The Big Bang Theory
John Mallett
The 'Big Bang' Theory?
Why do we think there was a 'Big Bang'?
History of the discoveries
Measurement of velocity and distance
Current view of the origin of universe
Latest information.
Using history to explain the slow growth of
understanding of the universe.
The 'Big Bang' will emerge as a theory.
There are many key discoveries to determine
distance and velocity.
Some history of 'Big Bang' theory
Cepheid Variable Stars 1784
The term Cepheid originates from Delta Cephei in
the constellation of Cepheus identified by John
Goodricke in 1784. A periodic yellow super giant (F6-K2)
Classical Very regular period order of days to months
4 - 20 times the mass of the Sun
100,000 times more luminous.
Type II Period of between 1 and 50 days
Half the mass of the Sun
Several sub groups
1- 4 days
BL Her
10 - 20 days W Virginis
> 20 days RV Tauri
Friedrich Bessel 1838 Parallax
First used to measure 61 Cygni
Only useful for quite close objects where
parallax can be measured.
Close stars in our galaxy
Proxima Centauri - has a parallax of 0.7687 ± 0.0003 arcsec
Henrietta Levitt 1908– Cepheid Variables
The discovery that there was a relationship
between the log of the period and the luminosity
Made on 1777 variable stars from Harvard
photographic plates.
She received almost no recognition in her
lifetime.
Ejnar Hertzprung 1913
Determined the accurate distance of several
Cepheids in the Milky Way by using parallax.
The scale of Cepheid distance could now be
used for any Cepheid.
Harlow Shapley – 1915
Used Cepheid 'Levitt's Law' to measure the Milky Way
Edwin Hubble – 1924
Used 'Levitt's Law' to show that Andromeda was a galaxy
like our own Milky Way but more distant.
Settled the 'Island Universe Debate'
Shapley – Curtis debate – were Andromeda and other
nebular within our galaxy?
Albert Einstein 1917 – Cosmological constant
A term in the General relativity to allow for a static universe.
At this time the universe was still considered static.
Einstein eventually said that this was the greatest mistake in his
life!
Edwin Hubble & Milton Humason – 1929
Used the 'red shift' of distant galaxy spectra to identify
velocity
Proposed from General Relativity by George Lemaitre -1927
Red Shift
Splitting light up into it's spectrum can show
characteristic absorption lines for elements.
Similar to the Doppler effect reducing the
frequency of a car as it goes away from you.
Edwin Hubble discovered that all distant
galaxies were moving away from us.
Hubble Constant – H0
Estimated as 68km/s per Mpc
1 Mpc = 3,260,000 Light Years
Faber - Jackson relation 1976
Related to elliptical Galaxies
Luminosity is proportional to (velocity dispersion)4
Calibrated by distance 'standard candles'
Tully – Fisher relation 1977
Related to spiral Galaxies
Uses the width or shift of the absorption line to
estimate luminosity
The use the inverse square law to arrive at
distance.
This relationship was calibrated using the other
distance 'standard candles'
Globular clusters
All the stars form at the same time
Serving as a cosmic clock...
Globular clusters
Globular clusters
The oldest observed globular clusters only
contain stars less than 0.7 solar masses.
So, much dimmer than our Sun
There are a number of uncertainties:
Difficulty in determining exact distance to globular clusters
Some uncertainty of brightness and mass.
The finer details of stellar evolution are still unclear.
So the best estimates of age of oldest clusters
is 11- 18 Billion years
The Universe must be at least as old as the
oldest cluster..
Saul Perlmutter and Adam Riess of the US and Brian
Schmidt of Australia 2011
Used white dwarf supernova type 1a in distant galaxies
to measure distance.
Type 1a supernova are always the same brightness
Slight difference in the colour (spectra) can indicate
velocity
They discovered that the expansion of the universe is
accelerating!
They got a Nobel Prize for Physics in 2011
Image of M101 – Hewelsfield Observatory – 28/3/2012
Type 1a Supernova
So where are we so far?
Evidence of expansion and acceleration of the
universe
Quantification of rate of expansion
Some really valuable and validated distance
tools
All based on some key assumptions:
Isotropic – Universe the same at all
distances and directions
Laws remain the same throughout the
universe
Some supporting observations.
Cosmic Microwave Background CMB
Distribution of Galaxies
Discovered in 1964 by Arno Penzias & Robert Wilson
1978 Nobel Prize
The radiation from the 'Big Bang'
The expansion of space causes the
wavelength to increase
The peak of this is now at 1.873mm
wavelength
Frequency of 160.2 GHz (2.725K)
Isotropic to 1 part in 100,000
WMAP Image of the CMB
Wilkinson Microwave Anisotropy Probe
Our Galaxy
Galaxy distribution
For 'Big Bang' to be valid distribution of matter
should have been symmetrical and Isotropic.
Current Problems with the 'Big Bang' Theory
Flatness problem
WMAP has determined the geometry of the universe to be
nearly flat.
Under 'Big Bang' cosmology curvature grows with time.
To be nearly flat would be a very big coincidence (like
balancing a pencil on its point)
Horizon problem
Calculating the distance of objects at the edge of our horizon
are so far apart that assuming universe is Isotropic that they
can never have originated at the same point.
Monopole problem (plasma physics particle with only one
magnetic pole!)
Cosmology predicts a large number of heavy stable
'magnetic Monopoles'
We have not yet seen any.
Orange curve – Closed high density universe that will
ultimately collapse back to singularity
Green – Flat critical density universe that will slow down and
settle at 3-4 times the current size
Red – Current thinking, Large fraction of matter is dark and
universe is accelerating.
Inflation to fix the problems!
A theoretical solution to the problems!
Developed as a theory by
Alan Guth, Andrei Linde, Paul Steinhardt & Andy
Albrecht
Provides a solution to all three problems and some
other more subtle problems
What is it?
A period of very rapid exponential growth prior to
the more gradual expansion
'Inflation'
It is an extension to 'Big Bang' theory