For almost seventy years, some of the world’s leading physicists have taken parallel universes seriously — and several of the most respected theories in physics predict them outright.
1957
Quantum physics
“Relative State” Formulation of Quantum Mechanics
Hugh Everett III · Princeton
The founding text of the many-worlds interpretation. The universal wave function never collapses — every possible outcome of a measurement is realised, each in its own branch of reality.
2002
Quantum physics
The Structure of the Multiverse
David Deutsch · University of Oxford
Explains what a single “universe” actually is inside the quantum multiverse — and what holds it together.
“The structure of the multiverse is determined by information flow.”
2003
Cosmology
Parallel Universes
Max Tegmark · MIT
Arranges parallel universes into four levels. The first — regions far beyond our cosmic horizon — follows from standard cosmology, which he considers practically uncontroversial.
“an identical copy of you about 101029 meters away”
2003
String theory
The Anthropic Landscape of String Theory
Leonard Susskind · Stanford University
String theory allows an enormous and varied “landscape” of possible universes, each with its own physical laws — ours is only one of them.
2014
Quantum physics
Many Worlds, the Born Rule, and Self-Locating Uncertainty
Sean M. Carroll & Charles T. Sebens · Caltech
Shows how the probabilities of quantum physics arise naturally in a world of many branches: an observer can know the whole state of the universe and still not know —
“which branch they are on.”
2015
Cosmology
A Brief History of the Multiverse
Andrei Linde · Stanford University
From the physicist who first proposed the inflationary multiverse in 1982: the world may consist of countless vast regions with different laws of physics — each so large it is, in effect, a universe of its own.
2018
Cosmology
A Smooth Exit from Eternal Inflation?
Stephen W. Hawking & Thomas Hertog
Stephen Hawking’s final paper. Even at the very end of his life he was working on the multiverse — proposing that it is finite and smoother than an infinite fractal of universes.
Parallel universes have not yet been confirmed by experiment, and some physicists — among them George Ellis and Paul Steinhardt — consider them untestable. The papers above are published by their authors; follow the links for the full texts.