Tag Archives: inflaton

The Inflaton and the Multiverse

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Last week’s announcement that cosmologists had found signals of gravitational waves from the primordial cosmic microwave background of the Big Bang made many headlines, even on cable news. If verified by separate experiments this will be ground-breaking news indeed — much like the discovery of the Higgs Boson in 2012. Should the result stand, this may well pave the way for new physics and greater support for the multiverse theory of the universe. So, in addition to the notion that we may not be alone in the vast cosmos, we’ll now have to consider not being alone in a cosmos made up of multiple universes — our universe may not be alone either!

From the New Scientist:

Wave hello to the multiverse? Ripples in the very fabric of the cosmos, unveiled this week, are allowing us to peer further back in time than anyone thought possible, showing us what was happening in the first slivers of a second after the big bang.

The discovery of these primordial waves could solidify the idea that our young universe went through a rapid growth spurt called inflation. And that theory is linked to the idea that the universe is constantly giving birth to smaller “pocket” universes within an ever-expanding multiverse.

The waves in question are called gravitational waves, and they appear in Einstein’s highly successful theory of general relativity (see “A surfer’s guide to gravitational waves”). On 17 March, scientists working with the BICEP2 telescope in Antarctica announced the first indirect detection of primordial gravitational waves. This version of the ripples was predicted to be visible in maps of the cosmic microwave background (CMB), the earliest light emitted in the universe, roughly 380,000 years after the big bang.

Repulsive gravity

The BICEP2 team had spent three years analysing CMB data, looking for a distinctive curling pattern called B-mode polarisation. These swirls indicate that the light of the CMB has been twisted, or polarised, into specific curling alignments. In two papers published online on the BICEP project website, the team said they have high confidence the B-mode pattern is there, and that they can rule out alternative explanations such as dust in our own galaxy, distortions caused by the gravity of other galaxies and errors introduced by the telescope itself. That suggests the swirls could have been left only by the very first gravitational waves being stretched out by inflation.

“If confirmed, this result would constitute the most important breakthrough in cosmology over the past 15 years. It will open a new window into the beginning of our universe and have fundamental implications for extensions of the standard model of physics,” says Avi Loeb at Harvard University. “If it is real, the signal will likely lead to a Nobel prize.”

And for some theorists, simply proving that inflation happened at all would be a sign of the multiverse.

“If inflation is there, the multiverse is there,” said Andrei Linde of Stanford University in California, who is not on the BICEP2 team and is one of the originators of inflationary theory. “Each observation that brings better credence to inflation brings us closer to establishing that the multiverse is real.” (Watch video of Linde being surprised with the news that primordial gravitational waves have been detected.)

The simplest models of inflation, which the BICEP2 results seem to support, require a particle called an inflaton to push space-time apart at high speed.

“Inflation depends on a kind of material that turns gravity on its head and causes it to be repulsive,” says Alan Guth at the Massachusetts Institute of Technology, another author of inflationary theory. Theory says the inflaton particle decays over time like a radioactive element, so for inflation to work, these hypothetical particles would need to last longer than the period of inflation itself. Afterwards, inflatons would continue to drive inflation in whatever pockets of the universe they inhabit, repeatedly blowing new universes into existence that then rapidly inflate before settling down. This “eternal inflation” produces infinite pocket universes to create a multiverse.

Quantum harmony

For now, physicists don’t know how they might observe the multiverse and confirm that it exists. “But when the idea of inflation was proposed 30 years ago, it was a figment of theoretical imagination,” says Marc Kamionkowski at Johns Hopkins University in Baltimore, Maryland. “What I’m hoping is that with these results, other theorists out there will start to think deeply about the multiverse, so that 20 years from now we can have a press conference saying we’ve found evidence of it.”

In the meantime, studying the properties of the swirls in the CMB might reveal details of what the cosmos was like just after its birth. The power and frequency of the waves seen by BICEP2 show that they were rippling through a particle soup with an energy of about 1016 gigaelectronvolts, or 10 trillion times the peak energy expected at the Large Hadron Collider. At such high energies, physicists expect that three of the four fundamental forces in physics – the strong, weak and electromagnetic forces – would be merged into one.

The detection is also the first whiff of quantum gravity, one of the thorniest puzzles in modern physics. Right now, theories of quantum mechanics can explain the behaviour of elementary particles and those three fundamental forces, but the equations fall apart when the fourth force, gravity, is added to the mix. Seeing gravitational waves in the CMB means that gravity is probably linked to a particle called the graviton, which in turn is governed by quantum mechanics. Finding these primordial waves won’t tell us how quantum mechanics and gravity are unified, says Kamionkowski. “But it does tell us that gravity obeys quantum laws.”

“For the first time, we’re directly testing an aspect of quantum gravity,” says Frank Wilczek at MIT. “We’re seeing gravitons imprinted on the sky.”

Waiting for Planck

Given the huge potential of these results, scientists will be eagerly anticipating polarisation maps from projects such as the POLARBEAR experiment in Chile or the South Pole Telescope. The next full-sky CMB maps from the Planck space telescope are also expected to include polarisation data. Seeing a similar signal from one or more of these experiments would shore up the BICEP2 findings and make a firm case for inflation and boost hints of the multiverse and quantum gravity.

One possible wrinkle is that previous temperature maps of the CMB suggested that the signal from primordial gravitational waves should be much weaker that what BICEP2 is seeing. Those results set theorists bickering about whether inflation really happened and whether it could create a multiverse. Several physicists suggested that we scrap the idea entirely for a new model of cosmic birth.

Taken alone, the BICEP2 results give a strong-enough signal to clinch inflation and put the multiverse back in the game. But the tension with previous maps is worrying, says Paul Steinhardt at Princeton University, who helped to develop the original theory of inflation but has since grown sceptical of it.

“If you look at the best-fit models with the new data added, they’re bizarre,” Steinhardt says. “If it remains like that, it requires adding extra fields, extra parameters, and you get really rather ugly-looking models.”

Forthcoming data from Planck should help resolve the issue, and we may not have long to wait. Olivier Doré at the California Institute of Technology is a member of the Planck collaboration. He says that the BICEP2 results are strong and that his group should soon be adding their data to the inflation debate: “Planck in particular will have something to say about it as soon as we publish our polarisation result in October 2014.”

Read the entire article here.

Image: Multiverse illustration. Courtesy of National Geographic.

CDM: Cosmic Discovery Machine

We think CDM sounds much more fun than LHC, a rather dry acronym for Large Hadron Collider.

Researchers at the LHC are set to announce the latest findings in early July from the record-breaking particle smasher buried below the French and Swiss borders. Rumors point towards the discovery of the so-called Higgs boson, the particle theorized to give mass to all the other fundamental building blocks of matter. So, while this would be another exciting discovery from CERN and yet another confirmation of the fundamental and elegant Standard Model of particle physics, perhaps there is yet more to uncover, such as the exotically named “inflaton”.

[div class=attrib]From Scientific American:[end-div]

Within a sliver of a second after it was born, our universe expanded staggeringly in size, by a factor of at least 10^26. That’s what most cosmologists maintain, although it remains a mystery as to what might have begun and ended this wild expansion. Now scientists are increasingly wondering if the most powerful particle collider in history, the Large Hadron Collider (LHC) in Europe, could shed light on this mysterious growth, called inflation, by catching a glimpse of the particle behind it. It could be that the main target of the collider’s current experiments, the Higgs boson, which is thought to endow all matter with mass, could also be this inflationary agent.

During inflation, spacetime is thought to have swelled in volume at an accelerating rate, from about a quadrillionth the size of an atom to the size of a dime. This rapid expansion would help explain why the cosmos today is as extraordinarily uniform as it is, with only very tiny variations in the distribution of matter and energy. The expansion would also help explain why the universe on a large scale appears geometrically flat, meaning that the fabric of space is not curved in a way that bends the paths of light beams and objects traveling within it.

The particle or field behind inflation, referred to as the “inflaton,” is thought to possess a very unusual property: it generates a repulsive gravitational field. To cause space to inflate as profoundly and temporarily as it did, the field’s energy throughout space must have varied in strength over time, from very high to very low, with inflation ending once the energy sunk low enough, according to theoretical physicists.

Much remains unknown about inflation, and some prominent critics of the idea wonder if it happened at all. Scientists have looked at the cosmic microwave background radiation—the afterglow of the big bang—to rule out some inflationary scenarios. “But it cannot tell us much about the nature of the inflaton itself,” says particle cosmologist Anupam Mazumdar at Lancaster University in England, such as its mass or the specific ways it might interact with other particles.

A number of research teams have suggested competing ideas about how the LHC might discover the inflaton. Skeptics think it highly unlikely that any earthly particle collider could shed light on inflation, because the uppermost energy densities one could imagine with inflation would be about 10^50 times above the LHC’s capabilities. However, because inflation varied with strength over time, scientists have argued the LHC may have at least enough energy to re-create inflation’s final stages.

It could be that the principal particle ongoing collider runs aim to detect, the Higgs boson, could also underlie inflation.

“The idea of the Higgs driving inflation can only take place if the Higgs’s mass lies within a particular interval, the kind which the LHC can see,” says theoretical physicist Mikhail Shaposhnikov at the École Polytechnique Fédérale de Lausanne in Switzerland. Indeed, evidence of the Higgs boson was reported at the LHC in December at a mass of about 125 billion electron volts, roughly the mass of 125 hydrogen atoms.

Also intriguing: the Higgs as well as the inflaton are thought to have varied with strength over time. In fact, the inventor of inflation theory, cosmologist Alan Guth at the Massachusetts Institute of Technology, originally assumed inflation was driven by the Higgs field of a conjectured grand unified theory.

[div class=attrib]Read the entire article after the jump.[end-div]

[div class=attrib]Image courtesy of Physics World.[end-div]