Thursday, January 28, 2021

Will there be big new discoveries in condensed matter physics?

 There are two aspects to this question concerning the future of condensed matter physics. First, are there big things to be discovered? If yes, will they be discovered?

I believe the first answer is yes for two reasons. First, the past hundred years have given us a continual stream of discoveries, many of them unexpected. Every time that things get a little boring, pretty soon there is something exciting and new. Second, condensed matter physics is all about emergent phenomena in materials. Emergent phenomena are extremely hard to anticipate or predict. Because of the combinatorics of chemistry, the list of possible materials to study is endless. CMP presents an endless frontier to explore. However, just because such a frontier exists does not mean that it will be explored. Successful explorers require courage, creativity, resources, time, and freedom.

I am concerned that the wild frontiers of condensed matter may not be explored. It is worth reflecting on who were some of the pioneers of CMP and the character of their institutional environments.  Consider Kammerlingh Onnes, Landau, Kapitsa, Anderson, de Gennes, and Leggett. Some common elements of the context (institutional, historical, political) in which they made their discoveries were time, stability, job security, mental space, and intellectual freedom. For example, Anderson spent almost three decades at Bell Labs in its heyday. Thanks to the monopoly of Bell in providing telephone services in the USA, the parent company had a very secure and stable income, providing it the ability to provide substantial financial and institutional support for basic research.

These pioneers played a long game. They had the freedom to fail, to choose research topics, and to change directions. They did not follow fashion and were fiercely independent thinkers. Andrew Zangwill highlights this about Anderson in his biography. They largely had the resources they needed and did not have to worry or fight for funding. Their daily life was very different from that of a researcher today. Their mental space was not filled with an endless stream of distractions such as emails, grant proposals, conferences, reporting, reviewing, committees, metrics, ... Most of their time and mental energy was simply focused on curiosity-driven research. 

Today, there is intense competition for funding, institutional status, and career benefits associated with obtaining it, and a pressure to produce in the short term "outputs" (papers) and "impact" (citations) and "national benefit" (technological, commercial, security, and social). This naturally leads to researchers working on "safe" projects in fashionable areas that they are confident will produce results in the short term.

I hope that I am wrong. But, I fear that great discoveries may be missed.

Monday, January 25, 2021

A popular introduction to emergence

 Emergence is central to condensed matter physics. Furthermore, arguably emergence is one of the most important concepts to come from science in the second half of the twentieth century. Emergence is central to many of the big questions in the sciences, both natural and social.

Hence, it is natural that in Condensed Matter Physics: A Very Short Introduction, I am dedicating a whole chapter to the subject. Here is my draft.

I welcome comments and suggestions, particularly if you are not a condensed matter physicist.

Wednesday, January 20, 2021

Where is materials research heading?

One way to answer this question is to look at the reports prepared every decade by the National Academies in the USA. I have recently been looking through the 2019 report, Frontiers of Materials Research: A Decadal Survey.

There are several reasons why I like to look at these reports. A previous post mentioned a similar 2007 report prepared for the USA Department of Energy.

I can learn a lot about materials science and engineering. See, for example, the figure below.

The reports help put condensed matter physics in the broader context of research in materials science and engineering. 

[Previously, I have argued that CMP is a particular approach to materials research and is distinct from materials physics. Although there is a significant overlap in the materials studied and some of the methods used, the driving questions are distinctly different].

The reports provide choice quotes for grant applications. Here is one from pages 24-25.

Key Finding: Basic research in fundamental science directions, meaning work that neither anticipates nor seeks a specific outcome, is the deep well that both satisfies our need to understand our universe and feeds the technological advances that drive the modern world. It lays the groundwork for future advances in materials science as in other fields of science and technology. Discoveries without immediate obvious application often represent great technical challenges for further development (e.g., high-Tc superconductivity, carbon nanotubes) but can also lead to very important advances, often years in the future. 

Key Recommendation: It is critically important that fundamental research remains a central component of the funding portfolio of government agencies that support materials research. Paradigm-changing advances often come from unexpected lines of work.

Here is one from page 6.

Key Finding: Quantum materials science and engineering, which can include superconductors, semiconductors, magnets, and two-dimensional and topological materials, represents a vibrant area of fundamental research. New understanding and advances in materials science hold the promise of enabling transformational future applications, in computing, data storage, communications, sensing, and other emerging areas of technology. This includes new computing directions outside Moore’s law, such as quantum computing and neuromorphic computing, critical for low-energy alternatives to traditional processors. Two of NSF’s “10 big ideas” specifically identify support of quantum materials (see The Quantum Leap: Leading the Next Quantum Revolution and Midscale Research Infrastructure).

The reports are based on the consensus of a range of experts. Hence, they arguably more objective than survey articles written in luxury journals by individuals hyping their field.

But, right now the reason I am reading this report is that I am writing the last chapter of Condensed Matter Physics: A Very Short Introduction, and need to address the question of where CMP is heading. Some earlier preliminary thoughts are here.

Here are a few of my thoughts about this report. I would love to hear the perspectives of others. 

First, I should give some important caveats. I have only skimmed the report. It was written by people who know much more than I. Writing a report that is based on a diverse community of interests and perspectives is extremely difficult. The main audience for such reports is not scientists themselves but rather funding agencies and policymakers.

The Summary begins with "The past decade has seen extraordinary advances in materials research" (page 3). Chapter 2 describes "significant advances" from the past decade. There is no doubt there have been many advances. It is great to read about them. Section 2.4 concerns Quantum Materials and Strongly Correlated Systems. Most of the advances described there are incremental advances from discoveries made before 2010, such as topological insulators. This haunts me with a nagging concern that CMP has not seen a big discovery in the past decade. For quantum materials is superconductivity in twisted bilayer graphene the leading candidate? Other suggestions?

A lot of attention is given to the potential of computational materials science, including when combined with data science methods (e.g. machine learning), topological matter, and quantum information processing in solid-state devices. However, I remain skeptical about the hype associated with these subjects, particularly with regard to technological applications. Big data need big theory too.

Significant attention is given to the relevance of materials research to USA defense, national security, and economic competitiveness. I wonder if this is because the report is being pitched to a MAGA government. Although I agree on the relevance, for many of us that is not the motivation for our interest in materials.

Update. In a comment below, David Sholl pointed out that NSF is not happy with the report. The background given there is also worth reading.

Tuesday, January 12, 2021

Emergence in biology

Emergence is one of the most important concepts developed by scientists in the second half of the twentieth century. Largely, independently of one another emergence was discussed, debated, and developed by physicists, biologists, social scientists, and philosophers.

Biology concerns phenomena at many different scales, some of which are nicely captured in the figure below, taken from here. At each scale, distinct phenomena emerge, with associated concepts, theories, and methods.

Ernst Mayr was one of the leading evolutionary biologists in the twentieth century and was influential in the development of the modern philosophy of biology. He emphasised the importance of emergence, contrasting the value of analysis with the limitations of reductionism (both defined below).

In Mayr's book, What Makes Biology Unique? Considerations on the Autonomy of a Scientific Discipline, chapter 4 is Analysis or Reductionism. 

Needless to say, the workers in the more complex branches of science saw in this [reductionist] claim only a ploy of the chemists and physicists to boost the importance of their fields. As Hilary Putnam said correctly: “What [reductionism] breeds is physics worship coupled with neglect of the ‘higher-level’ sciences. Infatuation with what is supposedly possible in principle goes with indifference to practice and to the actual structure of practice” (1973). 

What is the crucial difference between the concepts analysis and reduction? The practitioner of analysis claims that the understanding of a complex system is facilitated by dissecting it into smaller parts. Students of the functions of the human body choose as their first approach its dissection into bones, muscles, nerves, and organs. They make neither of two claims made by the reductionists 
(A) that the dissection should proceed “down to the smallest parts,” – i.e., atoms and elementary particles, and 
(B) that such a dissection will provide a complete explanation of the complex system. 
This reveals the nature of the fundamental difference between analysis and reduction. Analysis is continued downward only as long as it yields useful new information and it does not claim that the “smallest parts” give all the answers. 

... the view that composite wholes have properties not evident in their components has been widely accepted since the middle of the nineteenth century. The principle was already enunciated by Mill, but it was Lewes (1875) who not only presented a thorough analysis of the topic but also proposed the term emergence for this phenomenon.  
... emergence is characterized by three properties 
... first, that a genuine novelty is produced – that is, some feature or process that was previously nonexistent; 
second, that the characteristics of this novelty are qualitatively, not just quantitatively, unlike anything that existed before; 
third, that it was unpredictable before its emergence, not only in practice, but in principle, even on the basis of an ideal, complete knowledge of the state of the cosmos.

Mayr then discusses how in the first half of the twentieth century, emergence fell out of favour with biologists, such as J.B.S. Haldane, partly because the three characteristics above "appear at first sight to be in conflict with a straightforward mechanistic explanation."

How does this history relate to Phil Anderson and condensed matter physics?  This is nicely discussed by Andrew Zangwill in Chapter 12 of Mind over Matter. More is Different (1972) did not include the word emergence and Anderson did not use the term in print until 1981. Following Anderson's Nobel Prize in 1977, he received many invitations to speak to groups outside the physics community, including biologists, some of whom were fans of "More is Different".  This then exposed Anderson to the thinking and terminology of the biologists.

Aside: In a previous post, I discussed how Mayr described how prominent physicists such as Bohr and Schrodinger embraced vitalism.