What Astronomers Are Still Discovering About the Big Bang Theory

A half-century after it was confirmed, the theory still yields new secrets

Big Bang
An artist's rendition of the Big Bang. Photo by David A. Aguilar

On a bright spring morning 50 years ago, two young astronomers at Bell Laboratories were tuning a 20-foot, horn-shaped antenna pointed toward the sky over New Jersey. Their goal was to measure the Milky Way galaxy, home to planet Earth.

To their puzzlement, Robert W. Wilson and Arno A. Penzias heard the insistent hiss of radio signals coming from every direction—and from beyond the Milky Way. It took a full year of testing, experimenting and calculating for them and another group of researchers at Princeton to explain the phenomenon: It was cosmic microwave background radiation, a residue of the primordial explosion of energy and matter that suddenly gave rise to the universe some 13.8 billion years ago. The scientists had found evidence that would confirm the Big Bang theory, first proposed by Georges Lemaître in 1931.

“Until then, some cosmologists believed that the universe was in a steady state without a singular beginning,” says Wilson, now 78 and a senior scientist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. “The finding helped rule that out.”

That assessment seems a bit modest for a discovery that received the Nobel Prize in Physics in 1978 and is now, on its semicentennial, celebrated as the Rosetta stone of modern cosmology, the key that has allowed generations of scientists to parse the origins of the universe.

Avi Loeb was a toddler on a farm in Israel when Wilson and Penzias began investigating those mysterious signals. Today, he’s a colleague of Wilson’s at the Center for Astrophysics and chair of Harvard’s astronomy department, and one of the world’s foremost researchers on what has been called the “cosmic dawn.” The theoretical physicist, now 52, has published more than 450 papers on aspects of the early universe, including the formation of stars and galaxies and the origins of the first black holes. He has done pioneering work on the three-dimensional mapping of the universe, and he has explored the implications of the impending collision between the Milky Way and the Andromeda galaxy (which will not happen, he adds, for several billion years).

Loeb recently made headlines with a paper submitted to the journal Astrobiology suggesting that just 15 million years after the Big Bang, the temperature from the cosmic background microwave radiation was 0 to 30 degrees Celsius—warm enough, he says, to allow “liquid water to exist on the surface of planets, if any existed,” without the warmth of a star. “So life in the universe could have started then.” By contrast, the earliest evidence of life on Earth is only 3.5 billion years old. Loeb’s proposition would add about ten billion years to the timeline of life in the universe.

“I’ve been trying to understand the beginning of the process before the Milky Way and its stars were formed,” he says. “It turns out that the first stars were more massive than the Sun and the first galaxies were smaller than the Milky Way.” This period is compelling, he says, because “it is the scientific version of the story of Genesis. I don’t want to offend religious people, but the first chapter of the Bible needs revising—the sequence of events needs to be modified. It is true that there was a beginning in time. As in the biblical story, ‘Let there be light.’ This light can be thought of as the cosmic microwave background.”

Loeb’s cherubic demeanor and puckish sense of humor play well on his YouTube videos, and Time and Popular Mechanics have cited his influence among space scientists. The title of his paper “How to Nurture Scientific Discoveries Despite Their Unpredictable Nature” reflects his appreciation of the accidental, such as the story behind the Wilson-Penzias discovery.

Recently, Wilson and Loeb have been working together on efforts to map the black hole at the center of the Milky Way. “I think Avi is a theorist who is very good at picking problems to work on that have testable results,” Wilson says.

As for the rigors of exploring deep time and places where no humans are likely ever to tread, Loeb says, “It’s kind of thrilling, like finding a trail in the woods that nobody has thought about. There’s a lot of loneliness. You have to get used to thinking about ideas.”

On Thursday, February 20 at 7:30, Wilson and Loeb will be joined in a panel discussion by cosmologist Alan Guth and astronomer Robert Kirshner at the Harvard-Smithsonian Center for Astrophysics, in celebration of the 50th anniversary of the confirmation of the Big Bang Theory. Watch the discussion live on YouTube.

Get the latest on what's happening At the Smithsonian in your inbox.