Abstracts

Helge Kragh: Testability and Epistemic Shifts in Modern Cosmology

Not all philosophical problems of modern cosmology are modern: some are ancient, and others are postmodern. In my talk, I shall try to classify various kinds of problems, arguing that from a conceptual point of view some of the pertinent questions, such as the ontological status of "the universe", are very old indeed. The same is the case with certain epistemic questions, say, if absolute beginning can be recognized and accounted for scientifically.

Although I do not think that modern (say post-1990) cosmology is basically different from older versions, there are certain features in the modern development that stand out more clearly than earlier and invite critical considerations. I intend to focus on the notion of epistemic shifts, the claim that some fields of science (for example, multiverse physics) call for a new definition of what constitutes science, perhaps a definition that does not include empirical testability as a sine qua non. Claims of this kind involve not only philosophical reflection, but also have a sociological dimension: who have the right to define what science is and thus to demarcate science from non-science? (This question is not cosmological in nature, but turns up with particular force in modern cosmology.)

George Ellis: Key Issues in the Philosophy of Cosmology

The core issue for the philosophy of cosmology is, what constitutes an explanation in the context of cosmology? This has two specific aspects: what kinds of things are we trying to explain?, and how do we test if the kinds of explanation we are offering are valid? The question that results is: Do our models take reality seriously? What kinds of questions do we want our models to solve? What are the limits of our models? Specific issues relate to the nature of causation in cosmology, the testability of multiverse and cyclic theories, and the problematic nature of claimed physically realized infinities in cosmology.

A key issue is, what does it mean if we discover that the universe must have had a beginning? How do we handle the idea of creation of the universe and what kind of pre-existing entities might have been responsible or do we give up the idea of causation? Are there laws for the universe per se? What is the nature of physical laws and what is the nature of their existence? What kinds of causation can we envisage? An important point is that the philosophy of cosmology must adequately take reality into account. Remember the limitation of equations as representations of reality and consider the types of data that will be taken into account. Don't use equations and theories based on limited data to try to talk about the metaphysical meaning of the whole, and don't stretch equations beyond the limits of their validity. Some accounts of cosmology by scientists do not follow these precepts.

The most interesting issue in the future development of cosmology may well lie in the interaction between bottom-up and top-down effects in the physical universe. This relates to issues such as Mach's principle, the arrow of time, and the existence of life.

Dominico Giulini: Global Expansion versus Local Kinematics and Dynamics

Two characteristic questions arise when dealing with cosmological models in General Relativity:

1) How do we model local inhomogeneities in an "otherwise" homogeneous universe?

2) At what additional expense (as compared to the Newtonian context) can we employ familiar kinematical concepts, like relative velocity and acceleration, and how can we trace "trajectories" of objects from a distance in time-changing spatial geometries?

In my talk I shall highlight some of the fundamental issues associated with these questions. It will largely be based on our article in Reviews of Modern Physics, Vol. 82, 169-208 (2010). [Paper]

Jean-Christophe Hamilton: What Have We Learned from Observational Cosmology?

In the last decade a host of astrophysical observations have established the so-called Standard Model of Cosmology, often known as Lambda-CDM. Most of these observations are independent from each other and converge in an impressive manner towards a coherent description: an expanding flat and homogeneous Universe composed of 4% ordinary matter, 26% dark matter and 70% dark energy. Even the origin of the perturbations giving birth to the observed galaxies can be included in the Standard Model through the paradigm of inflation. However, if most (if not all) observables comply with this model, Dark Matter still resists direct detection, Dark Energy has so far escaped from a theoretical understanding and Inflation is still beyond direct measurement. The incredible success of Lambda-CDM in terms of modelling the large amount of data available and predicting features prior to their observation must not hide the lack of deep understanding of the physics involved.

Martín López Corredoira: Non-standard Models and the Sociology of Cosmology

I will review some theoretical ideas in Cosmology different to the standard "Big Bang": the Quasi-steady State model, Plasma Cosmology model, non-cosmological redshifts, alternatives to non-baryonic dark matter and/or dark energy, and others. These alternative theories are not at present as competitive as the standard model, mainly because they are not so developed. The fact that most cosmologists do not pay them any attention and only dedicate their research time to the standard model is in a great extent due to a sociological phenomenon ("snowball effect" or "Groupthink"). We may wonder whether Cosmology, the knowledge of the Universe as a whole, is a science like other fields of Physics or a dominant ideology.

Robert Brandenberger: Scenarios of Early Universe Cosmology: Philosophical and Physical Challenges

Both Standary and Inflationary cosmology suffer from the initial singularity problem with its resulting challenges for physics and philosophy. I will discuss further conceptual problems of our current cosmological models and indicate alternative scenarios which have a chance of resolving the initial singularity problem.

Chris Smeenk: The Predictability Crisis in Early Universe Cosmology

Many cosmologists have hoped to show that various features of the universe follow directly from physical laws, with no need to specify initial conditions. Finding such a theory would allow predictions of various features of the universe from first principles. Inflationary cosmology is often presented as fulfilling this hope: for a "generic" initial state, a period of inflation produces a homogeneous, flat, monopole-free bubble with an appropriate spectrum of density perturbations. However, the discovery that inflation is "generically eternal", leading to a vast multiverse of inflationary bubbles with different low-energy physics, threatens to undermine this common account of its predictions, due to the "predictivity" or "predictability" crisis. A prediction in this sense is a claim regarding the expected value of some observable quantity. Making a prediction requires both (1) a measure over the multiverse, and (2) some assumptions regarding our "typicality" among the reference class of observers.

In the first part of the talk, I will give a pessimistic assessment of attempts to make predictions in this sense. My emphasis will be on general points of contrast between cosmology and other physical theories where similar issues arise, rather than on detailed assessment of different proposed "measures". In the second part of the talk, I argue that the lack of predictions in the sense above does not threaten physical cosmology. Cosmological theories may still have a great deal of "predictivity" in the sense of allowing inferences to be drawn given some data used to constrain a model. I will assess some of the criticisms made of this approach in the literature, and assess the importance of the "measure problem" on this approach.

Marc Lachièze-Rey: Space, Time and Spacetime in Present Physics and Cosmology

The symmetries of general relativity (Lorentz and diffeomorphism invariances) imply the absence of space and time. A matter distribution breaks this symmetry and allows us to define a specific direction in spacetime, which may be conveniently called "time". In that way, the "cosmic time" in cosmology breaks the space-time covariance. I will show however that it does not benefit all properties usually associated to time. The resulting "problem of time" is a key issue in quantum gravity and cosmology. I will present some of its formulations with some proposed answers, and examine the issue of a physics without time.

Brigitte Falkenburg: Astroparticle Physics and The Empirical Basis of Cosmology

Astroparticle physics makes the bridge between particle physics, astrophysics and cosmology. It investigates the phenomenon of cosmic rays. For bringing the "astro" and the "particle" aspects of cosmic rays together, the concept of messenger particles is crucial: Cosmic rays are considered to be messenger particles that carry information from cosmic sources to the earth. A generalized concept of observation, which was developed by Dudley Shapere in 1982, sheds light on this crucial concept and its unifying functions. The measurement of these messenger particles contributes substantially to the empirical basis of cosmology. The spectrum of cosmic rays ranges from the 3K CMB to particles of 1021 eV which are supposed to stem from active galactic nuclei (AGN). The interpretation of the spectrum raises questions of scientific realism, unification and reduction which shed light on what is the empirical basis of cosmology.

Jeremy Butterfield: Philosophy of Cosmology: A Glimpse from the Outside

I will begin by setting aside some issues, including some old conundrums about cosmology. Then I will present some generalities about what it is, or could be, to explain initial conditions, and-or the values of physical constants: especially in relation to the ideas of selection effects, and a multiverse. I shall emphasise two points, as follows.

(1): Deductions from premises about the existence of humans (or about stable planetary orbits etc: in short, anthropic considerations) of (a) features of initial conditions, and-or of (b) ranges of values for a physical constants, typically violate some popular constraints on what counts as an explanation.

(2): The success of a multiverse explanation (of initial conditions, and-or the values of physical constants) does not in general depend on the multiverse's most striking---and most discussed---feature, viz. the equal reality of the different `cases' (i.e. the different parts or domains of the multiverse).

I shall end by asking how a recent result of Manchak about observationally indistinguishable spacetimes bears on the question whether the multiverse is observable.