Saturday, March 31, 2007

A tree in the forest

Speaking of networks... this is an amazing photo shot by the Swedish photographer Jocke Berglund I stumbled across yesterday:

Hurricane tree   © by Jocke Berglund

It's called Hurricane tree, and it has won the first prize in the The World in Our Hands category of the Adult awards for the Shell Wildlife Photographer of the Year in 2006.

It shows a spot in a Swedish forest which was hit by a storm in January 2005. This spot had the shape of a tree, and the heavy forestry machines which retrieved the scrambled logs created the curious pattern in the ground, resembling the trunc and the branching boughs. The grass under the tree is made of piles of logs.

t's a coincidence that the spot where the storm cut down the trees has the shape of a tree. But there is probably a subtle reason that the structure of the branching paths of the machines is so similar to the trunc and branches of a tree: both cover, starting from the root, the area of the whole "tree" in a very similar way. It's all networks!

Friday, March 30, 2007

Sexual Network

I have learned a lot at PI. Really. Among other things I have learned that these scribbles on the blackboard are not dots with lines, but nodes with links. And here is what you can do with them: Researchers Map the Sexual Network of an Entire High School :

[Published in: Chains of Affection: The Structure of Adolescent Romantic and Sexual Networks, Bearman, Moody and Stovel, American Journal of Sociology, 110, 1 (July 2004) 44-91.]

I could only find one homosexual relationship, which makes me kind of wonder how honest the students were about their relationships altogether. Anyway, I could have tought the students more. The essential thing to know is how to do exchange and expansion moves in the sin network:

[from hep-th/9712148]

Wednesday, March 28, 2007

Prehistoric Sidewalk

Last weekend, I decided to have a break, and visited friends who have a house in France and had invited me since long to join them there. So, I took off Thursday and Friday, and enjoyed the wonderful mild weather of early sprintime with my friends, mostly hiking and walking. The landscape around their place is just great, but what was most fascinating to me: You can literally walk over fossil remains of million years ago!

What looks like simple, terrace-like sheets of rocks in a small grove, at closer inspection, turns out to be a former seabed!

Can you spot it? There it is, next to the centre of the photo, the petrified shell of an ammonite! This is what you see when you take a closer look:

As every self-respecting amateur geologists would do, I put a hammer next to the fossil to better convey its size. This special specimen had been spotted by someone else before, who also had cleaned the spot a little bit. Wolfgang, my friend, was lucky and found another one some twenty metres away, which we could dig out using the hammer.

Our geological map told us that this spot shows rocks form the apto-albian period in the Lower/Early Cretaceous, in the time of the dionosaurs. They are called marnes bleus, or marls, and can contain quite large ammonites. They are about 100 million years old!

It is really hard to get a feeling for this enormous span of time - this nice interactive explorer of Deep Time may be a start.

When I came back, I learned from a report on BBC and the Scientific American about paper in Science just from last week, that I could walk over rocks about 40 times older! All I have to do is travel to Greenland. Some volcanic rocks there are now the oldest known rocks on the Earth's surface - more than 3.8 billion years old.

Update: There is a nice post about Geological Basics: the difference between chronology and stratigraphy at Highly Allochthonous, with a scheme of the different geological series that make up the geological timescale.


Tuesday, March 27, 2007


ATLAS (A Toroidal LHC ApparatuS) is the largest detector at the LHC, the World's largest microscope. The detector is designed to measure the broadest possible range of signals, rather than a specific signal, and is thus part of the philosophy to expect the unexpected. The funny looking endcaps are part of the muon detectors. You can see a very nice movie explaining the experiment at this website. When completed, ATLAS will be 46 metres long and 25 metres in diameter. You can follow the construction inside the cavern via this webcam (updated every 30 min). For more info, the Wikipedia entry is pretty useful. But the coolest thing is this 360 degree view of the cavern.

[click to enlarge]


Sunday, March 25, 2007

Guest Post: Huang Mei

Why did I become a physicist?

The day before I went back to my hometown for spring festival, I got an email from Stefan (I mean Dr. Scherer, my officemate from Frankfurt) that Sabine is inviting some physicists contributing to her Blog on the motives and the inspirations that had led them to study physics. They thought that my story might be interesting for Europeans and North Americans.

Physicists always ask and try to answer "why", but the question "why did I become a physicist?" is one of the most difficult questions I have met. I guess the most difficult task for us human beings is to understand ourselves, which should be the goal for biologists. Actually, being a biologist was even more attractive to me, but I chose to become a physicist, because to me a physical system and its evolution are much simpler than that of a biological one. We physicists always simplify problems, so today I will just focus on a linear equation with given initial condition and boundary condition, and leave the deeper question of "why" for future studies.

I am now a professional theoretical physicist in China. To me it was quite natural to become a physicist. When I was around 9 years old, my eldest brother brought to me the seed of being a physicist. What I did was just planting this seed in my mind, and making this seed sprout and slowly grow up.

I was born in a small village in a mountainous district of China. During that time, China was still in the latest stage of "culture revolution". I don't have any impression on culture revolution, but I still have memory about the People's Commune system. When I was five and half, my mother sent me to the preliminary school closest to my home. This school had only three classrooms and three teachers. My classroom was in very bad situation, its roof leaked whenever it rained. But I enjoyed going to school because I could find many friends playing games together. In the first two years, I didn't have any idea about what I was learning. Well, I learnt some Chinese characters such as "I love Beijing Tian-an-men", and I learnt counting from 1 to 100, and some basic calculating.

From the third grade year, I started to enjoy learning, especially mathematics. It was my father who really stimulated my interest in mathematics, and solving mathematical problems became the most interesting game in my childhood. Though from the third grade year, I became one of the best students in my class, I still didn't have any idea about my future, I also didn't have any idea about the world outside. I forgot to mention that in our village we didn't have electricity till the end of 1982, and we had the first TV set in the spring of 1986.

My eldest brother is one of the most important people in my life. In my forth grade year, he brought me a book about Marie Curie, a biography. He told me about the great woman scientist Marie Curie who twice won the Nobel Prizes, and he also told me about T.D. Lee and C. N. Yang who were heroes of our Chinese people. My brother learnt that in the cinema! He said that at that time, there was always a short documentary film about T.D. Lee and C. N. Yang before a movie began. My brother thought physicists are great. Therefore, when I was about 9 years old, even though I didn't have any idea about physics, I decided to become a great physicist.

I think the hero or idol plays rather important role in teenagers' life. Teenagers choose the direction of their future by choosing their heroes and idols, and they choose their heroes and idols by listening to their inner desires. The goal to become a great physicist was still too abstract and too far away for a nine year old little girl. There was a long journey to go?

Before I went to high school, my favorite subject was always mathematics. I enjoyed the happiness of solving all kinds of challenging mathematical problems, and analyzing and solving physical problems. My style was a kind of typical German style (of course neither my teacher nor I realized this) I enjoyed deriving everything logically and clearly step by step. (Hopefully physicists from Germany do not complain about this.)

It seems I was the only student in my class who continued physics study after high school. When I was sixteen and half years old, I became a student in physics department of Hua-zhong Normal University, which is in the capital city Wuhan of our Hubei province. I enjoyed very much the life in the university and also I enjoyed physics, especially quantum mechanics and statistics. I read more books on the history of modern physics, and I started to think some "deep" questions about the evolution of the universe and the microscopic world. Actually, I was more interested in self-organization of complex systems, but I started my career of research by investigating the QCD phase transition. There is a very good institute, the institute of particle physics (IOPP), in our university. The main research in IOPP is about QCD phase transition and heavy ion collisions. (In many ways, IOPP is very similar to ITP in Frankfurt.) Sometimes, professors from IOPP gave seminars for our undergraduate students, and we also had chances visit IOPP from time to time. I was very grateful to Prof. Liu, who was the director of IOPP and he spent much time and patience on me and my other two classmates. I started my graduate study in IOPP from the spring of 1994, and since then, I was on the right track of being a physicist. The story afterwards is just one straight line, so I am going to stop here.

Writing this article give me a chance to look back on my long journey of being a physicist. It was the great physicist like Marie Curie, T.D. Lee and C. N. Yang who motivated my dream of being a physicist. However, I think it is my inner desire which eventually drives me becoming a physicist. The simple answer to Sabine's question "why I became a physicist" is because I enjoy the happiness from understanding the unknown world, solving challenging problems and making discoveries. Sabine and Stefan, thank you for giving me such a chance! If you have plan visiting China, please drop me a message! I also hope to use this chance thank my eldest brother who turned out to be a manager in the bank though he dreamed to be a great writer. It is my eldest brother who brought me the seed of wisdom and provided me economic condition and spiritual support on my way of being a physicist.

Huang Mei is a 33 years old associate Professor at the Institute of High Energy Physics, Chinese Academy of Sciences in Beijing. She mainly works on the many-body system of quarks and gluons. Currently, she is studying strongly coupled system by using AdS/CFT. In her free time she likes to do some sports, read books, listen to the music...

See also the previous contributions to the inspiration-series by

and my related guest post at Asymptotia 'Sabine Hossenfelder: My Inspiration'.



The Jungfraujoch in Switzerland is Europe's highest altitude railway station. If you are interested to hear English with a Swiss accent, look at this video.

Besides the educational value of this post, I'm telling you that because my mum sends photos. I'm not entirely sure exactly why she's in Switzerland, or what she's doing there besides piping several megabites through myyahoo, but anyway.

For more cool photos from Switzerland see Global Warming arrives to Versoix.

Saturday, March 24, 2007

This and That

  • Several visitors ended up on this blog searching for 'Denzel Washington's marital status', for which we are the first Google hit. The reason you find in the footer, where I've put a quotation from the movie 'Deja vu': I asked you to explain it to me, not to talk science. In case you haven't seen the movie, it's kind of a weird wormhole-timetravel-romance with several closed loops. I was a bit disappointed by the ending because the story breaks its own inner logic for a more dramatic rescue scenario. Anyway. The quotation has to go, sorry. And I don't know whether he's married.

  • Next weekend, I will give PI's public lecture for the Black Hole Session:

    Frontiers of our Knowledge
    Presented by Sabine Hossenfelder, Perimeter Institute
    Summary: Theoretical and experimental physics work hand in hand to broaden our understanding about the universe that we live in and man's place in the world. In the 21st century, nature has given us quite some puzzles to solve, in the microscopic (particle physics) as well as in the macroscopic (cosmology) range. These open questions at the threshold of the unknown have lead theoretical physicists to formulate possible solutions whose experimental tests are awaited soon. I will talk about these current limits to our knowledge, and about the insights that new experiments like the Large Hadron Collider can provide us with. A central point will be the possibility of large extra dimensions and black hole production at the LHC.
    LOCATION: Bob room, 4th floor, Perimeter Institute for Theoretical Physics

    I am particularly proud of this maximally vague abstract. The problem is currently that besides the summary, I have no idea what I'm going to tell the people. In case you are around, drop in, I assure you it's going to be entertaining.

  • Some days ago, Jonathan Shock from Jon's Travel Adventures nominated us for the thinking blogger award.

    It turned out this is part of a meme, and I am supposed to nominate 5 further people who I think are worth the award. Though I find the idea of the award itself nice, I am 'thinking blogger' enough to realize that 'awarding' it through a meme it completely nonsensical, especially if the number of people awarded is (ideally) supposed to inflate exponentially. I don't know who started this, but this is a dead end and I'm not going to award anybody.

    Many thanks to Jonathan anyhow.

  • The funniest thing I've read in a while: stupid things people said in court. I'm not sure whether these are all confirmed quotations, but it's funny anyhow. If you ever thought you asked a stupid question, you can't top these:
    • Q: How many times have you committed suicide?
    • Q: Were you present when your picture was taken?
    • Q: How far apart were the vehicles at the time of the collision?

    For more, see this website. My favorite is this one:

    Q: Doctor, before you performed the autopsy, did you check for a pulse?
    A: No.
    Q: Did you check for blood pressure?
    A: No.
    Q: Did you check for breathing?
    A: No.
    Q: So, then it is possible that the patient was alive when you began
    the autopsy?
    A: No.
    Q: How can you be so sure, Doctor?
    A: Because his brain was sitting on my desk in a jar.
    Q: But could the patient have still been alive nevertheless?
    A: It is possible that he could have been alive and practicing law somewhere.

  • And the say of the week:

      "Reason will not lead to solution
      I will end up lost in confusion"

    ~The Cardigans

A nice weekend to all of you!

Friday, March 23, 2007

Filtering Gravity

Most of the time, checking the arxiv's new publications is kind of boring. It doesn't happen very often that someone comes up with a really new idea. Therefore I want to draw your attention to a recent paper that I found really interesting:

    Degravitation of the Cosmological Constant and Graviton Width
    Authors: Gia Dvali, Stefan Hofmann, Justin Khoury

    Abstract: We study the possibility of decoupling gravity from the vacuum energy. This is effectively equivalent to promoting Newton's constant to a high-pass filter that degravitates sources of characteristic wavelength larger than a certain macroscopic (super) horizon scale L. We study the underlying physics and the consistency of this phenomenon. In particular, the absence of ghosts, already at the linear level, implies that in any such theory the graviton should either have a mass 1/L, or be a resonance of similar width. This has profound physical implications for the degravitation idea.

If I understand it correctly, the idea is to look at the cosmological constant problem from a different point of view. The question that troubles many physicists is why the observed value of the cosmological constant is what it is, especially why it is not 120 orders of magnitude larger. In their paper, the authors point out that the question what we measure for the cosmological constant does depend on it's coupling to gravity. They propose a scenario of modified gravity in which the coupling strength of a source depends (loosely speaking) on it's typical size of structures. The more homogeneous the distribution, the less it couples to gravity. (More technically, one takes the Fourier transform of the density, and the coupling depends on the wavelength. Large wavelengths couple weaker.)

The cosmological constant is perfectly homogeneous, and therefore would couple only very weakly, or maybe not at all. In this work, they do not explicitly address the issue why it is non-zero or has the observed value, but I think this idea has a large potential.

The specific scenario that they investigated is one with a massive graviton. Because of the graviton acquiring a mass, additional polarizations arise. This concrete model is one example for the more general class of gravitational high-pass filters that they have proposed. The challenging question is of course whether this approach can be utilized to compute the value of the cosmological constant. What I find specifically intriguing is that in this case, the gravitational sector might be the cause for the observed value of the cosmological constant, and it would be essentially independent on the expected value from the matter fields.

Here is an example to underline the importance of filters. Last week, a disaster happened:

    From: System Administration
    Subject: [allusers] Spam Surge

    Last night at around midnight, a major increase in spam has caused an overload of the spam filter daemon. As an unfortunate result, the daemon gave up completely and let through all the spam until recently.

I received about 120 spam emails per hour. Luckily, I am essentially decoupled from this particular server.

See also: The Gravity Defyer


Wednesday, March 21, 2007

Canada is great...

"...because Canadians made it great. The people who built this country worked hard to realize their vision. They set us on a bold course to greater hope and opportunity. They had a passion for the free, prosperous and welcoming country they called Canada.
We stand on their shoulders.

Canada is a powerful idea. We are a modern nation that stands up for Canadian values in this world. We are prosperous and compassionate. Aspirational and welcoming. Independent and strong."

With these words, Canadian Finance minister Jim Flaherty announced the 2007-08 budget yesterday. You can read more praise of the Canadian nation in his speech here, but the really important thing is:

"The Perimeter Institute for Theoretical Physics in Waterloo, Ontario, which is devoted to the study of foundational issues in theoretical physics, is an example of [such] a world-renowned research institute. Since its creation in 1999, the Perimeter Institute has become a leader for Canadian research in the emerging field of quantum physics and a model for science education and outreach. The Perimeter Institute has demonstrated outstanding scientific merit, has a national reach and has received significant funding commitments from the private sector and the Government of Ontario. Budget 2007 provides $50 million to the Perimeter Institute in 2006–07 to support its leading research, education and public outreach activities."
[read the full report]

And while we're at praising - related: In 2007 Waterloo is again among the world's top seven intelligent communities.

Science and Democracy III

[I was reminded that I’ve promised repeatedly to continue the previous posts Science and Democracy I and II. To my own surprise I found an almost finished draft about the danger of using marketplace tactics in scientific research, and I added some recent comments out of the blogoshpere to underline my arguments.]

I vividly recall the first thing my supervisor told me when I was an undergrad: "You have to learn how to sell yourself." Since then I have repeatedly been given well meant career advises how to survive on the scientific marketplace (most of which I ignored, but I’m still around, so I guess I’m not doing too badly).

Many of my friends and colleagues in physics regard these marketplace tactics as an annoying but necessary part of the job. To begin with, this concerns me because I feel that there is a gap between how science is, and how it should be – and an unnecessary gap in addition. But more importantly, the application of economical considerations to scientific research is inappropriate, and the reason why I did not take these career advises is that I don’t want to support strategies that will hinder scientific progress on the long run. So, if you were hoping for some career advises, you're on the wrong blog.

Though comparisons between science and economics often have a grain of truth in them, they are doomed to fail when extended naively. Whether or not you believe in the infallibility of the 'Invisible Hand' [1], scientific theories are not sold like candy bars. If one uses an economical model to analyze the dynamics of research programs, one has to be aware of the limitations of this analogy.

I: The Marketplace of Ideas

The 'marketplace of ideas' is often claimed to act as a self-regulating mechanism that ensures progress in science. It is based upon the believe that all scientific theories when made accessible to the public compete freely among each other, until it eventually turns out which idea is the best description of nature.

Being an optimist, I have no doubts that this works if one looks at the history of mankind over centuries when nature is the ultimate judge on our scientific endeavors. However, there is no reason to believe that this automatically works on shorter time periods as well. On a time scale where we do not have nature to judge (typically a couple of years, maybe up to decades - that is how long grants and employments last), the scientific community is its own judge. The obvious difference to the economical marketplace is that we do not offer our ideas ‘for sale’ to a neutral target group, and depending on whether it is bought or not our product is a success or a disaster.

Ia: The Measurement Problem

No, we are selling our theories inside our own community. And our demand for products can easily be biased if the competitive pressure is high. The situation is significantly worsened by an increasing specialization into many sub-fields and a lack of communication between these fields. Needless to say, the genuine enthusiasm that researchers have for their own field does not improve neutral judgement. If you want to use the analogy to the economical marketplace here, you’d expect it to work even if products are only sold to company managers [2].

This difficulty to find criteria to judge on research programs might not have been a major issue in the previous decades, but it becomes increasingly important if

    a) the community grows to a complex system whose dynamics is little understood (E.g. the increasing influence of 'fashionable topics' is a typical sign for a non-linear feedback effect, the emergence of sub-fields with their own group dynamics is a sign for self-organization)
    b) changes in the sociological, cultural and technological context require adjustment of criteria
    c) financial and peer pressure endangers neutral judgement
    d) timescales that are set through (inappropriate) external constraints.

In other words, it’s a 21st century issue. With increasing complexity, we are left with a decreasing number of people who have an overview on the whole ‘marketplace’. Little people are funded independently of their projects, so their opinions are biased in favor of their own research. Under such circumstances, the ‘marketplace of ideas’ will eventually result in a small number of approaches caught in feedback loops of increasing separation.

As Thomas Dent remarked at 4:27 PM, June 29, 2006:

    It should be obvious that there is no theoretical physics analog of capitalism or the free market. In capitalism there is profit which can be measured objectively, and the one who can make profit wins, the one who cannot must get out of the game. […] Since there is no objective measure of success in theoretical physics, there can never be a free market. Simple.

I would add: there is no such obvious measure on the time scale relevant for funding today. But obvious or not, measures have to be applied, and are applied, and the least we can do is to chose them wisely. Being scientists, it should not be so hard for us to find out how science works best, and to analyze whether the current conditions are optimal.

Ib: Primary goals and Secondary criteria

The primary goal: to support the most promising approaches and researchers, is of little help when you are faced with a 3 inch pile of application documents. Instead, one commonly uses derived secondary criteria that have shown to be useful. There is nothing to object to this procedure, except that the validity of secondary criteria has to be readjusted every now and then. In a time like ours, when the sociological and technological environment changes rapidly, neglect of questioning and re-adjusting applied secondary criteria can result in misleading feedback effects and sub-optimal selection processes.

The best known example might be the citation index and number of publications. These criteria are of course correlated with the originality and quality of the research, but whenever possible, one should ask for primary goals to be met. (I am not telling you this because it is something new, or because I think people in hiring committees are stupid, but to make the matter less abstract.) Other secondary criteria that have grown important over the last decades are e.g. previous employment at well-known institutions, or classifiable work on mainstream topics.

There is an obvious danger in just rewarding those who meet secondary requirements. If these criteria do not exactly match the primary goals, one promotes tactics that are sub-optimal for scientific progress but optimal for career building (see section 'Survival of the Fittest'). If you combine that with the non-linear feedback effect in complex systems, things can easily go seriously wrong.

An issue related to the necessary re-adjustment of secondary criteria to primary goals is to guarantee fairness on the marketplace. The 'Invisible Hand' always needs to be balanced by politics to ensure the marketplace is really 'free' -- this is one of the earliest lessons we have learned from industrialization. If we want the ‘marketplace of ideas’ to optimize progress in science, we have to ensure that every idea gets a chance, irrespective of its origin [3] - the matter of origin plays no role for the question whether an idea is worth supporting.

Ic: Risky Research

Another important point is that supporting risky start-ups is one of the most relevant factors for progress. Unfortunately, this factor is severely neglected by present funding strategies. Sounds familiar? Okay, okay, it’s not my idea:

"Do you want a revolution in science? Do what businesspeople do when they want a technological revolution: Just change the rules a bit […] Create some opportunities for high-risk/high-payoff people […] The technological companies and investment banks use this strategy. Why not try it in academia? The payoff could be discovering how the universe works."

~ Lee Smolin, The Trouble with Physics (p. 331)

Risk averseness is a rather unsurprising consequence of insecurity caused by a lack of communication in a community falling apart into sub-fields. It is also supported by chronically short resources (if we hire anybody, then someone who works on what I find interesting), short-term funding (it takes time to work out new ideas, for more info see e.g. Temporary Display and comments to this post), and by falling for the derived secondary requirement 'If she's interested in what I do, she must be intelligent.'

In the absence of a final judgement by nature on our approaches, it is very short-sighted to discard alternative options. However convinced I am of my own research project, I always have to acknowledge the possibility that it turns out to be a dead end. As Albert Einstein said so nicely "Mathematics are well and good but nature keeps dragging us around by the nose." In the London debate, Nancy Cartwright underlined the need to keep doors open by referring to J.S. Mill's essay 'On Liberty'. She argues that in the absence of nature's judgement the smart thing to do is to not prematurely discard alternative options

    "We need to allow as much liberty as possible (for people in designing their lives) because we don't know what is the best way (to live). And that's in part because we don't know what are all the good alternatives to chose from."

II. Product Placement

Presenting our research results to colleagues is an essential part of our job, in written form as well as in seminars, talks, and discussions. Clearly presented arguments, and well structured seminars are definitely beneficial to progress. However, as with many things in life, it is a matter of balance. Advertisement should not become more important than content. The most entertaining presentation can not make an idea better than it is, and scientific arguments have to remain as honest as possible – even if this means drawing attention to the flaws of the product.

For example, Thomas Larsson remarked

    At 5:53 AM, March 17, 2007,
    There are some good things about the string/LQG conflict, though. Without it, I would not know about the limits of the string black hole prediction, nor would I know that LQG quantization does not work for the harmonic oscillator.

and illustrates with that a problem that arises when researchers feel the pressure to advertise their own work. Today, many praise results in a rather unbalanced way – not because they don’t know better, but because they have to compete with a large number of people. If you put a paper out and don’t have a prominent co-author, a catchy title and exaggerated claims is the way to get others to read it. This tactic is okay for fish sales on mediterranean markets, but it is very dangerous to the standard of scientific research. It leads to rather uncritical status reports in which problems are either not mentioned, or downplayed (and if this shortcoming is pointed out, the author will claim that the problem is obvious and widely known.)

Whether published articles are balanced crucially depends on the referee process [4]. One could say a lot about peer review, but to say the least, it doesn’t always work as it should, and many reports are not as objective as they ought to be. An example that I have repeatedly witnessed myself: when it comes to numerical simulations, it is common practice to point out where the model fits the data very good, and just not to mention the problematic observables. Most often, numerical simulations are hard to check, even if the code is available, and the not-so-good results just don’t get published.

Though this is not strictly speaking wrong, it is just not good practice as it is exactly understanding the failure of an approach that could lead to improvement. However, those scientists who elaborate on difficulties and drawbacks risk being understood as negative, or maybe just not exciting enough, and cause problems for themselves (and probably get the well meant career advise to better sell themselves): Here we have another gap between what would be beneficial for scientific progress (primary goal: understand model), and what is beneficial for the scientific career (secondary goal: hide bugs or declare them as feature).

Now that I think about it, why not include a blurb paragraph to papers with warnings. Like ‘Possible side effects might contain decaying vacua, ghost fields and tachyons.’ Or ‘Do not use this model in Lorentzian signature, and not after the electroweak phase transition. If you consider using it in more than three dimensions, or together with matter fields, please consult a doctor.’

:-) I know, I’m being silly. I apologize, it is far easier to retreat to sarcasm than to come up with constructive criticism.

Were was I?

Uhm, this is another example where marketplace tactics fail in scientific research. We don’t want to sell our theories to as many people as possible and optimize the citation index, but we want to optimize the quality and usefulness of publications.

Another excellent example that shows how advertisement can promote scientific nonsense when secondary criteria (here: holding patents) are in conflict with primary goals (here: quality of research), can be found at the post Micro Black Day.

III. Survival of the Fittest

The survival of the fittest is another catchy phrase (often used by those who profit from the current system) to claim that a natural selection process ensures progress in scientific research. The irony is that those who argue such actually explain why the system fails.

Survival of the fittest doesn’t mean survival of the strongest, the best looking or the most intelligent. It means literally, survivors are those who ‘fit best’. Survivors are those who adapt the behaviour that minimizes existential conflict with the environment.

Now, ask yourself, what is this environment in the context of scientific research? Well, it is our own community with the selection criteria that we apply. If these criteria are not optimal for scientific progress, we don’t only have the possibility but the duty to change it!

The optimization implied in the ‘survival of the fittest’ crucially depends on the environment and available resources. Whether you like the subtitle of Lee's book or not, he makes the important point that we have to ask how science works best – how it works now and here, how it works in this century, in this sociological and cultural environment - and whether the presently applied selection criteria are indeed optimal for progress. Whether the fitness that we reward is actually the fitness that we need. Whether our secondary criteria agree with the primary goals.

We have to blame ourselves if we accept the current conditions even though we know they are not optimal.

    Amara Graps: At 2:51 AM, March 10, 2007
    One reason why the current system has been going on for so long is that scientists are a mild-mannered bunch and are passionate about their work. They are prone to self-abuse to pursue those passions too, being willing to absorb the most degrading conditions.

Repeatedly, I have met colleagues who agree that the situation sucks, but they shrug shoulders and say, that’s just the marketplace. Where does it come from, this believe that passivity is a guarantee for progress?

    amused: Mar 17th, 2007 at 1:17 am
    Of course, that’s hardly a new point in these discussions, and the standard response is to shrug ones shoulders and say “oh well, that’s just market forces”. Which is true, but it’s also relevant to ask whether it is in the best interests of physics. Hopefully it’s not too controversial to suggest that the interests of physics in the long term are best served by ensuring as much as possible that jobs go to the “best” people, regardless of their preferred research topics.

We are scientists. We should be able to analyze the present situation, and to draw consequences. Science is not coming to an end if we fail to meet the challenges that the increasing complexity of our field has brought. But we run in danger to reproduce the failures of the economic marketplace: bubbles of nothing, that are a waste of time, money and energy.

If left without attention, the naïve believe that the marketplace will make things right ‘somehow’ can seriously hinder progress. Nature might have supported an approach that failed too early – because it wasn’t advertised well enough, or because the capital investment was simply insufficient to allow it to compete.


There are important differences between the economical and the scientific marketplace. The most obvious ones being the absence of a neutral measure (like profit), and the pitfalls of advertisement.

Currently the ‘marketplace of ideas’ works anything but optimal. Times have changed rapidly, and our community has grown significantly. These changes need to reflect in our organizational structure as well, or we run in danger of getting stuck in a dead end.

And it is easy enough to improve the situation:

  1. Question and doubt. Ask yourself whether the realized strategies are optimal for scientific progress, and if you don't think so, don't shrug shoulders. Don't accept criteria you have been taught are right without taking into account that times have changed.

  2. Analyze. Peer pressure, intense competition, short resources, project-dependent funding and short-term employment favours mainstream, conservative and low-risk work. Be aware of that. Remind yourself and colleagues that 'Good physics has to be open, critical, and responsive'. Research has shown that simply reminding people to think rationally influences their decisions.

  3. Trust yourself. Don't work on topics that you don't genuinely believe are relevant because you are afraid of your reputation. If this work is unavoidable, criticise - even if you are defeated, you make a contribution to science. (Hey - I told you, you're not getting career advises on this blog.)


It seems, this piece got quite lengthy...

One could write books about it...

Footnote [1]: The 'Invisible Hand' was indroduced by Adam Smith in his book 'The Wealth of Nations' (1776) to describe the self-regulation of the marketplace. From Wikipedia: Many economists claim that the theory of the Invisible Hand states that if each consumer is allowed to choose freely what to buy and each producer is allowed to choose freely what to sell and how to produce it, the market will settle on a product distribution and prices that are beneficial to the entire community. Adam Smith already pointed out that the Invisible Hand's regulation mechanism alone does not guarantee the well-being of the society and needs to be balanced by govenmental guidance "[...] uniformity of [the employee's] stationary life naturally corrupts the courage of his mind [..] His dexterity at his own particular trade seems, in this manner, to be acquired at the expence of his intellectual, social, and martial virtues. But in every improved and civilized society this is the state into which [...] the great body of the people must necessarily fall, unless government takes some pains to prevent it." Nevertheless, this metaphor is often abused to praise the merits of capitalism without given sufficient credits to its limitations. [Back]

Footnote [2]: In addition, there is also the question how our research is presented to the public - who after all pays us to explore the frontiers of our knowledge. This is an important point on its own but should not be mixed up with the question how the community selects promising researchers and research programs. Most people are crucially aware that it requires an appropriate education to judge on the value of very recent developments, and will rely on expert’s opinions for a good reason. The public is neither dumb nor ignorant. I welcome it very much that in the last decades - maybe starting with Hawking’s Brief History of Time - theoretical physics has become more accessible to the public. The resulting discussions of our research among non-experts are regarded by some scientists with concern and skepticism. I am sure it is only a matter of time until our community gets used to this attention and learns how to deal with this kind of feedback. I myself am perfectly sure this communication is inspiring for both sides - and one of the reason why I maintain this blog. [Back]

Footnote [3]: To give a concrete example, research papers should not be judged upon by the author. Researchers should not be selected because of the institutions they have connections to, or the country of origin. Conference invitations should not be made to famous people for the only reason that their name does attract interest – A scientific conference is not a rock concert. [Back]

Footnote [4]: At least one should be careful enought to use 'could' instead of 'does' and 'might' instead of 'will'. You can learn about the importance of weasel words here, in case you followed this discussion about this paper. [Back]

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Sunday, March 18, 2007

Guest Post: Yidun Wan

[Preface: Dear Readers of the Inspiration Series,

I realized that most of the guest contributions are too long to be read comfortably on screen. I have therefore put them together in a pdf-file, that you can download here. A nice Sunday evening to all of you,

Sabine ]

Why did I become a physicist? This, as normally a question for successful people, appears to be really hard for someone like me, who is still a PhD candidate with no splendid past. This is a hard question also because one can hardly answer it objectively and mathematically. However, being invited by Sabine Hossenfelder to write my answer as a guest post on her famous blog, it is my pleasure to try my best to say something, which may not be an satisfactory answer as expected by the host.

Prior to my story, I would like to spend some time on the word "physicist". Why? In English, one refers to physicists as those who do research in physics, including professors, researchers, postdocs, graduate students. However, the Chinese translation of a "physicist" (and more generally, a scientist) is not merely someone, who researches in physics, but one who has contributed to physics noticeably. The Chinese counterpart of a "physicist" in English should be a "physics researcher". Therefore, considering my situation, the question I am to answer should be better understood as "why did I become a physics researcher".

If I say that I simply have followed my destiny to become a physicist, you may laugh and think I am perfunctory, since this does not sound like what a physicist should say. Nevertheless, I am just telling the truth in an efficient way. To tell more details, it is better to first outline my history. Fourteen years ago, I began my undergraduate study in China. After four years, I obtained my first Bachelor's degree in Computer Science. One year later, I got my second one in Economics. Then I started to work in some Chinese company. Six years ago, I landed on the U.S.A. and continued my study in Computer Science as a graduate student. After one year and a half, I had the opportunity to switch to physics. Hence, I took a master's degree in Computer Science and quit. In the next two years, I had been doing research in applied physics (though theoretical calculation) in Canada, which brought me a master's degree in physics. Right after this, my world line extended to doing theoretical physics at the Perimeter Institute; now I still move on in the same direction—to explore the physical nature till the singularity of my life. Having read my brief history, you may take off now if not interested in any more detail.

So ladies and gentlemen, let us begin a time travel along my world line back to the past. In the summer of 2002, I often wandered around in the campus of the University of Pennsylvania, because a critical junction of my life came to me, which put me in front of two choices: to do research in Neural Networks towards a Ph.D. in Electrical Engineering, and to move to the University of Ottawa in Canada and begin my academic career as a physicist. Although the former option might be able to bring me a good life with stable job and income, I chose the latter one, as you already knew. There were two reasons. The first reason, obviously, was that I could then start to realize my dream of being a physicist. (I haven't explained why I love physics, but it is coming, just be a little bit more patient in the time travel. ) The second reason was related to my personal life; my girlfriend, who became my wife in that August, was to do her master's study at the University of Ottawa, so the only way for me to keep us together should be getting into the same university. The only shortcoming of going to the University of Ottawa was that I could not do pure theoretical physics but the so-called "theoretical" Fiber Optics, since the physics department there had only research groups in applied physics. Therefore, I decided to be enrolled in the master's program only in order to move to some other place where I can do theoretical physics later. Luckily, after two years stay in Ottawa, I successfully obtained my master's degree in physics and was admitted by the University of Waterloo, and joined the Perimeter Institute to pursue research in Quantum Gravity under the supervision of Prof. Lee Smolin. Since then I have been on the right track and become what I am now: a physicist.

Life is very unpredictable and is thus fascinating; a decision, which is apparently not perfect at the moment of being made, may turn out to be perfect at a later time. Take my decision of going to Ottawa as an example; it was not perfect for sure at that time because what I truly wanted to do was theoretical and fundamental physics. However, as soon as I entered Perimeter Institute, I realized that decision was so right. Why? Before I came to Ottawa, I actually had no any real background in physics and advanced mathematics; all I knew about physics and math was what I learned from my first year undergraduate physics course, some Electromagnetism I learned by myself, calculus and some complex analysis. With such a weak background, I would easily wash out quickly if I directly jump on some graduate program of pure theoretical physics. During the 2-year stay in Ottawa, I took graduate courses like "Quantum Mechanics", "Mathematical Methods in Physics", "Statistical Mechanics", and "General Relativity", and did a great job. Interestingly, I had no any problem of understanding Quantum Mechanics. The reason, I guess, was that I never learned Classical Dynamics systematically before I encountered the quantum one. Besides taking courses, I spent a lot time on learning useful math and physics by myself. Moreover, I also did some experimental physics, which input some concrete cognition of physics to my brain. In summary, having worked hard in that two years established me a relatively ok background in physics, which was of great help to me in my first year at PI. Every time when I look back, I am grateful to my experience in Ottawa, and hence to my decision made in the summer of 2002.

Our itinerary of time travel may be mis-programmed in the computer of our spacecraft; we now stop at my childhood. Anyway, let us accept this and turn around our craft to continue our trip from here to its future. I am not very confident of my memory about very early years in my life. So we would better to start from my second year in elementary school. I remember in that year every student in my class was asked to write an essay about his/her ideal. My essay looked like a science fiction, in which I imagined the world of twenty years later, and more importantly I was a scientist, but not a physicist in particular. Frankly speaking, this does not mean that I really wanted to be a scientist at the moment. Part of the reason was that I might be too young to understand what a scientist exactly is. The other part was that "being a scientist" was a common ideal of many Chinese children at that time, since we were taught to believe that making scientific contribution to our country and even the whole world is a sublime and holy career. However, I knew that I was definitely attracted by two mysterious entities: the universe and the being. I just had been able to tell which one, the universe or the being, I was more interested in until I met a book, "the First Three Minutes" by Steven Weinberg, which influenced my life to a large extent. I clearly remember it was in some day during my first year in junior high school when I borrowed the book (certainly the Chinese version) from the civic library of my hometown. "The first Three Minutes" vividly elaborated the story within the first three minutes of our universe, from which I first got to know that our universe originates from a singularity through a Big Bang in about 1.3 billion years ago. In fact, I was not able to understand the physics in the book and did not even know who Weinberg was; nonetheless, I was completely captivated by the splendid and gorgeous scene of the early universe illustrated by the book. At the time of reading the book, astonishment, doubt, and excitement had been always possessed me; strong eagerness to fully understand everything in the book in some day spurred me to take to be a physicist decoding the universe as my life-long ideal.

Irony of ironies, I did not appear to be very talented in physics when I was a child, and even when I was a teenager. My talent in literature (of course the Chinese one) and arts seemed much better than that in physics. This situation drastically changed only after I went to university, the South China University of Technology. The consequence was that I did not choose physics, but rather computer science as my undergraduate major, although to be a physicist had always been a dream hovering in my head. Another factor caused me to major in computer science was my parents, who made the decision for me; this was pretty natural in China, at least at that time.

During my undergraduate study, China was experiencing a rapid increase of her national economy; various enterprises, domestic or multinational, emerged; people became richer and richer. This big tide of economy also impacted me; I felt that to be a good businessman sounds not bad at all. Interestingly, to be adapted to the development of the our country, my university offered a new program, which allowed excellent engineering students to also major in International trade towards a Bachelor's degree in Economics. I, one ridiculously forgot his ideal at the moment, joined the new program. After graduation, I successfully found a job and planned to establish my own business in the near future. Nevertheless, soon I realized that was not the life I really liked and wanted. Watching the night sky decorated with shiny stars, the ideal to be a physicist woke up in my mind; I decided to go abroad to look for my dream. Therefore, after having worked for about half a year, I resigned and went back home to prepare for TOEFL and GRE, which are required by most American and Canadian graduate schools. I had to choose computer science again so that I could successfully be admitted by American universities, because applying for graduate study in physics in the States from China without a physics background was hopeless and it ought to be easier to switch major after getting an American degree. Unfortunately, at the end of 1999, my visa application was rejected by the US Consulate in Guangzhou, China; I tried another two times in sequence, but they were all rejected. In the next year, I had to re-apply for universities and also took some time to refresh my memory on advanced calculus and geometry, and general physics. After had painfully waited for almost a year, I finally got my US visa in the end of 2000. I then went to UPenn and began my life in North America.

Since we have already read my past related to physics after 2000, our time craft should directly fly back to our current time. Thanks everyone who joined our time travel! I would like to talk about why I selected quantum gravity, in particular Loop Quantum Gravity as my research area; however, this is not a short story, which can be clearly narrated within such a guest post. Anyway, what I wrote above should be sufficient to answer the question "why did I become a physicist".

I think my world line behaves like a damping oscillator along time, which although turns aside often from the way to be a physicist, eventually converges at being a physicist. So again, I have to say: "I simply followed my destiny."

Yidun Wan is a Ph.D. candidate affiliated with the University of Waterloo. He works on Quantum Gravity at the Perimeter Institute for Theoretical Physics, under the supervision of Prof. Lee Smolin. He blogs at Road to Unification and also maintains a personal webpage here. He is currently working on unifying matter with Loop Quantum Gravity.

See also the previous contributions to the inspiration-series by

Friday, March 16, 2007

Sword Blades

    "He took a shagreen letter case
    From his pocket, and with charming grace
    Offered me a printed card.
    I read the legend, "Ephraim Bard.
    Dealer in Words." And that was all.
    I stared at the letters, whimsical
    Indeed, or was it merely a jest.
    He answered my unasked request:
    "All books are either dreams or swords,
    You can cut, or you can drug, with words.
    My firm is a very ancient house,
    The entries on my books would rouse
    Your wonder, perhaps incredulity.
    I inherited from an ancestry
    Stretching remotely back and far,
    This business, and my clients are
    As were those of my grandfather's days,
    Writers of books, and poems, and plays.
    My swords are tempered for every speech,
    For fencing wit, or to carve a breach
    Through old abuses the world condones.
    In another room are my grindstones and hones,
    For whetting razors and putting a point
    On daggers, sometimes I even anoint
    The blades with a subtle poison, so
    A twofold result may follow the blow.
    These are purchased by men who feel
    The need of stabbing society's heel,
    Which egotism has brought them to think
    Is set on their necks. I have foils to pink
    An adversary to quaint reply,
    And I have customers who buy
    Scalpels with which to dissect the brains
    And hearts of men. Ultramundanes
    Even demand some finer kinds
    To open their own souls and minds.
    But the other half of my business deals
    With visions and fancies. Under seals,
    Sorted, and placed in vessels here,
    I keep the seeds of an atmosphere.

Amy Lowell, Sword Blades and Poppy Seed

Read the full text at Project Gutenberg

Thursday, March 15, 2007

Atomic Flowers

    Though I'm a nonmathematician, my work originates in intuitions which have consistently led to an art of visual mathematics. Such an art obviously has a special resonance for scientists and mathematicians, but being visual, it can be just as immediately engaging for general audiences. Its patterns invite mathematical analysis, but require none, and need only be seen as music need only be heard. The elegant economy found in the forms and dynamics of nature has always been an inspiration to me, and I have aspired in my work only to that profundity which might arise from subtle analytic rigor, much in the manner of science. Images of sculptures I have created over the last fifteen years can be seen in the following galleries. The galleries are devoted to representative works from distinct paradigms appearing in chronological succession up to present.

For more, see this website.

Wednesday, March 14, 2007

PI day

Today is march 14, or 3/14, as Americans will write - that's π day! It is such an important date that it even has its own website! Unfortunately, if you have a look at the first few decimals of π, you can see that you can't celebrate the π instant at 3 pm something in the afternoon, unless you use a quite awkward scheme to split the hour...

By a curious coincidence, π day is also the birthday of Albert Einstein: He was born on march 14, 1879, in this house in Ulm in southern Germany (the house was destroyed in 1944, so you cannot visit it any more):

(Source: Albert Einstein in Ulm)

As the celebrations of his 125th birthday, and the 100th anniversary of his Annus Mirabilis have brought us many many great websites about Albert Einstein, there is no big point in repeating here anything of all you have for sure read many times.

But did you know that Einstein himself might have had some trouble to recognise PI π in his birthday? As every child learns in school in Germany, dates are written in the form day, month, year. So, Einstein has written his birthday most probably as 14. III. 79, following the conventions of his time and using roman ciphers for the month. That's good to know if you want to make sense out of the date 4. I. 19 - it is January 4th, 1919. That's no special date, it just happens that Einstein lectured about "ponderable bodies" on that day, as he has written down in his lecture notes:

(Source: Albert Einstein Online Archive)

The lecture on 9.11. (that's November 9th, quite an important date in German history) fiel aus wegen Revolution - it was was cancelled "because of revolution"...

Coming back to Einstein and the π day, one might wonder whether Einstein's papers are encoded somewhere in the decimals of π. That's the case if π is a so called normal number. Unfortunately, no one knows so far whether π is normal or not, despite ongoing progress on this question.

The inverse question is much more easy to answer: Does π occur in Einstein papers? If we have a look in the famous Ist die Trägheit eines Körpers von seinem Energieinhalt abhängig? (Annalen der Physik 18 (1905) 639, here as PDF, the famous L = mV2 paper), this paper gets by without any π! OK, you may say, that's a short paper. What about the Elektrodynamik bewegter Körper (Annalen der Physik 17 (1905) 891, here as PDF - the electrodynamics of moving bodies, the SRT paper)? Surprise, there are only 4 πs in this 30 page paper, and only in relation with one expression for the energy density. If you really want to get rich in π better invest in Über die von der molekularkinetischen Theorie der Wärme geforderte Bewegung von in ruhenden Flüssigkeiten suspendierten Teilchen (Annalen der Physik 17 (1905) 549, here as PDF, the paper about Brownian motion) - I did not count them all.

What can we learn from all this? The special theory of relativity is not transcendental!

Happy π day!


Good physics is conflict

Last week, The Royal Society for the Encouragement of Arts, Manufactures & Commerce (RSA) organized a debate around the publication of Lee Smolin's book 'The Trouble with Physics' in Great Britain. It was moderated by the Chris Isham, and besides Lee Smolin, the guests were the physicist Michael Duff, and the philosopher Nancy Cartwright. You can download the audio on this website, and find a report on the evening here.


I meant to write a concise summary of this debate about, around, and with troubled physicists since Clifford picked up the topic and stormed another teacup. What I think about the alleged trouble with physics, I've written so often, you can read this, this, this, this, this, this, or this. And, if you really want, also this, and this.

However. I find it hard to get sufficiently upset, and since it's after midnight I'll keep it short. On the one hand I fail to see what is insulting about the book. If the book is insulting for anybody, then it is insulting for all of us theoretical physicist, and for the simple reason that it's never nice to be forced to face the own weaknesses. On the other hand, I agree with Clifford that this debate should not have been lead in the public. One way or the other, what was done was done, and what we should think about now is the future not the past, so could we please move on.

Essentially, the most interesting things were said by Nancy Cartwright. Okay, she used too many words that end with -ism, but she made the important point much better and clearer than Lee Smolin or Micheal Duff (1:02 min):

Physics must be open, critical and responsive [...] Physics, good physics, is conflict.

Therefore, instead of a lengthy writing, here is my summary:

WildWestSound.mp3 (~ 1.4 MB)

Have fun. (Background music: Scooby Shack by Fun Loving Criminals).

Tuesday, March 13, 2007


This morning I looked out of the window and I saw the neighbour's roof.

I mention this because I haven't seen the roof for several months. All I've seen is snow, snow, snow. The most annoying aspect of the snow was that I couldn't find my parking lot, the numbers being printed to the pavement. Repeatedly, I must have chosen the wrong spot, and found complaints on my windshield telling me I had parked on a private lot and would I please vanish. I put a precautionary note on my car saying, if this is not #34, and you are able to find it, please use mine.

And here it reappeared, ladies and gentlemen, #34

Sunday, March 11, 2007

Why I am a physicist: Stefan Scherer

After following the guest posts of our inspiration series for some weeks, Sabine pointed out that despite being a contributor of this blog, I haven't told my story. So, let me try to explain, how did I come to be a physicist, and what does it mean to me?

Sometimes I ask myself, am I a physicist? I have studied it, I have even a PhD in physics, but I am not currently following a research or academic carrier. Now, this is a situation shared by many physicists - probably more than in other sciences. Many of them find jobs in software, or, especially in places like Frankfurt, in finance. I have been very lucky, finding a job where I am keeping touch to what is going on in the science, at the crossroads of two passions of mine: physics and books. I currently work in the editorial office of a multi-volume reference work covering all areas of physics. So, I am keeping contact to physics more than most other physicists outside academia. Point I want to make, being a physicist is not so much a description of what you do, but of the educational path you have taken, and, first of all, of a certain curious, and at the same time analytic, way to look at the world around us.

On the other hand, when I look back and try to see why and how I became what I am now, there are many contingencies that have brought me where I am, and many junctions that may have lead to other directions.

When I was a kid, there may have been signs that I may become s scientist, but not specifically a physicist. I was very curious about nature - my mother was amazed that I could name all the birds in the big garden around our house, and even accurately draw pictures of some of them. Later, I remember, I was fascinated by the TV series of Jacob Bronowski and Carl Sagan, and vividly read the accompanying books my parents had offered me. As a teen, I discovered the volumes of the TIME-Life Science Library series my father had subscribed to years earlier, and I read again and again about Matter, the Planets, or Mathematics, understanding a little more every time. And I was quite frustrated by the Scientific American, which I found extremely interesting, but which was way above my head. All this may have qualified me for very different paths, and indeed, in high school, when thinking about what to study later on, I sincerely considered many options: For some time, wanted to go into computer science, following the steps of my uncle, and learning more about artificial intelligence which was very much en vogue then. But I also was thinking about studying archaeology, and even to become an interpreter - after all, I could learn foreign languages with ease, and the institutions of the European Union in Strasbourg, Luxembourg, and Brussels were not far away from the place where I grew up.

In fact, I do not remember how and why I took the decision to inscribe in physics. In the year before Sabine left Germany, she made a video for the Christmas party of the physics institute in Frankfurt, where she interviewed people about all kinds of things - it was a lot of fun! When she pointed the microphone at me, I replied without hesitation to her question that I had studied physics because of Supernova 1987A. Though this sounds like a good answer, it is most probably one of those reconstructions which our memory creates at hindsight to provide us with a straightforward story. On the other hand, there is for sure some truth to it, since I had developed a big interest in astronomy at that time, and the Supernova was a prime event in that year. There was no astronomy department in my "hometown" Saarbrücken university, so choosing physics probably was a logical step.

Saarbrücken is a small university, with the physics department focussing on condensed matter physics. I was quite impressed by the course on theoretical physics offered by Arno Holz, and after following closely his seminar on topological defects in condensed matter physics, it was clear for me that I would join his group for my diploma. Unfortunately, Arno Holz didn't live to see me finish my thesis. In a sense, his untimely death pushed my path through life in a new direction: The lecturer who took care of us students had close connections to a scientific publisher. He had translated several books, and was then looking for support with the translation of a text on the electronic structure of materials. With my faible for books, I thought this was a very interesting job, and did it. Indeed, I liked it so much that after my diploma, I decided to look for a position in publishing. I had luck and found a post with a publishing house in Frankfurt, where I immersed in the then new technologies of electronic media and prepared the German edition of a HTML based physics course.

Working with the quite small Frankfurt publisher, it was inevitable to learn to know Horst Stöcker, who was not only one of the "star authors", but had his office at the institute for theoretical physics just across the street, and looked in quite often. When he learned that for my diploma I had worked on phase transitions, he asked me if I would not be interested in investigating the phase transition to the quark-gluon plasma, and getting a PhD in his group. I then knew next to nothing about quarks and QCD, but this was an intriguing option to learn some cool new stuff, and to do some real research. So, over the next long years, I shared my time between the publisher's desk and the physics institute. And this not only earned me a doctorate, it literally widened my horizon: The institute in Frankfurt is quite big, and has collaborations and connections worldwide. There was a constant stream of postdocs and guests from all over the world, and I am really happy that I have had this experience to get to know all these people. And, of course, that I met Sabine, who's now my wife.

This may not have been a very typical career path, but somehow, I think, it fits with me. Still like the teen who was not sure what to study, I have many interests, and get manifold inspirations form friends and people I am interacting with. However, what intrigues me now especially in physics, that's the unity, the same principles and fundamental patterns which show up again and again in such a wide area of subjects, from condensed matter over molecules and atoms to the nucleus and elementary particles. This is just fascinating, and seeing and understanding such connections doesn't lose its thrill the more I know and learn. Being out of university now, I am happy that I have friends who keep me up to date - and that so much information is now available through the internet. There it still is, the endless frontier, and I am just curious and eager to know what it will show.

See also the previous contributions to the inspiration-series by
and Sabine's related guest post at Asymptotia 'Sabine Hossenfelder: My Inspiration'.


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Saturday, March 10, 2007

Decoherence Dance

On Saturday night, the 'Decoherence Dance' took place in the old PI building on King Street - hopefully the first of many to come. I used the opportunity to test the video option of my new digital camera, and was able to produce the movie below with the appropriately bad quality. I welcome myself to the YouTube generation.

(audio: Word Up by KORN)

Well, the first upload looked even worse. In case anybody knows how to keep the resolution better, let me know (I've already rescaled it to 360 x 240, turned off interlacing, and set the frame rate to 24).

Echo: DDR as a Test Model

This is a copy of my post at the blog to our discussion group 'Quantum Gravity in the Lab?!' about our meeting on March 6th. The discussion was lead by Michele Arzano, and this week's topic was 'Planck-scale departures from relativistic symmetries: test theories and status of predictions'.

Michele Arzano arrived as postdoc at PI around the same time as I did, in fall 2006. Before I start explaining what he told us in the discussion this week, let me point out that he's DJed for some while, and had the idea to organize PI's first 'Decoherence Dance' that will take place on Saturday in the old PI building. In case you're around, drop in... Michele has a quite impressive number of works on Hopf-algebras, black hole thermodynamics, and modified dispersion relations. Though he prefers to call these 'deformed dispersion relations' (DDR).

He started with explaining the general idea to confront a (not further specified) 'candidate theory of quantum gravity' (QG) with the real world by use of a test model. Such a test model, he explained, would generally have a 'main feature', and possible 'additional features'. I think of this as parameters which might not necessarily all vanish, but could do so under certain circumstances. An example that he gave later might be a DDR that could but doesn't have to come along with a violation of conservation laws, and the resulting threshold modifications.

Michele then briefly summarized evidence for DDRs from QG.

First, dispersion relations get modified in theories with non-commutative space-times. Such could arise in certain string scenarios, where Lorentz invariance is broken (for a review see e.g. Review of the Phenomenology of Noncommutative Geometry), or the non-commutativity arises through a modification of the Lie-Algebra from standard flat-space symmetries a to a κ-Minkowski Lie-Algebra (for references see e.g. Hopf-algebra description of noncommutative-spacetime symmetries).

Second, evidence for DDRs has been found in approaches from LQG (see e.g. Loop quantum gravity and light propagation, and Quantum symmetry, the cosmological constant and Planck scale phenomenology)

He then defined the test model by generally parameterizing an expansion of the DDR. The coefficient for the first non-vanishing term in energy over Planck energy Ep is the most important one:

Since the expansion parameter is typically less than 10-16, it is of utmost important whether the first power n is 1 or >1.

This deformation is what he referred to as the 'main feature'. Since this is not a theory, but only a single equation, this might come with additional features like a modification of energy-momentum conservation, or an energy dependent speed of light. Generally, he said, it is an open question whether the dynamics can be described by an effective field theory. The above expansion includes DSR approaches as well as an explicit breaking of Lorentz invariance with a preferred frame.

[At this point Michele had already talked one hour instead of half an hour.]

He summarized two prediction that arise from this approach.

  1. In the general case of a DDR the speed of a photon depends on its energy. This means that a signal composed of different frequencies shows an unusual dispersion. Roughly spoken, higher energetic photons are faster than one would think they are. The problem is that this difference in the time of flight is hard to detect, since the ratio of the photon's energy over the Planck energy tiny is for typical photons that we observe. However, a difference in time of flight can add up given that the signal composed of different frequencies travels over a long distance.

    If one inserts the typical scales it turns out that γ-ray bursts provide a source that would make such an effect - tiny as it is - observable with the GLAST satellite. The bursts have a high energetic contribution that can reach up to 1 GeV, and a typical distance of a Gpc. In the case of n=1, the accumulated difference in time of flight between the higher and lower energies becomes comparable to the typical duration of the burst itself (of the order milliseconds), and thus potentially detectable. (I mentioned that the energies inserted in the equation were taken in a specific restframe, that of the cosmic microwave background.)

  2. In case energy-momentum conservation is modified, one obtains a modification of thresholds for particle production. This effect has been used to explain the to-be-confirmed absence of the GZK cutoff for cosmic rays. To briefly recall the issue: cosmic rays are commonly believed to be created from incoming high energetic protons that are not produced in nearby sources. If the protons move fast enough relative to the cosmic microwave background however, they will eventually scatter on the background radiation and produce pions (pions being the lightest mesons). If the threshold for this reaction is crossed, the typical travel distance (mean free path) of the protons drops considerably, and they can not reach us any more. One thus expects a sharp cut-off in the spectrum that should occur for proton energies around 1019eV (in the earth rest frame. In the center of mass frame this is roughly a GeV).

    Whether the threshold is raised or lowered depends on the sign of η. I forgot whether positive or negative would raise the threshold as necessary, sorry. (As Joy pointed out, the experimental situation on the GZK cutoff is far from clear, and there are many issues that have to be taken into account. I mentioned that the energies inserted in the equation were taken in a specific restframe, that of the cosmic microwave background. Yes, I know, I insist on that point. )
[Somewhere around here the discussion exceeded 90 minutes. I think I must be the worst discussion leader that the world has ever seen.]

Michele didn't have the time to elaborate on the question whether or not n>1 effects would be observable as well.

In my opinion another test for the test model is whether or not it can be put into a consistent framework. It is unfortunate that this test model still only consists of a couple of equations, and can not be understood as a theory. I think the requirement of having the main- and/or additional features arise from a theory would significantly improve the reliability of the predictions, and help to clarify ambiguities of the model. Overall seen I find the approach interesting, though direct connections to quantum gravity seem to be weak, and more motivations than actual derivations. It is hard for me to judge on whether the discussed features must necessarily arise from certain approaches, or are just a general possibility that one can't (and doesn't want to) exclude. In this regard, I hope that Lee will enlighten us next week.

Suggested literature: