A Cambridge professor explains the Big Bang theory and the creation of the universe, writes Dick Ahlstrom.
The Big Bang Theory would be dismissed as a crackpot notion if it weren't for the hard evidence there to support it. Scientists can now describe with confidence how our universe formed from a single, cataclysmic explosion starting from something no bigger than the centre of an atom.
How something so unbelievably large could form from something so inconceivably small is the stuff of cosmology. It is also the subject matter of a talk to be given this evening by Malcolm Longair, professor of natural philosophy and head of the Cavendish Laboratory at the University of Cambridge.
Longair's talk, The Big Bang and its Aftermath, will explain what we know about the origins of the universe. It is one of a series of lectures organised by the Royal Irish Academy, The Irish Times and Depfa Bank plc to honour William Rowan Hamilton (1805-1865), arguably Ireland's greatest scientist. The Government has designated 2005 as Hamilton Year in this the centenary of his birth.
Longair, a noted expert at explaining the difficult concepts behind the Big Bang, acknowledges how improbable the theory sounds, but argues that there is powerful evidence to back it up. "It is all observation-based," he says. "We wouldn't believe a word of this if it wasn't from evidence."
Arrival at such a strange proposal came as scientific advance usually does, in steps with one discovery building from another. The discovery of spectroscopy, the study of light from an object as a way to understand its make up, allowed scientists in the 19th century to discover that celestial objects were moving relative to one another.
Something had to get stars and galaxies moving and the Big Bang theory was suggested by Belgian Georges Lemaitre (1894-1966). He proposed in 1927 that a primeval atom exploded to produce a massive outward push. Edwin Hubble in turn delivered irrefutable proof in 1930 that the universe was expanding by showing that the further away a galaxy was relative to the earth, the greater the velocity of that galaxy.
"The most significant discovery since then was the discovery of the cosmic microwave background in 1965," explains Longair. This is the glow now reaching us from all directions in the universe left over from the inconceivably hot explosion, something predicted by the Big Bang theory. It is a measurable temperature, currently standing at 2.73 degrees Kelvin.
Working from what astronomers can see now, cosmologists work backwards in a form of time travel that takes them gradually closer and closer to the moment of the Big Bang, Longair says. Innovation in observational techniques has brought us back to within several hundred thousand years of the explosion to a time when light first became visible in the expanding universe.
"The big skill of the game is to discover what happened over that long timescale," back to the explosion itself, says Longair. He doesn't worry about why the Big Bang took place, he only seeks to understand what happened when it did. "It is somebody else's job to decide why it happened."
Evidence is there all along the journey backwards in time to show the theory is based in fact. What we see now must be explained by the theory and the calculations that help define it.
One example is seen in the universe's current shape. Originating from an explosion, one might assume the universe might be shaped like a ball with an expanding edge, yet it is not. "It seems to be incredibly flat," says Longair. "It could have been like the surface of a sphere, but it isn't."
A key milestone in understanding why it does not have a random structure is a time just 10-43 seconds after the Big Bang when the then minute cosmos began a rapid increase in size, from smaller than an atom to more than a kilometre. Yet this expansion helps to explain the flat geometry and also the uniformity of the universe we see today.
"For reasons we don't fully understand, the universe must have gone through a period of exponential expansion," Longair explains. "What we want to do is to go back to 10-43 of a second."
Getting back there is helped greatly by the experiments being done by atom-smashers at centres such as CERN near Geneva and Fermilab in the US. Cosmological theories can be proven with experiments at these centres.
"We are pretty confident we have the (Big Bang) framework right, but it raises as many questions as answers," says Longair. CERN's Large Hadron Collider set for completion in 2007 will be the most powerful atom-smasher in the world, and may finally provide examples of Higgs particles. These theoretical particles will be delivered by CERN only if the theory holds true.
"We must see these particles to ensure our theories are correct," says Longair. "We are holding our breath and expecting really important information to come out of the CERN experiments."
• Prof Longair's free lecture is fully booked but unclaimed seats will be made available. It takes place tonight at 6.30pm in the Burke Theatre, Trinity College arts block.
In time all the stars will flicker and fall
It started with a "singularity", the moment before the Big Bang which created space and time. The singularity, no bigger than the centre of an atom, exploded producing temperatures up to trillions of degrees. Then just 10-43 seconds after the explosion the tiny universe begins to expand exponentially, at a phenomenal rate that lasted just 10-11 seconds (about a billionth of a second) to give an outward push to the boundaries of space time that continues to this day.
Where will it take us? To a colder, darker place, according to cosmologists. The universe is accelerating again, picking up speed as it expands. Matter will be spread too thin to coalesce, and over time the stars will finally go out one by one.