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Questions and Answers
What phenomenon explains the fluctuations in the density of visible baryonic matter in the universe?
What phenomenon explains the fluctuations in the density of visible baryonic matter in the universe?
Which cosmological model suggests that the Universe evolves from an initial state of higher density?
Which cosmological model suggests that the Universe evolves from an initial state of higher density?
What evidence supports the Big Bang theory based on observations of distant galaxies?
What evidence supports the Big Bang theory based on observations of distant galaxies?
What did Robert Dicke's group at Princeton hypothesize regarding the initial explosion of the Universe?
What did Robert Dicke's group at Princeton hypothesize regarding the initial explosion of the Universe?
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What significant discovery was made in 1964 that supported the Big Bang theory?
What significant discovery was made in 1964 that supported the Big Bang theory?
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What is the estimated temperature of the Cosmic Microwave Background Radiation as discovered by Penzias and Wilson?
What is the estimated temperature of the Cosmic Microwave Background Radiation as discovered by Penzias and Wilson?
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Which of these concepts refers to the model proposing that the Universe is in some equilibrium state?
Which of these concepts refers to the model proposing that the Universe is in some equilibrium state?
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What observable effect implies that galaxies are becoming increasingly distant from one another?
What observable effect implies that galaxies are becoming increasingly distant from one another?
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What does the inverse of the Hubble constant represent?
What does the inverse of the Hubble constant represent?
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What is suggested by Olber's Paradox in an infinite Universe?
What is suggested by Olber's Paradox in an infinite Universe?
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In building a cosmological model using Hubble's Law, what is the primary factor to measure over time?
In building a cosmological model using Hubble's Law, what is the primary factor to measure over time?
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What does the Cosmic Microwave Background represent?
What does the Cosmic Microwave Background represent?
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What concept is introduced by the idea of 'frozen-in structure' in the Cosmic Microwave Background?
What concept is introduced by the idea of 'frozen-in structure' in the Cosmic Microwave Background?
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What challenge does infinite size or infinite age of the Universe present?
What challenge does infinite size or infinite age of the Universe present?
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Why do we divide space into large numbers of thin spherical shells according to Olber's Paradox?
Why do we divide space into large numbers of thin spherical shells according to Olber's Paradox?
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If the Universe is finite in size or age, what is the implication for observational data?
If the Universe is finite in size or age, what is the implication for observational data?
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Study Notes
PH222 - Astrophysical Concepts
- Course title: Astrophysical Concepts
- Instructor: Aaron Golden
- Department: Centre of Astronomy, School of Natural Sciences
- University: University of Galway
Cosmology 1
- Focuses on the entire Universe, not individual objects like stars or galaxies
- Cosmology seeks to understand the origin, evolution, and eventual fate of the Universe.
- Questions include: how did the Universe originate?, what is the current state of the Universe?, and how will the Universe end?
Defining Cosmology
- Up until this point, study focused on individuals things, such as stars, dust clouds, and galaxies, or clusters of galaxies.
- Yet there is only one Universe encompassing everything.
Cosmological Principle
- The "Cosmological Principle" is a foundational assumption that the Universe is homogeneous and isotropic on the largest scales.
- Homogenous: General properties (like density and composition) are the same everywhere in the Universe. There isn't a special location in the universe.
- Isotropic: Physical properties of the Universe appear the same in all directions.
The Big Bang
- The Big Bang is the prevailing cosmological model for the universe.
- It states that the universe began in a hot, dense state that has expanded and cooled over billions of years.
- This is supported by evidence from the Cosmic Microwave Background (CMB) radiation.
The Universe's Structure
- Galaxies exist in groups, with our local group dominated by the Milky Way, Andromeda, and Triangulum galaxies.
- Galaxy clusters contain thousands of galaxies, bound together by gravity and containing an Inter-Cluster Medium (ICM).
- The Virgo Cluster is part of a larger structure called the Virgo Supercluster, which also includes the Local Group and consists of other groups and clusters of galaxies..
- The Virgo Supercluster has a diameter of about 33 Mpc (Megaparsecs).
Notable Structures
- The Virgo Supercluster contains over 1300 galaxies.
- The core of the Virgo Supercluster covers approximately one-fourth of the full moon and is 20 Mpc away.
- The Great Attractor, composed of tens of thousands of galaxies, produces an observable effect on the expansion of the Universe.
Baryonic Acoustic Oscillations (BAO)
- Galaxy clusters are connected in a web-like structure by filaments. These are areas where the density is concentrated
- Voids are regions with a lower density (less than 10% of the average density of the Universe)
- Voids range in size from 10-150 Mpc.
- The web-like structure is a relic of Baryonic Acoustic Oscillations – fluctuations in the density of matter within the early Universe.
The Cosmological principle and other concepts
- The CMB (Cosmic Microwave Background) is the afterglow of the Big Bang
- Olber's paradox is a thought experiment considering an infinite, static universe and how it is that the night sky is dark instead of bright.
- Olbers' paradox: an infinite, static universe should be infinitely bright, as every line of sight would eventually lead to a star. A finite Universe or Universe of finite age resolves the paradox.
- The Universe has a finite age.
Estimating the age of the Universe
- Using Hubble's Law, cosmologists calculate the age of the Universe.
How the Universe Evolved
- Visual representation of the history of the Universe, starting from the Big Bang, and highlighting key stages like the formation of galaxies and cosmic microwave background radiation.
The Cosmic Microwave Background
- The CMB is remarkably uniform but contains some evidence of structure formed from early density fluctuations.
- The CMB is a key piece of evidence supporting the Big Bang model.
What about 'Now'
- If the Universe is unconstrained and infinite, it introduces problems (like Olbers' paradox).
- If there is matter everywhere, why is the night sky dark?
Olbers' Paradox
- The paradox: if the universe is infinite and unchanging, it ought to be infinitely bright.
- Solutions: Universe is finite in size and/or age.
The Expansion Effect
- Upcoming study will utilize the expansion effect to create a cosmological model.
Cosmology with Newtonian laws
- Isotropy: The Universe is spherically symmetrical at any point in space.
- Gravity from outside a sphere centered on a point cancels out.
- The acceleration of a mass ‘m’ towards a point ‘a’ distance ‘r’ away is given by a specific formula. This formula is given, in terms of density at a reference time, derived from Newton's laws of gravity.
- This highlights that a static (not expanding) Universe is unlikely, given the effect of gravity.
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Description
This quiz explores the foundational aspects of cosmology, focusing on the origin, evolution, and fate of the Universe. Understand the key principles that guide the study of the cosmos, including the Cosmological Principle and the nature of the Universe itself.
