Google+

Astrophysicists Interrogate One Of Their Most Successful Theories

Ask any astronomer what inflation is, and you’ll hear about the moment when the universe’s primordial fireball expanded like a balloon on steroids, smoothing and flattening its initial wrinkles before it grew into the cosmos seen today.

Now, some physicists are trying to let a little air out of that scenario.

Generally regarded as one of the most successful theories about the early universe, inflationary cosmology is not exactly under attack. But a few scientists are questioning whether it deserves its reputation as completely untouchable. Inflation may be the best-developed explanation for many features seen in the modern universe, these researchers say, but it still has problems.

“The picture doesn’t really hold together,” says Paul Steinhardt, a theoretical physicist at Princeton University. “Either inflation needs a major overhaul or we have to think about some other approach to cosmology.”

In a paper posted online at arXiv.org in April, physicist Robert Brandenberger of McGill University in Montreal argues that scientists should continue exploring alternatives to inflation rather than just taking for granted that it’s right.

One such alternative, developed over the last decade, holds that the universe may not have begun with a single Big Bang, but rather experiences cycle after cycle of contraction and expansion. Another approach posits a world with a collection of tiny vibrating strings whose movements generate cosmic features currently explained by inflation.

Within the next few years, telescopes may collect enough data to distinguish among the options. Only then, say the inflation agnostics, will the picture hold together or fall apart.

“We really don’t know what happened in the early universe,” says Jean-Luc Lehners, a cosmologist at the Max Planck Institute for Gravitational Physics in Potsdam, Germany. “We know what the result was, but we don’t know how the universe got there.”

Those on both sides of the issue are quick to point out that inflation could turn out to be right. Inflation, says Andrei Linde of Stanford University, is “the only presently existing internally consistent theory of the early universe.” Linde developed some of the first versions of inflation, and thinks those who question it are either intellectually off-course or led astray by journalists looking for a story. “It is quite possible that eventually this theory will be generalized and extended,” he says. “But so far all attempts to replace it by something better failed.”

The big balloon

access

QUICK GROWTHIn the most well-accepted picture of the early universe, a period of rapid expansion called inflation follows the Big Bang. Inflation explains many cosmic features visible to astronomers today.B. Rakouskas

In 1981 Alan Guth, now of MIT, proposed inflation and showed that it could explain two mysteries about the universe: why it is so smooth and why it is so flat.

Distant reaches of the cosmos look very much alike, even though they are too far apart to have had any contact after the universe was born in the Big Bang, 13.7 billion years ago. But if the infant universe had ballooned outward ridiculously quickly before slowing to a more leisurely expansion rate, this inflation would have smoothed out primordial disorder differentiating one region of space from another. Just a minuscule fraction of a second of inflation would have spread matter out uniformly except for tiny clumps — fluctuations in the background density — to serve as seeds around which the first protogalaxies could grow.

Such an “inflationary” period would also put the universe into the finely balanced state seen today, in which space on large scales seems very close to flat.

In 1992, the Cosmic Background Explorer satellite, or COBE, confirmed a key part of Guth’s idea by measuring slight fluctuations in the leftover heat from the Big Bang. Later data from the Wilkinson Microwave Anisotropy Probe (WMAP for short) brought those cosmic fluctuations into even greater focus. Astronomers began talking about the arrival of an era of precision cosmology, in which detailed observations produced hard numbers that supported inflation.

But others aren’t so sure. “We can’t count the fact that our calculations agree with current observations as a success,” says Brandenberger.

He has several problems with inflation. For starters, its math doesn’t mesh nicely with emerging notions of particle physics; inflation doesn’t play well with ideas like string theory that attempt to unify quantum mechanics with general relativity.

Another problem, he says, is that inflation requires density fluctuations in the infant universe to have wavelengths smaller than the Planck length, below which regular notions about space break down. “This is not to say that the calculations are wrong, but the calculations are extrapolations into regions where we cannot trust them,” Brandenberger says.

Other recent work attempts to deal with new problems that inflation created. One phenomenon of concern is eternal inflation — inflation that never stops.

Guth’s original concept called for inflation to end after a fraction of a second. But Steinhardt and others soon discovered that inflation would continue forever in a few rare spots, spawning rogue areas that went on ballooning. “That now turns the story inside out,” Steinhardt says. “Instead of most of the universe being like us, most of the universe is inflating.”

With eternal inflation, an infinite number of “pocket” universes can pop into existence. And in a universe where anything that can happen will happen an infinite number of times, it becomes impossible to determine what events are more or less likely.

Guth himself has wrestled with that last point, known as the “measure problem.” In a paper posted at arXiv.org last year, he and Stanford’s Vitaly Vanchurin describe efforts to define probabilities of events in an eternally inflating universe.

Not understanding eternal inflation doesn’t mean inflation is wrong, though. “Many cosmologists, including me, believe that eternal inflation is the almost unavoidable consequence of our best understanding of the fundamental laws of physics,” says Guth — meaning even alternative theories would have to cope with eternal inflation somehow.

Other pasts

Of alternative ideas, the one with the most traction comes from scientists including Steinhardt and Neil Turok, now of Canada’s Perimeter Institute. It involves cycles of contraction and expansion (SN: 9/22/01, p. 184).

In this “cyclic scenario,” the Big Bang isn’t the beginning of space and time, but simply a transition from an earlier period in which the universe was contracting. It gets around the eternal inflation problem by smoothing out matter clumps during contraction. Any rogue areas are thus shrinking and don’t become a problem.

Only after a period of contraction does the universe reverse itself and expand outward, so that astronomers today see distant galaxies rushing away at an accelerating rate. Yet this universe has its own problems, most notably that researchers can’t properly describe the change from contraction to expansion.

Other alternatives to inflation include the “matter bounce” — which also relies on a switch from a contracting to an expanding universe, but using different mathematics. Brandenberger’s favorite, “string gas cosmology,” calls for a gas of tiny vibrating strings in the early universe, rather than a gas of particles, and thus meshes with string theory, he says.

Still, most scientists say inflation remains a much stronger candidate than any of the other proposals. “All these alternative models are not justified either by observations or theoretically,” says Viatcheslav Mukhanov of Ludwig Maximilians University Munich.

Ongoing experiments should reveal whether inflation will triumph in the end. Several efforts are now looking for a sign of inflation called gravitational waves. These disturbances ripple through spacetime from violent cosmic events like colliding black holes — or the Big Bang. Other clues may come from the European Space Agency’s Planck satellite, launched in 2009 to build on the success of COBE and WMAP (SN: 4/11/09, p. 16). Planck is hunting for another subtle imprint on the cosmic microwave background, with initial results expected next spring.

One final approach may be to bundle the alternatives to inflation together. Lehners, for instance, has been working to combine eternal inflation with the cyclic universe. Each pocket universe created by eternal inflation, he says, could replay the cyclic scenario over and over again, in a sort of best of both worlds.

In the end, physicists will undoubtedly keep exploring both inflation and its alternatives, and the final solution may lie somewhere in between. “It’s really harmful,” says Lehners, “to assume that we know what the answer is going to be.”

Source: Science News/ Alexandra Witze / Photo: Credit: J.-L. Lehners, adapted by B. Rakouskas

Entertainment

Abductee Seeks to Escape Kidnappers in Mindbending Sci-fi Thriller

  Rupture Film Review by Kam Williams Abductee Seeks to Escape Kidnappers in Mindbending Sci-fi Thriller Renee (Noomi Rapace) was leading an unremarkable existence in suburban Kansas City the day she was abducted by five strangers after her car broke down. Until then, she was just an average divorcee' doing her best to shield a young son (Percy Hynes White) from an embittered ex-husband's (Paul Popowich) vicious barbs.   Otherwise, … [Read More its Good for You.....]

Books

Cop under Fire

  Cop under Fire Moving Beyond Hashtags of Race, Crime and Politics for a Better America by Sheriff David Clarke, Jr. with Nancy French Foreword by Sean Hannity Worthy Publishing Hardcover, $21.99 272 pages ISBN: 978-1-617-95857-1 Book Review by Kam Williams “David Clarke refuses to bow a knee to political correctness, and he refuses to give his party over to the hands of black activists whose politics would destroy America. … [Read More its Good for You...]

Art

The Day After the Day Of

  The Day After the Day Of by Paul Ilechko   The sky sheds its tears. This morning is the morning of the day after. The day of mourning, the day after the day of.  I beseech the sky to shed tears in order to wash away the tears on my face.   This is the first day of the time after. This is the beginning of a new time, the days of pain, the days of sorrow. We are in mourning. The sky looks down and sheds its tears for … [Read More its Good For You...]

Real Estate

History Being Sold to the Highest Bidder

  History Being Sold to the Highest Bidder by Amy Lignor   For the longest time, scientists and archaeologists have been confused and bemused by various discoveries they’ve unearthed that offer little or no explanation as to the who, what, and why of the people who created these things or left them behind. Even now, in 2017, there are discoveries being studied; stories that were once legends now have actual bits of proof being found that … [Read More its Good for You.....]

Lifestyle

Make Way for Dulé!

  Dulé Hill The “Sleight” Interview with Kam Williams Make Way for Dulé! Born in Orange, New Jersey and raised in Sayreville, Dulé Hill began attending dance school when he was 3 years- old. He later received his first break as the understudy to Savion Glover on Broadway in “The Tap Dance Kid.” Dulé went on to perform the lead role in the musical’s national tour. And his additional stage credits include “Bring in ‘Da Noise, Bring in … [Read More its Good for You...]

Outdoors

Cajun Baby chooses Skeeter for a reason

  Cajun Baby chooses Skeeter for a reason By Craig Lamb Cliff Crochet, known on the pro bass tour as the Cajun Baby, has a lot to be proud of besides his south Louisiana roots. In Cajun country, boats are part of life, either for a livelihood or connection to the outdoors for recreation with friends and family. Crochet quote about Cajun roots. Crochet's resume includes 9 Top 10 finishes, three appearances in the Bassmaster Classic, and a … [Read More its Good for You...]

Sports

“Sin City” Becomes Acceptable?

  “Sin City” Becomes Acceptable? by Amy Lignor   So…what changes will occur if an NFL team hits Las Vegas? Not many, actually. Perhaps more of the ‘contract money’ will be lost considering the blackjack tables ARE right in the vicinity; however, NFL owners seem just fine with the fact that the Raiders will once again wave good-bye to their “Nation” and relocate to Sin City. But when you look at the news headlines, the NFL has and … [Read More its Good for You...]

Business

Buying & Selling: Learning the Art of the Tag Sale

  Buying & Selling: Learning the Art of the Tag Sale by Amy Lignor   When people speak about making a few extra bucks, there is more than one way to skin a cat these days. Perhaps you’re trying to save up for a vacation for the family to take this summer. Perhaps you are looking for collectibles to invest in. Oddly enough, many people do not realize what, exactly, was in Great Grandma’s house when she passed on to a happier place. … [Read More its Good for You...]

Travel

Vacations…Underground

  Vacations…Underground by Amy Lignor   There are millions of spots to visit and sites to see around the world when it comes to vacation time; however, there are also those you can’t necessarily “see.” In this world of digital technology and highly imaginative architecture that creates buildings that are higher and more “glitzy” than ever before, it is important to remember that in ancient times, people were building “down.” Various … [Read More its Good for You...]

Green Living

Creating the Perfect Vegetable Garden

  Creating the Perfect Vegetable Garden by Amy Lignor   Many are still dealing with that wintery mix Mother Nature just loves to toss down from the sky this time of year. Yet, that gardener living inside the soul – the one just dreaming of the sunny skies and lazy rainy days that are must-haves in order to grow the best vegetables possible – is already jotting down the facts, tricks and tips they need to know in order to make that … [Read More its Good for You...]