Tag Archive for: universe
Is the Universe Finite, or Is It Infinite?
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Standard cosmological models come in three flavors, open, flat, and closed,[Carroll] whose spatial curvatures are negative, zero, and positive. The open…
Is there Evidence for the Big Bang?
Big Bang Key PointsHubble's law (redshift of galaxies) and the Doppler effect provide direct evidence for the universe expanding away from our reference…
The Evolution of the Universe, Cosmic Web and Connections
The universe was not perfectly uniform when it started, some areas had a higher density than others. During the evolution of the universe, these areas…
Intro to the Big Bang and Infinity Concepts
In the cosmology section of the Physics Forums, I encountered many Big Bang and related infinity problems. Hence, in this article, I want to explain the…
Learn About the FLRW Metric and The Friedmann Equation
Previous Chapter: A Journey Into the Cosmos – The Friedmann Equation
Chapter 2- FLRW Metric and The Friedmann Equation
In…
Explore Coordinate Dependent Statements in an Expanding Universe
In this Insight, we will discuss the general Robertson-Walker (RW) universe, in which a set of co-moving observers with proper time ##t## observe the universe…
Learn About the Friedmann Equation and the Cosmos
This is an introduction to cosmology for someone who has some knowledge of calculus and basic physics. In this tutorial, we will take a journey into the…
A Poor Man’s CMB Primer: Quantum Seeds
The CMB establishes a record of ancient acoustic oscillations in the baryon-photon plasma. We've been studying how these primordial sound…
Where Did the Big Bang Happen?
According to standard cosmological models, which are based on general relativity and are found to agree well with observations, time and space did not…
Learn about the Big Bang and the Expansion of the Universe
The "ordinary Big Bang and expansion" (no inflation, no dark energy)
Einstein's General Relativity allows a solution (FLRW metric) where an empty Universe…
LightCone 8 Tutorial Part III – How Things are Computed
In Part I and Part II of this mini-series, we have briefly discussed the basic user interface and the use of charts to depict the LCDM cosmological model.…
LightCone8 Tutorial Part II – Charts
Part I dealt with the basic user interface of LightCone8. This part of the tutorial is about potentially useful cosmological insights to be gained from…
Was the Early Universe in a Disordered State?
No. The second law of thermodynamics says that entropy can only increase, so if the early universe had been in a state of maximum entropy, then the cosmos…
Radius of the Observable Universe in Light-years Is Greater than Its Age
The radius of the observable universe is about 46 billion light-years, which is considerably greater than its age of about 14 billion years. The radius…
What Is the Steady-state Model and Why It’s No Longer Viable
Introduction to the Steady State Model
Back in 2011, I wrote a FAQ entry for Physics Forums on the steady state model and why it is no longer viable.…
Is the Universe a Black Hole?
In the early universe, the matter was gathered together at very high density, so why wasn't it a black hole?The first thing to understand is that the…
Can We Tell Whether the Universe Is Rotating?
If you believe wholeheartedly in Mach's principle, then there is no way to test empirically for the rotation of the universe as a whole, since there is…
A Poor Man’s CMB Primer: The Birth of a Cosmic Background Radiation
The early universe was hot. So hot that nuclei boiled. The great thermal energy of the universe overwhelmed the confining efforts of the…
Learn Inflation Balloon Analogy Misconceptions
The Balloon Analogy is a simple-minded way to help describe (but not completely describe) two facts of cosmology that are difficult for many people to…
A Poor Man’s CMB Primer: Orientation of the Universe
This is a picture of the cosmic microwave background:Fig 1. The cosmic microwave background as seen by the European Space Agency's…
Inflationary Misconceptions and the Basics of Cosmological Horizons
Introduction
It is a common saying that during inflation "space expanded faster than the speed of light." This statement is meant to articulate the…