Towards a Realist View of Quantum Field Theory

Quantum field theories (QFTs) seem to have all of the qualities that typically motivative scientific realism. Alongside general relativity, the standard model of particle physics, and its subsidiaries, like quantum electrodynamics (QED) and quantum chromodynamics (QCD), are our most fundamental physical theories. They have also produced some of the most accurate predictions in the history of science: QED famously gives a value for the anomalous magnetic moment of the electron that agrees with experiment at precisions better than one part in a trillion. When it comes to actually articulating a realist reading of these theories, however, we run into serious difficulties. This chapter puts forward what I take to be the most promising strategy for developing a realist epistemology in this context. I set up the discussion by highlighting the difficulty of making sense of QFT in orthodox realist terms if we restrict our attention to perturbative and axiomatic treatments of the theory. I then introduce the renormalization group, and argue, drawing on previous work by Wallace (2006, 2011) and Williams (2017), that it points to a way of rescuing a realist reading of QFT. I close by considering some challenges facing this renormalization group based realism. Besides some brief remarks in this final section, I will mostly be bracketing the measurement problem and associated interpretive puzzles inherited from non-relativistic quantum mechanics

The twin origins of renormalization group concepts

This paper traces the origin of renormalization group concepts back to two strands of 1950s high energy physics: the causal perturbation theory programme, which gave rise to the Stueckelberg-Petermann renormalization group, and the debate about the consistency of quantum electrodynamics, which gave rise to the Gell-Mann-Low renormalization group. Recognising the different motivations that shaped these early approaches sheds light on the formal and interpretive diversity we find in contemporary renormalization group methods

Towards a Realist View of Quantum Field Theory

Quantum field theories (QFTs) seem to have all of the qualities that typically motivative scientific realism. Alongside general relativity, the standard model of particle physics, and its subsidiaries, like quantum electrodynamics (QED) and quantum chromodynamics (QCD), are our most fundamental physical theories. They have also produced some of the most accurate predictions in the history of science: QED famously gives a value for the anomalous magnetic moment of the electron that agrees with experiment at precisions better than one part in a trillion. When it comes to actually articulating a realist reading of these theories, however, we run into serious difficulties. This chapter puts forward what I take to be the most promising strategy for developing a realist epistemology in this context. I set up the discussion by highlighting the difficulty of making sense of QFT in orthodox realist terms if we restrict our attention to perturbative and axiomatic treatments of the theory. I then introduce the renormalization group, and argue, drawing on previous work by Wallace (2006, 2011) and Williams (2017), that it points to a way of rescuing a realist reading of QFT. I close by considering some challenges facing this renormalization group based realism. Besides some brief remarks in this final section, I will mostly be bracketing the measurement problem and associated interpretive puzzles inherited from non-relativistic quantum mechanics

First-passage theory of exciton population loss in single-walled carbon nanotubes reveals micron-scale intrinsic diffusion lengths

One-dimensional crystals have long range translational invariance which manifests as long exciton diffusion lengths, but such intrinsic properties are often obscured by environmental perturbations. We use a first-passage approach to model single-walled carbon nanotube (SWCNT) exciton dynamics (including exciton-exciton annihilation and end effects) and compare it to results from both continuous-wave and multi-pulse ultrafast excitation experiments to extract intrinsic SWCNT properties. Excitons in suspended SWCNTs experience macroscopic diffusion lengths, on the order of the SWCNT length, (1.3-4.7 um) in sharp contrast to encapsulated samples. For these pristine samples, our model reveals intrinsic lifetimes (350-750 ps), diffusion constants (130-350 cm^2/s), and absorption cross-sections (2.1-3.6 X 10^-17 cm^2/atom) among the highest previously reported.and diffusion lengths for SWCNTs.Comment: 6 pages, 3 figure

Evolution of Communal Roosting: A Social Refuge-Territory Prospecting Hypothesis

© 2018 The Raptor Research Foundation, Inc. Avian communal roosts provide insight into evolution and serve as focal points for conservation. Nonbreeding Crested Caracaras (Caracara cheriway; hereafter caracaras) use communal roosts, but evolutionary implications have not been explored. Though nonbreeding caracaras are nonmigratory, the scientific literature fails to explain seasonal differences in their movement and survival concurrent with seasonal consistency in their habitat and social ecology. In the Social Refuge-Territory Prospecting hypothesis we propose, socially subordinate nonbreeding caracaras precluded from breeding by habitat limitation use communal roosts as social refuges to avoid aggression from dominant territory holders during nonbreeding seasons, and engage in territory prospecting during breeding seasons. Communal roosts thus become central places from which to forage not for food, but for a breeding territory. Because foraging gains are stored as remembered information, competition costs resulting from public information are preempted. For the Social Refuge-Territory Prospecting hypothesis to be valid, two criteria need to be met. First, communal roost use needs to be higher during nonbreeding seasons. Second, a measure of fitness needs to be used to evaluate the hypothesis as an evolutionarily stable strategy. To meet these criteria, in this study we report that numbers of nonbreeding caracaras using a communal roost in Florida are higher during nonbreeding seasons (mean = 111.8 individuals/night) than during breeding seasons (mean = 60.7 individuals/night) as counted from August 2006-April 2009 (n = 407 counts). We also compare differential survival by season from previous work to demonstrate that by limiting exploratory movements to times when prospecting is most informative, nonbreeding caracaras balance maximizing survival against the likelihood of securing a breeding territory. Our hypothesis provides a unifying explanation for otherwise unexplained paradoxes in the ecology of nonbreeding caracaras, and may be useful in guiding conservation and expanding our understanding of the ecology of other communally roosting birds

Immunological Characterization and Neutralizing Ability of Monoclonal Antibodies Directed Against Botulinum Neurotoxin Type H.

BackgroundOnly Clostridium botulinum strain IBCA10-7060 produces the recently described novel botulinum neurotoxin type H (BoNT/H). BoNT/H (N-terminal two-thirds most homologous to BoNT/F and C-terminal one-third most homologous to BoNT/A) requires antitoxin to toxin ratios ≥1190:1 for neutralization by existing antitoxins. Hence, more potent and safer antitoxins against BoNT/H are needed.MethodsWe therefore evaluated our existing monoclonal antibodies (mAbs) to BoNT/A and BoNT/F for BoNT/H binding, created yeast-displayed mutants to select for higher-affinity-binding mAbs by using flow cytometry, and evaluated the mAbs' ability to neutralize BoNT/H in the standard mouse bioassay.ResultsAnti-BoNT/A HCC-binding mAbs RAZ1 and CR2 bound BoNT/H with high affinity. However, only 1 of 6 BoNT/F mAbs (4E17.2A) bound BoNT/H but with an affinity >800-fold lower (equilibrium dissociation binding constant [KD] = 7.56 × 10(-8)M) than its BoNT/F affinity (KD= 9.1 × 10(-11)M), indicating that the N-terminal two-thirds of BoNT/H is immunologically unique. The affinity of 4E17.2A for BoNT/H was increased >500-fold to KD= 1.48 × 10(-10)M (mAb 4E17.2D). A combination of mAbs RAZ1, CR2, and 4E17.2D completely protected mice challenged with 280 mouse median lethal doses of BoNT/H at a mAb dose as low as 5 µg of total antibody.ConclusionsThis 3-mAb combination potently neutralized BoNT/H and represents a potential human antitoxin that could be developed for the prevention and treatment of type H botulism

Assessment of the nucleotide modifications in the high-resolution cryo-electron microscopy structure of the Escherichia coli 50S subunit.

Post-transcriptional ribosomal RNA (rRNA) modifications are present in all organisms, but their exact functional roles and positions are yet to be fully characterized. Modified nucleotides have been implicated in the stabilization of RNA structure and regulation of ribosome biogenesis and protein synthesis. In some instances, rRNA modifications can confer antibiotic resistance. High-resolution ribosome structures are thus necessary for precise determination of modified nucleotides' positions, a task that has previously been accomplished by X-ray crystallography. Here, we present a cryo-electron microscopy (cryo-EM) structure of the Escherichia coli 50S subunit at an average resolution of 2.2 Å as an additional approach for mapping modification sites. Our structure confirms known modifications present in 23S rRNA and additionally allows for localization of Mg2+ ions and their coordinated water molecules. Using our cryo-EM structure as a testbed, we developed a program for assessment of cryo-EM map quality. This program can be easily used on any RNA-containing cryo-EM structure, and an associated Coot plugin allows for visualization of validated modifications, making it highly accessible

The Twin Origins of Renormalization Group Concepts

This paper traces the origin of renormalization group concepts back to two strands of 1950s high energy physics: the causal perturbation theory programme, which gave rise to the Stueckelberg-Petermann renormalization group, and the debate about the consistency of quantum electrodynamics, which gave rise to the Gell-Mann-Low renormalization group. Recognising the different motivations that shaped these early approaches sheds light on the formal and interpretive diversity we find in contemporary renormalization group methods