Brazil (4) "From a land of monsters to monsters in the sky"

A year or two into my PhD I started to work with colleagues in France. I learned lots from them, scientific and otherwise. In particular I learned the defining features of Scotland, as viewed from the rest of Europe: the Loch Ness Monster, and haunted castles. Nessie didn't surprise me but I hadn't been aware we were particularly haunted. The existence of a dedicated Wikipedia article seems to offer definitive confirmation, however (***FOR THOSE WHO DON'T ACTUALLY KNOW ME: IRONY ALERT!!!***).

I thought again recently of these defining characteristics. In São Paulo I'm a pretty exotic specimen. I thought I should offer a little bit of my exotic self to the city so we discussed a talk for the public, on a Scottish science story I have told often at home: CTR Wilson, the Ben Nevis Observatory and the origins of the study of cosmic rays. Lots of people, apparently, have found my webpages on these topics, come across one of the many appearances of the Cosmic Way roadshow, or heard me give a popular talk on these topics. Thinking of a title that would scream, "Scotland!!!" I mulled over the monster and the castles. I remembered a book I liked by an Italian astronomer, Paolo Maffei, called Monsters in the Sky (a nice book but a bit out of date now). The "monsters" of his title are the exotic objects of modern astrophysics, the black holes and exploding stars that are studied via the X-rays they emit. Some of the pioneers of X-ray astronomy, like Bruno Rossi, started out as cosmic ray scientists and adapted their expertise to this new subject. We know now that these same objects play major roles in the origin of the cosmic rays. Scientifically, we can indeed trace a line from CTR Wilson and the very beginnings of cosmic rays to the study of these outrageous objects, "monstrous" both in scale and in the challenges they present to our everyday ideas of the world. So the theme of "monsters" seemed to tie together all the strands of my talk together: "From a land of monsters to 'monsters in the sky'" was the title of the talk.

If I'd thought just a day or so longer I might have kept "ghosts" too. Wilson's Nobel Prize (still the only Physics Nobel for someone born Scottish) was for the invention of the cloud chamber, the device that brought electrons and ions, "phantoms" of the subatomic world, into the realm of the visible. "Monsters and ghosts: a Scottish tale of fundamental physics" might have been an even better title. Maybe next time.

We all thought this public talk was a nice idea but the timing was not good, there was no big high-profile event to attach it to, and a lot of end-of-teaching-year activities complicated finding a room for it. Anyway there was a nice audience for the talk, many familiar faces but at least one member of the public because I brought her with me. I enjoyed augmenting this familiar tale for a southern hemisphere audience, using MacKinnon tartan, Victorian paintings of highland cows crossing cloudy mountain passes, etc.; generally wallowing in cheesy Scottishness as well as, for instance contrasting the roughly 5 million population of Scotland and the 22(?) million of the São Paulo urban area.

Perhaps this was also a wee subconscious device to start turning my thoughts to home. I have only a few more days here until I swap fejoiada for black pudding, cachaça for whisky, temperatures between 20 and 30°C (not always with clear skies, to be fair, or even dry) for wind, rain, snow and short days. Home to a land of ghosts and monsters.

Brazil (3): A solar physicist takes a taxi ride

On the day I arrived a colleague kindly met me at the airport. On a Tuesday he could not bring his car (traffic congestion control measure) so we took a taxi to my new lodgings. I guess the phrase "South American big city taxi ride" will conjure up a particular, hair-raising image. Stereotypes concocted from a great distance so often turn out to be wrong; not this time. I'm sure we travelled at 60 miles an hour through dense traffic in busy streets. Over and over again we cut in front of other cars at what felt like well after the last possible minute to take some sliproad or junction. Our driver's eye and reflexes were fantastic. We'd have been in ten crashes at home but nobody even tooted their horn. Evidently drivers expect such craziness of each other. I said out loud, "this is exciting".

Here's a São Paulo taxi crossing the Avenida Higienópolis not far from Mackenzie University. The camera has frozen it but I expect it was travelling at high speed and dodging from lane to lane. I actually took this photo because I like the name, "Higienópolis". It also applies to the whole area: "hygiene town" and reflects how nice and clean it was, compared to Downtown, when they started expanding the city in this direction. It's still appropriate.

Much later it struck me that the taxi is a nice metaphor for some of the science that triggered my visit. The gas of the Sun's atmosphere is sitting quietly, atoms moving around randomly in all directions, with a range of speeds but none of them going too much above the average speed. Then from somewhere above them comes an electron or an ion at enormous speed, like one of those São Paulo taxis heading from the airport into the city centre. Unlike the taxis it has no skilful driver, only speed, and it just crashes into all the rest of the traffic, sending them flying in all directions with much greater speeds than they had before; heating them up and making them glow in various ways. Exactly why they glow holds our detailed attention. But of course we'd really like to know, "who ordered the taxi?" And why was it moving so quickly?

If a taxi crashes into a car all that happens is car and taxi get mangled and some fragments go flying off in all directions. When we look more closely at the collisions in the Sun's atmosphere things get a bit stranger. Most of the time no actual damage is done. A very fast-moving proton crashes into a slow-moving proton. Afterwards the slow-moving one is going faster than before, because it's had a big dunt, but both protons are still protons. No lumps are knocked off them, both are still intact. But if the incoming proton is going fast enough, things get weirder, a bit like a surreal, Looney Tunes version of such a car-crash. The two protons crash into each other, there's a bit of a blur, but afterwards, different stuff comes out and moves off. It's as though the taxi crashed into the car and then, afterwards, the car shot off in a new direction and not just the original but two new taxis also get spat out the far end of the collision, only different sizes and maybe colours from the original (protons don't have a "colour". But in the "Big book of science" type books I read as a kid they were always drawn as little red billiard balls, red for positive electric charge. Electrons were blue (negative) and neutrons were green.)

Let's stick with the taxi metaphor. A fast red taxi crashes into an identical, slow-moving red car. Afterwards we'd expect a red taxi and a red car to come shooting out of this collision. Instead we get a red taxi, a green car and a funny wee yellow, sort of half-size taxi. Before our eyes, the funny new car travels a short distance then changes into something else different again.

The taxi metaphor's running out of steam. Here's what happens: accelerated to very high energy by an uncertain process, a proton collides with another proton. After the collision some of the energy of the proton has been transformed into a new particle, called a pion. After about one hundred millionth of a second the pion changes into a different, less massive particle called a muon, and finally the muon decays and spawns an electron or a positron (the antimatter counterpart of the electron). The electron or positron emits gamma-rays (like X-rays only even more penetrating) which we detect with instruments above the Earth's atmosphere on satellites. Once we detect those gamma-rays we can follow this sequence of events backwards to learn about the protons that were accelerated in the first place.

My colleagues here in Brazil lead the world at observing very short wavelength radio waves from the Sun. Recently they've begun to explore the wavelengths between radio and infra-red, what is called Terahertz radiation. This is a frontier and they have made some discoveries that we don't completely understand yet. The stories I've described above might be part of understanding Terahertz radiation in solar flares and that's a big part of why I'm in Brazil.

Since arriving I've had other taxi rides that were not nearly as exciting as that first one. Was the driver thinking of proton-proton collisions and pions? That question will probably go unanswered but we can be more optimistic about the reasons that solar flares glow in Terahertz radiation.

Brazil (2)

When everything is different you're much more likely to experience those moments when you wake up to something you've been taking for granted, that has become part of life, that you stopped thinking about a long time ago. I've used Sao Paulo's excellent Metro system a couple of times now but it will take me some time to switch off that "what the hell" moment of irritation, when you don't get your ticket back. It's such a trivial thing, knowing that the barriers for the trains and the underground at home give you back your ticket, and you should keep it until you leave the train system through another barrier. When did any of us last give it a thought? But it's obviously more deeply engrained than I'd realised because I don't like it when it doesn't happen here.

It's not just the being away that's good, it's coming home again more awake.