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 3:47 PM EDT, Wed October 1, 2014
Julian Zelizer says Jimmy Carter's message about the need to restore trust in public officials is a vital one, decades after the now 90-year-old he first voiced it
updated 5:56 PM EDT, Wed October 1, 2014
Ford Vox says mistakes and missed opportunities along the line to a diagnosis of Ebola in a Liberian man have put Dallas residents at risk of fatal infection
updated 6:21 PM EDT, Wed October 1, 2014
Pepper Schwartz says California is trying, but its law requiring step-by-step consent is just not the way hot and heavy sex proceeds on college campuses
updated 10:17 PM EDT, Wed October 1, 2014
Mike Downey says long-suffering fans, waiting for good playoff news since 1985, finally get something to cheer about
updated 5:39 PM EDT, Wed October 1, 2014
Steve Israel saysJohn Boehner's Congress and the tea party will be remembered for shutting down government one year ago
updated 8:15 AM EDT, Thu October 2, 2014
Yep. You read the headline right, says Peter Bergen, writing on the new government that stresses national unity
updated 7:12 PM EDT, Wed October 1, 2014
Hong Kong's pro-democracy demonstrators are but the latest freedom group to be abandoned by the Obama administration, says Mike Gonzalez
updated 12:53 PM EDT, Tue September 30, 2014
Jeff Yang calls Ello a wakeup call to Facebook and Twitter, and a sign of hope for fast-rising upstarts Pinterest and Snapchat.
updated 10:23 AM EDT, Wed October 1, 2014
Paul Waldman says the Secret Service should examine its procedures to make sure there are no threats to the White House--but without losing the openness so valuable to democracy
updated 10:55 AM EDT, Wed October 1, 2014
Jesse Williams says the videotape and 911 call that resulted in police gunning down John Crawford at a Walmart reveals the fatal injustice of racial assumptions
updated 7:03 PM EDT, Tue September 30, 2014
Mel Robbins says officials should drop the P.C. pose: The beheading in Oklahoma was not workplace violence. Plenty of evidence shows Alton Nolen was an admirer of ISIS.
updated 3:11 PM EDT, Tue September 30, 2014
The Occupy Central movement has already achieved much by bringing greater attention to Hong Kong's struggle for democracy, William Piekos says..
updated 3:11 PM EDT, Tue September 30, 2014
The Occupy Central movement has already achieved much by bringing greater attention to Hong Kong's struggle for democracy, writes William Piekos.
updated 10:13 AM EDT, Tue September 30, 2014
As Prime Minister Narendra Modi visits America, Madeleine Albright says a world roiled by conflict needs these two great democracies to commit to moving their partnership forward
updated 10:04 AM EDT, Tue September 30, 2014
John Sutter: Lake Providence, Louisiana, is the parish seat of the "most unequal place in America." And until somewhat recently, the poor side of town was invisible on Google Street View.
updated 9:11 AM EDT, Mon September 29, 2014
Julian Zelizer says in the run up to the 2016 election the party faces divisions on its approach to the U.S.'s place in the world
updated 10:19 AM EDT, Mon September 29, 2014
Ruben Navarrette says Common Core supporters can't devise a new set of standards and then fail to effectively sell it.
updated 9:29 AM EDT, Tue September 30, 2014
Earlier this month, Kenyans commemorated the heinous attack on the Westgate Mall in Nairobi.
updated 2:59 PM EDT, Tue September 30, 2014
David Wheeler says Colorado students are right to protest curriculum changes that downplays civil disobedience.
updated 9:58 PM EDT, Fri September 26, 2014
Sally Kohn says when people click on hacked celebrity photos or ISIS videos, they are encouraging the bad guys.
updated 7:55 AM EDT, Fri September 26, 2014
Loren Bunche says she walked by a homeless man every day and felt bad about it -- until one day she paused to get to know him
updated 9:32 AM EDT, Tue September 30, 2014
ISIS grabs headlines on social media, but hateful speech is no match for moderate voices, says Nadia Oweidat.
updated 8:33 AM EDT, Mon September 29, 2014
A new report counts jihadists fighting globally. The verdict? The threat isn't that big, says Peter Bergen.
updated 5:37 PM EDT, Tue September 23, 2014
Ebola could become the biggest humanitarian disaster in a generation, writes former British Prime Minister Tony Blair
updated 12:58 PM EDT, Fri September 26, 2014
ISIS has shocked the world. But will releasing videos of executions backfire? Four experts give their take.
updated 10:39 AM EDT, Fri September 26, 2014
Eric Holder kicked off his stormy tenure as attorney general with a challenge to the public that set tone for six turbulent years as top law-enforcement officer.
updated 9:09 AM EDT, Fri September 26, 2014
LZ Granderson says Obama was elected as a war-ending change agent, not a leader who would leave behind for his successor new engagement in Iraq and Syria. Is he as disappointed as the rest of us?
updated 5:10 AM EDT, Wed September 24, 2014
Gayle Lemmon says the question now is how to translate all the high-profile feminizing into real gains for women
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT