Wednesday, May 31, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Raccoons attack Fermilab



Figure 1: A raccoon. Sometimes they also steal biscuits. Also, it's unbelievable, but I have probably found the dog who likes racooons, even baby raccoons. The family seems to be building special relationships. ;-)

Accelerator update:

Tuesday May 30

The midnight shift began with Recycler and Pbar conducting studies, and with the TeV in a dry squeeze.

At 1:24 AM, Operations reported a raccoon terrorist attack on the Linac gallery. It seemed to be a coordinated effort. Fortunately, by 1:53 AM, a joint force of operators and Pbar experts managed to drive the raccoons out of their hastily made fortifications. Then at 4:18 AM, the raccoons made what some thought to be a counter attack on the Division Headquarters, but others believed it to be only a simple reconnaissance incursion. No raccoons or civilians were either injured or captured during these encounters. Operator losses were low.

Tuesday, May 30, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Duff and Kalkkinen: exotic spacetime signatures

Michael Duff and Jussi Kalkkinen have two papers

in which they study what happens with field theories and string theory under various sign flips. The most important one is the signature of the spacetime geometry: the authors show that various facts about the theory depend on the space and/or time dimension modulo four - because of various well-known properties of the spinors. They also try to flip the sign of the string coupling - note that this would give a negative tension to D-branes - and they try to combine various flips to see which BPS branes survive and which don't.

My attitude to these questions is conservative:
  • the spacetime signature with one time (excluding multi-time theories);
  • a positively definite Hilbert space (excluding wrong sign kinetic terms for physical fields);
  • energies bounded from below (excluding a negative string coupling and similar things)
are necessary conditions for the slightly general and slightly specific notion of "consistency" in physics. The mathematical description in other signatures is just a convenient way to analytically continue the physics in the physical signature - for example via the Wick rotation. There is probably no new physics in these theories with different signs; just new ways to look at the same mathematics and new methods to calculate various things such as the quasinormal frequencies.

New physics is only found if you can formulate your insights in the context of the physical signature. In most cases, especially in flat space, the role of different signatures is just to continue a quantity across the complex plane of a variable. According to my definition of physics, you must continue it back to the physical signature to see "physics". It's usually obvious that you have not done anything by such a procedure. On the other hand, I still believe that the role of complexification and analytical continuation of various things will become important for our more complete understanding of black hole information issues and quantum cosmology in the future. The tricks used in the entropic principle (OVV) might be an example how the continuation could solve the vacuum selection problem.

As you can see, what I find more interesting are the questions whether the signature of various objects above - spacetime geometry; positivity of fields; positivity of the string coupling - is allowed to be flipped in the Planckian, ultrashort distance regime. This is one of the questions that has led the Bogdanoff brothers to write their somewhat controversial papers. As far as I know, no one has published "more correct" answers to some of the questions they have attempted to answer.

Henry Paulson may replace John Snow

Henry Paulson, the CEO of Goldman Sachs, only has one quarter of the hits of your humble correspondent or one twelfth of the hits of Lawrence Summers who was doing the same job a couple years ago. He was nominated to replace John Snow as the secretary of treasury.

Given the fact that the department of treasury

  • prints and mints all coins and banknotes of the world's main reserve currency,
  • collects all U.S. taxes through the IRS and pays all the bills on behalf of the U.S.,
  • supervises all national banks,
  • manages the federal finances and the public debt,
  • advises on domestic and international financial, economical, fiscal, trade, and tax policies,
  • enforces financial and tax laws,
  • and investigates tax evaders, counterfeiters, smugglers, forgers - besides their struggle against spirits distillers and gun law violators,

I think that there should be more attention given to the identity of the person who is chosen for this work, and I offer you the following

He certainly looks like an intelligent gentleman. A website that predicted that he would be chosen one month ago, also points out that Paulson is the chairman of The Nature Conservancy (yes, the website is at nature.org), an environmental organization with the annual income around 1 billion dollars (that's not a typo). Nice hobby. ;-)

Andrew Chamblin Memorial Lecture Fund

You are invited to contribute to the Andrew Chamblin Memorial Lecture Fund which has been set up to endow a lecture in Andrew's name in perpetuity at the University of Cambridge.

There will be memorial services for Andrew in Oxford on June the 9th and in Cambridge on June the 10th. Please see www.andrewchamblin.org for specific details.



Figure 1: Picture by Clifford Johnson

Please: any nonzero amount will be helpful. Because I didn't feel too rich or financially safe, I contributed $30 only: the cheque was sent from Cambridge in New England (which means in America) to "Cambridge in America" (which actually belongs to the English Cambridge). Colonization and especially decolonization may be confusing.

You will find the relevant PDF or WORD files for the U.S. or the rest of the world at this website:

Think about it and ask your colleagues, especially those who knew him, to think about it, too. Andrew Chamblin deserves it.

As soon as you decide to send the form, indicating that the gift is for Andrew Chamblin, together with your cheque or your electronic card number, you may also want to inform Jo Ashbourn
  • hacmemorial [at] yahoo [dot] co [dot] uk
so that she will add you to the list of donors if you wish to be added, or let her know that you prefer your contribution to remain anonymous. If you find snail mail inconvenient, you can also send "N" dollars and 64 cents where "N" is integer (identification) to me via PayPal, and every time the accumulated money exceeds $30, I will send all the collected resources to the fund.

Warning: PayPal subtracts a percentage for the operations and it can't be guaranteed that the amount you pay will exactly agree with what the fund receives; the paypal method is preferred for anonymous donors.



Don't be afraid to click the icon above. Several additional clicks are needed to complete the transaction.

Ooguri and Vafa's swampland conjectures

Today, I single out the first hep-th paper:

Hirosi Ooguri and Cumrun Vafa extend the swampland strategy how to crack the secrets of quantum gravity by formulating five conjectures that the set "M" of all consistent quantum gravity backgrounds (which is assumed to be the set of backgrounds of the fully "completed" string theory) probably satisfies:
  • "M" is parameterized by expectation values of dynamical scalar fields, i.e. there are no adjustable non-dynamical continuous parameters in string theory. That's a well-known piece of string theory folklore.
  • for any point "P0" of the moduli space "M", there exist points "P" in "M" that are arbitrarily far from "P0"; the metric is measured by the kinetic terms for the scalar fields defined as fields in the large dimensions. In other words, the diameter of "M" is infinite regardless of the way how you look at "M". Note that this is true despite the fact that the volume of the moduli space is finite whenever its dimension exceeds one, according to the first swampland paper.
  • in the previous picture, as you take points "P" that are very far from "P0", by distance "D", you will find a whole infinite tower of states whose mass is of order "exp(-A.D)" where "A" is a coefficient (exponent). We have an exponential in the formula because in the most obvious example, the distances are measured by the differences of the dilaton, and the powers of the coupling constant are exponentials of this dilaton. The existence of new light states may imply a breakdown of effective field theory, following particular rules.
  • the scalar curvature of the moduli space "M" near these points at infinity - where "P" lived - is never positive; the space resembles a saddle in these regions. The only way how the inequality may be saturated is that you deal with a one-dimensional moduli space.
  • every one-cycle in the moduli space "M" is contractible to a vanishing distance. This is morally true because otherwise the winding number around the moduli space, in the context of a compactification on a circle, would have a global symmetry (counting the winding number) and global symmetries don't exist in quantum gravity.
All these rules seem to be true in string theory but could be violated if you used a naive field-theoretical approach to quantum gravity. Your task is to verify these conjectures or disprove them, and if you don't disprove them, you should eventually prove them. ;-)

Monday, May 29, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Hep-th papers on Monday

Oriol Pujolas looks at the DGP model. If you don't know, the DGP model is a popular model among the phenomenologists in which you have a five-dimensional gravity with a 3-brane in it, and the action contains both the bulk 5-dimensional Einstein-Hilbert term ("integral R.sqrt(-g)") as well as an additional 4-dimensional Einstein-Hilbert term that is stuck on the 3-brane. The latter term is unlikely to appear in string theory, I think. At distances shorter than a crossover scale - usually assumed to be the Hubble scale without a good reason - gravity looks 4-dimensional. At longer distances, the bulk term starts to dominate and gravity is 5-dimensional. Pujolas studies quantum fluctuations in this model: the author computes some Green's functions, and a one-loop effective potential arising from the quantum fluctuations.

J.C. Bueno Sanchez and K. Dimopoulos study a new kind of inflation based on a rolling scalar field - a quintessence. Although the picture is string-inspired, it does not seem that they are talking about a specific well-defined background in string theory. Their description of the "trapped quintessential inflation" has many stages and it reads like a novel. The first stage of their inflation starts in a steep potential, hypothetically generated by non-perturbative effects in string theory. Then you reach an ESP - enhanced symmetry point - where you produce a lot of light particles. They argue that this leads to a period of inflation which I don't quite understand; is a strong particle production compatible with inflation? At any rate, the scalar fields eventually leave the ESP point and go into another steep region, which gives you reheating. Then the scalars freeze because of cosmological friction. It is fixed for a long time until the present, when it starts to behave as a quintessence and roll towards vanishing vacuum energy. A pretty complicated picture combining many pieces that are popular. It seems that we don't have enough data to check each wheel and gear of the construction (and similar constructions). As far as I am concerned, the "supply" of various detailed proposals about inflation exceeds the "demand" - as expressed by the observational data and the need to reconcile interesting ideas - by orders of magnitude.

Sunday, May 28, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Climate change: leading by example

In 1998, a famous company received the Climate Protection Award from the Environmental Protection Agency (EPA) for its

  • examplary efforts and achievements in protecting the global climate.

The company became even more famous in 2002. The company is popular with the media again. If you make a search at news.google.com for the company's name, you will receive 16,500 articles.

In a document linked below, the company declares itself as a key leader of the struggle against the climate change. Do you know which company we're talking about? The ecoterrorists among the readers surely praise the company at this moment and dream that the whole world is able to reconcile economics and environment as well as the company ;-), while they think that my negative relation to that company's policies is unjustified. If you still don't know which company it is, look at this PDF file posted on Steve McIntyre's blog.

One of the lessons of this story is that you should think twice before you decide whether you consider awards from environmental agencies to be a good sign or a bad sign.

Short world news:

  • During his visit to Auschwitz, Benedict XVI has criticized God for being silent during the era of holocaust. God was not available to comment on the criticism.
  • The earthquake in Indonesia killed more than 4611 people.
  • Microsoft will include a "JPEG killer" with Windows Vista, namely a new format WiMP - which does not stand for Weakly Interacting Massive Particles but rather Windows Media Photo. The same quality of pictures will take 50% of JPEG space only.

Gore: climate change is a religious issue

Al Gore has been saying that the global warming is a spiritual issue for some time. Now he has changed it to a purely religious issue during his performance in the New York City. He said:

  • Every faith tradition has teachings that are directly on point [to climate change]. ... The Book of Revelation [says] God will destroy those who destroy his creation. Whatever works. ... Noah was commanded to preserve biodiversity. ... If you believe what [NASA scientist] Jim Hansen said just a moment ago - if you believe, if you accept the reality that we may have less than 10 years before we cross a point of no return - if you believe that, this is a time for action.

Nevertheless, some people still argue that blinded religious bigots must always be Republicans. ;-)

Colombia: Uribe will be re-elected

A Harvard alumnus is going to win the second term as the president of Colombia. He will score 62% of the vote, The Reference Frame predicts, and be sure that we're right.

Alvaro Uribe who started in the Colombian Liberal Party (moderate social democrats) is very popular especially because he has been successful on the security front. For example, the number of murders dropped from 36,000 per year 2002 - when he was elected - to 15,000 in 2005.

Recall that Colombia used to be paralyzed by the Marxist guerillas, a rather weak government, and right-wing paramilitias that tried to do the job that the government was not able to do: to establish the order. The armed left-wingers are not only exterminating villages but also support drug trafficking: one half of cocaine sold on the streets of the U.S. and EU comes from the guerillas.

Indeed, things are black and white in this country.

What was Uribe's strategy? Well, his strategy to bring peace and order to Colombia was obvious: to shoot every armed communist that can be found but cannot be arrested, and to do it so efficiently that the paramilitias will accept that they are no longer necessary and can be disarmed. Sorry to say but the armed communists who simultaneously work as labor leaders undermining the Coca-Cola company should be no exception.

Shooting the Marxists was probably never too difficult for Uribe because the communist thugs from FARC have killed his father in 1983 - and of course they have also tried to assassinate Uribe himself many times. Uribe claims that the country must choose between him and a catastrophe, and he is probably close to the truth. What is the name of the catastrophe?

The first name of a rival is Carlos Gaviria who is a commie himself. Instead of praising Uribe for the clearly right approach, the communist rival criticizes Uribe for being a friend of the U.S. Fortunately, Uribe is 35 percent points ahead of Gaviria. Among other things, Uribe has signed a free trade treaty with the U.S. The GDP growth in 2005 was 5.3%, exactly like the 1st quarter of 2006 growth in the U.S.

I wish them the best, and I hope that once they completely defeat FARC, they may also be able to deal with the supporters of terrorism in neighboring countries - such as the bastard named Hugo Chavez in Venezuela.

Steinhardt and Turok: cyclic model and cosmological constant

Paul Steinhardt and Neil Turok propose their solution of the cosmological constant problem

based on the cyclic model. See also the Science magazine. What is their key idea? The full age of the Universe is not the usual 13.7 billion years but much more: exponentially more. The boring de Sitter eras take a lot of time, but the Universe always eventually collapses and starts a new life cycle. During this process, the value of the cosmological constant may be reduced: imagine the cosmological constant to be the potential energy of a complicated axion field.

This picture differs from the anthropic explanation because in their model, if you imagine that someone makes it truly well-defined (or even embedded in string theory), the cosmological constant is essentially a function of the total time since the beginning of the Universe. Because the relaxation time gets longer as the cosmological constant approaches zero, most of the time is spent in regions with a small cosmological constant. The small value is generic - unlike the anthropic picture where the small values are rare.

Although their explanations why the vacuum energy is small may look statistical, chaotic, and similar to the anthropic reasoning to us, the previous paragraph makes a lot of difference. They voice my usual counter-argument against the anthropic reasoning using rather clear and convincing words:

Gravity waves and spin entropy

New Scientist has promoted the following preprint

that proposes a method to observe gravitational waves via spin entropy and spin entanglement. Several people say that it is "quite an achievement" and there are only "some technical issues" that should be resolved. Frankly, I have no idea what they are talking about.

The basic mechanism underlying these 9 pages is the following simple fact.

Consider a particle with a well-defined momentum (or a wavefunction in the momentum space) and a well-defined spin state. Two-component spinors are always eigenstates of the angular momentum with respect to a particular axis in three dimensions. The particle discussed in this paragraph is described by a wavefunction that is a tensor product of the momentum state and the spin state.

Now you may want to boost the particle and switch to a difference reference frame (but please, don't switch to another blog - you won't find another Reference Frame anyway). The wavefunction in the new frame will no longer be a tensor product. You can easily see why: the wavefunction is not an eigenstate of any angular momentum in the new frame because the angular momentum in the new frame is the old angular momentum mixed with the boost generators in the old frame - and the state was not an eigenstate of the boost generator if the momentum wavefunction was general enough.

Friday, May 26, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Windows Media Player 11: cute

A reader has reminded me of

which is Microsoft's gift from the future. It will be a standard part of the next Windows operating system, Windows Vista, formerly known as Longhorn. So I installed it.

The installation of WMP11 is a moderately non-trivial event because the program can only be uninstalled by System Restore. But I assure you that you won't need it. Everything works, everything is smooth, and all bad reviews are invented by anti-capitalist Microsoft haters and should be ignored.

The design of WMP11 is simple and beautiful. When you play a video, the space is used efficiently even outside the fullscreen mode. The way how the songs, albums, and videos are viewed resembles Google Picasa2. In fact, your picture galleries may be viewed, too. Moreover, you may have been annoyed by a small bug of the Windows Explorer: the thumbnails of videos often showed a black rectangle only because it was the first image in the video. That no longer happens inside WMP11: a more intelligent picture from the bulk of the video is chosen instead.

The installation is straightforward and the settings from WMP10 may be kept.

WMP11 is available for all Windows XP Service Pack 2 editions. That includes Windows XP SCBUEB edition, both in the Professional and Home Edition varieties. If you don't know, Windows XP SCBUEB edition is the edition semi-castrated by the upgefuc*ked Eurobureaucrats. Instead of the proper full name, it must be called "Windows XP Professional/Home Edition N" on the territory of the EU in order to indicate that it is as good as the full Windows XP. It does not include any media player at all but the price is the same. ;-) A typical invention of smart eurobrains.

Every continent contributes something to the humankind, according to its innate aptitudes. America gives the world WMP11 - and URGE, a new online music purchase system that won't make Steve Jobs terribly happy - while my old Europe gives the world Windows XP SCBUEB edition. ;-) At least, the eurobrains are not powerful enough to prevent the SCBUEB users from downloading WMP11.

If you have not seen Microsoft's maps for some time, you should look at

It offers road, aerial, and bird's eye views, and may very well be better than all competitors.

Clifford Johnson and the word "theory"

Clifford Johnson has informed us that the most irritating thing he has encountered during his visit to his homeland was the phrase "special law of relativity" written on this poster with Albert Einstein in the London Museum of Science.

What does your humble correspondent think about these issues and Clifford's opinions?

Clifford has no problems

First of all, I am somewhat jealous that Clifford has the problems he has. ;-) Imagine. During a visit to one of the most important countries of this monstrous world - which is itself a shi*tty place as a classic noticed - a nearly invisible word "law" replacing the usual word "theory" is apparently the most breathtaking threat for our civilization.

The only Clifford's problem is that next Monday, his co-bloggers will effectively expel him from Cosmic Variance - or at least he will understand their remarks in this way - and he will announce it on this URL.

Let me start with some positive feedback.

I agree with Clifford that the proud scientists in 2006 are using the word "theory" as a compliment: a "theory" is a finite set of ideas, concepts, laws, and equations that is capable to describe a class of phenomena that have already been observed, and to predict features of new phenomena that may be observed in the future. A theory is the best result of a scientific or rational analysis of the world you can dream about.

Wednesday, May 24, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

New values of "g" and the fine-structure constant

Gerry Gabrielse, an experimenter from Harvard University, and his collaborators are going to announce new, more accurate values of the fundamental constants. Using their single-electron quantum cyclotron, they can see that the new magnetic moment of the electron is

  • g/2 = 1.001 159 652 180 85 (76).
As you can see, there are 13 significant figures or so - the value is six times more accurate than ever before. Using the cyclotron result for "g" above plus QED theorists from other universities, they can also deduce the value of the fine-structure constant. The theoretical calculation, starting with the terms
  • g/2 = 1 + alpha / 2 pi,
requires to calculate 891 diagrams with up to four loops, and the result for the fine-structure constant
  • 1 / alpha = 137.035 999 710 (96)
is ten times more accurate than the results from atom-recoil measurements. In fact, it is the first improvement of the accuracy in roughly 20 years. The precise value is sensitive on new physics at 130 GeV. All skillful numerologists are welcome to interpret the new data.

Tuesday, May 23, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Seth Lloyd: counting quantum operations in spacetime

Sean Carroll has written a bizarre text praising Slavoj Žižek and comparing him to Seth Lloyd, a quantum computation expert from MIT. ;-)

If you don't know, Žižek is a Slovenian postmodern philosopher and a science-hater, the kind of "smart guys" who have provoked Alan Sokal to write his hoax and submit it to Social Text. The real motivation for Alan Sokal's hoax was a political one: Sokal couldn't stand the fact that the postmodern philosophers and literary critics make it far too obvious that the core of the Left is intellectually pretentious, hypocritical, anti-scientific, and vacuous: Sokal himself is a leftist but a rational one.

On the other hand, Sean Carroll indicates that the only reason why he does not make the postmodern philosophy a starting point and punch line of his research - and why he only focuses his blog writing on these paradigms - is that it might be rejected by the referees.

Hep-th papers on Tuesday

Let me summarize each of the 24 hep-th papers that appeared last night.

Freed, Moore, and Segal argue that the electric and magnetic fluxes on a spacetime manifold can't be measured simultaneously because of a version of the uncertainty principle. That should not be unexpected. Only the electric potential or the magnetic potential may be chosen as a fundamental degree of freedom which makes their fluxes well-defined for a given configuration: the fluxes of the dual field are then undetermined.

Moreover, the authors argue that the uncertainty principle only applies to torsion classes. One of the implications is that the K-theory class of the Ramond-Ramond fields can't be physically measured. There also exists a less mathematically formal version of that paper even though I am a bit confused which of the two is addressed to the physicists. The insights have special consequences for self-dual form fields; they're connected with Pontrjagin dual groups.

Monday, May 22, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

David Weld: Cavendish-type experiments

David Weld from Stanford spoke about their Cavendish-type gravitational experiments. At distances around 20 microns, they can rule out a new force that would be 10,000 times stronger than gravity. In other words, if you parameterize the potential energy as gravitational plus Yukawa,

  • E = G . M . m ( 1 + alpha exp (-r/r0) ) / r
then assuming that r0 is around 20 microns, they can experimentally show that the absolute value of alpha must be below 10,000 or so. The paper about their previous experiment is here and we described it here. Unlike the torsion balance experiments (see also Eot Wash), their apparatus is spinning rather quickly. The apparatus involves piezoelectric bimorfs, laser interferometers, motors that work at low temperatures, cooling system, and many other things. We have discussed the submillimeter experiments many times which is why I won't repeat the details now.

Rotating black holes must be axisymmetric

Hollands, Ishibashi, and Wald offer their proof that rotating black holes, even the higher-dimensional ones, must be axisymmetric. In other words, they always admit a "rotational" Killing vector field. You should realize that the horizon is not necessarily spherical anymore if the number of spacetime dimensions exceeds four. A previous blog text about higher-dimensional black holes' uniqueness and unusual topologies was here.

Sunday, May 21, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Identity of CapitalistImperialistPig: poll

Update 2011: The right answer is actually not Kevin E. Cahill, as David M. told me, despite a huge number of similarities. The right answer is Edward Measure, a military's atmospheric scientist in Las Cruces, New Mexico. Note that the favorite quote on Facebook coincides with the quote on Pig's blog. In 2004, I exchanged an e-mail about string theory with Measure. He loved Zwiebach's book, among other things. In the following years, I was aware that Pig was visiting my websites from Zianet in Las Cruces.

Update: In 2009, pig claimed to be from Montana. An environment guy who was born in Helena, Montana and who moved to New Mexico is Paul Lavigne.
Frequent readers know CapitalistImperialistPig, often abbreviated as CIP. His blog is here:

CIP has been trained as a physicist, he has worked on atmospheric science most of his life, and is "damn mad at the moment". We know that he is 3/16 German and 1/16 Czech. The profit from stocks is enough to assure his happy life. CIP has told us that his wife is a teacher. His location is described as a Nowhere State University in Southwest USA.

Those of us who can track visits to our blogs know that the university is New Mexico State University and it is located in Las Cruces, New Mexico. His internet provider is zianet.com which is not much information because many people use it in New Mexico, don't they?

Who is CapitalistImperialistPig?
August Miller
Henry Rachele
someone I will mention in the comments
someone else
mysteries should remain mysteries
Free polls from Pollhost.com

Candidate 1: August Miller

August Miller is a professor emeritus at that university in the physics department and has been working on atmospheric science. He uses the zianet.com internet provider. The last name is German. His wife, Darlis Miller, is an emeritus professor, too. Miller is an amateur radio enthusiast with many e-mail addresses.

Candidate 2: Henry Rachele

Henry Rachele got his bachelor degree as a mathematician and physicist, much like the first graduate degree. Then he moved to meteorology where he worked most of his life, for the U.S. army labs in New Mexico.

Candidate 3: Ronald Pinnick

The last name of Ronald Pinnick sounds like "Pig". After working on nuclear tests, he was into atmospheric sciences, and is now in the CS directorate.

CIP: hint

CIP says that "he knows both of them, especially Henry" but he argues that "he is neither Henry nor Gus". So it is up to you to solve the puzzle. Incidentally, when you're learning Czech, be careful, especially if there are ice-hockey players around.

Saturday, May 20, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Princeton videos

On the page of

you can find many interesting lectures, for example

  • David Gross (4 lectures), introduced by Edward Witten
  • James Baker, ex-secretary of state
  • Tim Berners-Lee, inventor of the web
  • Hillary Clinton
  • Seymour Hersh, investigative journalist
  • Noah Feldman
  • Vera Rubin, co-discoverer of dark matter
  • Roger Penrose: Fashion, Faith, and Fantasy
  • Juan Maldacena
  • Lech Walesa

Revenge to a distasteful minister

If you want to see a newer video, namely from today, you can see this

  • communication between the former and current healthcare ministers of the Czech Republic

The former minister said: Before I start to moderate, allow me to deal with one purely personal issue. Thank you. - Smash. - Mr. minister Rath was warned in advance. I warned him through the press. It is my purely private matter. He deserves it. - Many dentists applaud.

BBC reports here.

A music videoclip is here.

A parody is here.

After the current minister returns, he says: Mr. doctor. We won't be solving it here. You attacked me from the back as a coward. Why didn't you face me as a real man? You are a coward! - Smash. Boom. Bang. Mr. Macek had to leave the conference hall. He explained that he hit Mr. Rath for educational purposes, and in order to defend the good name of Macek's wife: Rath claimed in the press that Macek only married her because of her money.

Friday, May 19, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Roger Penrose vs. holography

First of all, let me mention that Roger Penrose is a great mathematician, a highly influential mathematical physicist, and an original thinker. We mention his name hundreds of times every day in connection with many discoveries. For example, we investigate the Penrose limits of geometries; the Penrose causal diagrams; twistors; many other notions in general relativity (including methods to extract energy from rotating black holes).

Many people know the Penrose triangle or Penrose tilings. Our colleagues outside the mainstream also like the spin networks that he invented decades before "loop quantum gravity" was constructed.

Two weeks ago I was asked to comment on Roger Penrose's remarks about holography. His text will be written in italics and my answer in Roman fonts. Because it is based on a fast e-mail, the text below won't be perfect.

To summarize, Roger Penrose believes that holography must be wrong. Because some of his errors are easy to catch, let me make this comment public.

Roger Penrose: 31.16 The Road to Reality

Ecoterrorists attack Rona Ambrose

Rona Ambrose, the environment minister of Canada, is not only the official Canada's sexiest politician but also a potential new Iron Lady of Canada. ;-)

She realizes that the Kyoto protocol is expensive madness without any positive measurable effects. Moreover, Canada can't reduce the CO2 emissions as planned which is another good reason for Canada not to like the international treaty. Instead of the expected 6% drop of the CO2 emissions, the previous hypocritical liberal government led the country to a 35% increase.

Ambrose also realizes that Canada only produces 2% of the world's emissions. Surely the importance of Canada in similar issues is and should be well above 2%. The country is able to invent and install new technologies at places where it really matters if it turns out to be desirable.

The list of ecoterrorists who are not only uglier and less reasonable than the Canadian minister of environment ;-) but who are also overly aggressive and who attempted to attack Stephen Harper and Rona Ambrose includes

Shame on all of you. Incidentally, if you ask why I use the word "ecoterrorist", let me tell you that by ecoterrorism, I mean sabotaging industry, institutions, private and public assets, and factories whose working is important for the whole population, justified by arguments based on their "struggle for the environment".

Thursday, May 18, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Alex Vilenkin: probabilities in the landscape

Prof. Alex Vilenkin whose previous seminar was described here gave a talk about

  • The probabilities in the landscape.
Nima Arkani-Hamed introduced the speaker as a hero for many of us and a villain for others. Well, I was proud when I suddenly understood Nima's pun so I did not resist to announce my discovery. ;-) The speaker did a good job and did not get irratated by skepticism of some people in the audience. Of course, he realizes that the topic is somewhat controversial.

The probability distribution for different vacuum-depended quantities such as the cosmological constant is the product of
  • P = Prior times SelectionFactor
The first one measures the total fraction of the multiverse volume occupied by pocket universes or vacua with the desired value of the quantities. The second one measures the expected density of intelligent life in the given type of vacuum. If defined properly, it is the product of the density of stars, percentage of right-wing voters, percentage of people who understand string theory, percentage of people who read The Reference Frame, and several other factors.

Prof. Vilenkin explained that it is the SelectionFactor that drives many people up the wall. Well, it may be fair to say that I am driven up the wall by both of these factors. :-) The talk focused on the first one, the Prior.

The speaker showed beautiful colorful diagrams of the pocket universes. Each pocket universe starts as a bubble that expands, and inside this bubble, it looks like an FRW universe to the inhabitants but there can be many new bubbles inside each bubble - like M&M's inside bigger M&M's (or electrons inside electrons which are Universes, as Lenin believed).

In the causal diagram, you have the upper wedges attached to the far future (a horizontal line) representing the bubbles, and smaller bubbles inside them. The pictures are entirely hierarchical and there is no bubble collision in this model or any other causal relation between the different bubbles.

The task is to find the right measure that tells you which fraction of the volume of the branching bubbling multiverse contains one type of vacuum or another. The speaker (and Nima) explained that it is easy to create diffeomorphism invariant measures based on geodesics and proper distances, but there are infinitely many such definitions.

Their particular new breakthrough is based on the following construction. Take a minimal-surface 3D spatial slice across your universe at any moment. Fill it with many points. Draw geodesics from all these points directed into the future (that start as lines orthogonal to the slice). Each geodesic, as it continues to the future, will be visiting many types of universes and bubbles. You measure the relative abundance of a given type of a universe: Vilenkin argued that such a definition can be quantified with a finite length geodesic and the limit where the geodesic proper length goes to infinity exists.

Toby Wiseman did not like that the geodesics were treated as special trajectories. Well, I tend to think that geodesics are special and there are other laws of physics in which we have good reasons to think that the geodesics differ from other, more generic curves in spacetime. But I am not sure whether the anthropic probability distributions belong to the set of physical laws in which we know that geodesics play a special role. ;-)

Nima had some doubts about the existence of the limit. He was uncertain whether it is true that one half of integers are even (and thinking about other examples where the ratio could be ill-defined). Vilenkin argued that it is OK to say that one half of integers are even, and the limit in his construction is equally well-defined.

The final "prior" determining the weight of a given kind of vacuum in the probabilistic distribution (the prior) is obtained as the product of the relative abundance of a given vacuum along any chosen geodesic, explained above, and some reference scale volume "R^3" of the universe in a given bubble:
  • Prior = RelativeAbundanceOnGeodesic times R^3.
Recall that this prior must be multiplied by the expected probability of intelligent life to get the final predictions. Vilenkin also showed an independent equivalent derivation - by other anthropic authors (including Linde?) - of the same "Prior" where the distance of the different geodesics on the initial slice is not "epsilon" but rather "1/N". Honestly, I have not understood what's different between these "two" derivations except that "epsilon" is called "1/N" - and why I should view it as an independent or dual confirmation of anything.

The speaker has also mentioned other definitions of "Prior" that lead to different results.

Using the terminology from this blog's controversies, Cumrun Vafa protested and argued that one cannot operationally define these conjectured "probabilities" because they don't admit a frequentist definition. Since they are only based on untestable Bayesian reasoning, they should not be subject to scientific thinking.

One general "positivist" philosophical lesson of quantum mechanics, Cumrun argued, is that we should only talk about quantities that can be measured. As you can imagine, I knew very well where Cumrun was coming from, so that I can even add the right philosophical buzzwords to Cumrun's arguments :-), while Nima disagreed. Nima argued that we should replace the word "probability" by the word "confidence" and everything would be OK.

As far as the anthropic reasoning goes, I agree that such a confidence is calculable and the result that I obtained is zero. Don't worry: it is not a no-confidence vote; what we see is just a lack of confidence. ;-)

Vilenkin showed that their more refined analysis questions the uniform probability distribution of the cosmological constant in Weinberg's anthropically allowed anthropic interval "(-L,+500L)" where "L" is the observed value. The famous anthropic physicist from Tufts University argued that there could exist peaks and they could even exhibit a fractal structure.

Nima got a bit nervous because this was potentially bad news for the anthropic principle because this fact would naturally predict a higher cosmological constant than the observed one, and he immediately offered a one-sentence argument that everything is OK anyway :-), an argument that I cannot reproduce because I did not understand it.

Vilenkin said that by this single sentence, Nima has essentially scooped the speaker and presented the rest of the talk as Vilenkin planned it. ;-) On the other hand, Nima's argument was based on the hypothesis of a very large number of Universes, and Vilenkin said that this is not what the argument should be based upon.

Nima speculated that with a large number of universes the fractal structure can't arise because of the ergodic argument. In statistical mechanics, one must also assume the ergodicity as a first principle that can't be proved, so it is the same thing. Fortunately, when I mentioned that ergodicity can be proved for any particular ergodic statistical mechanical system - and when Vilenkin confirmed that point of mine - Nima agreed that the situation is not the same one after all. ;-)

Nima also added many interesting stories to this colorful seminar, including the observation that Nima was neither Chinese nor a bacterium, in a contradiction with the generic anthropic argument. For example, he also told us that there exists a program that can calculate whether the success of a physicist is a random fluctuation. The probability for Edward Witten is "10^{-192}" which is a rather small number. Given this non-generic fine-tuning, I asked Nima whether Witten should believe the anthropic principle even though the generic predictions fail so miserably for him. Nima essentially agreed that the answer is No. My next argument is - if Witten does not believe, why should the rest of us believe it? ;-)

Maybe the intelligent life should be defined to be just Edward Witten himself, which leads to predictions that differ by 192 orders of magnitudes from the anthropic predictions if some details are modified. There were other uncertainties in Vilenkin's calculation that could change the results by 240 orders of magnitude: for example, Vilenkin mentioned that some people do not include the volume into the probabilistic measure. A funny aspect of these discussions is that one can't quite distinguish which of the considerations are jokes and which of them are meant seriously. At least I can't distinguish them.

Earlier during the talk, Cumrun Vafa mentioned examples that lead to the same conclusion. He argued - and once again, I completely agree with him - that there are quantities whose values are non-generic because extreme values are needed for intelligent life. The amount of non-genericity of these quantities simply measures how lucky we are and good luck can't be used as a starting point for a quantitative calculation or justification of anything.

Vilenkin disagreed and responded with the example of the CMB quadrupole moment. It is just one number. Does it mean that it has no scientific value? Imagine that it is 20 sigma from the value predicted by your theory. Does it mean much to you? Needless to say, the answer of all colleagues who enjoy the Bayesian and anthropic reasoning is Yes. The answer of Cumrun and mine is essentially No. Science only becomes quantitative if its experiments are repeatable and its numerical predictions can be made increasingly more accurate. That's neither the case of the probability distribution in the landscape nor the case of a single multipole moment.

We just can't build the whole science on one number whose probability is "P", even if we would guess that a fundamental theory predicts a rather small value of "P". The reasoning based on one number is numerology. Science is about predicting a large number of quantities, preferrably an infinite number of quantities. If a theory only predicts one number, then it's not really a scientific one.

These debates have occured many times and most of us are becoming insensitive to the built-in controversies. The frequentist positivist people like Cumrun or me are convinced that this reasoning can't lead anywhere, and the anthropic people keep on trying. Good luck to them. ;-)

Luminiferous aether and physical motivation

101 years after the discovery of special relativity, some people still think that the luminiferous aether was a well motivated idea.

LDM wrote:

  • “If, as in those days, you believed in Maxwell and the wave equation, it was a VERY well motivated question to ask ‘what is it that is waving’ when light waves (not photons) propagate.”

Dear LDM,

the question “what is waving” was never physically motivated and only the people who misunderstand not only relativity but also the rudimentary philosophy of physics can say something else in 2006.

The aether is recognized as a gigantic dead end, a useless superconstruction, and a wrong theory, and it has always been one. The only positive thing about the aether is that some of the people who believed it in the 19th century have also done some extremely serious and important physics, unlike most of their followers in the 20th and 21st century.

The reality of Nature is encoded in the set of mathematical equations - Maxwell’s equations in this case - and they are the main story and the full story. Naive mechanistic ways to imagine “what is waving” should only be created for children in the kindergarden or other people who have some intellectual limitations that prevent them from understanding that equations themselves can be fundamental and they are fundamental and that the fields can live in empty vacuum.

Amplitude for existence of spacetime points

Monica Dance proposes to replace the metric tensor with one scalar field E(x) that is not really a scalar field and that gives points a nonzero probability to exist or not exist. ;-) Not sure why she thinks that this will mimick the metric tensor and Einstein's equations.

Nothing against her original ideas: they are exactly the type of alternative thinking about quantum gravity that Peter Woit and Lee Smolin, among others, have been calling for in the last many years, and they are still doing so.

One of them suddenly blames arXiv.org for accepting this kind of papers. It is hard to find a more obvious example of hypocricy because this paper is exactly the type of research that they want everyone else to do.

Wednesday, May 17, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Leonardo Rastelli: generalizing Schnabl gauge

Leonardo Rastelli (formerly from the #1 school in this list, now at YITP in Stony Brook) gave an intriguing talk at MIT about their

on string field theory. It is the first work by really famous authors (except for Yuji Okawa from MIT - sorry other guys if I missed someone) that depends on Martin Schnabl's exact solution for the tachyonic minimum in string field theory. Their main goal is to find the explicit solution in different gauges than Martin used.
The reader is expected to have read the previous article about these issues.

Leonardo started with some introduction to string field theory, surface states (the meaning will be explained below), and other concepts. He often used the level truncation calculation of various quantities which seems as 20th century physics to me. Once exact solutions can be found, the "miracles" that the level truncation works become rather unsurprising.

The fact that Martin's state solves the equations of motion implies infinitely many generalized Euler-Ramanujan identities. Barton Zwiebach showed these identities to Jeffrey Goldstone (MIT) - the father of X different bosons where X is the number of broken generators - and Goldstone said: these are recursive relations equivalent to a differential equation. So they found the right differential equation, generalized it to other values of "s", and solved it for each "s". For each "s", they have something that generalizes Martin's setup. For each "s", they have a closed subalgebra of the star-algebra of string fields.

Some videos

Here's a list:

Tuesday, May 16, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Be big

I just returned from the airport. Additional 4 hours have probably solved it. The negotiation at the airport took one hour because the smart woman from the yesterday's telephone reserved a flight from Frankfurt that departs 12 hours before the previous connecting flight arrives in Frankfurt. Usually it is the other way around: first you arrive at the airport, and then you depart and continue to another city. But apparently causality is not quite a universal rule. :-)

The FAS faculty meeting is getting started right now. Larry will definitely say a lot of wise things, and I am sure that even the segments will realize that what he says is deep and true. But I don't have to see it. When I was walking around the Science Center, Lisa and Melissa were making fun of me that I was not going to see "my man". Surely this is a lost battle and there is no point in seeing triumph in the politically correct, feminist faces. People who shared my ideals had to watch similar events in 1917, 1933, 1948, August 1968, and in many other moments of the human history.

Wednesday update: the meeting is described here.



Figure 1: Be big, Summers told the undergrads on Monday evening.

Fun dinner

I have just returned from the annual Society of Fellows dinner in the Fogg museum; a previous report from a similar event is here. It was a lot of fun. I have consumed about 6 glasses of Scotch with water, white wine, red wine, and champagne, and my immediate inability to determine the equilibrium horizontal SO(2) subgroup of SO(3) (or to hit the right key on the keyboard) is far from being unmeasurable. I am curious how this text will look to me tomorrow. ;-) As you can guess, I am trying to make the influence of the alcohol undetectable but it is not quite a trivial task. One thing seems clear: the human ability to control himself or herself can be compromised by toxic compounds a lot before the influence becomes truly damaging. ;-)

The event has been entertaining and one could have learned many things. Diane Morse, the secretary of the Society of Fellows, was celebrating 60 years last week so we were singing stupid drunk songs for her - congratulations! - and I was sitting next to Amy who is currently an extremely helpful part-time assistant of Diane. She told me a lot of interesting things, for example about her four-day-long stay in Canada after 9/11/2001 - the day of my PhD defense. She also follows all the stories of the daughters and sons of the recent fellows and the fellows from the recent past.

Monday, May 15, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Floods: what are newspapers good for

One of the 680 articles about floods in the Boston area randomly appeared in front of my eyes. Without these articles, I would not know that we are just in the middle of the worst rains in 10 or 70 years. If you look out of the window, it's not even raining right now and people don't have any umbrellas. According to the newspapers, you would almost expect an armageddon. Well, it's not an armageddon but a good time to try your canoe.



Figure 1: Men canoe down Central Street in Peabody, MA, today (Reuters photo).

Changing flights

Most of the billions of visitors will probably not be interested in this story, so please skip it. ;-)

I have just spent 4 hours on phone with Continental Airlines. Sometimes their system starts to beep instead of responding, sometimes the woman is not quite able to find the right flight and after 2 hours of discussions and silence that leads nowhere, my telephone runs out of battery.

Eventually another woman told me that there is a chance that the flight will be changed, as I was originally promised because they were not able to sell me a round trip ticket that would last for more than 9 months. But I will have to spend a few more hours by calling them tomorrow, and even if I am lucky, I will have to pick the new air ticket from the Logan Airport.

Still, the Continental Airlines flight for $1100 from Boston via Newark and Frankfurt to Prague takes 22 hours (twenty-two hours; it's not a typo) and there is no way how to change this "detail"; it was the best flight that they could offer me in August. If you count the events summarized above as one unit of stress, in the last two years or so I had to undergo about 93 units of stress; yes, of course, the number was chosen because of the United 93 flight. Although I predicted most of them because they were largely inevitable, I was not rational enough to have acted to avoid these things.

It's probably the highest time for me to act rationally. Having less than 7 weeks to buy an international air ticket is a problem. Being forced to depend on immigration bureaucrats who may give the visa after a year of hassle is a serious problem. A timebomb inside an institution in the form of insane politically correct radicals waiting to explode is a very serious problem. Let me censor the remaining 90 similar and potentially even more serious problems because it is likely that I am the only person among the readers of the blog who could survive even seeing the list. :-)

This article is also a note for me that I must spend Tuesday afternoon by calling them again. ;-)

Pleasure of finding things out

Many readers almost certainly have 50 minutes to watch this

The video is very insightful and entertaining although most of us know at least bits and pieces of it. He talks about the beauty of a flower - how physics only adds, not subtracts. There are many stories about his father - how he taught him the right philosophy but could not quite follow the calculus. Feynman also talks about his moral reasons to develop the bomb - the Germans were dangerous. After the war, he really thought that the world would be destroyed soon, so it was silly to build bridges. Then he explains why honors suck and how important for him it was to be actively irresponsible and sure that other people's expectations are their fault.



There is some discussion about QED and QCD, and his teaching of his son and daughter. The spatial and creative methods that worked for the son didn't work at all for the daughter who preferred the text of the book to be repeated. He also explains that because of the success of science, there is a lot of pseudoscience around - for example, social science and food science.

These people could know what they're doing but it's very unlikely: Feynman knows how difficult it is to observe the experiments properly and how easy it is to fool yourself. Finally, he says that we should try to find more about Nature instead of imposing our philosophical prejudices on Her. That explains why he had problems with some stories underlying religion. Feynman also knows how to live without knowing the answers; he is not frightened by ignorance.

Quasinormal update

Fu-Wen Shu and You-Gen Shen offer their 60-page-long

The use the monodromy technique to calculate not only the well-known zeroth order approximation of the highly-damped quasinormal frequencies - a topic previously discussed here on this blog - but also the first perturbative correction for a variety of types of perturbations of d-dimensional spherically symmetric neutral and charged black holes.

Concerning the previous literature: I don't want to mention my and Andy Neitzke's papers here because they're quite publicized, but what I want to mention is the 100-page-long paper of Jose Natario and Ricardo Schiappa that is doing a superb job in analyzing more or less all cases.

Back to Shu and Shen.

One of the topics to which they dedicate special attention is an apparent paradox that the black holes with a very tiny charge seem to have a different asymptotic behavior from the neutral black holes: the limit "q goes to 0" is not continuous. We have decided with Andy Neitzke that the resolution must be that if "q" is very small but finite, the Schwarzschild asymptotic behavior holds pretty well for a large number "n" of modes ("n" goes to infinity for "q" going to zero) but eventually the charged asymptotic behavior takes over. They are probably more detailed than Andy who described it in his paper on greybody factors even though I don't know so far what they exactly add.

As they also summarize in the last sentence of the abstract and elsewhere, they join those who confirm the viewpoint that the appearance of "ln(3)" in the quasinormal frequencies is a numerical coincidence for neutral black holes, not a general rule that could be used to support simple hypotheses about quantum gravity. I am not sure whether Lee Smolin reads this blog and whether he will again argue somewhere that loop quantum gravity can predict the correct numerical coefficient of the black hole entropy. More observant readers of this blog will know that this conjecture is safely ruled out.

Moreover, "ln(k)" for an integer value of "k" is no longer the coefficient predicted by loop quantum gravity anyway; the currently believed value is much more transcendental. See, for example, Krzysztof Meissner's paper and its 60+ followups.

Sunday, May 14, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Quasicrystalline compactifications

Two students have given a presentation on quasicrystalline compactifications. As you know, there exists no two-dimensional lattice (or the corresponding toroidal compactification) that would have a symmetry different from "Z_2", "Z_3", "Z_4", or "Z_6".

However, string theory compactified on a two-torus can have exotic discrete symmetries. Because of the winding modes, the dimension of the relevant lattice is actually doubled. And higher-dimensional lattices admit less usual discrete symmetries such as "Z_7". If your compactification has such as symmetry, you may orbifold by it. Because you used a different action on the momenta and the windings, your orbifold will be a so-called asymmetric orbifold. In a stringy sense, it is still an orbifold of the lower-dimensional torus.

Obtaining lattices with otherwise forbidden symmetries by a projection from a higher-dimensional lattice is a well-known procedure.


Figure 1: Penrose tilings (drawn by an L.M. Pascal program).

The relevant lattice structures - and especially the idea that higher-dimensional lattices can have more diverse symmetries than the lower-dimensional ones - is identical in both cases (orbifolds and tilings). What's not identical is that the Penrose tilings fully cover the plane: almost every point belongs exactly to one of the diamond-shaped tiles that some people used in their bathroom. In the particular case above, there are only two types of tiles.

The tiling is quasiperiodic: it is not strictly periodic, but an arbitrarily large finite segment of the tiling is found in infinitely many copies spread all over the plane.

How do you construct the tiling above? Start with a five-dimensional space "R^5". Inside that space, you find the obvious lattice "Z^5". Look at all possible two-dimensional "1 x 1" squares with vertices in this lattice. Some of them will be orthogonally projected onto a particular two-dimensional plane "P" inside "R^5" which will give you the tiling; below, I specify which of them. There are "(5 choose 2) = 10" different directions in which the two-dimensional squares can be directed, and the projections only have two possible shapes, with internal angles 36+144 degrees or 72+108 degrees.

OK, what is the plane "P" onto which you project? Consider a "Z_5" action on the five-dimensional lattice "Z^5". It generator "g" acts as
  • g (a,b,c,d,e) = (b,c,d,e,a).

This generator has five eigenvalues - the fifth roots of unity. The eigenvalue "lambda=1" corresponds to the vectors generated by "(1,1,1,1,1)". The remaining eigenvectors and eigenvalues are complex. But you can find a two-real-dimensional subspace "P" of the real space "R^5" where all vectors are combinations of the eigenvectors

  • (1,e,e^2,e^3,e^4) and its complex conjugate

and a similar subspace "Q" inside "R^5" with vectors that are combinations of the eigenvectors

  • (1,e^2,e^4,e^6,e^8) and its complex conjugate

where "e=exp(2.pi.i/5)". You will be projecting onto the plane "P" but you would get a similar picture if you chose "Q" instead of "P". Finally, I must say which two-dimensional squares will be projected and drawn on the plane "P". It will be those that are subsets (completely inside)

  • U = P + CUBE = { p + c; p in P, c in CUBE }

where "CUBE" is the "[0,1]^5" unit cube inside "R^5". Here, "U" is a codimension zero, five-dimensional "band" around the "P" plane. One can prove that with these choices, you will cover the whole "P" plane without any holes or overlaps.

Similar constructions exist for other groups and other lattices, including cases where you project onto a three-dimensional (or higher-dimensional) hyperplane instead of the two-dimensional plane, and what you get are quasicrystals. They're not periodic but they can have a "Z_5" symmetry - something that is not possible for ordinary three-dimensional rigorous crystals but something that can be realized in Nature, as we know from experiments.

The fact that you cover the plane exactly once plays no role in the orbifold compactifications, as far as I know. But the lattice considerations are analogous or even isomorphic. The virtue of these quasicrystalline compatifications is that you can project most - or even all - scalar fields out of the spectrum without any need to stabilize them: the required lattices only have the symmetries needed for orbifolding at special points of the moduli space. Of course, these constructions are still perturbative string theory, so all of them still have the dilaton (or the string coupling constant).

I believe that these constructions are among the understudied topics in theoretical physics. I say so despite the fact that during the duality revolution, the asymmetric orbifolds became less popular because it is less clear how they fit into the M-theory/D-brane/F-theory/Calabi-Yau landscape than it is for the geometric compactifications. My impression that you never know what is the strong coupling dual of the asymmetric orbifolds such as the quasicrystalline compactifications has been falsified: there are cases in which you know the answer: the strong coupling dual can be found by using the SO(5,5,Z) U-duality of type IIA on a five-torus fiber-wise.

Despite the small amount of interest in the models, I find the asymmetric orbifolds and the related free fermionic constructions to be attractive phenomenologically. The free fermionic models are free CFTs to describe perturbative heterotic strings in which you try to fermionize everything that you can: you just keep four bosons "X^mu" on both sides, and fermionize the "E8 x E8" current algebra, the six compact dimensions, and of course all the fermionic partners "psi". Besides "X's", you will end up with 44 left-moving fermions (on the bosonic side) and 20 right-moving fermions (on the supersymmetric side) in the light-cone gauge.

Now you're free to impose arbitrary GSO projections and create the corresponding sectors, as long as the modular invariance is preserved. Because you can treat the left-movers and right-movers more or less independently, including those that came from the compact bosons, which is why these constructions are at least morally asymmetric orbifolds. There are many independent GSO projections, and the minimal set that leads you to a GUT-like gauge group is called the NAHE set, after its discoverers. (NAHE is "beautiful" in Hebrew and "naked" in Czech.) See, for example, this 21st century more recent preprint.

A very attractive feature of the models based on the free fermions, the NAHE set of GSO projections, and on additional projections is that they automatically predict three generations of quarks and leptons. I still feel that it is not an accident. From Occam's razor viewpoint, these models are very efficient. The worldsheet is a collection of free fields. They predict the right gauge group structure, the right representations for the fermions, the right number of generations, and quantum gravity. As far as physics as opposed to mathematical beauty and/or complexity goes, do we really need anything else?

The models have also predicted the correct top quark mass, by a calculation that was not quite right, but we have already discussed this achievement.

Noam Chomsky and Hezbollah

Noam Chomsky has visited the headquarters of Hezbollah in Lebanon

and defended the Hezbollah's right to hold weapons. Now, according to the official U.S. sources, Hezbollah is a terrorist organization. Even according to the European Union, the military wing of Hezbollah is a terrorist organization.

However, it is an organization whose military power is openly supported by a well-known scholar from our city.

I find it hard to believe that someone can be so fanatically anti-American that he prefers to support an imported fundamentalist terrorist organization that follows the fanaticism of Ayatollah Khomeini and that is obviously hurting all decent citizens of Lebanon (the local newspapers in Lebanon agree with me). An organization that supports the control of Syria over the territory of Lebanon - the power of the same Syrian regime that was probably behind the assasination of Rafik Hariri.

It would be fine if one old guy had these unusual opinions. But when you realize that 90% of this city (and its universities) considers this person - despite, and in fact because of his extreme political opinions - to be an authority, it becomes hard to decouple yourself efficiently enough so that you avoid panic.

Saturday, May 13, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Climate CO2 sensitivity

...and editorial policies

See also:

RealClimate: saturated confusion (directly related)
CO2 - temperature relationship is the other way around
Climate sensitivity is defined as the average increase of the temperature of the Earth that you get (or expect) by doubling the amount of CO2 in the atmosphere - from 0.028% in the pre-industrial era to the future value of 0.056% (expected around 2100).

Recall that the contribution of carbon dioxide to the warming is expected because of the "greenhouse" effect and the main question is how large it is. The greenhouse effect is nothing else than the absorption (of mostly infrared radiation emitted by the Earth) by the "greenhouse" gases in the atmosphere, mainly water vapor - but in this case we are focusing on carbon dioxide, one of the five most important gases causing this effect after water vapor.



If you assume no feedback mechanisms and you just compute how much additional energy in the form of infrared rays emitted by (or reflected from) the surface will be absorbed by the carbon dioxide (refresh your knowledge about Earth's energy budget), you obtain the value of 1 Celsius degree or so for the climate sensitivity.

Friday, May 12, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Wati Taylor: correlations in the landscape

Washington Taylor was speaking about the problem to enumerate a particular perturbative class of vacua, to prove its finiteness, and to find some correlations - a work he has done with Michael Douglas and that will appear soon as a preprint.

He was considering the "Z2" orientifold of a "Z2 x Z2" orbifold of the six-dimensional torus in type IIA string theory. The "Z2" groups defining the orbifold reflect the coordinates as "----++" and "++----", so that their product (the third nontrivial element of the "Z2 x Z2" group) flips their signs according to the rule "--++--". The orientifold also reflect the toroidal directions as "+-+-+-".

You wrap D6-branes on various cycles. Each of these D-branes is parameterized by six integers "m1,m2,m3,n1,n2,n3" that encode the winding numbers on various allowed cycles: the three-cycle is a product of

  • (m1 a + n1 b) x (m2 c + n2 d) x (m3 e + n3 f)
various cycles ("a,b,c,d,e,f") of the six-torus. The tadpole cancellation condition seems to have four parts. You impose all of these conditions and ask how many different (supersymmetric) configurations of an arbitrary number of intersecting D-branes satisfy the constraints.

By one solution, you mean the information about the number of D-branes and their individual winding numbers (m_i,n_i); each such a solution typically becomes a moduli space. After you generate a potential, it can produce a larger number of stable vacua. But at this stage, you ask how many groups of vacua can you get.

The conditions define Diophantine equations - algebraic equations whose solutions are required to be integers - and Wati could prove that the number of solutions is indeed finite although it could a priori be infinite, using elegant methods from the high school mathematical olympiads. The general conclusion is that one can find a finite subset of the set of vacua M. I still think that this statement holds for every finite and for every infinite set M. ;-)

Moreover, if you want to consider not only random vacua from a set of 10^{350} vacua but even random subsets of this set, let me warn you that there are 2^{10^{350}} - which is almost 10^{10^{350}} - different subsets of the set of vacua. Thanks, Marcel, for being so incredibly picky. :-)

Eventually, Wati and Mike want to enumerate all the vacua that are orientifold-orbifolds of the six-torus with intersecting D-branes. They find about ten million solutions (for the winding numbers of the D-branes) whose number of generations is three, as estimated from the intersection number. Because they decide to only look at the solutions that respect a particular feature of the Standard Model, it turns out that they can list all of them in a polynomial time, evading "unsolvability" constraints that Denef and Douglas that were sort of codified for the "impossible mission" to find the vacuum with the right cosmological constant.

It turns out that approximately 10 models from this set survive because they have a semi-realistic gauge group. If the investigation of this class of vacua were motivated by a reliable and deep physical principle, you would be happy, of course. You would ask 10 students to look at each of them and check which of them is the right one. Unfortunately, it seems that Wati realizes - much like those of us who don't like the landscape discourse - that this whole exercise is physically unmotivated and there is no good reason to expect that one of these 10 particular vacua will be the right one.

But maybe someone should look at these ten vacua - they are quite simple!

So instead Mike and Wati want to apply analogous methods to look at broader classes of vacua with 10^{20} elements or so because this larger number may cover the parameter space finely enough so that one of these models (or more) will be indistinguishable from the observed low-energy action. Wati explains it differently:
  • The point of looking at a larger ensemble of models which agree with observed physics is to see whether they share additional features which may help make predictions beyond already observed physics. If we find 5 models with features X and Y of the standard model which all have feature Z which is not yet observed it is not very definitive. If we look in different parts of the string theory landscape and find that all 10^{20} models we know how to construct with features X and Y of the standard model have feature Z also it begins to carry some weight as a possible prediction.
I just don't understand this way of thinking. If you have five different models, then at least four of them are incorrect and cannot be used to make any predictions. If you have 10^{20} models, then it's even worse because at least 10^{20}-1 are wrong models which is incidentally a higher percentage than in the case of five models.

Whether a majority or a minority of the incorrect vacua shares some features is physically inconsequential - and if I gave the wrong models to influence the predictions, they could only influence them in the negative way. Whenever there is a plausible model that does not satisfy a certain rule, you can't trust the rule regardless of the number of models that do satisfy it.

We have lots of examples in which the reasoning above leads to incorrect conclusions - and moreover, most of the conclusions will depend on the chosen "representative class" of vacua and the measure (and relative weights of the classes) that we use to make the "predictions".

"Most" effective field theories are UV incomplete - and still, QCD is shockingly described by an asymptotically free, UV complete gauge theory. The correct theories or vacua describing the real world are sometimes generic but sometimes - in the more interesting and "elegant" cases in which we actually learn something new - they are extremely special and beautiful among the classes of theories of "similar complexity". The whole structure of string theory is an example because it is not only special but unique. The idea that we should look for "generic" vacua is nothing else than an irrational bias, and it is a kind of bias that goes in the opposite direction than everything good that has ever happened in the history of physics.

If you have a large enough class of random theories, surely there is a significant probability that you will approximate the currently known effective theory well enough. But that's something extremely different from finding the correct model or from making progress in physics.

In physics, one only finds the correct theory if it not only agrees with the known data but if it also agrees with the extra digits of quantities that will be measured with higher accuracy in the future or with completely new quantities and phenomena that are not known today. From this predictive viewpoint, it seems pretty clear to me that the classes of 10^{20} vacua - whatever they are - are as (un)motivated as the classes of 10 vacua, and the chance that the investigation of these two - populated and less populated - classes will turn out to be the right strategy is approximately the same in both cases.

The number of vacua on one side and the physical motivation to expect that a class of vacua is correct are two entirely different things, and indeed, I believe that if these two things are correlated, they are negatively correlated, not positively correlated. If someone in Pennsylvania finds the correct heterotic MSSM with the right fermion masses, will Mike and Wati argue that it does not matter because Wati and Mike can beat the heterotic guys by having 10^{350} wrong models that consensually predict different physics? I don't think so. 10^{350} wrong models is still less than one correct model.

Predictions from correlations?

Wati has also showed a different concept that I find as hard to swallow as the intentional search for the highly degenerate classes of vacua. By analyzing the large set of solutions for his orbifolds statistically, he wants to find correlations between various quantities such as the number of generations and something else. Wati describes the point of this enterprise as follows:
  • The point of looking for strong correlations is to ask whether in the context of the landscape we can find concrete predictions from string theory. In particular, if all string vacua with features X and Y also have feature Z and we observe features X and Y in nature then we can say that string theory predicts feature Z. If all the parameters of the standard model and beyond the standard model physics are uniformly and independently distributed in string theory vacua then we cannot use this approach to make predictions.
I agree that if the law "X & Y implies Z" is universal in all of string theory, then "Z" is a prediction of string theory once "X & Y" are observed. This is essentially the goal of the swampland program. But we don't need statistics for that. What Wati showed us was something different: non-universal laws that only hold in "most cases", that only hold "statistically", and I would never trust predictions based on such shaky grounds.

These correlations are expressed as "ENT(xy) - ENT(x) - ENT(y)" where "ENT(x) = -sum (p_i ln(p_i))" is the coarse-grained entropy of a statistical distribution "p_i" of different values "i" of a quantity (or a pair of quantities). Wati's result in his particular examples was that there was virtually no information in the correlations: the difference was one bit and the distributions of different quantities were essentially independent Gaussians.

Surely the physicists have not been working for 30 years to extract 1 bit of information - whose probability of being correct is moreover 50 percent. Even if there were any correlation, I would probably find such a correlation physically uninteresting. We know for sure that some of these correlations would agree with those observed in the real world, and some of them would not.

What will you do with this probable outcome? Will you overhype the "successful" patterns as evidence that the landscape reasoning is good, while you will be silent about the "unsuccessful" ones? I would count this activity as a part of astrology or catastrophic global warming theory, not physics. It's frustrating to see that this is what is apparently being intended.

I wonder whether the people who were producing the very convoluted microscopic theories of the luminiferous aether in the 19th century really believed that this was the way to say anything new about physics - or whether most of them did these things just to do something and keep their jobs. Einstein took over in 1905 and showed not only that the aether was a ludicrous fantasy - but moreover, the absence of the aether is one of the basic principles that underlies his relativistic revolution in physics. Today, all of us - except for those in loop quantum gravity - know that the aether is a silliness that is not realized physically and that was never well motivated.

My feeling about the random model building and random model guessing is somewhat analogous to the random construction of the aether from gears and wheels. We're missing something and we should not fool ourselves into thinking that we're not.

Thursday, May 11, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

Google Trends

Google offers you a new gadget to play with:

It allows you to see how the intensity of searching for various queries depends on time, where the searchers for particular queries are concentrated, and how various articles in the news affected the rates.

For example, you can search for famous blogs such as

Well, sorry, it does not work. Not enough results. OK, what else can I do than to give you a real example. :-(

You can also try to search for Woit. Well, again, reality forces me to switch to a real example. If you search for the last name of your humble correspondent, Google will try to convince you that the searchers are concentrated in

  • Princeton, NJ
  • Stanford, CA
  • Cambridge, MA
  • Prague, Czechia
  • Amsterdam, NL
  • Montreal, Canada
  • New York, NY
  • Toronto, Canada

Realistic. Analogously, string theory is concentrated in

  • Delhi, Mumbai, Seattle, Austin, L.A., San Francisco, San Diego,, Denver, Boston Philadelphia

Again, unfortunately, loop quantum gravity does not offer enough results to make any conclusions. Send complaints to Google if you have any.

Even more interestingly, you can separate several queries by commas and compare:

Lance Dixon: transcendentality expansions

These days, Lance Dixon - a co-discoverer of orbifolds in string theory, among other things - is an expert in multi-loop calculations in gauge theory. In his seminar, he has shown many technical points about the similarities of Feynman diagrams for scattering amplitudes in "N=4" supersymmetric gauge theory and in the pure QCD. The "N=4" theory is conformal and the infrared divergences make the interpretation of the loop amplitudes problematic, but the formulae for these amplitudes still reveal interesting mathematical patterns.

Wednesday, May 10, 2006 ... Français/Deutsch/Español/Česky/Japanese/Related posts from blogosphere

CSL-1 and confidence levels

When it was announced that CSL-1 was not a cosmic string in January, I forgot to link the preprint:

What I would like to be discussed is the confidence level. As you may remember, the spectra of the two components of CSL-1 were compared and argued to be identical at a confidence level exceeding 99.9% (page 3 here).

How do you interpret this number and what are the lessons? Should you interpret it as the probability that the two components were images of the same galaxy? Then it would indeed be quite shocking that CSL-1 turned out not to be a cosmic string.

My understanding is that the number 99.9% was calculated from the correlation between the spectra - treated as functions of the frequency. If these two functions were random, the confidence level would be very low. Because these two functions were much more correlated than two random functions of the frequency, they obtained a number that was so close to 100%. Please write down the exact formula - or AlGorithm - how 99.9% was calculated - if you know it.

But it seems to me that the actual procedure that led to the 99.9% figure did not care about the "generic" correlation between the spectra of two galaxies. It is probably very usual that two galaxies, especially two nearby galaxies, have a very similar spectrum. They have typically very similar abundance of all elements and their isotopes - or, more or less equivalently, the same percentage of stars of different types.

My guess is that if the correlation between these two spectra were compared with the correlation of spectra of other pairs of galaxies, the agreement would look much less spectacular. And this elementary step has not been done, I think. So it seems to me that the figure 99.9% was just a meaningless Bayesian random number whose precise value depends on "priors". And the case of CSL-1 was an example of a highly unrealistic prior.

Incidentally, PRIOR were malls in the socialist Czechoslovakia. It stands for "Přijdeš rychle i odejdeš rychle": you come quickly and you leave quickly. ;-) For example, in the late 1980s, one could not even buy a toilet paper. Once PRIOR was bought by companies such as Tesco or K-Mart, these problems completely evaporated. Capitalism works, socialism doesn't.

Was it correct to think that the agreement of the spectra meant that the probability that the components were images of the same galaxy exceeeded 99.9%? I think it is accurate to say today that the probability that such a prediction was a correct conclusion was below 0.1%. ;-)

OK, let me assume that it was not a correct estimate of the "subjective" probability that the components were truly identical. Was there a better algorithm that Sazhin et al. could have used to get a more sober prediction of the probability that the images are completely identical, based on the spectral analysis?

I am afraid that the answer is No - unless we know everything about the distribution of all galaxies, their spectra, and all of their correlations, including the dependence of the correlation on the proximity and other quantities. More realistically, I am afraid that even the most elementary procedure was not made - the impressive correlation between the spectra was not compared with the correlation of the spectra of other pairs of nearby galaxies. Correct me if I am wrong.

Bayesian estimates of probability are never quantitative science. The numbers representing the likelihood always have a subjective meaning. They depend on subjective assumption and temporary knowledge, and they are not subject to objective science. But despite this general statement, the estimates of probabilities can be done more or less rationally, and because we know that CSL-1 was not a cosmic string, it seems that the 99.9% estimate was not made too rationally.

It reminds me of the Bayesian estimates of the space shuttle failures. As Feynman argued after the Challenger disaster, the predictions of an extremely low error rate could have never been justified rationally because they could not have been based on the frequentist understanding of probability.