## About Me

- Steve Hsu
- Senior Vice-President for Research and Innovation, Professor of Theoretical Physics, Michigan State University

## Tuesday, March 30, 2010

### The price of eggs

From Aaron D. Levine, "Self-Regulation, Compensation, and the Ethical Recruitment of Oocyte Donors," Hastings Center Report 40, no 2 (2010): 25-36. More.

## Monday, March 29, 2010

### Crete talk: black hole information and decoherence

A reaction I sometimes get to this work is that: "Maldacena showed in AdS that measuring a certain correlator can determine whether black hole evolution is unitary (i.e., whether information is destroyed)". That is correct, but the measurement precision needs to be of order exp(-S), where S is the entropy of the hole. It turns out that is the same level of precision one needs to detect decohered Everett branches of a system with S degrees of freedom.

http://arxiv.org/abs/1003.5382The black hole information paradox and macroscopic superpositions

We investigate the experimental capabilities required to test whether black holes destroy information. We show that an experiment capable of illuminating the information puzzle must necessarily be able to detect or manipulate macroscopic superpositions (i.e., Everett branches). Hence, it could also address the fundamental question of decoherence versus wavefunction collapse.

Comments: 10 pages, 4 figures, contribution to proceedings of the 1st Mediterranean Conference on Classical and Quantum Gravity.

## Thursday, March 25, 2010

### SES and IQ

Vanderbilt psychologist David Lubinski sent me a recent paper addressing this issue -- Cognitive Epidemiology: With emphasis on untangling cognitive ability and socioeconomic status, Intelligence 37 (2009) 625-633. Among the figures is the following one, based on NLSY longitudinal data (the analysis was originally done by Charles Murray). It compares life outcomes of paired siblings (one of each pair required to be in the "normal" reference range of IQ), thereby controlling for SES. As you can see, IQ has a strong impact on education, earnings and social status even after family SES is controlled for. (Click for larger version of figure.)

Similar analysis shows that the correlation between SAT scores and college grades only decreases slightly when SES is controlled for. See also related post on non-shared environmental effects.

Below is a useful SES-SAT (or SES-IQ) syllogism, well supported by the studies at the two links above.

SES does not cause SAT (weakly at most). ***

SES does not predict college success, SAT does.

*** Someone recently asked me about the non-genetic or environmental variation in adult IQ. If we use a heritability range of .7-.9 (as deduced in twin studies; applicable for IQ in late adulthood and over a large range of childhood environments), then the resulting distribution of IQ differences for monozygotic twins would have SD = 5-8 points. That is, clones raised in different families would typically have IQ differences of around 5-8 points. Note, though, that very little of this difference is accounted for by SES -- most of it is due to non-shared environmental effects. For a lower heritability value such as .5 (perhaps more appropriate for adolescents), the expected variation between clones would be about 10 points.

## Tuesday, March 23, 2010

### Photos and long term memory

Why do I take photos of my kids or while traveling? The answer is so obvious it's a cliche: for the memories.

Remarkably, long term human memory capacity is probably only on the order of a gigabyte. Ask yourself what specific things you remember from the year 2000. How about your first day of class in college?

While the brain *processes* huge amounts of data (dominated by visual input), the amount of information *retained* is quite small -- no more than a few bits per second. When I ask you what your date's prom dress looked like, you are probably reconstructing it from conceptual primitives like "blue", "prom dress", or "velvet" :-) Do you think you could picture all of the girls you ever dated if you hadn't looked at their photographs over the years?

Looking at old photographs allows me to recapture and enhance otherwise elusive memories. Also, there's some selection bias in what one chooses to photograph: the memories triggered tend to be happy ones. Viva Espana! :-)

Human Memory: ... This makes the work of Thomas K. Landauer very interesting, for he has entirely avoided this hardware guessing game by measuring the actual functional capacity of human memory directly (See "How Much Do People Remember? Some Estimates of the Quantity of Learned Information in Long-term Memory", in Cognitive Science 10, 477-493, 1986).

Landauer works at Bell Communications Research--closely affiliated with Bell Labs where the modern study of information theory was begun by C. E. Shannon to analyze the information carrying capacity of telephone lines (a subject of great interest to a telephone company). Landauer naturally used these tools by viewing human memory as a novel "telephone line" that carries information from the past to the future. The capacity of this "telephone line" can be determined by measuring the information that goes in and the information that comes out, and then applying the great power of modern information theory.

Landauer reviewed and quantitatively analyzed experiments by himself and others in which people were asked to read text, look at pictures, and hear words, short passages of music, sentences, and nonsense syllables. After delays ranging from minutes to days the subjects were tested to determine how much they had retained. The tests were quite sensitive--they did not merely ask "What do you remember?" but often used true/false or multiple choice questions, in which even a vague memory of the material would allow selection of the correct choice. Often, the differential abilities of a group that had been exposed to the material and another group that had not been exposed to the material were used. The difference in the scores between the two groups was used to estimate the amount actually remembered (to control for the number of correct answers an intelligent human could guess without ever having seen the material). Because experiments by many different experimenters were summarized and analyzed, the results of the analysis are fairly robust; they are insensitive to fine details or specific conditions of one or another experiment. Finally, the amount remembered was divided by the time allotted to memorization to determine the number of bits remembered per second.The remarkable result of this work was that human beings remembered very nearly two bits per second under all the experimental conditions. Visual, verbal, musical, or whatever--two bits per second. Continued over a lifetime, this rate of memorization would produce somewhat over 10^9 bits, or a few hundred megabytes.

## Thursday, March 18, 2010

### Hangzhou photos

See here for an Economist special report on the Big Data deluge. Imagine you could observe 100+ million users transacting on a platform with 400 million item listings -- Taobao volume equals about 2 percent of all Chinese retail sales, and growing fast :-)

Yesterday we gave a presentation to about 200 technical staff who were attending a company-wide retreat at a resort outside Hangzhou.

Today I have to turn my physics brain back on as I am giving a talk at Zhejiang University (Zheda). Until now I have been simulating a social / computational scientist :-)

## Saturday, March 13, 2010

### Two book recommendations

The Lost Books of the Odyssey by Zachary Mason, a Borges-ian retelling of the Odyssey in 44 short stories.

Perfect Rigor by Masha Gessen, on Grisha Perelman and the proof of the Poincare / Geometrization Conjecture. I already knew a bit about the completion of Hamilton's program thanks to colleagues who work on Ricci flow. What I found most interesting in the book is the insider description of the Soviet math system, including the nurturing of young talents and the training for competitions like the IMO.

## Thursday, March 11, 2010

### Cognitive thresholds

This graph (click for larger version) shows the upper division in-major GPAs of U Oregon physics and math graduates from a 5 year period. The math GPAs were computed using a specific set of rigorous courses taken by graduate school bound majors. One might reasonably associate "mastery" of a subject with GPA > 3.5 -- roughly, the minimum threshold to be admitted to graduate school (i.e., students who earn equal numbers of A's and B's in their upper division core courses are borderline for most graduate programs). We find that no student with SAT-M less than roughly 600 was able to attain this level of mastery.

This data provides at least modest evidence for a

*cognitive threshold*required for physics and mathematics. That is, the a priori probability that a student with SAT-M < 600 will perform well enough to be admitted to graduate school in these subjects is extremely low. Note many poorly performing students switch majors, and hence do not populate the lower left corner of our graph.

A simple but plausible model for college performance might include two factors: 1. ability (measured by SAT) and 2. conscientiousness or effort (for simplicity, an uncorrelated random variable, probably normally distributed). The predicted GPA might depend linearly on the sum of the two factors, each measured in SD units. (See bottom figure here for a similar predictor of GPA.) Applying such a model to our data, we would conclude that even a student in the, e.g., 90th percentile of work ethic has a low probability of attaining mastery if their SAT-M score is below 600.

To reiterate, SAT-M 600 seems to be the lowest score at which even a very motivated student has a chance for mastery. From the data one might guess that only for SAT-M well above 700 do students have more than a 50 percent chance of obtaining GPA > 3.5. That is, a student with

*average*motivation or conscientiousness probably needs SAT-M well above 700 to have a high probability of obtaining mastery.

We were unable to find any similar threshold (either in SAT-V or SAT-M) in other majors, including economics, sociology, history, philosophy, biology, chemistry, etc. (More about this data set, including data on other majors, here.)

The percentile equivalents of SAT-M scores for various groups can be found here. For the total SAT-taking population, 600 is about 75th percentile. For the overall population, it might be 85th percentile. SAT-M of 750 is roughly 98th percentile for the total SAT-taking population.

For comparison, here is the analogous plot for English (black) and History (blue) majors versus SAT-R (verbal). If a threshold exists it is probably at SAT-R of 450 or so.

## Wednesday, March 10, 2010

### Great Firewall and blogging

I will be behind a certain Great Firewall next week, so blogging might be interrupted :-(

I have taken some precautions, we'll see how it goes.

## Tuesday, March 09, 2010

### The perils of precocity

Last night at dinner my 4 year old daughter asked me about death.

"Do all princesses grow old?" she asked.

"But I don't want to die!" she said, knowing, it seems, full well what that meant.

"We might go on to something else after we die," I offered.

"Oh." She thought about that for a while.

My son doesn't seem concerned about any of this, although he does occasionally ask me what the biggest number is. (He also wants to know about the biggest dinosaur and the fastest rocket.) I usually ask him to name the largest number he can think of, and then point out that I can always add one to that to get an even larger number.

When I was a kid I spent a lot of nights pondering life and death and infinity. I still do.

## Saturday, March 06, 2010

### James Cameron's machines

The Wizard: ... The fascination with the seeming invincibility of sophisticated mechanical objects, and an accompanying desire to slough off human flesh for metal (and a celebration of flesh so taut it may as well be metal: Cameron's camera loves to linger on the tightly muscled bodies, male and female, of the soldiers so often featured in his violent films), is a recurrent theme in the techno-blockbusters that cemented the director's reputation in the late 1980s and throughout the 1990s. Aliens famously ends with Weaver's character, Ellen Ripley, battling the dragonish alien monster queen after strapping herself into a giant forklift-like machine whose enormous pincers she mechanically controls by maneuvering her own slender arms—a technology that puts the puny human, finally, on a par with her gigantic, razor-toothed, acid-bleeding adversary.

... A violent variation on the same mechanical bodysuits reappears, memorably, in Avatar, which culminates in a scene of bloody single combat between a Na'vi warrior and the evil Marine colonel, who has strapped himself into one such machine. If anything, the recurrent motif of humans inserting themselves into mechanical contraptions in order to enjoy superhuman powers reaches its fullest, most sophisticated expression in the new movie, whose characters can literally become other, superhuman beings by hooking themselves up to elaborate machines. All this seems to bear out the underlying truth of a joke that Linda Hamilton, the actress who played Sarah Connor in the Terminator movies, told about her first, unhappy interactions with the director (whom she later married and divorced): "That man is definitely on the side of the machines."

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