Friday, August 31, 2007

Broadcast Yourself

The National Science Foundation, the Public Library of Science (PLoS) and the San Diego Supercomputing Center have launched SciVee, a website that allows scientists to upload and share short video lectures with paper outlines. The videos get DOI numbers and it is possible to refer to them as citations in future papers (or videos). Bora from PLoS goes so far to say that "Video is taking over science communication" and that "paper is outdated".

I am a scientist, not a movie star. I don't even like to speak in front of people, and should it one day become necessary to upload videos of myself to assure my chances on the job market, I will quit and maybe write a book titled 'Memoirs of an Outdated Scientist'. Uploading 15 minutes clips that summarize a topic might be nice to get a fast introduction to what might be an otherwise very dry and technical issue. But the success of videos depends greatly on professional support, rhetoric skills and, yes, also on the looks. These are all criteria that I'd rather want to stay out of scientific research. I appreciate attempts to make science more accessible for a broader audience, but when it comes to professional publications, I would not welcome a situation in which videos were taking over papers that I can print and read in bed.

Bottomline: I certainly don't think the paper is outdated.

[via Slashdot]

Thursday, August 30, 2007


Gee, I *really* should be cleaning up my apartment, but it seems today everybody wants to get upset about Tommaso's post about a talk by Lisa Randall. The scandal being that it does not only mention her work, but also her looks:

"Lisa Randall is notoriously not only an esteemed and well-known theorist, but also a quite attractive woman - a powerful mix, capable of turning to jello the knees of most men. Today she wore a nice black and white dress which left her shoulders and arms exposed, a necklace of mother-of-pearl, and a wide-band silver bracelet with colored stones. Her hair was collected in a pony tail. She looked nice and fit - for some reason it made me think she probably works out on a regular basis"

Despite the actually very interesting topic of her talk that could have been discussed, this is almost immediately followed by comments from Sean Carroll ("you contribute to an atmosphere in which women are outsiders to be gawked at ...") and JoAnne Hewett ("Got sex on your mind while writing this post, do you?") , and Clifford's post Still So Far To Go, who is embarrassed on behalf of everybody who can not only think about women's clothes but actually writes about it

"It’s so completely awful to do this sort of thing [...] From his comments in response to people pointing out the inappropriateness of it, it turns out that he really does not get it at all. Not a bit. It is really sad. It is so embarrassing too [...] since it is damaging to the cause of women in the field."

Which, needless to say, asks for Lubos' reply who fills us in with his analysis of Prof. Randall:

"[L]et me start by saying that I know Lisa Randall much more than these two guys [...] She is attractive and she is an exceptional athlete. [...] Does she enjoy to be admired for diferent things than being the most cited particle physicist between 1999 and 2004? [D]oes Lisa or other special women in science like to ignite interest and emotions in general? I think that I know enough to figure out the answer and the answer is Yes. You won't learn any details from me but I just find the general answer important."

In fact, I am not really interested to learn the details about why Lubos thinks Lisa likes to 'ignite emotions'. But anyhow, so Tommaso, who is now officially the sexist among the MALE physics bloggers, clarifies his writing in a second post "Am I a sexist?"

"If I venture in a description of a person I meet - be it a woman, a man, whatever - it is because this is my diary, and I want to keep a record of my ideas, my feelings, my thoughts."

Which would make for a nice discussion on the issue of privacy in the public domain. But I currently don't have the time to get into this.

Instead let me add my two cents. First, I find it very interesting that the mentioning of Lisa's necklace causes much more attention that the rest of Tommaso's post, which is actually quite good and worth reading. Those of you who usually don't comment on good readings but only on things you are offended by might think about whether this is a good behaviour to express appreciation. Second, I don't know Lisa Randall personally, but I recalled that she wrote a recent article in Discover magazine that I want to quote some paragraphs from and let her speak for herself:

"As soon as I arrived in Venice it was clear things would be a little unusual. Although I think of myself as a physicist when I’m at a conference, that is not necessarily what others see at first. On the ferry into Venice, I met the man in charge of the science department at the Vatican. He assumed I was on vacation and not particularly interesting until I told him I was the first speaker, after which we had animated exchanges about science and belief and evidence. He wasn’t the only one who didn’t think I was a scientist at first. As the conference was about to begin, the technical person ignored me but was very helpful to the person sitting next to me in the front row, even though I was about to go on stage! In fact virtually no one seemed to realize I was a scientist, including the media there. More disappointing, it didn’t even occur to anyone to ask.

Happily, after my talk about cosmology the situation completely reversed. People now knew who I was; they felt they had learned something and were eager to discuss my talk. For the few days I was there I had a marvelous time. I’m not complaining—I’m observing and questioning. Do preconceived assumptions and superficial first impressions matter?

[...] In Genoa, people knew who I was. But the fact that I was seen as different was brought home to me by the headlines and the interviews that concentrated on my being a woman doing science—still rare everywhere but extremely rare at the upper levels of science in Italy. Italian Vanity Fair published an interview with me that shows a refreshing open-mindedness to science in popular culture. But it was pretty funny when the publicity people hesitantly translated the title of the article for me: “The Beauty Is a Geek” (actually they said “genius” to be nice, but really it said “geek”). As they had anticipated, I was a little startled and a tad disturbed. Though flattering on one level, these comments are unsettling on another. I just don’t think of myself this way. Then I realized it’s precisely the point that is critical to get across. Why do we create totally separate categories—the beautiful woman and the geek man? It’s hard to believe that the expectation that these are incompatible qualities doesn’t make science less attractive for women (and many men).

The headlines were particularly jarring to me because I, like many other women doing science, try not to focus on being female. You just want to be a scientist like the others. But if this involves suppressing your personality, as these categories suggest, you might find that many women (not to mention some men) will be put off."

Happy Birthday!

Today, we celebrate the birthday of a top-physicist! And for a change, that physicist is still alive, doing fine, and an active blogger in addition... A very, very happy birthday to my husband :-)

Wednesday, August 29, 2007

Hiatus Announcement

Dear fellow Readers, Friends, and self-aware parts of the WWW:

I am moving into a new apartment. Presently I am sitting among scaringly unstable towers of boxes trying to figure out what to do with the burnt spots in the carpet. Not much I can do I guess. Except to let you learn from my mistakes: never direct an halogen lamp towards a synthetic carpet.

Anyway, I won't be at work the next days, and I don't yet have internet access in the new apartment. (In fact, I haven't even seen the apartment and as additional complication and can't recall the number.) Such, I apologize in advance that I won't be around as much as usual. Also, I might not be able to immediately delete spam comments, so please ignore drug advertisements or climate change awareness links for a couple of days.



A note to friends and relatives: My private phone number does not change.

Monday, August 27, 2007

Links and Things

  • is the Flickr equivalent for statistics. One finds all kinds of charts and rankings, data and graphs, sorted by fields (Economics, Entertainment, Health, Politics, Science, Society, Sports, Technology, Miscellaneous). Usually with sources, though the graphics aren't always that great. E.g. here we have physics publications, USA in contrast to 'all other' . You can also find evidence that Tuesdays and Fridays are the worst days to drive in LA, that the divorce rate in the USA is more than twice as high as in the EU, and the beginning terrorist can learn fatalities by tactic.

    Besides the general entertainment value the site offers rankings and options for discussion which I find nice. However, right now the database seems to be rather small, but this could become a pretty useful source of information.

  • Have your towels ready! Userfriendly explains the dark void! For more info, see here. (Thanks to Andi).

  • Checking which Google searches lead visitors to this blog always gives me the giggles. My favorite from the last week was 'Energy of the average fart' (which leads here).

  • A couple of weeks ago I've signed up for Google Analytics, which has some more features than SiteMeter. Among other things, it ranks the amount of visitors who came via Google search by the search tag. Most come here searching for 'Backreaction' (good), the second rank is hold by 'First day of fall' (weird), the third rank is 'Lee Smolin', directly followed by 'Peter Woit' (no comment).

  • The results of the Back-Reaction poll (the first!) from Aug 17 "I read science blogs because...": A total of 149 people (to date) voted. Most of them checked the option "because I am interested and learn a lot" (42.3 %), followed after a gap by "for news and gossip" (28.2 %) and "for the general entertainment value" (12. 1 %). As little as 3 people admitted on reading science blogs mainly to distribute their own believes. And nobody who ended up here by accident stayed long enough to vote.

    Overall, I think this test-poll went fairly well, though some more participants would have been nice. Maybe I should try to come up with a more interesting question.

  • Quotation of the week:

    "We can't solve problems by using the same kind of thinking we used when we created them."

    ~Albert Einstein

Sunday, August 26, 2007

MAGIC's observation of Gamma Ray bursts

A couple of days ago, the MAGIC collaboration posted a paper on the arXiv:

Probing Quantum Gravity using Photons from a Mkn 501 Flare Observed by MAGIC

which I didn't mean to comment on, but it seems it has caused quite an astonishing amount of discussion. The SciAm blog sees hints of a breakdown of General Relativity, Lubos Motl expresses his skepticism, Slashdot proclaims it is a test of String Theory, which then causes Buffy Woit to fight against the living dead predictions, thereby unfortunately claiming to be in agreement with Lubos, who returns the favor with a second post denying any agreement with "the critique of science", fading out in a characteristic rant about 'aggressive imbeciles'. Even the more reasonable article by Chris Lee on Ars Technica which cautions that quantum gravity has probably not "made a sudden leap forward" proclaims that "this is the first real data against which such a theory can be tested", the caution of which however leads the SciAm bloggers to nag that those "who have been loudly complaining about the lack of [observations that probe string theory] have gone silent."

This is the summary, status Sunday evening. In case I loose one or the other reader here, let me give you my opinion up front: there is no experimental evidence for quantum gravity, and none of the present theories can be tested with currently available data. If you're looking for sensations, you're on the wrong blog. I suggest you try one of those mentioned above instead.

As a prerequisite, the issue is an observation of gamma ray flares from the active galaxy Markarian 501. The data was taken in summer 2005, the most characteristic event being on July 9th. The peak energy of the flare was around a TeV, it lasts about 2 minutes. The emitted spectrum spreads over some orders of magnitudes. I'm not an astrophysicist and details elude me, so please don't ask me in which constellation Mkn501 can be found, or what the status is about understanding AGNs.

The point is that if one knew the emitted signal, brightness and spectrum, measuring what arrives on earth would allow one to conclude what happened to the signal on the way. If the signal propagates through vacuum, General Relativity (GR) tells you what to expect. There is a redshift, brightness drops, but these effects are well known and computable within GR. If what happened to a photon during travel would depend in some unusual way on the energy of the emitted photon, it would distort the shape of the signal. This is called dispersion. If a family has to get through a crowd of many people, the small children will be the first to arrive, and then have to wait for their parents who have a harder time pushing their way through. Such, what originally started as a localized group arrives with a time delay between various parts. A similar effect happens to an emitted signal of photons if there is a dispersion.

Problem is, for the case at hand the emitted signal is not so very well known. However, Likelihood analysis allows to examine how high the chances a signal is distorted in a certain way for different frequency regions, and for the observed flare the MAGIC collaboration concludes that its shape "is unlikely, and consequently that the time shift of 4 ± 1 min between the highest and the lowest energies is more probable." [astro-ph/70702008, p. 13]. The time of this delay would be about the duration of the signal itself.

In their new paper the MAGICians write one can circumvent knowing the true shape of the time profile at the source by basically taking the result and assuming a parameter dependent blurring has taken place that distorts the signal differently in different energy regimes. If one reconstructs the original signal with that assumption, one can examine it for certain features, and ask for the parameter that optimizes that feature. If I understand it correctly, they have performed analyses with respect to two such features. The one is to "maximize the total energy in the most active part of the flare" and the other is "to optimize the sharpness of the transformed signal".

In both cases it is found that the signal can be optimized if one reconstructs it with a certain assumed dispersion relation that depends on a parameter. The best fit for the parameter is not for exactly zero which would correspond to no dispersion, aka standard propagation. It is interesting though that both analysis with respect to different features seem to fit together. There comes the chi-square fit, et voila, one has a signal at 95% CL. That is to say the detected signal would be more probable if there had been a dispersion. It's not striking how much one can improve it, but one can.

But anyhow, now the clue is to call the fitting parameter MQG and claim it is an effect of quantum gravity (QG) , since "QG effects [...] cause the fabric of space-time to fluctuate on the Planck time and distance scales. It has also been widely suggested that this ‘foaming’ of space-time might be reflected in modifications of the propagation of energetic particles, namely dispersive effects due to a nontrivial refractive index induced by the QG fluctuations in the space-time foam and that one is "probing the Planck mass range for the first time". Depending on your preferences you might then argue this is either a prediction of string theory, or contradicting predictions of string theory. Or a prediction of LQG, or not a prediction of LQG.

What is even worse than the advertisement in the paper is the echo it has caused, which is more attention that I think is appropriate. What about all those hard working people who don't wrap their results into easily digestible catchy phrases? Won't they wonder what all their effort is good for if they see one gets much larger attention with things like this?

Yes, there are motivations, and indications that within certain scenarios one can have such a dispersion. I myself find this very exciting, but as the authors state themselves "The calculation of such effects is beyond the scope of current theoretical methods". Also, as Lubos has pointed out, the same collaboration had a preprint already in February about the gamma ray emission of the same source Mkn501, in which they attributed observed spectral features to different effects, and remarked "A somewhat more speculative issue that blazar emission permits to explore concerns non-conventional physics. Energy-dependent arrival times are predicted by several models of Quantum Gravity, [...]". Even given that the signal is confirmed by sufficient other data, and proves to be statistically significant, the most likely explanation I'd think would still be our lack of understanding of AGNs.

The problem I have with that paper is not the analysis itself (which I wouldn't have found remarkable enough to mention here) but that it is clearly sold as a made up sensation. The whole introduction doesn't belong there. If they want to analyze their data with respect to dispersion, then they should do that, and not take several further leaps of faith towards quantum gravity. If at all, then this belongs into the discussion, but neither in the abstract, nor in the introduction, nor the conclusion of a scientific publication - the first paper e.g. is much better balanced. All that they have found is with unconvincing confidence a signal can be 'optimized' if a dispersion relation had a parameter that happens to be somewhere by the Planck scale. That itself has nothing to do with quantizing gravity, neither with a "Break down of General Relativity" as the SciAm blog put it.

However, even if there was a dispersion, it wouldn't be clear at all that this has anything to do with quantum gravity. If the signal undergoes a dispersion, then the signal undergoes dispersion. Full stop. Everything else is speculation, and should clearly be called such. The question what an effective description has to do with the potentially underlying fundamental theory I call the 'Inverse Problem' - for more details, please see my previous post on Phenomenological Quantum Gravity.

To sum up: 1) There is the question whether the signal is significant 2) Even if it was, it would most likely be something that we haven't understood about astrophysical processes 3) Even if that was outruled there would be the question whether it had something to do with quantum gravity.

Bottomline: If one adds a parameter one can fit curves better. If the original fit was good, the parameter will be small. (Another example for this sort of analysis you find here.)

Now you can blame those who are conservative and would attribute a potential signal to old-fashioned physics to be boring and pessimistic, but the only thing you get from hyping non-results is more people wasting time with alleged 'effects' and made-up 'predictions'. Yes, I do think scientific publications should be conservative and cautious, especially if they claim to have evidence for new physics. Reading papers and follow-up articles with exaggerated claims about testing quantum gravity annoys me considerably. It's like strawberry yogurt where the fineprint says 'no fruit'.

Saturday, August 25, 2007

Mira, the Marvellous Star

You have probably seen already here, or here, this wonderful picture of a comet-like tail at a star:

It shows a trail of dust and gas the "asymptotic giant branch" star Mira has left behind, while speeding through the interstellar gas of our galaxy at 160 km per second. This tail extends over nearly two degrees in the sky, which means, given the distance to Mira, that it is more than 12 light years long! Unfortunately, one can not see it in optical telescopes: It is visible only in the ultraviolet. That's why no one had spotted it before this photograph was shot by the Galex (Galaxy Evolution Explorer) space telescope.

The tail of Mira can be seen only in ultraviolet light (top). In usual visible light (bottom), there seems to be nothing special around Mira (Source: Galex team, Caltech)

Mira is a star with a mass a little larger than our Sun's, but with a radius nearly as big as the orbit of Mars. Its surface temperature is a mere 2200 K, but due to its size, its total output of radiation is 8400 as big as that of the Sun.

Mira is in the late phase of its life as a star: it has a core of carbon and oxygen, which is surrounded by two layers where helium and the remains of hydrogen are burned. It is pulsating slowly, with a period of 332 days, and constantly blowing away quite big amounts of gas and dust - one tenth of the Mass of Earth per year - into its surroundings. This material is colliding with the interstellar medium. Du to the high proper speed of Mira, it is stopped in a bow shock hat is clearly visible on the Galex photos, and left behind as the tail. Julianne at Cosmic Variance has discussed in much more detail the fascinating astrophysics of Mira and shock phenomena in astronomy in general.

But even though Mira's tail doesn't reveal itself to the eyes of mundane hobby astronomers as me, the star is an interesting object to observe even with the naked eye: In the course of its 332 period, its brightness diminishes so much that it completely drops out of sight! That's in fact how Mira got its name.

In August 1596, Frisian cleric and spare-time astronomer David Fabricius was observing planet Mercury, when he spotted a star in the constellation of Cetus, the Whale, that he had never seen before and could not find in the catalogues and maps of stars where he tried to look it up. He knew about novae, stars that lighten up for some time and fade away again, such as Tycho's Nova of 1572, and thought that he had discovered one - and indeed, this new star increased its brightness first, but by October, it had become so dim that Fabricius lost it from view.

Mira, or Omicron Ceti, in Bayers 1603 stellar chart Uranometria: In this detail, it's the star right at the centre. (Source: Linda Hall Library of Science, Engineering, & Technology

But then, this funny star reappeared: Fabricius spotted it again in 1609, and independent of him, astronomer Johann Bayer had registered it in his map of stars, the Uranometria, and denoted it as "Omicron Ceti" according to the labelling system he had devised for his map - a name that is still in use today.

A systematic analysis of the different available observations by astronomer Holwarda in 1638 revealed that this star, Omicron Ceti, was a variable star, which changed its brightness on a regular basis with a period of 332 days. This was such strange a phenomenon that Hevelius, one of the most influential astronomers of the time, dubbed the star simply Mira stella, the marvellous star.

The change in visual brightness of Mira is dramatic, indeed. The diagram below, a collection of observations provided by the American Association of Variable Star Observers (AAVSO), shows the magnitude of Mira over the last 400 days: At the last maximum, in February, the magnitude peaked around 2...3, while the right now, Mira is close to its minimum, at mag 9. That's a difference by more than a factor hundred! Remember that the threshold for the visibility of stars by the naked eye is around mag 5...6, so right now, one needs a small telescope to spot Mira!

The light curve of Mira over the last 400 days. The approximate threshold for visibility by the naked eye is marked in red (Source: AAVSO)

The physical reason for this shift in brightness of Mira is quite interesting: On the one hand, the star is pulsating, and whenever it expands, its cools, and the maximum of its black-body-like emission spectrum shifts away from the visible - at an average surface temperature of 2200 K, it's in the infrared anyway. This means that the largest chunk of radiation is emitted in the infrared, and not in the visible part of the spectrum. Thus, in the infrared, changes in brightness would be much less dramatic.

But then, there is a second, funny effect, which enhances the change in brightness: If Mira cools down in the expanding phase of its pulsation, titanium monoxide molecules condense in its vast atmosphere, and these molecules absorb nearly completely the visible light from the inner layers of the star. I wonder whether there is a relation to the bright white colour of titanium dioxide...

So far, I have never tried to follow the appearance and the fading of Mira in the sky - but this winter, I will try to do so - the next maximum is expected for the first half of January 2008. Cetus the Whale is not such bright a constellation. However, located near the celestial equator, west of Orion, and in the southeast of the square of Pegasus, it is quite well visible in fall and winter from the Northern hemisphere. There are plenty of sky charts that help to locate Mira - but in general, is a good address to start:

Mira in Cetus west of Orion (Source:

At wikisky, they have even already integrated the Galex photo of the tail of Mira, so that one can see how it actually fits into the sky:

The Galex UV photograph of the tail of Mira at

But we have to keep in mind that unfortunately, even at Mira's maximal visual brightness, we can not see the spectacular tail...

  • The original Galex results have been published last week in Christopher D. Martin et al.: A turbulent wake as a tracer of 30,000 years of Mira’s mass loss history, Nature 448 (2007) 780-783; DOI: 10.1038/nature06003 (subscription required)
  • The paper about the dimming effect of titanium monoxide forming in Mira's atmosphere is M. J. Reid and J. E. Goldston: How Mira Variables Change Visual Light by a Thousandfold, The Astrophysical Journal 568 (2002) 931-938 (available online for free)
  • A comprehensive history of Mira is Dorrit Hoffleit: History of Mira's Discovery, online from the AAVSO.

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Friday, August 24, 2007


A couple of months ago I agreed to give a lecture for the ISSYP, held at Perimeter this summer. Then pleasantly forgot about it. It was only Wednesday, one day before my scheduled talk that I found out what the abbreviation means - the 'International Summer School for Young Physicists'.

Luckily I realized nobody had asked me for a title of the talk, so picked the first thing that came into my mind. An extended version of 'The World's largest Microscope' followed by an introduction about 'Large Extra Dimensions' because I was reasonably sure nobody else from the PI researcher would talk about something too similar. On the schedule however the titles read like a riddle of the sort "Which item does not belong there? Monday: Quantum Mechanics, Tuesday: Dark Matter, Wednesday: Quantum Gravity, Thursday: Sabine Hossenfelder, Friday: General Relativity."

Upon further inquiry how young is young I was told 11th graders. That's when I got really scared. 11st grade, I thought. Gee. They will ask all kinds of questions I can't answer. Derivation of synchrotron radiation? What's a Fermi in seconds, and how does one explain an UV cutoff to somebody who doesn't know neither what a virtual particle is, nor what UV means?

But, brave me, I faced the challenge and turned up at 9 in the morning (I am particularly proud to report I hit the snooze button only 5 times). Just to find a completely empty room, because the bus was late due to heavy rain. So I grabbed a coffee and when I came back there were 50 kids staring at me, some of which looked about as tired as me. Upon my appearance, a couple of them took out digital cameras which they used whenever something sparked interest (me dropping the pointer?). I hope none of them belongs to generation blog.

Anyway, approaching a birthday in the thirty-somethings I am a bit nostalgic these days. Staring at the kids I saw myself staring back, and I recalled a similar lecture I visited at the Frankfurt University while I was in school. There they were, all the serious scientists with multiple academic titles, IQs several standard deviations off the average, authors of books and technical papers, used to speaking in front of hundreds of people. All these researchers that knew quantum mechanics, differential geometry, and how to properly pronounce Nambu-Jona-Lasinio*. What I didn't know then, most of them were postdocs - their supervisors probably being busy with more serious things than talking to kids.

And I? I was intimidated. Seriously. And some of the kids sitting in my lecture were too, that's what I saw in these faces (I shouldn't have worn black, should I?). They only cracked up when I made a joke about Lee's office (if you've seen his office you'll know what I mean). The most difficult question they asked was why the background of my slides was a map of Middle Earth (but that's another story).

So I was wondering how intimidating is holding a PhD? Part of the distance I felt when sitting in this lecture (a looooong time ago) is probably due to German culture. In case you don't know, German language has a hierarchy problem: there are two ways to address people. Either with the colloquial 'Du' or with the formal 'Sie' [2]. The former is reserved for people you know well, friends and family, and for non-adults (that technically being 18, but obviously there is a certain grey scale here). Being a professor at a university definitely qualifies for 'Sie'. Unless dropping the formalities was explicitly offered, it's appropriate to address him (or her) with 'Professor Soandso'. After moving to the USA, It took me quite some while to get used to addressing basically complete strangers (older than me!) by first name.

But besides this, even in the English speaking countries there remains the barrier between those looking down from their ivory tower, and those wishing to climb up the stairs. So I am left wondering who was more intimidated by whom?

Needless to say, over the years my intimidation gradually vanished. If you've seen a professor crawling on all fours under a desk trying to bark like a dog, it slightly alters your view of 'being several orders off the average' - just believe me.

Footnote 1: The proper pronunciation is An-Jay-Al.
Footnote 2: See e.g. this brief article about
'Friends and Acquaintances' which is imho pretty much to the point.

Wednesday, August 22, 2007


While blogger was down most of the morning, I recalled a recent conversation about the arXiv's policies. Since not all of the readers around here are registered arXiv users it occurred to me that you might not know it's not possible to withdraw a paper from the arXiv. However, I have good evidence that most scientists are indeed human and occasionally make mistakes - and not in all cases realizing a problem is identical to solving it. The only way to deal with that on the arXiv is to replace the paper with an empty update, or with a dummy file. The previous version(s) of the submission however, remain available on the arXiv.

This happens more often than one might think. I just did an abstract search for 'withdrawn' which produced the warning 'Your query resulted in too many hits, only 1000 hits are being displayed.'.

I don't particularly like this. Nobody is eager to admit mistakes, and replacing a paper with the comment 'withdrawn' means it will appear in the next listing under 'replacements' with a clearly visible stigma. I think that probably some people who have realized a problem with an argumentation prefer to just leave the paper as it is, and hope nobody ever mentions it again. The result however is that weak or wrong ideas remain on the arxiv, publicly available. Yes, it's called a pre-print server, but nobody is required to add a comment saying: This paper has been rejected by 6 different journals because I've abused infinities (see previous post) and I've eventually understood why.

That is to say, for this reason I would think the arXiv quality might improve if it was possible to withdraw a paper - completely - from the listing.

However, on the other hand I am afraid it might encourage users to submit premature works, knowing that they 'could' withdraw if it turns out to be bullshit. Maybe public humiliation is the better tool to guarantee quality? And I guess I would miss some of the stage fright that comes with pushing the 'submit' button (and don't yet relax).

So, I am kind of undecided on that issue, what do you think?

Monday, August 20, 2007

After Work Chill-Out

Life is complicated. Why does my bank keep sending statements in Spanish, even though I've complained repeatedly that I don't speak Spanish? Where is my digital camera, and why do Canadians buy milk in plastic bags? There is nothing as nice as a solvable, well defined problem. I used to love finding bugs in fake proofs! For your amusement, here's a "proof" for 0=1 :

We start with an innocent looking natural logarithm

Use additivity of integration

And now we substitute y=x/2 in the first, and y=2x in the second integral, which yields

So, we now have ln(2) = 0, divide by ln(2) and voilà :-)

I believe somebody will explain the bug in the comments, so instead of spoiling your fun, I refer you there for debugging.

Sunday, August 19, 2007


"A string is an ordered sequence of symbols [...] Even variable length strings are limited in length; although, generally, the limit depends only on the amount of memory available [...] String concatenation is an associative, but non-commutative operation. The empty string serves as the identity element [...] Representations of strings depend heavily on the choice of character repertoire and the method of character encoding."
[extract from Wikipedia]

"A loop is a sequence of statements which is specified once but which may be carried out several times in succession [...] In many programming languages, only integers can be reliably used in a count-controlled loop. Floating-point numbers are represented imprecisely due to hardware constraints [...] Sometimes it is desirable for a program to loop forever, or until an exceptional condition such as an error arises. For instance, an event-driven program may be intended to loop forever handling events as they occur, only stopping when the process is killed by the operator."
[extract from Wikipedia]

    WHILE(wondering what's up with her today)

    IF(IQ > 100) THEN {smile;}
    ELSE {scratch head;}
    IQ = IQ + 1 ;

    END DO

Saturday, August 18, 2007

The Other Side

September first is approaching. For many of us postdocs this is the time for a move and for a new beginning, new places, new faces. Here at Perimeter Institute, the new postdocs have already started to arrive.

Those of you who are not working in the field know the names of maybe a handful of the top postdocs in that are out there. But folks, there are thousands of us who you've never taken notice of. And those who I've met have all one thing in common: they are dedicated to their The Other Side of Green Grasswork. The reason I'd think is fairly simple. If you don't care about the field enough, you can get a better paid job with a better contract elsewhere. I don't know anybody holding a PhD in theoretical physics who ended up being unemployed*, nobody who had a serious problem finding a position outside academia.

However, I spend a lot of time on this blog telling you how great this job is, but today I want to mention the other side, where the grass is not all that green (see figure to the right). Besides the obvious fact that not everybody likes to move around and leave behind friends and family, there is the issue how you get treated at work. And over the years I have heard a lot of very nasty stories about supervisors. See, the most common conversation starter at a conference is "Who are you working with?"... "And how is he?". Gossip gets passed around because it's relevant for us to know - preferably before we accept an offer.

Here at PI, we don't have supervisors and I am perfectly happy with my position, so the following doesn't actually apply to my current job. But here is, for all the postdocs that are presently busy packing moving boxes, a note to the supervisors:

1. R-E-S-P-E-C-T

The most common complaint about supervisors is lacking respect. If you've hired that postdoc for his scientific expertise, then how about you listen to what he has to say and don't ignore his opinion?
A very typical example that I have heard in too many versions, and from almost all areas, is the supervisor with the supposedly great idea who wants the postdoc to do a time-consuming calculation, but doesn't even take the time to explain the context, or doesn't want to hear any feedback. Yes that's a cliché, but that doesn't make it less annoying. Of course you have a great idea that will change the world! That's what everybody thinks.
Also, don't shove and push around your postdocs, don't expect us to do duties that staff should be doing (like sending/typing letters, taking care of travel arrangements, or making coffee.) Don't outsource your problems, and use us to take care of that journalist, to answer the crackpot's inquiries, or to handle administrative issues on your behalf. And please don't blame us for other people's mistakes including your own.
It all comes down to the obvious line: treat others like you want to be treated yourself. You don't get respect if you don't earn it. What you get instead is gossip.

2. Acknowledgement

If your postdocs gives your lectures while you're travelling, writes your referee reports that have been due a month ago, arranges seminars, organizes conferences you insisted to hold, or takes care of that graduate student who's been sitting in front of your office for several hours a small 'Thank you' would be appropriate every now and then.
More generally, we postdocs don't run on dark energy that we get out of the vacuum. We want to know whether our work is actually good for something, and appreciate some motivation. We can't improve if we don't know how well we are doing, and need some feedback, preferably in a timely and meaningful manner - both when things are going well and when improvements are needed. Ignorance is much more annoying than constructive criticism.

3. Guidance

Your postdoc relies on your experience. When it comes to proposals, applications, publishing, maybe giving an important talk, financial or general career questions your advise is needed. Your postdoc relies on you to introduce him to people who might be important for a project, expects you to point out relevant conferences that he might not be aware of, relies on you to mention related work that has been done possibly before he was even born. In most cases the default is to respect your intuition. Look - we know you have a headstart, but don't abuse our trust.
All of that however does only work if you actually provide this experience.

4. Integrity

Like it or not, you're a role model. Try to be fair and honest, reliable, available and approachable. Just believe me we are not wasting your time on purpose, and wouldn't bother you unnecessarily. Don't postpone and cancel appointments repeatedly, or proclaim you are too busy with more important tasks - you are not the only one who has other things to do, and I don't care whether you've been nominated for the Nobel prize. Being constantly busy doesn't prove you're important but that you can't cope with your schedule and, worse, aren't even able to improve your time management.
If your postdoc mentions a deadline, try to meet it, it was probably not her idea. A friend of mine worked 24/7 doing a calculation, the numerics, the write-up for a project which was under time pressure - yet the almost finished paper laid on his supervisor's desk for three months before he got as much as an 'okay' as reaction. What kind of a behavior is that? Another friend was running into financial trouble, yet was unable to schedule a meeting or even a phone call to explain the issue, and I know more than one postdoc who has explained (only half jokingly) that the best occasion to talk to his supervisor is when they both happen to be on the same conference.

5. Humanity

We don't expect you to be perfect, but in return try to realize we are only human. Don't expect your postdoc to work on weekends or late at night just because you do so, she might indeed have a life on her own. Don't even think about raising an eyebrow if he leaves 'already' at 7pm, or works 'only' 60 hours per week. Don't expect him to miraculously recover your lost password, have a backup of revision # 3.8 which you accidentally deleted, or find the bug in a 100,000 lines code over night. Instead, think for a moment where you'd be without him.
The easiest way to a good working environment is communication. I mean, one that goes both ways. You might find out your postdoc is actually worth the time talking to. Let's hope you find out before he leaves.

PS: Luckily, there are also many good supervisors around, and I'd like thank all of them for their time and efforts.

While browsing I found a summary of a small survey regarding the question 'What makes a good supervisor', from '99 by Mary Opperman at Cornell. You find the results here, it's very similar to what I've summarized above.

* With one exception who ended up in a sanatorium.

Thursday, August 16, 2007

This and That

I am somewhat busy these days, so my apologies for being more quite than usual. For your entertainment a couple of distractions I came across lately:

  • helps to 'waste your time more efficiently' - your employer will be thrilled to hear!

  • Carl Zimmer shows us a collection of scientist's tattoos in his post Branded with Science

  • I stumbled across this totally enchanting website of the Toronto artist Susy Bee (see painting below)

  • Which reminded me of the following joke:

    An astronomer, a physicist and a mathematician (it is said) were holidaying in Scotland. Glancing from a train window, they observed a black sheep in the middle of a field.

    "How interesting," observed the astronomer, "all Scottish sheep are black!"

    To which the physicist responded, "No, no! Some Scottish sheep are black!"

    The mathematician gazed heavenward in supplication, and then intoned, "In Scotland there exists at least one field, containing at least one sheep, at least one side of which is black."

    For more jokes of this kind, see here.

  • In case you missed it, Cosmic Variance discussed in detail the geek factor of eating colored candy. Those of you who are too nerdy to waste time with reality can play with M&M's online (zero calories!). For alternative Smartie-fun, see 'Blow Up Smarties', or shoot down your M&M's here.

  • Quote of the day:

    “It's not that I'm so smart , it's just that I stay with problems longer .”

    ~Albert Einstein

Tuesday, August 14, 2007

Hans-Christian Ørsted and electromagnetism

Hans-Christian Ørsted
Unification of the fundamental forces is one of the big, recurring themes of theoretical physics: How to merge gravity with the rest of the standard model of particle physics? What is the GUT for the strong and electroweak force? Salam, Glashow and Weinberg were awarded the Nobel prize for the unification of electromagnetism with the weak interaction. We take so much for granted the idea that there should be a unified description of the forces of nature that it's hard to imagine that when physics started to be the science we know today, even electricity and magnetism were considered as completely disparate phenomena.

In April 1820, Hans-Christian Ørsted, professor at Copenhagen University, prepared an experiment he wanted to demonstrate to the students in his lecture class. His intention was to show how an electric current through a wire, created by the electric voltage supplied by a Volta-type pile, heats up the wire and lets it glow. By chance, a magnetic compass was standing close to the wire, and Ørsted noted that the needle of the compass was deflected when the current was switched on. Ørsted was magnetised. He didn't have time to have a closer look at this phenomenon immediately, but three months later, he sent a detailed four-page report about his discovery, written in Latin, to colleagues all over in Europe, Experiments on the Effect of a Current of Electricity on the Magnetic Needle. He had found a connection between electricity and magnetism, by quite a peculiar force pointing not along the direct line connecting the current and the needle, but perpendicular to it.

Hans-Christian Ørsted and an assistant, preparing a demonstration experiment for a lecture to show how an electric current heats up a wire. By chance, there is a compass standing on the table for another demonstration, and Ørsted notes that the needle is deflected by the current. Illustration from Louis Figuier: Les merveilles de la science, ou Description populaire des inventions modernes (1867), page 713. The portrait of Ørsted above is also from this book, page 712.

Hans-Christian Ørsted was the son of a pharmacist. He studied pharmacy, chemistry, physics and philosophy at the University of Copenhagen where he became a professor in 1806. Before, he had spent three years travelling and studying in Europe. In Germany, he was deeply influenced by Johann Ritter, best known today as the discoverer of ultraviolet light. Ritter was a proponent of the German "romantic natural philosophers" of that time, who were deeply sceptical about the Baconian method of doing science by isolating and dissecting natural phenomena in experiment. Instead, these thinkers believed in a deep unity of all nature, and a balance between the attracting and repulsive aspects of a single force responsible for all phenomena. a physicist who believed there was a connection between electricity and magnetism. As Ritter, Ørsted had speculated that galvanism and magnetism had one common cause in the motion of some fluid. Hence, in fact, Ørsted was not completely surprised by his discovery, since he had thought much about such a relation before.

Ørsted was a man with many facets. As a professor in Copenhagen, he continued his research with electric currents and acoustics, developed a comprehensive physics and chemistry program for the University, established new laboratories, and discovered the element aluminium. But he was also interested in language and literature, wrote poems, and was a close friend to Hans-Christian Andersen, the author and poet most famous for his collection of fairy tales.

Hans-Christian Ørsted was born 230 year ago today, on August 14, 1777.

Skål, Hans-Christian Ørsted!

  • There is a beautiful web site about Ørsted, albeit in French, L'expérience de Hans-Christian Œrsted (1820), with biographical details, information about the experiment and its reception, and scans of Ørsted's original Latin report, Experimenta circa effectum conflictus electrici in acum magneticam, as well as the English and French translations, published as Experiments on the Effect of a Current of Electricity on the Magnetic Needle (Annals of Philosophy 16 (1820) 273-277) and Expériences sur l'effet du conflict électrique sur l’aiguille aimantée (Annales de chimie et de physique 14 (1820) 417-425), respectively.

  • More background about the German tradition of "Naturphilosophie" in the early theories on electricity, including Ritter and Seebeck, can be found in The Form and Function of Scientific Discoveries, the Dibner Library Lecture by Kenneth L. Caneva at the Smithsonian Institution Libraries, November 2000

  • A detailed account of the circumstances of the discovery of electromagnetism by Ørsted is given in (subscription required) Chance in Science: The Discovery of Electromagnetism by H.C. Oersted by Nahum Kipnis, Science and Education 14 (2005) 1-28, doi: 10.1007/s11191-004-3286-0.

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Monday, August 13, 2007

Saturday, August 11, 2007


In the previous post about Dangerous Ideas, Amara and Quasar brought up the issue of designer babies, and I want to give that discussion a somewhat different spin. If parents could customize their babies, most would try to choose the best premises for their children to be happy. Or would they prefer them to be successful? After all, eventually the new Einstein's fame might fall back onto his parents.

But there are many other things to consider. It's really not that easy, is it? Unconfirmed or not, if there is even an oh-so-slight possibility of a correlation between height and intelligence, wouldn't it be better if the kid was tall? On the other hand, intelligence doesn't necessarily make happy, does it? Neither does it guarantee wealth. But you also don't want to end up asking your daughter If You're So Dumb, Why Aren't You Rich?

And then there is the unavoidable question of boy or girl. In a progressive society as ours, we of course wouldn't fall for the prejudices of our ancestors who thought a man more worthy than only his rib. No, we would rely on what research says, and who wouldn't want a pleasantly smiling baby? So you might want to take into account that "As Infants, Girls Appear More Emotionally Stable than Boys: Boys were more likely to cry and fuss and to turn, twist [...] They were really just trying to get attention". (I couldn't find a study that says at which age this behaviour stops.) Anyway, if you still want a boy, make sure his ring finger isn't too long.

Gee, it's getting really complicated with the design, isn't it? And it's getting more complicated the more we think we know about humans. Wasn't that nice in those days when we could just have sex? *sigh* But nowadays, you know, we just want the best for the kid.

Besides all these important points, there's the question of looks. Yah sure, we all know good looks don't matter, it's the inner value that counts, blahblah. But it can't harm if the kid is tall, and blond, and has a perfect nose, can it? So, honestly, if you could change anything about your looks, would you?

Just among the two of us, I for my part would really like to be some inches taller. I'm not much of a designer babe, but it's mostly Italian and French women's clothes that actually come in sizes I can wear. Such, the outcome of my shopping trips is either unnecessarily expensive or unnecessarily unfashionable.

Anyway, before I start complaining about this fuzzy hair that runs in the family, consider for a moment a world in which everybody could change arbitrarily the way he or she looks. Customize your hair and skin color, heights, bra-size, whatever. Don't like your toes? Your butt? That belly fat? Blink it away (who needs toes anyway). Okay, done? What would we have then?

To begin with we'd have a lot of beautiful people that fit into designer clothes, and who change their looks according the the recent fashion. Now lets see where this gets us. Well, our perception of beauty has grown with evolution. Characteristics we prefer most often have a biological background, and are linked to health, fertility, intelligence. The subtleties however change over time, with culture and tradition. Interestingly, they change rather fast, that is within only a couple of generations. E.g. I'd guess most Kate's from today would find the probable status of Leopold's teeth utterly repelling, and I wouldn't touch a guy with a wig. Even more interesting is how attractive we consider body fat or a tan (rspt. absence thereof), ornamental extensions or various kinds of creative self-mutilation.

Humans differ from other species mostly through the amount of time they spend thinking about something else than survival. A considerable fraction of that time is spend thinking about themselves, and about what others think about them (one can iterate that some more times). So we've used our big brains to form a society that provides possibilities to sneak around what we consider evolutionary disadvantages. The (logical?) continuation being to directly influence the 'fitness' of our genes.

The pre-stage to this fitness-enhancement already exists: we bleach our teeth to a 'healthy white', shampoo ourselves sexy, remove unwanted hair, get breast implants, take hormones for the fatter muscles, and pills for softer skin (you find the links in your junk mail folder).

And we hear people proclaiming they do it for themselves because it makes them they feel better. Sadly, even after you subtract self-deception, I think to a certain degree this might actually be true. It makes us feel better if we do what we think is the best to make ourselves loved - whether or not it works on the long run:

    Breast implants linked to suicide risk

    "Women who receive implants for breast enhancement are three times more likely to commit suicide, according to a new report that offered a sobering view of an increasingly popular surgery. Deaths related to mental disorders, including alcohol or drug dependence, also were three times higher among women who had the cosmetic procedure, researchers said. The report in the Annals of Plastic Surgery's August issue was the most recent to detect a higher suicide rate among women who had their breasts enlarged, providing a gloomy counterpoint to studies that showed women felt better about themselves after getting implants. Though the study did not look at the reasons behind the suicides, senior author Joseph McLaughlin, a professor of medicine at the Vanderbilt University School of Medicine, said he believed that many had psychological problems before getting implants and that their conditions did not improve afterward."

However, once we've outlived our evolutionary programme that suggests a link between the appearances that are currently considered 'beautiful' and healthy spouses, these labels of attractiveness are destined to loose their appeal - or is there an universal kind of beauty that will survive? Can we rely on 'beautiful' tomatoes to be healthy, and harmful things to smell nasty?

Extrapolate that to the next generation and to other criteria than looks (do we really know what intelligence is?). If you design your 21st century boy according to your best understanding of optimal fitness you might just go completely wrong. Our knowledge has been overthrown repeatedly during the evolution of mankind, and there's no reason to believe our generation in exceptional in this regard.

Now you are faced with a situation where you will need to predict where evolution goes, so your spouse fits in optimally - and that prediction is affected by how much we believe in our prediction. Good thing we have such big brains to intelligently design our babies, eh?

    “If life were predictable it would cease to be life, and be without flavor”
~ Eleanor Roosevelt

Besides spending time on thinking about ourselves, another factor that seems to be characteristic to mankind is the arrogance that came with intelligence. The believe that we are capable to improve within a decade or two what nature has worked on for millions of years, and the conviction that we will be able to cope with all potential trouble we cause. It seems nature favors optimists, so we are loosing inhibitions to cause problems because we're sure we can solve them in time. I'm not against genetic engineering - it surely has a vast number of potential benefits. I'm just pointing out that if applied in abundance, there is the probability we kick off a boulder rolling downhills in our back, and we'll have to spend our last breath running ever faster, away from the spirits that we called.

But let us just for a moment humor the idea that we design away many of the links between beauty and fitness that evolution has left us with. The interesting question is then, if all our developed criteria for 'beauty' fail - what would they be superseded by? And what would that mean for our scientific endeavors?

    “How many leading theoretical physicists were once insecure, small, pimply boys who got their revenge besting the jocks (who got the girls) in the one place they could—math class?”

Not to mention those of us who had to endure the insecurity of the small, pimply boys (sorry, couldn't resist. This sentence is definitely a highlight of the book). Anyway, what would a world without all the small, pimply boys look like? More beautiful? More boring?

Our perception of beauty is strongly linked to us being human. It has been formed through millions of years of evolution. Is there any reason to expect what we consider 'beautiful' is of cosmic significance? I there any reason to expect that us favouring symmetric patterns is linked to a fundamental feature of nature's laws?

Some while ago I sat in a seminar on cosmic strings, and I saw an animation about structure formation within that scenario. My immediate reaction was disgust - for the simple reason that I was reminded of a pile of crawling worms. I'm really sorry about it, but I'd call this utterly ugly, and I'd see a chance this might consciously or unconsciously influence my decisions to work on a topic. If you think this is totally nuts, then what makes you think other people's 'GUT-feeling', their intuitive liking or disliking, is more reliable? How many people work in astrophysics because they find the Hubble images beautiful? How many people are discouraged from becoming scientists because textbooks are 'ugly' (or the boys are insecure and pimply). And does this affect progress in research?

But more seriously: These worms really made me think. Are we too caught up in our human prejudices for beauty? Can we understand how the universe works without abandoning the limitations of being human? And can we consciously do that?

    "One always overcompensates for disabilities. I'm thinking of having my entire body surgically removed."

See also: The Beauty of it all

Since I'm tired of accusations made by people who didn't read what I wrote, or were not able to understand it, here's what I said in a nutshell.
1) Our perception of beauty has developed with evolution. What reason do we have to believe it is good guidance to understand the fundamental laws of nature?
2) If we aim to intelligently design the next generation, we should be aware that we are limited by our own intelligence. Do we want to pass that on?
What I've not said is
3) All theoretical physicists were once insecure, small, pimply boys, and that's why they understand the universe
4) Big boobs are beautiful.

Friday, August 10, 2007

10 Things you didn't know...

... about lists with 10 Things you allegedly didn't know.
  1. The list contains between one and ten items you never cared to know.

  2. The list contains at least one item you already knew so you don't feel utterly stupid.

  3. Adding numbered list items is the easiest way to convert a badly written, unstructured text into a format that has the appearance of useful information.

  4. This doesn't change the fact that it's a badly written, unstructured text with irrelevant content that you'd never have read without numbers from 1 to 10.

  5. It makes it unnecessary to come up with an intelligent title.

  6. There are most likely more than 10 things you didn't know, but the author didn't know these either, and who cares whether point 6 has been rated an unconfirmed urban legend repeatedly.

  7. Counting down items gives a sense of drama and usually ends in disappointment.

  8. Counting up gives a sense of increasing irrelevance and usually ends with a supposedly funny final point.

  9. Not counting at all causes the reader to verify the author counted correctly.
  10. By the time you've reached the last item, you've forgotten the first.

So then maybe somebody could tell me why on earth these lists have become so incredibly popular during the last years?

Thursday, August 09, 2007

Dangerous Ideas

"What is your Dangerous Idea?" was the Edge annual question of 2006. I am a bit old fashioned and don't like scrolling on a screen, so I bought the book which I've just finished reading. (Okay, actually my husband bought the book, but he never got to read it, sorry bout that.)

The answers from 108 "top intellectuals" range from brilliant to bizarre. It's a good read if you are lying in the garden wiggling your toes. If you don't have time for that, let me highlight some of the more interesting contributions.

To begin with I want to mention the usual suspects from physics who promote their pet ideas:
  • There is Leonard Susskind whose dangerous idea is the anthropic principle, and that we are living in a vast multiverse of possible environments most of which are uninhabitable for life. Which he finds dangerous because it threatens "physicists' fondest hope - the hope that some extraordinarily beautiful mathematical principle will be discovered that would completely and uniquely explain every detail of the laws of particle physics" .

  • Brian Greene finds it dangerous that people might take Susskind seriously "The danger, if the multiverse idea takes root, is that researchers may too quickly give up the search for [...] underlying explanations."

  • Lee Smolin features the idea that the universal laws of nature have evolved by natural selection. I fail to see what's dangerous about that, but like the question he raises "What about the fact that laws of physics are expressed in mathematics, which is usually thought of as encoding eternal truths?" Consider what would happen if your bank starts claiming the laws of maths have just changed! Sounds like a dangerous idea to me.

  • And Carlo Rovelli finds it dangerous that we might understand General Relativity and Quantum Mechanics.

Besides this one finds a whole number of sociological problems pointed out that grow increasingly important with technological progress, e.g.
  • Philip Campbell mentions that public engagement in science and technology can seriously go wrong because "those half-baked [perceptions and discussions] carry influence on the Internet and in the media"

  • Geoffry Miller extrapolates 'Runaway consumerism' in an excellently written piece, and explains that we haven't made contact with aliens because they've all gotten addicted to computer games. More seriously, he argues that progress in part of our civilizations turns more and more from real to virtual life. Neglecting reality, so his prediction, will be the doom of these civilizations which will be outlived by societies of 'practical minded breeders'.

  • Marco Iacoboni writes about imitative violence. Research in neuroscience has shown that watching other people's actions is 'mirrored' in our brains. What then does all this violence shown in the media to us? It activates a mirror system that was probably meant for us to learn through watching...

  • And Freeman Dyson warns us of the domestication of biotechnology with "cheap and user-friendly do-it-yourself kits for gardeners to design their own roses and orchids and for animal breeders to design their own lizards and snakes - a new art form as creative as painting or cinema".

Now lets go to the more bizarre pieces:

I'd like to mention Denis Dutton's contribution "A Grand Narrative", because I wasn't able to find out what he tried to say. Rupert Sheldrake thinks it is dangerous that we don't know "how green turtles find Ascension Island from thousands of miles away to lay their eggs." My award for the most bizarre essay goes to Rudy Rucker who speculates that "the mind is some substance that accumulates near ordinary matter - dark matter or dark energy are good candidates." I am looking forward to seeing the equation of state for mind-condensation.

The most embarrassing essay is Matt Ridley's promotion of neo-liberalism who proclaims that 'no society has grown poorer and more unequal through trade, exchange, and invention' and that the way to choose is as little government as possible because 'this is the process that has given us health, wealth, and wisdom on a scale unimagined by our ancestors'. One is tempted to ask, exactly who is 'us'?

Luckily, Ridley's writing is balanced by Mihaly Csikszentmihalyi's contribution who correctly points out that it is dangerous to believe that the free market is 'the ultimate arbiter of political decisions, and that there is an "invisible hand" that will direct us to the most desirable future [...]. This mystical faith is based on reasonable empirical foundations, but when it is embraced as a final solution to the ills of humankind, it risks destroying both the material resources and the cultural achievements our species has so painstakingly developed.'

Further, there are several self-referral answers which find it dangerous that an idea can be dangerous, or find it dangerous to promote dangerous ideas (i.e. by writing a book about them?). Randolph Nesse redirects the question to 'unspeakable ideas', which according to his definition are 'ideas that are dangerous to anyone who expresses them'. As an example he suggests an idea that 'offers dramatic data - you could respond to your spouse's difficulties at work by saying, "If they are complaining about you not doing enough, it is probably because you just aren't doing your fair share." In the earlier days, this was called honesty. I find it a dangerous development that saying the truth could be perceived as an 'unspeakable idea'.

And what is your dangerous idea...?

Tuesday, August 07, 2007

The Physical Tourist in Frankfurt (1)

I can imagine some of our readers have been in Frankfurt am Main at least once - albeit in most cases only at the airport. If you have some time to kill, for example because of flight delays, or if you just want to see a bit of the town: the city centre of Frankfurt is easy to reach by a 10-minute ride with the S-Bahn from the airport, either to "Hauptbahnhof" (the main train station), or to "Hauptwache" (near the city centre) [1].

Besides the standard "places to see", the scientifically minded tourist might definitely want to have a look at the Senckenberg Museum, one of the largest museums of natural history in Europe. It is run by the Senckenbergische Naturforschende Gesellschaft and named after Johann Christian Senckenberg, a Frankfurt physician whose 300th birthday is celebrated this year. On display in the museum are for example the unique, 50 million year old fossils from the nearby Messel pit, but kids will probably be most fascinated by the skeletons of dinosaurs and mastodons - and by the true-to-life replicas of a Tyrannosaurus and a Diplodocus in the front yard of the museum.

The Senckenberg Museum with the replica of a Tyrannosaurus. The building on the left with the green dome covering a small astronomical observatory is the home of the Physikalischer Verein.

If you're standing in front of the museum [2], you will notice to the left a building with a small astronomical observatory on the roof - this is the home of the Physikalischer Verein, the "Physical Association". Both the Senckenbergische Naturforschende Gesellschaft and the Physikalischer Verein have quite an interesting history: They have been founded in 1817 and 1824, respectively, following a suggestion by Johann Wolfgang von Goethe at a visit to his hometown Frankfurt, as institutions of research and public outreach in the natural sciences. Foundation was not by the local ruler or government, but by private persons - Frankfurt citizens who until today operate and generously finance these science institutions out of personal memberships and private donations.

The building of the Physikalischer Verein at the corner Senckenberganlage - Robert-Mayer-Straße. It was constructed in 1907 and harboured the Physics Institute of the Frankfurt University between 1914 and 2005.

Since the time of its foundation, the Physikalischer Verein had been engaged in a lot of scientific activities: It organised astronomical observations to establish time for the City of Frankfurt, lectures on science for students and the Frankfurt citizens, and it sponsored research in physics, chemistry, and technology. To this end, the Verein paid lecturers and scientists and provided office and laboratory space for them. Early research at the Physikalischer Verein included, for example, the development of an electric telegraph by Samuel Soemmering, and the demonstration of the telephone by Philipp Reis. When the Frankfurt University was founded in 1914, all these activities were integrated into the physics institute of the new university, and hosted in a large building next to the Senckenberg Museum, which the Physikalischer Verein had built in 1907.

In the meantime, the physics institute has moved on to a new campus on the outskirts of Frankfurt, and the building is mostly empty, used only for public lectures on astronomy and observations at the telescope on Friday nights. There are plans to establish a Science Centre and a Planetarium on the premises, but currently, the building is dreaming of its exciting days in the past - for example, when in the early 1920s, Otto Stern and Walther Gerlach had been conducting here the famous experiment demonstrating space quantisation of magnetic moments for the first time.

The entrance door to the - now mostly empty and unused - building of the Physikalischer Verein. On the left is the plaque commemorating ...
... the Stern-Gerlach experiment, conducted here in 1921/22. The plaque shows schematically the apparatus of the experiment, and Stern and Gerlach to the left and right, respectively. The text says: "In February 1922, the fundamental discovery of the space quantisation of the magnetic moments in atoms was made in this building of the Physikalischer Verein, Frankfurt am Main, by Otto Stern and Walther Gerlach. The Stern-Gerlach experiment is the foundation of important physical and technical developments of the 20th century, such as the nuclear resonance method, the atomic clock, or the laser. Otto Stern was awarded the Noble prize for this discovery in 1943."

In the early Bohr-Sommerfeld theory for the quantisation of the motion of electrons in atoms, orbiting electrons could have only discrete values of angular momentum, and thus, only discrete magnetic moments. Moreover, in an external magnetic field, these magnetic moments were supposed to have only specific, discrete orientations with respect to the direction of the field. For example in silver atoms, which have one "hydrogen-like" valence electron, there should be only two possible orientations of the magnetic moment in an external field.

Otto Stern, who had been as a postdoc with Einstein in Prague and Zurich and had become an assistant to Max Born in Frankfurt in 1919, had the idea that one might check space quantisation of magnetic moments using atomic beams - a technique quite new at that time: atoms are evaporated from an oven into a vacuum, and with systems of apertures and screens, one can obtain well-defined, sharp beams. Stern and Born had successfully used this method to study the thermal velocity distribution and the mean free path of atoms, and Stern thought it should be possible to test if space quantisation is real:

If a beam of atoms with a magnetic moment passes through a magnetic field with a strong gradient, the gradient of the field causes a deflection of the atoms according to the orientation of their magnetic moments. Now, if the magnetic moments can have any orientation in the magnetic field (as in the classical theories of the atom of Lorentz and Zeeman), the deflection would have any value, and the beam would be smeared out. If, however, the magnetic moments could only have some discrete orientations in the magnetic field (two, for silver atoms), deflection would also be discrete, and the beam should split (in two beams, for silver atoms). Stern was confident that this splitting could be measured (Otto Stern: Ein Weg zur experimentellen Prüfung der Richtungsquantelung im Magnetfeld. Zeitschrift für Physik 7 (1921) 249; English translation in Zeitschrift für Physik D: Atoms, Molecules and Clusters, 10 (1988) 114), but he also knew that the experiment was tricky.

Fortunately, he had a colleague who was an expert in atomic and molecular beams: Walther Gerlach, assistant to the professor of experimental physics in Frankfurt since 1920. Stern had no trouble to convince him that they collaborate on this problem.

They had to cope with many technical and organisational problems: The experiment was quite delicate, requiring adjustments of the beam and magnets to within 0.01 millimetre, maintaining a vacuum for the beam, and detection of tiny amounts of silver atoms deposited by the beam. Moreover, funding was difficult because of the consequences of the war and the beginning inflation. They could get money for the experiment from grants of Einstein at the Kaiser-Wilhelm-Institut in Berlin, from Henry Goldman of Goldman and Sachs, and from entrance fees Max Born had charged for a series of public lectures on relativity [3].

But finally, in February 1922 - Stern had already left Frankfurt and moved on to another position in Rostock - Walther Gerlach succeeded in measuring the splitting, in quantitative agreement with the calculations of Stern.

The postcard Walther Gerlach sent to Niels Bohr on 8 February 1922 to tell him about the discovery of space quantisation. It shows a photograph of the beam splitting (actually, the width of the splitting is only 0.2 millimetre), with the note: "Attached the continuation of our work (Zeitschrift für Physik 8 (1921) 110): The experimental proof of directional quantisation. Silver without magnetic field / with magnetic field. We congratulate on the confirmation of your theory." (Source: Physics Today, Courtesy AIP Emilio Segrè Visual Archives). The same photos are also shown in the short discovery paper by Otto Stern and Walther Gerlach: Der experimentelle Nachweis der Richtungsquantelung im Magnetfeld, Zeitschrift für Physik 9 (1922) 349.

It's ironic, in a sense, that the theory Stern had used to calculate the splitting of the beams of silver atoms was wrong: as we know today, the splitting Gerlach eventually managed to observe is not caused by an electron orbital angular momentum taking on projections along the axis of the magnetic field of ±h/2π, but by the electron spin, which is only have as large and has projections ±h/4π. However, thanks to the electron g factor of 2, the value of the splitting coincides, again, with the calculation of Stern.

These subtleties notwithstanding, the Stern-Gerlach experiment is now one of the prototypical experiments showing quantum physics at work - and in case you have time to kill in Frankfurt, you can have a look at the place where all this has happened some 85 years ago.

[1] To check out connections using public transport, the website of the local transport authority,, is very helpful - useful connections are Airport-Hauptbahnhof, Airport-Hauptwache (city centre), or Airport-Bockenheimer Warte (Senckenberg Museum and Physikalischer Verein).

[2] For a first orientation, is as usual helpful. The dinosaurs in the yard aren't yet there in the aerial photo.

[3] A full account of the very interesting circumstances around the discovery of the Stern-Gerlach splitting can be found in Stern and Gerlach: How a Bad Cigar Helped Reorient Atomic Physics, by Bretislav Friedrich and Dudley Herschbach, Physics Today, December 2003, pages 53-59 (PDF), and Space quantization: Otto Stern's lucky star, also by Friedrich and Herschbach, Daedalus, Winter 1998.

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