Monday, March 31, 2008


Complex Adaptive Systems: An Introduction to Computational Models of Social Life

By John H. Miller and Scott E. Page
Princeton University Press (March 5, 2007)













Sunday, March 30, 2008

Lost in Translation

Ever wondered what happens if you use an algorithm to translate a text back and forth to French, German, Italian, Portuguese, and Spanish? You can to this with the super-babelizer Lost in Translation. As an example, here is the translation of the first paragraph of 0801.3471 (for no specific reason).

The original:

Classical General Relativity in more than four spacetime dimensions has been the subject of increasing attention in recent years. Among the reasons why it should be interesting to study this extension of Einstein’s theory, and in particular its black hole solutions, we may mention that

  • String theory contains gravity and requires more than four dimensions. In fact, the first successful statistical counting of black hole entropy in string theory was performed for a fivedimensional black hole. This example provides the best laboratory for the microscopic string theory of black holes.

  • The AdS/CFT correspondence relates the properties of a d-dimensional black hole with those of a quantum field theory in d − 1 dimensions.

  • The production of higher-dimensional black holes in future colliders becomes a conceivable possibility in scenarios involving large extra dimensions and TeV-scale gravity.

  • As mathematical objects, black hole spacetimes are among the most important Lorentzian Ricci-flat manifolds in any dimension.

And the translation:

Traditional general of relativity in more than four masses of that the time of the space was the subject of the increase attention these the slipped years. To the relations of transformation, so that he had that to being interesting, to this extension of the theory of Einstein to study and in the detail of the relative solutions to perforate black color, that we can we mentioned this
  • The theory of the series of the characters will count the force of the gravity and it more has the necessity of the one of mass four. They executed the first guessed right statistical client of the entropy of the black color that really perforates in the theory of the series of the characters the end to perforate the black color of the fivedimensional. This better example releases the laboratory available for the microscopic theory of the series of the characters of the black color of the perforations.

  • The correspondence of AdS/CFT connects the characteristics of a D dimensional schwarzen that the sacadores with those with a theory of the zone of the section of the time in the D without mass 1.

  • The production of the perforations that the high-dimensional-black color in her the future transforms of colliders inside the great possibilities imaginable ones into the writing of the suggestion adds of the film and in the fairs of TeV the force of the gravity.

  • As matemati of the messages those we belong spacetimes of the black color that the sacadores to the tubes the greatest piece of the important Stocherkaehne I gave curly Lorentzian in each possible measurement.

I hope that clarifies everything.

Makes me wonder why there is no requirement these translation maps be invertible.

Thursday, March 27, 2008

This and That

Wednesday, March 26, 2008

Hazardous Quantum Mechanics

Quantum mechanics is hazardous - make sure to wear a lab coat and protective goggles when handling delicate formulas!

(Found under the heading "Research" at, the online job market for higher-education professionals who are aiming to develop their career in Germany, Austria or Switzerland. I wonder what the operators of the web site know and think about their target group?)

Tuesday, March 25, 2008

10 effects you should have heard of

  1. The Photoelectric Effect

    Light falling on a metal plate can lead to emission of electrons, called the "photoelectric effect". Experiments show, for this to happen the frequency of the light needs to be above a threshold depending on the material. This finding was explained in 1905 by Albert Einstein who suggested that the light should be thought of as quanta whose energy is proportional to the frequency of the light, the constant of proportionality being Planck's constant. Einstein received the Nobel Prize in 1921 "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect."


  2. The Casimir Effect

    This effect was first predicted by Hendrik Casimir who explained that as a consequence of quantum field theory, boundary conditions that can for example be set by conducting (uncharged!) plates, can result in measurable forces. This Casimir force is very weak and can be measured only at very small distances.


  3. The Doppler Effect


    Recommended reading: The Physics Classroom Tutorial.

  4. The Hall Effect


    Recommended reading: Our post on The Quantum Hall Effect.

  5. The Meissner-Ochsenfeld Effect


    Recommended watching: Amazing Physics on YouTube.

  6. The Butterfly Effect

    "A legendary butterfly flapping its wings in Rio changes the weather in Chicago. (I have lived in Chicago and personally suspect that nothing can change the weather there.) It always appears to be the same butterfly whenever anyone tells of this example. One would think it possible to imagine, by a vast conceptual leap, some other example. Maybe a moth in Omaha, perhaps, or a starling in Sheboygan. Whatever winged creature is responsible, the point is that any small change in a chaotic system can, and typically does, have large and amplifying effects. Thus this sensitivity implies that the detailed initial conditions - how fast, at what angle, and precisely how the starling flapped its wings - would have to be known to infinite precision to predict the result."

  7. The Hawking Effect



  8. The Zeeman Effect/Stark Effect




  9. The Mikheyev-Smirnov-Wolfenstein Effect


    Recommended reading: The MSW effect and Solar Neutrinos.

  10. The Sunyaev-Zel'dovich Effect



  11. Bonus: The Pauli Effect


    Recommended reading: Our post Happy Birthday Wolfgang Pauli.


Saturday, March 22, 2008

How the Easter Bunny gets its Eggs

As every child in Germany knows, before and around Easter, hares are extemely busy, because they have to colour thousands of eggs and to hide them carefully in the gardens and woods, often together with chocolate eggs and chocolate bunnies.

Spoiler warning: Plot and/or ending details follow.

I do not remember at which age I become aware that the eggs my brother and I went searching on Easter morning had actually been coloured by my father the night before. But colouring eggs has been a traditional thing to do ever since in our family the night before Easter.

You just start by hard-boiling a dozen of eggs for about 8 to 10 minutes - best use a large pot, and give plenty of salt in the water to avoid premature breaking of the shells. While the eggs are boiling, prepare cans with the colourant. The dye my father has always been using comes in small tablets, which are dissolved in a mixture of hot water and vinegar.

The boiled eggs are put, still hot, in the colour bath, and let there for about five minutes each. There are several other methods to colour eggs, for example with "natural" colourants from plants, or with colourants for use with cold water. But, as a long experience shows, this procedure really works best and gives the most satisfactory results.

Once the eggs are coloured, you can rub them with some bacon rind to give them a nice, shiny finsish. Voilà!

All that remains to do: hide them! But try to make sure that you will find them again before next Easter.

Happy Easter!

Friday, March 21, 2008


Easter is coming. In case you share my holiday confusion which seems to be wide spread in multi-national workplaces, Easter is an official holiday in Canada, it is not in the USA, it is in Germany, and (as my husband informs me for quite obscure reasons) it is not in Rumania. Feel free to add your observances.

Just to remind you what Easter is about: it's the time of the year when the bunnies lay eggs, and we sacrifice the last chocolate Santa-Claus, which will be reborn on Easter Monday. It's the time of the year when German Rabbis argue with the Pope about the wording of prayers and other nations spray-paint chickens. It's the time of the year when the stores have to rearrange their seasonal event's section to make place for Mother's day, and kids put the chocolate eggs under the sofa pillows, so watch out.

Here in Waterloo, we still have snow but it's slowly melting. Yesterday I got caught between a remaining 2m snowbarrier and a potholy street with muddy puddles. An approaching bus managed to produce a very impressive wall of dirty ice-water that soaked my clothes from head to the toes. Spring is coming! And it's about time cause I accidentally threw one of my last gloves down the garbage chute. However, I just talked to my neighbor who informs me his father is a meteorologist and (blahblahblahblah) it will apparently remain below zero around here for at least the next two weeks.

A very happy Easter to all of our readers :-)

Thursday, March 20, 2008

Experimental Traffic Jams

You may have already come across this nice movie of a large-scale physics experiment:

From Traffic jams without bottlenecks—experimental evidence for the physical mechanism of the formation of a jam by Yuki Sugiyama et al., New J. Phys. 10 (2008) 033001 (including movies).

If ever you have been driving on a crowded highway, chances are high that you have taken part in a similar "experiment", just that no one has captured it on film and put it on YouTube. This happened to me last Monday on my way to work: First, I got stuck in a traffic jam at the merging of three lanes into two - no wonder in rush-hour traffic. But then there was a second full stop, a few kilometres down the road, and for no obvious reason at all - no construction site, no junction, no accident... it was the classical phantom traffic jam.

This kind of annoying phenomenon occurs on roads with a steady traffic flow if the distances between cars become too small: As soon as a car slows down a bit for whatever reason, the following car must break also, and so on. And because drivers are humans and have a reaction time, they break ever later, and ever stronger, and at one point, they come to a full stop. This stop then moves "upstream", in the opposite direction of the traffic flow - it's a shockwave-like phenomenon that has been intensively studied by German physicists since the 1990s.

But it seems that no one so far has checked the models that describe the phantom jams in a controlled fashion, and so, the Japanese guys have set up an experiment: Take 22 cars, put them on a road, and tell the drivers to go on at a constant speed. As so often in physics, periodic boundary conditions are a useful trick to simulate a much larger system - the cars are driving on a circular track. It doesn't take long before the shockwave develops.

Here is a chart, taken from the paper, that shows the evolution of the flow of the cars:

The horizontal axis shows distance along the circular track, the vertical axis indicates time. The lines trace the paths of each of the 22 cars. The flatter the line, the higher the speed, and a vertical segment of the line means halt. One can see how a perturbation of the steady flow set in after just 40 seconds around metre 150 of the track. At closer inpection, the culprit seems to be a car that was a bit slower than the others for a while. Speeding up (the kink in the orange circle) doesn't help - the following cars have to break, and the phantom traffic jam can't be avoided anymore. The plot shows nicely how the perturbation - the zone of zero velocity (aka the jam) - travels at constant speed in the direction opposite to the traffic flow.

Too bad - phantom traffic jams just happen, it's all physics...

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Monday, March 17, 2008

Can Technology make us Happy?

"Can Technology make us happy?" was the question raised in one of the discussions at the SciBarCamp I attended last weekend. Lead by Diane Nalini and Lee Smolin, it was a very lively and fun meeting. Since in addition to the discussion being well attended I am bad with recalling names anyhow I won't even attempt to reproduce who said what in reply to whom. Instead, I will just summarize my thoughts on the matter.

What kind of a question is this anyhow?

To start with I want to set the stage for how to interpret the question. I was sitting next to a white haired man who proclaimed he "loves watching Fox News" (because that tells him - directed at Lee - "how your fellow citizens are really like"), and he certainly left me with the impression that he was very happy about that.

This reminded me of an article I read last month about a criticism of 'educational' children's TV by Aric Sigman, a US psychologist living in Britain. He was quoted (in this article) by saying

"Television makers will always justify themselves by saying that children enjoy their programs," Sigman said. "They say they make children smile and laugh.

"But children will also smile if you give them cocaine. The argument that children enjoy something or laugh at something is not the basis on which you decide what is good for them."

Notwithstanding the question of whether or not that specific BBC program Sigman was referring to can compete with cocaine, the point is well made. There are lots of examples for behaviour that make humans happy on the short term, but on the long term will lead to more unhappiness. Addictions of any kind fall into that category. That's why people try to give up smoking. That's why parents tell their children not to eat chocolate all day long. And that's why by now people make new years resolutions not to check their emails all ten minutes, and the Departments of the Canadian government urge their employees to turn off BlackBerries over night. Because despite the dopamine kick when you have new mail, on the long run it can have side-effects like increased stress and attention deficit.

Thus in the following I will understand happiness as that of the sustainable kind, such that it does not on the long run lead to damage. I believe that was meant with the question raised, but given some of the comments I just wanted to clarify this in the beginning.

Do you want to live in the last century?

One of the most frequent arguments I have heard for why technology increases happiness is that the circumstances of our living have objectively considerably improved during the last centuries. Since I am not a technology enthusiast, I have repeatedly encountered the question that was also raised in this meeting "But who would want to live in the last century?". Underlying this criticism is the implicit assertion that people living in the last century must have been less happy than we are now.

To give credit to the steady increase in life-expectancy, Ruut Veenhoven proposed to use the 'Happy Life-Expectancy' (HLE) as a measure, which is the life-expectancy in years multiplied by average happiness - a factor that increases with improving medical supply. There are factors that are absolute about happiness. For example seeing children suffer from illness or war is certainly a cause of pain that, if avoided, objectively increases happiness. The same goes for generally covering all basic human needs like clean water, food, housing.

Most of these basic needs are fulfilled for the majority of people living in North America and Europe [1]. Further economical growth does not correlate with happiness in any obvious way. As Robert Hill from the University of New Brunswick puts it "Measures of average happiness in industrialized countries typically show little or no upward trend over time, despite substantial growth in real per capita incomes."

I therefore want to mention two other factors besides the absolute level of the circumstances that remain important even in industrialized countries with a high living standard

A) Change

Change in itself has a positive meaning for many of us. Stagnation results in frustration, and lack of novelty is perceived as a troublesome crisis. This is not so surprising as contempt and satisfaction with the state of things can't have been much of an evolutionary advantage over those cave-men who where constantly trying out new ways to use nature for their purpose. I.e. the time derivative matters.

B) Knowledge

Knowing (or believing) that other people live in better circumstances, are happier, wealthier, prettier, have greener grass, more sex, and whiter teeth lowers the own happiness. I.e. the spatial derivative matters as well.

[If anybody can point me towards references supporting/defeating the importance of these factors, this would be greatly appreciated.]

How people weight these both factors is of course individually different, and differs also among nations. The question of improvement for example is very much tied to hope and faith, and it is in this regard quite interesting that a study by the National Bureau of Economic Research asserts

"while "poor and left-wing Europeans" are unhappy about inequality, [i]n the United States, in contrast, the poor may believe in "social mobility" (so that being poor now doesn't mean they will be poor in the future) and thus be less concerned than Europeans about inequality."

(One may wonder however how much attention should be paid to a study by a Bureau of Economic Research which claims that believing in "social mobility" -aka the American dream - is the way towards happiness. Says the middle-class, middle-left, middle-European. It is also worthwhile to note that such happiness which relies on psychological factors is vulnerable to ego blows like e.g. an economic crisis.)

Taking into account factor A), since we all live in the 21st century and know how our life is like, even if we would be willing to accept a lowered life-expectancy we most likely wouldn't be happy to be thrown into a lower standard environment. Happiness is path dependent - it doesn't only depend on where you are and what you see, but it depends on where you've been before and what you've seen before. It is an interesting question whether it makes you unhappier about your own situation to imagine the potentially much better circumstances of living people might have in the year 2200.

Interestingly, there was one person in this meeting who indeed said he'd like to live around the time of Maxwell when electricity was invented. I think he made a good choice there, it must have been a tremendously interesting time with a lot of change and progress.

To come back to the effects of technology: Technology changes our world incredibly fast. Think of how much has changed in your life within the last 15 years. You take your cellphone everywhere, can log onto a wireless in almost every café, and have your music collection stored on an MP3 player smaller than your hand. Many of us just like to try new things. I am not much of a gadget person (in that I hardly ever buy something) but since early childhood I have a fascination for buttons that in some sense still exists. You'd push and something would happen! I just loved pushing buttons of all kind, whether that was the elevator, the stereo, or everything on the car's dashboard. Today I see adult men pushing buttons on fancy looking electronic equipment in the Futurestore. Falling in love with remote controls probably isn't encoded in our DNA but playing with and understanding new toys likely is.

And we get used to new gadgets so fast. We no longer wonder when somebody on the streets talks into the air - because we know he most likely wears a headset and is on the phone. We have navigation systems with GPS, sleep with our cell-phones or BlackBerries, and pay our bills online. I've gotten used to people who start typing on their handheld in the middle of a conversation, and I am reasonably sure I have several friends who check their emails while sitting on the loo.


The article quoted above is from 2003.

It is this constant novelty and improvement about technology that keeps people happy when their basic needs are fulfilled, not the actual level of complexity of the technology. The twist is now if one identifies technology = change = improvement one is tempted to believe it is technology that makes us happy. Needless to say, it is far from necessary that technology will always lead to improvement of the quality of our living that increases happiness.

    "Futures made of virtual insanity
    now always seem, to be governed by this love we have
    For useless, twisting of our then new technology
    Oh now there is no sound for we all live underground

    ~ Jamiroquai

Left Behind

For both factors A) and B) too much variation, over time or space respectively, is as undesirable as too little.

B) Inequality is very much a source of competition and keeps us going. Maybe your neighbor's grass is indeed greener, and maybe the highways in Europe are indeed better, and maybe the streets in Toronto are indeed cleaner. Our constant wish for improvement is very often what eventually leads to progress, and knowing that others do better can be a huge motivation. However, it can also be a source of jealousy and anger. If inequality is too large as that there is hope the higher level can ever be achieved, it can lead to violence because the less fortunate have to fear they are being left behind. You see these tension in many large cities where the very rich live right next to the very poor, in countries where social barriers are to high to be crossed (again it matters what people 'believe' how high these barriers are) .

A) Technological improvement isn't necessarily a source for happiness. (I hesitate to use the word progress here, since I'd think progress should imply improving happiness.) Humans need time to adapt to change, and if time is insufficient those who can't adapt will be left behind. Having learned that technological improvement leads to more happiness, we see a rapid incorporation of new technologies into our lives. This however means for many people that they are in a constant pressure of learning new things, or they will no longer be adequate for their job. Peer pressure is also an important factor in this regard.

If you don't have a TV, no cellphone, no high speed Internet access at home, don't write emails, are not on Facebook, not on MySpace, and don't know what Twitter is... - Gee, what century do you life in? Do you actually exist?

The capacity of the human brain to process new information is finite. It is hard to say when this capacity will be reached, and our working memory will no longer be sufficient. Not all of us will reach it at the same time, and those who reach it first will be left behind. There are limits to how many news feeds we can follow, and how many people in our social networks we can really keep up contact with. More scary, our understanding of the economical and ecological systems that are at the very base of our well-being is very insufficient.

Maybe we are close to reaching the stage at which humans start falling behind and are no longer able to cope with the change they have caused themselves. But I would guess that with the invention of the automobile there have been voices saying the human brain wasn't meant to deal with speeds as high as 30km/h, yet it turns out after some practice driving a car at much faster speed feels pretty much natural.

Once and again, the human brain has proved to be a marvelous result of natural selection. But no matter how marvelous, if the changes we cause continue to take place faster than the evolution of our brain - as has been the case for several thousand years now - then there will be some time when our brain reaches its limits, when we will no longer be able to fully grasp the change we are causing ourselves.

If technological progress becomes too fast as that we can really understand and appropriately act on its implications, we start to move on very slippery terrain.

Choosing between worms

I think it was Michael who pointed out that technology is nothing but a tool. It is intrinsically neither good or bad, and the outcome depends on how we use it. People make mistakes with new tools, and it takes some time to learn how to use new technologies appropriately. Somebody else mentioned that there is a huge pressure to use technologies to begin with, and not really an option to just not use them, instead we might end up being forced to "choose between worms" (so I finally figured out what was in Pandorra's box).

I very much agree that we have to learn how to deal with new technologies, that making mistakes is often unavoidable but that in most instances they can be corrected. This requires however that there is sufficient time, and a mechanism in place to make these corrections. As I argued in an earlier post The Spirits that We Called, I am concerned that the rapid distribution of the internet and the unregulated development of its features messes with the institutions of our societies and our political systems that are meant to deal with these technological changes to begin with.

To borrow a term from Homer-Dixon's book "The Ingenuity Gap", one has to wonder whether we have the social ingenuity to appropriately deal with the changes we have already caused. And that is the actual problem.


I want to mention some examples of where technologies have unwanted drawbacks that were brought up in this discussion, and I invite you to submit yours in the comment section (I will add them). Unsurprisingly, much was about the Internet, esp. the Web2.0, but feel free to to comment on technological developments in a broader sense

  1. Splitting of Communities
    I think it was Lee who mentioned this first, and it was later picked up by others. The believe that the internet allows access to all kinds of opinions and thus supports open-mindedness is doubtful. Yes, in principle the internet allows us to collect an abundance of information, and to connect with millions of people all around the globe - people who belong to all kinds of nations, political orientations, and religions, and have a large variety of opinions.

    But in practice most of us put together own social networks of necessarily limited size, because it is just not feasible to deal with all of that information (this goes along the lines of the previously mentioned necessity to filter and structure when faced with information overflow).

    However, in contrast to our actual neighbors, relatives, or people we meet in cafes and so on, it is very easy to keep an online social network 'clean' of disturbing influence. Like, I can forward your email into my junk folder, remove you from my friend's list, and delete your comments. Even better, if I have picked the right people, they will support the decision to do so and reward my in-group favourism. Outside the virtual world it is much harder to get my friend's husband/landlord/cousin to shut up on family meetings (not to mention these guys I meet in cafes). The websites we check daily belong in many instances to some kind of community whose general sentiment we like, and we stick to forums where we share a common interest. The example was mentioned that changing on the internet from the camps of Clinton to Obama is like entering another world.

    Thus, in many instances the possibility to select people in our networks can indeed increase gaps in our community instead of bridging them.

  2. Distortion of Online Communication
    Somebody pointed out that scientific discussions on blogs in many instances are overloaded by noise and insults (a comment that caused many people to nod). It is sad, but though blogs would offer the possibility to build and improve global scientific networks, one has to wonder whether the impression that is de facto raised by such discussions in the public about the way science is done, is favourable or damaging. To generalize the issue, especially non-verbal online communication between people who don't know each other personally is attached with difficulties. Failing to realize limits of people's abilities to adequately express themselves, combined with lacking patience, a low attention-span, the usual temptations of anonymity, and cyber-disinhibition in general results in ugly social phenomena in the virtual world that can very really affect people's happiness.

  3. Impact on Social and Political Systems
    I just want to list the previously mentioned point that the impact of mass media like TV and especially the internet on our social and political systems is very poorly understood and potentially worrisome. As a recent example, read this article of how cellphones spread hate messages in Kenya. It is easy to dismiss such events, and to believe oneself is immune to such hypes. But go ask yourself how often you are affected by things you have read. Especially if one has heard and read about a topic repeatedly it will acquire some status of importance. And as things are with the internet, some importance leads to some more importance. The internet is a tool that affects the opinions of millions of people, and it does without doubt influence the way we form opionons and make decisions.

  4. Industrialization
    There is an abundance of drawbacks that came with the industrialization era that were only realized with delay, such as air and water pollution, health and environmental hazards in chemicals, side effects of food preservation such as lack of certain vitamins or overdose of metals used for storage.

  5. Civilization Diseases
    We were not evolutionary trained to live with an abundance of food, or to sit in a chair 12 hours a day. Neither where we meant to cope with constant noise, frequent travel over several time-zones, or staring at a screen for hours and hours. In many cases, overweight, back-, stomach- and sleeping problems are a result of these changes.

  6. Teaching and learning
    There were several examples of how the use of technologies in teaching can have drawbacks. I believe it was Diane who mentioned that teaching via Powerpoint presentations, and making them accessible online leads the teacher to believe they can go through topic faster than appropriate (they can just look at it again later), makes students believe they don't need to take notes (which would be beneficial to structure thoughts), or lowers attention generally (if I don't get it, I can download it tomorrow). I don't teach myself, but I've heard similar remarks about making lectures accessible online - it leads students to believe they can always look up things later, yet they don't actually do it, or if, they do it last minute - just because it is possible.

  7. Information Overload


Many of us equate technology with progress, improvement, and an increase of happiness. Even if the actual value of a gadget in terms of progress is not clear, they are often a source of novelty, and novelty - in technology, as much as in art, entertainment, science, or your peer group's gossip - can be pretty much addictive. For these reasons, technological developments are mostly considered positive changes, which in turn leads us to push forward these changes and incorporate them rapidly into our daily lifes.

But it must not necessarily be the case that these changes are good and lead to increased happiness. It needs time for us to judge on the advantages and drawbacks of changes. Dealing with unwanted side-effects is not an easy task, not one that takes place automatically, and not one that an invisible hand guides; it requires care, thought, and political institutions that ensure happiness is sustainable even on the expenses of dopamine-kicks. Instead of 'Can Technology make us Happy?', the question we should then actually ask is
    If technology makes us unhappy, will we be able to realize and correct our mistakes in a timely manner?

[1] According to my site tracker that covers on the average more than 90% of all visitors of this blog.

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Saturday, March 15, 2008


This weekend, I am at the SciBarCamp in Toronto, the first science Bar Camp! Having been told the name 'Bar Camp' is a pun on 'Foo Camp' (also known as "unconference"), I queried Wikipedia on the origin of this word. As the entry on foobar explains "Neither foo() nor bar() accomplish anything useful." The first association I had to SciBar was Psi-bar (a notation commonly used for anti-particles), and the first thought that crossed my mind when hearing 'Foo Camp' where the Foo Fighters (actually, these FooFighters) but it seems the camping sort of foos are Friends Of O'Reilly who like to hang around at the bar, though this is apparaently a backronym. The emergence of the name in itself would probably make a good topic for a PhD thesis in linguistic.

Either way, according to the website, the camp is on various edges, so for example the edge of science, the edge of technology - and, on my German-gauged organization scale, certainly on the edge of chaos. As I recently read, allegedly the edge of chaos is where complex systems solve problems most efficiently. However, if I am faced with a schedule on a flip chart that has been crossed out, rewritten, and rearranged so many times it is just unreadable, I have my doubts about the efficiency of spontaneously arising self-organization. Especially if one has a 100km commute to the conference site to have a look at said flip chart.

Okay, leaving aside my disliking of words that start with the syllable 'un', the workshop is packed with interesting people, definitely fun, and so far an extremely inspiring and thoughtprovoking event. Since it seems that my de facto negligible complaint has more words than my expression of enthusiasm, and I am currently in lack of adjectives that would appropriately describe my impression, I will just click on some of these buttons in the wysiwyg editor... and voila, there we have boldfaced enthusiasm ;-)

More about the SciBarCamp later, need to un-wind now. (Is the traffic on Gardiner ever not 'moving slowly'?). A nice weekend to all of you.


Friday, March 14, 2008

Wednesday, March 12, 2008

Here it goes again

I am back in my office at PI. There was indeed a guy sitting at the next desk (see footnote [1]), but he was only temporarily visiting for the weekend workshop on Origins and Observations of Primordial Non-Gaussianity - apparently the presently hottest topic in Cosmology. Should I find the time, I will write a post on it sooner or later.

The copy of the OpenLab 2007 arrived, which looks very nice in the bookshelf next to the 2006 edition, and I am looking forward to the 2008 version. Besides this, bills are piling up in my mail slot, papers are still piling up on my desk, and snow is still piling up in the parking lots. Speaking of snow, you might want to meet the man who wants even more snow. Compared to last year this winter has been very mild, so congratulations, Canada for preserving your national Igloo.

The previously photographed potholy street now has an orange warning sign saying 'ROUGH ROAD'. Since running on snow isn't much fun, and the indoor track in Waterloo was closed due to an ice hockey championship (or something like this), I retreated to running on the treadmill. This is admittedly one of the most depressing sport scenarios I can imagine, but one finds vision even in PI's gym, if only because the equipment apparently comes from a company with name 'VISION'.

Oops, I'm running late for the colloq.

OK, Go

Tuesday, March 11, 2008

Historical Meme: Seven Things about Richard Carrington

Tommaso Dorigo has tagged us with one of those blog memes - in this case, a variant of the Historical Meme. The idea is to

  • link to the person who tagged you,
  • list seven random or weird things about your favourite historical figure,
  • tag seven more people at the end of your blog and link to theirs,
  • let the tagged people know by leaving a note on their site.

In backreaction's editorial office, history-related stuff ends up on my desk, so I'll try my best to keep the meme alive. Actually, I do not have a favourite historical figure - there are just way too many -, so I'll specify seven small facts about an interesting historical figure I've just been reading about, Richard Carrington (the Wikipedia entry is still quite brief...)

  • Richard Carrington was born in 1826 in Chelsea, England. He studied at Cambridge to become a cleric, but discovered his fascination for astronomy

  • His father, a wealthy brewer, agreed that he constructed his own, private observatory at Redhill, Surrey. Working there, Carrington established an accurate Catalogue of Stars of the Northern Sky, which won him the Gold Medal of the Royal Astronomical Society in 1859.

    A series of large sunspots in March 2001 (Credit: SOHO)

  • During daytime, he didn't rest, but embarked on a long-term systematic study of sunspots. Analysing his data, he discovered the differential rotation of the Sun, implying that the Sun could not be a solid, rigid body, as current wisdom stated at that time.

    A Solar Filament Lifts Off (Credit: TRACE, NASA, via APOD, July 25, 2004)

  • While making his daily observations of sunspots, he became, on September 1, 1859, the lucky eyewitness of one of the largest solar flares in the last few hundred years. A solar flare is a huge explosion in the Sun's atmosphere, when turbulent magnetic fields slingshot large amounts of ionised gas into interstellar space. When this plasma hits the Earth's magnetic field, a few hours after the flare, the result is a "Geomagnetic Storm", which can affect power grids, electronic equipment - and causes splendid auroras. In the wake of Carrington's flare, spectacular auroras could be observed up to about ±30° latitude.

    The Aurora Borealis above Bear Lake, Alaska (Credit: Wikipedia)

  • Following the death of his father, he took care of the brewery. He tried to keep on his solar observation program, and his activities as a secretary for the Royal Astronomical Society. But to his growing frustration, he had to note that he could not manage both the brewery and his strict observational schedule at the same time. He even sold his observatory.

  • In the hope to be able to follow his fascination for astronomy full-time again, he tried to get the positions of the director of the university observatories of Cambridge and Oxford when they had job openings, but without success. Finally, he brought himself to sell the brewery, established a new private observatory and tried to tie in with his earlier work, but with not much success.

  • His wife was stabbed by a former lover, and had to take strong medication in the aftermath. She died from an overdose of sedatives. Carrington died ten days later, on November 27, 1875, officially of a brain haemorrhage.

I've learned all these things from a very readable book with a somewhat silly title, The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began, by Stuart Clark. It's not only about Carrington, but about how during the 19th century, the study of the Earth's magnetic field, the observation of sunspots, and the developments of spectroscopy and atomic theory started astrophysics and our understanding of the Sun and the stars - here is a review.

OK - Sabine was quite reluctant to propagate the meme, because it may just annoy the affected bloggers who could feel compelled to waste their time contributing something. So, I'll introduce a mutation and transmit it to five blogs only instead of seven, and allow for a crossing of the language barrier. Here are the tags: What is Einstein's Moon?, Text&Blog, Highly Allochthonous, The Greenbelt, and Theorema Egregium.

Update (March 14):
Here is a brief genealogy of the meme, as reconstructed by the links:

There is an essential mutation of the meme at Magistra et Mater, changing "word 2" from "Share seve random and/or weird things about yourself" to "about a historical figure of your choice". So, I consider that post the starting point of this meme. The minor change from "of your choice" to "favourite" happened already at Heavenfield, who also gives a partial account of the early path of the meme.

I have tagged The Greenbelt, who had in fact already been tagged before - and, as it happens, together with Chris at Highly Allochthonous - along this line:

Nevertheless, The Greenbelt had a short dead time (my tribute to Talk like a Physicist Day) and agreed to participate once more. So, until I will have figured out how trackbacks work, here are links to the meme's next generation so far:

Monday, March 10, 2008

Dangerous Implications?

Last week I came across a new paper by Cosimo Bambi and Katherine Freese
    Dangerous implications of a minimum length in quantum gravity
    arXiv:0803.0749 [hep-th]

    Abstract: The existence of a minimum length and a generalization of the Heisenberg uncertainty principle seem to be two fundamental ingredients required in any consistent theory of quantum gravity. In this letter we show that they naturally predict dangerous processes which somehow must be suppressed. For example, long-lived virtual super--Planck mass black holes may lead to rapid proton decay. Possible solutions of this puzzle are briefly discussed.

Since I've been working on quantum field theories with a minimal length and a generalized uncertainty principle for a while (for a brief intro, see here), reading the paper was somehow mandatory. It is an interesting examination, but I don't agree on the conclusions drawn in the paper. Here is in a nutshell what I read out of the paper:


Heisenberg's usual uncertainty principle relates the measurement uncertainties in position and momentum space to each other. Within this context, it is possible to localize particles arbitrarily good in position space only on the expenses of losing more and more information about their momentum. To measure smallest distances you need to probe your sample with very small wavelengths, i.e. with large energies. In standard quantum mechanics, you can in principle measure arbitrarily precise if you can only probe your sample with particles of high enough energies. This is why we build larger and larger particle colliders, and accelerate particles to higher and higher energies.

However, General Relativity tells us that all energy gravitates. If you use a probe with a very high energy density you will get spacetime around it to curve. But all particles have to move in that curved spacetime. Such, if you get the probing particle near your sample whose position you want to measure, the background becomes dynamical, and the sample will wiggle. This gravitationally induced motion causes an additional uncertainty.

This effect is strictly speaking always present, but since the gravitational interaction is so weak compared to the other interactions, one can neglect this additional contribution in all experiments that we have ever done. One can however expect this effect to become relevant when enough energy is clumped into a region small enough so gravitational perturbations are no longer negligible. This will typically happen somewhere at the Planck Scale, and leads to a so-called 'generalized uncertainty' in which the position uncertainty has a minimum at the Planck length that one can not get below no matter what. If you go to even higher energies, the distortions only become worse. Thus, the generalized uncertainty typically increases with higher energies.

This kind of thought experiment can be somewhat straightened, for a very nice introduction see e.g. section II A of
    Quantum gravity and minimum length
    By: Luis J. Garay
    arXiv: gr-qc/9403008
And also recommendable is
    On Gravity and the Uncertainty Principle
    By: Ronald J. Adler, David I. Santiago
    arXiv: gr-qc/9904026

(Both papers are very readable). One should keep in mind though that besides the general sentiment being plausible, these arguments are not `derivations', since we don't yet have an observationally confirmed theory of quantum gravity to derive from. They are thought experiments - no more, no less - meant to investigate certain general aspects one can expect of quantum gravity. Different arguments lead to slightly different versions of generalized uncertainty principles, which indicates the limitations of such considerations - so far, there is no specific version of generalized uncertainty [1]. The Bambi and Freese paper uses another argument which says if you increase the energy in a space time region to measure more and more precise, you will eventually just form a black hole and not learn anything more precise than this. That's essentially what Giddings and Thomas dubbed so aptly "The End of Short Distance Physics" (hep-ph/0106219).

The consequences of such a generalized uncertainty principle have been examined extensively since the early nineties, most notably by Achim Kempf, see e.g. "On Quantum Field Theory with Nonzero Minimal Uncertainties in Positions and Momenta" (hep-th/9602085), who considers even more general generalized uncertainties.

Virtual Black Holes

Another ingredient to the paper are virtual black holes. In particle physics, virtual particles are not 'really' produced in scattering experiment, they only come into life in intermediate exchanges. Black holes can at least in theory be 'really' produced in particle collisions if a high enough energy is centered in a small enough region of space. Black holes with masses close by the Planck mass evaporate extremely fast, and in this process they can violate certain conservation laws like e.g. baryon number. This is because the black hole doesn't care what it was formed of, it just evaporates democratically into all particles of the Standard Model [2].

If black holes can be produced in particle collisions, one would expect them to also appear in virtual exchanges, where they could mediate baryon or flavor violating processes, e.g. proton decay. Since the black holes are rather heavy and short lived these process are usually very suppressed though. This was for example examined in

    Proton Decay, Black Holes, and Large Extra Dimensions
    By: Fred C. Adams, Gordon L. Kane, Manasse Mbonye, Malcolm J. Perry
    arXiv: hep-ph/0009154

They used the virtual black holes to set constraints on the size of extra dimensions. In the presence of 'large' (meaning, larger than the Planck scale) extra dimensions one can expect the production of black holes no longer to be suppressed by the usual Planck scale but by the new, lowered, one. Then, these processes are significantly enhanced. This problem doesn't only occur for virtual black holes but essentially for all higher order operators who are no longer suppressed because the Planck scale usually is far off. Either way, the Bambi and Freese paper isn't concerned with extra dimensions.

Dangerous Implications

If I understand that correctly, Bambi and Freese in the paper essentially argue that the generalized uncertainty, which has a minimum position uncertainty, should also result in a minimum time-uncertainty (see e.g. "Quantum fluctuations of space-time" by Michael Maziashvili, hep-ph/0605146). One can construct similar thought experiments to the one mentioned above by attempting to build more and more precise clocks to measure exactly when a particle will e.g. decay. Again, General Relativity puts a limit to these efforts. (By starting from the uncertainty principle instead of from the commutation relations one circumvents virtuously to address the question what actually a time operator is supposed to be, see e.g. John Baez on The Time-Energy Uncertainty Relation.) This argument usually employs some Lorentz-symmetry (you bounce a particle back and forth via some distance to get a time measure), so one thing that springs into mind is whether one still has this Lorentz-symmetry.

Either way, the point they are making in the paper is now that the lifetime of virtual states with masses above the Planck scale should with the generalized uncertainty not as usual become shorter and shorter, because it can never drop below Planck time. Now, in comparison to the usual scenario these virtual contributions should become more important. In the paper they provide some general estimates that would arise from such a scenario, e.g. for proton decay and find
"that super–Planck mass virtual black holes predict naturally dangerous processes, clearly inconsistent with the observed universe. In particular, rapid baryon number violating processes may lead to predictions of proton decay lifetimes that are ruled out by experiment."

Question Mark

Well, if you've followed this blog for a while (e.g. this post on 'test theories' or this recent progress report), you probably know what I am going to say. This is all well and fine, but estimates based on dimensional argumentation can't replace a consistent model that includes a generalized uncertainty relation. The uncertainty relation is derived from the commutation relations of position and momenta. If you 'generalize' it, you need to modify these commutation relations. This is actually the better starting point, also the one most commonly used, and this modified commutator in quantum mechanics has its equivalent in quantum field theory.

Such a modification however, has a couple of consequences. The one is that you can't have a minimal length without also having a modification of special relativity. The other one is that in some cases one also has a modified dispersion relation (though not necessarily so, since the modification can factor out). The most important one in this context is that one has a modification of the measure in momentum space. Essentially, high momentum states are less populated. This modification of the measure in momentum space is not optional; it is a consequence of the generalized uncertainty principle. This was probably first pointed out in the above mentioned paper by Kempf. You find some details on the relations between these ingredients in my paper hep-th/0510245 [3].

I do not see how the estimations in the Bambi-Freese paper take into account that within a scenario with a generalized uncertainty principle the measure in momentum space is modified, which naturally suppresses virtual particles with masses above the Planck mass. As one would expect from a theory with a minimal length, this provides essentially a natural regulator, and all virtual contributions above the Planck scale are very suppressed.

Related, some years ago I calculated loop contributions in an extra-dimensional scenario with Kaluza-Klein excitations, by using a model with generalized uncertainty (see hep-ph/0405127). These excitations can become arbitrarily massive, which usually poses a problem, much like the massive virtual black holes considered by Bambi and Freese. In the scenario with the minimal length, these very massive virtual contributions are suppressed, and the result is naturally regularized (since it's with extra dimensions, the usual renormalization schemes don't work).

Besides this, I admittedly have a general problem with putting black holes with masses considerably above the Planck scale in Feynman loops. One should keep in mind that the quantum aspects of black holes become important only if the curvature on the horizon is in the Planckian regime, which is the case for Planck mass holes. If one increases the mass (and they are talking about a thousand times Planck mass in the paper), the curvature drops and the black hole becomes classical very fast. This is also the reason why the semi-classical treatment for Hawking-evaporation is extremely good up to the very late stages of decay.

I wrote an email to one of the authors about these concerns, and I am courious to hear what they think. I will keep you updated on that.


So I agree with the conclusion in the paper that "this problem must somehow be addressed". But unlike what they suggest I don't think it needs a new symmetry for it, it needs in the first place a consistent quantum field theory that incorporates a minimal length. Since the minimal length acts as a regulator at the Planck scale, I expect it to suppress these processes.

Post Scriptum:

As it seems Lubos Motl has already commented on the same paper. Since his writing is as usually entertaining, let me briefly summarize his criticism.

Lubos begins with doubting the author's authority "First of all, you can see that the authors are complete outsiders in quantum gravity.", an excellent starting point for a scientific argument. His next point about the allegedly confused notation in the Bambi-Freese paper probably means that he didn't even bother the check the first some references which could have clarified his problem. Lubos then proceeds to his speciality, content free ad hominem attacks
"In the literature, most of the talk about the "minimum length" in quantum gravity is a vague sloppy babbling of incompetent people who don't have enough imagination to ever understand how Nature actually solves these things - think about profoundly and permanently confused authors such as Ng, Amelino-Camelia, Hossenfelder, and dozens of others."

Which he then attempts to explain with
"In reality, something new is indeed going on at the Planck scale, but to assume that 1.) it must be possible to talk about distances even in this regime and 2.) all the distances must always be strictly greater the Planck scale is a double naivite."

Sadly, this shows that despite all the effort I made explaining my model to him - on his blog, on this blog, and by email - was completely wasted. Otherwise he should at least have noticed by now that the minimal length in my model is a wavelength, and besides this the model has not very much in common with Ng and Amelino-Camelia's work. But this unfortunate limitation of his mental capability is explained with the following sentence
"If you actually look at any consistent realization of quantum gravity - and we have quite many setups to do so, including AdS/CFT, Matrix theory, perturbative string theory, and more informal descriptions of quantum gravity involving effective field theory - you will see that the "generalized uncertainty principle" in the strict Bambi-Freese sense is certainly wrong."

Which we should probably translate into "my head is full with string theory, and nothing else will fit in", the poor guy. This problem is further clarified in his statement
"Even if you are a bizarre, speculative alternative physicist who thinks that the reality is described by an entirely different theory of quantum gravity than the theory we still call "string theory", you must agree that string theory provides us with one or many realizations (depending how you count) of a physical system that satisfies all the consistency criteria expected from a theory of quantum gravity."

Well, as a scientist I don't have to agree on an description of reality as long as there is no experimental evidence whatsoever. I can't but wonder who of us is bizarre and speculative. Lubos continues his argumentation in the usual manner ( "I think that every competent person would agree with me ..." etc). The only thing that's surprising is that neither the name Smolin nor Woit appears in his writing. So maybe this is an improvement, and it leads me to hope that the air in Pilsen might clean his mind.

The only reason why I am telling you that (and break my own no-link policy) is that despite his disgusting way of writing, as far as I can tell, the conclusions he draws seem to be compatible with mine: "very large black holes "in loops" cannot cause any very large violation of the baryon and lepton numbers."

[1] In most cases, a first order approximation is used with an integer for the first power in energy over Planck mass that appears, and an expansion parameter of order one.
[2] At least that is what most people in the field believe today. Just to make sure I want to add that nobody has ever seen a real black hole evaporating.
[3] The paper was originally titled 'Self-consistency in Theories with a Minimal Length'. However, one of the referees didn't like the title, so it got published as 'Note on Theories with a Minimal Length', where the essential word 'self-consistency' dropped out.

Saturday, March 08, 2008

International Women's Day

This is just to remind you that today, March 8th, is International Women's Day.

If you're a man, take a moment to imagine how much more boring the world would be if your coworkers all had Y chromosomes. Take a moment to appreciate your girlfriend's constant reminder to eat more healthy, and your wife's habit to brush real or imaginary dust off your shoulders.

And if you're a woman, well, we all know who actually makes things happen in this world, don't we?

[See here for picture information]

Thursday, March 06, 2008

Lunar Eclipse from Mauna Kea





Thanks to The Ridger from thegreenbelt for the link!

Wednesday, March 05, 2008

Talk like you want

I've been notified that Pi day this year (3/14) has been declared the 'Talk like a Physicist Day' (see also). Apparently, the day even got its own dot com, a website which skillfully manages to distract from absence of content by carefully arranged layers of unprofessional design. Except possibly the 37 Scrabble Points which look to me like an IKEA ad, and desperately ask for the association 'Talk like an Ass'.

Since I have been notified of this remarkable upcoming event repeatedly, I herewith want to let you know I am passively boycotting this ingenious idea. I considered actively boycotting it, but this seems to require not talking like a physicist, and would pretty much mean I couldn't talk a whole day. Since it's a Thursday that doesn't sound feasible. Reasons for my boycott

a) I would forget about it anyway.

b) I find so-and-so appreciation, remembrance, or activity days outside public holidays an annoyance that clutters my organizer.

c) I honestly don't know what it's supposed to mean to 'talk like a physicist' except for being a physicist and talking.

d) It seems to suggest physicists have a 'special way of talking' which is basically what this blog tries to disprove.

e) I would forget about it anyway.

That is to say, please spare me announcements like this, especially if they are bulk mails with lines like 'I enjoy reading your blog'.

If you think I am in a particularly foul mood, you are correct. That's because after I had to spend a night in a smelly hotel room, and flights I was booked on were cancelled twice, I finally made it back to Toronto. Unsurprisingly, my-stupid-bag went elsewhere. The American Airlines personnel assured me it would be on one of the cancelled flights. I doubt it, but was too tired to investigate the issue further. The highlight of my conversation with one of the employees was my remark "I am very pleased your country is steering into a major recession, and I hope you will be unemployed before you know how to spell 'bullshit'." Now I am of course sorry about it, but women in uniform are terrible. I am serious, men are usually several orders of magnitude nicer. And that was the last time I flew American.

Humm. Seems I said this already last year.

Either way, should I ever utter a sentence like 'I feel strange attraction. Is this love or is it dark matter', please hit me really hard and increase the Lithium dosage.

I promise, after 24 hours of sleep my mood will improve considerably. So, good night for now.