## Tuesday, August 31, 2010

### Taiwan photos

Still recovering from stomach bug. Click for larger versions.

First day at kindergarten.

The walk to school.

Humanities and social science building.

Update: a few more photos -- click for larger versions.

Exploring around campus:

One of many big bookstores in Taipei. This one occupies several floors of a shopping mall tower. About 10-20% of the books were in English.

### Last Train Home

This documentary captures the hard realities behind Chinese economic development. Specifically, the plight of migrant workers -- something I discussed earlier here.

This quote from the director says it all:

"There is a complex economic chain between the rich lifestyles of developed countries and the hard work of Chinese peasants who are trying to survive. At the two ends of the chain, neither party understands the other."

“Many times I was in tears at all this misery ... If you were on this train with hundreds of migrants around us — it stinks, it’s dirty and everyone’s trying to survive, just to see their kids.”

## Monday, August 30, 2010

### Taiwan, week one

Some miscellaneous thoughts on my first week in Taiwan.

I have done no physics or serious thinking, other than while lying in bed :-( Instead, I've been busy with mundane things like:

visiting Carrefour several times
visiting Costco twice
visiting IKEA

registering for cellphone service

getting the kids started at kindergarten

getting an ID card

getting a $3 ($100 NT) haircut -- nobody is cheaper than me :-)

catching a stomach bug ...

Most of these things were accomplished with two kids in tow, which makes the degree of difficulty significantly higher :-)

We are living on the Academia Sinica campus (flickr photos; the photo up top is of the languages and literature building), within a short walk of the gym (olympic size pool!), the kindergarten, libraries and our offices. The weather here is hot and humid at the moment (the climate is technically "subtropical monsoon"), so even a short walk in the middle of the day leaves me sweaty. It will be a tough adjustment from the mild conditions in Eugene, although I must say the vegetation here has a lush beauty which is very different from Oregon.

Our apartment is quite small compared to the 4000 square feet we occupy in Eugene. So far the kids seem not to mind -- they have been very adaptable throughout this trip. Anyone who wants to live green should try urban Asia -- the per capita carbon and energy footprint here is a fraction of that in the US -- but most Americans would have a hard time with the sacrifices.

A major motivation for choosing to come here for sabbatical was to enhance our kids' language abilities. They are fairly bilingual already, but I don't have a good feel for exactly how much Mandarin they really understand (although they do already make fun of my pronunciation :-). Their kindergarten is conducted entirely in Mandarin, and so far they are getting along just fine.

Kids eating at the cafeteria.

Lego creations.

## Thursday, August 26, 2010

### Sabbatical has begun

Greetings from the other side of the Pacific!

It appears that settling in here is going to take some time. Things were a lot easier when it was just me traveling the world. A professor wife and four year old twins add extra layers of complication ...

Please allow for increased latency (and dropped packets!) in communication :-)

## Tuesday, August 24, 2010

### Connect the dots

I thought I'd share this beautiful graphic of human genetic variation from the blog Gene Expression. The original paper from Science.

For panel A, PC1 = 20% of the variance, PC2 = 5%, and PC3 = 3.5%. For panel B, PC1 = 11%, PC2 = 6%, PC3 = 5% and PC4 = 4%.

## Saturday, August 21, 2010

### Jacare

Ronaldo "Jacare" Souza is one of the top jiujitsu fighters of all time -- 5 time world BJJ champion! His potential in MMA is still unrealized.

If you have Showtime, you can watch Jacare fight tonight on the Strikeforce Houston card. The light heavyweight fight featuring Mo Lawal should also be interesting. Lawal is a top freestyle wrestler, also making the transition to MMA.

Here's a highlight video. Jacare is Portuguese for alligator :-) His judo skills are apparent, although getting a takedown on a BJJ guy isn't exactly hard. By the way, that little tapping motion by the opponent means the fight is over :-)

Watch Jacare dominate Olympic silver medalist (Greco) Matt Lindland in an earlier fight:

## Friday, August 20, 2010

### Growing up in Iowa

SF: Remember you asked me what a "kike" is?

Me: Yeah. Where does it come from?

SF: I asked my dad, and he said "If Steve Hsu ever calls you a kike you call him a fucking chink!"

## Thursday, August 19, 2010

### Junk DNA and copy number variation

Wow, amazing genomic phenomena described in this new research: an explicit demonstration of the impact of copy number variation, and "dead" junk DNA revitalized by a mutation!

NYTimes: The human genome is riddled with dead genes, fossils of a sort, dating back hundreds of thousands of years — the genome’s equivalent of an attic full of broken and useless junk.

Some of those genes, surprised geneticists reported Thursday, can rise from the dead like zombies, waking up to cause one of the most common forms of muscular dystrophy. This is the first time, geneticists say, that they have seen a dead gene come back to life and cause a disease.

... As they studied the repeated, but dead, gene, Dr. Tapscott and his colleagues realized that it was not completely inactive. It is always transcribed — copied by the cell as a first step to making a protein. But the transcriptions were faulty, disintegrating right away. They were missing a crucial section, called a poly (A) sequence, needed to stabilize them.

When a mutation added back this sequence, the dead gene came back to life. “It’s an if and only if,” Dr. Housman said. “You have to have 10 copies or fewer. And you have to have poly (A). Either one is not enough.”

But why would people be protected if they have more than 10 copies of the dead gene? Researchers say that those extra copies change the chromosome’s structure, shutting off the whole region so it cannot be used. ...

## Wednesday, August 18, 2010

### Asian-Americans in the Ivy League: A Portrait of Privilege and Discrimination

All of this should be common knowledge by now, but of course most of it can't be openly discussed in the mainstream media.

IBTimes: ... While "Asians" -- defined broadly as people who can trace their ancestry to East Asia, Southeast Asia, South Asia and the Pacific Islands -- account for only about 5 percent of the U.S. populace, they are believed to represent up to 20 percent of the enrollment at the top Ivy League schools.

However, the irony is that if the admission criteria and process in all U.S. universities were completely fair and equitable -- that is, based purely on academic qualifications -- the Asian weighting in the elite colleges would likely be significantly higher.

... Consider what happened in California -- a state with a very high Asian population of about 13 percent -- in late 1996. Voters passed Proposition 209, a referendum that essentially revoked Affirmative Action measures and deemed that entry into public colleges -- including the huge University of California (UC) system -- should be entirely race-blind.

"A direct consequence of this was that the percentage of Asian-Americans at universities like Berkeley, UC-Irvine, and UCLA immediately skyrocketed," said Stephen D.H. Hsu, a professor of physics at the University of Oregon in Eugene. "At those institutions, the Asian-American representation currently approaches 50 percent."

... The word "quota" is controversial and politically-charged; one must be careful when using it. However it's difficult not to conclude that some elite universities do indeed impose a quota -- officially or subconsciously -- upon Asian enrollment in order to control their numbers at some specified levels.

Consider a recent study undertaken by Thomas Espenshade, a Princeton sociologist. He calculated that in 1997 African-Americans who achieved scores of 1150 scores on two original SAT tests had the same chances of getting accepted to top private colleges as whites who scored in the 1460s and Asians who scored perfect 1600s.

Or put it another way, Asian applicants typically need to score an extra 140 or so points on their SATs to compete "equally" with white students.

Miller of Babson College also wrote that "most elite universities appear determined to keep their Asian American totals in a narrow range. Yale's class of 2013 is 15.5 percent Asian American, compared with 16.1 percent at Dartmouth, 19.1 percent at Harvard and 17.6 percent at Princeton."

However, white students are similarly victimized by admission policies at some elite schools.

Espenshade discovered that when comparing applicants with similar grades, scores, athletic qualifications, and family history for seven elite private colleges and universities: whites were three times as likely to get accepted as Asians; Hispanics were twice as likely to win admission as whites, and African-Americans were at least five times as likely to be accepted as whites.

Moreover, if all elite private universities enacted race-blind admissions, the percentage of Asian students would jump from 24 percent to 39 percent (similar to what they already are now at Caltech and Berkeley, two elite institutions with race-blind admissions; the former due to a belief in meritocracy, the latter due to Proposition 209).

What Asian-Americans are enduring now is reminiscent of the travails of American Jews in the 1930s and 1940s, when colleges like Harvard and Yale imposed quotas to limit their numbers at these elite institutions. And like many of those Jews from seven or eight decades ago, numerous Asian-American students today come from poor, humble immigrant households.

To head off some of the usual comments, yes, it makes sense (in terms of narrow institutional interests) for the top schools to impose a soft quota on Asians. No use spooking older alumni donors with an off-putting student body composition, or diluting the brand so carefully developed over the years. I predict most of the elites will ease into a higher Asian representation over the next 20 years or so.

## Tuesday, August 17, 2010

### Physics Envy

A reader referred me to this excellent paper by Andy Lo and Mark Mueller. Mark and I were both Harvard postdocs at the same time. I seem to remember long conversations about both physics and finance in the Dunster dining room :-)

Warning: Physics Envy May be Hazardous to Your Wealth!

The quantitative aspirations of economists and financial analysts have for many years been based on the belief that it should be possible to build models of economic systems - and financial markets in particular - that are as predictive as those in physics. While this perspective has led to a number of important breakthroughs in economics, physics envy has also created a false sense of mathematical precision in some cases. We speculate on the origins of physics envy, and then describe an alternate perspective of economic behavior based on a new taxonomy of uncertainty. We illustrate the relevance of this taxonomy with two concrete examples: the classical harmonic oscillator with some new twists that make physics look more like economics, and a quantitative equity market-neutral strategy. We conclude by offering a new interpretation of tail events, proposing an uncertainty checklist with which our taxonomy can be implemented, and considering the role that quants played in the current financial crisis.

While physics envy might be a problem for economists or theoretical biologists, making physics your career (as opposed to becoming a quant, as Mark did) is certainly hazardous to your net worth!

### Fallows and Roach on the Chinese economy

Charlie Rose video (30 min). Via Maoxian -- see you in Beijing or Taipei :-)

### Asymptotic safety, singularities, and gravitational collapse

New paper! I'm ready for some vacation :-)

While I find asymptotic safety an intriguing idea, it would be disturbing for a truly fundamental model of gravity to have singularities.

http://arxiv.org/abs/1008.2768

Asymptotic Safety, Singularities, and Gravitational Collapse

Roberto Casadio, Stephen D.H. Hsu, Behrouz Mirza

Asymptotic safety (an ultraviolet fixed point with finite-dimensional critical surface) offers the possibility that a predictive theory of quantum gravity can be obtained from the quantization of classical general relativity. However, it is unclear what becomes of the singularities of classical general relativity, which, it is hoped, might be resolved by quantum effects. We study dust collapse with a running gravitational coupling and find that a future singularity can be avoided if the coupling becomes exactly zero at some finite energy scale. The singularity can also be avoided (pushed off to infinite proper time) if the coupling approaches zero sufficiently rapidly at high energies. However, the evolution deduced from perturbation theory still implies a singularity at finite proper time.

An Italian, an Iranian, and an American physicist walk into a bar ...

### Sabbatical plans

In a week I'll be leaving for a year of sabbatical. I will be based at Academia Sinica in Taipei, Taiwan. If you need to get in touch with me, email is probably the best option :-)

During September I will be in Benasque, Spain for a workshop on quantum decoherence. More photos. The last time I was in Benasque was the inagural summer for the Center. There was no building yet, so activities were held in a vacant elementary school. The tiny desks and chairs were piled up in one of the classrooms and new Ikea-like furniture was installed for us. It's nice to see that they've built a fancy facility now. Hopefully we'll have some good weather in the Pyrenees!

During October I will visit BGI (formerly Beijing Genomics Institute) in Shenzhen, China. I'll be involved in a project that I've been thinking about since I was a kid! What was science fiction then is just becoming possible today.

## Sunday, August 15, 2010

### Dyson, the bomb, and the Japanese surrender

This interview with Freeman Dyson pointed me to the recent reanalysis by historian Tsuyoshi Hasegawa of the Japanese surrender at the end of WWII. There is an old controversy over whether the atomic bombs or the entry of the USSR played the decisive role. Were the bombs necessary at all? Dyson mentions (about 30 minutes into the interview) that, due to Hasegawa, he is now 90 percent confident that they were not. This despite his close association with many of the Manhattan Project figures (Oppenheimer, Bethe, Teller, Feynman and others), and his acceptance for sixty years that atomic weapons played the key role. Dyson's recapitulation in the interview is quite good (it starts at about 20 minutes); see also here.

I recently learned from Donald Keene's diary translations (see also here) that Japanese modernizers had been worried about the Russian threat since the Meiji era.

Dyson also has some interesting comments about space exploration and genomics immediately following the discussion about nuclear weapons. I almost skipped listening to this interview, having spent several hours with him relatively recently. But someone as knowledgeable and brilliant as Dyson will always generate surprising insights.

Hasegawa's book: Racing the Enemy: Stalin, Truman, and the Surrender of Japan

Summary: ... According to Hasegawa, Japanese leaders' diaries and testimonies suggest that the imminent Soviet invasion was more influential in compelling them to accept the Potsdam conditions. Although Emperor Hirohito's desire to end the war became more urgent after Hiroshima, only on August 9 after the Soviet declaration of war did he clearly say that "it is necessary to study and decide on the termination of the war" [26]. The other peace advocates in the Foreign Ministry on the same day began to urge acceptance of the Potsdam ultimatum [27]. The reactions of the more hawkish military officials seem to have been similar. Both Admiral Toyoda and Army Deputy Chief of Staff Kawabe were surprised at the news of Hiroshima but were not ready to temper their views on continuing the war [28]. Many military officials hoped to mount a final defense, but had counted on Soviet neutrality in order to do so [29]. The Soviet declaration of war destroyed those hopes, and severely weakened the war faction's leverage within the government.

The major strength of Hasegawa's work, and one reason for its new arguments, is its in-depth analysis of Japanese primary sources. Few previous historians in the US had consulted the personal writings of figures like Toyoda, Kawabe, and Tanemura. But Hasegawa also makes more extensive use of Allied primary sources, including the memoirs and diaries of Truman, Byrnes, Brown, and others, which play a key role in his argument about the intent of the Potsdam Proclamation. Hasegawa's careful scholarship has significantly enriched our understanding of the intentions behind the demand for "unconditional surrender," as well as the dynamics behind the Japanese decision to surrender.

I recently had a memorable conversation with a colleague (another former Junior Fellow) who is a professor in the history department. Despite early evidence of talent in mathematics, he decided to study history because he wanted a career in which his abilities would continue to grow and deepen well into maturity. He preferred to reach the peak of his powers late in life, rather than suffer the continuous decline so dreaded by precocious young geniuses in theoretical subjects. I begin to see his point.

## Thursday, August 12, 2010

### A sequel to The Two Cultures

C.P. Snow's The Two Cultures gets a useful update with Jerome Kagan's The Three Cultures, which adds social sciences to the mix. Kagan is insightful and has a good understanding of each of the three cultures (sciences, humanities, social sciences) that he analyzes in the book. Of course, I prefer Snow's original to the update :-)

Snow: I remember G. H. Hardy once remarking to me in mild puzzlement, some time in the 1930s, Have you noticed how the word "intellectual" is used nowadays? There seems to be a new definition which certainly doesn't include Rutherford or Eddington or Dirac or Adrian or me? It does seem rather odd, don't y'know.

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is the scientific equivalent of: Have you read a work of Shakespeare's?

I now believe that if I had asked an even simpler question — such as, What do you mean by mass, or acceleration, which is the scientific equivalent of saying, Can you read? — not more than one in ten of the highly educated would have felt that I was speaking the same language. So the great edifice of modern physics goes up, and the majority of the cleverest people in the western world have about as much insight into it as their neolithic ancestors would have had.

Kagan: The birth of this manuscript was the need for a summer writing project married to the accidental spotting of C. P. Snow’s Two Cultures near the shelf where I was searching for a book in Harvard’s Widener Library. After reading Snow’s 1959 essay the following weekend, it became clear that revisiting Snow’s thesis 50 years later allowed me to organize my thoughts about the state of scholarship in the American academy and to synthesize my unhappiness with the dramatic ascent of the natural sciences in the years following World War 2, which intimidated the other two scholarly communities.

A deep theme in The Three Cultures centers on the different meanings of truth; that is, what does an individual point to when he or she declares, “I believe that idea to be true.” The correspondence between a statement and a reliable observation is the usual meaning of truth for both scientists and the public. However, mathematicians and some physicists accept the logical consistency of a mathematical argument as a second, different definition. The physicists who call themselves string theorists believe that their equations are true, even though many phenomena assumed by the equations have never been observed.

Many humanists accept the semantic coherence of a text and its correspondence with the readers’ intuitions as a related, but distinctive, definition. Readers of John Rawls’s Theory of Justice or Richard Dawkins’s book on selfish genes regard the texts as capturing the truth, even though many statements lack correspondence with observations and do not use formal arguments. William Styron’s Sophie’s Choice, Dostoevsky’s Crime and Punishment, and Tennessee Williams’s Camino Real have the ring of truth for those whose semantic networks are in accord with those of the authors.

The related concept of “ethically right” belongs to another meaning network that shares the semantic node correct with the concept true. All who are certain that no human should harm or torture an innocent are convinced of the correctness of this belief which, unlike truth, involves a contrast between good and bad.

The final chapter of The Three Cultures is penetrated with personal ethical evaluations of the changes in the ambience of the research university, including the epidemic of a naked seeking of celebrity, the erosion of faculty loyalty to the university or the student body, the surrender by both administration and faculty to the seduction of political correctness, and the faculty acquiescence to demands to account for their time, to publish enough papers to announce that they possess a work ethic and, if possible, to bring overhead money to the college treasurer. Alfred North Whitehead, Max Planck, Niels Bohr, Rita Levi-Montalcini, and Marie Curie would have been puzzled by this new breed of academic scholar.

## Wednesday, August 11, 2010

### Japanese diaries

So Lovely a Country Will Never Perish: Wartime Diaries of Japanese Writers

I had a look at this in the bookstore recently -- it is beautifully written and translated. Both Keene and the diarists he has translated have exceptional psychological insight into an interesting time in Japanese history. There are many striking anecdotes. For example, one diarist records the applause of cinema goers in occupied Japan during American newsreels showing kamikaze fighters striking US ships.

See also Modern Japanese diaries: the Japanese at home and abroad as revealed through their diaries, which chronicles the impressions of early Japanese travelers visiting America, Europe and other parts of the world.

## Tuesday, August 10, 2010

### SeekingArrangement: all about the Benjamins

We wrote about the high-end "dating" site SeekingArrangement.com (founded by an MIT grad) here. See the SA blog comments for back and forth between real life sugar babies and sugar daddies :-)

Vanity Fair: ... I had become a member a few weeks earlier, partly as a social experiment and partly out of genuine desperation. I was frustrated with my job, which offered little upward mobility, and was thinking about quitting it to pursue my goal of becoming a full-time freelance writer. Holding me back were my lack of savings and my fear of sacrificing a regular paycheck. If I had a hefty allowance from a generous benefactor, though, I figured that I could take the leap comfortably.

... The site, which launched in 2006, has about 420,000 members, of which roughly one-third are sugar daddies and two-thirds are sugar babies (sugar mommies account for less than one percent). While sugar daddies pay $49.95 per month for a premium membership (or$1,200 a month for Diamond Club certification, which requires verification of one’s net worth through tax-return data), as a sugar baby I was able to join for free. I uploaded two photos and listed some general information about myself, and I stated “open, amount negotiable” in the space that asks what you’re looking for. (Seeking Arrangement skirts the issue of prostitution by promoting the exchange of “intimacy and companionship” for “gifts.”) I took a deep breath and posted my profile, determined to focus on New York–based single men claiming to be worth at least $10 million. ... When Charlie—divorced, late 50s, worth about$50 million—asked to meet me, I tried to remain hopeful. I sauntered into the Mercer Hotel in jeans and a gray cardigan one frigid Sunday morning, scouring the crowd for a tall, gray-haired man. He spotted me first and tapped me on the shoulder.

“Here you go—just a token,” Charlie said, extending his hand.

I examined my gift—an iPod—and said, “Thank you,” determining to be extra pleasant during brunch.

We both ordered eggs, and by the time our food arrived I had grown to like Charlie. For starters, he provided an earnest explanation for joining Seeking Arrangement.

“I can’t separate the fact that I have resources from who I am,” he said. “It’s part of me. And it’s something I have to offer twentysomethings.”

“I completely agree.”

“I married young, you know. And I remained married for nearly 30 years while I was raising my kids.”

“How old are they?”

“It’s not weird at all,” I said.

Charlie turned to Seeking Arrangement, he explained, because most of the women he had been meeting wanted to settle down. “I don’t want another family,” he said.

“I promise you I’m not in the market for one,” I told him, and then asked, “Have you ever done this before?”

“I’ve never been in one of these relationships, exactly. But I’ve certainly been generous with previous girlfriends. And since joining the site, I’ve been on a few coffee dates. Pretty positive experiences, actually. I met an editor for a fashion periodical, a translator for the U.N., and a girl whose dad”—he stopped to laugh—“whose biological dad had just cut her off. The only negative experience I had was with a girl who was dating a hedge-funder. She said he had given her her nose and her Birkin bag, but that she needed cash. A bit mercenary for my taste.”

Here is a segment that features the founder:

## Monday, August 09, 2010

### Laughlin interview

I highly recommend this interview with Bob Laughlin (1998 Nobel for fractional quantum hall effect). Laughlin discusses topics ranging from energy and carbon emissions (topic of his new book) to globalization and innovation (he was President of KAIST for 2 years) to philosophy of science (emergent phenomena, Confucianism, Monism!). He even notes that elite higher education is a signaling racket :-)

[About 1 hour into the podcast. Discusses flash memory, blue diodes, flat screen displays.]

... All I can tell you is that this is playing out now and we'll see. ... Maybe it's true you can do without all that manufacturing capability. However, this is not what we are talking about. What we are talking about is innovation and American innovation. I think American innovation is not nearly as great as the proponents say it is. Because they are not telling the truth.

Shout out to Tiko:

Laughlin Nobel biography: ... A few days after the Nobel Prize announcement I got the following wonderful e-mail from Andrew Tikofsky, one of my best graduate students, who is now on Wall Street:

Hi Bob, Ian McDonald, Steve Strong, and I are getting together for a beer near Grand Central Station this coming Tuesday in honor of your prize. You are cordially invited to attend.

### IQ regression from Terman data

A reader sent me a link to some data on regression from Eysenck's book The Structure and Measurement of Intelligence. (I actually own this book but had forgotten about these results!) Eysenck quotes from the Terman study:

1528 California children with IQs of 140 or higher were followed into adulthood in order to assess the importance of IQ in adult success and adjustment. The mean IQ of those that married and had children was 152; that of their spouses, 125. The mean IQ of this whole group of parents was 138.5. The mean IQ of 1571 of their children was 133.2, a little less than the parents and showing some regression to the mean.

These results show very little regression -- less than would be predicted from the estimates given in my earlier post. However, I suspect a correction needs to be applied as the Terman study was done before the Flynn Effect was understood. If the same version of the Stanford Binet was used on the parents and children, without Flynn re-norming, then the children were not as exceptional as implied by the 133 average given above. If we take the Flynn Effect in mid-20th century America to be about 10 points per generation (this is just a rough guess), then the 133 should be corrected to about 123, and is pretty consistent with the estimate I gave of: 100 + .6(38.5) = 123, which assumes narrow sense heritability h^2 = .6.

The discussion by Eysenck uses higher heritability numbers (note the non-negligible V_CE = variance due to common environment). If the Terman study used re-normed tests then their data would be evidence for much less regression than in my estimates.

## Saturday, August 07, 2010

### Entropy of black and white holes

Below are some remarks on black (and white) hole entropy which may help clarify the discussion (see also comments) elicited by Lubos Motl's blog post on my recent paper.

Apologies to most of my readers, who are not theoretical physicists! We will return to blogging on other topics soon :-) If you like this kind of discussion, see Lubos' blog -- he is one of the few people on the planet who can write with clarity and frequency on these topics!

In the discussion below I define entropy to be the logarithm of the number of distinct quantum states which are consistent with a particular coarse grained description of an object. For example, suppose there are N quantum states that correspond (when probed by a coarse detector) to a ball of stuff with ADM energy M and radius R. Then the entropy of this object is S = log N. Also note that I assume purely unitary evolution of quantum states.

In my paper I was interested in white holes described by the time reversal of a black hole spacetime. I was specifically interested in white holes in isolation -- i.e., surrounded by vacuum. If the black hole was formed by the collapse of some object (e.g., a star), the corresponding white hole will "explode" at some point, disgorging the original star. Lubos points out that this sequence of events is unlikely on entropic grounds: if one assumes that the white hole has entropy of order of order its area in Planck units, and the matter disgorged has much less entropy than this, the white hole explosion seems to violate the second law of thermodynamics. Do the white holes I consider actually have area entropy?

Note that there is a one to one mapping (via time reversal) of black hole and white hole interior states. The subset of black holes that are formed by the collapse of ordinary objects like stars has much less than area entropy. In fact, their entropy is bounded by a coefficient not much larger than unity times their area to the 3/4 power: A^{3/4}. This can be deduced from an entropy bound on ordinary matter in nearly flat space (see links below). Using the one to one property mentioned above, this gives us an estimate of the entropy of white holes which explode into ordinary matter like a star or dust ball.

How do we produce the black holes that account for the vast majority of the A entropy? Not by ordinary astrophysical processes. Instead, we have to start with a small black hole and allow it to slowly accrete energy. (There are other methods; see links below.) However, a black hole which slowly accretes energy will at the same time emit Hawking radiation. The time reversal of this kind of hole is not an isolated white hole, it is a white hole bathed in incoming radiation from the past light cone. This type of (most entropic) black hole IS quite similar to its time reversed white hole counterpart, unlike the isolated holes I studied. See figure below.

I am making a distinction between two types of coarse grained objects: 1. black hole of mass M, but I know nothing more about the object or its history and 2. black hole of mass M, but I know it was formed from, e.g., a star. The two categories of objects have radically different entropy because in case 2 I can restrict the quantum state to a small subset of the states in case 1 (I have more information about the object).

To summarize, the white holes I studied are obtained via time reversal from a tiny subset all possible black holes. However, these are the black holes actually produced by known astrophysical processes (supernovae, galaxy formation, etc.), and their time reversed evolution does lead to an explosion. Whether such objects are of interest is left up to the reader :-)

Talk slides (source of the figure above).

A review article: Monsters, black holes and the statistical mechanics of gravity, http://arxiv.org/abs/0908.1265.

See also: What is the entropy of the universe? http://arxiv.org/abs/0801.1847, also discussed here (source of figure below).

Figure 3 caption: Ordinary matter (star, galactic core, etc.) collapses to form an astrophysical black hole. Under unitary evolution, the number of final Hawking radiation states that are actually accessible from this collapse is $\sim \exp M^{3/2}$, i.e.~precisely the number of ordinary astrophysical precursors (\ref{th1}). It is therefore much smaller than the the number of $\sim \exp M^2$ states a black hole, and its eventual Hawking radiation, could possibly occupy if nothing about its formation process were known.

## Tuesday, August 03, 2010

### White holes, entropy and comments for Lubos

Lubos Motl doesn't like my recent paper (arXiv:1007.2934) on white holes. Lubos is a very smart guy, so I take his remarks seriously.

Before getting to his comments, let me say a few things about what I did in the paper.

A. The "white hole" I analyzed is just a classical background which is the time reversal of (part of) a black hole spacetime. The initial data for this spacetime can be obtained from a spacelike slice across the usual black hole spacetime ("after" the horizon has formed), and need not include the singularity.

B. I imposed the condition of isolation (vacuum) outside the white hole at early times. This is equivalent to requiring no radiation in the future of the original black hole spacetime. An unusual boundary condition, but corresponds to the "isolated" white hole I was interested in investigating.

C. I used Hawking's method (i.e., Bogoliubov transformation of in- and out- modes) to study the future behavior of the white hole, or, equivalently, the initial preparation of the black hole required to prevent it from radiating.

It should be clear from the summary that my paper can be read as merely analyzing the black hole spacetime with a nonstandard future boundary condition and then interpreting the results in time reversed language. ("Look ma, no white hole"!) That is, the methods I use have exact time reversal invariance built in. In the paper I note that an isolated white hole and an isolated black hole behave differently. That is not a violation of time reversal invariance applied to an entire spacelike slice because the time reversal of an isolated black hole (which radiates into its future) is not an isolated white hole -- rather, it is a white hole bathed in incoming radiation (from its past) at the Hawking temperature (see figures in the paper). However it does contradict the idea that the time reversed evolution of the hole can be understood independently of its environment (i.e., what is outside its horizon).

Lubos makes a number of remarks in his blog post. I try to summarize them below, together with my comments. He may make other claims as well that I haven't addressed.

1. We know from string theory that black holes and white holes are the same thing. Well, let me first point out that not everyone believes in string theory as the correct theory of quantum gravity (i.e., describing our universe) at 99.9 percent confidence level. Secondly, if a semi-classical calculation like mine suggests differences between the behavior of an isolated white hole and an isolated black hole, isn't it interesting to reconcile that with what AdS/CFT predicts? Although I am not an expert on AdS/CFT I suspect that the time reversal invariance of the CFT boundary state only implies time reversal of the entire bulk state (i.e., on an entire spacelike slice) and not of the black hole alone. If so, there is no contradiction with my results -- see above. Perhaps someone can clarify this for me?

2. Hawking clearly said the same in his 1976 paper. That was my impression on first reading, but since all of his arguments center on the case of a black hole in equilibrium with a bath at equal temperature, it is unclear (at least to me) how this can be generalized to an isolated white hole. That was one motivation for my investigation.

3. Entropic arguments imply that white holes (as obtained via (A) above) are extremely unlikely: specifically, a highly entropic white hole should not explode into lower entropy ejecta. I understand the argument but don't place as much confidence in it as Lubos does. The uncertainty is not about the 2nd Law but about the interpretation of black or white hole entropy.

Lubos does not want me to consider classical spacetimes generated by the initial data obtained in (A) above. Even if one accepts that such spacetimes are highly improbable, that does not mean that they shouldn't be studied. (For example, if you are a many worlder there are some branches on which exploding white holes are observed!) Apparently it is in bad taste to think about (exploding) white holes, but perhaps Lubos should tell this to, e.g., Frolov and Novikov.

Now, a little analysis of the cognitive dissonance (conflicting priors ;-) between Lubos and me. When I say "white hole" I mean the time reversal of some classical black hole spacetime. I consider this (time reversed) spacetime of theoretical interest, even if it results from strange initial conditions. I use what I know (general relativity + quantum fields in slightly curved space) to probe the more mysterious issues (black hole entropy, quantum gravity, ... ). This follows Wheeler's approach of "radical conservatism" -- take the physics you trust with high confidence, and extrapolate to extreme conditions until something interesting happens! Lubos is a true believer in string theory, so to him a black hole is this stringy thing about which we already know almost everything, including that its entropy is due to countable internal microstates, it is dual to some YM configuration through holography, etc. This will likely elicit a shriek of anger from Lubos (or he will just call me dumb), but I consider all of those claims plausible but perhaps not true in our universe: string theory may turn out not to describe Nature.

Finally, there is also some discussion of my paper here and here, but it seems that both authors are slightly confused about the results (perhaps this is my fault for not being clear :-). For example, the requirement that white holes "explode" is not a consequence of my analysis, but just follows from time reversal of the black hole formation event (see, e.g., Frolov and Novikov or figures in the paper). I am only studying the quantum effects (i.e., equivalent of Hawking radiation), which are a correction to the classical evolution.

## Sunday, August 01, 2010

### More SciFoo 2010 notes

Some quick notes. I don't know if I'll have the energy to put in a full set of links, but you can pursue any of these topics with your own google searches. I'm sure I missed a lot of good sessions -- too much good stuff going on :-)

Great talk on the Pirahã and Chomsky's universal grammar by Dan Everett. (The Pirahã have no words for distinct numbers and no recursion!)

Long discussion with Erik Verlinde about his idea that gravity is an emergent entropic force.

Dinosaurs and reptiles cannot gallop, with the exception of one weird crocodile -- Paul Sereno.

Ed Felton can uniquely identify individual physical objects (e.g., a particular sheet of paper) using an optical scanner, and, using cryptography, produce a digital signature (i.e., printed directly on the object) that proves that the particular object isn't counterfeit. This has tons of interesting applications.

Frank Wilczek got me excited about graphene. Max Tegmark got me intrigued about 21 cm radio waves and a funny FFT telescope.

Tsutomu Shimomura's startup may drastically reduce the cost of LED lighting.

Sendhil Mullainathan's research explores the psychological consequences of scarcity.

A few more photos from the closing session. Sorry my photos are so boring but we got a warning from one of the Google organizers right at the beginning not to take photos outside of certain restricted areas. Earlier post here.