2020.
|
'The RT Formula
and its Discontents: Spacetime and Entanglement'
This essay is concerned with a
number of related proposals that claim there is a
link between spacetime topology and quantum
entanglement. How seriously should we take these
proposals?
|
| 2020. |
'Spacetime
as a Quantum Error-Correcting Code?'
This essay seeks to
understand recent proposals that link aspects of
the AdS/CFT
correspondence with quantum
error correction codes (QECCs). The
AdS/CFT correspondence is a dictionary that
relates aspects of a (d+1)-dim "bulk" gravitational
theory to a d-dim
"boundary" quantum field theory. One apparent
problem with this dictionary is called the "bulk
locality paradox": A standard way of
representing a bulk field in terms of boundary
fields (the AdS-Rindler representation) seems to
entail that any given boundary field must be a
multiple of the identity. This is very similar
to a necessary and sufficient condition for
QECCs, and this has motivated some
authors to suggest we view the bulk theory
as a code subspace that protects quantum
information in the boundary from erasure. What
in the world could this mean? |
2019.
|
'Why Be Natural?'
Only because naturalness
underwrites a non-trivial notion of emergence for
effective quantum field theories (and, arguably,
not because it's empirically warranted, or more
probable, or underwrites a central dogma of
effective field theories)... |
2018.
|
Non-Locality
in Instrinsic Topologically Ordered Systems'
Intrinsic
topologically ordered (ITO) condensed matter
systems are claimed to exhibit two types of
non-locality: one type associated with topological
properties, and the other associated with quantum
entanglement. This is supposed to allow ITO
systems to encode information in the form of
quantum entangled states in a topologically
non-local way that protects it against local
errors. This is a Big Deal, since it could make
possible topological quantum computation. But
topological non-locality is very different
conceptually from quantum entanglement
non-locality. Is the Big Deal based on a
misunderstanding of these two senses of
non-locality? Mathematicians
seem to realize the importance of the distinction,
but it's unclear if condensed matter physicists
do, too. |
2017.
|
'Topological
Order and Emergence'
Topologically
ordered systems play a prominent role in
current research in condensed matter physics
(examples include integer
and fractional
quantum Hall systems, topological
insulators, and topological
superconductors). These systems cannot be
characterized by the standard Landau-Ginsburg
theory of phase transitions that has informed much
of the discussion, in both the physics and the
philosophical literature, of emergence in
condensed matter systems. Nevertheless many
authors claim topologically ordered systems
exhibit emergence. This essay tries to make sense
of these claims.
|
2016.
|
'Emergence and
Mechanism in the Fractional Quantum Hall Effect'
A fractional
quantum Hall (FQH) system can be described
in at least four distinct ways: (i) as a system of
strongly coupled electrons in the presence of an
external magnetic field; (ii) as a system of
weakly coupled composite fermions (electrons with
an even number of attached magnetic fluxes) in the
presence of a modified external magnetic field;
(iii) as a system of composite bosons (electrons
with an odd number of attached magnetic fluxes) in
the absence of an external magnetic field; or even
(iv) as a system of strongly correlated electrons
in "long-range entangled" states. These
alternative formulations can be viewed as
providing the bases of four distinct mechanistic
explanations of the FQH effect. Many authors have
claimed that FQH systems exhibit emergence. Taking
them seriously, it seems to me, makes trouble for
"mechanism-centric" accounts of emergence that
require the specification of a unique causal
mechanism. My preference is for a "law-centric"
account of emergence in which novel emergent
behavior is underwritten by distinct, dynamically
robust laws (as opposed to causal mechanisms). I
think such a "law-centric" account of emergence
does just fine in explainging emergent behavior
associated with the FQH effect.
|
2015.
|
'Pragmatists and Purists
on CPT Invariance in RQFTs'
Greenberg
(2002) claims that the violation of CPT
invariance in an interacting RQFT entails the
violation of Lorentz invariance. This claim is
surprising since standard proofs of the CPT
theorem require more assumptions than
Lorentz invariance, and are restricted to
non-interacting, or at best, unrealistic
interacting theories. This essay analyzes
Greenberg's claim in the context of the debate
between pragmatist approaches to RQFTs, which
trade mathematical rigor for the ability to derive
predictions from realistic interacting theories,
and purist approaches, which trade the ability to
formulate realistic interacting theories for
mathematical rigor.
|
2014.
|
'Three Principles of
Quantum Gravity in the Condensed Matter Approach'
Research on quantum
gravity (QG) has historically relied on
appeals to guiding principles. This essay frames
three such principles within the context of the
condensed matter approach to QG. I first
identity two distinct versions of this approach,
and then consider the extent to which the
principles of asymptotic
safety, relative
locality, and holography
are supported by these versions. The general hope
is that a focus on distinct versions of a single
approach may provide insight into the conceptual
and foundational significance of these principles.
|
2013e.
|
'Emergence in
Effective Field Theories'
This essay considers the extent to
which a concept of emergence can be associated
with effective
field theories (EFTs). I suggest that such a
concept can be characterized by microphysicalism
and novelty underwritten by the elimination of
degrees of freedom from a high-energy theory, and
argue that this makes emergence in EFTs distinct
from other concepts of emergence in physics that
have appeared in the recent philosophical
literature.
|
2013d.
|
'CPT Invariance, the
Spin-Statistics Connection, and the Ontology of
RQFTs'
CPT
invariance and the spin-statistics
connection are typically taken to be essential
properties in relativistic quantum field
theories (RQFTs), insofar as the CPT and
Spin-Statistics theorems entail that any state
characterized by an RQFT must possess these
properties. Moreover, in the physics literature,
they are typically taken to be properties of
particles. But there is a Received View among
philosophers that RQFTs cannot fundamentally be
about particles. This essay considers what proofs
of the CPT and Spin-Statistics theorems suggest
about the ontology of RQFTs, and the extent to
which this is compatible with the Received View.
|
2013c.
|
'The Emergence of
Spacetime in Condensed Matter Approaches to
Quantum Gravity'
Condensed matter approaches to
quantum gravity suggest that spacetime emerges in
the low-energy sector of a fundamental
condensate. This essay investigates what
could be meant by this claim. In particular, I
offer an account of low-energy emergence that is
appropriate to effective field theories in
general, and consider the extent to which it
underwrites claims about the emergence of
spacetime in effective field theories of condensed
matter sysrtems of the type that are relevant to
quantum gravity.
|
2013b.
|
'Category-Theoretic
Structure and Radical Ontic Structural Realism'
Radical Ontic Structural
Realism (ROSR) claims that structure exists
independently of objects that may instantiate it.
Critics of ROSR contend that this claim is
conceptually incoherent, insofar as (i) it entails
there can be relations without relata, and
(ii) there is a conceptual dependence between
relations and relata.
In this essay, I suggest that (ii) is motivated by
a set-theoretic formulation of structure, and that
adopting a category-theoretic
formulation may provide ROSR with more support. In
particular, I consider how a category-theoretic
formulation of structure can be developed that
denies (ii), and can be made to do work in the
context of formulating theories in physics.
|
2013a.
|
'Effective Field Theory'
An effective
field theory (EFT) of a physical system is a
theory of the dynamics of the system at energies
small compared to a given cutoff. For some
systems, low-energy states with respect to this
cutoff are effectively independent of ("decoupled
from") states at high energies. Hence you can
study the low-energy sector fo the theory without
the need for a detailed description of the
high-energy sector (this makes calculations
easier, plus you don't have to worry about thorny
issues like renormalizability). Many physicists
currently think that the Standard Model of
particle physics is an example of an EFT of an, as
yet, unknown high-energy theory. This essay is a
general review of EFTs; in particular, it
identifies two conceptually distinct types
("Wilsonian" and "continuum"), and considers how
they might be interpreted, and alos what they say
(and do not say) about the notion of emergence.
|
2011.
|
'QFTs in
Classical Spacetimes and Particles'
According to a Received View among
philosophers, relativistic quantum field theories
(RQFTs) do not admit particle interpretations.
This view requires that particles be localizable
and countable, and that these characteristics be
given mathematical expression in the forms of
local and total number operators. Various results
(the Reeh-Schlieder
theorem, the Unruh
Effect, Haag's
theorem) then indicate that formulations of
RQFTs do not support such operators. These
mathematical results, however, don't hold for
non-relativistic QFTs (NQFTs). I point out
that this is due to the absolute temporal
structure of the classical spacetimes associated
with NQFTs. This seems to suggest that the choices
that the Received View makes in mathematically
representing its intuitions about the nature of
particles are (implicitly) informed by
non-relativistic intuitions.
|
2010.
|
'Relativity and
Quantum Field Theory'
Relativistic quantum field theories
(RQFTs) are invariant under the action of the
symmetry group of a Lorentzian spacetime--a
spacetime that admits a Lorentzian (i.e.
"relativistic") metric. Non-relativistic
quantum field theories (NQFTs) are invariant under
the action of a symmetry group of a classical
spacetime--a spacetime that minimally admits
separate absolute spatial and temporal metrics.
This essay is concerned with cashing out two
impliciations of this basic difference. First, it
suggests that a Received View that claims RQFTs
cannot support particle interpretations is perhaps
implicitly biased with non-relativistic intuitions
(this is argued for in more detail in 2011).
Second, the relations between RQFTs and NQFTs also
suggest that routes to quantum gravity are more
varied than is typically acknowledged. In
particular, they suggest it should be conceptually
possible to construct a quantum theory of gravity
by taking the "thermodynamic limit" of a
relativistic "particle" (i.e. finite degrees of
freedom) theory of gravity (although I have no
idea how this might be made more precise).
|
2008.
|
'Condensed Matter
Physics and the Nature of Spacetime'
Some condensed matter systems
exhibit low-energy behavior that can be described
by effective field theories that are formally
similar to field theories that appear in other
areas of physics. The "acoustic" spacetime
research programme, for instance, is based on
modeling general relativity by teh low-energy
behavior of superfluid Helium 4 (and similar
systems). Aspects of the Standard Model of
particle physics can be modeled by the low-energy
behavior of superfluid Helium 3-A, and aspects of
conformal field theories (for which twistors
come in handy) can be modeled by the low-energy
behavior of the edge of 4-dim quantum Hall
liquids. This paper evaluates such examples and
considers what they have to tell us about the
nature of spacetime; in particular, how they might
impact the debate between substantivalists and
relationalists.
|
2006.
|
'Spacetime
Structuralism'
This paper goes hog-wild with a
number of different mathematical formalisms (twistors,
Einstein algebras, geometric
algebra) that can be used to formulate
classical field theories. The point is to indicate
that if you're predisposed to read ontology off of
your formalism, then you'd be advised to dig deep
and go for some notion of structure, seeing as how
alternative formalisms can be very different
beasts, indeed.
|
2004.
|
'Theories of
Newtonian Gravity and Empirical
Indistinguishability'
There's not just one, but many theories
of Newtonian gravity. Some are in flat
spactimes, others are in curved spacetimes. Are
they really different theories, or just different
ways of formulating the same basic theory?
Inquiring minds want to know...
|
2003.
|
'Einstein Algebras and
the Hole Argument'
Einstein algebras are abstract
algebras that encode the essential structure
associated with general relativity (GR). They've
been suggested, and rejected, as a way to avoid
the Infamous Hole
Argument against one way of interpreting GR.
This paper points out that some physicists are
trying to use them to construct theories of
quantum gravity, and that this gives them a bit
more respectability than they've typically been
afforded.
|
2001.
|
'What Should
Philosophers of Science Learn from the History of
the Electron?' (with John Norton)
That it's structure that's retained
across theory change, and that structure is kinda
hard to define in a precise way (although we do
make an effort).
|
2000b.
|
'The
Coordinate-Independent 2-Component Spinor
Formalism and the Conventionality of Simultaneity'
Some philosophers of spacetime have
claimed that the structure associated with
half-integer-spin (fermionic) fields can settle
the debate over the conventionality
of simultaneity. This paper disputes this
claim, in particular by calling attention to how
fermionic fields can be represented in a
manifestly coordinate-independent way.
|
2000a.
|
'Against Particle/Field
Duality: Asymptotic Particle States and
Interpolating Fields in Interacting QFT (or:
Who's Afraid of Haag's Theorem?)'
This paper tries to indicate how the
LSZ formalism that's used by practicing physicists
suggests ways of interpreting fuzzy concepts like
"particle" and "localization" in quantum field
theory (as well as dealing with Haag's
theorem). And that these ways are to be
preferred to the ways suggested by more abstract
(and expressively incomplete) formalisms (like the
algebraic formalism).
|
1999.
|
'Weinberg on QFT:
Demonstrative Induction and Underdetermination'
This paper reviews an argument by
Steven Weinberg that seeks to establish a
particular formulation of quantum field theory as
the only type of quantum theory in accord with the
relevant evidence and satisfying two basic
physical principles. The paper reconstructs
Weinberg's argument as a demonstrative induction
and indicates it's role as a (potential) foil to
the underdetermination argument in the debate over
scientific realism.
|
1998.
|
'Whitehead's Theory of
Gravity'
Everything you ever wanted to know
about Whitehead's theory of gravity...
|