Universe (Beginning)

This is a list of various theories and models that have been proposed to explain the beginning and evolution of the universe.

Big Bang Theory

The most widely accepted theory, proposing that the universe began from an extremely hot and dense singularity about 13.8 billion years ago and has been expanding ever since.

Inflation Theory

An extension of the #Big Bang Theory, suggesting that the universe underwent a rapid exponential expansion during the first fraction of a second after the Big Bang.

Steady State Theory

An earlier theory proposed by Fred Hoyle, Thomas Gold, and Hermann Bondi, which posited that the universe has no beginning or end but is in a constant state of expansion with new matter being continuously created. It has largely been abandoned in favor of the #Big Bang Theory due to observational evidence.

Cyclic Universe Theory

Suggests that the universe undergoes an eternal sequence of cycles, each consisting of a Big Bang followed by expansion, contraction, and a Big Crunch, leading to a new Big Bang.

Ekpyrotic Theory

Proposes that the universe resulted from the collision of two three-dimensional "branes" in a higher-dimensional space, with the Big Bang being the result of this collision.

String Theory / M-Theory

These theories propose that fundamental particles are actually "strings" or higher-dimensional objects. They include models such as the "brane" cosmology, where our universe is a 3D brane in a higher-dimensional space, and the Big Bang might be due to collisions or interactions with other branes.

Quantum Cosmology

Combines quantum mechanics and general relativity to explore the early universe. Includes models like the "no-boundary" proposal by Stephen Hawking and James Hartle, which suggests that the universe does not have a boundary or edge in time.

Multiverse Theories

Suggest that our universe is just one of many universes in a "multiverse," each potentially having different physical constants and properties. These theories include the "bubble universe" model, where different parts of the multiverse can have different histories.

Loop Quantum Cosmology

An approach within loop quantum gravity that attempts to describe the universe's early moments using quantum principles. It proposes a "Big Bounce" rather than a Big Bang, where the universe might have contracted before expanding.

Pre-Big Bang Models

Theories suggesting that our universe's Big Bang was preceded by a different cosmological state or phase, which could involve a contracting phase or an entirely different cosmological framework.

Hawking-Turok Model

A variant of the cyclic model, proposing that the universe emerged from a quantum bounce in a higher-dimensional space, with no singularity and no classical Big Bang.