A journey through the Universe

Michael Burton

School of 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.


The 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 reached.  From 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.


Note: the text refers specifically to the Movie, not to the pictures which accompany this text.  The captions, however, refer to the pictures shown below.

Earth  36,000 km or 0.1 light seconds

We 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 moving westwards.


Moon  384,000 km or 1.3 light seconds

As 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.


Mars   ~100 million km or 5 light minutes

Mars 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.


Asteroid Belt ~300 million km or 15 light minutes

We 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 belt.  Many are pock-marked from collisions with other, small rocks.  No planet managed to form here, probably a result of the gravitational perturbations that would have been introduced on any proto-planetary body by Jupiter.


Io          ~700 million km or 40 light minutes

As 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.


Jupiter     ~700 million km or 40 light minutes

Jupiter 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 depths).  Notice 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.


Saturn           ~1.4 billion kilometres or 80 light minutes

Saturn 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 plane.  They 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.

Zodiacal Light

Notice 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.

The Kuiper Belt and Oort Cloud   

~100 to ~50,000 Astronomical Units (14 light hours to 0.8 light years)

The 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.



Alpha Centauri         4 light years

We now leave the Solar System and travel out into our Galaxy.  We pass by our nearest star, Alpha Centauri, which turns out to be very similar to Sun in mass (and hence size and temperature).  It is, however, a double system and the companion star is clearly seen here.  The radio noise from the Earth starts to quieten, at last!

The Eagle Nebula (Messier 16)     7,000 light years

Finally we get beyond the reach of human radio signals (a sphere about 65 light years in radius) and it all goes quiet.  It remains this way until we reach the microwave background itself!  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 are pointing).  In a hundred thousand years the columns will be no more, though possibly some new stars will have formed from the gas inside them.


Milky Way Galaxy    30,000 light years

We 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 Clouds.  The old, yellow stars of the central bulge of our Galaxy, surrounding the galactic centre, can also be clearly seen.


Magallenic Clouds    (Large Cloud 160,000 light years, Small Cloud 200,000 light years)

Satellite 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 (upper right).  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 from Sydney!  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 weeks afterwards.



Centaurus A  13 million light years

This 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 dust lane.


The Realm of the Galaxies ~1 billion light years

On 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 Radiation   13 billion light years

Our best current estimates place the Universe's origin (the "Big Bang") at 13.4 +/- 1 billion years ago.  A few hundred thousand years after the Big Bang is the first event we can see, the cosmic microwave background radiation (CMBR).  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.


Jodie Foster

And 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!

Ellie Arroway (Jodie Foster) listening in for ET! (Time Warner)
(This was one part of the film where artistic 
licence was liberally applied for effect!)



Contact Web Site

The 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 .  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.



Further Information



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