Tuesday, December 22, 2020

Phil Anderson biography is now available

The biography, A Mind Over Matter: Philip Anderson and the Physics of the Very Many by
Andrew Zangwill is now out. I just ordered my copy.

I am looking forward to reading it and will eventually post a review. I look forward to hearing comments from others. 

Update. I received my copy and have already read two-thirds of it. Loving it!

Friday, December 18, 2020

Lessons from the discovery of liquid crystals

I recently learned a little about the history of the discovery of liquid crystals, stimulated by Soft Matter: A Very Short Introduction by Tom McLeish. Besides being a fascinating story there are lessons about the importance of curiosity-driven research, interdisciplinarity, serendipity, and the long road to technology.

Friedrich Reinitzer (1857 - 1927) was a botanist and chemist who worked at the Institute of Plant Physiology in Prague. He was studying cholesterol with the aim of determining its molecular weight. He produced crystals of cholesteryl benzoate and measured their heat capacity as a function of temperature. Aside: For chemists today this measurement is known as differential scanning calorimetry (a constant source of heat is added and the temperature measured as a function of time). 

In 1888, Reinitzer observed that the crystal melted at 145.5 degrees Celsius (signified by absorption of heat), forming a milky liquid. However, at 178.5 degrees Celsius, there was a second absorption of heat, and the liquid became transparent. This suggested that there were two melting transitions. Puzzled by this Reinitzer consulted the physicist and crystallographer, Otto Lehmann, who promoted the idea that this was a new state of matter, which he dubbed a "liquid crystal" (or flowing crystal).

Today, cholesteryl benzoate is classified as a chiral nematic liquid crystal, which is also sometimes known as a cholesteric liquid crystal, in honour of the first one. A schematic of the ordering is shown below.

The milkiness was not explained until the 1960s by Pierre-Gilles de Gennes, who exploited an analogue with a superconductor in a magnetic field.

More detail is in the paper
Michel Mitov 

This discovery of liquid crystals was the first of many cases where a new state of matter was discovered by a thermodynamic measurement. Others include superfluid 4He (the lambda transition) and superfluid 3He, as I have recently highlighted.

Thursday, December 10, 2020

Emergence and a heap of sand

A piece of gold metal is shiny but a single gold atom is not.
Tin is a superconductor but a single tin atom is not.
Water is wet but a single water molecule is not.
A brain thinks but a single neuron does not.
Shininess, wetness, and thinking are all emergent phenomena. The whole is greater than the sum of the parts. More is different. Although these ideas come from twentieth-century science I recently learn that there are ancient antecedents. According to Wikipedia

The sorites paradox (/soʊˈraɪtiːz/; sometimes known as the paradox of the heap) is a paradox that arises from vague predicates. A typical formulation involves a heap of sand, from which grains are individually removed. Under the assumption that removing a single grain does not turn a heap into a non-heap, the paradox is to consider what happens when the process is repeated enough times: is a single remaining grain still a heap? If not, when did it change from a heap to a non-heap?

What is the minimum number of gold atoms needed to produce shininess?

How large must a grain of tin be for it to superconduct?

When spontaneous symmetry breaking is involved there are subtleties. Strictly, speaking it only occurs in the thermodynamic limit, i.e. for an infinite system. However, for a finite system, one can observe some properties associated with symmetry breaking such as rigidity. These issues can be addressed in the laboratory with ultracold atoms and with metallic grains of superconductors, both of which can be produced with controlled numbers of particles, ranging from a few hundred to billions. There also are some resonances with the problem of trying to identify the quantum-classical boundary. 

Finally, piles of sand were central to the discovery of self-organised criticality.

Friday, December 4, 2020

The most essential critical thinking skill for citizens?

 I believe that there is one verb that describes the mission of universities (think) and that teaching a discipline means teachings students how to think in accord with that discipline.

But, what about high school? What are the key critical thinking skills that all students should learn? In particular, what is needed they can become engaged citizens who play a constructive role in a democracy.

I wonder if the most essential skill is to be able to consider an issue and critically evaluate different perspectives on the issue. Consider issues that are often topics of public debate (and acrimony): taxation, immigration, government regulation, freedom of speech, funding health care, covid lockdowns, capitalism, socialism, ... 

These are all complex issues and there is a wide range of perspectives on each of them. First, a student (citizen) should be able to acknowledge the existence of different perspectives. Second, objectively identify (or at least understand) the essential content of the different perspectives. Third, identify (or at least understand) the strengths and weaknesses of each of the perspectives, including acknowledging the level of evidence including its uncertainty. Fourth, compare and contrast these strengths and weaknesses. Fifth, be able to make the case for the perspective they may prefer. This may be too ambitious. But, it is a desirable goal.

I should point out that I am not at all proposing something postmodern/relativist along the lines of "all views are equally valid" or that "all views should get equal air time." Rather, such exercises and skills should lead to the ability to see why extremist and crackpot views should not get the attention or credibility that too often they do.

How does one achieve this? A concrete example is provided by an Indian newspaper presents opinion columns with Left, Right, and Centre views on specific issues.

There is a related but distinct skill that all citizens should desirably have, empathy, i.e. the ability to put oneself in the shoes of another (their context, background, and life experience) and see why they hold the views they do. This is more of an emotional skill, rather than an intellectual one. This skill enables one to understand and communicate better with those who have wildly different views than our own.

What do you think? What critical thinking skills do think should be promoted? What is realistic?