Battle of the Big Bang: Inflation, Quantum Gravity, and the Cosmos Without a Beginning

Overview

This Royal Institution talk explores how cosmologists piece together the universe’s origin, tracing our oldest memories back to 14 billion years and examining the battles between competing theories from the Big Bang to inflation and beyond.

Key Themes

The discussion covers the historic debate between the steady state and Big Bang models, the role of the cosmic microwave background as evidence, the implications of inflation as a pre-Big Bang mechanism, and the quest for a quantum theory of gravity. It also delves into time machines, no boundary proposals, and the science-religion dialogue, concluding with a call for observational missions that could illuminate the earliest moments of the cosmos.

Introduction and The Oldest Memory

The talk opens with a reflective exercise on the oldest memory each of us can recall, then connects this to the primordial memory of the universe around 14 billion years ago. The speakers frame the journey as a battle for understanding the cosmos, where discovery is coupled with uncertainty and intellectual conflict.

Battle 1: The Expanding Universe

The pioneers Einstein and the lesser-known Georges Lemaître (the father of the Big Bang) are introduced in a historical showdown over whether the universe expands. Einstein’s general relativity implies a dynamic geometry of space-time, which can yield an expanding cosmos, a prediction initially resisted by Einstein but later vindicated by evidence such as Hubble’s observations. The role of Henrietta Leavitt and standard candles is highlighted as a critical path to proving the universe’s expansion and its far-flung galaxies' recession speeds, encapsulated by Hubble’s law.

Battle 2: The Fate of the Early Universe

Two competing scenarios are contrasted: the hot, dense Big Bang and the steady-state model in which new matter is created as the universe expands. The debate culminates in the discovery of the cosmic microwave background, which strongly supported the Big Bang and challenged steady-state ideas. Early contributions from Canadian physicists and other pioneers are acknowledged as part of this unfolding story.

What the CMB Teaches Us

The CMB is described as a near-uniform bath with tiny fluctuations that encode the primordial sound waves and the seeds of cosmic structure. The Milky Way’s foreground must be removed to reveal the primordial signal, which informs our understanding of the early universe’s conditions and the subsequent growth of galaxies.

Time to Inflation and Beyond

Inflation is presented as a solution to the horizon problem, positing a period of exponential expansion that makes the CMB uniform across the sky and explains the small-scale fluctuations observed today. The talk covers how inflation implies a pre-Big Bang phase and how it may lead to a multiverse, with eternal inflation generating vast numbers of pocket universes. The presenters also discuss debates within inflationary theory and the controversy surrounding empirical testability and the multiverse concept.

Time Machines, No Boundary, and Alternative Cosmologies

Beyond inflation, the conversation surveys cyclic models, the possibility of universes emerging from black holes, and the no boundary proposal suggesting a quantum cosmology in which time may emerge from a higher-dimensional geometry, potentially removing the classical singularity. The speakers explain the status of these ideas as speculative but scientifically motivated paths to answer what came before the Big Bang.

Science vs Religion and the No Boundary of Faith

A discussion on whether cosmology can inform or constrain religious belief follows, including debates around the Kala cosmological argument and the fine tuning question. The talk cautions against over-interpreting cosmology as definitive proof of metaphysical claims while noting the interesting interplay between science and faith in the history of cosmology.

Final Battle: Observational Horizons and the Future of Cosmology

The speakers conclude by outlining observational campaigns and instruments that might uncover gravitational waves from the early universe or refine CMB measurements. They emphasize that the ultimate winner in this battle will be guided by data, with missions that map the large-scale structure and detect primordial gravitational waves helping to distinguish between competing theories.

Closing Thoughts

The talk ends with a hopeful message: science and curiosity empower humanity to understand the cosmos and ourselves, urging continued investment in ambitious missions and the fusion of science with broader humanistic inquiry.