Ions are the 99%

Remember what you were taught in chemistry at school? It was very exact. Water is solid at 0°C, gas at 100°C, and liquid in between. Metals are solids; oxygen and nitrogen are gases. Gases like oxygen, nitrogen, hydrogen and chlorine are invariably molecules containing two atoms of each element. Atoms like their outer "shells" to be "full" and join up with other atoms to reach this stability. Oxygen is electronegative: it likes to grab electrons. You never hear of an oxygen giving up its electrons to some other type of atom.

But there is nothing universal about this.

These are what, by A level at any rate, we call "standard conditions" - 25°C, Earth's atmospheric pressure, Earth's gravity, and with all the protections of Earth's atmosphere from the violent radiation from space.

Of course, we learn that it's not like that everywhere. The pressure at the bottom of the sea, for instance, is intense - "if you went there, you'd end up the size of a chip," my Chemistry teacher told us when we were about 13. And up at the top of the atmosphere, in the ozone layer, you hear about photodissociation and ultraviolet light (the type that is dangerous if you're out in it too long) snapping ordinary two-atom oxygen molecules in half, leading to each single oxygen atom joining up with a normal two-atom pair to make a three-atom molecule of ozone.

But all this is just on our little planet Earth: a tiny, tiny place in our great Universe.


(The Pale Blue Dot.)

What about on other planets? Well, we know the gas giants, such as Jupiter, are made largely of hydrogen. Jupiter is almost 318 times more massive than Earth, though less dense; and its gravity is gigantic. It is therefore hypothesised that hydrogen in its core is likely to be solid, behaving like a metal. (If you look on the Periodic Table of the elements you'll see that hydrogen, H, actually rests right above lithium, sodium, potassium etc. - due to having one electron in the outermost "shell"; and arrangements in common like this create characteristics in common.)

(Jupiter from NASA/JPL/Cassini's Photojournal. The Great Red Spot is on the right. On the left is a black circle - it's the moon Europa's shadow. It's worth zooming in!)

But Earth and Jupiter are planets. That means they're compact, cold and - in our cases; not in the case of Mercury, for example - there is a protective atmosphere. Off a planet, this stabilising gentleness is gone.

In space, you often get one atom - or fewer - knocking about in every cubic centimetre (it varies, of course, for example whether you're near a star or in a nebula or inside or outside a galaxy, etc. etc. In the meantime, you might enjoy this little bulletin of interstellar medium facts, from a lecture in Ohio). At sea level, the "standard conditions" on Earth, you get 100,00,000,000,000,000,000 or so. Marcus Chown likes to remind us that atoms are so numerous that every breath that you take will contain an atom breathed in by Marilyn Monroe!

This of course makes it pretty easy for molecules to find and bond with each other. In space, to be able to do this is very rare.

Apart from on nice cool compact places like planets, the only places you're likely to find actual molecules are inside nebulae. It wasn't until last August that it was announced that molecular oxygen - the type of oxygen we breathe in - was discovered in space. Molecular hydrogen of course is better known, and carbon monoxide - the same type of carbon monoxide that is poisonous - is a good "tracer". That means that it's easy to find by its spectrum, so astronomers look for it as an indication of what else is going on around the place.

There is, according to the APOD I nicked it from anyway, molecular gas here. It's been able to form molecules because - although even though those dark "pillars", similar to the marvellous "Pillars of Creation", are devastatingly empty and thin compared to what we know - the environment is dense enough to block out a lot of light. ("Light" is a loose term for what stars give out. You've probably heard of ultra-violet radiation damaging your skin. That's the same type of thing as light, but it's a shorter wavelength we can see. Shorter still are X-rays. Hot stars and energetic environments give those out too. Longer include microwaves, infra-red, etc.) This does two things. Firstly, it allows the gas to cool and condense. Secondly, a lot of light in space (electromagnetic radiation) is "ionizing": it knocks the electrons' atoms right off!

99% of atoms in space are ions. Lone electrons, or (as "ion" usually means) a charged nucleus - a proton if it's hydrogen, or a ball of protons and neutrons if it's anything else. Some of these nuclei may retain some of their electrons. This completely changes their properties - they become much more affected by electric and magnetic fields, for example.

Stars are almost all ions - unless they're incredibly cool stars. So is most of the interstellar medium. All that radiation flying around is no match for poor lonely atoms. They might find an electron and combine with it, but chances are it'll be knocked off again before too long.

And this is the norm. The orderly, neutral molecules that make up the Earth we know behave as only 1% of the matter in the Universe behaves. The upper atmosphere is full of ions that bear the brunt of the stronger radiation from the Sun. By having their electrons knocked off, they absorb the energy and let the rest of the planet go relatively unmolested!

This ionization is what we noticed going on when we discovered the "Pea" galaxies: that oxygen, that really electronegative atom that loved electrons, was present and getting two electrons knocked off. (Of course there was a great deal more hydrogen, but oxygen shows up better in the spectrum.) This happens pretty frequently in space, of course, but things were really firing up in those peas!

One of the units I'm studying this semester is called "Astrophysical Plasmas". You'll have heard that matter is a solid, a liquid or a gas. If they taught you much science, you'll have heard of the fourth state: plasma. Plasma, as you've probably guessed by now, is the state of matter when some or all of the atoms' electrons have been torn off, whether by radiation or electricity or intense heat. It behaves like a gas - even in the centres of stars where it is millions of times denser than any environment you get on earth. Most of the Sun is a plasma, as is the solar wind that triggers the Aurora.

You'll have seen gorgeous pictures of the Aurora from the ground, for example this lovely picture from Alaska Photographics - and also this footage of the Aurora in real-time from the Bad Astronomer is breathtaking to watch.

Looking at it from space, you can see that it's going on very high up in the atmosphere . . .

. . . and, in fact, that the Earth's magnetic field direct the charged particles from the solar wind to form rings around the poles (in this case, the South pole - the Aurora Australis).

The Aurora is caused when charged particles strike oxygen and nitrogen in the magnetosphere of the Earth's upper atmosphere. The molecules don't zoom around in those dancing curtains. It's different areas being struck at different times - like the light from a torch moves around when you point the torch in different directions.

What happens is ionization, or excitation of an electron - the same mechanism, but without enough energy to actually kick the electron free! Two charged particles from the Sun strike, say, two nitrogen atoms. One loses its electron altogether - and becomes an ion, one of the "99%". The other's electron gets "excited", into a higher energy state, but doesn't actually lose the electron. Later, the nitrogen ion finds an electron (maybe the one it had before, maybe another) to recombine with. This releases energy in the form of blue light. The other nitrogen atom's electron also falls back into a lower-energy state, releasing red light. (This process is described here.)

The oddness of ions doesn't stop there. Our lecturer gave us the example of a gyroscope: that when you push it forwards, it will move left or right; and charged particles can behave in this counterintuitive way, too. (We write about parallel and perpendicular vectors quite a lot in Astrophysical Plasmas - and, if you don't mind, I'm not going to go into that here, for I may well make a fool of myself.)

I mentioned earlier that the properties change and that magnetic fields have an effect on them. Ions in a magnetic field will gyrate as if they are sliding along a spring: round and round (in opposite ways depending on their charge!), and along, sometimes at right angles to forces acting on them. And sometimes they will reach a point in the magnetic field where they are "mirrored" - it is as if they hit a brick wall and are bounced straight back in the other direction.

And this is what helps create the van Allen belts around our little blue planet.

The van Allen belts, although - like the Earth's upper atmosphere - help protect us from solar radiation, are dangerous areas spacecraft have to watch out for. They are lobes of ions from the solar wind and our own atmosphere that are held in place by the Earth's magnetic fields. Some ions travel along in a banana-shaped object from the North Pole to the South, and vice versa - because when they stray too near the pole, the Earth's magnetic field lines become closer and closer together, and eventually this causes the "mirroring" of the particle - and it will zoom back off in the banana-shaped orbit. It's a bit like a skateboarder on one of those amazing curved platforms in the park, who doesn't go quite fast enough to get to the top and rushes back down again. He speeds up as he reaches the bottom and zooms his way back up the other end - but slows again towards the top. It's a constant motion, like a pendulum; potential and kinetic energy swap places again and again as the particle goes back and forth.

Charges make particles do very strange things.

Mini Spinni: The antics of atoms in space

I'd been wondering about emission spectra for a while. To summarise it, what happens is this: electrons exist in "orbits" round atoms. You can think of these orbits simply, like planets orbiting the Sun, or in a more sophisticated manner, as a "wave of probability" of where the electron will be at any given time. There are fixed orbits for the electrons (imagine Mercury being able to jump into Venus or Earth's orbit, but not to a random place in between), and being struck by a photon can boot an electron up into a higher one. This is an unstable, i.e. higher-than-minium-energy state, so at some point later the electron will fall back down again, re-emitting a photon as it does so.

My dilemma was this: if the electron needs a certain amount of energy to move up one or more orbits, and emits exactly the same amount when it returns to its ground state, shouldn't the two cancel out? I.e. why should we see any absorption and emission spectra at all?

I asked our wonderful Chemistry tutor, Tim, this in Brighton two years ago. He told me to think of it as light travelling in particular directions. In the case of absorption spectra, it absorbed it at a particular angle (the light travelling between the source and your eye via it) and radiated it out in a halo, so you didn't really see the re-emitted radiation. And with emission spectra it's vice versa.

Quite by accident I came across some information about hydrogen in space. The interstellar medium is full of hydrogen. Even in regions of "empty" space, i.e. not clouds, hydrogen is present in individual atoms (HI in astronomy notation; a new language to learn after many years of thinking of that as an H-radical). When the temperature is below 100K, or in a denser region, the atoms form molecular hydrogen, or H2, as we find it on Earth. In hotter regions, with starforming activity, the hydrogen is likely to become ionised. In chemistry terms, it is H+ (+ should be superscript!); in astronomy notation, it is HII, or ionised hydrogen. Ionised means that a photon has hit the electron with enough energy that it has knocked it clean off the atom.

So that's the HII galaxies Tom and the zooites are collecting. Hang on. HII emission lines? Emission lines from a proton all by itself, without the electron to be booted up and down any orbit at all? I don't know why I didn't think of it before, but there you go. I asked in the thread, and mukund vedapudi soon came up with the answer. In short, in regions that are hot enough (the vicinity of massive blue stars you get in bright blue galaxies), hydrogen nuclei (protons) and their electrons are constantly recombining as well as ionising. The recombining releases a characteristic emission line just like the Balmer or Lyman series (when the electron drops down to the second and innermost orbit respectively).

But we also detect hydrogen in space with radio waves. How? Photons which fire electrons up into higher orbits need (to the best of my knowledge) to be more energetic than radio waves. Take this picture, from an article about it.

(Credit: sciencedaily.com - the detection of 5 hydrogen clouds in space.)

You can detect hydrogen in clouds and out. In fact there's a specific way to detect cold (but above 100K) lonely HI atoms, because they emit radio waves of 21cm.

I just found out the way they do this. It's to do with spin. I learned enough about that to establish that the Pauli exclusion principle states that no two electrons can exist in the same orbit with the same spin. They can spin one way or the other. That's why you get the s-orbital in hydrogen, and then another s-orbital and three p-orbitals in lithium to neon in the Periodic Table. Each orbit contains room for 2 electrons, provided they're spinning opposite ways.

I hadn't consciously realised that atomic nuclei have a spin as well. But they do. And in the simplest atom we know, hydrogen, which is just a proton and an electron, it's simple enough to keep track of the spin of each. And just like electrons in orbits, when more than one state is available, the system will prefer the one with the lower energy. That is when the electron and the proton's spin are opposite, not equal.

(Credit: odin.physastro)

In a moderately warm environment, not cold or dense enough for H2 to form, hydrogen atoms can collide, the energy of which knocks them into the state of parallel spins. They will later revert to opposite spins, emitting radiation with a wavelength of 21cm. This allows us not only to detect that there is warm-ish, thin, atomic HI about, but also (using redshift) to measure the radial velocity - i.e. whether it is coming towards us, or heading away.

Why doesn't this work for molecular hydrogen? Basically because molecular hydrogen works quite differently. Both electrons are in a hazy cloud of probability around both protons, and the molecule has a great deal more symmetry. This makes dense hydrogen clouds harder to detect (which is probably why it made the news when 5 were detected in the story above). This is also true of most gases, such as oxygen, in space, because they tend to exist in pairs.

Except, for instance, in the important case of carbon monoxide.

Carbon and oxygen have a different number of protons, neutrons and electrons, which makes them behave differently. Oxygen, for instance, is just dying to grab two electrons to fill up its remaining p-orbitals; we call it "electronegative". (In water it is quite greedy and the electrons spend more overall time around it than around hydrogen, which is why water molecules are dipoles.) This means that carbon monoxide will not have that symmetry which insulates it from our beady eyes.

Carbon monoxide undergoes rotational transitions like atomic hydrogen, HI, so we can detect radio waves from it, at the higher frequencies than HI of 1.3 and 2.6mm. It is relatively common in space. Astronomers believe that it is also found pretty much where hydrogen clouds are, so it's a useful tracer for them. For molecules to form, gas has to be cold. And for a cloud to become dense, it has to be cold. And for stars to form, a cloud has to be dense. Isn't it ironic that star formation can't take place unless the environment around it is cold enough?

That is why radio waves, the longest wavelength of the electromagnetic spectrum and its lowest energy, can forewarn us of some very energetic events in the future. It is because of some of the smallest particles in the Universe altering the way they move around.

Update, 14th May: EigenState on the forum has had a chance to read this post, although I promise I did warn him it might make his hair stand on end. He kindly gave me some great science feedback, well worth a read - he knows a lot more than I do. Here it is.

Book Review: "Copenhagen" by Michael Frayn

I got punched in the throat a few weeks ago. No, not literally, but by a piece of literature: not even a book, but a play by Michael Frayn. Not only that, but I fear I have let myself get drawn into a bitter historical argument. I generally try hard to avoid doing this - I refuse to read "The God Delusion" because I believe such debates are a complete waste of time, changing nobody's opinion and merely causing hurt.

Copenhagen was the occupied capital of Denmark which Werner Heisenberg visited, watched closely by the Gestapo, one night in September 1941 to visit and talk to his old mentor and close friend Niels Bohr. It is the title of a play both historical and scientific, and the most fascinating I have ever read. It is the home of the Niels Bohr Institute, where the Copenhagen Interpretation - the new way of describing atoms, using quantum mechanics - was born, after difficult but exhiliarating years of debates and struggles between physicists all over Europe.

I love the story of those scientists. Most of them were young, and breaking new ground, and they fought to the point of tears and avoiding each other for weeks. They were spaced all over Europe, yet operating closely - "Everyone in and out of each other's departments." "Papers and drafts of papers on every international mail-train." I wish I'd been there! I feel the same way about Galaxy Zoo. I honestly believe we might change the face of science and in the long term science education. But my God I get het up if there's the slightest sign that our standards are at risk.

It was Chris's fault that I ordered a copy of this play. I read it again and again at the time - early November last year. The science was enthralling, as was the story. (I didn't feel a need to watch the play, let alone a film - the dogma that "it is always easier to understand when you see it" has never applied to me.) It took several reads to establish exactly what they were talking about, how much each character knew. Their perspectives keep flipping from past to present to future (or rather, from the 1920's to 1941 to after the war, since, in the play, they are "all of us dead and gone"), which was an added brain-teaser until I knew all the steps. It was like having to learn a piano piece or a dance back to front before I could start appreciating the finer points.

Anyway, I picked it up again somewhat absent-mindedly a couple of weeks ago. And again I was reading it over and over. Until suddenly one evening it was like being punched in the throat because what happened was so terribly sad. As a teenager, Heisenberg had had a terrifying time towards the end of the war. Aged 20, his university supervisor took him along to hear Niels Bohr speak, which was a thrilling event. "The war had been over for four years, but we were still lepers . . . in Germany we worshipped you. Because you held out your hand to us." Heisenberg challenged the mathematics Bohr was using, and Bohr came to meet him afterwards. It was the start of a seventeen-year friendship; Heisenberg was almost adopted into Bohr's family. "In the whole history of physics no two men were ever closer," wrote Thomas Powers many years later.

But in 1939 there was war again, and soon Denmark was invaded. Bohr and Heisenberg were both patriots and on opposite sides. Worse, Bohr's mother was Jewish, and in 1943 he had to escape being rounded up by crawling down the beach on his hands and knees in the dead of the night to be smuggled away on a sailboat.

"Copenhagen" looks back on an intriguing, eternally confusing event that took place in 1941: Heisenberg visited Bohr and clearly told him that Germany was working on a nuclear project. But afterwards, the two could not agree on what had been said, or even where. Heisenberg was depressed afterwards, and Bohr clearly angry with Heisenberg for the rest of his life. Heisenberg was no Nazi supporter, but he was clearly working for the regime. Bohr concluded that he wished to provide Hitler with an atomic bomb. Heisenberg claimed that he wished no such thing and was in fact trying to avoid it, perhaps even asking Bohr's advice in going about doing so. Today, many scientists and historians disbelieve Heisenberg and feel his behaviour was immoral and arrogant. What did the two of them say to each other?

That is what the characters in the play try to answer. It deliberately takes place in an unrealistic "afterlife": all three characters are dead, but get together - as they both decided not to do in real life, because trying to resolve it only made it worse - to try and work it out. They also fail to work it out in the play, but at least they explore it and at least each man gets his say.

Present in the conversation are, indirectly, the audience, who take the place of the Gestapo, and the people who subsequently interrogated Heisenberg for many years afterwards. Directly present is Bohr's wife Margrethe. In real life she and Niels were devoted to each other. She typed up all Bohr's papers and he plainly discussed all his research with her. She was less enthusiastic about Heisenberg than Bohr was, and discouraged her husband from allowing him to visit in 1941. The play opens with them debating whether or not to invite him, and they agree that he can come on the condition that they don't discuss politics. (But physics and politics, as Heisenberg remarks, are "painfully hard to separate".) Her presence requires the two physicists to use "plain language", so the audience can understand the science; and she disbelieves most of Heisenberg's explanations. "Every time he explained it became more obscure."

Much of the play is told in a sort of monologue, the characters speaking to nobody and everybody simultaneously. "We operated like a business." "Chairman and managing director." "Father and son." "A family business." It sounds as if they are taking parts singing in a choir. During pauses in the conversation, they follow each other's thoughts: "Silence. And of course they're thinking about their children again." "The same bright things. The same dark things. Back and back they come." Many times the play returns to "the same moments I [Bohr] see every day" - his eldest son, Christian, drowning in a sailing accident. Apparently Bohr and Heisenberg could finish each other's sentences, and once you're used to it, it sounds like close relatives talking. At other times, they argue about the things they and the other scientists did in the past - "shoot" each other by beating each other to it writing papers, skiing, piano-playing, hiking, and Schrödinger's visit during which Heisenberg was angry and jealous and Bohr talked Schrödinger to the point of illness. These snippets are both hilarious and some real philosophy to chew on - "that particle that goes through two slits at the same time" being compared to skiing at 70 k.p.h, and making a decision about which way to swerve when necessary!

Even during the most heated moments of the play, Frayn can suddenly make me snort with laughter, by the two men knowing each other so well. "The speed he skis," Heisenberg remarks of Bohr, "he has to do something to keep the blood going round. It was either physics or frostbite." Later, Heisenberg challenges the Bohrs to murder him as an enemy, adding that this would not be immoral in a war, and that all they have to do is tell someone what he said. At white heat, Bohr interrupts: "My dear Heisenberg, the suggestion is . . ." "Most interesting. So interesting that it never even occurred to you." Bohr was famous for saying "this is most interesting". Frayn brings it out very well how widely Bohr was loved. He has the characters mention that Bohr was dubbed "the Pope" by his students, that it is impossible for anyone to accuse him of ever having done anything wrong. I get the feeling that whatever Heisenberg hoped to gain from the Copenhagen meeting, Bohr's kindness would have been a real encouragement to go ahead with it.

That closeness, I think, is the tragedy - that for seventeen years that there was this special cooperation, the shared excitement and science and walking and talking - and then, because of the war, it died.

There is strangeness. There are differences between the characters and the real people, of course. There is eerie unease when they can't agree on what they said or where, or who did what during their science. Some of things they say sound odd. It particularly struck me early on, when Heisenberg has, in their memories, just arrived at the Bohrs' house in 1941. Bohr says: "I believe you had some personal trouble . . . I'm so sorry." It took a few reads of the commentary to establish that this meant Heisenberg had been interrogated by the Nazis for teaching "Jewish physics" (i.e. relativity). He was accused of being a "White Jew" and forbidden ever to mention Einstein in his lectures. Heisenberg's reaction is very odd: "A slight misunderstanding . . . These things happen. The question is now resolved. Happily resolved . . ." Surely he wasn't happy about it. He was still treated with suspicion, and he could hardly have been anti-Semitic or happy with the persecution taking place. In 1933, when Hitler came to power, Hans Geiger dismissed Hans Bethe from his post as assistant without the slightest regret, and Heisenberg offered Bethe a job despite the dangers he must have known this would bring. Bethe sensibly refused and went to work in the USA.

It is so obvious it is almost a cliche that Heisenberg's life, aims and activities are rather a parallel to his legacy, uncertainty. Michael Frayn is clearly fascinated by human motivation. (I read a linguistics book when I was 15 and have since been used to the idea that we have a dozen different motivations at a time for every word we say.) Frayn wrote: "He wanted to distance himself from the Nazis, but didn't want to suggest that he had been a traitor. He was reluctant to claim to his fellow-Germans that he had deliberately lost the war, but he was no less reluctant to suggest that he had failed them simply out of incompetence." Robert Butler, writing in the commentary of the student edition, points out, "The position for many 'good Germans' was that they wanted Germany to win the war and Hitler to lose it."

This is not enough for many critics of the play. Frayn writes two postscripts, in which he baldly details the criticisms, accepting some and refuting others. (He writes with the confidence of one whose work is good enough that he need not really fear any criticism.) There are many, but just as I can't mention every point in the play I liked without this blog post ending up the size of the Encyclopedia Britannicca and spoiling too much of the plot for you, I won't go through them all. I will mention the one I thought was silliest, though: apparently, there were loud calls for more condemnation of the Nazis. As Frayn points out, the evil of the Nazi regime is "a given". For goodness sake, we don't need yet another sermon on what we don't need telling; the physics and the ethical debates and the mixed-up memories are far more fresh and exciting!

Personally I think it's a sort of trendy modern hysteria. Few people alive today remember the war, so we don't know quite what it was like and therefore whether it might happen again. It's not reality to us, it's a nightmare. It must be fended off. Sadly, people are so worried about what other people think of them that one can't even mention the war without ritual condemnation of the Nazis! Tell me honestly, do you really think that unless someone goes out of their way to state otherwise, they're pro-Holocaust? An old friend of mine accused me of sounding so simply for using the word "Jewish", not in a remotely derogatory way. In my father's school days it was quite acceptable to mention the fact that someone was Jewish; it was like mentioning that I wear glasses or that Spain is sunny. (One of the mostly-Jewish school football teams dubbed themselves "The Smelly Yids"!) Another friend of mine was once warned never even to say "black coffee". Oh, and when discussing schoolkids with one another, teachers who wish to avoid trouble must say "pupil", not "boy" or "girl", because apparently any assumptions that might be made are more important than the actual information they wish to give or obtain.

I think this is wicked. To forbid mention of someone's culture and heritage is to deny them a face. It's also to subtly imply that there is something wrong with their gender or nationality or what have you, but that you personally are too smugly refined to say so. And similarly, to assume everybody guilty of sympathy with the Holocaust unless they go on and on about it is to contribute to another culture of suspicion.

(Mealy-mouthed-ness - using the correct words, or not - doesn't mean anything, anyway. Genocide goes on today and not only do we not do any more about it than we did for the Jews during the war - I doubt the victims of Darfur for example will get another country to live in - we daren't mention the fact that it does. As Amnesty International pointed out the other day, it's inadvisable to use the word "genocide" even during an admission that it is actually taking place. I'm not kidding about people "not having a face", either, or why would there have been those two films a few years ago about the "human sides" of Hitler and Jesus? Because people are so silly they actually need proof that every human has a "human side". How babyish.)

Getting back to the play, I also hugely admire Frayn's attempt to tackle very difficult science. He describes himself in the postscript as "a non-scientist" who "can't offer any opinion on the physics". He was certainly braver than the newspaper reviewers. Butler offers seven reviews mentioning the reviewer's own ignorance of science and fear that they needed a physics qualification to understand the play - fears which were mostly dispelled, it seems. It's sad that people are frightened of science. I hope citizen science will help put an end to that; we wouldn't be frightened of a play about art or music. Frayn's ability to have the characters talk understandably, but as scientists, about fission, neutrons, and quantum physics, is brilliant. He has a glossary of some of the lines used at the end of the book. For "that particle", he makes a double joke: "One of the mind-bending aspects of quantum mechanics is that when a particle is faced with the choice of going through one of two slits it appears to go through both of them. (Don't ask.)" Because, of course, "asking" - or using light to "see" the particle - would deflect its path anyway!

* * *

Frayn's masterpiece intrigued me enough to get Thomas Powers's "Heisenberg's War: The Secret History of the German Bomb". It seems impossible to get what is politically correctly termed "a balanced view" - Heisenberg has attackers and defenders. P. L. Rose's book, "Heisenberg and the Nazi Atomic Bomb Project, 1939-1945: A Study in German Culture", for example, is an attack, if that is more to your taste.

Now, like the mealy-mouthed folks I criticise, I wasn't there during the war. But I have a relative who's lived in a terrifying dictatorship abroad, and I'm a history fanatic and an Isabel Allende fan, and like most people I've had the odd instance where I've had to be sly to win a fight because to open my mouth too wide would have been disastrous - so I don't consider myself totally ignorant. I feel an intense admiration for and sympathy with Frayn's Heisenberg, and I think the things his fellow physicists and historians feel he should have done were not actually any better than what he did.

We come to a major question now, which I had never really considered before: Why didn't the Germans manage to build a bomb?

When I was younger I assumed it was simply that America was more powerful and advanced. As one learns more, one finds out that Germany had been bursting with impressive physicists - but the expulsion of the Jews, such as Einstein, sent the brains off to America and brought poetic justice. What about the physicists who stayed in Germany? One physicist, Weizsäcker, stated: "History will record that . . . the peaceful development of the uranium engine was made in Germany under the Hitler regime, whereas the Americans and the English developed this ghastly weapon of war."

Hardly. Take this review by Ian Kaplan: "Those [physicists] who remained in Germany fell into one of three categories: (1) they were Nazis, like Nobel Prize winner Johannes Stark; (2) they could not leave, for what ever reason, or (3) they were selectively blind to the regime around them and its implications . . . The evidence of the Farm Hall transcripts is morally damning. Heisenberg and his colleagues knew about the murder going on around them, but they still worked on the German nuclear program. They did not build a nuclear weapon because they did not know how."

Perhaps there was a fourth reason for not leaving Germany: that one's family and friends and students and fellow countrymen were there too, and one does not abandon all these people lightly. Do we call on all Americans to emigrate if they disapprove of the Iraq war or Guantanamo? Am I going to condemn myself to exile over Ian Tomlinson? No, there are people here besides the police and the government, and I'd rather stay and work here with them. Exile is not a happy future. If the scientists had all left, Nazis would have been put in their places anyway, and then goodness knows what would have happened.

It is possible that the scientists did not know how to build a nuclear weapon; Heisenberg claims that he had some idea, though he had actually got several points wrong. But perhaps - and if you think about it, this isn't as pathetic an excuse as it sounds - they did not want to know. Towards the end of Allende's first novel, "The House of the Spirits", a Communist in danger of being murdered by Pinochet's soldiers explains to his lover that he cannot tell her where he hides: "If they find you, it's better if you don't know anything." The German project, when found by the Allies, turned out to be very primitive, and they claimed they only wished for an energy source. If this is true, one can hardly blame them for wanting that much. People were starving and freezing.

Heisenberg claims in the play that he had hoped that physicists across the world could collectively refuse to build atomic bombs, and then mankind would be safe from the worst of destruction. This was a futile hope. There was no way the Allies would agree to that, and his team could hardly tell Hitler later that they refused to cooperate. But I got interested enough to Google the transcripts from Farm Hall, the house in which ten physicists including Heisenberg were imprisoned (though very well treated) for six months, and their horrified reactions after they heard about Hiroshima are hardly "morally damning":

HAHN: . . . For [Uranium-93] they must have an engine which will run for a long time. If the Americans have a uranium bomb then you’re all second-raters. Poor old Heisenberg.
LAUE: The innocent!
HEISENBERG: Did they use the word uranium in connection with this atomic bomb?
ALL: No. . .
HEISENBERG: Then it’s got nothing to do with atoms, but the equivalent of 20,000 tons of high explosive is terrific. . .
HAHN: At any rate, Heisenberg, you’re just second-raters and you may as well pack up.
HEISENBERG: I quite agree.
HAHN: They are fifty years further advanced than we.

. . .

WEIZSÄCKER: I don’t think it has anything to do with uranium. . .
HEISENBERG: I don’t believe that it has anything to do with uranium. . .

. . .

WEIZSÄCKER: I think it’s dreadful of the Americans to have done it. I think it is madness on their part.
HEISENBERG: One can’t say that. One could equally well say, "That’s the quickest way of ending the war."

Later:

HEISENBERG: We wouldn’t have had the moral courage to recommend to the Government in the spring of 1942 that they should employ 120,000 men just for building the thing up.
WEIZSÄCKER: I believe the reason we didn’t do it was because all the physicists didn’t want to do it on principle. If we had all wanted Germany to win the war we would have succeeded.
HAHN: I don’t believe that. But I am thankful we didn’t succeed.

. . .

KORSCHING: If one hasn't got the courage, it would have been better to give up straightaway.

[At this point, Gerlach, at who this remark was aimed, stormed out and was later found weeping in his room. Meanwhile the debate continued:]

DIEBNER: [The Reich authorities were only interested in immediate results.] They didn't want to work on a long-term policy as America did.
WEIZSÄCKER: We were all convinced that the thing [bomb or reactor? Nobody knows] could not be completed during this war.
HEISENBERG: Well, that's not quite right. I would say that I was absolutely convinced of the possibility of our making an uranium engine but I never thought that we would make a bomb
and at the bottom of my heart I was really glad that it was to be a Maschine and not a bomb. I must admit that.
WEIZSÄCKER: If you had wanted to make a bomb we would probably have concentrated more on the separation of isotopes and less on heavy water.

Why are they discussing what they are thinking now? Why not while they were working together? Well, it's suicidal to say exactly what you think in a dictatorship or war. You don't know if your neighbour might turn you over to the authorities. They were probably all trying to guess what all the others were thinking; Diebner, in "Copenhagen", is criticised as having "ten times my [Heisenberg's] eagerness [to build a bomb]". But after the bomb had exploded, they knew they had lost. It was too late, they had no more to lose now.

In "Copenhagen", Gerlach is described as "our old Government administrator". He does not seem to have been a Nazi, but was afraid of what might happen to him if he returned to Germany now, and felt responsible for the defeat and deaths of his fellow Germans. Otto Hahn, as Heisenberg said, "wants to kill himself, because it was he who invented fission, and he can see the blood on his hands". He had contemplated suicide years before when he realised what fission could do. Major Rittner, their host/warder, and the other physicists, were very worried about Hahn that night, but Hahn also found time to comfort Gerlach:

HAHN: Are you upset because we did not make the uranium bomb? I thank God on my bended knees that we did not make an uranium bomb. Or are you depressed because the Americans could do it better than we could?
GERLACH: Yes.

Powers states at the beginning of his book that the American scientists feel no guilt at working on the atomic bomb, and Frayn reiterates this in his play - Margrethe asks incredulously, "You're not implying that there's anything Niels needs to explain or defend?" - though he later cites two Americans, including Oppenheimer, feeling revulsion at what their weapon has done. But the German scientists appear to be condemned for both having a project to do, and for failing to complete it. "Hands that had actually worked on the bomb wouldn't touch mine," Heisenberg laments in the play.

I still admit there's a lot I don't know, and I must find the courage to read the critical literature as well as the supportive. But I will say one last thing: those who judge Heisenberg and the other physicists harshly might like to read the Göttingen Manifesto.

Grazie Half65 for ARP 142

I'm insanely excited today over a 16 by 16 pixel picture: a favicon from Half65! It is the beautiful ARP 142 galaxy system, the individual galaxies known as NGC 2936 and NGC 2937.

Credit: SDSS. To zoom in and out and explore around, look at Navigate.

This was the first really "interesting" galaxy I found at Galaxy Zoo No. 1. Ah, the old days - I was living in Brighton, classifying in the computer room when I should have been revising for my chemistry exams. (Actually I did much better than I expected - I thoroughly recommend reading 1 page of notes, doing some classifying to relax the brain and let it sink in, and then reading another page of notes, rather than cramming it all in at once!) The forum which changed my life had not yet been born. Fortunately, a temporary blog was set up by a kind enthusiast, Salmon Chase, and it was one of the first things I posted. My friend Gill's husband named it "the penguin galaxy" and it seemed to catch on!

Of course, I didn't know anything about galaxies at the time, or how to search SDSS, and it was a while before I found out it was called ARP 142. What can we tell about it just from looking at it?

The "egg" the "bird's head" is "looking at" is an elliptical galaxy; the "bird's head" itself is a wonderful merger, with dark dust lanes and bursts of star formation at the top towards the "beak". My impression is that it has been dragged round anticlockwise in a quarter-circle. It's quite peculiar that the elliptical appears so unaffected, but perhaps its stars are closely bound enough not to be so disrupted - or perhaps there's something I'm missing. I checked their redshifts, to see if perhaps the elliptical was further away and looks bigger than it is. It isn't. It's closer to us: z=0.023, while the merger is 0.024. Behind the star at 1 o'clock is a small irregular galaxy known as UGC 5130. Apart from that, it seems to be a relatively empty area.

We can also look at the spectrum. This is an emission spectrum (drat - I haven't written about those yet, though I covered absorption spectra and their history this week*):

What exactly does an emission spectra mean for a galaxy? It means it is very energetic. It probably indicates star formation. Well, we can see that from the blue splodges anyway. And why should that be?

When a hot light source - an energetic photon - hits an electron in an atom, the electron leaps up to higher orbit. Perhaps the next-highest (think of the Earth leaping up to Mars's orbit), or several orbits higher (Earth leaping into Saturn or Neptune's orbit). It has to be of a very, very specific energy - a particular wavelength of light - just the right amount of energy to boost the photon to a specific place. Too high or low and the photon will be sent on its way. But even then, atoms and subatomic particles don't like to be in a higher energy state than they have to be, so eventually the atom falls back down again, emitting that photon again. But since the photon's gone off in any old direction rather than the one it was originally heading in - towards us - that wavelength of light is missing in the spectrum.

That's a hot light source and a cool atom. What about a cool light source and a hot atom? That's where emission spectra come in. That's when the electron was already up in a higher-than-necessary orbit - "in an excited state", as we say - and shoves the photon off in our direction. And that's when the spectrum shows huge peaks.

In this case, the highest peak is of H-alpha, or Hα. That means the electrons are falling from the third orbit to the second, rather like Mercury falling from Earth's orbit down to Venus's. There is also a bit of H-beta (from the 4th to the 2nd) and an even littler bit of H-gamma (from the 5th to the 2nd). That clump of star formation the camera is focussed on in this case is not as violent as some galaxies. The peas, for example, have high OIII emissions - oxygen with two electrons knocked off. I'll write about them in another blog post!

All the above I was able to get out of my eyes and SDSS. Doubtless somebody smarter than I currently am could get a lot more, such as the exact data for the colour filters . . .

The galaxy system is from the ARP catalogue: the Atlas of Peculiar Galaxies, drawn up by Halton Arp. Its number is between 102 and 145, into which category fall the elliptical and elliptical-like galaxy types (of which there's a lovely catalogue here).

ARP 142 is in Hydra. There's a fantastic picture you can zoom right in on on this site, in which it looks more like a bird than ever! That site describes it as "emanating", though is not specific on what is being emanated. You can also find it on skyfactory.

A paper has been written by McCain et al on "ARP 142: Another interacting galaxy with very large internal motions". (As again is clear visually, I think!) Intriguingly, the Hα is not coming off the elliptical, but off the merger - which was once, according to their research, a spiral which is gradually being stripped by the elliptical - not quite the same as my quarter-circle impression above! They state that there is a massive "velocity difference", but I'm not clear on whether that means of the galaxy's movement, or whether the Hα is moving at that speed. Evidently that means ionisation is taking place, but shock waves are unimportant. (Recall they are very important in barred spirals and are often a trigger for star formation in spiral arms . . .) Looking at it visually backs up this conclusion; blue galaxies are full of star formation while ARP only has the odd burst of it here and there.

There's just so much to learn!

P.S. Happy Mother's Day.

P.P.S. Grazie Half for correcting my spelling :D

P.P.P.S. *But I did later. Here is the story of emission spectra, and a wonderful story it is too.