Thursday, July 02, 2015 ... /////

Introduction to double field theory 1/2

Guest blog by Olaf Hohm of MIT

First of all I would like to thank Luboš for giving me the opportunity to write a guest blog on double field theory (previously mentioned here).

This is a subject that in some sense is rather old, almost as old as string theory, but that has seen a remarkable revival over the last five years or so and that, as a consequence, has reached a level of maturity comparable to that of many other sub-disciplines of string theory. In spite of this, double field theory is viewed by some as a somewhat esoteric theory in which unphysical higher-dimensional spacetimes are introduced in an ad-hoc manner for no reasons other than purely aesthetic ones and that, ultimately, does not give any results that might not as well be obtained with good old-fashioned supergravity. It is the purpose of this blog post to introduce double field theory (DFT) and to explain that, on the contrary, even in its most conservative form it allows us to attack problems several decades old that were beyond reach until recently.

The Hindu: an interview with Ed Witten

A big portion of the world's string theorists gathered in Bengalúru, India last week. The local newspapers have published a couple of stories – e.g. about Ashoke Sen etc. One fresh interview in The Hindu is titled

‘Supersymmetry may show up at the new run of LHC’
Šubašrý Desikan has talked to Edward Witten who was introduced as the "world's only physicist who has won the Fields Medal".

Much like in most interviews since 2006 or so, the first question was a deeply unoriginal one about the empirical character of string theory. Witten answered that physicists are interested in string theory because of its elegance and especially because it seems to be the only way to reconcile the two pillars of the 20th century physics, quantum mechanics and general relativity.

Wednesday, July 01, 2015 ... /////

Tsipras' surrender letter: the timing of a loser

To sell while you are crumbling is too late

Twelve hours ago, at midnight Prague Summer Time, Greece became the first country that defaulted to the IMF among the countries that were widely considered developed at the moment of the default. I have been 90% sure that this event was unavoidable at least since June 5th or so. People who claimed that the European politicians "wouldn't allow" something like that have been shown spectacularly wrong.

Some EU politicians may religiously worship the memes about the integrated Europe. But these politicians have neither the absolute power nor the bottomless wallet. They face many people – including important people – whose thinking is more realistic. Even more importantly, they face the laws of physics. The convergence of Greece towards the collision with the default was as guaranteed as the implications of the laws of gravity. People just won't pay €1.6 billion for free – and that was the only way how Tsipras and comrades wanted the money to be paid. A few cheesy clichés about Europe's unity won't make anyone throw €1.6 billion into a black hole that has been known to be black for 5 years or so.

Tuesday, June 30, 2015 ... /////

Memories, asymptotic symmetries, and soft theorems

Last Monday, the Strings 2015 annual conference started in Bengalúru, India. Now it's over. With three exceptions, the written documents used by the speakers are posted on the page with talk titles and videos. Unfortunately, most of the videos have still not been posted; the last released ones were added 4 days ago.

(Update July 1st: thank God, the videos are available.)

There have been numerous interesting talks at the conference. Some of them are nice reviews. In order to focus on talks with a truly new original content that is sufficiently conceptual to be appropriate for a semitechnical blog, let me pick Andy Strominger's talk (PDF), not only because Andy celebrates his 60th birthday in a month.

Monday, June 29, 2015 ... /////

Puerto Rico and Greece: a comparison of two defaults

Excessive pensions and similar expenses are always the main problem

The center-left populist government of Puerto Rico just announced that the islands (one big plus many small ones) won't be able to repay their \$70+ billion public debt. These announcements just happen to come at the same time when Greece is expected to go bankrupt (tomorrow in the evening). It's tempting to compare these two economies.

I think that there are some huge differences as well as some amazingly accurate similarities – both of which are being heavily underestimated. Let us look at those.

First, just to be sure, Greece is a country in Southwestern Europe (in the Balkans), very close to Asia and Africa, and it's been considered the weakest link of the European Union and the Eurozone for many years. On the other hand, Puerto Rico is an island East from Cuba that has been governed by the U.S. federal government since the 1930s but it is not officially incorporated as a state. We may say that Puerto Rico is the weakest link of the U.S. – and the U.S. dollar zone.

To summarize, these two defaulting entities have totally analogous relationships to their larger umbrella territories or currency areas. I believe that many Americans who tell the Europeans that Europe "should" bail Greece out again totally fail to realize that their relationship with Puerto Rico is totally analogous. If it's right for Europe to bailout Greece again, the U.S. government should surely bailout Puerto Rico as well, shouldn't it? One could argue that Puerto Rico is politically "closer" to the government in D.C. than Greece's solidarity distance from Berlin, Helsinki, Bratislava, or even Brussels. Puerto Rico's main leader "is" Obama in some sense – but the Greeks' main leader is neither Merkel or Hollande nor Tusk or Juncker.

Sunday, June 28, 2015 ... /////

Gay marriage: constitutional revisionism is extremely dangerous

I have nothing against gays. My co-existence with gays has been very good and dozens of witnesses exist to confirm my extraordinary tolerance, to say the least. I think that there are biological reasons for gays' inclinations and these inclinations are compatible with their life or individual health.

A part of my understanding of the human freedom implies that people may insert their organs wherever they want – as long as they don't harm the freedom and dignity of others. And in a democratic system, voters or their elected representatives may ensure tax breaks for those who insert these organs at the right places. The desired frequency and locations may be specified in the illustrations embedded in the laws.

I won't think that they are wise if they do such things but nations surely have the right to establish their internal rules according to their tastes. In general, people in Czechia are extremely tolerant about these matters. Since 2006, we had "civil unions" for gays. But on the other hand, there exist virtually no "enthusiastic advocates" of homosexualism in my country, no "warriors" arguing that the unions have to be called "marriages". We may be just too mature or phlegmatic for such simple new forms of religion. Since the age of 10, Czechs generally know how babies are created etc.

But what I find unacceptable is the rewriting of the meaning of words and the meaning of laws and constitutions designed to achieve certain political goals.

Saturday, June 27, 2015 ... /////

Referendum about survival 5 days after death?

During the night, the world has learned about a shocker. It is the first one among the "unpleasant and unexpected Greek surprises" the world may face because it was incapable of forcing Greece into formal bankruptcy at a moment chosen by the creditors – not by Syriza.

A model of Greece's behavior in coming days or weeks

Alexis Tsipras scheduled a referendum about the creditors' proposals on July 5th. If the date were different, it could be interpreted as an effort of the cowards to get rid of their duties and their responsibility. With the referendum, they could say: It's the nation who screwed itself, isn't it?

However, the problem is that the referendum is supposed to take place on July 5th. Unless Syriza 100% surrenders in about 80 hours – and it's been suggested that the actual time that remains is shorter – Greece will be in the IMF arrears since July 1st.

By the IMF rules (although not by the rules of the rating agencies), it will be in the state of bankruptcy. The European Central Bank will be forced to withdraw the support for all the Greek commercial banks. Those will collapse. The country will completely run out of hard cash. The circulation of the hard currencies will stop.

The country will be effectively out of the Eurozone whether or not the elimination will be formally announced by that time.

Friday, June 26, 2015 ... /////

Muslim world is unsafe for Western tourists

Three Islamist attacks took place today. Some injuries in a mosque Kuwait, a beheaded manager in a U.S. company in France; and 28 or more people shot at a beach in Tunisia.

Beheading looks scary but I am obviously much more shocked by the Tunisian beach. I/we have been to Tunisia twice, in Summers of 1997 and 2008. I think we were in Sousse – the place of the attack – in 1997. And it was certainly Tabarka in 2008.

Quantum computers won't end people's confusion about quantum mechanics

On his blog Štetl optimized, MIT complexity theorist Scott Aaronson announced an essay he wrote for PBS,

Can Quantum Computing Reveal the True Meaning of Quantum Mechanics?
It starts by sketching the description of Nature in terms of probability amplitudes before it switches to the "interpretations". He mentions three – many worlds, pilot wave theory, and quantum mechanics as discovered by its discoverers, in this very order. Bullšiters about "interpretations" never even agree how many interpretations they consider seriously. They only agree that the only correct one – which serious physicists have used from 1925 – isn't at the top. This negative attitude is the only glue that integrates that "community".

(By the way, "Štatl" is a local name for Czechia's 2nd largest city, Brno. The local dialect, "hantec", is a mixture of Czech, Gypsy, German, Yiddish languages and the local argots. "Štatl" is almost certainly a Yiddish contribution and the word is "the same" as the word in Aaronson's blog name.)

Aaronson's main point is that the most important consequence of having quantum computers – if and when they are built – wouldn't be practical ones (simulation or codebreaking). Instead, the top consequence would be that the quantum computer would be "the most dramatic demonstration imaginable that our world needs to be described by a gigantic amplitude wave". Well, I don't think so.

Wednesday, June 24, 2015 ... /////

Greece: complete surrender or full collapse

For two or three days, the world was fed by the news that a Greek proposal has impressed the creditors and the deal was around the corner. We heard those things once again.

Today in the morning, we learned that a part of the creditors rejects the proposal. Which part? It's no secret that the International Monetary Fund finds the proposal unacceptable. Tsipras and his comrades only want to increase the taxation – by adding and increasing various taxes attacking the rich and the corporations – but the IMF knows that this is no recipe for growth. If Greece has any chance to become a growing economy able to repay at least a part of its debt, the policies that are needed are exactly the opposite ones. Reduce the spending, reduce the taxation of those who create jobs, and increase the taxation for those who don't (especially the sales tax that is linked to and therefore discourages consumption).

Also, IMF still thinks that the Greek debt is too high (even after the haircuts) so the creditors should accept a new haircut. They don't want to and they have the holy right not to agree with such things, of course.

Confederate flag has at least the same right to fly as Quran

In Germany and Czechia, among other countries, the sale of the Nazi symbols (and the promotion of these ideas) is regulated by the law and nearly banned. The regime has done terrible things, including the murder of 6 million Jews in a plan that was meant to be the "final solution".

The ideology and the people behind the regime got to power by using the excessive tolerance of the democratic system, its toothlessness, and the ban was introduced as a common-sense preventive measure that arguably decreases the probability that a similarly bad evolution is repeated in the future.

The anthem is at least as good as the U.S. anthem.

Americans have often told me that the ban meant that we, the Central Europeans, don't have any respect for the freedom of expression. A ban like this would never take place in the U.S., I was often told, because it's up to the free Americans to choose what they believe. They are treated as the adults and so on.

Except that a much more innocent symbol, the flag of the Condederate States of America, is in the process of being banned in the U.S. The president claims that it only belongs to the museum. Hillary Clinton says that the symbol has no place in the U.S., not even in the museums. She says so despite the fact that she and her husband were rumored to have been closet fans of the Confederacy.

CMS cooling magnet glitch not serious, detector will run

LHC rumor: serious problems with the CMS magnet. Possibly, little to none useful data from CMS this year.
Fortunately, this proposition seems to be heavily exaggerated fearmongering at this point.

Monday, June 22, 2015 ... /////

Strings 2015: India

I think that the cost-and-benefit analysis implies that it's not a good idea for me to describe most of the talks at the annual string theorists' conference. If there are volunteers, especially among the participants, I will be happy to publish their observations, however.

Sunday, June 21, 2015 ... /////

Locality, nonlocality, and anti-quantum zealots

Quantum field theories and string theory, the two most viable types of quantum mechanical theories, respect the Lorentz invariance, the basic symmetry that defines Einstein's special theory of relativity. This symmetry guarantees that no information can be sent superluminally or instantaneously: there can't be any action at a distance. The relativistic locality ends up being equivalent to the relativistic causality: the cause must precede its effects, $t\lt t'$, in all inertial systems.

In quantum field theory (defined through the canonical quantization), we may derive the canonical coordinates $\phi(x,y,z)$ and the canonical momenta $\partial_0 \phi(x,y,z)$ from the Hamiltonian. The usual procedures guarantees that the $t=0$ equal time commutators say that$[\phi(x,y,z),\partial_0 \phi(x',y',z')] = 0$ for $(x,y,z)\neq (x',y',z')$. The Lorentz invariance of the Heisenberg equations motion subsequently guarantees that the commutator is zero at later times, too. The (super)commutator of two fields always vanishes at all spacelike separations.

This vanishing commutator has a straightforward and far-reaching consequence. If we make a decision around the point $(x,y,z)$, the decision may be interpreted as a part of the measurement of some observable $F(x,y,z)$. Around the point $(x',y',z')$, we may measure operators such as $G(x',y',z')$. Because $F$ and $G$ (super)commute with one another, it follows that the decision associated with $F$ cannot influence the result of the measurements of $G$. Whether we make the $F$-decision or not, the theory will make the same predictions for all measurements of the type $G$. And because the results of all measurements that are possible in principle encode everything that is meaningful in physics, we see that there is no action at a distance. The Lorentz invariance guarantees that no $F$-decision can ever influence a $G$-measurement at a spacelike separated point.

There is no nonlocality. There is no action at a distance. There is no doubt about this statement.

Friday, June 19, 2015 ... /////

When a PC professor talks to sane people

Milan Kohout is a man who attended the same basic school as I did when I was 8-10 (but he did so many years before me). He was a dissident in the communist Czechoslovakia. At some point, he emigrated to the U.S. and moved to Roxbury, a black neighborhood in Boston. He became a radical fighter against the evil called the white people, and a super hardcore communist despising the money, banks, and the European and American civilization. He is an "artist" – see some Google images associated with his name.

Check e.g. his nude critique of religion and multiply it by 100 to have an idea about his life's work.

We have been in the Czechoslovak pub in Boston (e.g. Harvard pub) together many times, and we also drank beer in pubs in Pilsen – sometimes accidentally – most recently just a few months ago. He's a professor of some softer-than-diluted-excrement subject at Tufts university. Sometimes, his proclamations sound so insane that I have always thought that he was just making fun. But he wasn't. His opinions are genuine. You may imagine that even some of the most far left loons at Harvard and elsewhere are right-wingers relatively to Mr Kohout. But they're still pretty close to each other. ;-)

Sitting and experiencing gravitational redshift isn't enough for decoherence

Most of the contemporary research into "foundations of quantum mechanics" isn't good, if I kindly and generously avoid the word "šit", and a recently celebrated 2013 paper

Universal decoherence due to gravitational time dilation
by Igor Pikovski, Magdalena Zych, Fabio Costa, and Časlav Brukner that just got published in Nature Physics (even though it has only collected 6-9 citations in those 18 months) isn't much better. Well, maybe it is slightly better than the worst papers in this category.

It was enough to win some praise in Nude Socialist (probably because they mindlessly view Nature Physics as a stamp proving quality; "Einstein kills Schrödinger's cat: Relativity ruins quantum world" is a really, really painful and completely wrong title) as well as a more sensible response at Backreaction.

Just like in all other cases, anti-quantum zeal is the main driving force behind similar papers. In particular, these people just don't like Schrödinger's cat. Much like Schrödinger himself, they believe that the linear superpositions of macroscopically distinct states (e.g. alive cat and pure cat) must be banned or "absurd", as Schrödinger has said. What these folks and especially the inkspillers in assorted Nude Socialists seem incapable of getting is the fact that Schrödinger was completely wrong. The superpositions are always as "allowed" as the pure vectors we started with. There is nothing "absurd" about them.

This rule about the "legality" of all the superpositions is the superposition postulate of quantum mechanics and it holds universally and everywhere in the Universe. However, the superpositions don't mean anything absurd. When we're only interested in the question whether the cat is alive or dead, the cat is alive or dead, not alive and dead at the same moment. The options "alive" and "dead" are orthogonal to one another which means, according to the quantum mechanical formalism, mutually exclusive.