An abridged version will appear in "The Routledge Handbook of Scientific Realism", ed. Juha Saatsi.
https://arxiv.org/abs/1606.04071

For a PDF version of the article, click here.

SCIENTIFIC REALISM AND PRIMORDIAL COSMOLOGY

Feraz Azhar 1,2 & Jeremy Butterfield 3


1 Department of History and Philosophy of Science, University of Cambridge,
Free School Lane, Cambridge CB2 3RH, United Kingdom
2 Program in Science, Technology, and Society, Massachusetts Institute of Technology,
Cambridge, MA 02139, United States of America
3 Trinity College, Cambridge, CB2 1TQ, Cambridge, United Kingdom


Abstract: We discuss scientific realism from the perspective of modern cosmology, especially primordial cosmology: i.e. the cosmological investigation of the very early universe.

We first (Section 2) state our allegiance to scientific realism, and discuss what insights about it cosmology might yield, as against "just" supplying scientific claims that philosophers can then evaluate. In particular, we discuss: the idea of laws of cosmology, and limitations on ascertaining the global structure of spacetime. Then we review some of what is now known about the early universe (Section 3): meaning, roughly, from a thousandth of a second after the Big Bang onwards(!).

The rest of the paper takes up two issues about primordial cosmology, i.e. the very early universe, where "very early" means, roughly, much earlier (logarithmically) than one second after the Big Bang: say, less than 10−11 seconds. Both issues illustrate that familiar philosophical threat to scientific realism, the under-determination of theory by data - on a cosmic scale.

The first issue (Section 4) concerns the difficulty of observationally probing the very early universe. More specifically, the difficulty is to ascertain details of the putative inflationary epoch. The second issue (Section 5) concerns difficulties about confirming a cosmological theory that postulates a multiverse, i.e. a set of domains (universes) each of whose inhabitants (if any) cannot directly observe, or otherwise causally interact with, other domains. This again concerns inflation, since many inflationary models postulate a multiverse.

For all these issues, it will be clear that much remains unsettled, as regards both physics and philosophy. But we will maintain that these remaining controversies do not threaten scientific realism.


Keywords: scientific realism, primordial cosmology, inflation, multiverse


Table of Contents

INTRODUCTION

COSMOLOGY AS A SPECIAL CASE FOR SCIENTIFIC REALISM
Scientific realism, and how cosmology bears on it
No laws of cosmology? No worries
Ascertaining the global structure of spacetime?

A SMIDGEON OF WHAT WE NOW KNOW
Four snapshots of the early universe ...
as viewed by a scientific realist

THE VERY EARLY UNIVERSE: INFLATION?
The idea of an inflationary epoch
An inflationary epoch solves three problems
What caused the accelerating expansion?
The inflaton field
Connecting the inflaton to the CMB
A plethora of models

CONFIRMING A MULTIVERSE THEORY
Eternal inflation begets a multiverse
A proposed scheme
Distinguishing three problems: measure, conditionalization, and typicality
The Srednicki-Hartle proposal: frameworks
Different frameworks, same prediction

ENVOI

REFERENCES

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