky over how cuts in the higher education budget would be achieved.

Adam Afriyie suffered from the disadvantage of being in a party who seem to have consciously steered themselves away from concrete policy statements, spending a lot of time criticising the government but unable to enunciate much clear policy of their own. Concrete policies included a deferment of the REF Impact statements for 2 years (announced this morning), and the waiving of student debts for those going on to teach science. The statement that the "zeitgeist" of David Cameron would lead to increased charitable giving to the medical was met with the online equivalent of wry laughter, as a policy this seems particularly empty. The enthusiastic support of Chris Grayling (Tory shadow home secretary) for the sacking of Professor Nutt and his own rather confused position on the hiring and firing of scientific advisors, did not go down well.

Evan Harris, described in the Daily Mail as "Dr Death", seemed to do particularly well, he may well have known that the audience was broadly on his side, as a party not in power the Liberal Democrats have not had the opportunity to wind up the science and technology community through the routine decisions of government. Furthermore academic scientists at least could well be described as "broadly lefty". However when engaged in the politic-ing which was inevitable when bringing together politicians in the run up to a general election, he did appear to apply his own twist rather than an obvious parroting of the party line. On the policy front: the Liberal Democrat conference recently approved an amendment, which puts meat on more general mutterings that "something must be done" about libel reform. He also highlighted, as a policy, that money used in the recently rescinded cut in VAT could have gone more usefully into a scientific stimulus package.

All of the spokesman were clear on the importance of science in both policy decisions and in economic terms, and they all seemed keen to make both politicians and civil service scientifically literate.

I believe the existence of this debate is welcome, I don't recall it happening in the run up to previous elections. To my mind the relatively new technology of a webcast supplemented by background twitter feed (on the #scidebate hashtag), really helps facilitate this debate, particularly in a. The larger question is how do we make science an issue for the wider voting public, given it's significant policy and economic impact.

It seems inevitable that the next few years will involve some pain in the science and technology sector, as it has across most areas of government. None of the speakers gave any indication that science and technology will receive special treatment over the next few years.

Saturday, January 09, 2010

The science of Shrek

A lot of science goes into making a computer animations like Shrek or effects-heavy feature films, such as the remake of The Poseidon Adventure or Pirates of the Caribbean.

This science is something I'm interested in these days: Why does skin look like skin, hair look like hair and fabric look like fabric? There is a traditional physics approach to this which involves measuring stuff with complicated looking equipment and drawing graphs. This is part of the job, but another important component is the work of people interested in photorealistic computer graphics.

If you think computer graphics is all computer games and obvious stuff like Shrek, then check out Autodesk's Fake or Foto test. Good photorealistic computer graphics are really good these days. Update: Actually, just watch this, full-screen.

There are three steps to making an image, or an animation, using photorealistic computer graphics:

Firstly, make a model of the scene in the computer, this should include the location and type of camera and lights as wells as the shape of objects in the scene. The shape is defined in terms of a "polygon mesh", this is basically a fishing net in the shape of the thing you're interested in. Usually "polygon" means triangle in this context. If you're doing an animation then you can automate some of the scene generation by running physical simulations of objects in the scene. That's to say, if you want a bouncing ball, you don't have to make a set of scenes by hand with each scene showing the ball in a slightly different location - you can do this automatically. There is academic research here because efficiently simulating the motion of more complicated things like liquids, or 3601 plastic chairs, is really hard.

Secondly, give the objects in the scene optical properties like colour, transparency, shininess etc. A key feature of the optical properties is the way a material reflects light. This is the difference between a piece of chalk and a mirror, both reflect pretty much all the light that falls on them but if you shine a spotlight on a piece of chalk then that light ends up all over the place, whilst with a mirror the light all leaves in one direction. There is an interesting compromise to be made here, chalk scatters light as it does because of its rough surface. Now this can either be handled by making a very detailed model of that surface roughness (lots of triangles) and then treat each triangle as a little mirror, or I can make a very simple model of the surface and just say "If light hits here it can be scattered anywhere". This is another area of academic research: how do I efficiently model a complicated material like fabric, because I really don't want to put in every single fibre in a piece of fabric?

Thirdly, simulate light in the scene: make light come out of the lights and follow it as it bounces through the scene (if it doesn't hit a camera at the end of it's journey, it doesn't count!). This final stage is known as 'rendering' or ray tracing. Ray tracing because in this model the photons travel in straight lines, "rays", between collisions with objects in the scene. This is a laborious process, at best a photon (a little bit of light) can contribute a fraction of one pixel in the final image and worse, when you fire the photon out of your virtual light you don't know whether it will even hit the virtual camera (which is the only way you're going to see it). Repeat the firing of photons out of the lights in all different directions, many times in order to build up an image, the more photons you fire the sharper, less noisy your final image will look. In order to build up a reasonable size, reasonable quality image you will need millions of virtual photons. For photorealistic rendering it can take hours to render a single image. There is academic research in trying to do this more efficiently.

Skin is another tricky material to model, the problem is that it's a little bit transparent: if you simply bounce light off the surface it ends up looking a bit odd. However, if you let light leak into the skin a bit, then things look much better:

The trick is to do this in a computationally efficient way, in fact this work won the Oscar for Technical Merit 2003 and ended up being used on Gollum in Lord of the Rings.

I went to a presentation, at SIGGRAPH (an enormous computer graphics conference) on the special effects for The Poseidon Adventure. The fluid dynamics simulation in this film are fantastic, when the ship sinks waves sloosh around impressively, but it looks a bit odd towards the end. It turns out this is because in the simulation they turned down gravity to make the waves bigger, and then hand paint on a splash right at end, as the Poseidon sinks below the waters. In the end this science serves what is ultimately an artistic, and a commercial, endeavour.

You can play with this sort of stuff for free, Blender is a very fine open source 3D design program used to build scenes (interface takes some getting used to) and luxrender is a physically based render, it's based on the code described in the book: Physically-based rendering.

p.s. If you what to know how donkeys can talk, I don't know.

Saturday, January 02, 2010

SomeBeans' feeling for snow

As you may have gathered from the header for my blog and my profile picture, I'm rather fond of snow. Although this love has been with me for many years, it was science which got me into skiing: science is very international, and a couple of my students grew up close to the Alps and naturally went skiing every winter. This was the spur that sent me and The Inelegant Gardener on our first skiing holiday, in the Austrian village of Westendorf. After a week of being too hot, too cold, too much in pain, too scared: in the car back from the airport we swore we wouldn't book a second holiday for at least a week, we lasted three days before booking the next trip!

Why is it so addictive? Perhaps it's the massive amount of light you get from a blue sky and a white ground at a time of winter's deepest darkness, perhaps it's the gorgeous scenery made magical by snow, perhaps it's the feeling of moving at speed with little effort, or the feeling of powdery snow piling up to your knees as you glide, with your skis submerged, through fresh snow.

Between looking at the spectacular views, eating the goulash soup in the toasty mountain restaurants, gliding down the mountain with grace and elegance and the moments of panic when discovering you are on a piste somewhat beyond your ability, there is much of scientific interest to be found on the mountains.

To start with there are snowflakes, lots of snowflakes:

Growing up in England, I'd never really believed that snowflakes had six-fold symmetry - English snow seems to come in big puffy flakes or rain. Actually to demonstrate the point, we have just been subjected to a fall of little icy pellets. Whilst skiing I was exposed to proper perfect snowflakes which I watched settling on my coat arm as I trundled up a slow chairlift. The difference is all down to how cold the air is and how much water vapour there is in it, this is shown in the snowflake shape diagram here. Actually, this simplifies things a little: the diagram shows what you get when you make snow in the laboratory under carefully controlled, fixed conditions. In real life a snowflake will experience a range of conditions as it falls to earth, which will all contribute to the shape it's in when it lands. In England this means 'an irregular blob', in the Alps it means 'pretty snowflake'. You can find out much more about snowflakes on Kenneth G. Libbrecht's website.

There are also sundogs, I've seen these a couple of times on days when there is diamond dust in the air:

Sundogs are the short arcs of light either side of the sun. These form under certain atmospheric conditions, bloody cold ones in my experience, the air is filled with tiny thin, hexagonal plates of ice, which drift gently to earth. As they fall they align so that their flat faces are parallel to the ground. They act like little prisms, the little prisms mean that light coming towards you from the sun is thrown out to the side - leaving a gap close to the sun and a bright spot further out. Since they are aligned relative to the ground the sundogs are most obvious either side of the sun (as opposed to a ring all the way around). This is explained in more detail here, along with many other atmospheric optical effects.

Snow also impinges on my own field: the physics of appearance. Consider this: water in a glass is a colourless, transparent liquid; ice (made properly) is similarly transparent, yet clouds (made from tiny water droplets) and snow made from crystals of transparent ice are white. The difference being the microscopic structure of the material. Calculating the details of the reflectivity of snow and clouds is an active area of research for people interested in atmospheric physics, and climate change.

There are so many other things I left out of this post such as wind-sculpted snow, glaciers and the mechanics of skiing itself (although I've found that thinking too much about what I'm attempting to do on skis normally leads to a fall). There is a book dedicated to mechanical aspects of skiing: The Physics of Skiing by David Lind and Scott Sanders.

Ever the keen observer, I have discovered that the hairs in my nostrils freeze when the air temperature is around -10°C, take a deep breathe through your nose: if you get a prickling sensation then it is at, or below, -10°C. I did try snowboarding once, and from this learnt where my coccyx was and just how much it could hurt! And by the power of wikipedia, I discover there is a special name for this hurt: coccydynia.