Thursday, December 31, 2009

Happy New Year!

We wish all our readers a good start into the year 2010! We want to use this last day of the year to thank you all (yes, you all) for your visits, comments, feedback, links, and for making this blog so interesting!

Here's our 2009 visitor statistic, shown is the weekly average:

And here is the country share for an average day (not an annual average). Shown are only countries with a share larger than 1%:

Perc.Country Name

34.25%United StatesUnited States





4.11%United KingdomUnited Kingdom










1.14%United Arab EmiratesUnited Arab Emirates

1.14%Saudi ArabiaSaudi Arabia


Seems the Swedes have still somewhat to catch up :-)

And here's Backreaction's Best of 2009. If you have some hours of 2009 left to kill, check these out:

Wednesday, December 30, 2009

What is a scientific prediction?

After my bachelor's degree I changed field from mathematics to physics. I wanted to understand, at least to some extend, the world around me. Mathematics seemed to entail an infinite amount of possibilities whose each and every relevance wasn't clear to me while physics is tied to reality by experiment. Basically the reason why I'm a phenomenologist today is that I know how easy it is to get lost in the mathematical universe, and that this getting lost has clearly addictive qualities.

In the last decade in high energy physics one could notice a trend towards more phenomenology. While I welcome this for obvious reasons, here as in any aspect of life one can desire too much of a good thing. I've read quite a few of papers where the word "phenomenology" was used merely as decoration, and in other cases "phenomenological" is essentially an excuse for inconsistency. Such fashion trends in the community and their side-effects however aren't really surprising. What is surprising though is that the demand for "predictions" has been picked up by the public and has been used sometimes inappropriately as a measure for scientific quality. Thus I thought it would be worth clarifying what a scientific prediction is and isn't.

1. A scientific prediction is a statement about a future event.

That is to say the prediction was made without knowing whether it is correct. Strictly speaking this doesn't necessitate it to be about a future event, but it's hard to reliably show one didn't know about a measurement that was already made (a possible scenario is that available data wasn't analyzed with regard to a specific hypothesis). If you calculate the cosmological constant to be in agreement with the today measured value it's not a prediction, it's a postdiction. While it is certainly preferable to calculate the outcome of an experiment before it was done to avoid confirmation bias, this isn't always how it works. Sometimes theory is ahead, but sometimes the data is in already and awaits a theoretical explanation. Science is in the first line about understanding. Explanations, even if not predictions, are valuable. However, if there is something genuinely new about an explanation it will typically also imply new predictions.

2. A scientific prediction is based on a scientific theory. That means in particular it is reproducible (by everybody with the appropriate education), consistent, and the theory it is based on is not in conflict with available data already.

If you dreamed a meteoroid will crash into the White House on New Year's day, that's a prophecy, not a scientific prediction. Same for the recurring remark that the LHC might create angels at 14 TeV collision energy. That's funny, but not a scientific prediction. You may find it inconvenient that your theory be reproducible because this means other people must be able to understand it without your help. However, if you aren't able to communicate how your theory connects to state-of-the art science, it's your fault and not everybody else's fault. Likewise, if your theory comes with a prescription only to use it for this effect, but not for this effect because it doesn't work there for reasons only you understand, that's not a scientific theory. If your theory predicts a fourth lepton generation but has the side-effect that atoms are unstable, tough luck. See here for what it means for a theory to be consistent.

3. A scientific prediction is falsifiable. In practice this means often it's implausifiable.

Falsifiable means that your prediction can be shown to be wrong. This typically though not always implies the prediction has to be quantitative. "You will die" is not a scientific prediction: if you're still alive in 200 years, it could still be you will die someday. "At least 99.99% of people your age who smoke 1 pack per day will be dead 80 years from now," is a scientific prediction because 80 years from now you can look at the data and see whether I was correct (or rather somebody else will have to look, cough).

In physics, scientific theories often contain parameters and a measurement does not indeed falsify the theory but constrain the parameters until they are constrained so much it's point- and useless to consider a theory further. A good example is Brans-Dicke theory. If there are deviations from general relativity of the Brans-Dicke type, they are so small you can forget about them. Same for violations of Lorentz-invariance, time-variation of the structure constant, and so on. These are not falsified but tightly constrained. Reason why in high energy physics new theories are often not actually falsifiable is that for a new theory only small deviations from already extremely well confirmed theories are allowed. We know that our present theories are correct to high precision and new theories cannot differ by much or they are false already. If the deviation is too small however, it becomes unmeasurable.

As you can guess, implausibility is not binary but a continuous scale, thus people frequently disagree on exactly when to discard a theory. (MOND anybody?) As far as I am concerned everybody can decide for themselves how to waste the time of their life, as long as they don't waste other people's time.

That a theory is implausified rather than falsified is quite common if very good theories are available already as in theoretical physics. But in other fields falsification is easier. The dopamine level might just not correlate with schizophrenia. Holy water doesn't sanitize your hands. The world is older than 10,000 years, etc.

A statement is a scientific prediction if all three above explained requirements are fulfilled. If you you have suggestions for improvement of my definition, please leave in comments.

What you should have learned from this post:

  • Not every statement about a future event is a scientific prediction. More commonly it is a prophecy.

  • While making predictions is a merit of a theory, it's neither a substitute for scientific quality nor an indicator for promise.

  • Explanatory power of a theory can be valuable even if not predictive.

  • Theories in physics often have free parameters that can be constrained, rather than an ansatz being generally falsified.

Tuesday, December 29, 2009

Find of the Week


The anonymous referee is thanked for their comments on this manuscript. GFL acknowledges support from ARC Discover Project DP0665574. GFL also thanks the possums that fight on his back deck at 4am, waking him up and giving him plenty of time to think before his kids wake up at 6am, and also thanks Bryn and Dylan for reintroducing him to Jason and the Argonauts.

Geraint F. Lewis, Matthew J. Francis, Luke A. Barnes and J. Berian James, Mon. Not. R. Astron. Soc. 381, L50–L54 (2007), "Coordinate confusion in conformal cosmology,"
arXiv:0707.2106v1 [astro-ph].

Saturday, December 26, 2009


While the LHC is hibernating until February next year, outreach efforts are not on hold. Here in Germany, there is a nice exhibition on tour, called "Die Weltmaschine". This means literally the "world machine" – somewhat better than the "big bang machine", but finding a catchy but not misleadingly bombastic name for the LHC seems to be a challenge.

Anyway, the exhibition, organized by DESY, the German particle physics laboratory based in Hamburg, was on display this December in Heidelberg, in the large foyer of the Kirchhoff Institute for Physics of the University. Experimentalist from Heidelberg are contributing to the ATLAS, ALICE, and LHCb experiments.

The exhibition provides a nice introduction in the known facts and open issues of particle physics, and in the techniques to accelerate particles and detect and analyse the collision products. I was there on Saturday afternoon last week, and was surprised that quite a lot of people were around, despite the cold and the snow that had gripped Heidelberg that weekend.

The most fascinating exhibit to me was a spark chamber, where the ionisation of gas by charged particles triggers sparks between high-voltage wires.

Although this is detector technology that is not used anymore at the LHC, it is compelling how it makes visible the constant shower of ionising particles in the cosmic radiation, which we usually are completely unaware of. It was quite easy to catch a couple of events with my digital camera, just by photographing the chamber at random moments:

The next stopover of the exibition will be Frankfurt – if you are around by chance in the second half of January, it is worth a visit.

Friday, December 25, 2009

Merry Christmas!

We wish all our readers happy holidays and a merry Christmas! And if you're not christmassing we wish you a great time anyway.

To continue our blog's Christmas tradition, we have a little fun quiz for you. In times of Google it's actually not easy too come up with something that is neither too difficult nor too easy to answer. However, since Google is still working on their picture recognition software here's a pixelized question. Whose noses are these:

Hint: These are all very well known (living) scientists in the high energy physics/quantum gravity community.

The correct answer is an ordered list of six names. The first who posts the correct answer in the comments wins the 2010 Hubble wall calendar, and I put on top a NORDITA pen and a neck lanyard. If it looks like you're not getting anywhere, I'll leave more hints in the comments. Ready? Set. Go!

The day will be coming when your phone does recognize noses...

Tuesday, December 22, 2009

So this is Christmas

Last weekend, I flew to Germany in an attempt to escape the Swedish snow just to find Germany equally white yet ten degrees colder. Several airports were closed, dozens of flights got cancelled, the highways were a disaster. To top things off, when we arrived in Stefan's apartment we found the heating didn't work. You see, the apartment has a brand new energy-efficient floor heating. It's so efficient it doesn't heat. The thermometer lingered at 10°C, Nome, sweet Nome. Landlords are on vacation in Guadeloupe. We sent them a text message saying, I paraphrase, fix the frikkin heating and we wish you a happy melanoma.

This brought up memories of a friend who did his first postdoc in NYC and ended up sleeping in the kitchen during the winter because the stove was the only reliable heat source. No kidding. But, hey, Germany, you're almost there! Consequentially, we thought it's the right conditions for some serious Christmas bakery.

Baking activities start with a visit to the parental kitchen, grabbing everything that looks useful, for example the huge collection of cookie cutters and related utensil (it also never harms to have a look into the fridge and the wine rack). It follows a Google search for the recipes, and sending the husband to the grocery store. You do have a rolling pin, yes? Wait. Last time we used a wine bottle. No, he still doesn't have a rolling pin. Pleasantries of living in German suburbia, stores are closed from noon to 3pm. Let me submit this manuscript then. And where's the maintenance guy who wanted to look at the heating? And can you grab me a coke on the way?

Sun starts setting and it looks like we're ready to go, so turn on the stove then. He doesn't know how to turn on the stove. Never used it before. Can't be so difficult, can it? What's this button for, and what's this light and is this on now. Where's your laptop. The laptop. Yes, for the recipe. Where's the mixer. The mixer. Here's the mixer.

Can't bake, no music. Your laptop can do music right? Wait, here, online radio. Get a bright smile in only 6 months, no braces. Must be an US station then. War is over. Good, butter. Butter is too cold, in the microwave. Microwave doesn't work. Why doesn't the microwave work. Because it's unplugged. Okay, mixer out, microwave in, on, where's the sugar? Did you take the sheet out of the oven? Why aren't the eggs in the fridge. Let's open the wine. Is this your phone ringing? The scale doesn't work, battery is dead. Pling. Shit, butter is too hot now. Why doesn't the mixer work? Because it's unplugged. Microwave out, mixer in. Don't you have a splitter. Jingle bells. Oops, flour on the laptop. Drums please for the cookie dough. Way too sticky. Hand me the wine. Wass the recipe sayin? Put in fridge for 3 hours. 3 hours? Put in freezer for 5 minutes then. Can you answer the phone? Your stove stinks. Did you see this month's SciAm is about the multiverse. No, really?

Where's the 3rd pack icing sugar? The 3rd? Yes, I think two times 250 is less than 600. Ohm. Okay. We'll scale it down. 5/6 times 8 eggs is. Ooh. How much flour? Doesn't matter, scale doesn't work anyway. Here's my favorite story of the year: Plumber goes bankrupt and sets out to blow up clients who haven't paid their bills. That happened only some miles from here. Well, you better pay your bills, man. Here's the splitter. Wait, shit, there goes an egg. Santa Claus is coming to town? Take the dough out of the freezer. Damn, it's frozen to the plate. Where's the rolling pin. Okay, now it's glued to the table. Why did you buy walnuts for the hazelnut cookies? Ohm. First round into the oven! Oops, egg yolk on the laptop. Have we send any Christmas cards yet? Why not? More wine?

Did you put the sugar in the fridge or was that me? Second sheet into the oven. Did you hear that JHEP will be published by Springer from Jan 2010 on? Let's do some little Springer's then. How's your colleagues taking it hat Springer is now part of the Swedish empire? Who's dreaming of a white Christmas? Can you sprinkle some chocolate here? Oops, chocolate on the laptop. I think you could need a new one. These cookies smell very done. Hothothot. Not on the plastic! Watch out, the cable. Did I tell you I've put together the Christmas quiz for the blog. The blog. Yes, the b l o g. What's the phone doing on the baking sheet? When you're done eating the cookies, can you figure out where the cinnamon is?

24 hours later: the cookie turnout rate is higher than 50%, the laptop survived it, and the house is now nicely warm. And in case you missed the essential piece of information: We will continue our Christmas tradition from 2007 and 2008 and have a little quiz for you also this year. It is presheduled for Dec 25th 8am East Coast Time.

Recipes used to heat the house: Butterplätzchen and Haselnussmakronen.

Sunday, December 20, 2009

From a Distance

So pretty!

Who wouldn't want to be able to travel faster than the speed of light?

Friday, December 18, 2009

Let it Snow

We've had a little bit of snow here in Stockholm the last days. (Yes, Rhett, that's what we call snow). Not the heavy Ontario-kind of snowfall with 2 feets in 3 hours, but a two days lasting persistent drizzle that made it up to a feet or two, depending on how far you're outside the city.

Ingrid had mentioned that the local Christmas tree would be right in front of my window. Since then I had nightmares of blinking Christmas lights that would spoil my nightrest till Newyear. The technical term is "preventive pessimism." The tree however turned out to be decently minimalistic and developed its full beauty with some inches of snow on it.

This brought to mind a reader question: do you celebrate Christmas?

I am flying to Germany on the weekend and will be on vacation until the first week of January. Thus, expect blogging to be photo-heavy and sparse. But I promise continuation of the causal diagrams will follow sooner or later :-)

Thursday, December 17, 2009

What is Natural?

Our recent discussion on my post The Nature of Laws brought up a new topic that deserves a post on its own: What is Natural? I have frequently found physicists arguing something to be natural or unnatural. I usually stay clear of this for reasons that I hope to get across in the following.

First, arguably everything we observe in Nature is "natural." Thus, calling anything that we observe - may that be the Yukawa couplings or homosexuality - "unnatural" is an oxymoron. Likewise, calling something we do observe "natural" is as meaningless as calling apples "biologic."

But I'm not a linguist. Thus, leaving aside the question whether "natural" is a good nomenclature, what physicists refer to as unnatural are dimensionless parameters much smaller or larger than one. The qualifier "dimensionless" is essential since it is meaningless to talk about the value of dimensionful constants: In the right unit system they are always equal to one. (The Earth weighs exactly one Earthmass. Clearly an indication for intelligent design.) If you don't have dimensionless constants, you take ratios.

For example General Relativity. You have two parameters there. The one is the Planck mass, the other one is the cosmological constant. Take the fourth power of the Planck mass and divide it by the measured value of the cosmological constant, the ratio is 10120. That's what is commonly called unnatural. (The ratio of the cosmological constant to the present matter density on the other hand is about one. Since the density however is time-dependent, this then causes what is known as the "coincidence problem:" why are they about equal "right now." See, it's hard to satisfy a physicist.)

This notion of naturalness goes back to Paul Dirac. Sometimes used is also a refinement of naturalness offered by 't Hooft ("Naturalness, Chiral Symmetry and Spontaneous Chiral Symmetry Breaking") which takes into account that perfect symmetries too are unnatural and thus small parameters are okay if they arise from small violations of these symmetries. In his article, 't Hooft had the following to say about the cosmological constant: "Quantum Gravity is not understood anyhow so we exclude it from our naturalness requirements."

If you follow this line of thought it naturally brings you to the fine-tuning and hierarchy problems in the standard model.

Now let me tell you why I stay clear of these arguments. It doesn't matter how you turn it, in the end our notion of naturalness is based on what evolution has taught us is natural. The bears your ancestors hunted down did not differ in size more than some orders of magnitude, if you go into a forest you're unlikely to find a tree 1017 meters high, and so on. We are used to things being somehow average. In addition, our brains are constructed to look for simple, all-encompassing explanations which we find "beautiful." That's why books like "Men are from Mars, Women are from Venus" are bestsellers, that's why we look for patterns in the masses of the standard model, and that's why there are so many string theorists. (And isn't that a beautifully simple world-view?)

The naturalness arguments are eventually based on the idea that whatever a fundamental theory looks like, it does conform to this ideal: There's one or only a few parameters. They are neither fine-tuned nor appear in unreasonably large ratios. We, the stuff we are made of, and our universe, is somehow "natural," "average" or "mediocre." However, if you continue to ask "why" at this point you'll notice how the scientific basis crumbles away under your feet. Why should this be? Because very small parameters make you feel uneasy? Because you don't find many parameters a satisfactory explanation? Because it's not pretty? Because it smells like intelligent design?

It's not that I don't share the perception that a theory that unifies all the particle interactions with only a few parameters of order one and a few dimensionful ones would be "beautiful" and seems "natural." After all, my ancestors too did hunt bears. Neither do I discard the value of such considerations. They are useful guides, they show us the limitations of our current theories and point us into a direction. I however also think one should not elevate naturalness to a sacred principle. Maybe Nature is just "unnatural." Maybe the parameters in the standard model come about in a process much more complex anybody has imagined so far. Maybe they are just coincidence. Maybe Tegmark is right and we live in a level 5 multiverse or swhatever.

Bottomline: The universe just doesn't care whether you like it.

Sunday, December 13, 2009


Tomorrow it's my turn to bring the cake for our Institute's weekly social event. Thus, I spend an hour turning Ingrid's kitchen upside-down trying to figure out where she might store the the mixer and the baking tin. She has a huge collection of sticky tupperware but no baking tin. But, well organized German that I am, I do have an original Dr. Oetker baking tin that I imported to the US of A. You can't trust them with baking over there, you see. Whatever they do, it always comes out half-baked. They call it "chewy." American bakery just doesn't crumble properly. Maybe that's why so many of them are overweight. It's all the crumbles that they don't miss.

It only takes another hour to find the right moving box and undust the baking tin, well organized German and all. While searching I also find the laptop speakers and think it might be nice to have some Christmas songs in the background. Well, I sold my stereo and Ingrid's looked like the ghost of tube-radio's past, so I opted out. The speakers I think I bought from somebody at PI who was about to move - what was his name again and where is he now? After disentangling the cables it occurs to me that, needless to say, the plug won't fit into the European outlet. But, the organized German does of course have an adapter. Somewhere. More sorting through boxes. Having found the adapter, I figures there's no outlet left. But surely Ingrid has a splitter somewhere? Yes... it's probably right next to her baking tin.

Who is Ingrid you might wonder. Jah-ha. You see, the reason for my writing today is an instance of christmassy gratefulness to the readers of my blog and the hospitality of the Swedes. If you remember, I had trouble finding a place in Stockholm which, as I meanwhile learned, is quite a common problem. As a reaction to my blogpost, a kind reader from Toronto wrote to the helpless female blogger and got me in contact with his sister-in-law, living in Ontario but originally from Stockholm. This reader's sister-in-law turned out to have a friend whose father's wife, by name Ingrid, was looking to sublease her apartment. And this is where I live now. This is way to abstruse for me to make it up. So if you were wondering what blogging is good for, now you know. Wonderful things happen if you blog! Like Clifford showing me around LA, or a local reader near Rome offering me her clothes to wear when Al Italia forgot my bag in Palermo. Yes, blogging taught me the world is full of lovely people.

It takes some getting used to subleasing though. While I appreciate not having to buy new furniture and equipping a new household, the abundance of blue-and-yellow colored things in this apartment is astonishing. For example the bedsheets with MILLENIUM on it. (Let's just store them in the other apartment till the next millenium party.) The hook in the bathroom is engraved with "Ingrid," and if the morning is early or the night late this causes me some identity issues - what's my name again and where am I now?

And then there's the plants. I suddenly own two dozen plants. I desperately waved my frequent-flyer card trying to indicate the plants and me might not make happy flatmates, but to no avail. Now every time I come home there's the plants in the corners saying bad girl, bad girl, haven't watered me, bad girl. Reason why I'm not watering the plants is that, well, Ingrid's watering can must be with the baking tin and the splitter.

Back to my baking efforts, I meanwhile managed to decipher the Swedish baking recipe, or so I hope (Häll smeten i formen. Grädda kakan i nedre delen av ugnen.), and the cake is happily burning while I am blogging to the tune of the Carol of the Bells. Icing sugar on it, et voilà. (Come on, icing sugar was invented to hide the burned spots, no?) Now where does Ingrid have the aluminium foil?

Besides my cake, the news of today is that Sundance has joined the bloggers! You find him with his girlfriend Yana at Meandering Marsupials or "Where the bloody hell are we?" where you can follow them on a bike-tour from Ontario to California.

Saturday, December 12, 2009

To whom it may concern

It is my pleasure to write this letter,
He is not just good, he is simply better,
A promising researcher, young yet mature,
He will be an asset, of that I am sure.

Hard-working, clever, and enthusiastic,
His papers, you see, are clearly fantastic,
Truly original, careful and bold,
Few are around of the same mold.

Great intuition, resourceful and skilled,
Self-motivated and also strong-willed,
With large potential and independent,
Well-organized and extremely talented.

Exceptional, brilliant, a rising star,
His first Nobelprize cannot be far!
(He further has a solid training,
He'll do your numerics without complaining.)

An example of passion and determination,
I recommend him without hesitation,

Yours sincerely.

Wednesday, December 09, 2009

She figures there's way to go

The European Commission just published "She Figures 2009" (download PDF here), a summary of data covering aspects of gender inequality in the European Union. The statistics used in this publication are drawn from Eurostat, the European Commission services’ official data source and correspondents in various member countries.

I didn't read the full 160 pages, but here's two interesting figures. The below shows the percentage of men (yellow) and women (purple) in different stages of scientific career in science and engineering. From the left to the right the career level increases. The figure summarizes data from 2002 and 2006. While at the entry level there's 31% women (up from 30% in 2002), and at the PhD level the percentage has increased to 36% (up from 33% in 2002), at the level of tenured faculty there's only 11% left (up from 8% in 2002).

[Click to enlarge]

The other interesting figure is the composition of boards that are responsible for making decisions for scientific research directions such as scientific commissions, R&D commissions, councils, committees and foundations, academy assemblies etc (they are listed in the report in detail). The figure below shows the percentage of woman in these boards by country. From left (highest percentage) to right (lowest) we have Sweden, Norway, Finland, Croatia, Denmark, Bulgaria, Iceland, Italy, Slovenia, France. The last five are the Czech Republic, Cyprus, Israel, Poland, Luxembourg. The dark pink bars are the average values for several groups of countries in the EU.

[Click to enlarge]

Overall I got the impression the situation is improving, but very hesitantly so. Way to go Europe, way to go.

Monday, December 07, 2009

Hello from Utrecht

I'm giving another seminar, this time in Utrecht. I haven't been to the Netherlands since I was a teenager, when I spent several summers in and around the IJsselmeer. Nice to see things haven't changed much. Here's what my arrival in the hotel looked like. Room #24. It's on the uppermost floor. - ? - No, sorry, no elevator.

Yesterday afternoon I took a walk around town. The preferred mode of transportation is biking. That's because the Dutch still have problems driving a car: I got almost run over by a car going backwards through a one-way street. Another thing that hasn't changed is the large living-room windows facing the walkways, so that one can look directly into other people's houses. Quick survey of the Dutch Sunday-evening program: watching TV, dinner, watching TV, feeding the fish, surfing the web, playing with the kids, watching TV, doing calculations writing a love letter, mysteriously closed blinds, staring back at the stranger gazing into the living room.

And if one doesn't go by bike, one goes by boat. That's the Netherlands in a nutshell I suppose. I feel scarily close to groundwater everywhere.

My seminar went well, and now I have to hurry to dinner.

Sunday, December 06, 2009

The Nature of Laws

It occurred to me I haven't bothered you with my random thoughts for a while, so here's a topic that keeps coming back to me: The consistency of laws. In mathematics it's the whole point, in physics it's a guiding principle, but when it comes to our societies' legal system, the consistency of laws is considerably more murky.

As a teenager, I had a period when I was convinced that direct democracy would be the answer to all flaws in our democratic system. I also thought that the reason why we do not have a direct democracies is that it was in practice unfeasible. After all, Germany has some more inhabitants than Switzerland. With the advent of the internet, so I thought, direct democracy should eventually become practicable - globally! - and lead to flourishing of democracy.

I was really excited about that prospect for some while, until it occurred to me that there are other good reasons why a representative democracy is preferable, reasons that our, your, and their funding fathers thought about, and that a teenager needed some time to figure. It is ironic that a decade later I found the excitement about direct democracy echoing back at me from the internet, lacking exactly the awareness of the merits of representation that I had been lacking.

One of these merits of a representative democracy is what Jaron Lanier referred to very aptly as “low-pass filtering.” Opinions are easily influenced by all kinds of events and peripheral news, and in times when hypes pass around the globe in next-to-no time these opinions are in addition strongly amplified. One couldn't base any decent policy on such a constantly changing background of opinions.

Another problem that is that even without the high-frequency noise, people's opinions are inconsistent. He was a strong defender of freedom of speech, untill that blogpost proclaimed his product is a big piece of shit. Nuclear power plants are great, unless they are in your backyard. And abortion is evil until your teenage daughter dies in labor.

These are several variations of inconsistencies between laws on different level. The constitution (basic law!) is on the most fundamental level. It's what defines your nation. These laws are, for good reasons, very hard to modify. But they are also very general and with that quite vague when it comes to concrete applications. In other cases they are just outdated and require new interpretations; a good example is property rights in times of file sharing. But the point is that all laws more concrete for specific situations should be in agreement, read: consistent with, the fundamental laws.

If law was maths, one could derive everything from the basic axioms, but of course that's not strictly possible. One of the main reasons is that eventually our legal system is based on words that lack precise definitions and interpretations that change with time and context. But still, measures have to be taken to make sure no laws exist that are in conflict with each other, and that means in particular no newly passed law should be in conflict with the agreed-upon basic laws. Otherwise the legal system is inconsistent.

One problem of that sort that has made a lot of headlines in the last years is gay marriage in the USA. If your country grants equal rights to all its citizens they better be all allowed to marry their partners. It's not a question of public opinion, it a question of consistency with the constitution and a case for the constitutional court. As we've seen, the public opinion is indeed, sadly enough, inconsistent. But that's only my opinion of course, and I'm not the constitutional court.

MinaretAnother problem of that sort, the one that triggered this post, is Switzerland's ban on the building of minarets in a recent referendum. Yes, that is correct. Nevermind religious freedom. But hey, the Swiss Justice Minister says the decision is “not a rejection of the Muslim community, religion or culture.” No? Then what is it? Let's see:
“Supporters of a ban claimed that allowing minarets would represent the growth of an ideology and a legal system - Sharia law - which are incompatible with Swiss democracy.”
The catholic church is of course a great example for democracy. But more importantly, banning minarets cures the symptoms, not the disease. It's a pointless, stupid, ineffective and constitutionally doubtful decision that should never have been allowed as referendum to begin with. If you have problems with certain practices a religion exercises, it's them that you should ban, not their architecture. I'm glad Switzerland is not in the European Union.

Now that I've voiced my outrage, let me say the underlying question is of course a tricky one. What questions is it that you can pose to a group (crowd, electorate) and get a useful answer? James Surowiecki in his book “The Wisdom of Crowds,” has summarized many research results that have targeted this question. But many questions still remain open and, what is worse, none of these results seem yet to have made it into application.

Knowing which questions one can pose to a group under which circumstances and expect a useful answer is important for our lives on many levels. Just take the question whether a group of successful scientists is able to select the most promising young researchers. It's not that I actually doubt it, what bothers me more is that we don't know. We are still operating by trial and error, and this is one of the reasons why I say we need to finish the scientific revolution.

Since I'm afraid these thoughts have been a little too random and I've lost the one or the other or the other or the other reader, let me wrap up: Direct democracy is not always the best option, and inappropriate use can result in inconsistencies. If you want intelligent decision making - in a referendum, in your committee, in your company - you better first figure out under which circumstances which way of aggregating opinions has proved to be successful.

    “Public Opinion... an attempt to organize the ignorance of the community, and to elevate it to the dignity of physical force.”
    ~Oscar Wilde

Friday, December 04, 2009


The other day we were discussing how unfortunate it is that the "quantum gravity" group at Perimeter Institute is called quantum gravity, even though it excludes string theory, which is another group. However, I couldn't really come up with a better name. The actual problem seems to me that string theory is part of quantum gravity, condensed matter, particle physics, and mathematical physics, so maybe it's them who shouldn't be name-givers for a group? What do you think?

Tuesday, December 01, 2009

This and That + Interna

I recently learned there's no W in the Swedish language. How eird is that? More generally, living in a country where I don't understand the language has taught me how tiny the actual information content of spoken language is. Like, there's the woman behind me who waves my glove around "Blablablablabla," she says. What I hear is "Did you lose your glove?" Then there's the women at the register looking at my bakery bag. "Blablablablabla," she says. "How many rolls are that?" Is what I hear. I always buy eight, because that's the only number I know how to pronounce. And then there's the guy in the mall "Blablablabla Systembolaget," upon which I point towards the liquor store.

Yes, I learned one or the other word in the past two months, one of which is "Systembolaget," the only place one can buy alcoholic beverages in Sweden and basically the equivalent to Ontario's LCBO. One difference though is that in Sweden the wines are not ordered by country, but by price. More eirdness.

That I've found the closest liquor store however, I should point out, is not the reason for my blogging being a little sparse lately. The actual reason is that I'm sitting on a huge pile of application documents for our postdoc positions. Thank you for your interest in Nordita! This isn't the first time I'm doing this, but reading hundreds of letters of recommendation is invariably as humiliating as debilitating. And sometimes amusing. Here's some gems from letters I came across "he is much better than he looks," "we have shared a common nightmare," and "he spends endless hours on delving about various aspects with a tireless face," which sounds to me like an advertisement for Botox.

Anyway, some other things that I've come across lately is this nice selection of high speed photos of fluids, my mother sends this video for everybody who is Windows-Vista-damaged, and this graph gave me a good laugh. Besides this, I just uploaded a paper, so check the arXiv tomorrow.

Saturday, November 28, 2009

The Causal Diagram of the Black Hole

A week ago, I explained the idea of causal diagrams, or Penrose-Carter diagrams, and we discussed the diagram for the static black hole metric shown below.
Causal diagram of eternal black hole

As I pointed out, though a solution of Einstein's field equations, this diagram does not actually describe a situation we find in reality. The black hole shown in this diagram is accompanied by a white hole, and both have existed since forever, and will continue to exist, unchanging, until eternity. Today, I thus want to discuss the metric for a realistic black hole, a black hole formed from collapse of matter. I will also briefly touch on the evaporation but, as you know if you've been around for a while, the exact way the evaporation proceeds, in particular the final stage, is still under debate.

To obtain the causal diagram of the black hole, recall that Einstein's field equations are local and the black hole solution is a vacuum solution. Yes, that is right. This means that in General Relativity empty space is not necessarily flat. (Flat meaning the curvature tensor vanishes identically. Empty space however has a property called "Ricci-flatness.") If we want to describe collapsing matter, we thus know that outside of that matter the previously found solution, depicted above, still holds. So, what we do is drawing into the diagram the surface of the collapsing matter, and keep the part that is outside that matter. This is shown below.

Cutting the Causal diagram of the Schwarzschild black hole

Now the blue shaded part is the one that no longer correctly describes the black hole that forms from collapse and has to be discarded. This means in particular that the white hole as well as the second asymptotically flat regions are both gone and do not exist in real world situations (addressing a concern that Andrew brought up in the previous post).

What we do then is to attach an interior solution that does not describe vacuum. In some simplified cases this can be done explicitly. For example if the collapsing density is homogeneous (which would be a piece of a FRW-metric), or if it is null dust (described by the Vaidya-metric). Then, one can calculate the interior solution and use a matching condition to join both parts together. For our purposes however, we don't have to bother with the details since we just want to capture the causal structure. For what the causal structure is concerned, the inside solution is rather dull. There is nothing specific going on. The radius just shrinks until it falls below the Schwarzschild radius associated to its total mass. Then the horizon forms, and the matter collapses to a singular point. This is shown in the diagram below.

Causal diagram of the not-evaporating black hole

Note that there is no particular meaning to curves that are exactly horizontal or vertical, we are thus free to deform them, which has been done to make the r=0 curve vertical. This is fine as long as we make sure that the null curves on 45° angles remain the same, and thus spacelike remains spacelike and timelike remains timelike.

As pointed out in the previous post, the use of radial coordinates means that ingoing curves look as if they are reflected at r=0 when they actually go through. The lightray marked v0 in the above figure is the last light ray that just manages to escape the forming horizon. It is in this background, not the static background, that Hawking did his calculation which showed that black holes do emit radiation.

Knowing the black hole, once formed, emits radiation of course brings up the next question: how do we incorporate the evaporation into the diagram? One can add the evaporation of the black hole by using another non-vacuum patch that describes outgoing radiation which leads to a decreasing of the mass. The Schwarzschild-radius of the black hole then gets closer to the singularity until both, the horizon and the singularity, vanish in the endpoint of evaporation. In this process, the event horizon remains lightlike. What changes for the observer at scri minus is the mass associated to the black hole. When the black hole is completely evaporated, we are left with a spacetime filled with very dilute radiation. This spacetime is to good precision flat and described by another piece of Minkowski metric. If you patch the pieces together you get the diagram below.

Causal diagram of the evaporating black hole

If you followed me so far, then we are now in an excellent shape to discuss the black hole information loss problem, which can basically be read off the causal diagram, and the possible solutions Lee and I classified in our recent paper. Let me know in the comments if you're interested in another post on that.