Skip to main content

How the Big Bang discovery came about

By Meg Urry
updated 8:40 AM EDT, Mon March 31, 2014
Astronomers using the Hubble Space Telescope have pieced together this picture that shows a small section of space in the southern-hemisphere constellation Fornax. Within this deep-space image are 10,000 galaxies, going back in time as far as a few hundred million years after the Big Bang. Click through to see other wonders of the universe. Astronomers using the Hubble Space Telescope have pieced together this picture that shows a small section of space in the southern-hemisphere constellation Fornax. Within this deep-space image are 10,000 galaxies, going back in time as far as a few hundred million years after the Big Bang. Click through to see other wonders of the universe.
HIDE CAPTION
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
Wonders of the universe
<<
<
1
2
3
4
5
6
7
8
9
10
11
>
>>
STORY HIGHLIGHTS
  • Meg Urry describes the sequence of discoveries that lead to evidence of "inflation"
  • Urry: Inflation, far faster than speed of light, happened in the first instant of the universe
  • Urry: Theory began 80 years ago with Edwin Hubble: Telescope named after him
  • Urry: After inflation, the universe went into more "sedate" pace of Big Bang we see now

Editor's note: Meg Urry is the Israel Munson professor of physics and astronomy at Yale University and director of the Yale Center for Astronomy and Astrophysics.

(CNN) -- For the past week-and-a-half, people have been marveling over the discovery of evidence supporting "inflation," the theory describing the birth pangs of the Big Bang 13.7 billions years ago. What do these findings mean and how did they come about?

Lots of articles reported the news, but I am going to try to explain it in depth. Stick with me, because this is one of the most exciting astrophysical discoveries in decades.

Meg Urry
Meg Urry

Humans have wondered about the origin of the universe for millennia, and last week's news brought us a little closer to an answer. What this development means, basically, is that for the first time, we may be seeing what happened in the first billionth of a trillionth of a trillionth of a second of the universe.

Assuming this discovery is verified by other similar experiments, it means the very birth of the universe can be studied. These will tell us about the physics of matter and energy well beyond the reach of earthly particle accelerators like the Large Hadron Collider.

In a press conference on March 17, leaders of the Background Imaging of Cosmic Extragalactic Polarization (BICEP2) experiment announced their discovery of evidence of gravitational waves -- predicted by Einstein's theory of General Relativity -- that were generated by the near-instantaneous expansion of the universe by some 50 factors of 10, or a factor of 100 million, trillion, trillion. Those waves were predicted by the theory of inflation, developed 30 years ago by Alan Guth, Andrei Linde and others.

Inflation is the instantaneous initial expansion, far faster than the speed of light, that "describes the propulsion mechanism that drove the universe into the period of tremendous expansion that we call the Big Bang," as Alan Guth put it. Incidentally, the term "Big Bang" was coined as an insult by a physicist who didn't like the theory.

The Big Bang idea itself is simple. Edwin Hubble -- after whom the Hubble Space Telescope is named -- showed more than 80 years ago that our universe is expanding. Objects in space are not hurtling outward: Space itself is becoming bigger over time. That means the distance between two galaxies grows even if neither galaxy is moving through space at all.

By extrapolating the Hubble expansion backward, we have long known that the universe was once smaller by many, many factors of 10. All the mass and energy of the entire universe squeezed into such a tiny volume would have been much hotter and denser. Then, as the universe expanded over time, the energy density went down, so the temperature cooled. This Big Bang idea implied that cool relic radiation should be visible today.

Indeed, this Big Bang glow of radiation was discovered in the early 1960s by two Bell Labs engineers, Arno Penzias and Robert Wilson, who were trying to build the world's best radio antenna.

Ripples in space-time revealed
A Big Bang breakthrough?

Their instrument recorded a mysterious irreducible low-level noise from every direction. Apparently worried that the surface of the antenna horn had been corrupted by, um, debris from pigeons roosting inside, the engineers repeatedly disassembled and cleaned the antenna, to no avail.

Physicists later connected this measurement to the Big Bang prediction of a cosmic microwave background, for which Penzias and Wilson were awarded the Nobel Prize in 1978. As a colleague at Bell Labs joked, referring to their obsession with pigeon droppings, "They went looking for dung and came up with gold. For most of us [scientists], it works the other way."

The Big Bang idea was well established by the 1980s. But it did not explain important pieces of the story.

First, the universe looks pretty homogeneous and isotropic -- that is, galaxies in any one direction look very similar to galaxies in the opposite direction, no matter how distant. The number of galaxies, their masses, their shapes and their stellar content are remarkably similar, to the furthest reaches we can observe.

This is surprising because the Big Bang-Hubble expansion implied that very distant regions should never have been in causal contact. How then could they be so similar? Here is a simple analogy: Imagine a thermos of ice water and a thermos of hot tea. As long as these two liquids are separate, they will have different temperatures. But if the two liquids are combined, the mixed liquid will quickly reach an intermediate temperature. Similarly, two well-separated regions of the universe can be alike only if they were at one time in contact.

The theory of inflation explains this quite naturally: If at the beginning the universe inflated at an extraordinarily rapid rate -- much faster than the Hubble-measured expansion today -- then all parts of the universe visible today were once in contact. That means they had the same initial physical conditions (such as temperature and density), so that similar stars and galaxies eventually formed out of the cosmic soup.

Inflation also explains why the universe has a very "flat" geometry -- something revealed in the 1990s by analysis of the spatial distribution of tiny fluctuations (hot and cold spots) in the cosmic microwave background radiation.

In principle, other geometries of space were possible. For example, a two-dimensional surface can be flat like a table; convex like the surface of a sphere (also called closed); or concave like the surface of a saddle (also called open).

For the universe to be flat requires a very precise balance. It has infinitely more ways to be open or closed, with strong curvature, weak curvature, or anything in between. But to be flat -- well, that's like balancing on a knife edge. Inflation naturally explains this odd fact.

Specifically, the idea is that, at the very beginning, the universe must have inflated enough to stretch the fabric of space until no trace of curvature remained. Imagine inflating a beach ball to the size of the Earth: you can easily see the curvature of the beach ball in your hands but once it's hyper-inflated, any piece of its surface seems very flat, just as the Earth feels flat locally.

The enormous inflation in size would effectively erase the initial conditions in the universe. Whatever the initial temperature, for example, inflation would cool the universe to absolute zero. Even if the initial universe were very lumpy, after inflation we can see only a very smooth, local part of the original volume -- and it would seem perfectly flat.

After about one hundred millionth of a trillionth of a trillionth of a second, according to theorists, whatever repulsive gravity caused inflation then transformed into a hot, dense soup of particles and energy. At this point, the Big Bang expansion that Hubble discovered took over.

How inflation began and how it ended are not yet understood, but this simple idea of inflation neatly explains otherwise odd characteristics -- isotropy and flatness -- of our universe.

Still, until now, there had been no direct evidence of inflation. What BICEP2 saw was the imprint of inflation on the cosmic microwave background radiation.

Specifically, inflation should have generated a lot of gravitational waves -- that is, it would cause propagating ripples of space itself. Such waves have a characteristic pattern, squeezing space rhythmically in one direction then the perpendicular direction, like two hands pressing a rubber ball top to bottom then side to side.

This distortion of space causes a special pattern of polarization in the Cosmic Microwave Background radiation. So what is polarization?

Light is a wave that oscillates back and forth -- polarized light oscillates preferentially in one plane. Because most light is a mix of random directions of polarization, its net polarization is zero. But any scattered light, like sunlight reflected off water, is polarized -- which is why polarized sunglasses cut down substantially on glare.

BICEP2 scientists searched for that special pattern of polarization in the cosmic microwave background that would show the evidence of inflation, working for several years analyzing and reanalyzing their data.

As they ran through every possible check of the analysis, team members finally began to believe they had detected the first direct signs of inflation.

Now other experiment teams are redoubling efforts to find the same signal -- or to find contradictions. The reported BICEP2 signal is unexpectedly strong, so it should be within reach of at least some of these experiments.

Physicists around the world know: the BICEP2 discovery is only the beginning of the story. If this result is verified by independent experiments, new, more accurate experiments will be designed to better measure the polarization imprint. This in turn will tell us about how matter and energy behave in conditions much hotter and denser than on Earth or any other place in the cosmos.

As Carl Sagan once said, "Extraordinary claims require extraordinary evidence." Let the observations begin.

Follow us on Twitter @CNNOpinion.

Join us on Facebook.com/CNNOpinion.

The opinions expressed in this commentary are solely those of Meg Urry.

ADVERTISEMENT
Part of complete coverage on
updated 5:01 PM EDT, Wed October 22, 2014
Paul Callan says the grand jury is the right process to use to decide if charges should be brought against the police officer
updated 12:19 PM EDT, Thu October 23, 2014
Theresa Brown says the Ebola crisis brought nurses into the national conversation on health care. They need to stay there.
updated 6:35 PM EDT, Tue October 21, 2014
Patrick Hornbeck says don't buy the hype: The arguments the Vatican used in its interim report would have virtually guaranteed that same-sex couples remained second class citizens
updated 9:36 AM EDT, Fri October 24, 2014
Paul Begala says Iowa's U.S. Senate candidate, Joni Ernst, told NRA she has right to use gun to defend herself--even from the government. But shooting at officials is not what the Founders had in mind
updated 6:08 PM EDT, Thu October 23, 2014
John Sutter: Why are we so surprised the head of a major international corporation learned another language?
updated 5:54 PM EDT, Thu October 23, 2014
Jason Johnson says Ferguson isn't a downtrodden community rising up against the white oppressor, but it is looking for justice
updated 12:21 PM EDT, Fri October 24, 2014
Sally Kohn says a video of little girls dressed as princesses using the F-word very loudly to condemn sexism is provocative. But is it exploitative?
updated 4:06 PM EDT, Tue October 21, 2014
Timothy Stanley says Lewinsky is shamelessly playing the victim in her affair with Bill Clinton, humiliating Hillary Clinton again and aiding her critics
updated 10:14 AM EDT, Thu October 23, 2014
Imagine being rescued from modern slavery, only to be charged with a crime, writes John Sutter
updated 12:00 PM EDT, Tue October 21, 2014
Tidal flooding used to be a relatively rare occurrence along the East Coast. Not anymore, write Melanie Fitzpatrick and Erika Spanger-Siegfried.
updated 7:35 AM EDT, Tue October 21, 2014
Carol Costello says activists, writers, politicians have begun discussing their abortions. But will that new approach make a difference on an old battleground?
updated 9:12 AM EDT, Tue October 21, 2014
Sigrid Fry-Revere says the National Organ Transplant Act has caused more Americans to die waiting for an organ than died in both World Wars, Korea, Vietnam, Afghanistan and Iraq
updated 2:51 PM EDT, Tue October 21, 2014
Crystal Wright says racist remarks like those made by black Republican actress Stacey Dash do nothing to get blacks to join the GOP
updated 6:07 PM EDT, Tue October 21, 2014
Mel Robbins says by telling her story, Monica Lewinsky offers a lesson in confronting humiliating mistakes while keeping her head held high
updated 9:29 AM EDT, Mon October 20, 2014
Cornell Belcher says the story of the "tea party wave" in 2010 was bogus; it was an election determined by ebbing Democratic turnout
updated 4:12 PM EDT, Mon October 20, 2014
Les Abend says pilots want protocols, preparation and checklists for all contingencies; at the moment, controlling a deadly disease is out of their comfort zone
updated 11:36 PM EDT, Sun October 19, 2014
David Weinberger says an online controversy that snowballed from a misogynist attack by gamers into a culture war is a preview of the way news is handled in a world of hashtag-fueled scandal
updated 8:23 AM EDT, Mon October 20, 2014
Julian Zelizer says Paul Krugman makes some good points in his defense of President Obama but is premature in calling him one of the most successful presidents.
updated 10:21 PM EDT, Sun October 19, 2014
Conservatives can't bash and slash government and then suddenly act surprised if government isn't there when we need it, writes Sally Kohn
updated 8:05 AM EDT, Wed October 22, 2014
ISIS is looking to take over a good chunk of the Middle East -- if not the entire Muslim world, write Peter Bergen and Emily Schneider.
updated 9:00 AM EDT, Mon October 20, 2014
The world's response to Ebola is its own sort of tragedy, writes John Sutter
updated 4:33 PM EDT, Fri October 17, 2014
Hidden away in Russian orphanages are thousands of children with disabilities who aren't orphans, whose harmful treatment has long been hidden from public view, writes Andrea Mazzarino
updated 1:22 PM EDT, Sat October 18, 2014
When you hear "trick or treat" this year, think "nudge," writes John Bare
updated 12:42 AM EDT, Sat October 18, 2014
The more than 200 kidnapped Nigerian schoolgirls have become pawns in a larger drama, writes Richard Joseph.
updated 9:45 AM EDT, Fri October 17, 2014
Peggy Drexler said Amal Alamuddin was accused of buying into the patriarchy when she changed her name to Clooney. But that was her choice.
updated 4:43 PM EDT, Thu October 16, 2014
Ford Vox says the CDC's Thomas Frieden is a good man with a stellar resume who has shown he lacks the unique talents and vision needed to confront the Ebola crisis
updated 4:58 AM EDT, Sat October 18, 2014
How can such a numerically small force as ISIS take control of vast swathes of Syria and Iraq?
updated 9:42 AM EDT, Fri October 17, 2014
How big a threat do foreign fighters in Syria and Iraq pose to the West? It's a question that has been much on the mind of policymakers and commentators.
updated 8:21 AM EDT, Fri October 17, 2014
More than a quarter-million American women served honorably in the Iraq and Afghanistan wars. Now they are home, we have an obligation to help them transition back to civilian life.
updated 4:27 PM EDT, Thu October 16, 2014
Paul Begala says Rick Scott's deeply weird refusal to begin a debate because rival Charlie Crist had a fan under his podium spells disaster for the Florida governor--delighting Crist
updated 12:07 AM EDT, Thu October 16, 2014
The longer we wait to engage on Ebola, the more limited our options will become, says Marco Rubio.
updated 7:53 AM EDT, Wed October 15, 2014
Democratic candidates who run from President Obama in red states where he is unpopular are making a big mistake, says Donna Brazile
updated 12:29 AM EDT, Thu October 16, 2014
At some 7 billion people, the world can sometimes seem like a crowded place. But if the latest estimates are to be believed, then in less than a century it is going to feel even more so -- about 50% more crowded, says Evan Fraser
updated 12:53 PM EDT, Mon October 20, 2014
Paul Callan says the Ebola situation is pointing up the need for better leadership
updated 6:45 PM EDT, Wed October 15, 2014
Nurses are the unsung heroes of the Ebola outbreak. Yet, there are troubling signs we're failing them, says John Sutter
updated 1:00 PM EDT, Wed October 15, 2014
Dean Obeidallah says it's a mistake to give up a business name you've invested energy in, just because of a new terrorist group
updated 7:01 PM EDT, Wed October 15, 2014
Fear of Ebola is contagious, writes Mel Robbins; but it's time to put the disease in perspective
updated 1:44 PM EDT, Tue October 14, 2014
Oliver Kershaw says that if Big Tobacco is given monopoly of e-cigarette products, public health will suffer.
updated 9:35 AM EDT, Sat October 18, 2014
Stop thinking your job will make you happy.
updated 10:08 PM EDT, Tue October 14, 2014
Ruben Navarrette says it's time to deal with another scandal involving the Secret Service — one that leads directly into the White House.
updated 7:25 AM EDT, Tue October 14, 2014
Americans who choose to fight for militant groups or support them are young and likely to be active in jihadist social media, says Peter Bergen
updated 9:03 AM EDT, Mon October 13, 2014
Stephanie Coontz says 11 years ago only one state allowed same sex marriage. Soon, some 60% of Americans will live where gays can marry. How did attitudes change so quickly?
updated 4:04 PM EDT, Tue October 14, 2014
Legalizing assisted suicide seems acceptable when focusing on individuals. But such laws would put many at risk of immense harm, writes Marilyn Golden.
updated 9:07 AM EDT, Mon October 13, 2014
Julian Zelizer says the issues are huge, but both parties are wrestling with problems that alienate voters
updated 6:50 PM EDT, Mon October 13, 2014
Mel Robbins says the town's school chief was right to cancel the season, but that's just the beginning of what needs to be done
updated 11:43 AM EDT, Sat October 11, 2014
He didn't discover that the world was round, David Perry writes. So what did he do?
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT