What Was Cosmic Inflation? The Quest to Understand the Earliest Universe

Cosmic Inflation?


The Big Bang. The discovery that the Universe has been expanding for billions of years is one of the biggest revelations in the history of science. In a single moment, the entire Universe popped into existence, and has been expanding ever since.

We know this because of multiple lines of evidence: the cosmic microwave background radiation, the ratio of elements in the Universe, etc. But the most compelling one is just the simple fact that everything is expanding away from everything else. Which means, that if you run the clock backwards, the Universe was once an extremely hot dense region

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

Let’s go backwards in time, billions of years. The closer you get to the Big Bang, the closer everything was, and the hotter it was. When you reach about 380,000 years after the Big Bang, the entire Universe was so hot that all matter was ionized, with atomic nuclei and electrons buzzing around each other.

Keep going backwards, and the entire Universe was the temperature and density of a star, which fused together the primordial helium and other elements that we see to this day.

Continue to the beginning of time, and there was a point where everything was so hot that atoms themselves couldn’t hold together, breaking into their constituent protons and neutrons. Further back still and even atoms break apart into quarks. And before that, it’s just a big question mark. An infinitely dense Universe cosmologists called the singularity.

When you look out into the Universe in all directions, you see the cosmic microwave background radiation. That’s that point when the Universe cooled down so that light could travel freely through space.

And the temperature of this radiation is almost exactly the same in all directions that you look. There are tiny tiny variations, detectable only by the most sensitive instruments.

Cosmic microwave background seen by Planck. Credit: ESA

When two things are the same temperature, like a spoon in your coffee, it means that those two things have had an opportunity to interact. The coffee transferred heat to the spoon, and now their temperatures have equalized.

When we see this in opposite sides of the Universe, that means that at some point, in the ancient past, those two regions were touching. That spot where the light left 13.8 billion years ago on your left, was once directly touching that spot on your right that also emitted its light 13.8 billion years ago.

This is a great theory, but there’s a problem: The Universe never had time for those opposite regions to touch. For the Universe to have the uniform temperature we see today, it would have needed to spend enough time mixing together. But it didn’t have enough time, in fact, the Universe didn’t have any time to exchange temperature.

Imagine you dipped that spoon into the coffee and then pulled it out moments later before the heat could transfer, and yet the coffee and spoon are exactly the same temperature. What’s going on?

Alan H. Guth
Alan H. Guth. Credit: Betsy Devine (CC BY-SA 3.0)

To address this problem, the cosmologist Alan Guth proposed the idea of cosmic inflation in 1980. That moments after the Big Bang, the entire Universe expanded dramatically.

And by “moments”, I mean that the inflationary period started when the Universe was only 10^-36 seconds old, and ended when the Universe was 10^-32 seconds old.

And by “expanded dramatically”, I mean that it got 10^26 times larger. That’s a 1 followed by 26 zeroes.

Before inflation, the observable Universe was smaller than an atom. After inflation, it was about 0.88 millimeters. Today, those regions have been stretched 93 billion light-years apart.

This concept of inflation was further developed by cosmologists Andrei Linde, Paul Steinhardt, Andy Albrecht and others.

Inflation resolved some of the shortcomings of the Big Bang Theory.

The first is known as the flatness problem. The most sensitive satellites we have today measure the Universe as flat. Not like a piece-of-paper-flat, but flat in the sense that parallel lines will remain parallel forever as they travel through the Universe. Under the original Big Bang cosmology, you would expect the curvature of the Universe to grow with time.

The horizon problem in Big Bang cosmology. How is it that distant parts of the universe possess such similar physical properties? Credit: Addison Wesley.

The second is the horizon problem. And this is the problem I mentioned above, that two regions of the Universe shouldn’t have been able to see each other and interact long enough to be the same temperature.

The third is the monopole problem. According to the original Big Bang theory, there should be a vast number of heavy, stable “monopoles”, or a magnetic particle with only a single pole. Inflation diluted the number of monopoles in the Universe so don’t detect them today.

Although the cosmic microwave background radiation appears mostly even across the sky, there could still be evidence of that inflationary period baked into it.

The Big Bang and primordial gravitational waves. Credit: bicepkeck.org

In order to do this, astronomers have been focusing on searching for primordial gravitational waves. These are different from the gravitational waves generated through the collision of massive objects. Primordial gravitational waves are the echoes from that inflationary period which should be theoretically detectable through the polarization, or orientation, of light in the cosmic microwave background radiation.

A collaboration of scientists used an instrument known as the Background Imaging of Cosmic Extragalactic Polarization (or BICEP2) to search for this polarization, and in 2014, they announced that maybe, just maybe, they had detected it, proving the theory of cosmic inflation was correct.

Unfortunately, another team working with the space-based Planck telescope posted evidence that the fluctuations they saw could be fully explained by intervening dust in the Milky Way.

Planck’s view of its nine frequencies. Credit: ESA and the Planck Collaboration

The problem is that BICEP2 and Planck are designed to search for different frequencies. In order to really get to the bottom of this question, more searches need to be done, scanning a series of overlapping frequencies. And that’s in the works now.

BICEP2 and Planck and the newly developed South Pole Telescope as well as some observatories in Chile are all scanning the skies at different frequencies at the same time. Distortion from various types of foreground objects, like dust or radiation should be brighter or dimmer in the different frequencies, while the light from the cosmic microwave background radiation should remain constant throughout.

There are more telescopes, searching more wavelengths of light, searching more of the sky. We could know the answer to this question with more certainty shortly.

One of the most interesting implications of cosmic inflation, if proven, is that our Universe is actually just one in a vast multiverse. While the Universe was undergoing that dramatic expansion, it could have created bubbles of spacetime that spawned other universes, with different laws of physics.

Multiverse Theory
Artist concept of the multiverse. Credit: Florida State University

In fact, the father of inflation, Alan Guth, said, “It’s hard to build models of inflation that don’t lead to a multiverse.”

And so, if inflation does eventually get confirmed, then we’ll have a whole multiverse to search for in the cosmic microwave background radiation.

The Big Bang was one of the greatest theories in the history of science. Although it did have a few problems, cosmic inflation was developed to address them. Although there have been a few false starts, astronomers are now performing a sensitive enough search that they might find evidence of this amazing inflationary period. And then it’ll be Nobel Prizes all around.

Polar Telescope Casts New Light On Dark Energy And Neutrino Mass

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Located at the southermost point on Earth, the 280-ton, 10-meter-wide South Pole Telescope has helped astronomers unravel the nature of dark energy and zero in on the actual mass of neutrinos — elusive subatomic particles that pervade the Universe and, until very recently, were thought to be entirely without measureable mass.

The NSF-funded South Pole Telescope (SPT) is specifically designed to study the secrets of dark energy, the force that purportedly drives the incessant (and apparently still accelerating) expansion of the Universe. Its millimeter-wave observation abilities allow scientists to study the Cosmic Microwave Background (CMB) which pervades the night sky with the 14-billion-year-old echo of the Big Bang.

Overlaid upon the imprint of the CMB are the silhouettes of distant galaxy clusters — some of the most massive structures to form within the Universe. By locating these clusters and mapping their movements with the SPT, researchers can see how dark energy — and neutrinos — interact with them.

“Neutrinos are amongst the most abundant particles in the universe,” said Bradford Benson, an experimental cosmologist at the University of Chicago’s Kavli Institute for Cosmological Physics. “About one trillion neutrinos pass through us each second, though you would hardly notice them because they rarely interact with ‘normal’ matter.”

If neutrinos were particularly massive, they would have an effect on the large-scale galaxy clusters observed with the SPT. If they had no mass, there would be no effect.

The SPT collaboration team’s results, however, fall somewhere in between.

Even though only 100 of the 500 clusters identified so far have been surveyed, the team has been able to place a reasonably reliable preliminary upper limit on the mass of neutrinos — again, particles that had once been assumed to have no mass.

Previous tests have also assigned a lower limit to the mass of neutrinos, thus narrowing the anticipated mass of the subatomic particles to between 0.05 – 0.28 eV (electron volts). Once the SPT survey is completed, the team expects to have an even more confident result of the particles’ masses.

“With the full SPT data set we will be able to place extremely tight constraints on dark energy and possibly determine the mass of the neutrinos,” said Benson.

“We should be very close to the level of accuracy needed to detect the neutrino masses,” he noted later in an email to Universe Today.

The South Pole Telescope's unique position allows it to watch the night sky for months on end. (NSF)

Such precise measurements would not have been possible without the South Pole Telescope, which has the ability due to its unique location to observe a dark sky for very long periods of time. Antarctica also offers SPT a stable atmosphere, as well as very low levels of water vapor that might otherwise absorb faint millimeter-wavelength signals.

“The South Pole Telescope has proven to be a crown jewel of astrophysical research carried out by NSF in the Antarctic,” said Vladimir Papitashvili, Antarctic Astrophysics and Geospace Sciences program director at NSF’s Office of Polar Programs. “It has produced about two dozen peer-reviewed science publications since the telescope received its ‘first light’ on Feb. 17, 2007. SPT is a very focused, well-managed and amazing project.”

The team’s findings were presented by Bradford Benson at the American Physical Society meeting in Atlanta on April 1.

Read more on the NSF press release here.

Astronomers Find Giant Structures From the Early Universe

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Looking back to when our Universe was about half the age it is now, astronomers have discovered the most massive galaxy cluster yet seen at so great a distance. The researchers say that if we could see it as it appears today, it would be one of the most massive galaxy clusters in the universe. The cluster, modestly named SPT-CL J0546-5345, weighs in at around 800 trillion Suns, and holds hundreds of galaxies. “This galaxy cluster wins the heavyweight title,”said Mark Brodwin, from the Harvard-Smithsonian Center for Astrophysics. “This cluster is full of ‘old’ galaxies, meaning that it had to come together very early in the universe’s history – within the first two billion years.”


Using the new South Pole Telescope, Brodwin and his colleagues are searching for giant galaxy clusters using the Sunyaev-Zel’dovich effect – a small distortion of the cosmic microwave background, a pervasive all-sky glow left over from the Big Bang. Such distortions are created as background radiation passes through a large galaxy cluster.

They found the heavyweight cluster in some of their first observations with the new telescope.
Located in the southern constellation Pictor (the Painter), the cluster has a redshift of z=1.07, putting it at a distance of about 7 billion light-years, meaning we see it as it appeared 7 billion years ago, when the universe was half as old as now and our solar system didn’t exist yet.

Even at that young age, the cluster was almost as massive as the nearby Coma cluster. Since then, it should have grown about four times larger.

This optical image of the newfound galaxy cluster highlights how faint and reddened these galaxies are due to their great distance. Credit: CTIO Blanco 4-m telescope/J. Mohr (LMU Munich)

Galaxy clusters like this can be used to study how dark matter and dark energy influenced the growth of cosmic structures. Long ago, the universe was smaller and more compact, so gravity had a greater influence. It was easier for galaxy clusters to grow, especially in areas that already were denser than their surroundings.

“You could say that the rich get richer, and the dense get denser,” quipped Harvard astronomer Robert Kirshner, commenting on the study.

As the universe expanded at an accelerating rate due to dark energy, it grew more diffuse. Dark energy now dominates over the pull of gravity and chokes off the formation of new galaxy clusters.

The main goal of the SPT survey is to find a large sample of massive galaxy clusters in order to measure the equation of state of the dark energy, which characterizes cosmic inflation and the accelerated expansion of the universe. Additional goals include understanding the evolution of hot gas within galaxy clusters, studying the evolution of massive galaxies in clusters, and identifying distant, gravitationally lensed, rapidly star-forming galaxies.

The team expects to find many more giant galaxy clusters lurking in the distance once the South Pole Telescope survey is completed.

Follow-up observations on the cluster were done using the Infrared Array Camera on the Spitzer Space Telescope and the Magellan telescopes in Chile. A paper announcing the discovery has been published in the Astrophysical Journal.

The team’s paper is available at arXiv.

For more information on the South Pole Telescope, see this link.

Source: Harvard Smithsonian Center for Astrophysics