journey through the Universe
Physics, University of New South Wales
Contact, the movie from Time Warner starring Jodie Foster and Matthew
McConaughey, and based on Carl Sagan's novel of the same
name, is about the first contact humans make with life beyond
the Earth. This
might well occur through the means of radio communication.
Surrounding the Earth is an expanding sphere of radio
waves, now over 60 light years in radius, the product of
transmissions from radio and TV stations.
These could be detected by an advanced extraterrestrial
intelligence, who might then send back a signal to us as
a means of exchanging a greeting.
For instance, in Contact,
a signal is picked up from the broadcast of the opening
ceremony of the Berlin Olympics in 1936 (the first truly
global TV broadcast made by humans) at a kind of galactic
railway hub located around the star Vega.
Vega is a young star still surrounded by a proto-planetary
cloud of debris, situated some 27 light years away from
us. A radio
signal is then sent back to us, carrying the original transmission
in it (which features Hitler prominently!), but having encoded
within it another more complex message.
As we discover as the film progresses, this is a
set of instructions on how to build a space transportation
device to reach the hub at Vega.
In theory, such a signal could be received on Earth
anytime after 1990, the round-trip time for a light or radio
signal to travel to Vega and back.
3 minute opening sequence of Contact
is an imaginary journey away from the Earth, out through
our Solar System, then through and out of our Galaxy, through
our Local Group of galaxies, and into the realm of the galaxies,
finally ending close to the moment of creation, with the
microwave background radiation, which marks the limit of
the observable Universe.
The journey is at ever-increasing speeds, and indeed
is soon taking place at super-luminal velocities.
Initially we can hear the radio static arising from
the combined transmissions of all the radio stations on
Earth. As we
move further away that fuzz diminishes, until we reach the
point where no radio transmission from the Earth could have
then, till the edge of the Universe, there is complete quiet.
The presence of humans on the Earth could not have
been detected at such distances by anyone out there.
In the rest of this description we now make that
journey and view the highlights seen along the way.
the text refers specifically to the Movie, not to the pictures
which accompany this text.
The captions, however, refer to the pictures shown
36,000 km or 0.1 light seconds
start in geostationary orbit above the night-time
Earth, looking down at the south-eastern part of the
USA (Florida is clearly visible to the lower right). The noise from the combined radio stations of Earth is deafening!
As the Earth rotates the Sun rises in the East.
The terminator between day and night is seen
384,000 km or 1.3 light seconds
we start to move away from the Earth, we pass by the
Moon, a dead world marked by the craters from asteroid
impacts, a reminder of the final period in the violent
formation process that lead to the creation of the
planets and moons in our Solar System.
~100 million km or 5 light minutes
in the next planet beyond Earth.
It is a small, rocky world, about half the
radius of the Earth.
In the first billion years of so of our Solar
System it had an atmosphere and oceans, and possibly
even some simple forms of life. Now the atmosphere has mostly disappeared, the heat from the
planets interior nearly all radiated away, and Mars
is a lifeless world.
However, it shows the signs of a more active
past: canyons, hundreds of kilometres long can be
seen, volcanoes that dwarf any on Earth, polar caps
of carbon dioxide ice, all overlaid with the colour
of red dust.
Belt ~300 million km
or 15 light minutes
pass through a region containing hundreds of thousands
of rocks and boulders, some a few metres in diameter,
the largest over 100 km in size, known as the Asteroid
are pock-marked from collisions with other, small
planet managed to form here, probably a result of
the gravitational perturbations that would have been
introduced on any proto-planetary body by Jupiter.
~700 million km or 40 light minutes
we approach Jupiter we first pass by Io, innermost
of its 4 large moons or 'Galilean' satellites.
Io is a seething volcano, its interior kept
in a molten state by the immense tidal forces from
Jupiter, whose friction melts the rock.
~700 million km or 40 light minutes
is the giant of the planets, over ten times the diameter
of the Earth. It is a gas giant, composed primarily of molecular hydrogen
(in gaseous, liquid and molten forms at ever-increasing
the "Red Spot", a hurricane over twice the
size of the Earth that has been blowing since at least
1610, when Galileo first applied the telescope to
viewing the heavens.
As we move away from Jupiter a couple of other
moons can be seen passing by. The
4 Galilean satellites, together with bands in the
atmosphere, and the Red Spot, can readily be seen
through small telescopes.
The positions of the Moons can also be seen
to change from night to night.
~1.4 billion kilometres or 80 light minutes
is rightly known as the "Lord of the Rings".
Second only to Jupiter in size amongst the
planets, it is another gas giant comprised mostly
of molecular hydrogen.
Its ring system is truly spectacular, and can
easily be seen through a small telescope.
It comprises billions of small particles of
ice and dust orbiting around Saturn in its equatorial
are too close to Saturn for a moon to exist (tidal
forces would tear it apart) but are kept in their
place by resonances from moons exterior to them.
also the backdrop behind Saturn.
The Zodiacal Light, scattered sunlight off
dust particles in our Solar System, particularly in
the Asteroid Belt, can be clearly seen.
This is set against the star field that is
our Milky Way galaxy. The Sun now appears very faint and distant, and starts to blend
in with the Milky Way.
Kuiper Belt and Oort Cloud
to ~50,000 Astronomical Units (14 light hours to
0.8 light years)
Kuiper Belt is a second, outer asteroid belt, which
includes Pluto and many other icy bodies and 'short
period' comets such as Halley.
It lies in the plane of the Ecliptic, along
with the planets, but merges into the Oort Cloud
at greater distances.
The Oort Cloud is like a halo around the
Sun, a reservoir containing trillions of comets,
which occasionally get perturbed inwards so they
pass near the Sun and are seen by us.
They may represent debris left over from
the formation of the Solar System, or could be material
picked up by the Sun during its 250 million year
journey around the centre of the Galaxy.
4 light years
now leave the Solar System and travel out into our
pass by our nearest star, Alpha Centauri, which turns
out to be very similar to Sun in mass (and hence size
It is, however, a double system and the companion
star is clearly seen here.
The radio noise from the Earth starts to quieten,
Eagle Nebula (Messier 16)
7,000 light years
we get beyond the reach of human radio signals (a
sphere about 65 light years in radius) and it all
It remains this way until we reach the microwave
We pass along the plane of the Milky Way, occasionally
going through spiral arms and clouds of molecular
gas in which stars are forming.
In this particular instance we pass through
a nebula known as the Eagle Nebula, and made famous
by the Hubble Space Telescope picture of its "elephant
trunks". These are actually dense columns of molecular gas (dense means
about 1 million molecules per cubic centimetre, ten
million, million times less
dense than the air we breath!), approximately one
light year in length.
These have resisted
the processes of star formation longer than the rest
of the cloud, but are being eaten into by the intense
UV radiation produced by the young stars at the centre
of the Eagle Nebula (not seen in this view, but a
few light years away in the direction the columns
In a hundred thousand years the columns will
be no more, though possibly some new stars will have
formed from the gas inside them.
30,000 light years
now begin to climb out of the plane of our Milky Way
galaxy and look back at the spiral arms from which
we have come.
We see the bubble of gas that is the Eagle
Nebula, and how small it is in relation to the galaxy.
Spiral arms are regions of slightly higher
density in which stars are preferentially forming,
hence their spectacular youthful blue appearance.
They are in fact compression waves moving around
the galaxy driven by an external perturbing gravitational
force, possibly from our satellite galaxies, the Magallenic
old, yellow stars of the central bulge of our Galaxy,
surrounding the galactic centre, can also be clearly
Clouds (Large Cloud 160,000 light years, Small Cloud 200,000
galaxies of our own, the Clouds are actually been
torn apart and cannibalised by the Milky Way.
The LMC is to the fore and the SMC to the rear
They can be clearly seen by the naked eye on
a dark site when there is no Moon.
However, it's virtually impossible to see them
The Clouds are the site of active star formation.
The Tarantula Nebula, containing the spectacular
30 Doradus region, is clearly seen.
The glowing red nebulae are of hydrogen gas,
ionized by the UV radiation from massive young stars.
Near here a star exploded as a supernova in
1987, and was visible to the naked eye for several
A 13 million
is the closest "active" galaxy to us, and
is one of the brightest radio sources in the sky.
The radio emission comes from lobes that extend
about one million light years beyond the optical galaxy,
much further than the distance to the Magallenic Clouds
from us! They
are powered by a compact "central engine",
most likely the result of accretion of matter onto
a massive black hole.
The conversion of gravitational potential energy
into kinetic energy is sufficient to power a jet which
drives relativistic particles this immense distance
away from the core.
In the optical, Centaurus A is an "elliptical
galaxy", but whose appearance is dominated by
the dust lane that runs across it, obscuring the core
of the galaxy from our view.
At infrared wavelengths it is clearly visible.
Star formation is occurring throughout the
The Realm of the Galaxies
~1 billion light years
the largest scales the basic building block of the
Universe are the galaxies, and as we travel further
and further away our view is dominated by the multitude
of different galaxy types we pass by; spirals, ellipticals
and irregulars. At these great distances we are even starting to see the processes
of galaxy formation, as sub-galactic clouds merge
into one another and drive bursts of star formation.
The Cosmic Microwave Background
billion light years
best current estimates place the Universe's origin
(the "Big Bang") at 13.4 +/- 1 billion years
few hundred thousand years after the Big Bang is the
first event we can see, the cosmic microwave background
This is the time when the Universe became transparent
to radiation, and occurred after it had cooled sufficiently
for protons and electrons to combine to make hydrogen
atoms, which no longer scatter radiation.
The furthest we can possibly see back is to
the CMBR - beyond that the Universe is essentially
a thick fog.
finally, as we travel further back to the moment of
creation, and the centre of it all, we end our journey
with Jodie Foster as a child, wondering about how
it all came to be!
Arroway (Jodie Foster) listening in for ET! (Time
(This was one part of the film where artistic
licence was liberally applied for effect!)
Contact Web Site
SETI Institute, who are conducting a search for alien
life in much the way depicted in Contact,
have a web site on the movie at URL http://www.seti.org/Page.aspx?pid=584 .
Further background information about the movie,
the people and places it is based on, as well as the
science which underpins it, can be found there.
There is also a set of Teachers Guides available
to help you bring the experience to the classroom.