Wednesday, August 25, 2021

The emergence of condensed matter as a fundamental force in physics

What shapes the emergence and influence of a specific new academic discipline or research field? How much does context matter?

How is the discipline defined? By the objects studied, methods used, central concepts, questions asked, goals, or key discoveries? And, who gets to define the discipline: text-book authors, current researchers, distinguished academics, or university managers?

It may depend on who you ask. A discipline can be viewed from intellectual, historical, institutional, political, economic, and sociological perspectives. It all depends on what questions you ask.

Arguably, for most of the twentieth-century physics was considered the dominant field of science. We also observe today that condensed matter physics is a dominant force in physics. This is reflected in many different measures, such as numbers of practitioners, journal articles, PhDs, citations, and Nobel Prizes.

How did this happen? 

Joseph Martin is a historian who explores this question in his 2018 book, Solid State Insurrection: How the Science of Substance Made American Physics Matter. He looks particularly at physics in the USA in the political and economic context of the Cold War, focusing on the rise of solid-state physics, and its metamorphosis into condensed matter physics. The role of institutions such as government, industry, and the American Physical Society (journals, conferences, divisions) is carefully examined. Public testimony of Phil Anderson against the SSC (Superconducting SuperCollider) in 1989 is considered to be a watershed moment and highly symbolic. 

The book is carefully researched, beautifully written, and contains important new insights. I highly recommend it.

In exploring these issues I think it important to find a balance between two extremes. On the one side, there are purists and idealists who claim that physicists are the best (or even only) people to provide a useful and reliable perspective. Science is all about reality, facts, and truth, and contexts (social, political, economic) are completely irrelevant. At the other extreme are the social constructivists who think science is just about politics and power, both inside and outside the university community. Martin is to be commended that he does not tend towards either of these extremes.

A Physics Today article is adapted from the book When condensed-matter physics became king and gives a useful summary.

To whet your appetite for the whole book, a good place to start is the concluding chapter. Martin offers two fascinating counterfactual histories: one where the Manhattan Project failed, one where APS did not keep industrial physicists in the fold.

the most active frontier of the twentieth century was not the high-energy frontier, but the complexity frontier. It was the demystification of the properties of complex matter and the applications of those properties, which remade our technological world, from home computing, stereo equipment, and cookware to communication, transportation, medicine, and warfare.

This is a tendentious framing, but it serves a purpose: it exposes the historiographical contingency of the disproportionate focus on nuclear physics, high energy physics, and cosmology, alongside the historical contingency of the dominance those fields assumed over public discourse about physics in the second half of the twentieth century. Two counterfactual scenarios help to probe that contingency further, each of which offers heuristic utility by throwing into relief the role solid state physics played, despite lacking the public acclaim of its sibling subfields, in securing the prominence of American physics.

First, given the high degree of institutional volatility in the early post–Second World War era, it is easy to imagine a counterfactual scenario in which solid state physicists migrate away from physics and into chemistry, metallurgy, and engineering, much as electrical engineering had some decades earlier. It was a contingency about which the field’s founders actively worried, and the American Physical Society council was demonstrably squeamish about clearing the type of institutional space that would give the society a more industrial flavor. Without solid state, which accounted for a large proportion of the postwar population boom, physics would have stayed smaller and grown more slowly.

We can imagine a second counterfactual scenario in which the Manhattan Project never acquired the scale or resources it needed to construct a working bomb before the end of the war in the Pacific... Suppose, for whatever reason, the Second World War ends without a dramatic, public demonstration of the power of the nucleus...  In this second scenario, solid state physicists would have been well positioned to become much more politically influential in the early Cold War, in particular on the strength of radar research,..

Aside. Earlier I posted about a nice article Martin wrote about public perceptions about condensed matter physics.

Thursday, August 19, 2021

Einstein on big questions

The mere formulation of a problem is far more essential than its solution, which may be merely a matter of mathematical or experimental skills.

To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.

I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.

Albert Einstein and Leopold Infeld (1938), The Evolution of Physics

I recently encountered this quotation in The Poetry and Music of Science: Comparing Creativity in Science and Art by Tom McLeish. I have heard many times the "Imagination is more important than knowledge" quote, sometimes as a dubious justification for dubious ideas. However, I did not know the context. 

My postdoctoral advisor, John Wilkins tried to drill into me, the idea in the first paragraph, that just coming up with a well-defined formulation of a problem could be a significant advance. This idea certainly had some impact on me, since I sometimes hear my non-scientist wife quote it!

On reflection, I am afraid that I too easily lose sight of this priority of defining problems, just like the method of multiple alternative hypotheses. Good science is hard.

Why am I reading this article? What question am I trying to answer?

Why am I writing this paper? What question am I trying to answer?

What is the problem I assigning a student to work on? Is it well-formulated?

Defining good research questions is hard work and requires discipline.

Thursday, August 12, 2021

Springy stringy molecular crystals

Perfect crystals are elastic. When a stress is applied and then removed the crystal will bounce back to its original shape. However, in reality no crystal is perfect. If the applied stress is too large the crystal will fracture. Understanding fracture is a big deal in materials science and involves some fascinating physics, including the role of topological defects. 

There are two distinct properties: elasticity and plasticity. They are associated with temporary and permanent changes in shape in response to an applied stress.
They are quantified by the elastic stiffness and the tensile strength, respectively. They reflect material properties at quite different length scales. 

A beautiful and accessible short introduction is 
Bart Kahr & Michael D. Ward 

This is a commentary of some work by a few of my UQ chemistry colleagues, who have made and studied a molecular crystal that is incredibly flexible, as seen in this movie.

Anna Worthy, Arnaud Grosjean, Michael C. Pfrunder, Yanan Xu, Cheng Yan, Grant Edwards, Jack K. Clegg & John C. McMurtrie 

A particular advance is that they use a synchrotron to perform spatially resolved X-ray crystallography to determine how the crystal structure varies spatially within a bent crystal. 

The material of interest has quasi-one-dimensional antiferromagnetic interactions and has been studied theoretically by my condensed matter theory colleagues.

Elise P. Kenny, Anthony C. Jacko, Ben J. Powell

But there is more...
A recent Science paper describes ice fibers that were particularly flexible.

Peizhen Xu, Bowen Cui, Yeqiang Bu, Hongtao Wang, Xin Guo, Pan Wang, Y. Ron Shen, Limin Tong

Monday, August 9, 2021

Emergence of complex patterns

I think it is amazing how in the universe we see diverse and beautiful patterns and structures. Even relatively simple systems can self-organise to produce things one would not expect or predict. Consider clouds, turbulent flows, leopard spots, a tree leaf, spiral galaxies, biological cells...
It is also amazing and beautiful that we can develop relatively simple mathematical models that can produce similar patterns.
This is emergence!

Here is a beautiful example that recently came to my attention.

The associated PRL is

Faraday-Wave Contact-Line Shear Gradient Induces Streaming and Tracer Self-Organization: From Vortical to Hedgehoglike Patterns

Héctor Alarcón, Matías Herrera-Muñoz, Nicolas Périnet, Nicolás Mujica, Pablo Gutiérrez, and Leonardo Gordillo

There is also a Physics story too.

Monday, August 2, 2021

Chemical fingerprints on blood diamonds

“Fortunately, the majority of gentlemen who are persuaded to steal things don’t really know a huge amount about science”

This is a choice quote in a fascinating article, New Australian technology tracks down gold thieves and blood diamonds ["New tech to trace dodgy diamonds" in the print edition] in the Australian Financial Review (AFR) Weekend.

It describes the work of John Watling, Chief Scientist at the company Source Certain. Basically by measuring the relative amounts of different trace elements [chemical impurities] in a sample of gold or diamond one can determine what mine that it has come from.