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There has been a widening divide between two broad approaches to theoretical equivalence in physics: to what we mean when we say that two physical theories are fully equivalent, saying all the same things about the world but perhaps in different ways. On the one side is the formal approach to equivalence. Formal accounts say that physical theories ...

It has long been thought that observing the effects of quantum gravity is effectively impossible, since gravity is so much weaker than other forces: consider, for instance the utterly insensible gravitational attraction of a magnet, compared with the very sensible magnetic force it exerts. But by drawing on ideas from 'quantum information theory' (...

This proposed symposium brings together four philosophers of physics to discuss the interrelated web of topics surrounding theoretical equivalence in physics, the structure of physical theories, and the interpretation of those theories. In particular, it offers a variety of perspectives on the recent flowering of work on formal notions of equivalen...

Wilhelm (2021) has recently defended a criterion for comparing struc- ture of mathematical objects, which he calls Subgroup. He argues that Subgroup is better than SYM∗, another widely adopted criterion. We argue that this is mistaken; Subgroup is strictly worse than SYM∗. We then formulate a new criterion that improves on both SYM∗ and Sub- ...

For as long as astrophysicists have considered the large-scale structure of the cosmos, discoveries on the subject have been taken to provide critical empirical insights relevant to theorizing in fundamental physics. This close connection between the two subjects is most familiar in the context of the relativistic hot 'Big Bang' model of the expand...

I will use the simple case of a harmonic oscillator to introduce and resolve three novel puzzles about physical symmetries. One puzzle is that the fact that boosts are symmetries of Newtonian mechanics is not particularly important for explaining why a spring inside a ship remains invariant under constant boosts of the ship. A second puzzle is that...

Black hole complementarity is an influential set of ideas that respond to the black hole information paradox. Unpacking this literature, I argue that black hole complementarity is about the consistency of quantum characterizations of an evaporating black hole and I delineate two consistency claims—i.e., two principles of black hole complementarit...

Analogue experiments have attracted interest for their potential to shed light on inaccessible domains. In 1981, Unruh found a striking mathematical analogy between the propagation of light waves near a black hole and the propagation of sound in fluids. In fact, a number of distinct such 'analogue' systems can be found, from hydrodynamical systems ...

Longstanding common lore in fundamental physics insists that research on the problem of developing a high-energy theory of quantum gravity (QG) is almost certainly a topic for the theoretician alone. Discriminating signatures of QG in data are just too difficult to come by, whether by means of experimentation (in the context of high energy physics)...

Thermodynamics is an unusual theory. Prominent figures, including J.C. Maxwell and E.T. Jaynes, have suggested that thermodynamics is anthropocentric. Additionally, fruitful contemporary approaches to quantum thermodynamics label thermodynamics a ‘subjective theory’. Here, we evaluate some of the strongest arguments for anthropocentrism based o...

Taking the formal analogies between black holes and classical thermodynamics seriously seems to first require that classical thermodynamics applies in relativistic regimes. Yet, by scrutinizing how classical temperature is extended into special relativity, I argue that it falls apart. I examine four consilient procedures for establishing classical ...

How should one remove “excess structure” from a physical theory? Dewar (2019) presents two ways to undertake such a task: first, one could move to a reduced version of the theory, where one defines the models of the theory only in terms of structure that is invariant under the symmetries of the theory. Second, one could move to a sophisticated ...

No-go theorems attract widespread interest in the philosophy of physics. These results from the foundations of physics are distinctive for their logical force and counter-intuitive implications. A classic example that has attracted much philosophical attention is Haag's theorem, a result in quantum field theory showing that a certain standard metho...

Teitel (2021) argues that formal approaches to equivalence cannot be illuminating, since they run afoul of trivial semantic conventionality: the idea that “any representational vehicle can in principle be used to represent the world as being just about any way whatsoever.” In this paper, I consider the relationship between theoretical equivalen...

While it is known that our current theories of quantum interactions and gravitation cannot describe the Planck scale, the effective scale at which the unification of forces into a quantum theory of gravity occurs is yet unknown. The attempts to build new theories are recently being complemented by an intense program aiming at deriving a phenomenolo...

A new argument is given for the thesis that only symmetry-invariant physical quantities are real. Non-invariant quantities are dynamically epiphenomenal in that they have no effect on the evolution of invariant quantities, and it is a signifcant theoretical vice to posit epiphenomenal quantities.

I formulate an account of theoretical equivalence for effective quantum field theories. To start, I propose the `Easy Ontology' approach to interpreting what effective theories say about the physical world. Then I show how the Easy Ontology approach can be used to articulate an account of theoretical equivalence. Finally, I discuss the relationship...

Two conceptions of thermodynamics are distinguished. On one, thermodynamics is a resource theory, a theory about how agents with specified means of manipulating a physical system can exploit its physical properties to achieve specified ends, such as obtaining useful work. On the other, thermodynamics has been severed from its roots in technological...