Symmetry and Symmetry Breaking

Posted on by Simon Fokt

Introduction: Symmetry considerations dominate modern fundamental physics, both in quantum theory and in relativity. Philosophers are now beginning to devote increasing attention to such issues as the significance of gauge symmetry, quantum particle identity in the light of permutation symmetry, how to make sense of parity violation, the role of symmetry breaking, the empirical status of symmetry principles, and so forth. These issues relate directly to traditional problems in the philosophy of science, including the status of the laws of nature, the relationships between mathematics, physical theory, and the world, and the extent to which mathematics suggests new physics.

This entry begins with a brief description of the historical roots and emergence of the concept of symmetry that is at work in modern science. It then turns to the application of this concept to physics, distinguishing between two different uses of symmetry: symmetry principles versus symmetry arguments. It mentions the different varieties of physical symmetries, outlining the ways in which they were introduced into physics. Then, stepping back from the details of the various symmetries, it makes some remarks of a general nature concerning the status and significance of symmetries in physics.

What are dark matter and dark energy?

Posted on by Simon Fokt

Summary: According to the currently accepted model in cosmology, our universe is made up of 5% of ordinary matter, 25% cold dark matter, and 70% dark energy. But what kind of entities are dark matter and dark energy? This chapter asks what the evidence for these entities is and which rival theories are currently available. This provides with an opportunity to explore a well-known philosophical problem known as under-determination of theory by evidence.

The origins of the universe: laws, testability and observability in cosmology

Posted on by Simon Fokt

Summary: How did our universe form and evolve? Was there really a Big Bang, and what came before it? This chapter takes the reader through the history of contemporary cosmology and looks at how scientists arrived at the current understanding of our universe. It explores the history of astronomy, with the nebular hypothesis back in the eighteenth century, and in more recent times, Einstein’s general relativity and the ensuing cosmological models. Finally, it explains the current Standard Model and early universe cosmology as well as the experimental evidence behind it.

Interpreting Quantum Theories: The art of the possible

Posted on by Simon Fokt

Publisher’s Note: Traditionally, philosophers of quantum mechanics have addressed exceedingly simple systems: a pair of electrons in an entangled state, or an atom and a cat in Dr. Schrodinger’s diabolical device. But recently, much more complicated systems, such as quantum fields and the infinite systems at the thermodynamic limit of quantum statistical mechanics, have attracted, and repaid, philosophical attention. Interpreting Quantum Theories has three entangled aims. The first is to guide those familiar with the philosophy of ordinary QM into the philosophy of ‘QM infinity’, by presenting accessible introductions to relevant technical notions and the foundational questions they frame. The second aim is to develop and defend answers to some of those questions. Does quantum field theory demand or deserve a particle ontology? How (if at all) are different states of broken symmetry different? And what is the proper role of idealizations in working physics? The third aim is to highlight ties between the foundational investigation of QM infinity and philosophy more broadly construed, in particular by using the interpretive problems discussed to motivate new ways to think about the nature of physical possibility and the problem of scientific realism.

Reasoning without the principle of sufficient reason

Posted on by Simon Fokt

Abstract: According to Principles of Sufficient Reason, every truth (in some relevant group) has an explanation. One of the most popular defenses of Principles of Sufficient Reason has been the presupposition of reason defense, which takes endorsement of the defended PSR to play a crucial role in our theory selection. According to recent presentations of this defense, our method of theory selection often depends on the assumption that, if a given proposition is true, then it has an explanation, and this will only be justified if we think this holds for all propositions in the relevant group. In this paper the author argues that this argument fails even when restricted to contingent propositions, and even if we grant that there is no non-arbitrary way to divide true propositions that have explanations from those that lack them. The author gives an alternate explanation of what justifies our selecting theories on the basis of explanatory features: the crucial role is not played by an endorsement of a PSR, but rather by our belief that, prima facie, we should prefer theories that exemplify explanatory power to greater degrees than their rivals.

How the Laws of Physics Lie

Posted on by Simon Fokt

Publisher’s Note: Nancy Cartwright argues for a novel conception of the role of fundamental scientific laws in modern natural science. If we attend closely to the manner in which theoretical laws figure in the practice of science, we see that despite their great explanatory power these laws do not describe reality. Instead, fundamental laws describe highly idealized objects in models. Thus, the correct account of explanation in science is not the traditional covering law view, but the ‘simulacrum’ account. On this view, explanation is a matter of constructing a model that may employ, but need not be consistent with, a theoretical framework, in which phenomenological laws that are true of the empirical case in question can be derived. Anti?realism about theoretical laws does not, however, commit one to anti?realism about theoretical entities. Belief in theoretical entities can be grounded in well?tested localized causal claims about concrete physical processes, sometimes now called ‘entity realism’. Such causal claims provide the basis for partial realism and they are ineliminable from the practice of explanation and intervention in nature.

Do Newton’s Rules of Reasoning Guarantee Truth … Must They?

Posted on by Simon Fokt

Abstract: Newton’s Principia introduces four rules of reasoning for natural philosophy. Although useful, there is a concern about whether Newton’s rules guarantee truth. After redirecting the discussion from truth to validity, I show that these rules are valid insofar as they fulfill Goodman’s criteria for inductive rules and Newton’s own methodological program of experimental philosophy; provided that cross-checks are used prior to applications of rule 4 and immediately after applications of rule 2 the following activities are pursued: (1) research addressing observations that systematically deviate from theoretical idealizations and (2) applications of theory that safeguard ongoing research from proceeding down a garden path.