COSMOLOGY – PHYS 30392
INTRODUCTION
giampaolo.pisano@manchester.ac.uk
http://www.jb.man.ac.uk/~gp/
Giampaolo Pisano - Jodrell Bank Centre for Astrophysics
The University of Manchester - January 2013
Let me introduce myself !
• Name: Giampaolo Pisano
• Education: Physics Degree and PhD in Astronomy
• Working group: Jodrell Bank Centre for Astrophysics
• Research: development of radio to sub-mm astronomy instrumentation,
mainly involved in Cosmic Microwave Background projects
• Teaching: this is my first year teaching this course and I am still preparing it !
Your feedback is vital for success of this course and for your learning
• Office: Turing building Room 3.220
• e-mail: giampaolo.pisano@manchester.ac.uk
• Hallmarks: you might have noticed already... I have a Strong Italian Accent !
INTRODUCTION
→ What is Cosmology ?
Early Scientific Cosmologies
Modern Cosmology
Course Description
Recommended Texts
References: Liddle, Introduction to Modern Cosmology - Chap 1
Ryden, Introduction to Cosmology - Chap 1
Harrison, Cosmology - Chap 1
What is Cosmology ? Definitions and subjects
• Cosmology is the study of the Universe, or cosmos, as a whole
“Kosmos”: harmony or order Harmonious whole of all reality
+ “- logia” : discourse, study
• Cosmology deals with:
• very large distances
• long timescales
• very big objects
• Cosmology is the study of:
• space and time
• primary cosmic constituents
• form and frame of the expanding universe
• Distances ranging from the Planck scale to 104 Mpc:
A span of 61 orders of magnitude !
Very small and very large are intimately related in cosmology
What is Cosmology ? Scientific approach
• Basic sciences focus on specialised domains of the universe
• Fragmentation into closely related sciences of greater specialisation:
Ex: Physics particle physics, nuclear physics, atomic ... etc
• Cosmology draws knowledge from other sciences, such as Physics and
Astronomy, and assembles a physically all-inclusive cosmic picture
Cosmology aims to assemble the cosmic jigsaw puzzle
• The Universe is richly textured with structures on a vaste range of scales
It looks extremely complex ! :o)
Simplification
We study the properties of an idealised, perfectly smooth model Universe
Entire galaxies as small objects
What is Cosmology ? Philosophical points
• Cosmology deals with fundamental questions about the Universe:
• its past, present and future
• being finite or infinite
• having a beginning and an end
Many subjects are still obscure and not understood
• We have “models of the Universe”:
We cannot guess the true nature of the Universe,
it is still mysterious and unknown
• What determines the way that human beings think also determines the
design they perceive in their universe:
Human beings represent the universe perceiving
and thinking about itself
Cosmology ultimately based on observations of the Universe around us
INTRODUCTION
What is Cosmology ?
→ Early Scientific Cosmologies
Modern Cosmology
Course Description
Recommended Texts
References: Liddle, Introduction to Modern Cosmology - Chap 1
Ryden, Introduction to Cosmology - Chap 1
Harrison, Cosmology - Chap 1
Egyptians
• One of the egyptian models of the Universe included:
- a flat Earth (earth god Geb)
- covered by a solid dome (sky goddess Nut)
- supported by the god of air Shu
The Earth was believed to be flat and with finite size
Babylonian astronomy (~2000 BC)
http://abyss.uoregon.edu/
Babylonian world map
~500 BC
- Skilled astronomers
- Compiled star catalogues
- Recorded the movements of the planets
Babylonian six-level Universe
- Were able to predict apparent motion of moon, planets and even eclipses !
- Cosmos based on water, vault of heaven creating dry space above flat Earth
- Earliest astronomy with any influence on us:
~360 day/yr; sexagesimal system; 24 hr day, 12 zodiac signs
All done as religious worship, they did not develop natural
explanations of celestial movements
Ancient Greeks
• More precise and sophisticated observations
• Earth and Moon are spherical, Sun much further away than Moon
• Stars distance much greater than Earth’s diameter
Pythagoras (580-500 BC)
• Harmony of universe governed by mathematical relations
• Two-sphere Universe: central spherical Earth surrounded
by outer sphere of fixed stars, undetermined motion of
planets between the spheres
Eudoxus (408-355 BC)
• Many-spheres Universe: central spherical Earth surrounded by concentric
and rotating spheres, intermediate spheres supported the planets
Aristotle (384 - 322 BC)
Lunar sphere
Sublunar
realm
Celestial
realm
• Geocentric system: Earth at the centre of the Universe
• Adopted Eudoxus ‘many-spheres’ model defining:
- phyical things occupied the sublunar realm
- ethereal things occupied the celestial realm
• Outermost celestial sphere supported the fixed stars Finite universe
This model could not explain retrograde motions of the planets...
Ptolemy (87-150 AD)
Hawley & Holcomb
Planets retrograde motion
• Perfect motion should be in circles
• Complex combination of circular motions to explain the motion of planets:
Eccentric circles, epicycles & equants (Wrong but very successful !)
• This final form of the Aristotelian universe did last for ~ 1500 years !
It failed to incorporate many developments in Greek science like....
Aristarchus (310-230 BC)
• Heliocentric system: Earth and planets orbiting around the Sun !
Archytas (428 - 347 BC): Is there a Cosmic edge ?
“What happens to a spear when it is hurled across the outer boundary of the universe?”
Aristotelian
Wall-like
Medieval
Marshy
Stoic
Cliff-like
Epicurian
Infinite
Finite Universe
Sphere of fixed stars as
“Dark cosmic wall”
Space ends gradually
Physical Etheric realm
Finite cosmos of stars
with centre and edge,
surrounding infinite void
Infinite, centerless,
edgeless Universe
Copernicus (1473 -1543)
• Heliocetric system from Aristarchus
• Ptolemic system too complicated !
• Earth and planets moving in circles around the Sun, at the centre
• Finite system
• Retrograde motion explained by this theory
• Still not as accurate as Ptolemaic system
However, the Sun is still at the centre of the Universe
Digges (1543 -1595)
• Modification to the Copernican system:
Dispersal of sphere of stars throughout
unbounded space
Bruno (1548 -1600)
• Edgeless, centerless Universe Centre is everywhere
“Universe of infinite extent, populated with numberless
planetary systems teeming with life ..countless Suns,
..an infinity of worlds..”
Supported Copernican system, burnt at the stake in 1600
Tycho Brahe (1546 -1601)
• Showed that if the Earth moved about sun then the relative
positions of stars should change Parallax
• No evidence, thus either Earth fixed or stars very far away!
Rejected Copernican system
Kepler (1571 -1630)
• The heliocentric model works if planets move on ellipses!
• Work was based on the observational data of Brahe
Galileo (1564 -1642)
• Introduced the telescope in astronomy and observed
Jupiter’s moons
• If moons could orbit a planet why couldn’t planets orbit sun!
Supported Kepler’s models
Descartes (1596 -1650)
Vortical fluids system
• Infinite and centerless universe
• Continuous matter of varying density:
No vacuum possible
• Forces acted by direct contact:
Gravity from pressure of fluids
Planetary orbits from the vortical motion of matter
Each vortex a solar system
Newton (1642 -1727)
• Famous laws of motion & inverse square law of gravity:
Explained Kepler’s empirical laws
• Existence of absolute space: Vacuum possible
• Infinite even distribution of stars similar to our own Sun:
The universe is static, but inherently unstable
The birth of modern cosmology
Kant (1724 -1804)
• Starting from T. Wright ideas he hypothesised that:
Milky Way is a lens-shaped distributions of stars
Fuzzy nebulae are similar milky-way systems
Milky-ways perhaps clustered together and so on...
(we would call it a fractal universe)
Herschel W. (1738-1822)
• Discovered Uranus
Milky Way
• Nearby stars not evenly distributed
Identification of a disk-shaped assembly of stars
• However, the Sun still at the centre
Shapley (1885-1972)
• We are some two-thirds of the radius away form the centre
of the Galaxy
• However, our galaxy still considered at the centre of the
Universe
Einstein (1879-1955)
• Developed his theory of gravitation General Relativity
• He thought the Universe was static at the time but,
matter tends to fall together under gravity, so:
Hubble (1889-1953)
Static universe impossible..?
• Established definitively that some of the observed
“nebulae” were indeed distant galaxies
He showed that the universe is expanding
INTRODUCTION
What is Cosmology ?
Early Scientific Cosmologies
→ Modern Cosmology
Course Description
Recommended Texts
References: Liddle, Introduction to Modern Cosmology - Chap 1
Ryden, Introduction to Cosmology – Par. 2.2
Harrison, Cosmology - Chap 7
The Cosmological Principle
- Modern cosmology is based on the:
Cosmological Principle
There is nothing special about our location in the Universe
Apart from local irregularities, the Universe looks the same everywhere
Notes
• The principle is an approximation that holds better and better the larger
the length scales considered: very large regions (> 100 Mpc), still much
smaller than the Universe, containing millions of galaxies
• We expect these regions to look more or less like every other one
Modern Cosmology
• Cosmology is shifting from qualitative to quantitative thanks to the improving
observational technology
• The current Standard Cosmological Model for the Universe is the
‘Hot Big Bang Model’, that is almost universally accepted
• We will apply thermodynamics, atomic physics, gravitation to grand scales
• We will avoid General Relativity with a bit of cheating...
Notes
• In Cosmology there is no perceived wisdom, often details remain blurred
• Ever changing observational situation
• Sometimes observations lag behind theory
• Anyway, cosmological models not eventually supported by observations
remain pure speculation
Hot Big Bang Theory
• The best description we have of our Universe is given by the:
Hot Big Bang Model
The Universe has expanded from an initially hot and dense state to
its current cool state, and the expansion is still going on today
Notes
• The Cosmological Principle is at the basis of the Hot Big Bang Cosmology
Steady State Universe
• Alternative theory where the Universe does not evolve and looked the
same forever, material created to fill the gaps as it expands
However, observations strongly support the Big Bang
and we will not study the Steady State theory
Hot Big Bang Theory
NASA
In this course will study many theoretical aspects and observational
evidences implied by this theory
INTRODUCTION
What is Cosmology ?
Early Scientific Cosmologies
Modern Cosmology
→ Course Description
Recommended Texts
References: Bluebook on School of Physics and Astronomy Website
Course Aims
1. To provide a broad overview of modern physical
cosmology, without detailed mathematics
2. To make clear the connections between basic physical
ideas and modern cosmology
3. To make students aware of the limitations and
uncertainties in our current cosmological models
Course Learning Outocomes
On completion of the course, students should be able to:
1. Explain the concepts of the expansion and curvature of space to an
interested layperson.
2. Summarize the main evidence in favour of the Big Bang, inflation, dark
matter and dark energy.
3. Relate the density of the universe to its rate of expansion and understand
how this relation is modified by a cosmological constant.
4. Make quantitative calculations of physical processes in the early universe.
5. Relate observed to physical properties of distant objects given the
luminosity and angular size distances.
6. Describe the main events of the universe's history and locate them
approximately in time and redshift.
Course Syllabus (1/2)
• Introduction (1 lecture): what is cosmology, early and modern cosmologies.
• Observing the Universe (2 lectures): darkness at night, large scale
structures, homogeneity & isotropy, expansion, particles in the Universe.
• Geometry of the Universe (2 lectures): the equivalence principle, general
relativity concepts, curved spaces, Robertson-Walker metric.
• Dynamics of the Universe (2 lectures): Friedmann, fluid and acceleration
equations, cosmological constant.
• Cosmological models (2 lectures): single-and multiple-component
universes.
Course Syllabus (2/2)
• Observational parameters (2 lecture): expansion rate, cosmological
distance ladder, density and deceleration parameters, age of the Universe.
• Density of the Universe (3 lectures): radiation, visible matter, dark matter,
gravitational lensing.
• The early Universe (4 lectures): Big Bang, baryogenesis, inflation,
nucleosynthesis, recombination, last scattering surface.
• The Cosmic Microwave Background (2 lectures): theory of fluctuations,
dipole and acoustic peaks, reionization, polarisation.
• Problems and alternatives (2 lectures): what we do not know.
Other informations
• Lectures: broken up into two 50 minutes parts with 10 minutes break
• Exam: 1 hour 30 minutes examination in May/June
• Example classes: examples sheets, and model answers will be issued
• Feedback will be offered by examples class tutors during week 3, 7 and 11
• Lecture slides: after each lecture they will be on
Blackboard and www.jb.man.ac.uk/~gp/
INTRODUCTION
What is Cosmology ?
Early Scientific Cosmologies
Modern Cosmology
Course Description
→ Recommended Texts
Recommended Texts
• Main textbooks:
Liddle, A.
An Introduction to Modern Cosmology
2nd ed. (Wiley)
Ryden, B.
Introduction to Cosmology
(Addison Wesley)
Useful References
• Textbooks often used:
Serjeant, S.
Observational Cosmology
(CUP)
Harrison, E.
Cosmology: the Science of the Universe
2nd ed. (CUP)
Additional References
• Other texbooks that will be used sometimes:
Peacock, J.A.
Cosmological Physics
(CUP)
Hawley, J.F & Holcomb, K.A.
Foundations of Modern Cosmology
(Oxford)
Next Topic: OBSERVING THE UNIVERSE
Darkness at Night
Universe at different Wavelengths
Large Scale Structures of the Universe
The Cosmic Microwave Background
Homogeneity and Isotropy
The Expansion of the Universe
Particles in the Universe