Universe Articles

Tag Archive for: universe

infinite universe

Open, Flat, or Closed Universe: What Curvature Tells Us

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Direct answer: Cosmologists classify the universe as open, flat, or closed based on spatial curvature. Current cosmic microwave background (CMB) measurements…
Evidence for Big Bang

Big Bang Evidence: CMB, Redshift & Element Abundances

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Big Bang: Key PointsHubble's law (redshift of galaxies) and the Doppler effect provide direct evidence that the universe is expanding away from our…
Cosmic Web Connections

Cosmic Web Connectivity: How It Shapes Galaxy Evolution

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Introduction The universe was not perfectly uniform at the beginning; some regions had higher density than others. Over time these higher-density regions…
bb_infinity2

Big Bang, Infinity, and the Universe’s Shape Explained

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The Big Bang was not an explosion from a point in space. It was the appearance of a singularity, a moment where spacetime itself breaks down and cannot…
journeycosmos3

Learn About the FLRW Metric and The Friedmann Equation

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Previous Chapter: A Journey Into the Cosmos – The Friedmann Equation                Chapter 2- FLRW Metric and The Friedmann Equation In…
expandinguniverse

Explore Coordinate Dependent Statements in an Expanding Universe

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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…
cosmosintro

Learn About the Friedmann Equation and the Cosmos

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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…
inflation5

A Poor Man’s CMB Primer: Quantum Seeds

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 The CMB establishes a record of ancient acoustic oscillations in the baryon-photon plasma. We've been studying how these primordial sound…
universestart

Did the Big Bang Have a Center? The Physics Explained

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The Big Bang did not happen at a single point in space, so it has no center. Standard cosmological models based on general relativity treat the Big Bang…
universeexpand

Big Bang Models: Expansion, Dark Energy, Inflation

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Big Bang and expansion (no inflation, no dark energy) Empty-universe solution (FLRW) Einstein's General Relativity allows a solution (the FLRW metric)…
lightcone7_3

LightCone 8 Tutorial Part III – How Things are Computed

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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.…
lightcone72

LightCone8 Tutorial Part II – Charts

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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…
earlyuniverse

Why Wasn’t the Early Universe at Maximum Entropy?

No. The second law of thermodynamics states that entropy can only increase over time. If the early universe had begun in a state of maximum entropy, the…
observableuniverse

Why the Observable Universe Is Bigger Than Its Age

The observable universe has a radius of about 46 billion light-years, far larger than its age of roughly 14 billion years. This happens because space itself…
steadystate

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.…
blackholesuniverse

Why the Big Bang Wasn’t a Black Hole: Cosmology Explained

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The Big Bang was not a black hole because it happened everywhere in space at once rather than at a single point, and because the near-perfect homogeneity…
universespinning

Is the Universe Rotating? What Physics Tests Reveal

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All current astronomical observations are consistent with zero global rotation of the universe. Solar-system data set a model-independent upper limit of…
birthcmb

A Poor Man’s CMB Primer: The Birth of a Cosmic Background Radiation

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 The early universe was hot. So hot that nuclei boiled. The great thermal energy of the universe overwhelmed the confining efforts of the…
balloonanalogy

The Balloon Analogy Explained: Cosmic Expansion Without a Center

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The balloon analogy uses pennies glued to an inflating balloon to show two ideas from modern cosmology: that unbound regions of the universe expand roughly…
cmb

A Poor Man’s CMB Primer: Orientation of the Universe

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 This is a picture of the cosmic microwave background:Fig 1. The cosmic microwave background as seen by the European Space Agency's…
CosmologicalHorizons

Inflationary Misconceptions and the Basics of Cosmological Horizons

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Introduction It is a common saying that during inflation "space expanded faster than the speed of light."  This statement is meant to articulate the…