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Astrophysics in the
21st Century:
The big questions answered?
Rachel Webster
July Lecture 2002
Two Big Questions:
• What is the future
of the universe?
• Is there
extraterrestrial life
in the universe?
What is the Big Bang?
A model to describe the universe:
How it started
How it is today
How it will end…….
Early universe
(1) Hot
(2) Expanding: gets cooler
(3) Very uniform on large scales,
but seeds of galaxy formation
Cosmic Microwave Background (CMB)
from COBE 1990’s
Dipole anisotropy
1 part in 1000
Milky Way emission
1 part in 100,000
Early structure
few parts in 1,000,000
The universe now
Expanding: Hubble Law, velocity  distance
Cosmic Element Abundance: explicitly predicted
Cosmic Microwave Background: perfect black body
These three measurements establish the
fundamentals of the Big Bang
The universe is expanding
The scale of space is getting bigger, but the
things inside it held together by gravity etc,
stay the same size
We measure the size or scale of the universe
with the letter ‘a’
one equation!
(energy equation)
How does the size of the
universe change with time?
1  da 
4G 2
2
a  a  k
  
2  dt 
3
2
‘curvature’
‘velocity’
‘gravity’
Cosmological constant
or vacuum energy
Einstein’s Greatest Blunder?
He included it in the equations
because he didn’t realise the
universe was expanding.
Then he wanted to get rid of it.

Let’s deal with k. It describes the geometry of space.
k>0
k=0
k<0
Fluctuations in the cosmic microwave background
tell us the universe is flat or k=0.
2000
How does the expansion velocity
change with time?
1  da 
4G 2
2
a  a  k
  
2  dt 
3
2
0
1
a
a
2
Expansion with time
gravity
vacuum
energy
relative
velocity
time
(deccelerating)
(accelerating)
Expansion of universe
deccelerating
constant
accelerating
Supernova are extremely bright
(can be seen a long way away)
and have fixed brightness (standard candles)
Supernova 1987a in the
Large Magellanic Cloud
They can be used to measure the
change in expansion velocity
So how will the universe unfold?

Expanding forever
Matter
Is there anything left to understand?
• Verification that the supernova and
CMB results are correct
• Measurement of all the cosmological
parameters to a few %
• Next tier of questions: why does
the universe have this structure?
How will we do that?
Microwave Anisotropy Probe (MAP):
data collected
PLANCK to fly in about 2007
MAP
SNAP: still just a dream
Big Bang Questions without answer:
Why do we have dark & baryonic matter?
What came before the Big Bang?
What is vacuum energy?
Why did life emerge?
Life in the Universe?
- the search
1.
2.
3.
4.
Finding planets – easy!
Finding Earth’s – the next step
Finding life
Finding intelligence
The Greeks:
In some worlds there is no Sun and Moon
In others they are larger than our world,
And in others more numerous.
In some parts there are more worlds,
In others fewer (…);
In some parts they are rising, in others falling.
There are some worlds devoid of living creatures
Or plants or any moisture.
Democritus 460-370 BC
Extrasolar planets: the gravity method
a planet orbiting a star causes the star to wobble
Can detect 3 m/sec
But must detect 0.1 m/sec to find an Earth.
This motion masked by stellar gas motions.
How many planets have we found?
101 this week:
http://exoplanets.org
http://planetquest.jpl.nasa.gov
Finding small planets:
Need new techniques &
space telescopes
Blocking the light – transits
Jupiter causes 1% of the light to be blocked
Earth would be 0.01%
Detected in HD 209458 in 1999
Kepler Mission
funded by NASA Discovery Program
• To fly in about 2006
• Uses the transit method to find Earth-like planets
• Monitors many stars at a time –
½% chance that the planet is aligned for a transit
• Will find hundreds of Earths, some in the habitable zone
Next technique to be tested:
Just look!
Direct imaging is hard, as the contrast is a billion to
one in the optical; and a million to one in the infrared
But we could be clever and cancel the star’s
light with nulling interferometry, just leaving the planet
Interferometry: adding lightwaves together
Nulling interferometry: cancelling lightwaves
A simulated image
planet
Finding life
Use ourselves as a
template.
Water! Planets in
a habitable zone
Spectrum of the
atmosphere
Then target likely planets
for life-signs…molecules
with a new, more sensitive
telescope
Terrestrial Planet Finder
More than 120 organic
molecules found in space
More than 120 organic molecules
found in space
Astrophysics in the 21st Century:
The big questions answered?
Within 15 years, a cosmological model with
the critical parameters measured to a few %
Within 50 years other planets with life, and
visitors on the way
By the end of the century, changes probably
beyond my comprehension….I won’t be here to
comment!
Some say the world will end in fire
Some say in ice.
From what I’ve tasted of desire,
I hold with those that favour fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.
Robert Frost