Cosmology: The Big Bang Theory

Study Notes

Theories of the Origin of the Universe

The Big Bang Theory

The most widely accepted theory of the origin of the universe
Proposes that the universe began as a singularity, an infinitely hot and dense point, around 13.8 billion years ago
This singularity expanded rapidly, and as it did, it cooled and formed subatomic particles, atoms, and eventually the stars and galaxies we see today

Key Evidence Supporting the Big Bang Theory

Cosmic Microwave Background Radiation: the residual heat from the initial explosion, detectable in the form of microwave radiation throughout the universe
Abundance of Light Elements: according to the Big Bang Theory, the universe was once so hot that it was able to create light elements, such as hydrogen, helium, and lithium, from protons and neutrons
Large-scale Structure of the Universe: the universe's vast galaxy clusters and superclusters are consistent with the idea that the universe began in a very hot and dense state

Other Theories of the Origin of the Universe

Steady State Theory: proposes that the universe has always existed in its current form, with no beginning or end
Plasma Universe Theory: suggests that the universe is shaped by electromagnetic forces and plasma, rather than gravity and general relativity
Eternal Inflation Theory: proposes that our universe is just one of many in an infinite multiverse, with new universes constantly being created through eternal inflation

Open Questions and Debates

What caused the Big Bang?
What is the nature of dark matter and dark energy, which are thought to make up a large portion of the universe's mass-energy budget?
Is the universe part of a larger multiverse, or is it a standalone entity?

The Big Bang Theory

Most widely accepted theory of the origin of the universe
Universe began as a singularity, an infinitely hot and dense point, around 13.8 billion years ago
Singularity expanded rapidly, cooling and forming subatomic particles, atoms, and eventually stars and galaxies

Key Evidence Supporting the Big Bang Theory

Cosmic Microwave Background Radiation: residual heat from the initial explosion, detectable as microwave radiation throughout the universe
Abundance of Light Elements: universe was once so hot that it created light elements like hydrogen, helium, and lithium from protons and neutrons
Large-scale Structure of the Universe: galaxy clusters and superclusters consistent with a hot and dense universe origin

Alternative Theories of the Origin of the Universe

Steady State Theory: universe has always existed in its current form, with no beginning or end
Plasma Universe Theory: electromagnetic forces and plasma shape the universe, rather than gravity and general relativity
Eternal Inflation Theory: our universe is one of many in an infinite multiverse, with new universes created through eternal inflation

Open Questions and Debates

Cause of the Big Bang unknown
Nature of dark matter and dark energy, which make up a large portion of the universe's mass-energy budget, unknown
Whether the universe is part of a larger multiverse or a standalone entity unknown

Description

Explore the most widely accepted theory of the origin of the universe, proposing a singularity that expanded rapidly around 13.8 billion years ago. Learn about the key evidence supporting this theory.