Study Notes on Steady State and Oscillating Universe Theories

The steady state theory provides a cosmological perspective that maintains the universe has always been expanding and will continue to do so indefinitely.
Mechanisms of Expansion: As the universe undergoes expansion, the formation of new stars and galaxies occurs at a rate equivalent to the rate at which old ones become unobservable.
Observability Factors: Older celestial bodies eventually become unobservable to us due to two primary factors:
- Large distances from the observer.
- Recession velocity (the speed at which a celestial body moves away from the observer).
Stability of Density: Despite the continuous physical expansion, the average density of the universe remains constant. Because the density is unchanging, the theory is termed "steady state."
Constant Matter Creation: To maintain a constant density as the volume of the universe increases, matter is continuously created throughout space.

Core Principles of the State of the Universe:
- The universe has no beginning and no end.
- It has always existed and will always remain present.
- The universe is homogeneous in time and space, meaning it looks identical at any given time and from any location.
- It creates new matter as it continuously expands.
Historical Proponents: The theory was proposed in 1948 by three key figures:
- Hermann Bondi
- Thomas Gold
- Fred Hoyle

Scientific Inconsistencies: The theory is not parallel with the fundamental Law of Conservation of Energy and Mass, as it requires the spontaneous and continuous creation of matter from nothing.
The Cosmetic Microwave Background (CMB) Radiation:
- The discovery of CMB radiation in 1965 served as a pivotal turning point in cosmology.
- It provided significant evidence supporting the explanations provided by the Big Bang theory.
- Following this discovery, many scientists rejected the steady state theory.
Radiation Distribution: Recent scientific findings reject the hypothesis that cosmic radiation resulted from a supernova event. It has been proven that radiation is equal in every direction of the universe, a consistency that could not result from localized phenomena like supernovae.

Definition: The Oscillating Universe theory, also referred to as the Pulsating Theory, suggests that the universe exists in a perpetual cycle of expansion and contraction.
Stages of the Cycle:
- Expansion: The universe expands following a Big Bang.
- Energy Depletion: Once all the energy generated after the Big Bang has been exhausted, the expansion will cease.
- Contraction: The universe will then begin to contract.
- Approaching Singularity: As the universe contracts, it approaches a point of singularity.
- Repetition: Upon reaching the singularity, the universe will expand again.
Serial Universes: This theory suggests that our current universe might be the first in a probable series of universes, or perhaps the $n^{th}$ universe in an infinite series.

The Big Crunch: This phase occurs when the expansion of the universe reverses. The universe collapses inward, eventually resulting in the formation of a singularity.
The Big Bounce: This term was used by the proponent of the theory to describe the birth of a new universe resulting from the singularity at the end of a Big Crunch. The oscillating universe is essentially a combination of the Big Crunch and the Big Bang.
Proponent: The theory was proposed by Richard Tolman, a professor at the California Institute of Technology (Caltech).

Violation of Physical Laws: The suggestion that the universe would collapse on its own after reaching full expansion contradicts several current laws of physics.
Dark Energy and Dark Matter: The theory does not align with the currently postulated existence of dark energy and dark matter.
Alternative Ends of the Universe: Current scientific consensus favors different scenarios for the end of the universe, specifically:
- Big Freeze
- Heat Death

Expansion Agreement: Both the Steady State Theory and the Big Bang Theory agree on the fundamental principle that the universe is currently expanding.
Comparison of Key Concepts:
- Steady State Theory focuses on constant density and continuous matter creation.
- Oscillating Universe Theory focuses on cycles governed by a Big Crunch followed by a Big Bang (Big Bounce).
- Steady State is associated with Bondi, Gold, and Hoyle (1948).
- Oscillating Universe is associated with Richard Tolman.
- Both theories face significant scientific challenges: Steady State violates mass-energy conservation, while Oscillating Universe violates modern understandings of dark energy and the likely "Big Freeze" trajectory of the universe.