It all started with a Big Bang

by Rebecca Priestley / 27 December, 2012
Our whole universe was in a hot dense state – but then what happened?
A timeline of the evolution of the universe/Getty Images

QUESTION: What is the current thinking and research on the Big Bang? asks Waikanae’s Wendy Armstrong. For some insights, I spoke to University of Auckland professor of physics Richard Easther.

ANSWER:'The Big Bang itself is something that physicists don’t currently understand,” says Easther, “but we can say that it happened around 13.7 billion years ago. The primordial universe was enormously hot and enormously dense and expanding really quickly. But from about one trillionth of a trillionth of a trillionth [10-36] of a second after the Big Bang, we can describe the universe and develop testable theories about it.”

As the universe expanded, it cooled, gaining the ability to form more and more complicated structures. A millionth of a second after the Big Bang, quarks coalesced to form protons and neutrons, which each contain three quarks. A few minutes after the Big Bang, protons and neutrons came together to form simple atomic nuclei. Then, about 380,000 years after the Big Bang, the universe was cool enough for electrons to attach themselves to nuclei and form electrically neutral atoms. The first stars ignited a few hundred million years after the Big Bang, and galaxies and clusters of galaxies were arranged in a “cosmic web” that grew and evolved as the universe expanded.

The first descriptions of the Big Bang and the expanding universe emerged in the 1920s, inspired by Einstein’s invention of general relativity. Astronomers – starting with Edwin Hubble – showed that “distant galaxies are all moving away from us. The more distant the galaxy, the faster it’s receding, exactly as the Big Bang theory predicts.”

Modern astrophysicists calculate detailed histories of the universe, from the first instants after the Big Bang through to the birth of galaxies and the stars within them, and the evolution of the galaxies themselves. “When we’re looking at distant parts of the universe, we’re also looking at very old parts of the universe, so we can check these predictions against what we see in the sky.”

Easther says that the stunning agreement between what astrophysicists see and what theory predicts means modern cosmologists find the evidence for the Big Bang and the expanding universe overwhelming. However, our understanding of the universe is far from complete, and our current picture of the Big Bang raises many new questions, which makes cosmology one of the most active topics in physics today.

Much of Easther’s own research focuses on inflation, an era just after the Big Bang when the expansion of the universe dramatically accelerated. “There are lots of theories as to why inflation happened. By working out their detailed predictions, I can compare these predictions to what we see in the sky. The great thing is that we finally have good enough astronomical data to say that some theories are wrong and other theories are not yet wrong – or maybe even right.”

Another big question: was the Big Bang a one-off event? “Physicists do explore theories of the Big Bang itself. These are currently very simplistic but one thing they all seem to have in common is that the event we call the Big Bang happens more than once. Consequently, many cosmologists – including me – suspect other universes exist that are self-contained and disconnected from ours.” As for the future of our universe, it’s continuing to expand at an accelerating rate. “That will lead to a universe where galaxies are few and far between, very old and very cold.”

Until then, Happy New Year.

2013 is the International Year of Mathematics of Planet Earth: Send your mathematically themed questions, and regular science questions, to


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