The European Science Foundation Network for Philosophical and Foundational Problems of Modern Physics

9.00

Dr Harvey Brown
(Oxford)

Relativity as a "constructive" theory: a defence of the Pauli-Eddington-Bell interpretation

10.15

Dr Henrik Zinkernagel
(Grenada)

Cosmology and the Meaning of Time

11.15

Coffee

11.45

Dr Edward Anderson
(London)

Plausible first principles for geometrodynamics?
General relativity can be formulated in a number of ways.  One such is geometrodynamics: the dynamics of 3-geometries.  Whereas Arnowitt--Deser--Misner and Dirac obtained this by laborious rearrangement of the Einstein field equations, Wheeler asked whether it could be made to rest instead on ``plausible first principles".  Hojman--Kuchar--Teitelboim derived geometrodynamics from spacetime first principles.  More recently Barbour, Foster, Kelleher, O Murchadha and I have been working on the derivation from 3-space principles.  In this talk I explain the 3-space approach (TSA).  I briefly mention how general relativity is not uniquely picked out by the TSA.  I relate the TSA to Kuchar's scheme which presupposes spacetime.  I show that the TSA is ``plausible" in that the usual full set of fundamental matter fields can be included.  I investigate how the relativity principles, the principle of equivalence and the gauge principle may arise in the TSA.
References:
S.A. Hojman, K.V. Kuchar and C. Teitelboim, Ann. Phys. 96 p 88 (1976).
J.B. Barbour, B.Z. Foster and N. O Murchadha, Class. Quantum Grav 19 p 3217 (2002), gr-qc/0012089.
E. Anderson and J.B. Barbour, Class. Quantum Grav. 19 p 3249 (2002), gr-qc/0201092.
E. Anderson, Phys. Rev. D68 p 104001 (2003), gr-qc/0302035.
E. Anderson, PhD Thesis, University of London (2004).
E. Anderson, J.B. Barbour, B.Z. Foster, N. O' Murchadha, Class. Quantum Grav. 20 p 157 (2003), gr-qc/0211022.
E. Anderson, J.B. Barbour, B.Z. Foster, B. Kelleher and N. O' Murchadha,  forthcoming.
K.V. Kuchar, J. Math Phys 17 p 777; p 792; p 801 (1976).

14.00

Dr Simon Saunders
(Oxford)

Frame-dependence: pros and cons

15.15

Prof Andreas Bartels and Prof Holger Lyre
(Bonn)

Structural realism and the generality of the hole argument

16.15

Tea

16.45

Dr Oliver Pooley
(Oxford)

What is Observable in Special and General Relativity?

9.00

Prof Gerard Emch
(Florida and Oxford)

Symmetry and the Symplectic Geometry of Gravitational Wave Causality

10.15

Prof Dennis Dieks
(Utrecht)

Another look at general covariance and the equivalence of frames of reference
In his general theory of relativity Einstein sought to generalize his special relativistic principle of relativity to a principle according to which all frames of reference, regardless of their motion, are equivalent. He thought to have achieved this aim through the general covariance of the equations of GRT: because the equations take the same form in every frame of reference, all frames are physically equivalent. There seems to be a consensus among philosophers of relativity that Einstein was mistaken here: form invariance of the equations does not imply physical equivalence of frames. We will argue, however, that Einstein's position is not unreasonable at all. Although there are certainly physical differences between reference frames in general relativity, these differences should be seen as fact-like rather than law-like. By contrast, in classical mechanics and in special relativity the differences between inertial systems and accelerated systems have a law-like status. The fact-like character of the differences between frames in general relativity justifies regarding them as equivalent in the same sense as inertial frames in special relativity are equivalent.

11.15

Coffee

11.45

Prof Massimo Pauri
(Parma)
and Dr Luca Lusanna
(Florence)

General Covariance and the Objectivity of Spacetime Point-events
We show the unique capabilities of the ADM Hamiltonian approach to metric gravity to get new insights into a series of foundational issues of GR. Our results - valid for the Christodoulou-Klainermann class of models of the theory - include: a) finding the "last remnant of physical objectivity of space-time" by means of a physical individuation of point-events in terms of the intrinsic degrees of freedom of the gravitational field; b) a counter-example to the frozen-evolution picture; c) the definition of extended, non-inertial, space-time laboratories in which tidal-like and generalized inertial effects can be separated (though not invariantly); d) a main conjecture (which would entail invariance of the above separation) about the relation of the Dirac and the Bergmann definitions of observable; e) a disclosure of the dynamical nature that the traditional "conventions" about distant simultaneity assume in canonical metric gravity: different "conventions" within the same üniverse" are simply gauge-related options; f) an implementation of the physical individuation of point-events through a well-defined empirical procedure leading to an operational definition of space-time. At the end, a peculiar holistic and structuralist view of space-time emerges.
References:
* L.Lusanna and M.Pauri, The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity - I: Dynamical Synchronization and Generalized Inertial Effects, pre-print.
* L.Lusanna and M.Pauri, The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity - II : Dirac versus Bergmann Observables and the Objectivity of Space-Time, pre-print.
* M.Pauri and M.Vallisneri, Ephemeral Point-Events: is there a Last Remnant of Physical Objectivity?, essay for the 70th birthday of R.Torretti, Dialogos 79, 263 (2002) (gr-qc/0203014).
* L.Lusanna and M.Pauri, General Covariance and the Objectivity of Space-Time Point-Events: The Physical Role of Gravitational and Gauge Degrees of Freedom in General Relativity (gr-qc/0301040).
* M.Dorato and M.Pauri, Holism and Structuralism in Classical and Quantum General Relativity, Pittsburgh-Archive, ID code 1606, February 10, 2004.
* L.Lusanna, The Rest-Frame Instant Form of Metric Gravity, Gen.Rel.Grav. 33, 1579 (2001) (gr-qc/0101048).
* L.Lusanna and S.Russo, A New Parametrization for Tetrad Gravity, Gen.Rel.Grav. 34, 189 (2002)(gr-qc/0102074).
* R.De Pietri, L.Lusanna, L.Martucci and S.Russo, Dirac's Observables for the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge, Gen.Rel.Grav. 34, 877 (2002) (gr-qc/0105084).
* D.Alba and L.Lusanna, Simultaneity, Radar 4-Coordinates and the 3+1 Point of View about Accelerated Observers in Special Relativity (gr-qc/0311058).
* J.Agresti, R.DePietri, L.Lusanna and L.Martucci, Hamiltonian Linearization of the Rest-Frame Instant Form of Tetrad Gravity in a Completely Fixed 3-Orthogonal Gauge: a Radiation Gauge for Background-Independent Gravitational Waves in a Post-Minkowskian Einstein Space-Time, to appear in Gen.Rel.Grav. (gr-qc/0302084).
* L.Lusanna, Towards a Unified Description of the Four Interactions in Terms of Dirac-Bergmann Observables, invited contribution to the book Quantum Field Theory: a 20th Century Profile, of the Indian National Science Academy, ed.A.N.Mitra, forewards by F.J.Dyson (Hindustan Book Agency, New Delhi, 2000) (hep-th/9907081).

14.00

Prof Istvan Nemeti and Prof Hajnal Andreka
(Budapest)

On the logical foundation of spacetime theories
We will discuss two kinds of connections between logic and relativity.
(1) Logical foundation of relativity. Foundation of Mathematics (FOM) bulletinboard (http://www.cs.nyu.edu/pipermail/fom/, December 2003 - February 2004) contains several postings by leading logician Harvey Friedman in which he proposes to export the methodology, spirit, and machinery of Foundational Thinking from the area of Foundations of Mathematics to a similar foundation of relativity which eventually would provide logic-based axiomatic foundation for both special relativity and general relativity. Of course, one begins with special relativity (but keeping an eye open for the direction of general relativity). The above aims coincide with the ones our group has been pursuing (leading to a broader cooperation).
A precise conceptual analysis of relativity emerges on these foundations elaborated purely in first-order logic (FOL). E.g. we formalize (in FOL) Einstein's SPR (Special Principle of Relativity) and we calibrate its deductive role/power in the hierarchy of axioms/postulates/principles of relativity theory. As an example illustrating the uses of this precise logic-based framework we do the following. Although it is customary to derive NoFTL (No Faster Than Light travel) from SPR, we show that SPR does not entail this conclusion logically. On the other hand, making some of the usual tacit assumptions explicit, we prove NoFTL from these tacit assumptions without using SPR. Then we discuss what extra power SPR adds to these tacit assumptions. Material on the above can be found in the web-site
http://www.math-inst.hu/pub/algebraic-logic/Contents.html, e.g. [1]-[4]
below.
(2) In the other direction, relativity theory can influence FOM, too! The Relativity |--> Logic  connection is discussed in [5]-[7]. Besides Malament-Hogarth-Tipler (beyond Turing) computability, we will also connect these ideas to CTC's in spacetimes popularly named "time-travel". E.g. mathematical logic can be applied to discussing how much of the consistency constraints imposed by the possiblility of time-travel are dictated by purely logical considerations and how much are generated by the resources of physical theories. Cf. Christian Wuthrich [W], [ESW].

References:
[1] Andreka-Madarasz-Nemeti: Logical axiomatizAtions of spacetime.
http://www.math-inst.hu/pub/algebraic-logic/lstsamples.pdf
[2] Madarasz-Nemeti-Toke: Generalizing the logic-approach to spacetime towards general relativity.
http://www.math-inst.hu/pub/algebraic-logic/loc-mnt04.pdf
[3] Andreka-Madarasz-Nemeti: Introduction to logical analysis of relativity theories.
http://www.math-inst.hu/pub/algebraic-logic/PartI.ps.gz .
[4] Madarasz: Logic and relativity (in the light of definability theory). http://www.math-inst.hu/pub/algebraic-logic/diszi0226.ps.gz (big file)
[5] Etesi-Nemeti: Non-Turing computations via Malament-Hogarth spacetimes. http://www.math-inst.hu/pub/algebraic-logic/turing.pdf
[6] Hogarth: Predictability, Computability, and spacetime.
http://www.math-inst.hu/pub/algebraic-logic/Hogarththesis.ps.gz
[7] Andreka-Nemeti: Questions on Kerr spacetime.
http://www.math-inst.hu/pub/algebraic-logic/kerr.ps
[W] Wuthrich: Does modern phyusics permit the operation of time machines? http://aardvark.ucsd.edu/grad_conference/wuthrich.pdf
[ESW] Earman-Smeenk-Wuthrich: Take a ride on a time machine.
http://philsci-archive.pitt.edu/documents/disk0/00/00/09/65/index.html

15.15

Prof Sir Roger Penrose
(Oxford)

Quantum Superpositions of Spacetimes: do they Reduce Because of a Clash of Principles?

16.15

Tea

16.45

Dr Nick Bostrom
(Oxford)

9.00

Dr Fay Dowker
(London and Perimeter Institute, Waterloo)

The Causal Set as the Deep Structure of Spacetime
One approach to solving the problem of quantum gravity is based on the causal set hypothesis, which states that the deep, quantum structure of spacetime is discrete and is what is known in mathematics as a ``partial order'' or ``poset'', a kind of extended family tree. Causal set theory has now reached a stage of maturity in which both foundational issues and phenomenological questions can be addressed concretely. An example of the former is the question of what the observables of quantum gravity are (in other words, what is the solution of the ``problem of time'' in the causal set context). An example of phenomenology is the ``Lucretius effect'' of causal set discreteness on the propagation of massive particles.
Relevant papers:
1)Background Causal Set material, all by Rafael Sorkin and available from his website
http://www.physics.syr.edu/~sorkin/some.papers/
(i) A Specimen of Theory Construction from Quantum Gravity
(ii) First Steps with Causal Sets
(iii) Spacetime and Causal Sets
2) ``Observables'' in Causal Set Cosmology
http://arxiv.org/abs/gr-qc/0210061
3) The Lucretius effect (``swerves'')
Quantum Gravity Phenomenology, Lorentz Invariance and Discreteness
http://arxiv.org/abs/gr-qc/0311055

10.15

Dr Carl Dolby
(Oxford)

Life in an Energy Eigenstate: The Problem of Time in Quantum Gravity

11.15

Coffee

11.45

Dr Joy Christian
(Oxford)

Passage of Time in a Planck Scale Rooted Local Inertial Structure
http://arxiv.org/abs/gr-qc/0308028
It is argued that the `problem of time' in quantum gravity necessitates a refinement of the local inertial structure of the world, demanding a replacement of the usual Minkowski line element by a 4+2n dimensional pseudo-Euclidean line element, with the extra 2n being the number of internal phase space dimensions of the observed system. In the refined structure, the inverse of the Planck time takes over the role of observer-independent conversion factor usually played by the speed of light, which now emerges as an invariant but derivative quantity. In the relativistic theory based on the refined structure, energies and momenta turn out to be invariantly bounded from above, and lengths and durations similarly bounded from below, by their respective Planck scale values. Along the external timelike world-lines, the theory naturally captures the `flow of time' as a genuinely structural attribute of the world. The theory also predicts expected deviations--suppressed quadratically by the Planck energy--from the dispersion relations for free fields in the vacuum. The deviations from the special relativistic Doppler shifts predicted by the theory are also suppressed quadratically by the Planck energy. Nonetheless, in order to estimate the precision required to distinguish the theory from special relativity, an experiment with a binary pulsar emitting TeV range gamma-rays is considered in the context of the predicted deviations from the second-order shifts.

AFTERNOON FREE

9.00

Prof Don Howard
(Notre Dame USA)

Spin, Space, Symmetries, and Statistics: Some Questions about Covariance, Nonseparability, and Particle Identity in the 1920s

10.15

Prof Michel Ghins
(Louvain)

Revisiting the Equivalence Principle in General Relativity
Relevant paper:
Studies In History and Philosophy of Modern Physics 32, March 2001, 33--51
doi:10.1016/S1355-2198(00)00038-1

11.15

Coffee

11.45

Dr Julian Barbour
(Oxford)