Why the Quark Gluon Plasma is a Banana

When I was in 5th grade, our biology teacher dropped out for a longer period. For whatever reasons, she was temporarily replaced by our maths teacher. He was about to be retired soon, and had not taught biology for more than 20 years. Now he saw himself faced with the task of giving "sexual education" to a bunch of 11 year olds.

After having extensively discussed various forms of STDs, we all were completely sure we would never ever have sex in our life. Our teacher then proceeded to safe sex, and eventually produced a banana to explain the proper use of a condom. He was clearly struggling with words he hardly ever used in his life, and the banana seemed to us a very theoretical example for a very involved practical situation.

I thought about this banana, when I was in very interesting seminar at the KITP last week by Pavel Kovtun, titled

How Can AdS/CFT Be Useful for Heavy Ion Physics?

There, in this seminar room, all the stringy guys were talking about jet suppression, shear viscosity and central collisions! It was equally weird as hearing your maths teacher talk about sex.

In the talk, it was explained how the AdS/CFT correspondence can be used to model certain properties of heavy ion collisions. I find this an interesting topic, with a clear connection to phenomenology, which I often miss in talks at the KITP.

It also reminded me of a colloquium by Joe Polchinski that I heard about 3 years ago at LBNL. The only thing I can recall was that he said something like the quark gluon plasma is a black hole. He most likely said more, but I was too nervous to listen, since own seminar (the first seminar I ever gave outside my home institution) was scheduled for the following lunch meeting. Consequently, the only thing that was in my head while I was giving my seminar (which btw had nothing to do neither with heavy ions nor with black holes or qcd) was what the fu*k a black hole has to do with the quark gluon plasma, and why I ever agreed to give this seminar.

Had someone told me at this point that I would end up at UCSB three years later, no way I would have believed it.

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1. AdS/CFT

So, here are the rough basics that I hope are sufficient to get into the spirit. Strongly coupled QCD is messy soup, and calculations are nasty. It turns out however, that above the critical temperature, a conformal field theory is a pretty good description of the messy soup (see slide 8 of talk or picture below). Plotted is the energy density (epsilon), normalized to that of a Stefan-Bolzmann gas (subscript SB). The colored curves are lattice calculations, the black line is a conformal field theory - the maximally supersymmetric yang mills theory, which comes with two parameters: the coupling constant g, and the number N of the gauge group SU(N).

So it seems, instead of QCD at finite temperature, it's a reasonable try to model some properties of the mess with a conformal theory, like the mentioned super yang mills theory (SYM).

That by itself does not make things less messy, but now one uses the AdS/CFT correspondence! And here, the miracle happens: the 4-dimensional SYM gets translated into 5-dimensional gravity in some space called AdS₅ x S⁵ . Which is much easier to deal with.

One can then translate quantities from the 4-dimensional field theory into the 5-dimensional gravity in this specific space. E.g. the

The stress-energy tensor in SYM translates to a graviton on AdS₅ x S⁵

A state in the field theory translates to a state in the dual geometry

An operator in field theory translates to a field in the dual geometry

Etc. if you want to specify the type of particles you are looking at (fermions, gauge fields), things get more complicated, but are doable. Most importantly

The thermal equilibrium state in SYM translates to a black hole in AdS₅ x S⁵

And so, Marcus, I am very proud to say that at least my time at UCSB enabled me to answer the question what the QGP has to do with a black hole.

However, the general relativity one has now translated the field theory into, is classical only for large N. For small N, one would need to know quantum gravity - or string theory. It is usually assumed that N is 'large enough', which might or might not include N=3.

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2. Applications

Using the above translation, one can now examine observables. A prominent example is e.g. the shear viscosity and it's lower bound. But also the photon and dilepton emission rate, or the energy loss of particles traveling through the messy soup can be investigated. Besides Pavel's talk, you might want to check some of his papers. It seems to me, he is working on an enormous amount of related stuff. Some more references about the topic

• Minkowski-space correlators in AdS/CFT correspondence: recipe and applications
  D.T.Son, A.O.Starinets


• The Hydrodynamics of M-Theory
  Christopher P. Herzog


• Viscosity in Strongly Interacting Quantum Field Theories from Black Hole Physics
  P.Kovtun, D.T.Son, A.O.Starinets

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3. Problems

There are most likely a whole number of theoretical, analytical and numerical problems with the approach that I am not aware of, and therefore will not mention. Starting from the question whether N=3 is indeed a large number, or the assumption of thermal equilibrium, I have the vague impression there are more subtleties than I can (or want to) imagine.

Still, I think it's a reasonable try to use AdS/CFT for SYM to model properties of heavy ion collisions. Instead of, say, some hydrodynamical description, un-quantized numerical models, or cost- and time consuming lattice calculations.

The biggest problem I have with the scenario is the formation and time evolution of the fireball. Thermal equilibrium might correspond to a black hole in the dual theory, but what describes the collision, or the following hadronization?

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The intention to use often very abstract mathematical theorems for direct applications is definitely something I welcome, esp. since the front research in theoretical physics is falling more and more apart into sub-fields.

It requires quite some courage to go to a heavy ion conference as a string-theorist, something Pavel did last month, which really surprised me. I am not sure though whether the average heavy ion physicist would already consider the approach to be more than a theoretical example for a practically very involved situation.

To come back to the banana issue: I am very relieved to tell you that I, and most of my classmates, eventually recovered from my maths teacher's lectures. We all figured out how to properly use a banana.

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Acknowledgements: I would like to thank Pavel for his patience with my questions, and I apologize for the banana. I could not resist the temptation.

Anti-Gravitation

Today, I gave a telephone interview to a very nice young man for the print version of Welt der Wunder about black holes - apparently a topic of fatal attraction. To my amazement, it turned out, he was born the same day as I, in the city where my parents still live (and no, Lubos, I am not a schizophrenic hermaphrodite - at least not that I know).

Puzzled by the guy knowing my birthday, I googled my name - and I was surprised to find (besides my birthday in the google-cache) this article about my recent work on Anti-Gravitation

• Assumptions are repulsive, especially about gravity
  Tom Siegfried

which gives a very accurate brief summary of the idea:

"Electric charges can be positive or negative. Opposite electric charges attract each other; like charges repel. Gravity, on the other hand, seems to be always attractive -- all masses move toward each other. Apparently all matter has a positive gravitational charge, and like gravitational charges attract. If there was such a thing as negative mass, it would behave in the opposite way and push away all ordinary matter, a prospect that most physicists find repulsive -- except for Sabine Hossenfelder. "

So, for those of you who always want to know more, here is the story about anti-gravitation that is not in the paper:

Briefly after I finished high school and started studying at Frankfurt University, I moved to the Bockenheim, where the old campus was located. Unfortunately, I made a wrong move and ended up lying in bed the next two weeks. Whenever I turned my head, several nerves between my head and toes went up in sudden fireworks. Essentially, I stared at the ceiling for two weeks, wishing I had some anti-gravitational device to lift my furniture.

Besides shouting at my boyfriend and eating too much chocolate, I started wondering why there are no negative "charges" in general relativity. At this time, I was blissfully unaware of several reasons why this would not be possible, the most pressing one being the stability of the vacuum, others you find addressed in the Anti-Gravitation FAQs.

I am afraid, I annoyed my roommate with my anti-gravitation theories for quite a while. And I was stubbornly insisting I did not understand his concerns why this would not make sense.

(Anti-gravitation was not the only 'theory' I kept discussing with him. At some point we named them SH's Incredible Theories - SHIT. )

Then I got distracted from the anti-gravitation for the next years. Well - I had to write a diploma thesis, and make my PhD.

But the topic kept coming back whenever I had some free time. Just that the time was never enough to make it publishable. My last summer was very frustrating in many regards, I was absolutely certain my research would never go anywhere, and I would be unemployed by next year. While I was conference hopping in Europe, I wrote together what conclusions I had so far about the anti-gravitation. And I put it on the arxiv, praying it would be enough, hoping that someone might find it sufficiently interesting to finish what I wasn't able to finish.

The reactions on the paper were: none.

Though the first version of the paper was crowded with typos, it turned out to be a very useful basis to annoy other people by handing them a copy, and asking for objections. There were far less objections than I was prepared to discuss. And those that came were easily to answer. The most common reaction was: "uhm. interesting. uhm. why don't you talk to. uhm... [someone else]."

The most reasonable discussion I had for a long time was with one of my ex-boyfriends (credits go to Andi). Who is not even a physicist, but who understood far more of the idea, and the problems, than several over-educated brains before him.

Meanwhile, the guy who I shared the apartment with when I had my back problems, and who I had bugged several years with my anti-gravitational obsession, got a postdoc position at Perimeter Institute. During a phone conversation last October, anti-gravitation slipped in (again), and after listening very politely to my lengthy explanations, he said "uhm. interesting. uhm. why don't you talk to. uhm, Lee."

I thought, great idea, much better some guy at PI thinks I am nuts than the people I have to talk to every day. So I sent my paper to Lee. I am not sure whether he actually read it. But the conversations I had with him, and several others, since that time where encouraging enough for me to answer several depressing referee reports, and to send the paper to PLB, after it was rejected by PRD.

The revised version which was accepted for publication last month, is considerably improved, and I am enormously grateful for all the discussions I had with the two Stefans, Jim, Lee, Petr and (in the early days...) with Marcus. Unfortunately, the version in PLB is extremely shortened. I have been told repeatedly that the content is indeed much clearer now, after several revisions and shortenings, than in the first version. Though that might be true, imo the latest version suffers from a severe lack of applications. Needless to say, there is work to be done.

I am still not completely convinced whether there is some point I have been missing all the time, but I guess I will never find out unless I keep on discussing the idea. The ansatz has several problems that I know of -- probably I am the one most familiar with all of them -- and every second day I get stuck in a dead end. The other days though, everything makes perfect sense.

I am still waiting for objections.

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Note added: see also the discussion in the PhysicsForums.

Complicated

You have a problem, I bet you do. Be grateful for it. Humans are funny, when they don't have problems, they make some.

On Friday, I declined the offer from the German Science Foundation for the Emmy-Noether-Fellowship. Something I have been delaying for some while. After all, didn't I want to go back ever since I came to the US? I got up in the middle of the night to make the phone call. Just to realize that it's a holiday in Germany. So, I sent them a lengthy email, which essentially tells them that I am sorry and they are stupid. Hope they get the message.

I miss my mum esp. on weekends, she always did my laundry. The apartment complex where I live has in toto 3 mashines for ~ 100 apartments (one of which currently is blue and green cause some kiddo apparently forget wax colors in a pocket). In addition, everybody does their laundry on Saturdays. So, I am out of sensible choices and down to the stuff I never wear. I ended up wearing all white, and since I was already at it, I finished the outfit with white shoes.

I made some attempts to go to the beach, but each time I left the apartment it started raining. Then I thought, I could as well go to work and get some stuff done. Apparently, I missed the exit on the highway and when the 'check engine' light turned on, I found myself halfways between San Francisco and Santa Barbara. I ended up sitting in a Cafe on the highway, vaguely pushing some details on the Higgs-mechanism around in my head. Took about 2 minutes until some old men sat at my table, stating

"You look like a deep thinker."

I tried unsuccessfully to stop frowning my forhead and said

"Maybe botox would help."

I only write this here, so the joke is not completely wasted. Without any further introduction, the old guy said his name was Pete, and then he told me almost every detail about his life I never wanted to hear. Joerg calls that agressive friendliness.

Turned out, Pete lived in New Orleans with his wife for 20 years. Then she got cancer. She always wanted to see San Francisco, but never had, so they moved to SF. She died 3 months later. He stayed. That was 30 years ago. I estimated him to be 80 or so.

Now he is about to move to LA because he has meet a women (very hairy eyebrow wiggeling). She is married, but apparently her husband is not doing too well. So, Pete is waiting for him to die any time soon. I wonder where 80 year old people meet. At the cemetary? No, they met in the bus, standing next to each other. "Standig is much better for the back than crouching - like you do!" and I got a lecture about sitting upright.

Then another old guy with a dog appeared. He was a friend of Pete and completely bald. The dog did not hesitate to immediately push his head between my legs and I spilled cold coffee on my white shirt. After five minutes or so, I yelled at the guys to stop excusing, and found it a good time to leave. The bald guy remarked "You are not a dog person". I said "Very observant" which he found very flattering and I got to see a lot of brilliant white fake teeth.

I mumbled some nice-to-meet-yous and Pete asked:

"Why are you wearing white?"

"Cause it's complicated.", I said.

Back on the highway, I remembered that the reason why I studied physics was that I did not understand it. I always thought it must be possible to make all that confusing stuff less complicated. I am still working on it.

Life's like this you
You fall and you crawl
And you break
And you take
What you get [...]

Why'd you have to go and make things so complicated?
~ AVRIL LAVIGNE

Wine and Cheese Physics

On the far end of my desk there is a pile of papers with a post-it saying: READ ME. Yesterday, it reached the critical height and dropped off the desk. So, I made a brave attempt to sort it out, the result of which are now 8 smaller piles of papers, mostly unread except for abstract and conclusions.

(There was a 9th pile with trash, which finally only consisted of one paper that I printed twice by accident.)

Surprising for myself, the biggest pile was made of papers circling around Bell's inequality, hidden variables, and the interpretation of quantum theory. I conclude that part of my mind is occupied with something very weird, not that I know exactly what.

I can hear Horst sighing to PLEASE stick to 'butter and bread physics'. I call myself very, very lucky to have had the opportunity instead to mostly do my 'cheese and wine physics'. Amazingly it seems that some of the cheese and wine has turned into butter and bread lately. Like the 'weird' black holes at LHC stuff, or the 'useless' minimal length model, etc.

(You don't yet believe in Anti-Gravitation, come back next year.)

Anyway, here are two recent papers that I read and that I found quite interesting

• Emergent Probabilities in Quantum Mechanics
  Olaf Dreyer
• Relational EPR
  Matteo Smerlak, Carlo Rovelli

I like the first one better, it adds some new point to the "how" of the measurement process, though it seems to me it has some missing links - the picture is kind of incomplete.

The latter is nicely summarized in Alejandro's blog, you can also find some discussion in Christine's blog and in the Physicsforum. I am not sure it really says something new, but it is a nice starting point if you want to know something about relational quantum mechanics. The main idea is that the question whether a wave-function is 'collapsed' or not depends on the observer. Everything is relative, even quantum mechanics. This avoids problems with the non-locality of the collapse which one has in the usual description: there is no paradox because both observers have to compare their measurement before they can talk about the result.

What I also found in the pile of papers:

• A recipe for Pina Colada.
• A letter of recommendation from someone I don't know about someone I don't know. But it's such a nice American-style letter that I will keep it. (Meaning: for a German it appears as if the writer is desperately trying to get rid of the guy).
• A note on the new CD from Die Sterne, that I wanted to order (but it's not available on amazon.com). Their last album 'Das Weltall ist zu weit' (the universe is too large) was pretty good (after the previous one was rather mediocre). I especially like the song "Wir sind wie Du", and I will close today with some of it's lyrics

Wir sind der Morgen
Wir sind das Erwachen
Wir sind die Möglichkeit,
die Welt zu erschaffen




Wir sind die Lebenden
Wir sind die Vielen
Wir haben nichts,
also nichts zu verlieren.




Wir sind die Quelle,
Der Anfang der Welle
Und hör zu:
"Wir sind wie Du!"

Phase transition or cross over?

So, since last Friday, finally, I am a happy, new "Dr. phil. nat.". Of course, I am not yet allowed to call myself officially like that - I have to wait until I have in my hands the "Zeugnis". This is only possible in two weeks, after the Promotionsbüro's Easter vacation is over. Everything has to be very orderly in Germany ;-)

In the meantime, I can take a breath, and try to realize what has happened. Getting a PhD is - that is my impression just now - not a sharp phase transition, but a very smooth cross over, starting with the handing in of the written thesis, and ending late after the defense is over.

I was quite a bit nervous before the defense, mainly because I had prepared the final version of my talk only the night before, and thus had not really much time to practice the text I wanted to say. The problem was, I thought that I have 15 to 20 minutes for my presentation, and I knew that it was to long for that period. But then, fortunately, the first thing that Carsten, the head of the examination committee, said was that the procedure begins with a talk of 25 to 30 minutes. I immediately got relaxed.

I think I got through my talk quite successfully in 25 minutes, interrupted by Horst only once or twice, and was ready to face the discussion. The start was a little bumpy: first, there was only colored chalk to write on the blackboard (and remember always to start with the most backward board), and than, I needed a little help to figure out the De Broglie wave length of the particles involved in my code: Roskos open the discussion with the question why the purely classical calculations I am using in my simulations can be justified. Of course, it is easy to write "lambda = hbar/p" on the blackboard, but then, it was not so easy for me any more, at that moment at the blackboard, to expand this fraction by c, use the famous "hbar · c = 197 MeV · fm", and conclude that a nucleus with an energy of 160 GeV (and a corresponding momentum of 160 GeV/c) has a wave length of roughly 1/1000 fm. But with a little help, I reached that conclusion.

It got a bit better when Roskos started asking about Debye screening, a concept he was fond of recognizing from his solid state physics, but then he asked whether I had studied plasma oscillations in my model, which I had to admit I had not, although, of course, I said, this would be an very interesting thing to do, one would expect plasmons to exist in the model, that the search is numerically involved, and that plasma oscillations and plasma instabilities are a hot topic to understand thermalization in the early phase of heavy ion collisions, blah blah. Fortunately, nobody asked about the typical frequencies of plasma oscillations and how to calculate them...

Then, Horst asked me to explain the differences between phase transitions and cross over, and how all this relates to the Kosterlitz-Thouless transition. That later transition was the topic of my diploma thesis, and I was surprised that he really asked this question, since the relation is quite far-fetched, to say the least. Anyway, I was quite successful in plotting the phase diagrams of QCD matter and simple water on the blackboard - although, if you plot the diagram of nuclear matter as a function of density in temperature, keep in mind that there are two lines, tracing the coexistence region of the first order transition, which should meet at the critical point. My first guess of that plot on the blackboard, unfortunately, was a little different.. However, I was quite convincing, I think, in explaining the critical point, critical opalescence, and the absence of sharp differences in density or whatever in a cross over beyond the critical point. I also guess that the audience may have been impressed by my explanations of vortices acting like Coulomb charges and undergoing an ionization transition in the Kosterlitz-Thouless transition, and the analogy to the instanton liquid that drives the chiral transition.

Horst went on asking about some new mechanism to create super-heavy elements, not using the famous cold valley, which I could not answer, since I had skipped the relevant talk of Zagrebaev at last weeks ISHIP conference. Instead, I could make him happy with a schematic plot of collisions of heavy ions at energies in the 100-MeV range and the time scales involved, and the relevance to the creation of conditions suitable for the diving into the lower continuum of the Dirac sea. I guess that everyone who has spent some time in the Frankfurt institute has heard about the funny things that happen when "Z·alpha > 1" and the vacuum spits out positrons ;-)...

The next round of questions went to Klaus Peters, of the IKF, in Frankfurt since last year. He asked me about the different quarks, and the experiments that show the existence of the different families. It is a little bit funny, but one of the relevant plots, the number of hadrons versus dimuons produced in electron-positron annihilation as a function of energy, I knew that from my job as editor of Greiner's textbooks at Harri Deutsch. So, this was really useful for something :-). To his next question, about the prediction of the charm quark, I could, unfortunately, only propose the buzzword GIM mechanism and Glashow, Iliopoulos, Maiani, and that it is related to the weak interactions, but in fact I spent one hour of the afternoon last Sunday to figure out that its about the "suppression of flavor changing neutral currents", which are not observed, but are a consequence of naive Cabbibo mixing - this can even be found in the Wikipedia! His questions about pentaquarks (the reason why I had asked him to take part in my examination committee), again, I could answer. The funny thing is, like in all examinations, that sometimes it is just important to guess what the examiner wants to hear - in this case, "higher Fock states" which are mixed to the valence quark wave function, which can mix with pentaquark states. It took a while until I had figured out that he wanted to hear just this notion.

Finally, in the last round of "official" questions, Carsten came back to the details of my model, asked about comparisons to his Friedberg-Lee model, and about elliptic flow. There is, of course, a big fuzz about elliptic flow at RHIC, which seems to exhibit beautiful quark number scaling for a large number of hadrons. I could tell him something about all this - it was a hot topic at Strange Quark Matter the weak before. I would be happy if I could study it with my model. Unfortunately, it is hard to get enough statistics, and the initial pressure is not high enough, probably because there is no hard core repulsion between quarks in my model. I tried to impress everyone by mentioning the Alder-Wainwright simulations of the early 1960's that showed that hard core repulsion is enough to obtain a reasonable simulation of fluids, and that's why, i tried to argue, my model is not a strongly coupled QGP.

At that point, Carsten decided that the questioning had been long enough. I could have go on for a while, and Walter Greiner gave me the occasion, since in the round "questions from the public", he asked if I had heard Kampert's ISHIP talk about cosmic rays. I had not, but I said it was probably about the first runs of the AUGER experiment in Argentina, and made a plot of the spectrum of cosmic rays with the knee and the ankle and the questionable events at highest energies, where photo-pion production with photons of the microwave background should decelerate protons and prevent them from reaching the earth, and that this may be relevant to possible modifications of special relativity blah blah...

But then, eventually, it was really over. Usually, at this point, the audience has to leave the seminar room, so that the committee can decide about the outcome of the examination. This time however, since the seminar room was completely full with people, the committee left, and found its decision somewhere else. When they came back some 10 minutes later to announce that the result was "sehr gut", and to congratulate me, this was, strictly speaking, the moment of the phase transition to the PhD.

For me, however, it is washed out to a smooth cross over - I have not yet completely reached the new state.

Are You Loosing Your Edge?

Two weeks late I finally wrote the referee report I mentioned previously. For a change, it was a manuscript written in understandable English and the report was a very positive (though the paper was extremely boring). While doing so, I found the letter I wrote to the TIME article "Are we loosing our edge?", which I mentioned in a previous post. In this article, the necessity of Bush's American Competitiveness Initiative was emphasized. Though I believe that there is lots of stuff going wrong in science (not only in the US), the whole article is pretty short sighted.

Anyway, here is the letter:

One of the most attractive factor for me to come to the US for research was that my work would be appreciated. People in the US have a genuine interest and pride in their national research programs. The flip side of this is a lacking ability for self-criticism which severely worsens when funding drops. Who points out own shortcomings when fearing to loose financial support? Instead, the own achievements are overemphasized, which then misleads future decisions on funding.

I had to experience that the tolerance and open-mindedness foreign scientists are welcomed with is contrasted by an sometimes unbelievable arrogance and ignorance for the achievements of other countries. It surprises me every day anew that most US citizens really believe their "standard of living is far higher than that of any other nation". What the US needs is certainly not more competitiveness! What it needs is to acknowledge that there is intelligent life outside the US. What it needs is worldwide cooperation, in a world where progress is made most efficiently by exchanging - and not buying - knowledge and people. You conveniently forget to mention that the www, as we use it today, was invented by Tim Berners-Lee, a British scientist, and 'went public' at CERN, an international research organization in high energy physics, located in Geneva, Switzerland.

For those who did not read the article, the latter remark referred to a listing of innovations by US scientists, among other the internet

Internet:

After the Soviet Union beat the U.S. into space with the launch of Sputnik I, the first satellite, in 1957, the Department of Defense created the Advanced Research Projects Agency to kick-start innovation. It named Joseph Licklider to find ways to protec the U.S. against a space-based nuclear attack, and he believed a communucations network was key to those efforts. The first Net went live in Oct. 1969 with the University of California, Los Angeles, talking to the Stanford Research Institute. In 1990 the National Science Foundation expanded the system connecting university networks. It reached the public in 1992.

Had that been the whole story, you would not be reading this blog right now.

Congratulations

HE DID IT!!! HE DID IT!!! Very very special congrats to

DR. STEFAN P. SCHERER

...and thanks to my mother for sending the photos...

from left to right: Stefan, Carsten, Adrian, Brachmann, Alex

and -- judging from the blackness of clothes -- I guess the ear on the far left is Andi's

Stefan and Horst (this is *not* the seminar room)

Young and Stupid

This afternoon I got stopped on the 101 by a police car some 30 miles south of Santa Barbara. Stefan is convinced that I can smell radar controls, so I was driving exactly at the limit, but the guys were suspicious about my car. Pulling to the right, I forgot that I own a CA drivers licence and my accent got significantly worse. I waved around with my pinkish German licence, claiming that I just moved here recently and had no idea that a front plate is required, and I am so sorry, officer.

It might have helped that I was wearing my favourite dress. Still, I had to open the trunk and let the guy poke around in my trash. Stefan left me with the bottle of wine he won for his poster at the SQM. He had neatly packed it into a plastic box with some tacos and even a bottle opener - no disasters with my thoughtful future husband. At least I had managed to put the wine in the trunk, where it still is. Anyway, the officer was very puzzled about the bottle opener and made some remark that sounded like 'always be prepared, huh'. I gave him evil look No. 17, which he chose to misinterpret as a nasty girls look and his colleague began to giggle. I promised to get a front plate (as I have promised several times before) and check my signal lights (seems some aren't working) and ignored the speed limit the next 30 miles.

Back at the department, I was lingering around in the kitchenette, waiting for the coffee machine. Someone-whose-name-I-probably-should-remember came by, and asked me whether I was a new grad. stud. Having explained that I am neither new nor a grad stud, but actually a postdoc here since last year, he apologized, but left me wondering how old I have to get, before I am mistaken as the secretary instead.


This was kind of a lengthy introduction why I started reading popular science books. Again - I did not touch any since 10th grade or so, being fed up with always the same incomplete and impossible to understand explanations. Last year however, I was at some airport being faced with the omnipresent Nora Roberts and Dean Koontz products. Besides this, there was the usual selection of improve-your-life books and travel guides.

Therefore, I settled on Brian Greene's Elegant Universe, something that I would not have bought in a sensible book store.


Reading the first chapters -- most of which I skipped, because they explain very basis stuff -- a women sat next to me and started some smalltalk. She had also read the book, found it incomprehensible and much too complicated. Since she saw me skipping the first chapters, she assumed I had the same problem. This made me realize that I actually must have learned SOMETHING during the last TWELFE years of education. I did not tell her I found the book kind of trivial.

I mean, usually I read papers on the arxiv and it happens only rarely that I really understand one. In some sense that is depressing and sometimes I have the impression that I have not learned anything since I left high school.

So, since that time, I have read several recent popular science books, about which I might post sometime. I read them not so much because of the scientist-for-non-scientist-part but to remind me how important it is to step back every now and then, and focus on the basis that we share.

In my opinion, it is a huge problem that the front of research has split so much, that only small groups of people are really able to follow each others work. Is it good that most of the new papers are so specialized, that their content is no longer extractable without digging into a whole collection of papers, circling around some sub-sub-hybrid model and it's possible relationship with the zeros of the zeta function or whatever? It is good that it takes several decades, if not a whole career, to get an overview about the status on any field of interest? And why do I often find that papers seem to be written on purpose such that they are as incomprehensible as possible?

I keep thinking that I am just young and stupid. But I can't avoid having the impression that in a time of such rapid expansion in scientific knowledge, it is more important than ever to keep things together and enable people to get an overview without drowning them in details. The living reviews in physics are an excellent step into this direction.

Have a nice weekend,

B.

Mini Black Holes

The last days I was at the conference Strangeness in Quark Matter, which was strange indeed. It was nice to meet all the people, and surprising how many I knew. Walter Greiner's 70iest birthday was an occasion to tell some funny stories. As so often, I got the impression that the Heavy Ion community is actually a large family, where people stick together even though they can not stand each other, and bad habits get passed on to the next generation.

Anyway, before I begin to wonder why I kicked myself out of the field, let me come to the reason of this post. My PhD adviser Horst gave a talk about Black Hole production at the collider. I had an earlier post 'Risky Black Holes' where I told you about the governmental guy who was concerned about the danger of Black Hole production at the LHC. He wrote back several times, asking for exact probabilities for every possible scenario, and circled around the question what probability to destroy the whole planet when LHC is switched on is acceptable? 0.001% ? 0.000000000000000000000000001 % ?

Also, last week I received an email from a guy writing for a German newspaper who apparently is about to plan an article about extra dimensions and black holes for the Sunday edition.

Some of you might know that the reasons I worked on black holes are quite obscure, and that I repeat at least twice a year that I don't want to work on it any more. What's so complicated about quitting is that the interest in the topic is so large! Black holes always make a good topic at BBQs, and everyone thinks he has something to say about extra dimensions. Even though I appreciate the discussion, I can't avoid having the impression that the scientific content is in most cases entertaining but doubtful. E.g. I learned that cosmic rays are black holes that are created on our brane, then go into the extra-dimensions, grow there, then come back to our brane and make an ultra high energetic cosmic ray. Sounds exciting, huh? But is that scientific?

So here is a quite general statements:

If the Hierarchy problem (the gap between the Elektroweak and the Planck scale) is only an apparent problem and the Planck scale is much lower, then black hole production is one of the most general predictions that we can make about what is going to happen. The assumptions are plain and simple, too much energy in too little space leads to a collapse.

However, though we think we know how the Hawking radiation looks like, we have no idea what the final decay looks like. Therefore, most details of the black hole's signature are strongly model dependent and should be treated carefully.

In addition to this, the required models with extra dimensions are not really understood, esp. regarding the stabilization, the evolution in the early universe (or time dependence in general), and at least I don't feel comfortable with the mechanisms to confine particles to the brane. Also, extra dimensions are surely not a theory of everything, so there should be more about it.

This is not to say that one should not investigate speculative ideas, just that one should try to stay as close as possible to reliable assumptions. I don't think there is any point in examining weird and even weirder scenarios on shaky ground. That's nice for a BBQ party but not really scientific.

Hi!

Hello to all of you and thanks for the invite!

To start with (and in lack of any other ideas what to post) I want to introduce you to

The Physicists' Bill of Rights

We hold these postulates to be intuitively obvious,
that all physicists are born equal, to a first approximation, and are endowed by their creator with certain discrete privileges, among them a mean rest life, n degrees of freedom, and the following rights which are invariant under all linear transformations:

1. To approximate all problems to ideal cases.
2. To use order of magnitude calculations whenever deemed necessary (i. e. whenever one can get away with it).
3. To use the rigorous method of "squinting" for solving problems more complex than the addition of positive real integers.
4. To dismiss all functions which diverge as "nasty" and "unphysical".
5. To invoke the uncertainty principle when confronted by confused mathematicians, chemists, engineers, psychologists, dramatists und anderen Schweinehunden.
6. When pressed by non-physicists for an explanation of (4) to mumble in a sneering tone of voice something about physically naive mathematicians.
7. To equate two sides of an equation which are dimensionally inconsistent, with a suitable comment to the effect of, "Well, we are interested in the order of magnitude anyway."
8. To the extensive use of "bastard notations" where conventional mathematics will not work.
9. To invent fictitious forces to delude the general public.
10. To justify shaky reasoning on the basis that it gives the right answer.
11. To cleverly choose convenient initial conditions, using the principle of general triviality.
12. To use plausible arguments in place of proofs, and thenceforth refer to these arguments as proofs.
13. To take on faith any principle which seems right but cannot be proved.

I wish you all a Happy Easter!

Out of the blue

Out of the blue, I got this Email from Bee inviting me to contribute to her blog. And who could say no to a charming personality as Bee?

The first thing I had to do was to create a username. So I started thinking and decided for one and of course it wasn't available. I started thinking again (and again and again) and figured that a lot of stuff I would probably be writing about in this blog would be about me feeling like a complete alien in the country of the free. And then I had this nice conversation/discussion over lunch with one of my bosses who attested me, that I was really thinking and arguing like a european - whatever he wanted to say with that! Well, therefore I decided to go for "Eurogirl", which - of course - was also taken, so I became "Eurogirl_de".

Would be nice if some superhero powers and a fancy superhero outfit would come with this username - so I could bring the absolute basic necessities to this country, for example: ground nuts of all sort for an affordable price, bigger tampons, eatable cheesecake, toilett paper with more than one layer, mineral water that acutally contains minerals, ...

Well, I guess I got a little pissed this week. Eventually I found the time to have my car washed. Besides the fact that my order "basic wash, underbody wash and wax" was understood as "basic wash, underbody wash and vacs" everything went fine there. Taking some time to appreciate that my car was shiny again I saw some spots on the hood and took a closer look on my 3 month old car (it's a nice, beautiful and really small Chevy). Obviously some stones had hit the hood and left some marks/scratches there - so far nothing really to worry about - I ordered a small bottle of the paint a few weeks ago, so I was prepared. However taking a closer look I spottet rust! On my 3 month old car! Well, I guess that was bound to happen - taking into account the quality of roads and the amount of salt on the streets. Definitely have to make a mental note for that. Wash your car every month and check for scratches. Great - but hey, what's the problem? I got soooo much free time!

Okay, so I still have my job to cheer me up. Hah. Okay, I admit it wasn't that bad this week and I really stumbled across a really nice homepage. Actually I was looking for some information on Christoffel Symbols that I had come across while reading a paper. Not that this things were used in this paper - but what the heck, probably the authors thought that they might show the rest of the world that they now this stuff. Nevertheless I finally wanted to know what these things are and googled for some information on general relativity (at least that much I knew) and found this really weird homepage (regrettably most of it is in german):Principle of Existence - dedicated to "proof" that special and general relativity are wrong and are basicaly only a conspiracy theory and all experiments and everything else around it has been forged or misinterpreted. Ah, the main point: Everything can be explained by "The Principle of Existence". Splendid! He really put a lot of effort there - so if your bloodpressure happens to be too low - this site is a real cure for that. Especially the forum.

Oh, the real highlight of this week: I found new hope to get good bubble tea in the area.

Have a good one,
Eurogirl

Peer review II

Last week, I received a manuscript that I was asked to referee. Since already 3 other manuscripts are lying on my desk (somewhere) waiting to be refereed, and the topic was pretty outside my field, I decided to let the editors know that I am not suitable as a referee. Being blessed with one of these online services, I clicked on the wrong link in the email and got thanked for having agreed to referee the paper.

Now I actually have to read this thing. Though at second sight it turned out to be more interesting than I initially thought.

Anyway, I had an engaged discussion on the weekend on the publishing issue that I would like to share with you.

We all know that the pressure to publish in peer reviewed journals is not improving quality in research. On the contrary, it leads people to favor publishing more of less quality. The reasons why some papers get published, whereas others don't, are sometimes just mysterious, sometimes clearly due to the authors names. Peer review, it seems, does not work as it should. And the number of publications, and their citations are - at least in my opinion - not necessarily a way to single out good research. However, the question is, what can there be done about it.

Some points that we came up with.

1. The referee should have some advantage from refereeing a manuscript. In such a way that (s)he is motivated to think about the content and make reasonable suggestions. I am mostly thinking in terms of credibility. I suspect that most journals probably have an internal ranking for referees anyway, but what does the referee ever get out of writing good reports? One might also consider giving some kind of bonus for writing reports in time. I would happily pay $ 50 for actually receiving a report within 2 weeks!
2. Being mentioned in acknowledgements should be rated higher. People who are frequently mentioned in acknowledgements show that they are engaged in discussions, are able to understand and criticize theories, and are active part of research. This is the more important, as those who don't want to be part of fashion waves often end up with less publications. As to my papers, the quality improves significantly with every person I can discuss its content. (Restrictions apply).
3. The number of citations should be normalized to the number of active workers on the field. At least approximately.
4. I would find it enormously helpful if the arxiv would allow reviews on the papers, maybe similar to those at amazon. You might argue that a good physicist should be able to judge on the quality on a paper by himself. Though that is in principle true, it is absolutely inapplicable if you are new in a field and try to get into it. Some kind of quality index, or references to basic papers on the field will help newcomers to get to the central questions much faster - and with less wasted toner. In addition, the possibility of having reviews on the arxiv would make it unnecessary to have follow up papers titled 'A note on gr-qc/...' and 'A remark on a note on ...' etc.

Another point that I have argued against is the idea of double blind refereeing process. First, it does not work when the papers are already on the pre-print archive before submitted to the journal. You then would have to make sure to only accept manuscripts not on the pre-print server, which would make the pre-print idea completely absurd. Second, it would only lead authors to write their papers such that for everyone in the field it's clear who the author is. Third, I actually do think that the credibility of the author is an input the referee might want to consider.

If you have further suggestions, let me know!

Best,

B.

Finally, I made it.

After the third trial (and two errors) Bee's invitation was not dismissed by my spam filter and finally I made it: my first contribution to Bee's blog.

One thing right away: it's not gonna be something great I am about to post and I might not have the time to post stuff very often (I suppose this will keep the average quality of the contributions much higher than in any other possible scenario :-) ).

What's new on my side: nothing in particular. I am going to spend some time this week listening to talks from Frank Wilczek, whose visiting, one of the scientist who identified asymptotic freedom as a property of QCD. His public lecture has the title: 'The Universe is a strange place' which might be true, but somewhat even more so because we human beings make it one locally (although I don't think the latter is the subject he is going to talk about).

Elsewise I am going to give three lectures, two on quantum mechanical scattering theory and one on statistical mechanics this week.

Not much room for new scientific discoveries with this dense program,
anyhow, I try to figure out - like the last few months - what associate particle correlation measurements can tell us about the properties of the QCD medium in heavy ion collisions:
indeed, 'the universe' might be 'a strange place'.

Crisis

Joerg told me yesterday that Los Alamos now has a Starbucks. That is progress in physics!

Last week, I stumbled across this paper

String theory and the crisis in particle physics
Authors: Bert Schroer

which I still haven't finished but I would recommend it anyway. Not so much because I like it - its pretty agressive, something that I don't think is going to help in any regard. But because its good that there are people openly discussing their problems with string theory. It might sound silly, but when you are a grad stud and you try to decide which way to go, string theory looks like a save bet. At least it used to. It's promising and promising and promising.

Anyway, when you have gone far enough to actually understand the not so promising sides, it's most often too late, or at least inconvenient, to change field. And, probably, you are hooked by the community.

Yeah, I confess, I wanted to become a string theorist at some point. Didn't work out though. I probably wasn't promising enough myself. And the community wasn't really so thrilling.

The more critical voices there are, the more people will discuss it, the more opinions the ongoing physicist will hear. Even if every string theorist will stand up and argue against it, the impression that will last is that there is doubt. And that is better than nothing.

For the Germans, see also the article in the SZ (thanks to Stefan for scanning).

Schleifen statt Faeden

The translation of the last sentences is roughly

However, Hofmann sees his commitment more in fundamental physics than in one of the fields. "When they beat each other up, one has to mediate between them and say: go out and play, then we will see which tower falls."

Best,

B.

Peer review

Folks, you might have seen this very interesting paper

Interpretation of Quantum Field Theories with a Minimal Length Scale
Authors: S. Hossenfelder

which I have discussed and discussed and discussed on New Year, then forgotten, then rediscovered on my desk, rewritten, more discussed and eventually posted on the arxiv!
Yeah! Its always a great day when a paper is so finished, SO FINISHED, its screaming to be read by as many people as possible.

Reactions so far: none.

Except the ususal email from Padmanabhan, who claims I should cite every single of his papers, related or not. Which reminds me that I looked up his website at some point, and read this absolutely great article, which let me laugh the whole day. Some quotes:

God expects us to be moral, kind to others and brush our teeth twice each day.

[Note: Since this set encompasses most of the religions, obviously there are variations in the theme; some Gods expect us to brush the teeth only once a day. Such differences of opinion, of course, have led to major conflicts and wars.]

[...] Once this is realised, it is clear why all the answers given above are correct or why all of them are incorrect and -- most importantly -- why it does not matter. In fact, all those answers -- and millions more which can be constructed -- are all the same answer in different disguises. In a way, they are not even different from the questions!

I hope that clarifies everything. Maybe I should send the latter remark as an answer to the referee's report. When I obtain one.

As a side remark: at the same day I submitted a manuscript to PRD and another manuscript to PLB. The day PRD acknowledged receipt of the manuscript, PLB accepted its manuscript for publication...

Signs

And I always thought it never rains in Southern California! Unfortunately, its been raining the whole weekend. Stefan was surprised to find that it is actually true what I told him again and again. If its raining, water stays in the streets and runs into the houses. Someone should tell the poor Californians that its not so really smart to have the middle of the junction be the deepest point of the road! Even my favourite Cafe was closed due to flooding. And no, the rain was not really heavy.

Anyway, so I stayed at home and tried to sort out some papers. I have been trying lately to get some idea what the mysterious Loop Gravity is about. I still don't know. I made one or the other attempt to look at Lee's lectures. Which you find very nicely commented on Christine's blog. The only thing I learned so far was the sentence 'Don't trust me on the signs.' Which could be written in the abstract of all of my papers.

What I found very useful though was

An Introduction to Spin Foam Models of Quantum Gravity and BF Theory
Author: John C. Baez

Which seems to be understandable if one takes more than a weekend to look at it. What that has to do with Quantum Gravity or, even worse, reality, is still very mysterious to me.

Der alte Winter in seiner Schwäche

Somehow, winter in Germany seems not to come to an end this year. I can not remember that there has been for once so much snow still in march. But at least, daylight is already clearly longer, and this afternoon was nice and sunny. So, I decided to stop working at six, got in my car and drove in the Taunus, using the Autobahn along Bad Homburg to Oberursel, and went up to the Feldberg. This is a nice place to walk around in the snow and with a great view of the Frankfurt region. In springtime and summer, there are always lots of bikers up there. Not today, of course, but instead, funny enough, there were lots of caravans parked in the snow. I was quite amazed about this first, and there were dogs barking all around, but then I realized that there was or will be some dogsled race.

There is a look-out tower on the Feldberg, and although night was already falling, I decided to climb up. Its costs you 1.60 € and some 120 steps, and ususally is worth the effort, since the view from up there is not blocked by trees.



The photo shows the view in the direction towards Frankfurt. The hilltop in the foreground is the Altkönig, where some celtic remains can be found. The lights to the right are Frankfurt International Airport, and at the left, one can guess the city skyline.

Unfortunately, when I was up there tonight, the view was not the best, with new snow showers approaching from the west.



But that gave me the chance to take this silly photo when I was down from the tower again and it was really getting dark. You guess what it is?



No, not some stars in the sky - just snowflakes in the flashlight of my small camera...

Long distance

Today I was one the phone for HOURS. Discussing elementary questions like which flower arrangements I want on the wedding reception. Having repeated several times that I absolutely don't care, my mother insisted on hearing my opinion. I went for white white (as opposed to cream white) and burgundy (though I said blood red). Needless to say that my mother immediately objected and told me I want apricot.

Then why does she ask for my opinion in the first place.

Not to mention that my boss dropped in when several photos of bridal dresses suddenly plopped around on my screen. You see, getting married is really funny.

Okay, I am being unfair. Just that my mum doesn't get the point that I am at WORK when she calls at 9pm from Germany.

Sadly that's a problem I have heard from many others. Time shift 6 hrs and up causes problems in the best relationships. Sometimes I think my poor fiance :-) just never sleeps.

Is America Flunking Science?

Two weeks ago I read this very amusing article in TIME

''Are We Losing Our Edge?''
http://www.time.com/time/archive/preview/0,10987,1156575,00.html

which roughly states that science in the US is getting worse. Some attempts were made to analyze the issue which didn't lead anywhere. E.g. the political situation is completely underestimated. I know lots of people who leave the US because they simply don't want their children to grow up in a country like this. After a rought count, I found that I know about 40 people who went for research from Europe to the US. Only one stayed longer than 10 years.

The reason why I bought the magazine at all was that I found the amount of self-criticism astonishing for US citizens! But maybe not surprisingly, the statement that America is 'flunking science' (for the Germans: flunking means 'durchfallen') could not be left standing alone. Therefore the article is followed by the comment

Don't Believe the Hype. We're Still No. 1
What the doomsayers don't say: America is a marvel of creativity
http://www.time.com/time/archive/preview/0,10987,1156589,00.html

where it was basically stated that no other country is as great as the US. I absolutely love this comment:

[...] the U.S. leads the world by an immense margin in just about every measure of intellectual and technological achievement[...]

America is heartily disdained by its coddled and controlled European cousins for its cowboy capitalism[...]

I suspect most Europeans would pity America for its cowboy capitalism, as well as for this statement.

Anyway, I wrote a letter to this article. Which naturally was not printed. When I find it, I post it sometime. Best,

Bee

Unhealthy Internet

When Bee asked me to join her blog, I first felt very honoured, but then I thought, oops, what can I write about?

Well, on the othe hand, there are often lots of things and curiosities one comes across during the course of a day, for example that using the internet is unhealthy. This was a piece of news in the big German news service spiegel online, citing a Health warning for internet users in the Australian Sydney Morning Herald, which again reported a survey conducted by some North American technology and market research company called Forrester research.

But, I guess, even when this piece of news has travelled around the globe once, it is a bit silly, nevertheless: It should be evidend to everyone that working at a computer screen is not the best you can do to your eyesight and your back. On the other hand, it is also known that using the internet in general goes hand in hand with a reduced use of television. Now, is laying on my sofa with my ibook and browsing the internet more unhealthy than watching TV? The important thing to do would be, in any case, to follow the advice of my grandma and eat enough carrots (but oops, was she really right with that?)... Or, even better, not to spend the whole evening in front of the screen, and that's why I stop for now with my first post. Luckily, I have already some idea about what to blog next.