Search Results

Why be Hanged for Even a Lamb?

Nancy Cartwright

in Images of Empiricism: Essays on Science and Stances, with a Reply from Bas C. van Fraassen

This chapter examines van Fraassen's motivation for restricting his scientific theoretical commitments to claims about observables. Many critics have argued that the observable/unobservable ... More

This chapter examines van Fraassen's motivation for restricting his scientific theoretical commitments to claims about observables. Many critics have argued that the observable/unobservable distinction van Fraassen draws on is either an illegitimate distinction, or can't play the important philosophical role van Fraassen wants it to. The importance of this distinction is discussed. It is argued that what we fundamentally care about is what we will experience under the possible courses of action open to us, and hence we have a (non-epistemic) reason to try to control what we experience. This gives us special reason to form beliefs about what we are capable of observing.Less

Tests Of The Gauge Structure Of QCD: Colour Factors

GÜNTHER DISSERTORI, IAN G. KNOWLES, and MICHAEL SCHMELLING

in Quantum Chromodynamics: High Energy Experiments and Theory

This chapter examines the QCD lagrangian, focusing on the gauge group governing the dynamics of strong interactions. Experiments are described which verify that QCD is based on the gauge group SU(3). ... More

This chapter examines the QCD lagrangian, focusing on the gauge group governing the dynamics of strong interactions. Experiments are described which verify that QCD is based on the gauge group SU(3). After explaining how the so-called colour factors allow pinpointing of the gauge symmetry, experimental observables sensitive to the colour factors are introduced and experimental distributions are compared to theoretical predictions. The results show that the dynamics of QCD are consistent with the expected SU(3) symmetry, the correct ratio of the strengths of the quark-gluon to the gluon-gluon coupling, and the number of colour states of the gluon. The results are also interpreted as a limit on the mass of the gluino, the supersymmetric partner of the gluon.Less

Basics of treatment effect analysis

Myoung-Jae Lee

in Micro-Econometrics for Policy, Program and Treatment Effects

For a treatment and a response variable, the ‘causal effects’ of the former on the latter is of interest. This chapter introduces causality based on ‘potential-treated and untreated-responses’, and ... More

For a treatment and a response variable, the ‘causal effects’ of the former on the latter is of interest. This chapter introduces causality based on ‘potential-treated and untreated-responses’, and examines what type of treatment effects are identified. The basic way to identify treatment effect is to compare the average difference between the treatment and control (i.e., untreated) groups. For this to work, the treatment should determine which potential response is realized, but should otherwise be unrelated to the potential responses. Biases can result if this condition is not met due to some observed and unobserved variables affecting both the treatment and response. Avoiding such biases is one of the main tasks in causal analysis with observational data. The treatment effect framework has been used in statistics and medicine, has appeared in econometrics under the name ‘switching regression’, and is closely linked to ‘structural form equations’ in econometrics. Causality using potential responses gives a new look to the old workhorse ‘regression analysis’, enabling the interpretation of the regression parameters as causal parameters.Less

Unobserved Heterogeneity

Manuel Arellano

in Panel Data Econometrics

Unobserved heterogeneity is one instance in where correlation between observables and unobservables may be expected. This has been a pervasive problem in cross-sectional analysis. A major motivation ... More

Unobserved heterogeneity is one instance in where correlation between observables and unobservables may be expected. This has been a pervasive problem in cross-sectional analysis. A major motivation for using panel data has been the ability to control from the possibly correlated, time-invariant heterogeneity without observing it. This chapter analyses fixed effects models, heteroskedasticity and serial correlation, likelihood approaches, and nonlinear models with additive effects.Less

BOSONIZATION

Thierry Giamarchi

in Quantum Physics in One Dimension

This chapter explains bosonization, a useful technique for describing the low-energy properties of one-dimensional systems. Bosonization is introduced by presenting a model on which this method is ... More

This chapter explains bosonization, a useful technique for describing the low-energy properties of one-dimensional systems. Bosonization is introduced by presenting a model on which this method is essentially exact. This allows for the derivation of precise formulas that can be used for other models as well. Bosons are mapped with fermions and the effect of the interactions is examined. A one-dimensional system with spin is also discussed, and renormalization equations for sine-Gordon Hamiltonians are presented and analyzed. Furthermore, the generic phase diagram of a one-dimensional chain is obtained.Less

Operator mechanics

Efstratios Manousakis

in Practical Quantum Mechanics: Modern Tools and Applications

This chapter discusses the need to use operator in quantum mechanics and how the operators relate to observables.

Simultaneous observables

Efstratios Manousakis

in Practical Quantum Mechanics: Modern Tools and Applications

This chapter discusses when two observables, which are represented by operators, –can be simultaneously observable. The chapter discusses the uncertainty principle in the general case and when two ... More

This chapter discusses when two observables, which are represented by operators, –can be simultaneously observable. The chapter discusses the uncertainty principle in the general case and when two operators can share eigenstates. It also discuss the consequences of symmetry.Less

Basic Quantum Mechanics

Stephen C. Rand

in Lectures on Light: Nonlinear and Quantum Optics using the Density Matrix

Chapter 2 begins with a discussion of the de Broglie wave concept that is the foundation of quantum mechanics. The idea that particles can exhibit wave‐like behavior is an important part of the ... More

Chapter 2 begins with a discussion of the de Broglie wave concept that is the foundation of quantum mechanics. The idea that particles can exhibit wave‐like behavior is an important part of the explanation of why atoms have discrete energy levels and make transitions in which electromagnetic radiation is absorbed or emitted at specific frequencies. Important aspects of how quantum systems may be observed and how they develop in time are presented. The Schrödinger equation is introduced and the importance of the wavefunction covered. Mathematical simplifications that arise from considering symmetry are covered. Several examples of simple quantum systems are presented in which the calculation of electronic energy structure based on boundary conditions is illustrated.Less

Real Anti‐realism: The Evidential Approach

Sherrilyn Roush

in Tracking Truth: Knowledge, Evidence, and Science

This chapter argues that confirmation theory is relevant to the debate between epistemological realism and anti-realism about scientific theories, because typical realist and anti-realist claims ... More

This chapter argues that confirmation theory is relevant to the debate between epistemological realism and anti-realism about scientific theories, because typical realist and anti-realist claims about evidence are measure-dependent. It contends that no known measure makes Constructive Empiricism viable, but this is not the victory for the realist that it is assumed to be. Using the measure (standard of evidence) most suited to defending the realist’s general claims, it is argued that this standard is not actually fulfilled for any high-level theories in science. However, it is fulfilled for many low-level claims that go beyond observables. Whether the catch-all for a hypothesis can be evaluated is the crucial question for realism and anti-realism.Less

The Basic Theory of Quantum Mechanics

Bas C. van Fraassen

in Quantum Mechanics: An Empiricist View

Covered are Hilbert space, vector, and operator representations of pure and mixed states, measurable physical quantities (observables), Gleason's theorem, Lueders’ Rule, unitary operators, and ... More

Covered are Hilbert space, vector, and operator representations of pure and mixed states, measurable physical quantities (observables), Gleason's theorem, Lueders’ Rule, unitary operators, and Schroedinger's Equation, symmetries of the Hamiltonian and the corresponding conservation laws, and superselection rules.Less

Critique of the Standard Interpretation

Bas C. van Fraassen

in Quantum Mechanics: An Empiricist View

Von Neumann's unification of Schroedinger's and Heisenberg's formalisms came with an interpretation of quantum theory involving two principles. The first is that assertions about the values of ... More

Von Neumann's unification of Schroedinger's and Heisenberg's formalisms came with an interpretation of quantum theory involving two principles. The first is that assertions about the values of observables are equivalent to assertions about the quantum‐mechanical state of the system. This is sometimes known as the ’eigenvalue–eigenstate link’, since it equates an observable having a value with the system being in an eigenstate of that observable. The second is his Projection Postulate—i.e. the postulate that during measurement there is a ’collapse of the wave packet’. It is argued that the theory does not force these principles on us, and that there are severe difficulties in this interpretation, despite also its more recent defences.Less

QCD Analyses

GÜNTHER DISSERTORI, IAN G. KNOWLES, and MICHAEL SCHMELLING

in Quantum Chromodynamics: High Energy Experiments and Theory

While perturbative QCD deals with free quarks and gluons, experimentally, usually only multi-hadron final states are observed. This chapter focuses on how to extract information about QCD from the ... More

While perturbative QCD deals with free quarks and gluons, experimentally, usually only multi-hadron final states are observed. This chapter focuses on how to extract information about QCD from the observable final states. After explaining the general phenomenology, it discusses the problem of selecting events of a certain class from the set of all the interactions recorded by an experiment. It then defines appropriate observables which are sensitive to the dynamics of QCD. Given such variables, the issues of corrections for detector effects —such as finite acceptance, efficiency and resolution, hadronization corrections, which go back from the observable hadron level to the theoretically accessible parton level, and systematic uncertainties — are addressed. The analysis strategies are illustrated by the examples of structure function measurements from deep inelastic scattering, jet cross sections in proton-antiproton collisions, and the determination of jet rates in electron-positron annihilation.Less

EVOLUTION OF NUCLEAR STRUCTURE

R. F. Casten

in Nuclear Structure from a Simple Perspective

A focus on the excitations of a given nucleus is known as the ‘vertical’ approach to nuclear structure and has been the empirical cornerstone of nuclear physics and the inspiration for countless ... More

A focus on the excitations of a given nucleus is known as the ‘vertical’ approach to nuclear structure and has been the empirical cornerstone of nuclear physics and the inspiration for countless nuclear models. On the other hand, the ‘horizontal’ approach looks at changes in various observables across different regions of the nuclear chart (or even across the whole chart). This chapter outlines some of the elements of a horizontal approach that focuses on the evolution of the nuclear structure. This approach offers important insights not only about nuclear structure, but also phase transitions in finite nuclei, the properties of newly discovered nuclei, and the underlying shell structure. Two types of approaches, known as valence correlation schemes and correlations of collective observables, are considered. Many of these ideas are especially applicable to the new exotic nuclei that are becoming available with the advent of radioactive beams.Less

Measurements in Relativistic Quantum Mechanics

Heinz-Peter Breuer and Francesco Petruccione

in The Theory of Open Quantum Systems

This chapter develops the theory of measurements in relativistic quantum mechanics. The presentation is based on the idea to consider the state of a relativistic quantum system as a functional on the ... More

This chapter develops the theory of measurements in relativistic quantum mechanics. The presentation is based on the idea to consider the state of a relativistic quantum system as a functional on the set of space-like hypersurfaces in Minkowski space. This idea leads to a manifest covariant time-evolution equation, known as Schwinger–Tomonaga equation, and allows a relativistic formulation of the projection postulate of quantum measurement theory. This postulate is used to study a number of applications to local and non-local measurements, to the erasing of local information, and to the restrictions on the measurability of non-local quantities imposed by the causality principle. The relativistic projection postulate further enables the discussion of many important problems from a unified perspective, such as EPR-type experiments, measurements of Bell state operators, exchange measurements, and quantum teleportation.Less

Is Particle Physics Particle Physics?

Laura Ruetsche

in Interpreting Quantum Theories

This chapter develops a case for attributing quantum field theory a particle ontology. When the space of physical states of the theory resides in a Fock space, the observables constituting a particle ... More

This chapter develops a case for attributing quantum field theory a particle ontology. When the space of physical states of the theory resides in a Fock space, the observables constituting a particle notion circumscribed by that Fock space are fundamental in the sense that they form a complete set, so that every state of the theory can be understood in terms of values assigned those observables. The Unruh effect, in which an observer accelerating uniformly through Minkowski spacetime in its vacuum (i.e. no-particle) state observes a thermal distribution of particles, is often presented as a challenge to particle interpretations. Arguing that the standard form of the challenge is miscast, the chapter recasts it in a stronger form: unitarily inequivalent Fock space representations circumscribe incommensurable particle notions, so if physical states reside in multiple, unitarily inequivalent Fock space representations, no single particle notion can be fundamental.Less

Beyond the Perception-Behavior Link: The Ubiquitous Utility and Motivational Moderators of Nonconscious Mimicry

Tanya L. Chartrand, William W. Maddux, and Jessica L. Lakin

in The New Unconscious

Perception and behavior are inextricably intertwined such that people automatically behave as they perceive. This “perception–behavior link” refers to the unintentional, nonconscious effects of ... More

Perception and behavior are inextricably intertwined such that people automatically behave as they perceive. This “perception–behavior link” refers to the unintentional, nonconscious effects of social perception on social behavior. The perception of observables may activate specific behavioral representations, trait constructs, or stereotypes. Mimicry is a manifestation of the perception–behavior link at its most fundamental level. It is no more than copying another's observables and requires only the ability to perceive the behavior in the other person and the ability to form the behavior oneself. There is now considerable empirical evidence that people mimic a variety of observables, including speech, facial expressions, physical mannerisms, moods, and emotions. This chapter focuses on automatic imitation, which appears to be a result of the perception–behavior link. After reviewing the evidence for nonconscious mimicry, it explores the origins and utility of behavioral mimicry and argues that it serves a “social survival” function today. This chapter concludes that nonconscious mimicry may be an unidentified strategy in the repertoire of behaviors that help people get along with others.Less

Effective Field Theory of Large-Scale Structure

Tobias Baldauf

in Effective Field Theory in Particle Physics and Cosmology: Lecture Notes of the Les Houches Summer School: Volume 108, July 2017

The lectures featured in this chapter review the observables relevant to the large-scale structure (LSS) of our Universe. The chapter introduces an effective field theory (EFT) that allows us to ... More

The lectures featured in this chapter review the observables relevant to the large-scale structure (LSS) of our Universe. The chapter introduces an effective field theory (EFT) that allows us to analytically describe the growth of fluctuations into the non-linear era, with uncertainties better controlled than in classical linear perturbation theory. Topics covered in the chapter include random fields in three-dimensional space, Fourier space conventions, the shape of the matter power spectrum, Gaussian random fields, estimators and cosmic variance, dynamics in the Newtonian regime, a perturbative solution of the fluid equations, the EFT approach, the Lagrangian perturbation theory, biased tracers, and redshift space distortions.Less

The formal framework of linear-response TDDFT

Carsten A. Ullrich

in Time-Dependent Density-Functional Theory: Concepts and Applications

This chapter discusses the linear-response framework of time-dependent density-functional theory (TDDFT). It begins with a thorough and self-contained exposition of general linear-response theory for ... More

This chapter discusses the linear-response framework of time-dependent density-functional theory (TDDFT). It begins with a thorough and self-contained exposition of general linear-response theory for many-body systems. The time-dependent as well as the frequency-dependent response are discussed. Several exact representations and properties of the density-density response function are reviewed, such as the Lehmann representation and fluctuation-dissipation theorem, and the Kramers-Kronig relations. It is shown how several important spectroscopic observables are obtained from linear-response theory. Then, the TDDFT formulation of linear-response theory is derived. The key quantity in this formalism is the so-called exchange-correlation kernel. The remainder of the chapter demonstrates how this linear-response formalism can be used to calculate excitation energies in principle exactly with TDDFT. The Casida equation is derived, as well as several approximate schemes. A comparison is made with time-dependent Hartree-Fock theory.Less

The Mathematics of Quantum Mechanics

Jeffrey A. Barrett

in The Conceptual Foundations of Quantum Mechanics

Quantum mechanics is written in the language of linear algebra. On the Schrodinger picture the theory represents quantum-mechanical states using the elements of a Hilbert space and represents ... More

Quantum mechanics is written in the language of linear algebra. On the Schrodinger picture the theory represents quantum-mechanical states using the elements of a Hilbert space and represents observable physical properties and the standard dynamics using the linear operators on the state space. We consider the mathematical notions for understanding and working with the standard formulation of quantum mechanics. Each mathematical notion is characterized geometrically, algebraically, and physically. The mathematical representation of quantum-mechanical superpositions is discussed.Less

Sceptical veils of various fabrics

Tim Button

in The Limits of Realism

Chapter 5 raised problems for external realists who accepted a bracketed empiricist theory of empirical content. Many external realists do, indeed, accept such a theory of empirical content. But in ... More

Chapter 5 raised problems for external realists who accepted a bracketed empiricist theory of empirical content. Many external realists do, indeed, accept such a theory of empirical content. But in fact, no matter how the external realist explains her Cartesianism Principle, similar problems arise. In addition to the veil of sensations, it is possible to consider: a veil of Fregean senses that prevents access to ordinary objects; a veil of phenomena that prevents access to the noumena; a veil of observables that prevents access to unobservables; and a veil of flux that prevents access to the Forms. All external realists must accept that, by their own lights, any statement with empirical content is just more theory and so fails to constrain reference.Less