Interna

Lara and Gloria are now 7 months old. During the last month, they have made remarkable progress. Both can now roll over either which way, and they also move around by pushing and pulling. They have not yet managed to crawl, but since last week they can get on all fours, and I figure it's a matter of days till they put one knee in front of the other and say good-bye to immobility. They still need a little support to sit, but they do better every day.

While the twins haven't paid any attention to each other during the first months, now they don't pay attention to anything else. Gloria doesn't take any note of me if Lara is in the room, and Lara loses all interest in lunch if Gloria laughs next door. The easiest way to stop Gloria from crying is to place her next to her sister. However, if one leaves them unattended they often scratch and hit each other. I too am covered with bruises (but hey, it rattles if I hit mommy's head!), scratches (how do you cut nails on a hand that's always in motion?), and the occasional love bite that Lara produces by furiously sucking on my upper arm (yes, it is very tasty). Gloria is still magically attracted to cables, and Lara has made several attempts to tear down the curtains.

Lara and Gloria are now at German lesson 26: da-da, ch-ch, dei-dei-dei, aga-a-gaga. It is funny that they make all these sounds but haven't yet attempted to use them for communication. They just look at us with big eyes when we speak and remain completely silent. Though they seem to understand a few words like Ja, Nein, Gut, Milch. They also clearly notice if I speak English rather than German.

For the parental reading, this month I've enjoyed Ingrid Wickelgren's article "The Miracle of Birth is that Most of Us Figure Out How to Mother - More or Less." Quoting research that shows some brain is useful for parenting too, she writes:

"To take care of a baby's needs, mom needs to be able to juggle tasks, to prioritize on the fly, rapidly, repeatedly and without a lot of downtime... Mothering tests your attention span, ability to plan, prioritize, organize and reason as much as does a day at the office."

Well, it somewhat depends on what you used to do in that office of course. But yeah, I suppose some organization skills come in handy for raising twins. I won't lie to you though, singing children's rhymes isn't quite as intellectually stimulating as going with your colleague through the new computation. But Gloria always laughs when I read to her the titles of new papers on the arXiv.

On the downside, the Globe and Mail reported the other day on "Divorce, depression: The ugly side of twins," summing up "the infant treadmill":

"Cry. Breastfeed. Bottle-feed. Burp. Breast pump. Diaper. Swaddle. Ninety minutes of baby maintenance, then 90 minutes of trying to stay on top of sleep and domestic chores, then repeat. And so on."

Oh, wait, they forgot cleaning the bottles, doing the laundry, picking up baby because she's been spitting all over herself, washing baby, changing her clothes, changing bed sheets, putting baby back into bed, putting bottles into sterilizer, put laundry into dryer, take the other baby out of bed because she's been spitting... Indeed, that's pretty much how we spent the first months. But it gets better and thanks, we're all doing just fine.

You can also disregard all the above words and just watch the below video. And if you think they're cute, don't forget they'll get cuter for two more months, so check back ;-)


PS: Oh, and please excuse the green thing in the video. New software and I haven't yet really figured out how it works.

Prediction is very difficult

Niels Bohr was a wise man. He once said: "Prediction is very difficult, especially about the future." That is especially true when it comes to predictions about future innovations, or the impact thereof.

In an article in "Bild der Wissenschaft" (online, but in German, here) about the field of so-called future studies, writer Ralf Butscher looked at some predictions made by the Fraunhofer Institute for Systems and Innovation Research (ISI) in 1998. The result is sobering: In most cases, their expert panel didn't even correctly predict the trends of already developed technologies over a time of merely a decade. They did for example predict the human genome would be sequenced by 2008. In reality, it was sequenced already in 2001. They did also predict that by 2007 a GPS-based toll-system for roads would be widely used (in Germany). For all I know no such system is on the horizon. To be fair, they said a few things that were about right, for example that beginning in 2004, flat screens would replace those with cathode-ray tubes. But by and large it seems little more than guesswork.

Don't get me wrong - it's not that I am dismissing future studies per se. It's just that when it comes to predicting innovations, history shows such predictions are mostly entertaining speculations. And then there are the occasional random hits.

I was reminded of this when I read an article by Peter Rowlett on "The unplanned impact of mathematics" in the recent issue of Nature. He introduces the reader to 7 fields of mathematics that, sometimes with centuries delay, found their use in daily life. It is too bad the article is access restricted, so let me briefly tell you what the 7 examples are. 1) The quaternions who are today used in algorithms for 3-d rotations in robotics and computer vision. 2) Riemannian geometry, today widely used in physics and plenty of applications that deal with curved surfaces. 3) The mathematics of sphere packing, used for data packing and submission. 4) Parrondo's paradox, used for example to model disease spreading. 5) Bernoulli's law of large numbers (or probability theory more broadly) and its use for insurance companies to reduce risk. 6) Topology, long thought to have no applications in the real world and its late blooming in DNA knotting and the detection of holes in mobile phone network coverage. (Note to reader: I don't know how this works. Note to self: Interesting, look this up.) 7) Fourier transform. There would be little electrodynamics and quantum mechanics without it. Applications are everywhere.

Rowlett has a call on his website, asking for more examples.

The same issue of Nature also has a commentary by Daniel Sarewitz on the NSF Criterion 2 and its update, according to which all proposals should provide a description of how they will advance national goals, for example economic competitiveness and national security. Sarewitz makes it brilliantly clear how absurd such a requirement is for many branches of research:

"To convincingly access how a particular research project might contribute to national goals could be more difficult than the proposed project itself."

And, worse, the requirement might actually hinder progress:

"Motivating researchers to reflect on their role in society and their claim to public support is a worthy goal. But to do so in the brutal competition for grant money will yield not serious analysis, but hype, cynicism and hypocrisy."

I fully agree with him. As I have argued in various earlier posts, the smartest thing to do is reducing pressure on researchers (time pressure, financial pressure, peer pressure, public pressure) and let them take what they believe is the way forward. And yes, many of them will not get anywhere. But there is nobody who can do a better job in directing their efforts than they themselves. The question is just what's the best internal evaluation system. It is puzzling to me, and also insulting, that many people seem to believe scientists are not interested in the well-being of the society they are part of, or are somehow odd people whose values have to be corrected by specific requirements. Truth is, they want to be useful as much as everybody else. If research efforts are misdirected, it is not a consequence of researchers' wrongheaded ideals, but of these clashing with strategies of survival in academia.

Blablameter

"Vigorous writing is concise."

~William Strunk, The Elements of Style (1918)

Fun: Die Zeit writes about Bernd Wurm who studied communication science and got frustrated by the omnipresence of empty words in advertisements and press releases. So he developed a software, the "Blablameter," that checks a text for unnecessary words and awkward grammar that obscures content. The Blablameter ranks text on a scale from 0 to 1: the higher the "Bullshit Index," the more Blabla. You find the Blablameter online at www.blablameter.de; it also works for English input. In the FAQ, Wurm warns that the tool does not check a text for actual content and is not able to judge the validity of arguments, it is merely a rough indicator for writing style. He also explains that scientific text tends to score highly on the Blabla-index.

Needless to say, I couldn't resist piping some abstracts of papers into the website. Here's the results, starting with the no-nonsense writing:

• Towards Loop Quantum Supergravity (LQSG)
  Norbert Bodendorfer, Thomas Thiemann, Andreas Thurn
  
  Bullshit Index : 0.08
  Your text shows no or marginal indications of 'bullshit'-English.



• Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics
  Anthony Aguirre, Max Tegmark, David Layzer
  
  Bullshit Index :0.24
  Your text shows some indications of 'bullshit'-English, but is still within an acceptable range


• Unitary Evolution and Cosmological Fine-Tuning
  Sean M. Carroll, Heywood Tam
  
  Bullshit Index :0.31
  Your text shows indications of 'bullshit'-English. It's still ok for PR or advertising purposes, but more critical audiences may be skeptical.



• Relative locality: A deepening of the relativity principle
  Giovanni Amelino-Camelia, Laurent Freidel, Jerzy Kowalski-Glikman, Lee Smolin
  
  Bullshit Index :0.38
  Your text shows indications of 'bullshit'-English. It's still ok for PR or advertising purposes, but more critical audiences may be skeptical.



• Introduction to Quantum-Gravity Phenomenology
  Giovanni Amelino-Camelia
  
  Bullshit Index : 0.46
  Something's getting a bit fishy. You probably want to sell something, or you're trying to impress somebody. It still may be an acceptable result for a scientific text.


• Loop Quantum Gravity and Cosmology: A dynamical introduction
  Martin Bojowald
  
  Bullshit Index :0.52
  Something's fishy. Obviously you want to sell something, or you're trying to impress somebody. Are you sure that you have a real message, and if so: who would understand it?


• Thermodynamical Aspects of Gravity: New insights
  T.Padmanabhan
  
  Bullshit Index :0.66
  This reeks. I bet you're a PR-Expert, Politician, Consultant or Scientist. If there is a message, it's unlikely it will reach anyone.
  

And yes, I did pipe in some text from this blog. My performance seems to have large fluctuations, but is mostly acceptable.

Did you come across anything with a Blabla-Index smaller than 0.08 or larger than 0.66?

Do cell phones cause tinnitus?

Forget about cancer caused by cell phones, what about that ringing in your ear? About 10-15% of the adult population suffer from chronic tinnitus. I've had a case of tinnitus after a back injury. Luckily it vanished after 3 months, but since then I'm very sympathetic to people who go nuts from that endless ringing in their ear. A recent study by a group of researchers from Vienna now looked into the correlation between cell phone use and tinnitus. The results are published in their paper Tinnitus and mobile phone use, Occup Environ Med 2010;67:804-808. It's not open access, but do not despair because I'll tell you what they did.

The researchers recruited a group of 100 sufferers that showed up in some hospital in Vienna. They only picked people for whom no physiological, psychological or medical reason for the onset of their tinnitus was found. They excluded for example patients with diseases of the middle ear, hypertension, and those medicated with certain drugs that are known to influence ear ringing. They also did hearing tests to exclude people with hearing loss, of which one might suspect that their tinnitus was noise induced. Chronic tinnitus was defined as lasting longer than 3 months. About one quarter of the patients had had it already longer than 1 year at the time of recruitment. 38 of the 100 found it distressing "most of the time," and 36 "sometimes." The age of the patients ranged from 16 to 80 years.

The researchers then recruited a control group of also 100 people that were matched to the sufferers in certain demographic factors, among others the age group, years of education and whether they lived in- or outside the city.

At the time the study was conducted (2004), 92% of the recruits used a cell-phone. (I suspect the use was strongly correlated with age, but no details on that in the paper). At the time of onset of their tinnitus, only 84% of the sufferers had used a cellphone, and another 17% had used it for less than a year at that time. The recruits, both sufferers and controls, were asked for their cell phone habits by use of a questionnaire. Statistical analysis showed one correlation at the 95% confidence level: for cellphone use longer than 4 years at the onset of tinnitus. In numbers: In the sufferer's group, the ratio between those who had used a cellphone never or less than one year to those who had used it more than 4 years was 34/33. In the control group it was 41/23.

They then discuss various possible explanations, such as the possibility that cell phone radiation affects the synthesis of nitric oxide in the inner ear, but also more banally that a "prolonged contrained posture" or "oral facial manoeuvres" affect the blood flow unfavorably. (Does chewing gum cause tinnitus?)

The result is just barely significant, i.e. just at the edge of the confidence interval. There's a 5% chance of that result happening just coincidentally by unlucky sampling. So the researchers conclude very carefully that "high intensity and long duration of mobile phone use might be associated with tinnitus." Note that it's "associated with" and not "caused by." Needless to say, if you Google "cell phones tinnitus" you'll find several pages incorrectly proclaiming that "The researchers concluded that long term use of a mobile phone is a likely cause of tinnitus," or that the "study suggests cell phones may cause a chronic ringing in the ears." If such a Google search lead you here, the study concludes nothing of that sort. Instead, the authors finish with saying that there "might" be a link and that the issue should be "explored further."

So, do cell phones cause tinnitus? Maybe. Should you stop sleeping with the phone under your pillow? Probably.

In any case, I was left wondering why they didn't ask for phone habits generally. I mean, if it's the posture or movements connected with calling, what's it matter if it's a cell phone or a landline?

Book review: World Wide Mind by Michael Chorost

World Wide Mind
The Coming Integration of Humanity, Machines, and the Internet
By Michael Chorost

Is it surprising that self-aware beings become increasingly aware of their self-awareness and start pushing the boundaries? The Internet, Google, iPhones and wifi on every street corner have significantly changed the way we interact, share information and solve problems. Meanwhile, neuroscientists have made dramatic progress in deciphering brain activity. They have developed devices that allow to type using thoughts instead of fingers and monkeys with brain implants have learned how to move a robot arm with their thoughts. These are two examples that Michael Chorost discusses in his book, and that he then extrapolates.

Chorost's extrapolation is a combination of these developments in communication and information technology and neuroscience: Direct brain-to-brain communication by thought transmitted via implants rather than by typed words, combined with wireless access to various soft- and hardware to supplement to our cognitive skills.

I agree with Chorost that this "World Wide Mind" is the direction we are drifting, and that the benefits can be huge. It is interesting though if you read the comments to my two earlier posts that many people seemed to be scared rather than excited by the idea, mumbling Borg-Borg-Borg to themselves. Is is refreshing and also curageous then that Michael Chorost in his book addresses the topic from a quite romantic viewpoint.

Chorost describes himself as a short, deaf, popular science writer. He wears a Cochlear implant that allows him to hear by electric stimulation of the auditory system (content of his previous book, which I however didn't read). Chorost started writing "World Wide Mind" single and finished as a married man. He writes about his search for a partner and what he learned along the way about communication and what today's communication on the internet is lacking. The ills produced by our presently incomplete and insatisfactory online culture he believes will be resolved if we overcome the limitations of this exchange. He does not share the pessimism Jaron Lanier put forward in his book "You are not a gadget". (He does however share Lanier's fondness of octupi and a link to this amazing video with the reader.)

In "World Wide Mind" Chorost wants to offer an outlook of what he believes is doable if today's technology is pushed forward hard enough. He focuses mostly on optogenetics, a recently florishing field of study that has allowed to modify some targeted neurons' genetic code such that their activity can be switched on and off by light signals (most famously, this optogenetically controlled mouse running circles in blue light). He also discusses what scientists have learned about the way our brains store and process input. Chorost then suggests that it seems doable to record each person's pattern of neuronal activity for certain impressions, sights, smells, views, words, emotions and so on (which he calls "cliques") and transmit them to be triggered by somebody else's implant in that person's brain where they would cause a less intense signal of the corresponding clique. That would then allow us, so the idea, to share literally everything.

Chorost offers some examples what consequences this would have that seem to me however quite bizarre. Improving on Google's flu tracker, he suggests that the brain implants could "detect the cluster of physical feelings related to flu -- achiness, tiredness, and so on -- and send them directly to the CDC." I'm imagining in the future we can track the spread of yeast infections via shared itchiness, thank you very much. Chorost also speculates that "The greater share of the World Wide Mind's bandwidht might be devoted to sharing dreams" (more likely it would be devoted to downloadable brain-sex), and that "linking the memory [of what happened at some place to the place] could be done very easily, via GPS." I'm not sure I'd ever sleep in a hotel room again.

He barely touches in one sentence on what to me is maybe the most appealing aspect of increased empathy, a bridging of the gap between the rich and the poor, both locally and globally, and his vision for science gives me the creeps for it would almost certainly stiffle originality and innovation due to a naive sharing protocol.

"World Wide Mind" is a very optimistic book. It is a little too optimistic in that Chorost spends hardly any time discussing potential problems. He has a few pages in which he acknowledges the question of viruses and shizophrenia, but every new technology has problems, he writes, and we'll be able to address them. The Borg, he explains, are scary to us because they lack empathy and erase the individual. A World Wide Mind, in contrast, would enhance individuality because better connectivity fosters specialization that eventually improves performance. Rather than turning us into Borg, "brain-to-brain technologies would be profoundly humanizing."

It is quite disappointing Chorost does not at all discuss the cognitive biases we know we have, and what protocols might prevent them from becoming amplified. Nor does he, more trivially, address the point that everybody has something to hide. Imagine you're ignoring a speed limit sign (not that I would ever do such a thing). How do you avoid this spreading through your network, ending up in a fine? Can you at all? And let's not mention that reportedly a significant fraction of the adult population cheats on their partner. Should we better wait for the end of monogamy before we move on with the brain implants? (It may be close than you think.) And, come to think of it, let's better wait for the end of the Catholic Church as well. Trivial as it sounds, these issues will be real obstacles in convincing people to adapt such a technology, so why didn't Chorost spend a measly paragraph on that?

Chorost's book is an easy read. On the downside, it lacks in detail and explanation. His explanation of MRI for example is one paragraph saying it's a big expensive thing with a strong magnet that "can change the orientation of specific molecules in a person's body, letting viewers see various internal structures clearly." And that's it. He also talks about neurotransmitters without ever explaining what that is, and you're unlikely to learn anything about neurons that you didn't already know. Yes, I can go and look up the details. But that's not what I buy a book for.

"World Wide Mind" sends unfortunately very unclear messages that render Chorost's arguments unconvincing. He starts out stressing that the brain's hardware is its software, and so it's quite sloppy he then later, when discussing whether the Internet is or might become self-aware, confuses the Internet with the World Wide Web. According to different analogies that he draws upon, blogs either "could be seen as a collective amygdala, in that they respond emotionally to events" and Google (he means the search protocol, not the company) "can be seen as forming a nascent forebrain" or some pages later it can be seen as an organ of an organism, or a caste of a superorganism.

Chorost also spends a lot of words on some crazy California workshop that he attended where he learned about the power of human touch (in other words, the workshop consisted of a bunch of people stroking each other), but then never actually integrates his newly found insights about the importance of skin-contact with the World Wide Mind. This left me puzzled because the brain-to-brain messaging he envisions is able to transfer one's own neuronal activity only, which means essentially rather than tapping on your friend's shoulder, you'd have to tap your own shoulder and send it to your friend. And Chorost does not make a very convincing case when he claims that we'd be easily able to distinguish somebody else's memory from our own because it would lack in details. He does that after he discussed in length our brains' tendency to "confabulation," the creation of a narrative for events that didn't happen or didn't make sense to protect our sense of causality and meaning, something he seems to have forgotten some chapters after explaining it.

In Summary: the book is very readable, entertaining and it is smoothly written. If you don't know much about the recent developments in neuroscience and optogenetics, it will be very interesting. The explanations are however quite shallow and Chorost's vision is not well worked out. On the pro-side, this gives you something to think about yourself, and the book requires with only 200 pages not a big time investment.

Undecided? You can read the prologue and 1st Chapter of the book here, and Chapter 4 here. Michael Chorost tweets and is on facebook.

Collective excitement

I woke up this morning to find my twitter account hacked, distributing spam. I'm currently reading Michael Chorost's new book “World Wide Mind” and if his vision comes true the day might be near when your praise of the frozen pizza leaves me wondering if your brain has been hacked. Book review will follow when I'm done reading. If the babies let me that is. Here, I just want to share an interesting extract.

On the risk of oversimplifying 150 pages, a “clique” is something like an element of the basis of your thoughts. Might be a thing, a motion, an emotion, a color, a number, and so on, like e.g. black, dog, running, scary... It's presumably encoded in some particular pattern of neurons firing in your brain, patterns that however are different from person to person. The idea is that instead of attempting brain-to-brain communication by directly linking neurons, you identify the pattern for these “cliques.” Once you've done that, a software can identify them from your neuronal activity and submit them to somebody else where they get translated into their respective neuronal activity.

In Chapter 10 on “The Future of Individuality,” Chorost speculates on the enhanced cognitive abilities of an interconnected World Wide Mind:

“[I]magine a far-flung group of physicists thinking about how to unify quantum mechanics and general relativity (the most important unsolved problem in physics). One of them has the germ of an "aha" idea, but it's just a teasing sensation rather than a verbally articulated thought. It evokes a sense of excitement that her [brain implant] can pick up. Many cliques in her brain would be activated, many of them subconsciously. The sensation of excitement alerts other physicists that something is up: they suddenly feel that sense of aha-ness themselves. The same cliques in their brains are activated, say these: unification problem, cosmological constant, black holes, Hawking radiation.

An apparent random assortment, but brains are good at finding patterns in randomness. New ideas often come from a fresh conjunction of old ones. In a group intimately familiar with a problem, the members don't need to do a whole lot of talking to understand each other. A few words are all that are needed to trigger an assortment of meaningful associations. Another physicist pushes those associations a little further in his own head, evoking more cliques in the group. Another goes to his keyboard and types out a few sentences that capture it, which go out to the group; perhaps they are shared on a communally visible scratch pad. The original physicist adds a few more sentences. Fairly rapidly, the new idea is sketched out in a symbology of words and equations. If it holds up, the collective excitement draws in more physicists. If it doesn't, the group falls apart and everyone goes back to what they were doing. This is brainstorming, but it's facilitated by the direct exchange of emotions and associations within the group, and it can happen at any time or place.”

Well, I'm prone to like Chorost's book as you can guess if you've read my last year's post It comes soon enough in which I wrote “The obvious step to take seems to me not trying to get a computer to decipher somebody's brain activity, but to take the output and connect it as input to somebody else. If that technique becomes doable and is successful, it will dramatically change our lives.”

Little did I know how far technology has come already, as I now learned from Chorost's book. In any case, the above example sounds like right out of my nightmare. I'm imagining, whenever one of my quantum gravity friends has an aha-moment we're all getting a remote-triggered adrenaline peak and jump all over it. We'd never sleep, brains would start fuming, we'd all go crazy in about no time. Even if you'd manage to dampen this out, the over-sharing of premature ideas is not good for progress (as I've argued many times before). Preemies need intensive care, they need it warm and quiet. A crowd's attention is the last thing they need. Sometimes it's not experience and knowledge of all the problems that helps one move forward, but lack thereof. Arthur C. Clarke put it very well in his First Law:

“When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.”

The distinguished scientist may be wrong, but he certainly will be able to state his opinion very clearly and indeed have a lot of good reasons for it. He still may be wrong in the end, but by then you might have given up thinking through the details. Skepticism and debunking is a central element of research. Unfortunately, one sometimes throws out the baby with the bathwater of bad ideas. “Collective excitement” based on a sharing of emotions doesn't seem like the best approach to science.

Love to wonder

The July issue of 'Physik Journal' (the membership journal of the German Physical Society) has an interview with Jack Steinberger. Steinberger is an experimental particle physicist who in 1988 won the Nobelprize, with Leon Lederman and Melvin Schwartz, for his 1962 discovery of the muon neutrino. He is German born, but his family emigrated to the USA in 1934. Steinberger just celebrated his 90st birthday. What does a physicist do at the age of 90? Here's an excerpt from the interview (by Stefan Jorda):

You still come to your office at CERN every day?

I came by bike until last year, but then I fell and now I take the bus. I get up at five and arrive at half past six.

Every morning?

Not on Saturdays and Sundays. But I have nothing else to do. I read my email, then I go to the arXiv and look at the new papers in astrophysics. On the average, it's about 50 to 100, many of them are very bad. I read the abstracts, this takes one and a half hour, then I print those 5 to 10 that may be of interest to me. I try to understand them during the rest of the day. Then at 4pm I take the bus back home.

Since when are you interested in astrophysics?

In 1992 COBE detected the inhomogeneities in the cosmic microwave background, that was wonderful. It was a big challenge for me, as a particle physicist, to understand it, because one has to know general relativity and hydrodynamics. Back then I was still a little smarter and really tried to learn these things. Today I am interested for example in active galactic nuclei. The processes there are very complicated. I try to keep track, but there are many things I don't understand, and a lot simply is not understood.

(Any awkward English grammar is entirely the fault of my translation.)

Should I be lucky enough to live to the age of 90, that's how I would like to spend my days, following our ongoing exploration and increasing understanding of nature. Okay, maybe I would get up a little later. And on Saturday I'll bake a cake or two because my grand-grand children come for a visit. All nine of them.

"Men love to wonder, and that is the seed of science."

~Ralph Waldo Emerson

Finetuned

Melvin the Machine: a Rube Goldberg machine with a twitter account.

Melvin The Magical Mixed Media Machine from HEYHEYHEY on Vimeo.

[via, more info]

Getting cuter by the day...

If you've been wondering what age babies are the cutest, there's a scientific answer to that. Yes, there is. In the year 1979, Katherine A. Hildebrandt and Hiram E. Fitzgerald from the Department of Psychology at Michigan State University published the results of their study on "Adults' Perceptions of Infant Sex and Cuteness."

A totally representative group of about 200 American college students of child psychology were shown 60 chromatic photographs of infant faces: 5 male and 5 female each for six age levels (3, 5, 7, 9, 11, and 13 months). The babies were photographed by a professional photographer under controlled conditions when their facial expressions were judged to be relatively neutral, and the infants' shoulders were covered with a gray cape to hide clothing.

The study participants were instructed to rate the photos on a 5-point scale of cuteness (1: not very cute, 2: less cute than average, 3: average cuteness, 4: more cute than average, 5: very cute). The average rating was 2.75, ie somewhat less than averagely cute. The authors write that it's probably the selection of photos with neutral facial expressions and the grey cape which accounted for the students' overall perception as slightly less cute than average. And here's the plot of the results:
So, female cuteness peaks at 9 months.

For the above rating the participants were not told the gender of the child, but asked to guess it, which provided a 'perceived gender' assignment to each photo. In a second experiment, the participants were told a gender which however was randomly picked. It turned out that an infant perceived to be male but labeled female was perceived to be less cute than if it was labeled male. Thus the authors conclude that cuter infants are more likely to be perceived as female, and cuteness expectations are higher on females.

Partly related, Gloria just woke up:

Why do we live in 3+1 dimensions? Another attempt.

It's been a while since we discussed the question why we experience no more and no less than 3 spatial dimensions. The last occasion was a paper by Karch and Randall who tried to shed some light on the issue, if not very convincingly. Now there's a new attempt on the arXiv:

Spacetime Dimensionality from de Sitter Entropy
By Arshad Momen and Rakibur Rahman
arXiv: 1106.4548 [hep-th]

We argue that the spontaneous creation of de Sitter universes favors three spatial dimensions. The conclusion relies on the causal-patch description of de Sitter space, where fiducial observers experience local thermal equilibrium up to a stretched horizon, on the holographic principle, and on some assumptions about the nature of gravity and the constituents of Hawking/Unruh radiation.

What they've done is to calculate the entropy and energy of the Unruh radiation in a causal patch of any one observer in a de Sitter spacetime with d spatial dimensions. Holding the energy fixed and making certain assumptions about the degrees of freedom of the particles in the radiation, the entropy has a local maxium at d= 2.97 spacelike dimensions, a minimum around 7 and goes to infinity for large d. Since the authors restrict themselves to d less or equal to 10, this seems to say for a given amount of energy the entropy is maximal for 3 spacelike dimensions. Assuming that the universe is created by quantum tunneling, the probability for creation is larger the larger the entropy, thus it would be likely then that we live in a space with 3 dimensions.

To calculate the entropy one needs a cutoff the value of which is fixed by matching it to the entropy associated with the de Sitter horizon, so that's where the holographic principle becomes important.

Not only is it crucial that they add an upper bound on the number of dimensions by some other argument, their counting also depends on the number of particles and the dimensions they can propagate into. They are assuming only massless particles contribute, and these are photons and gravitons. Massive particles even with small masses, the authors write, are "unacceptable" because then the cutoff could be sensitive to the Hubble parameter. By considering only photons and gravitons as massless particles they are assuming the standard model. So even in the best case one could say they have a correlation between the number of dimensions and the particle content. Also, in braneworld models the total number of spatial dimensions isn't necessarily the one determining degrees of freedom at low energy; a possibility the authors explicitly say they're not considering.

Thus, as much as I'd like to see a good answer to the question, I'm not very convinced by this one either.

This and That

Some random things that caught my attention recently:

• If you like PhD comics, they're working on a movie: Trailer here.


• The Helmholtz-Zentrum Dresden-Rossendorf set a new world record for magnetic fields with 91.4 teslas.


• You have 1 week left to work out some detail of the 100 year spaceship and send in an abstract for the public symposium Sep 30 - Oct 2nd in Orlando "intended to seed creative energy to “kick-start” the long term research goals." It's for sentences like this that you hire PR people.


• Partly related, I learned the other day from SciAm that the new buzzword after "synergy" and "horizontal integration" is now "convergence." So let's converge on something then.


• Also, the new-name creationists have switched from iIng everything from iKnow to iDontcare and are now replacing spaces with dots, following the ICANN's decision to allow customizable URL suffixes. Ironically though, Google seems to replace the dot with a space if you search for a tag. Anyway, I see huge potential for the arXiv. No more SUSY or MSSM, it's now mond.4u and beyond.higgs. Leave your physics-themed suggestions in the comments!


• Something to look at: Camouflage art.


• And something else to look at: Dear Photograph


• If you like the comic series Asterix and Obelix, you'll love this Study of traumatic brain injuries. To quote from the conclusions "Roman nationality, hypoglossal paresis, lost helmet, and ingestion of the magic potion were significantly correlated with severe initial impairment of consciousness (p ≤ 0.05)."

Interna

So we're back in Germany. For the next months, I'm on parental leave again and Stefan works 9 to 5. Lara and Gloria are now almost 6 months old. They can now both roll over from back to belly, though not the other way round, and they've discovered their feet which make good toys that don't fall out of reach. They can grab and hold things, give them from one hand to the other, and bang them not only in their own but also in other people's faces. They can meanwhile eat quite well from a spoon, though they try to grab the spoon which makes feeding inevitably a mess.

Lara entertains us with a large variety of funny sounds ranging from moo-moo over uee-wee to fffff. The latter is particularly amusing when executed with a mouth full of mashed carrots. Gloria too finds distraction in her 5 minutes older sister and often turns to look at her or rolls into her direction. If Lara burps, Gloria laughs. Lara's hair finally seems to start growing, and it turns out to be lighter than it was at birth. Her eye color on the other hand is turning more brownish by the day. Gloria is still blue eyed and has a hint of blond hair.



Yes, my life has become very pink.

The girls now sleep reasonably well at night, but are more demanding during the day. Lara in particular manages to move around without actually being able to crawl and then gets stuck in all sorts of impossible positions. Gloria apparently loves to chew on cables, and it's good she doesn't have teeth yet. In the coming weeks, we'll have to childproof the apartment.

I have, to my great delight, meanwhile received parental benefits from the Swedish Försäkringskassan, at least for a couple of months, after I managed to convincingly explain I'm indeed still insured with them. The problem seems to have been caused by some EU agreement that assigns me to a German health insurance during my stay here. On the Swedish side however the health and social insurance are both in the domain of the same institution, so they seem to have concluded I'm back in Germany for good, never mind that I'm paying taxes in Sweden. Now they have some difficultly figuring out how many days I'm eligible for since Stefan doesn't live in Sweden. The Germans on the other hand have so far refused to pay a single cent of Stefan's benefits since they don't know what the Swedes will pay for me. The bottomline is we're still sitting on piles of paperwork and money is short. We've also learned of several people who've had similar difficulties which is both comforting and frustrating.

Our Saab's oil leak caused us some more headache than anticipated. Here in Germany we were told the broken part, some rusty hose, would have to be shipped from Sweden. Since we were on the way to Sweden anyway, we contacted some repair place there after arrival just to be told that Saab has only one warehouse for spare parts left, which is in Nyköping, and the part we need is out of stock. They could put in an order for fourhundredsomething Euro, and it might come in anything between next month or never. The car making more insulted noises by the day, I had the great idea to Google for 'Saab spare parts' in Swedish. Two days later I picked the part up from the post office; it came to about 25 Euro. To my amazement, it was indeed the right part and it's being replaced right now. Lesson learned: If you need a spare part for your car, buy it online yourself and bring it to your dealer.

Weather here in Germany is brilliant, 36 Grad, Es wird immer heisser, Es ist Sommer! and the women's soccer world cup has just begun.

No I wont agree to disagree

In a recent NYT article, I learned about the "argumentative theory of reasoning," suggested by Dan Sperber, a French social and cognitive scientist, who is director of the International Cognition and Culture Institute. The essence of his theory seems to be that the evolutionary purpose of argumentation is to win an argument. That, apparently, is a groundbreaking hypothesis as his colleagues mostly argue that the purpose of reasoning is to find the truth, leaving them puzzled why the human brain works so inefficiently to that end. Sperber's postdoc Hugo Mercier has a website that lists the predictions of this theory, most of which are actually postdictions.

I think they've forgotten to disentangle argumentation by subject. There's arguably arguments that for the sake of natural selection you're better off finding out the truth. You can convince me all you want that drinking distilled water will cleanse your soul, you're not going to reproduce 6 feet under. But if the argument is about getting your way (what's for dinner?) then you might indeed be better off packing on arguments in your favor and leaving out those that contradict you. The problem is of course that it's difficult to switch from one mode of argumentation to the other. That's why it's beneficial if scientists have some formal training in which they learn, if not actually the names of well-known cognitive biases, so at least procedures that have proven efficient in avoiding pitfalls of human cognition, cognition that has evolved for other purposes than, say, finding evidence for dark matter.

In any case, this reminded me of a little book I once saw on a bargain bin, "50 ways to stall a discussion." ("50 Arten, sich quer zu stellen" by Frans Krips, you can download it here.) If you ever sat in the 5th installment of yet another seemingly endless committee meeting, consider that everybody else read the book and took the advice very seriously. Here's a sample from the 50 ways:

1. This was not sufficiently discussed
2. We don't have enough information
3. We should first find out how the matter has been dealt with elsewhere
4. This is much too fast
5. Deficient use of language
6. Inadequate standard
7. We first have to discuss some other problem
8. There are other problems of higher societal relevance
9. One just can't do it this way
10. You can't expect that from the people
11. We've discarded so many plans, who cares if we discard yet another
12. We tried this already in 1976
13. We haven't yet assessed the impact of our last decision
14. Who exactly is responsible?
15. We should contact an expert
16. We have to set priorities straight
17. We need a committee on this aspect

And then there is of course the Web2.0 deadlock: we have to agree to disagree. It too fails to differentiate between seeking for truth and seeking for compromise. We can agree to disagree on all matters of taste: Pizza or Sushi? Pink or blue? NIN or RHCP? but when it comes to science, disagreement means one of us is wrong. Finding the right answer is what science is all about. So it's Pizza tonight, dammit.

[Img Src: Very Demotivational]

Exploring Self-perception: Zakaryah Abdulkarim

[Last month, I volunteered for a study at the department of neuroscience at Karolinska Institute, if just out of curiosity to see the place. Eventually it didn't work out with my participation, but I got to meet Zakaryah, a student at the Institute, who kindly agreed to tell us a little about his work there. I certainly learned some new vocabulary. Enjoy!]

I read that you are looking for volunteers for a project. Can you tell us what this is all about?

Yes. The project that I am currently involved in is one in the field of cognitive neuroscience. It is part of the research conducted in the lab of Dr. Henrik Ehrsson at the Department of neuroscience, Karolinska Institute. In this project we use an established perceptual illusion called ‘the body swap illusion’ (Petkova & Ehrsson, 2008) in which healthy participants experience the body of a shop mannequin as their own body to understand the behavioral and neural mechanisms underlying the self-attribution of a whole body to oneself. In particular, we are interested in understanding the neural mechanisms underlying the unitary experience of owning an entire body rather than a set of fragmented body parts. My project will contribute important behavioral and physiological data in support of a neuroimaging study conducted by my direct supervisor PhD-candidate Valeria Petkova.

In my experiment the participants wear head-mounted virtual reality displays, through which they see the mannequin’s body. They then receive simultaneous visual and tactile stimulations of various body parts and fill out a questionnaire regarding their experience. Alternatively they might see a knife approaching the mannequin, in which case the sweating of their palms, the so called galvanic skin response, which is a measurement of the sympathetic nervous systems response to dangerous stimuli is measured via electrodes attached to the fingers of the participant. Since the knife is approaching the mannequin and not the body of the participant, the sweating of the palm is used as an objective measurement of the perception of the body ownership illusion.

What is that sort of research good for?

Understanding the perceptual and neural mechanism involved in how we perceive our own body might be useful in the development of neuroprosthetics. Further, understanding the mechanism underlying the healthy perception of body ownership can help develop diagnostic and therapeutic tools in the treatment of pathological disturbances of the bodily self perception in different groups of patients (i.e. stroke, paraplegia, schizophrenia, anorexia etc.). Finally, the results of this type of research are beneficial for some industrial applications, for example in the field of virtual reality, telerobotics or telepresence.

What future studies would you like to do?

I would probably want to investigate more exactly which areas of the brain are involved in producing this feeling of body ownership and various ways to manipulate this. In particular, it would be interesting to see if one could affect this illusion pharmacologically, and how the illusion is correlated to the features of the subjects, because interestingly, not everyone experience this illusion.

What are the presently most pressing open questions in the field?

Here are some examples:

- What are the exact characteristics (i.e. type, receptive field etc) of the neuronal population involved in the neural computation of body ownership?

-What is the exact role of each node in the neural network indentified to be associated with the sense of owning a body. With other words what is the specific role of the ventral premotor cortex, the intraparietal cortex, the putamen, and the cerebellum?

- What is the interplay between body ownership and the sense of agency in the mechanism of self-awareness?

Do you see any relevance for physics or a role for physicists in that kind of research? If so, what?

Of course! Aside from all the technical equipment that is needed to perform these studies, e.g. MRI-scanners, galvanic skin electrodes etc., this research brings up a lot of fundamental questions about how we perceive ourselves and our surroundings, how we make decisions, how effects on different scales interplay, and I believe physics can contribute a lot to those discussions.

For somebody interested in this research, what further reading can you recommend?

One could read some scientific articles about it, however those can be hard to understand if you do not have a background in medicine or neuroscience. I would recommend those who are interested to read bookchapters about this kind of research, which exist in most of the new books in cognitive neuroscience, for example this.

If I'm in Stockholm and interested volunteering for your or similar research, how do I get in contact?

If you are in Stockholm and interested in participating, the best thing to do would probably be to send me an email, my email-adress is: zakaryah.abdulkarim[at]stud.ki.se. The requirements differ depending on the study, but usually there is some experiment in our lab that one can participate in.

---

Zakaryah is a medical student at Karolinska Institute. In his free time, when he isn’t at Alba Nova taking some evening course that is, he likes exercising, hanging out with friends, and enjoying what the vegetarian cuisine has to offer.

Nonlocal correlations between the Canary Islands

Bell's inequality is the itch on the back of all believers in hidden variables. Based on only a few assumptions it states that some correlations in quantum mechanics can not be achieved by local realistic hidden variables theories. The correlations in hidden variables theories of that type have to fulfill an inequality, now named after John Bell, violations of which have been observed in experiment, thus hidden variables don't describe reality. But as always, the devil is in the details, and if one doesn't pay attention to the details, loopholes remain. For Bell's inequality, there are actually quite a few of them, and to date no experiment has managed to close them all.

The typical experiment for Bell's theorem makes use of a pair of photons (electrons), entangled in polarization (spin). The two particles are send in different directions and their polarizations are measured along different directions. The correlation among the pairs of repeated measurements is subject to Bell's inequality. (Or the more general CHSH inequality).

The maybe most obvious loophole, called the locality loophole, is that information could be locally communicated from one measurement to the other. Since information can maximally be transmitted by the speed of light this is the case if, for example, the second measurement is made with delay to the first, such that the second measurement is in the forward lightcone of the first. Another loophole is that the detector settings may possibly be correlated with the prepared state without any violations of locality if they are in the forward lightcone of the preparation. Since in this case the experimenter cannot actually set the detector as he wishes, it's called the freedom-of-choice loophole.

A case where both loopholes are present is depicted in the space-time image below. The event marked with "E" is the emission of the photos. The red lines are the worldlines of the entangled electrons or photons (in an optical fiber). "A" and "B" are the two measurements and "a" and "b" are the events at which the detector settings are chosen. Also in the image are the forward lightcones of the event "E" and "A".


So that's how you don't want to make your experiment if you're aiming to disprove locally realistic hidden variables. Instead, what you want to do is an experiment as in the second figure below, where not only the measurement events "A" and "B" are spacelike to each other (ie they are not in each other's lightcone), but also the events "a" and "b" at which the detector settings are chosen are spacelike to each other and to the emission of the photons.

Let us also recall that the lightcone is invariant under Lorentz-transformations and thus the statement whether two events are spacelike, timelike or lightlike to each other does not depend on the reference frame. If you manage to do it in one frame, it's good for all frames.

Looks simple enough in a diagram, less simple to actually do it: Entanglement is a fragile state and the speed of light, which is the maximum speed by which (hidden) information might travel is really, really fast. It helps if you let the entangled particles travel over long distances before you make the measurement, but then you have to be very careful in getting the timing right.

And that's exactly what a group of experimentalists around Anton Zeiliger did and published in November in their paper "Violation of local realism with freedom of choice" (arXiv version here). They closed for the first time both of the two above mentioned loopholes by choosing a setting that disabled communication between the measurement events as well as between the preparation of the photons and the choice of detector settings. The test was performed between two Canary Islands, La Palma and Tenerife.


[Image Source: Lonely Planet]
The polarization-entangled pairs of photons were produced in La Palma. One was guided to a transmitter telescope and sent over a distance of 144 km to Tenerife, where it was received by another telescope. The other photon made 6km of circles in a coiled optical fibre in La Palma. The detector settings in La Palma were chosen by a quantum random number generator 1.2 km away from the source, and in Tenerife by another similar but independent random number generator. The measurements violated Bell's inequality by more than 16 standard deviations.

What a beautiful experiment!

But if you're a believer in local realistic hidden variable theories, let me scratch your itch. You can't close the freedom-of-choice loophole in superdeterministic hidden variables theories with this method because there's no true randomness in that case. It doesn't matter where you locate your "random" generator, its outcome was determined arbitrarily long ago in the backward lightcone of the emission.

New Painting

Okay, it's not really new. I actually started it last fall, but only finished this week. It's called "Herbstschatten" (Shadow of fall). Click to enlarge.

Extra Dimensions at the LHC: Status Update

The Planck scale is the scale at which quantum gravitational effects are expected to become important. An extrapolation of the strength of gravity gives a value of 10¹⁶TeV, which is far out of reach for collider experiments. In the late 90s however, it was pointed out by Arkani-Hamed, Dimopoulous and Dvali, that this extrapolation does not hold if our spacetime has additional spacelike dimensions with certain properties. If that was the case, the true Planck scale could actually be at a TeV, an idea that is appealing because it does away with the question why the Planck scale is so large, respectively why gravity is so weak, to begin with. The answer would be, well, it isn't, it is only apparently so: Our naive extrapolation doesn't hold because space-time isn't four-dimensional. (For more details, read my earlier post.)

This (and other) extra dimensional models with a lowered Planck scale have been very popular at the beginning of the last decade and caused an extraordinarily high paper production which reflects not only the number of theoretical particle physicists, but also their desperation to put their skills to work. The most thoroughly analysed consequence of such models are the modification of standard model cross-sections through virtual graviton exchange and the production of black holes at the LHC. The latter possibility in particular received a lot of attention in the media due to some folks who accused physicists of planning the end of the world just to increase their citation count. (For more details, read these earlier posts.)

In any case, the LHC is running now, data is coming in and models are being sorted out, so what's the status?

In arXiv:1101.4919, Franceschini et al have summarized constraints from the LHC's CMS and ATLAS experiments on virtual graviton production. For the calculation of the contributions from virtual gravitons one needs to introduce a cut-off Λ of dimension energy that, next to the lowered Planck scale, becomes another parameter of the result. The constraints are then shown as contour plots in a two parameter space, the one parameter being the 'true' fundamental Planck scale, here denoted M_D, and the other one being mentioned cut-off, or its ratio to M_D respectively. One would expect the cut-off to be in the range of the lowered Planck-scale, though it might be off by a factor 2π or so, so the ratio should be of the order one. The figure below (Fig. 6 from arXiv:1101.4919) shows the bounds for the case of 4 additional spacelike dimensions:

The continuous line is the constraint from CMS data (after 36/pb integrated luminosity. Don't know what that means? Read this), and the dashed line is the constraint from ATLAS. The shaded area shows the excluded area. As you can see, a big part of the parameter space for values in the popular TeV range is meanwhile excluded.

Now what about the black holes? A black hole with a mass a few times the lowered Planck mass would already be well described by Hawking's calculation for particle emission, usually called Hawking-radiation. It would have a temperature (or average energy of primary emitted particles) of some hundred GeV. Just statistically, a big fraction of the emitted particles carry color charges and are not directly detected, but they form color strings that subsequently decay into a shower of hadrons, ie color neutral particles (pions, protons, etc). This process is called hadronization, and the event is called a jet. Depending on how many jets you get, it's a di-jet, tri-jet or multi-jet. The black hole's Hawking radiation would typically make a lot of particles and thus contribute to the multi-jets. One expects some multi-jets already from usual standard-model processes ("the background"), but the production of black holes should significantly increase the number. The figure below (from this paper by the CMS collaboration) shows an actual multi-jet event at the LHC:


In the paper arXiv:1012.3375 [hep-ex], the CMS collaboration summarized constraints on the lower mass of black holes in models with extra dimensions. For this, they analyzed the amount of multi-jet events in their data. The figure below (Fig 2 from arXiv:1012.3375) contrasts the predictions from the Standard Model with those of models with black hole production, for events with multiplicity N larger than 3 (that includes jets, but also photons, electrons and muons that don't hadronize).

On the vertical axis is the number of multi-jet events per bin of 100 GeV, on the horizontal axis the total transverse energy of the event (if you don't know what that means think of it as just the total energy). The solid blue line is the Standard Model prediction, the shaded area depicts the uncertainty. The various dotted and dashed lines are the predictions for the number of such events for different values of the minimal black hole mass, usually assumed to be in the range of the lowered Planck scale. These lines are created by use of event generators, ie numerical simulations. From this and similar data, the CMS collaboration is able to conclude that they haven't seen any black holes for minimum masses up to 4.5 TeV. CMS has an update on these constraints here, where they've pushed the limits up to 5 TeV, if not with amazingly high confidence level.

Some comments are in order though for the latter analysis. It argues with the production of multi-jets by black holes. This is a reliable prediction only for black holes produced with masses at least a few times above the lowered Planck scale. The reason is that a black hole of Planck mass is a quantum gravitational object and it is not correctly described by Hawking's semi-classical calculation. How to correctly describe it, nobody really knows. It is for the sake of numerics typically assumed that a black hole of Planck mass makes a final decay into a few particles. But that's got nothing to do with theory, it is literally just a subroutine in a code that randomly chooses some particles and their momenta such that all conservation laws are fulfilled. (The codes are shareware, look it up if you don't believe it.)

That procedure wouldn't be a problem if that was just some pragmatic measure to deal with the situation that has no impact on the prediction. Unfortunately it is the case that almost all black holes that would be produced at the LHC would be produced in the quantum gravitational regime. The reason is simply that the LHC is a hadron collider, and all the energy from the protons is redistributed on its constituents (called partons). As a result of this, the vast majority of the black holes produced have masses as low as possible, ie close by the new Planck scale.

What that means is that it is actually far from clear what the CMS constraints on excess of multi-jets mean for the production of black holes. A similar argument was recently made by Seong Chan Park in Critical comment on the recent microscopic black hole search at the LHC, arXiv:1104.5129.

Summary: It clearly doesn't look good for models with a lowered Planck scale. While it is in many cases not possible to falsify a model, but just to implausify it, large extra dimensions are becoming less plausible by the day. Nevertheless, one should exert scientific caution and not jump to conclusions. The relevance of CMS constraints on multi-jets depends partly on assumptions about the black holes' final decay that are not theoretically justified.

Question for the experts: Why do the curves in Fig 2 of the CMS paper seem to have a bump around the mininum black hole mass even though N > N^min?

Stronger than the universe

Two weeks ago, we had hail here in Stockholm. At that time I was homewards bound on the highway, and that's where I would be staying for half an hour while rescue crew scratched a motorbike off the middle lane. On the radio run "Heartbreaker" by Dionne Warwick. It's one of these songs I've heard a million times but never listened to, girl in love, guy who doesn't call, same old story. "Why do you have to be a heartbreaker, When I was bein' what you want me to be?" I probably wouldn't call her either. There's Swedish "nyheter" on the other frequencies, but I already knew the weather was sucking greatly, the highway was clogged, and the rest I wouldn't understand anyway, that being the state of my Swedish. Hail drumming on the car roof, Dionne sang "My love is stronger than the universe," and the physicist in me couldn't avoid asking WTF is that supposed to mean? (It's not a four letter word. No, it isn't.)

Okay, so the universe is supposed to have a strength. It springs to mind the gravitational force exerted by all the mass in the universe. Since you can't place yourself outside the universe (probably where Dionne's guy sits) the question is what's the force acting on you while inside, caused by the expansion of the universe? Well, we know that bound systems up to galactic scales don't take part in the expansion, but let's forget that for a moment and pretend the universe would try to rip lovers apart on planetary surfaces. If Dionne's non-caller was as far away from her as he could possibly get on Earth, ie 10,000 km or so, the force comes to 10^-26N. Not very impressive. The laws of attraction might get you into trouble, but actually gravity is even weaker than the weak force.

No, we have to think about this differently. We should be asking what's the strength of the structure of the universe? So, as everybody knows, the universe is made of strings, and a string has a tension which is something like the square of the Planckmass, take or give some orders of magnitude. Putting all dimensionful units back in, that comes out to be about 10⁴⁴N. We could compare this to the force acting on Dionne on the surface of a neutron star, which is a measly 10¹⁴N. Yes, clearly, there's string theory on the radio. Though I suspect you'd get pretty much the same answer asking what it takes to break a link in a fundamental spin network.

Passing by the accident zone I contemplate the lack of friction and the forces at work. The radio plays Tori Amos, Little Earthquakes. It doesn't take much to rip us into pieces.

Four links to Paul Dirac

The other day I was wondering out aloud whether somebody had ever checked the average number of co-authors to the next Nobelprize winner, because sometimes it seems to me like everybody knows everybody in theoretical physics. And it's not even a small community. Well, I don't know if anybody has actually measured the diameter of the physics coauthor network, but I saw this morning that the AMS has a tool to calculate 'collaboration distance' which is pretty much self-explanatory:


So, let's see how far I'm away from Paul Dirac coauthor-wise...


Not so far actually, thanks to Lee. Dirac's paper on the list above is a Nature article from 1952 on the question "Is there an Aether?" What about Albert Einstein then?

And go:


With 5 links to Albert Einstein! That's less than I would have guessed. With 6 links you can probably connect any two authors.

Unfortunately, the AMS database doesn't seem to contain experimentalists. Neither could I find any description of the algorithm used. It runs amazingly fast, and it makes me a little suspicious that in no query I tried did I get two paths with the same length, though that might have been coincidence.

So, have fun playing around.

On the Importance of Phenomenology

Quantum gravity has the potential to revolutionize our understanding of space, time, and matter and with it redefine our own place in the world. While my main interest is in finding the fundamental theory, I work on the phenomenology of quantum gravity because there is a need for it. The quest for a theory of quantum gravity is more than 75 years old, and though a lot has been learned along the way we are still waiting for a theory of quantum gravity that is connected to and confirmed by data. There is no way around phenomenology one way or the other; it is the necessary connection between theory and experiment. Here I want to reflect on the role phenomenological models have played in the history of physics and why they play an important role also in our search for a theory of quantum gravity.

If you know one thing about theoretical physics, it's Albert Einstein's name. While Einstein was inspired and guided by his contemporaries, both in theory as well as in experiment, his achievements are remarkable examples for the power of pure thought combined with mathematics. Einstein is not the only example; Dirac's equation that describes relativistic particles with spin 1/2 is another case where an axiomatic approach lead to predictions that were later confirmed by experiment, leaving us in awe of genius and the beauty of equations.

In the history of science these examples are however rare, and it is exactly because of their rarity that they impress us. An axiomatic approach towards the reconciliation of general relativity and quantum mechanics will, I am sure, if pursued vigorously, eventually lead to success. But the question remains if pure thought is sufficient to find the right starting point, for there might be more than one, some of which leading to theories incompatible with observations. And an axiomatic top-down approach brings with it a heavy load of developing mathematical tools along the way, detours to insight that can take a long time. In the history of science, physicists have often taken the freedom to go ahead and write down phenomenological models that were indeed not justified by any solid basis. And while rightfully met with skepticism, again and again they have been successful with it, thereby helping along the development of more and more fundamental theories.

The above mentioned example of Dirac's equation an instructive one. In the non-relativistic limit, Dirac's equation in the presence of an electromagnetic field reduces to the Pauli-equation which describes the coupling of electrons to electromagnetic fields with a gyromagnetic ratio of 2. It was derived by Dirac from his equation in 1928, but already in 1925 two Dutch graduate students, Samuel Goudsmit and Georg Uhlenbeg, had used a phenomenological model to describe the structure of atoms and the response of ions to magnetic fields. Their model did not make much sense since, classically, the gyromagnetic ratio should be one. Naturally, many physicists were not convinced by the model and Pauli even advised the students not to publish it. Yet, it described experiments well and Dirac's later derivation of their model from his equation served to document the validity of Dirac's theory.

Another example is Pauli's exclusion principle, according to which no two fermions can occupy the same state. It was postulated and used since 1925, among other things to explain the Zeeman effect. Yet it was not until the development of quantum field theory and an understanding of the properties of multi-particle states in 1940 that a derivation was achieved.

Coulomb's law, Ampere's law and Biot-Savart's law can be derived from Maxwell's equations, but they were known and in use long before that, significantly contributing to the development of the full theory of electrodynamics. Fermi's theory we know today is an approximation of the electroweak gauge theory, but was in use long before that, teaching us lessons in renormalizability. The Rahleigh-Jeans law and Wien's law for the spectrum of thermal radiation were combined in Planck's law. In 1900, Planck constructed a derivation for this radiation spectrum based on the, back then unfounded, assumption that the energy of photons is quantized and proportional to the frequency. It predated Einstein's explanation for the photoelectric effect by 5 years. The constant of proportionality that Planck introduced is now called Planck's constant and it was the starting shot for quantum mechanics.

Due to the difficulty to analytically describe the formation of bound states in Quantum Chromodynamics (QCD is asymptotically free, ie it's easier to deal with it the higher the energy) still today most of the models used are phenomenological and many predate the development of QCD. There is for example the the Nambu-Jona-Lasinio model, the Gell-Mann-Levy model or the String-Lund model, all of which have significantly contributed to our understanding of the structure of elementary matter.

One could at this point speculate which present day phenomenological models will turn out to have lead the way towards the now searched-for theory describing the fundamentals of space and time. It springs to mind String cosmology and Loop Quantum Cosmology, searches for deviations from Lorentz-invariance, extra dimensions, or signatures of space-time discreteness. The models currently in use are not derived from a fundamental theory. Instead, they aim to incorporate and allow tests for specific features the fundamental theory might have, like additional dimensions or modified Lorentz-invariance. But these models, even if they turn out to be incompatible with experiment, are guides on our search for the correct theory. Guides that, after 75 years, we have good use for.