Science

I recently enriched my vocabulary with expressions like “marginal product of labor,” “price elasticity,” and “isoquants”. The Edgeworth Box. Partial equilibrium. Certeris Paribus. Hutzelpoh.br /br /And why is that? Because, well, we have an increasing group of people here at a href=”http://perimeterinstitute.ca/”PI/a sharing an interest in complex systems. For reasons you find in your daily newspaper, these meetings have turned into more or less regular discussions about economic models, and I thought opening a textbook on the matter might be a good idea. See, a href=”http://www.perimeterinstitute.ca/en/Events/The_Economic_Crisis_and_Implications_for_Science/The_Economic_Crisis_and_its_Implications_for_The_Science_of_Economics/”we’ll even have a conference here to save the world economy/a. I gracefully declined being among the local organizers. Not until I can say “asset-backed securities” and “collateralized debt obligations” without blushing.br /br /Thus, one could find last week on the quantitative finance arXiv a paper by Samuel Vazquez on a href=”http://arxiv.org/abs/0902.3840″emScale Invariance, Bounded Rationality and Non-Equilibrium Economics/em/a, and a href=”http://arxiv.org/abs/0902.4274v1″emTime and symmetry in models of economic markets/em/a by Lee Smolin. Among other things, Lee discusses the question of gauge symmetries in economic models. For an introduction into the topic, I recommend Eric Weinstein’s talk on “Gauge Theory and Inflation,” that you can find at PIRSA: a href=”http://pirsa.org/06050010/”06050010/a.br /br /A remark on footnote 11 of Lee’s paper. Of course there is private health insurance also in Europe. The difference to the USA is that health insurance companies are required to provide a governmentally set minimum of coverage, and it is mandatory to at least have this coverage (which in Germany is referred to as “insurance duty”- Versicherungspflicht.) The USA is besides South Africa the only developed nation without universal health coverage.br /br /Further, it is unclear to me in exactly which sense education in Europe is supposedly more or less “socialized” than elsewhere. As far as I know, the USA too has a a href=”http://en.wikipedia.org/wiki/Public_school”public school system/a. And though France and Sweden traditionally have not had and still don’t have tuition fees for universities, a href=”http://www.unibz.it/en/students/fees/default.html”Italy/a/span, a href=”http://www.tostudyinspain.com/spain-cost-of-living/”Spain/a and the a href=”http://www.studychoice123.nl/web/site/default.aspx?m=nieuwsamp;id=161″Netherlands/a do. a href=”http://www.studis-online.de/StudInfo/Gebuehren/tuition_fees.php”In Germany tuition fees for public universities have been discussed on and off over the last years, and presently regulations differ from state to state/a. But there are of course a href=”http://en.wikipedia.org/wiki/Private_university”private universities/a also in the European Union that will happily charge you money for a degree. (I’m not an expert on the European Union just because I have a European passport, please correct me if I’m wrong.)br /br /That having been said, I think what Lee meant is that there are a lot private universities in the USA, the tuition fees are the highest worldwide, and that the health insurance coverage is despite being entirely privatized and not mandatory also more costly and less efficient than in the EU. The consequences of that and the conclusions to draw could fill books, and are hardly appropriately taken care of in that footnote.div class=”blogger-post-footer”"You do not really understand something unless you can explain it to your grandmother.” ~ Albert Einsteinimg width=’1′ height=’1′ src=’http://res1.blogblog.com/tracker/22973357-3542682633060388571?l=backreaction.blogspot.com’//div

The world was different 20 years ago. German radio reported these days that many teenagers have only a vague idea that back then, Germany was cut in half by a daunting wall. On a lighter note, today’s kids may also have difficulties to imagine that there was no WorldWideWeb at that time.br /br /a onblur=”try {parent.deselectBloggerImageGracefully();} catch(e) {}” href=”http://info.cern.ch/Proposal.html”img style=”display:block; margin:0px auto 10px; text-align:center;cursor:pointer; cursor:hand;width: 400px; height: 230px;” src=”http://1.bp.blogspot.com/_AWa1cp-Somo/Sa2_1zv2IzI/AAAAAAAAAYk/fnnrOKECs-g/s400/www20.jpg” border=”0″ alt=”"id=”BLOGGER_PHOTO_ID_5309110466884543282″ //abr /br /But can you believe it? The beginnings of the wonderfully worldwide web go back to the time when the Iron Curtain was still dividing Europe. br /br /In March 1989, English computer scientist a href=”http://www.w3.org/People/Berners-Lee/”Tim Berners-Lee/a, then working at CERN, had set himself a bold task. As he had noted, iMany of the discussions of the future at CERN and the LHC era end with the question - “Yes, but how will we ever keep track of such a large project?”/i. So, he prepared a a href=”http://www.w3.org/History/1989/proposal.html”proposal/a to iprovide[] an answer to such questions/i. He introduced ithe idea of linked information systems/i and isuggested steps we should take to involve ourselves with hypertext now/i.br /br /His boss, Mike Sendall, sympathetically judged these ideas as ‘vague, but exciting’, and Tim Berners-Lee was allowed to continue following his vision. With the help of his colleague Robert Cailliau and a few students, he created the World Wide Web, designed and built the first web browser, and developed and started the first Web server, CERN HTTPd.br /br /The rest is a href=”http://en.wikipedia.org/wiki/History_of_the_World_Wide_Web”history/a.div class=”blogger-post-footer”"You do not really understand something unless you can explain it to your grandmother.” ~ Albert Einsteinimg width=’1′ height=’1′ src=’http://res1.blogblog.com/tracker/22973357-2028400454079196118?l=backreaction.blogspot.com’//div

a href=”http://4.bp.blogspot.com/_ws8XY4ubvXg/SaghxFepPWI/AAAAAAAAAus/b87VSwRovdE/s1600-h/newspaper.jpg”img id=”BLOGGER_PHOTO_ID_5307529288024145250″ style=”FLOAT: right; MARGIN: 0px 0px 10px 10px; WIDTH: 200px; CURSOR: hand; HEIGHT: 150px” alt=”Newspaper” src=”http://4.bp.blogspot.com/_ws8XY4ubvXg/SaghxFepPWI/AAAAAAAAAus/b87VSwRovdE/s200/newspaper.jpg” border=”0″ //aThe Internet has brought severe challenges for journalism, and especially for science journalism. The vast majority of private websites are financed through advertisements, which is impossible to miss. Exceptions to this are publicly funded governmental or educational institutions, and rare cases that are financed through donations like Wikipedia. Advertisements are more profitable the more visitors a website has, which thus puts a major incentive on popularity. Though this incentive has always been present, it is today much more pronounced than with a clientele of subscribers, and the breathlessness of infotainment with an emphasis on novelty contributes its part. The trend of print newspapers has thus been to cut back on the length of reports, to make them increasingly simplistic, and to provide additional web content in an effort to adapt to the changing demands of the customers.br /br /This however has not sufficed to keep newspapers financially healthy. Reporting on results of a recent survey among newspaper executives, researchers on the a href=”http://www.journalism.org/”Project for Excellence in Journalism /asummarize that the newspaper of today “has fewer pages than three years ago, the paper stock is thinner, and the stories are shorter. There is less foreign and national news, less space devoted to science, the arts, features and a range of specialized subjects”. Well over half (59%) of the 259 newspapers participating in the survey have reduced full-time newsroom staff over the past three years, mainly because of financial pressures. Roughly the same number (61%) also reported a decrease in their space available for stories. 46% of survey respondents said that the resources devoted to cover international affairs dropped within the last three years, 41% report a drop for national politics, and 24% for science reporting.br /br /While this development is of general concern, it is particularly so for scientific reporting, where attention to detail, background knowledge, and accuracy are essential. Quality of information is relevant for citizens to make decisions, and it should thus be in our prime interest. The problem underlying this erosion of newspapers substance (both in budget and content) is with the link between personal interests and the resulting overall trend, a classical case of public choice. We have gotten used to information being provided for free, and to all the advantages and amenities connected to it. We consider it a public service. If this information was provided for the actual coast it causes, likely many people would not pay this price, thus eroding the basis of our democracies. Free information is desirable to keep our societies functioning well. The problem is, its provision is done by people who need to eat and sleep. Consequentially, they should be financed as providers of public service, either by governmental subsidies, or as tax-free non-profit organizations.br /br /This is a discussion which is overdue, I was thus glad to see Swensen and Schmidt recently picked up the question of alternative financing models in their recent NYT article a href=”http://www.nytimes.com/2009/01/28/opinion/28swensen.html”News You Can Endow/a.br /br /Related: a href=”http://backreaction.blogspot.com/2009/02/do-we-need-science-journalists.html”Do we need science journalists?/a, a href=”http://backreaction.blogspot.com/2008/12/when-capitalism-fails.html”When capitalism fails/a and a href=”http://backreaction.blogspot.com/2007/11/fact-or-fiction.html”Fact or fiction/a.div class=”blogger-post-footer”"You do not really understand something unless you can explain it to your grandmother.” ~ Albert Einsteinimg width=’1′ height=’1′ src=’http://res1.blogblog.com/tracker/22973357-6569806170083966098?l=backreaction.blogspot.com’//div

Craig Hogan, from the University of Chicago, has written several papers predicting a noise that gravitational wave interferometers would be able to detect. This noise would be a signature of a href=”http://backreaction.blogspot.com/2007/07/planck-scale.html”Planck-scale/a uncertainty if a certain type of holography was realized in Nature. The a href=”http://geo600.aei.mpg.de/”GEO600/a interferometer near Hannover, Germany, would due to its construction details be particularly well suited to detect this noise.br /br /And indeed, the experimentalists seem to be seeing such “holographic noise” in the frequency range between 300 and 1500 Hertz, even tough its detection is unpublished. Its occurrence is quoted in Hogan’s paper (a href=”http://arxiv.org/abs/0806.0665″0806.0665/a) as “private communication,” but implicitly acknowledged on a href=”http://www.sr.bham.ac.uk/news.php”the website of the Astrophysics and Space Research Group at the University of Birmingham/a, a partner of the GEO600 collaboration: “To test the theory of holographic noise, scientists from Hannover and Birmingham will shift the frequency of GEO600’s maximum sensitivity towards higher frequencies,” and they carefully add “Even if it turns out that the mysterious noise is the same at high frequencies as at the lower ones, this will not constitute proof for Hogan’s hypothesis. It would, however, provide a strong motivation for further study.”br /br /Ununderstood noise in experiments is a good prediction to make, especially with large detectors. a href=”http://en.wikipedia.org/wiki/Aleph_(CERN)”CERN’s Large Electron Positron Collider/a (the tunnel of which is now reused for the a href=”http://www.cern.ch/lhc”LHC/a) was a href=”http://wwwae.ciemat.es/l3/slnote_orbit94.ps”sensitive to the tides in Lake Geneva/a, and a href=”http://www.aei.mpg.de/pdf/illustrationsDocs/geo_final.pdf”GEO600 is sensitive to the tides in the North Sea, and registers even smallest Earthquakes in the South Sea/a.br /br /But still, we are all looking, waiting, hoping for signatures of Quantum Gravity.br /br /Thus, NewScientist reported that a href=”http://www.newscientist.com/article/mg20126911.300-our-world-may-be-a-giant-hologram.html?full=true”our world may be a giant hologram/a, in a quite balanced article which quotes Karsten Danzmann of the a href=”http://www.aei.mpg.de/english/contemporaryIssues/home/index.html” target=”nsarticle”Max Planck Institute for Gravitational Physics/a in Potsdam: “We work to identify [the] cause [of the noise], get rid of it and tackle the next source of excess noise. In this respect I would consider the present situation unpleasant, but not really worrying.”br /br /uspan style=”font-size:130%;”Graviational Wave Interferometry/span/ubr /br /The idea underlying Hogan’s prediction is that our world might have holographic properties, in which case not all three dimensions of our spacetime would encode really independent degrees of freedom. This conjectured property would become noticeable only at very large distances. A device that was able to measure distances in orthogonal directions at long distances and to high precision could be sensitive to this fundamental limit of encoding details, and be subject to a new kind of uncertainty. Gravitational wave interferometers provide exactly such a device. The holography would show up as noise in the detector.br /br /Gravitational waves create distortions in our space-time that make themselves felt as tiny changes in lengths which are not the same for all three spatial dimensions. Interferometers lead a laser through a beam-splitter that splits the beam into two orthogonal directions into the “arms” of the interferometer, bounce the beam back on mirrors at the end of these arms, and compare the phases of the light when it comes back. This procedure can detect tiny deviations in the arm lengths which will change the phase shift. A common way to enhance the sensitivity of interferometers are “recycling techniques” that basically artificially increase arm lengths by reflecting the beam several times back and forth. GEO600 would be particularly sensitive to the holographic modification of quantum mechanics Hogan is proposing because the laser is reflected through both arms several times, whereas a href=”http://en.wikipedia.org/wiki/LIGO”LIGO/a, a href=”http://www.virgo.infn.it/”VIRGO/a and a href=”http://tamago.mtk.nao.ac.jp/”TAMA/a use so called Fabry-Perot arms that reflect the beam in each arm separately. You find a very useful illustration of this difference between LIGO and GEO600 a href=”http://www.physics.umd.edu/courses/Phys798g/Paik07/Lecture0410.pdf”in Peter Shawhan’s presentation, slide 19 and 20/a.br /br /That is how the narrative goes.br /br /Stefan and I then looked up Hogan’s papers and tried to find out what the underlying model is. Since many points remained unclear to us, I wrote an email to the author who replied almost immediately and patiently answered my questions. He also agreed to be quoted here, which I hope will clarify some points better than Stefan and I could have done.br /br /span style=”font-size:130%;”uHolography/u /spanbr /br /Hogan works with a modification of quantum mechanics in which position operators at different times fail to commute and instead the commutator is proportional to the Planck length eml/emsubp/sub and a measure of distance between the positionsbr /div align=”center”[xsub1/sub, xsub2/sub] = eml/emsubp/sub emL /em(1)/divbr /(Eq (3) from a href=”http://arxiv.org/abs/0706.1999″0706.1999/a) In the cases considered in the paper xsub1/sub and xsub2/sub are taken for different events 1 and 2 on a lightcone, and denote the coordinates in a direction orthogonal to the lightpath connecting 1 and 2. While the proper distance between the events actually is null, emL/em measures the spatial length of the connecting lightpath. In usual quantum mechanics, the commutator (1) vanishes. In Hogan’s theory it can deviate arbitrarily much from the ordinary case, depending on how large emL/em is, but this deviation would only become noticeable at large distances. One obtains from this commutator an uncertainty relationbr /center? xsub1/sub ? xsub2/sub eml/emsubp/sub emL/em/2 (2)/centerbr /(Eq (7) from a href=”http://arxiv.org/abs/0706.1999″0706.1999/a), which is then basically the origin of the noise in the interferometer*.br /br /Let me start with the question of motivation. The Holographic Principle is the conjecture that all the information about a volume of spacetime is actually encoded on its surface. This conjecture originated from black hole thermodynamics: the entropy of the black hole is proportional to its surface. The Holographic Principle is supported by string theoretical considerations. There is no experimental evidence for it. The a href=”http://en.wikipedia.org/wiki/Holographic_principle#Experimental_test”Wikipedia entry on the Holographic Principle /ainterestingly refers to the NewScientist article as an experimental test.br /br /There is however no derivation of Hogan’s modified commutator in any of his papers from the Holographic Principle, there are just many references to papers by Susskind, t’Hooft, Bekenstein, Busso and so on. We are thus actually dealing with an approach that is conjectured to be related to a conjecture. The motivation Hogan provides is from the black hole entropy. He is claiming that his modified version of position uncertainty is necessary for consistency in the black hole entropy and that of its radiation, a conclusion I could not follow (seea href=”http://www.prime-spot.de/holo.txt” estimate/a, comments are welcome).br /br /To be fair, this motivation from the black hole entropy does not appear in Hogan’s later papers. And despite the missing relation to the usual Holographic Principle one might consider his particular sort of holography and its consequences.br /br /span style=”font-size:130%;”uLorentz Invariance/ubr //spanbr /But let us have a closer look at the modification of quantum mechanics Hogan is proposing. In his approach, the Planck length plays a special role; combined with the distance emL/em it determines when the new effects would become important. One should be wary of any framework that does such since lengths are not invariant under Lorentz transformations - there is a restframe in which the Earth is of Planck length. Thus, by merely writing down an equation that renders the Planck length special, one creates a problem (see eg my post on a href=”http://backreaction.blogspot.com/2006/05/minimal-length-scale.html”emThe Minimal Length Scale/em/a). This is already a serious issue in “Deformed Special Relativity” (DSR) which claims to have found a way to leave the Planck length invariant under a modified sort of Lorentz transformations. Unfortunately, this doesn’t work well in position space (a href=”http://arxiv.org/abs/gr-qc/0612167″see paper/a) and creates all kinds of unappealing secondary problems, such as the need for a modified addition law of momenta and a missing macroscopic and multi-particle limit. Hogan doesn’t mention any of this in his papers.br /br /The problems with Hogan’s approach are actually worse than that of DSR, as one can see by looking at (1) and (2). In (1) we have two quantities of dimension length on the left side that undergo Lorentz-contraction, while on the right side there is only one, since il/isubp/sub is supposedly invariant. But as becomes particularly clear from (2), there is an additional problem, since emL/em is orthogonal to the x axis - recall that it was a projection down along this axis. Thus, if one performs a boost in direction x, the left side of the inequality (2) can become arbitrarily small, but the right side remains as it is. This equation thus can clearly either not hold in all reference frames or requires some serious modification of Lorentz transformations. The former would imply Lorentz invariance is broken, and this case is very closely studied and tightly constrained by experiment. The latter implies all the problems of DSR and more, since there needs to be taken care of the unusual way orthogonal directions are treated.br /br /Hogan clarifies in an email that he is considering the latter. With regard to the question of the invariance of the Planck length, he writes “The theory itself does not violate Lorentz invariance, but a particular apparatus or measurement does, by singling out a particular frame. There is no preferred direction in the theory.” And “I am working with the idea is that the Planck length really is fundamental and the same to all observers. An object can’t Lorentz-contract below that; instead, some other physics kicks in, such as Matrix degrees of freedom in M theory.”br /br /(a href=”http://arxiv.org/abs/0812.1285″Which I believe might refer to this recent paper/a.) With regard to the question of the relation of transverse boosts, he adds:br /br /“In a holographic theory, you can’t boost transversely; the wavefront is already moving at c. A boost would change the direction of the wavefront, and the observables.br /br /I admit to writing down the relations in an arbitrary lab frame. The relationships of the position states depend on the frame; if emL/em is Lorentz contracted by a longitudinal boost, the indeterminacy is less. In a highly boosted frame, emL/em becomes the Planck length, and the indeterminacy is also a Planck length, reducing to the Planck scale noncommutativity. You can’t boost more than that; in a holographic theory, once you have boosted that much, you have reached the 2D dual description, essentially living on the light sheet.”br /br /Incidentally, Giovanni Amelino-Camelia considered that gravitational wave interferometers might detect Planck scale noise already in a a href=”http://arxiv.org/abs/gr-qc/0306019″2003 paper “emQuantum-gravity-motivated Lorentz-symmetry tests with laser interferometers”/em/a. Without the holographic twist however, he concluded that the necessary sensitivity is out of reach.br /br /span style=”font-size:130%;”uBottomline/u /spanbr /br /Hogan is proposing an interesting modification of quantum mechanics that is holographic in the sense that it constrains the precision of measurements connected by lightpaths into directions orthogonal to each other. It is expressed through a modified commutation relation for position operators. The relation to the common Holographic Principle is not entirely clear to me, but it is an approach one can consider nevertheless. It does however necessitate a modification of Special Relativity in order to accommodate the invariance of the Planck length, and an appropriate transformation behavior of orthogonal directions. So far, Hogan’s model has not addressed these issues that I believe pose significant challenges as to its consistency. Though I find the possibility that Planck scale physics might already have been detected exciting, I would appreciate an exposition of the framework that clarifies these points. It is certainly a long shot but, you see, if your shot is long enough, you might reach a stable orbit.br /br /In reply to my suggestion to blog about it, Hogan wrote “On the blog, you are certainly welcome to post a piece on this — indeed I hope it will help raise more discussion about it. Up to now I am interacting more with the experimental community, who seem to have a more urgent need to understand it!” Thus, having done my part, your comments are welcome.br /br /strongUpdate:/strong Thomas Dent points out that unlike what I wrote the GEO600 noise was published in a href=”http://www.iop.org/EJ/abstract/0264-9381/25/11/114043″emThe status of GEO 600/em, H Grote et al 2008 Class. Quantum Grav. 25 114043/a, and plots can be found online a href=”http://www.geo600.uni-hannover.de/geocurves/files/s5/typical_s5_lpsd.png”here/a and a href=”http://www.geo600.uni-hannover.de/geocurves/files/theoretical/all_550_v4.png”here/a. It is unclear to my why Hogan’s papers do not refer to these publications.br /br /br /hr /br /span style=”font-size:85%;”* Let me add here that it is not clear to me what emL/em is in the general case, since we are talking about a “distance” between wave-functions whose position is an operator, whereas emL/em is a c-number. If you look at the definition of emL/em in Fig (2) of /spana href=”http://arxiv.org/abs/0706.1999″span style=”font-size:85%;”Hogan’s paper /span/aspan style=”font-size:85%;”you find that the operators xsub1/sub and xsub2/sub have suddenly lost their operator-hats. I am further not sure how the approach of this paper corresponds to that of /spana href=”http://arxiv.org/abs/0806.0665″span style=”font-size:85%;”later papers/span/aspan style=”font-size:85%;”. Thus, despite this pictorially making sense, I am missing an operationally well-defined explanation what emL/em is in the general case of this modification of quantum mechanics./spandiv class=”blogger-post-footer”"You do not really understand something unless you can explain it to your grandmother.” ~ Albert Einsteinimg width=’1′ height=’1′ src=’http://res1.blogblog.com/tracker/22973357-1045444488317587639?l=backreaction.blogspot.com’//div

I am presently readinga href=”http://www.amazon.com/European-Dream-Jeremy-Rifkin/dp/1585423459″ Jeremy Rifkin’s book “The European Dream,”/a which is quite an interesting comparison between the United States of America and the “United States of Europe,” as he calls it. It is as much about the American Dream as the dreamers and their European ancestors. The book is however full of sweeping generalizations. Though I can find some truth in most of what he writes, I find it hard to swallow statements likebr /blockquote“Americans covet exclusive space. Each person strives to be self-contained and autonomous. That’s why we put a premium on privacy. Europeans seek inclusive space - being part of extended communities, including family, kin, ethnic and class affiliation. Privacy is less important than engagement.”/blockquotebr /Which doesn’t make much sense if I consider Microsoft ran into problems with European privacy rights where Americans didn’t care. This morning a complete stranger told me her friend Gerald just had a triple bypass some days before his 70th birthday. Not that I asked. Maybe it’s just me, but these things happen to me constantly on this side of the Atlantic. I yet have to find a German who’d tell a random seat neighbor on a plane about her daughter’s affair with the pharmacist. So much about the Americans’ desire for privacy.br /br /Another example:br /blockquote“We Americans [...] if we can afford it, we’d much prefer to place our home at the very top of a hill, and at a distance from our nearest neighbors, afford us a daily reminder of our autonomy.”/blockquotebr /That must be why millions of Americans have gathered in mega-cities like LA, Chicago and New York.br /br /That being said, I am not sure how much to trust Rifkin’s elaborations on the American Dream either. Thus, I though I’ll pass on the question: what does the American Dream mean to you?div class=”blogger-post-footer”"You do not really understand something unless you can explain it to your grandmother.” ~ Albert Einsteinimg width=’1′ height=’1′ src=’http://res1.blogblog.com/tracker/22973357-6544275292646246711?l=backreaction.blogspot.com’//div