final exam!!!
 Today we will discuss Cosmology and the Big
Bang
 Wednesday we will finish the Big Bang, have a
short discussion of Life in the Universe, and
review for the final exam
 Remember:
Cosmological Redshift


We now know 3 kinds of
redshift
Doppler shift


Gravitational shift


due to motion
due to distortion of space-time by mass
Cosmological shift


due to stretching of space
 not due to relative motion
as space stretches, the wavelength stretches
and becomes longer
AST 1002
Planets, Stars and Galaxies
the Beginning&End of Time
Today’s Lecture: purpose & goals
1)
2)
3)
4)
5)
The “Beginning”
The Age of the Universe
The “End of Time”
Life in the Universe
Review for Final
Thinking Back in Time

We can calculate the age of the
Universe using Hubble’s Law
v = H0 x d 
But
d = v/H0

tHubble = 1/H0
distance = rate x time
(the time here is how long the expansion has been
going on  The Age of the Universe)

If Ho = 70 km/(s.Mpc), what is the age of the
Universe, THubble?
tHubble = 1/H0
1 sec.Mpc 106 pc 3.26 l.y. 1013 km
= 70 km ( Mpc )( pc ) ( l.y. )
3.26x1019 sec
1 hr
1 yr
)(124dayhr)(365.25day
)
= 70
= 4.657x1017 sec (3600sec
= 1.475x1010 yr = 14.7 Billion Years!!
At the Beginning

Originally all the energy (and
matter) of the Universe was
condensed into an incredibly small region


Energy, matter, space and time were all very
different than today 



MUCH smaller than the size of a proton
 what we call matter was then almost entirely energy
(gamma-ray photons)
need a new “theory of everything” to understand
 not yet possible
 11-dimensional space??? (models are very weird)
During early expansion, space-time and gravity
became separate from energy and mass

particles and antiparticles were being created from energy
and annihilating into energy all the time
Glow of the Universe

The early Universe was very
hot and dense



Eventually the Universe
cooled enough to form hydrogen atoms



glowed with blackbody
radiation
but so dense the light kept
getting absorbed (opaque)
blackbody radiation could now travel freely
That time called “recombination of the Universe”
Light from that time should be all around us
and be detectable.

3K background radiation
Cosmic Microwave Background

(CMB)
This light should be cosmologically
redshifted


Mostly into microwave region
CMB was first seen in 1960s

Pensias & Wilson
(Bell Labs)
– won Nobel prize
in physics for this


twenty years after prediction
COBE satellite mapped the CMB




measured the spectrum
wonderful match between theory and data
 Temperature = 2.73K
cooled glow from recombination era.
Incredibly uniform across sky.
Composition of Light Elements

Big Bang model predicts the percentage of light
elements




Hydrogen (1H), deuterium (heavy hydrogen, 2H), helium
(4He), lithium (7Li), beryllium (9Be), boron (10B and 11B),…
elements formed before recombination out of cooling extremely
hot plasma (created out of light!)
percentages depend upon density and temperature of early
Universe, and how fast it cooled.
Observed percentages agree with Big Bang model
predictions


Almost all that was created as hydrogen (1H) and helium
(4He), with only trace amounts of anything else.  must have
cooled from something very hot.
Notice no stable mass 5
Helium
or 8 isotopes

Big Bang model predicts the percentage of light elements, &
observed percentages agree with Big Bang model predictions
 Almost all that was created in the Big Bang was hydrogen
(1H) and helium (4He), only trace amounts of anything else.
4
 Helium ( He), was enriched in Main Sequence stars
12C), and the elements up to Iron
 Carbon (
(56Fe), created in massive Blue Giants and
dying Red giant and Supergiant stars
197Au)
 The heaviest elements, like Gold (
and Uranium (235U), were created only in
supernovae
ENRICHMENT
Formation of Structure

(early in the Universe)
Normal matter was spread fairly evenly


Dark matter was not distributed smoothly



WMAP and Boomerang (follow-ups of COBE)
show the seeds of that nonuniformity)
clumps remained
Expansion spread things out


due to interactions and radiation
but gravity held large clumps of dark matter
together
Dark matter attracted normal matter

source of galaxies and structure
Fate of the Universe



The Universe is expanding
But gravity should be pulling it back in
So what should the Universe’s fate be:




Continue expanding forever
Have expansion keep getting slower forever and stop at infinite
time
Expansion stops and eventually Universe collapses upon itself
These possibilities are called

open universe
– ends in cold dark blackness


flat universe
closed universe
– ends in blinding white light
“Big Crunch”
Enough Matter?

The amount of matter in the Universe helps determine its
fate



if there is enough mass, gravity wins
given H0 = 70 km/(s Mpc), critical mass density is 8x10-27 kg/m3
define MASS as the actual density of mass in the Universe
divided by the critical density



MASS < 1 is an open universe
MASS = 1 is a flat universe
MASS > 1 is a closed universe
Enough Matter?





Visible matter (stars in galaxies, & hot
gas)

only 2% of critical density; MASS =
0.02
Dark matter in galaxies

(measured by galaxy rotation curves)

about 10 times as much; MASS = 0.2
Dark matter between galaxies

(measured by watching galaxies
fall inward in galactic clusters
and from gravitational lensing)

raises total to 30% of critical density

MASS = 0.3
We do not observe enough matter to
cause the Universe to be closed
But it’s not the end of the story…
Is the Expansion Slowing Down?
Use Type 1a supernovae







a standard candle
use brightness to determine
distance
use redshift to determine speed
compare them
data lies below prediction (galaxies
are speeding up!!)
Answer: Strangely enough…
the rate of expansion is speeding up!

Life?
Is Life Out There?
What evidence do we have of life beyond Earth?



What possibilities are there?




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Actually, so far, we have no direct evidence
of life beyond Earth!!
Requires complex carbon chemistry 
only around population I stars.
(in liquid water)  narrow temperature
range btwn melting & boiling points of water
Requires long-lived worlds  probably not
around blue giant stars or in binary or
multiple stars systems
Mars
Europa, Titan(?)
Comets/Asteroids
Terrestrial planets/
moons in other
systems
The Search for Life

We search for intelligent life using
radio waves





radio waves travel far distances at the speed of light
not produced by most stars
seems fairly easy to develop technology
possible to communicate information
Numerous large radio
telescope arrays around
the world
SETI



Search for ExtraTerrestrial
Intelligence (SETI)
There are numerous programs
First search, Project Ozma, was in 1960


200 hours of observing two nearby stars
Project Phoenix


privately financed US project
search 2 billion channels for each of
1000 nearby stars


stars similar to the Sun and at least
3 billion years old
about half done – nothing yet
SETI Still Going

SERENDIP Project


search for signals using regular
radio telescope observations from
the Arecibo telescope in Puerto
Rico
you can participate by downloading
a screen saver which analyzes SETI
data while your computer is idle


www.setiathome.ssl.berkeley.edu
Allen Telescope Array


series of 1000s of small
satellite dishes
funded by Paul Allen
(of Microsoft)
Drake Equation

What are the factors to determine
the chance there is advanced
intelligent life out there?

number of stars (T)


number of planets/moons (npm)



Recent searches seem to show many
number of planets/moons where life does actually
start (fl)


200,000,000,000 in our galaxy!!
carbon chemistry, liquid water, long-lived
number of times life becomes intelligent (fc) (??)
length of intelligent civilization that can
communicate with stars (L)

We’ve only been able to do it for ~40 years – which
is totally insignificant!!
N = T x npm x fl x fc x L
Messages from Earth


We have tried to communicate
with other life
Probes


Pioneer and Voyager carry plaques
and recordings
Radio signals


been emitting radio signals
since the 1940s –
 “the Honeymooners”, “I
Love Lucy” etc.
sent several messages
 Arecibo broadcast – 1974
 Encounter 2001