Sleeping Beauty and Quantum Mechanics

This is a repost of an article I wrote in 2014.  Note that Sean Carroll also wrote about this, and he’s an author of the cited paper.

My newest favorite philosophical dilemma is the Sleeping Beauty problem.  The experiment goes as follows:

1. Sleeping Beauty is put to sleep.
2. We flip a coin.
3. If the coin is tails, then we wake Sleeping Beauty on Monday, and let her go.
4. If the coin is heads, then we wake Sleeping Beauty on Monday.  Then, we put her to sleep and cause her to lose all memory of waking up.  Then we wake her up on Tuesday, and let her go.
5. Now imagine Sleeping Beauty knows this whole setup, and has just been woken up.  What probability should she assign to the claim that the coin was tails?

There are two possible answers.  “Thirders” believe that Sleeping Beauty should assign a probability of 1/3 to tails.  “Halfers” believe that Sleeping Beauty has gained no new relevant information, and therefore should assign a probability of 1/2 to tails.  The thirder answer is most popular among philosophers.

This has deep implications for physics.

[Read more…]

Magic-Angle Graphene Superconductors

A couple weeks ago, there was an exciting discovery in my (former) field of research. It was found that if you take two layers of graphene, and rotate one of the layers by a “magic angle” of 1.1°, then you can create a superconductor.

Some brief background on superconductors. A superconductor is a kind of material that conducts electricity with zero resistance. That means you could transport electrical power without any energy loss. Or you could create so much electrical current that it creates a powerful magnet (used in MRI machines). Superconductors also have special magnetic properties that allow for magnetic levitation (used in maglev trains). But superconductors need to be cooled below a certain temperature to work, otherwise they’re just ordinary materials.

As of 1957, physicists have a working theory of superconductors, but the theory only explains certain varieties of superconductors, called conventional superconductors. Magic-angle graphene is an unconventional superconductor.

So, why would you ever try rotating two layers of graphene? Graphene is simply a layer of carbon atoms that form a hexagonal pattern. If you overlay two hexagonal patterns with a bit of rotation, you create what’s called a Moiré pattern.

Two hexagonal grids, one rotated by 10 degrees, form a moire pattern when overlaid.

[Read more…]

Paper: Asexuality in China’s Sexual Revolution

This is a repost of an article I wrote in 2015, for The Asexual Agenda.  A few small changes were made to incorporate corrections by commenters.

It’s well-known that English asexual communities are dominated by people in the US, UK, Canada, and Australia. [The Asexual Agenda] has made minimal efforts to include voices from other countries, but one of our blind spots is China. You know, that one country that has three times more people than the US, UK, Canada, and Australia combined.

The thing is, between the language barrier and the Great Firewall, hardly anyone in the English-speaking community knows anything. The closest we’ve gotten is our interview with Robin, but Taiwan isn’t the same as Mainland China at all. And given the complete lack of communication, it’s possible that asexuality in China is so different as to be unrecognizable.

That’s why I was interested to see this recent paper: Asexuality in China’s Sexual Revolution: Asexual Marriage as a Coping Strategy. By Day Wong, in Sexualities, February 2015.

[Read more…]

Biased Tests

[cn: Bayesian math]

Suppose that I create a test to measure suitability for a particular job. I give this test to a bunch of people, and I find that women on average perform more poorly. Does this mean that women are less suitable for the job, or does it mean that my test is biased against women?

Psychologists do this all the time. They create new tests to measure new things, and then they give the tests to a variety of different groups to observe average differences. So they have a standard statistical procedure to assess whether these tests are biased.

But I recently learned that the standard procedure is mathematically flawed. In fact, rather than producing an unbiased test, the standard procedure practically guarantees a biased test. This is an issue that causes much distress among psychometricians such as Roger Millsap.

Following Millsap, I will describe the standard method for assessing test bias, sketch a proof that it must fail, and discuss some of the consequences.

[Read more…]

Paper: Attack of the psychometricians

Suppose that you want to demonstrate that baby boomers are more narcissistic than other generations, or that women are more agreeable and neurotic than men, or that people of different races have different amounts of intelligence. How do psychologists do that? Can they in fact do that?

Typically, the method is to come up with a bunch of questions that superficially appear to measure the intended characteristic. Then the questions are “validated”, for example, by making sure the questions all correlate with one another. Once the questionnaire is declared valid, psychologists can then measure a variety of different groups and make far-reaching claims about how our current political/social situation was caused all along by the thing that they happen to study.

If you find this methodology questionable, but aren’t sure exactly what went wrong, you might be interested in hearing about psychometrics, the field concerned with psychological measurement. According to psychometricians, part of the problem is that psychologists are failing to follow best practices. That is the subject of this paper:

Borsboom, D. (2006). The attack of the psychometricians. Psychometrika, 71(3), 425–440.

[Read more…]

Paper: Overbooking flights

In recent news (cn: autoplay), a United Airlines passenger was unwillingly dragged off a plane to make seats for employees. The incident was partially blamed on the common practice of airlines to deliberately overbook flights in order to make up for all the no-show passengers.

While I won’t discuss the particulars of this incident, I am willing to do something that most journalists are not: read relevant academic literature. I just picked one paper that appeared to have a sufficiently broad perspective:

Marvin Rothstein, (1985) OR Forum – OR and the Airline Overbooking Problem. Operations Research 33(2):237-248.

The basic problem is that many people who buy airplane tickets don’t show up. In 1961, the Civil Aeronautics Board (CAB) reported that 1 out of 11 ticket sales were no-shows. These numbers are about the same today, with 7-8% no-shows. The airlines could create wait lists to fill the empty seats, but it would be impossible to contact the wait-listed customers in a timely fashion unless they were already present at the gate.

[Read more…]

Paper: Tops and Bottoms

cn: This post discusses m/m sex and genitals. I don’t joke about sex, so if you’re expecting sex jokes stop expecting that.

When I was reading that article about gay loneliness, I followed a reference to “A Longitudinal, Mixed Methods Study of Sexual Position Identity, Behavior, and Fantasies Among Young Sexual Minority Men” by Pachankis et al.

“Sexual position identity” refers to “top” or “bottom” or “versatile”. I would guess that most of my readers are already familiar with these terms, but I don’t want to be presumptive so I’ll just spell it out. The identity terms refer to sex positions in anal sex, with “top” being the insertive position, “bottom” being the receptive position, and “versatile” meaning no strong preference either way.

I will be upfront about my prejudices. These identity labels don’t make much sense to me. If people prefer one sex position over another that’s fine but an identity labels aren’t really useful unless they convey some information that a lot of people need to know. The only people who really need to know are sexual partners, or I suppose potential sexual partners. And we’re talking specifically anal sex, which contrary to stereotypes is not actually the most common sexual practice between men. So, sex position identity labels might make sense if you have a lot of sexual partners, but not otherwise. Given the prevalence of sex position identity labels, I strongly suspect that they are fulfilling some other function, like being a vehicle for stereotypes.

Yes, there are top and bottom stereotypes. Bottoms are supposed to be more submissive and feminine. I don’t understand it. [Read more…]