Wednesday, September 30, 2009

Hello from Atlanta

So here I am in the US of A one more time, after a reasonably pleasant British Airways flight. I usually try to avoid British Airways since my my baggage seems to like it at Heathrow so much it sometimes stays there for several days, but this time it arrived with me. I can report that British Airways has a very well working online service, and a decent movie selection. I picked Eddie Murphy in "Imagine That," with humor suited for 3 year olds, and with too much of a moral message. On the upside, it didn't lose much by being squeezed on a 10 x 15 cm touchscreen with a square lattice and interruptions by your pilot's updates about the status of the lavatories.

US border control has new visa waiver forms that now also ask for a phone number and email address where you can be reached during your stay. Even if you have applied for a visa waiver through ESTA online, as is now required, you still have to fill out the paper form which seems very pointless to me. Meanwhile, the Americans don't only take photos of travellers and prints of both index fingers, but scan all fingers of both hands. I'm waiting for the day they will ask for a DNA sample and do a 3-d whole body scan. Or maybe I just haven't noticed they already do that. However, since I managed to not only cut my left index finger on Monday but basically tore off most of the skin, the all-finger scan probably saved me a frowned forehead hanging above a black uniform.

The hotel with the roof damage booked me into a residence for long-term stays. The room here has a completely equipped kitchen, and every evening there is a "social hour" in the community room. In my jetlagged condition, it took me half an hour to figure the reason why the internet connection didn't work was the absence of a power cable for the modem. By noon, room service had relocated the missing piece, and now a 30cm ethernet cable ties me to the wall, but yeah, as you notice, I can blog.

As previously mentioned, I am here for the Atlanta Conference on Science and Innovation Policy that starts tomorrow. It will be held at Georgia Tech. This morning, I took a walk across campus. While the buildings aren't very remarkable, it is clean and nicely arranged with lots of green areas. Below a photo from the student center (click to enlarge).

Participants of the conference actually had to apply for a talk by submitting a paper already in February. I am quite excited my paper was accepted, since it's the first time I am at a conference on this topic.

Frequent readers know well about my interest in the working of the academic system. What you didn't know so far is that supported by a mini-grant from a generous sponsor called SubMeta (kindly pointed out to me by Garrett on this very blog) I was finally able to commission the survey I had first suggested about two years ago in the comments to my post The Trouble With Physics: Aftermath. The survey was conducted by the Social Science Survey Center at UCSB in April this year. If you are a physicist working on a non-profit institution in the USA or Canada, you might have received a survey invitation. A total of 1815 people filled out the survey, despite some of the questions admittedly being very lengthy and cumbersome. This corresponds to a response rate of 14.42%, which is not bad at all.

I've been sitting on the results since 2 months already, but due to my move I haven't had much time to look at them very carefully. At some point I will tell you more details about the results, some of which are very interesting, though I find them also bothersome. I have about 48 hours left to put together my talk, which means converting 350 pages of tables into pretty plots.

Thus, back to work...

Sunday, September 27, 2009


After 3 weeks in Sweden, the only word that comes to my mind is "neat." It's clean, it's green, the air is fresh, the garbage is meticulously separated, cyclists wear helmets and leave their bikes in park-and-ride stations to jump on the train. Now I am wondering. Where to they hide the smelly suburbs, the homeless people and the ugly industry areas?

I am trying to find something to complain. So far my only point of complaint is that health insurance in Sweden is so universal it's incomprehensible you could not have a health insurance. Unfortunately, it hadn't occurred to the immigration office that one might hold a German passport but not move to Sweden from Germany. Thus, I was expected to come with an EU insurance card. Needless to say, since I haven't lived in Europe for 6 years, I don't have such a fancy card. I had to repeat this about 4 times to the same person and was met with a blank stare. When it eventually entered her brain that I did move here from Canada, German citizenship or not, she ingeniously concluded then I must have a Canadian health insurance card. Indeed, I do. Just that it expired when I moved out of country.

The bottomline is that in effect I currently don't have any health insurance, meaning I have to pay my bills on my overdrawn Canadian credit card, collect the receipts, and hope that I get a return once the Swedes have sorted out their paperwork.

It took me two full weeks to figure out how the health insurance system works in Sweden, since nobody bothered to tell me, assuming I was born with that knowledge. You see, you don't get a contract with a health insurance company. Instead, everybody who pays taxes is automatically covered by the governmental health insurance, which is processed by an institution called Försäkringskassan. Uneducated immigrant that I am, I was waiting for somebody to tell me the name of the insurance company, hand me a plastic card with a number, and give me a booklet with benefits. I suspect there must be some sort of private insurance companies that one can use for additional coverage, but it doesn't seem to be something many people bother with.

The other news this week is that the moving company announced my household will be delivered on Monday. I've lived out of a suitcase the past 6 weeks and find myself not missing anything. Still, I hope my boxes will arrive in good condition. This also means I will finally move out of the guest apartment that the institute provided, and into my own apartment.

Shortly after this, I am leaving for a conference in Atlanta with the creative name Atlanta Conference. The hotel where I had a reservation let me know two days ago that due to a flooding they have a roof damage. Several of their rooms are unusable and the hotel thus totally overbooked. They are trying to relocate me. It's not entirely clear to me how a flooding causes a roof damage but anyway I hope they will sort things out. Not sure what the internet connection will be like, thus blogging might be sparse.

Saturday, September 26, 2009

Seminar in Uppsala

Yesterday, I gave a seminar at the Ångstrom Laboratory in Uppsala. That means I now know two cities in Sweden! The Ångstrom Laboratory is a very modern building with lots of glass. In contrast to PI's building however, the colors are warm, and the interior is human friendly, though it has a certain lack of areas with blackboards. See, there's always something to complain.

I talked about "Phenomenological Quantum Gravity," and after some initial struggle with my computer it went pretty well. The talk is a summary of the prospects of detecting effects of quantum gravity at the LHC in scenarios with large extra dimensions, micro black holes, models with a minimal length scale and Deformed Special Relativity. It has an update about the current status of time delays in gamma ray bursts and the recently vanished holographic noise. The slides (pdf) are here. It doesn't really attempt to be a review, instead it is a rather biased perspective that focuses on the areas that I have worked on. One day, I will make the effort to put together an actual review.

A smart young man in the audience raised his hand and said that Smolin in his book claims the observation of an energy dependent dispersion in gamma ray bursts would outrule string theory, but now I was saying it wouldn't. Indeed, it wouldn't. The day will come when my hair stands upright at the mere mention of Smolin and his book. Please read this post and comments for clarification.

The audience was very attentive and in the cases when I forgot something relevant for later understanding, somebody would promptly ask the right question. I was very impressed. I will be doing some traveling with this talk: In October I will be in Potsdam for a seminar, and in late November in Frankfurt for a colloquium. Frankfurt wins the award for the lowest maintenance seminar schedule ever. If you have a desire for hearing a talk about the phenomenology of quantum gravity, let me know :-)

Friday, September 25, 2009

Looking back at Perimeter Institute

As you probably read already on Peter Woit's blog, the current issue of Nature has an article about Perimeter Institute, titled "The edge of physics," as well as what is supposed to be a review on Howard Burton's book "First Principles" by Joao Magueijo. You can read my review here.

Unfortunately, both articles are access restricted so the majority of our readers won't be able to look at them. Let me briefly summarize that "The edge of physics" is a well-written brief description of how PI came to be, and what it is today. It brings forward a healthy skepticism on some issues. For example that "Lazaridis has had an unusually strong hand in the management of Perimeter," to which the new director Neil Turok comments that "the make up of the board helps give the place a risk-taking spirit that is more in keeping with a Silicon Valley start-up than an academic venture."

There is some truth to both. Focusing power usually helps things run faster and doesn't make it necessary to please everybody. On the other hand, it's likely to piss off people who believe that their opinion is worth listening to. Unfortunately, most people with a degree fall into this category. As you can guess, the Power-of-Mike issue is frequently discussed among newcomers, and a point usually not addressed in public. It is thus interesting to find it mentioned in this article. In practice however, that power structure has no consequences unless you're involved into the highest level of administration, or you're a person of principle who cares about the basics of the system. Idealistically, I find it an uncomfortable position, in particular if the mission statements babble something about a "flat hierarchy." Practically, it works pretty well, probably because Lazaridis is a smart man.

The article also tells an anecdote in which Nima Arkani-Hamed and Freddy Cachazo work till 4am before they collapse, which, probably unintentionally cynically, is summarized as "the kind of effort that Turok wants: undirected, unconventional, ambitious." It's not that I have never worked till 4am, but people who do this frequently don't display ambition but a miserable time management combined with an unhealthy dose of masochism. You can blame that on my European upbringing, but I believe that time to relax is an essential ingredient to sustainable creative work.

To move on to the second article, Joao Magueijo's review of Howard Burtons' book isn't much of a review, but rather an expression of his opinion about the change PI has undergone since its startup. And it is not a positive opinion. Something went wrong along the way, is what Joao writes "the sought utopia had become a dystopia." He criticizes Howard for being an "insecure country cousin awed by the sophistication of established scientists and their fancy dinner parties."

Well. I haven't been at PI in its early days, but I've had the opportunity to follow its development during the past three years. It is of course true that PI has changed, and it is still changing. You can't run an Institute with 100 people as you run a place with 10, and PI is supposed to grow to more than twice its current size, both in facilities as well as researchers.

Part of the change growth brings is in administration. You'll need some sort of policies and procedures. You'll need some way to efficiently get information to where it needs to be, to coordinate efforts. You'll set up meetings, and committees, circulate drafts of guidelines, and discuss for several hours who is supposed to cleans the coffee mugs.

Another part of the change is social. The more people are at a place, the more difficult it becomes to encourage interdisciplinary exchange. At some point, researchers will begin to cluster into groups according to their prime interests. This has at PI reflected in the formal introduction of research groups like you find at any other physics department. I personally find this very disappointing and an (unnecessary) step into the wrong direction. In contrast, the Santa Fe Institute for example has chosen to keep its research staff deliberately small to avoid exactly this falling apart. When I arrived in Waterloo in 2006, PI had just about reached the size where it was basically impossible for everybody to know everybody. This represents quite a dramatic change from what must have been one large family to an increasingly larger group of researchers who just happen to share the same employer.

But the most serious part of the change is one in spirit. And that is what I think Joao is mostly criticizing. There is an inherent and unsolvable tension between trying to create an institute that is "different," and trying to create an institute that "competes with other top-institutes." You either play according to everybody else's rules and adjust, or you give them the finger, make your own rules, and accept that you will be regarded with skepticism. Unfortunately, I have heard that tension being denied repeatedly by various people at PI. I think it is possible to find a balance between both, the risky quirky and weird stuff with a high nonsense factor, and the established mainstream research programs that are promising to pursue. In most places, the emphasis is on the latter. PI was meant to have the emphasis on the former, but the trend I have witnessed is one towards adjustment with the heatbath. That is the natural thing to happen if new people come in who bring their expectations, their opinions, and their strategies from elsewhere. Especially if these people sit on temporary contracts and know they will be thrown back into the heatbath. Working against this trend requires conscious effort. And that effort hasn't been made.

Joao Magueijo btw left PI briefly after I arrived. I recall being disappointed because it was good to have somebody around who had worked on the phenomenology of quantum gravity. Not to mention that he's a cool guy. Meanwhile, PI has a new director, and though I didn't have much overlap with Neil Turok, my impression is that he is full of energy and eager to lead PI into a new phase, the recently launched PSI program is part of that. Yet where PI's change will lead, I don't know.

My experience with PI has been very good. I found it to be a welcoming and openminded place where, best of all, I could just do what I wanted. German as I am, the disorganization and maladministration I encountered was utterly frustrating, but then this sort of dysfunction isn't specific to PI. And since the limousine transfers from the airport are mentioned in the Nature article, unless it falls under moving expenses you have to pay them from your travel grant.

In any case, I wish PI the best luck. And I hope that the place remains truthful to its original goals.

Thursday, September 24, 2009


While Chad is celebrating the first reviews on his book How to teach physics to your dog, and the whole universe eagerly awaits that Sean Carroll's book finally makes it from eternity to here, we hear that also Joao Magueijo will bless the world with a new book. After his first book "Faster than the speed of light," dealt with his own research life, the new one is about Majorana's disappearance. Here is the blurb from

A Brilliant Darkness: The Extraordinary Life and Mysterious Disappearance of Ettore Majorana, the Troubled Genius of the Nuclear Age

"A theoretical physicist reveals one of the greatest untold stories of 20th-century science: the tormented genius, who discovered a key element of atomic fission, then disappeared and was never seen again. On the night of March 26th, 1938, nuclear physicist Ettore Majorana boarded a ship in Palermo, cash and a passport in hand. He was never seen again. "A Brilliant Darkness" tells the story of Majorana and his research group, nicknamed 'the Via Panisperna Boys', who unknowingly discovered atomic fission in 1934. As Majorana, the most brilliant of the group, began to realize what they had found, he became increasingly troubled, and his mental state, never terribly healthy, became unstable. Did he commit suicide that night in Palermo? Was he kidnapped? Did he stage his own death? As author Joao Magueijo narrates Majorana's tragic life and bizarre disappearance, he also offers a surprising look at the dark underbelly of science-not only its ethical difficulties but its often complex group dynamics. The momentum generated by the Via Panisperna Boys is the type that takes science in unpredictable directions: it can lead to grossly amoral errors such as eugenics, breakthroughs such as the discovery of the structure of DNA, or highly attractive dead ends such as string theory. The atomic bomb is just one of many troubling results of this dynamic. This gripping story not only chronicles Majorana's invaluable discovery - the Majorana neutrino - but also reveals new clues about one of science's most alluring mysteries. "
Time to make your Christmas wishlist :-)

Wednesday, September 23, 2009

Light Bulbs and the Solar Energy Production

As of this September, regulations in the European Union ban the the manufacture and import of 100 Watt incandescent light bulbs, as a measure to cut down energy consumption. While this has created a bit of a fuss and lead people to hoard traditional light bulbs, I actually do not remember the last time when I had used a 100 Watt light bulb. I probably won't miss it – unless for a very nice comparison for the energy production of the Sun.

The Earth is at distance r = 150 million km = 1.5 × 1011 m from the Sun. The incoming total electromagnetic energy flux from the Sun at the Earth per unit area, the so-called solar constant, is C = 1360 W/m² = 1.36 × 103 W/m². Assuming that the energy flux from the Sun is the same in all directions, this means that the energy output per second of the Sun, called luminosity by astronomers, is L = 4 π r² × C = 3.85 × 1026 W. This corresponds, by the way, to the mass equivalent of roughly 5 million metric tons per second: dm/dt = L/c² = 4.27 × 109 kg/s. The Sun has a radius of R = 7 × 108 m. If we naively assume that energy production is the same throughout the whole volume on the Sun, the power density of the solar energy production would amount to ε = L/(4 π/3 R³) = 0.268 W/m³ This is a remarkably tiny number! Of course, energy production in the Sun happens only in the central part, where temperature and density are high enough to sustain nuclear fusion reactions. This central part extends to roughly 10 percent of the solar radius, so that we can estimate the energy production in the core to about ε ≅ 300 W/m³ This is the energy output of three 100 Watt bulbs per cubic metre!

Actually, this back-of-the envelope estimate is not that bad at all. Energy production in the Sun by nuclear reactions is now very well understood, in particular since the "Solar Neutrino Puzzle" has been solved. This knowledge about the Sun's inner parts is encoded in what is called the "Standard Solar Models".

A lot of information and papers on solar models are available from the web site of the late John Bahcall, and from this long list of models, I picked the data set for the model BP2004, which gives all kinds of physical quantities as a function of radial distance from the centre of the Sun.

Energy production can be inferred from the luminosity as a function of radius – there is difference between these quantities when heat is absorbed or released, but this difference is negligible for the current steady state of the Sun's interior. This yields the following figure:

Energy production in the Sun's centre drops to zero beyond roughly one quarter of the solar radius. And in the inner core, it is nearly 300 Watt per cubic metre.

Of course, beyond the energy balance, it's quite unphysical to imagine the solar interior as a vacuum lit by light bulbs. Due to the gravitational pull, density, pressure and temperature are enormous, and beyond anything we can imagine from everyday experience. Here are radial profiles of density, pressure, and temperature of the Sun. Data are taken again from solar model BP2004. Note that the plots now have a logarithmic scale. For better comparison with everyday numbers, I have added the density of water, atmospheric pressure multiplied by a factor of 1 million, and the melting point of iron, multiplied by 100.

There is, of course, another difference between the light from the Sun and a 100 Watt light bulb – that's the spectrum of the light. An incandescent light bulb is a quite inefficient light source, as most of the energy is radiated in the infrared. The solar spectrum, instead, peaks in the visible range.

But, leaving aside the huge differences in density, temperature and ambient pressure, and the different spectra, here is a nice comparison:

My small kitchen has a volume of about 25 cubic metre. So, I should light it with 75 bulbs of 100 Watt each to "simulate" the solar interior. This would be very bright, and blow the fuses, but it is a quantity conveniently to imagine, compared to the huge numbers we usually deal with in astronomy!

Here is another way to arrive at the order of magnitude of "100 W light bulbs per cubic metre" for the solar energy production – thanks to Bee for insisting on this estimate:

The solar disk in the sky has a diameter of half a degree. The incandescent inner part of a 100 Watt light bulb, with a diameter of about 2.5 cm, appears under an angle of half a degree in a distance of about 3 metres. A spherical cluster of 100 Watt bulbs at a distance r appearing under the same angle and containing (r/ 3 m)² bulbs will produce roughly the same apparent luminosity as the single bulb at a distance of 3 metres. At the distance of the Sun, such a cluster should contain 0.25 × 10²² light bulbs. Actually, the luminosity of the Sun is about 1600 times higher than that - meaning that the Sun is about 1000 times brighter than than a 100 Watt light bulb in a distance of three metres. This seems quite reasonable indeed!

Monday, September 21, 2009

Update on the GEO 600 "Mystery Noise"

If you recall, the gravitational wave experiment GEO 600 had reported unexplained noise above the theoretical prediction. Craig Hogan suggested this unexplained noise might be an effect of quantum gravity. This does not work easily in a straightforward setting but necessitates the introduction of a new version of holography. I previously commented on Hogan's theoretical framework in my post "Holographic Noise."

Hartmut Grote from the GEO 600 collaboration kindly replied to my inquiry about the status and let me know

"In GEO600 we recently found that there is no more unexplained noise in the region from 150 to 300 Hz, if we use a different readout method, which points to the fact that the unexplained noise in this region might be associated with the former readout method, and not be of any fundamental type (i.e. holographic).

However, this does not change much in the current discussion of wether GEO is limited by holographic noise or not, as Craig Hogan already agreed some time ago, that the low-frequency rise in the noise in GEO would not be holographic noise. Hogans latest prediction is a flat (in frequency spectrum) noise, and we have not yet made an experimental statement about this in GEO.

So in summary:
Mystery noise in GEO disappeared in the region 150-300Hz, but Hogan anyway was not suggesting any more that holographic noise would be limiting GEO at these frequencies since a while."

Thus, a big bunch of the "mystery noise" has found a non-mysterious explanation. It is not entirely clear yet how much is left to explain and whether there will be anything mysterious about what is left. GEO600 might then just about reach the required sensitivity to test the remainder of Hogan's prediction. The experimentalists plan to improve the sensitivity in the coming year and hope to eventually be able to settle the question.

Tuesday, September 15, 2009

This and That

  • Did you know that next Thursday, Sep 24th 2009, is the first "Postdoc Appreciation Day?" I'm not kidding, the US Postdoctoral Association was apparently fed up with America having an "Appreciation Day" or "Remembrance Day" for about all and everybody - except postdocs. Tomorrow for example is "National Day of Prayer and Remembrance for the Victims of Hurricane Katrina," and on Thursday is the "Sneakers at Work Day." The "Postdoc Appreciation Day" will also fall into the "National Farm Safety and Health Week" and the "Prostate Cancer Awareness Week." In any case, the Association suggests you organize for example a coffee hour, a happy hour or a Karaoke night.

  • Jörg Schlatterer, Postdoc at the Albert Einstein College of Medicine in New York, suggests to found an International Postdoc Forum (IPF). Though I just escaped the postdoctoral life, I am totally in favor of this idea - just that it seems to me like I've heard similar suggestions several times before and nothing ever came out of it. There would definitely be a huge benefit from an international association of postdocs that could provide e.g. advice on national differences and difficulties with settling in a foreign country, fractured retirement options and absence of unemployment insurance. One of the problems is if you're not in your home country you have no voice neither at home (because hey, you left, now good luck) nor in the new country (because hey, you work here but please don't have an opinion).
    Together with a colleague Schlatterer wrote a brief article for the newsletter of above mentioned US Postdoc Association:
    "Although many characteristics of postdoctoral research positions vary between disciplines, institutions, and nations, some challenges are universal. Poorly defined roles and responsibilities, unstable and uncompetitive salaries, lack of benefits, variable mentorship quality, and access to courses and career development programs are common complaints. It is important to consider how research communities around the world can meet these challenges, and what an International Forum for Postdocs (IFP) might contribute."

    It is however very hard to get academics to organize in any way. They are typically primarily work-oriented and community involvement that isn't CV suitable is distraction and a waste of time. In any case, I wish the IPF good luck.

  • From my research life: Three weeks ago, there was a paper on the arXiv by Manuel Hohmann and Mattias Wohlfarth, offering a "No-go theorem for bimetric gravity with positive and negative mass". I yesterday posted a reply showing the no-go theorem does not apply to my model.

  • Something to look at: Viruses of Glas:

    Via Matt Brown.

Saturday, September 12, 2009

The Minimal Length in Quantum Gravity: An Outside View

I recently came across a paper by Amit Hagar
    “Minimal Length in Quantum Gravity and the Fate of Lorentz Invariance”
    Studies of History and Philosophy of Modern Physics 40(3): 259-267 (PDF)

Amit Hagar is an assistant professor at Indiana University's Department of History and Philosophy of Science, and he has taken an interest in the history of a minimal length and the current discussion about deformations of Lorentz invariance. And it is true indeed that the existence and implementation of a minimal length in quantum gravity is an intriguing open question. Hagar uses it as “a case study for highlighting the delicate balance between conservatism and innovation that characterizes the process of constructing new physics.”

I find his paper very refreshing, though in some aspects misleading and the argumentation incomplete.

To briefly summarize the basics,

there are many motivations, stemming from different approaches to quantum gravity and various thought experiments, that there is a fundamental limit to how well we can resolve structures (for a summary see eg “Quantum gravity and minimum length” by Luis J. Garay and “On Gravity and the Uncertainty Principle” by Adler and Santiago). This limit is generally thought to be at or close by the Planck scale. This is far off what we can experimentally test today, thus the lack of experimental data.

However, such a finite minimal distance scale causes a problem with Lorentz invariance since Special Relativity tells us a ruler in motion towards us appears shortened. A minimal length better shouldn't appear shorter than minimal. This reasoning thus creates the need to modify Special Relativity, which is very hard to do in a self-consistent and observer independent way. Attempts have become known under the name “Deformed Special Relativity.” Such modifications of Special Relativity can imply modified dispersion relations and an energy dependent speed of light, though the theoretical basis for these theories is presently incomplete and partially inconsistent. Note that modified dispersion relations are quite easily obtained also from preferred frame effects. The point of DSR has been that it does respect relativity of inertial frames.

I have argued in this paper that the alleged problem isn't since there is no observation and thus no contradiction without an interaction. The only thing necessary for self-consistency is then that no interaction can ever resolve structures below the Planck scale, but there is no need to modify the Lorentz boosts for freely propagating particles. This is, in a nutshell, the main difference between my model and the standard DSR approach.

DSR is generally thought to be not a fundamental theory on its own, but an approximate description applicable to incorporate effects of quantum gravity in the particle/quantum field context. People differ on what approximation it is supposed to describe, but the point is there might not be an obvious way to find such a modification in the fundamental theory since it could only be an effective description. Take as an example friction. There's no friction inside the atom, and there's no friction in planetary orbits either. Yet on intermediate scales Cosmopolitan avidly advocates lubricants.

The point of view I've been taking (which of course isn't shared by everybody) is that quantum field theory with a minimal length and DSR is a way to incorporate still little understood quantum gravitational effects that would be described by a fully consistent yet-to-be-found theory into the old-fashioned theories we already have by adding a generalized uncertainty principle, a modification of dispersion relations and a deformation of momentum space. I like this approach because it bridges the gap towards phenomenology. It is however unsatisfactory there is presently no derivation from fundamental principles.

But to come back to Hagar's paper,

he studies some arguments that have been raised against such deformations of Lorentz invariance and finds the criticism wanting. On the other hand, he also finds the theoretical motivation for having such a modification unconvincing, though the attempt to do so makes a nice object of study for the philosopher

“While so far there seems to be little physical motivation for deforming the standard energy-momentum dispersion relations (apart from the fact that there are good reasons to think that a fundamental QG theory will involve spatial discreteness), from the methodological perspective I am interested in here the attitude within the QG community towards DSR exemplifies nicely the aforementioned delicate balance between conservatism and innovation.”
I can basically picture the string theorists among the readers grinding their teeth. I'll leave it up to you whether you think reasons for spatial discreteness are “good,” since it is actually a different question than whether there is a finite resolution, and the matter of discreteness is thus not relevant to the topic under discussion. One can have a fundamentally finite resolution of structures without spatial discreteness, and one can also have spatial discreteness without violations of Lorenz invariance. Unfortunately, these issues are quite often confused. Hagar does mention these differences later on, but this introduction of his paper is somewhat misleading.

Hagar discusses an argument by Schützhold and Unruh according to which a position space description of DSR either involves large scale non-locality inconsistent with our current theories and observations, or it necessitates a preferred frame. Hagar concludes the argument is unconvincing since it makes use of unwarranted assumptions about the Fourier transformations in such a framework. While I agree with Hagar's criticism, I did a similar analysis in this paper without making use of Fourier transformations and came to essentially the same conclusion: If one has an energy dependent speed of light, one either needs a preferred frame, or one needs an external parameter to label Lorentz transformations. This parameter is commonly chosen to be an energy (don't ask the energy of what), but besides the ambiguous interpretation this is a non-local modification that seems to me as unnatural as implausible [1].

Anyway, despite me finding the argumentation in Hagar's paper rather incomplete, I very much like the attempt to disentangle the discussion and approach it from a logical and objective basis. You see, I have stakes in the issue, so has everybody else who has worked on the topic. If you read a random paper on DSR it will tell you how natural such a modification is, how plenty the motivations, how great the prospects to experimentally test it - and be kinda brief on the “well-known” inconsistencies. Hagar's paper makes a nice contrast to this by telling the story as it really is.

I wrote an email to Amit Hagar,

and he kindly replied, letting me know he is “an avid reader of [my] blog and papers, and the truth is they have very much inspired [his] looking into this interesting debate.” I am very flattered. But what's even better is that he tells me he plans to write a book on the history and philosophy of the minimal length, starting from Heisenberg up to now. I think it is a great idea. The history of the topic is full with beautiful thought experiments and arguments about their implications, and the whole field would benefit from a clear summary.


[1] Such modifications run under the keyword “energy dependent metric.” Note that we are talking here about an energy dependent metric in position space, not momentum space.

Thursday, September 10, 2009


I arrived in Stockholm! I have a new office, a keycard for the building, I know where the library is, how to use the printer, and my photo is on the Nordita website. I also have a mail slot. The only mail in this slot is a letter from Lufthansa, and contains my brand new frequent traveller card. This card qualifies me to bring along a golf bag for no extra charge. You see, my career is prospering.

Other things are progressing more slowly. Such it turned out that some centuries ago there was a summer student here with first name Sabine who is blocking my email address, and it's apparently impossible to get a phone contract in Sweden if you're not a native Swede in 3rd generation or a member of the royal family. Okay, I'm somewhat exaggerating, but frankly what business is it of the phone company if I paid taxes in Sweden last year.

Nordita is presently running a program on the Quantum Hall effect, from which I unfortunately didn't catch much because I spent the last days running through Stockholm filling out forms. I already have a bad consciousness about it. Amazing how fast things catch up with you. I miraculously managed to open a bank account even though I had been told it wouldn't work. The bank employer btw asked indeed if I have relatives in the royal family. So just to clarify the matter, I don't have relatives in any royal family, at least not back to the 16th century.

Other lessons learned this week
  1. An apartment without phone is very empty.

  2. You're not a person without a person number.

  3. Unless you're Swedish, "sju" (seven) isn't pronounced remotely as you think.

  4. Stockholm bikers get very upset if you run on the bikelane.

  5. Swedish tastebuds are evidently immune to salt, cinnamon and cardamom.

  6. Salty licorice is a prescription-free nauseant.

  7. The Swedish word for finished/out of stock is slut.

Monday, September 07, 2009

Virtual Shipspotting

Sabine has arrived in Stockholm, but her household is still in transit. Actually, the latest news from the moving company was that her belongings are on a ship named "Stuttgart Express", en route to Southampton, England, and scheduled to arrive at Stockholm in early October.

On Saturday, out of curiosity, I googled for that ship, and was completely amazed about the amount of information I could find.

The "Stuttgart Express" is a 16-year old cargo vessel, 294 metres long, and with a deadweight of 67680 tons:

The "Stuttgart Express" (photo via

According to the ship's itineraries history, the Stuttgart Express has left Halifax, Nova Scotia, on Saturday, August 29 at 20:30 UTC, and reached the English Channel on Friday, September 4, around noon. Though, it didn't stop in Southampton, but went straight on to Antwerp, Belgium, where it arrived at the port on Saturday, September 5, at 9:30 in the morning.

The ship spent Saturday in Antwerp, and left for England early on Sunday morning. However, destination was not Southampton, but a place on the southern bank of the Thames estuary:

No idea what it did there, there seems to be no port, but maybe it has bunkered fuel. Anyway, it left that place this morning before five,

heading for … Bremerhaven, Germany.

Right now, the Stuttgart Express has passed the island of Norderney in the Wadden Sea:

No idea when it will arrive at Southampton to disembark the container, but somehow, the next four weeks have to be spent.

The Stuttgart Express via

Friday, September 04, 2009

Celebrating the Launch of FAIR

Hidden in the woods about 10 km southeast of Frankfurt International Airport is GSI, the Helmholtz Centre for Heavy Ion Research. GSI is an accelerator laboratory for research with beams of all kinds of ions up to uranium. It is best known for its discoveries of new elements, such as Copernicium, and for exploration of the use of beams of carbon ions in tumor therapy. But there is also research done in heavy ion collisions to study properties of nuclear matter, in plasma physics, and atomic physics, where heavy ions allow to probe quantum electrodynamics in strong electromagnetic fields.

In the upcoming years, GSI will expand enormously, through the construction of FAIR, the Facility for Antiproton and Ion Research.

A plan of GSI, and the new FAIR complex, shown in red. From the flyer "FAIR: Facility for Antiproton and Ion Research" (PDF file).
FAIR is a large international project, with a billion-euro budget. It will consist of several accelerators and storage rings, and provide high-intensity beams of heavy ions and antiprotons, and secondary beams of rare and unstable nuclei. Many different experiments will study phenomena as diverse as compressed baryonic matter, nuclear structure relevant for astrophysics, antiproton-proton collisions for hadron spectroscopy, or properties of high-energy irradiation for biophysics and materials research.

Construction of the FAIR accelerators has not begun yet, but yesterday saw the topping-out ceremony of the first hall built, the testing hall, where parts of the accelerators, bending magnets and experimental equipment will be thoroughly checked before deployment in the facility.

The topping-out, or "Richtfest," is a quite typical German tradition: Once the raw structure of a building up to the roof has been erected, a ceremony and subsequent party with the building owner, the architects, and the craftsmen is held. It's an occasion for a few solemn speeches, an occasion for politicians to pose for photos, and for exchanging best wishes for the future of the project.

As we were in the area yesterday, we used the opportunity to attend the topping-out, and to say hello to some old friends. Let's also not forget that following the ceremony there was the annual GSI summer party, idylically taking place at a small lake next to the facilities.

Here is the Scientific Director of GSI, Professor Dr Horst Stöcker, greeting the guests.

After the greetings, a representative of the German Federal Ministry of Education and Research, Andreas Storm, spoke a few words and affirming the importance of FAIR and the funding of the project.

Storm said a lot of nice words, among other things he mentioned that the GSI recently had the honor to name the newly discovered chemical element "Copernicium" after its discoverer. Since unfortunately Copernicus died more than 450 years ago, the actual discovery was done by a group to whose leader Storm referred to as Ms Sigurd Hofmann. Hofmann probably doesn't often get mistaken for being a woman. Storm btw is totally hip and has a twitter account.

The below photo shows the pulling up of the "Richtkranz" to the ceiling (to the tune of Ode to Joy on Saxophone and bass, not bad at all):

And here is the master builder, in the traditional dress of a carpenter, toasting on the future of the building. The ceremony was finished by throwing the glass to the floor.

And if you like ducks, here's a photo from the little lake where we then went and grabbed some cake and sausages.

For more about FAIR, there is a flyer "FAIR: Facility for Antiproton and Ion Research" (PDF file, 4.2 MB), and a longer "FAIR brochure" (PDF file, 17.9 MB).

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