Landmark Discovery: New Results Provide Direct Evidence for Cosmic Inflation

The BICEP telescope located at the south pole. Image Credit: CfA / Harvard

Astronomers have announced Nobel Prize-worthy evidence of primordial gravitational waves — ripples in the fabric of spacetime — providing the first direct evidence the universe underwent a brief but stupendously accelerated expansion immediately following the big bang.

“The implications for this detection stagger the mind,” said co-leader Jamie Bock from Caltech. “We are measuring a signal that comes from the dawn of time.”

BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) scans the sky from the south pole, looking for a subtle effect in the cosmic microwave background (CMB) — the radiation released 380,000 years after the Big Bang when the universe cooled enough to allow photons to travel freely across the cosmos.

The CMB fills every cubic centimeter of the observable universe with approximately 400 microwave photons. The so-called afterglow of the big bang is nearly uniform in all directions, but small residual variations (on the level of one in 100,000) in temperature show a specific pattern. These irregularities match what would be expected if minute quantum fluctuations had ballooned to the size of the observable universe today.

So astronomers dreamed up the theory of inflation — the epoch immediately following the big bang (10-34 seconds later) when the universe expanded exponentially (by at least a factor of 1025) — causing quantum fluctuations to magnify to cosmic size. Not only does inflation help explain why the universe is so smooth on such massive scales, but also why it’s flat when there’s an infinite number of other possible curvatures.

While inflation is a pillar of big bang cosmology, it has remained purely a theoretical framework. Many astronomers don’t buy it as we can’t explain what physical mechanism would have driven such a massive expansion, let alone stop it. The results announced today provide a strong case in support of inflation.

In Depth: We’ve Discovered Inflation! Now What?

The trick is in looking at the CMB where inflation’s signature is imprinted as incredibly faint patterns of polarized light — some of the light waves have a preferred plane of vibration. If a gravitational wave passes through the fabric of spacetime it will squeeze spacetime in one direction (making it hotter) and stretch it in another (making it cooler). Inflation will then amplify these quantum fluctuations into a detectable signal: the hotter and therefore more energetic photons will be visible in the CMB, leaving a slight polarization imprint.

E-modes (left side)
E-modes (left side) look the same when reflected in a mirror. B-modes (right side) do not. Image Credit: Nathan Miller

This effect will create two distinct patterns: E-modes and B-modes, which are differentiated based on whether or not they have even or odd parity. In simpler terms: E-mode patterns will look the same when reflected in a mirror, whereas B-mode patterns will not.

E-modes have already been extensively detected and studied. While both are the result of primordial gravitational waves, E-modes can be produced through multiple mechanisms whereas B-modes can only be produced via primordial gravitational waves. Detecting the latter is a clean diagnostic — or as astronomers are putting it: “smoking gun evidence” — of inflation, which amplified gravitational waves in the early Universe.

“The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky,” said co-leader Chao-Lin Kuo from Stanford University, designer of the BICEP2 detector.

Polarization patterns imprinted in the CMB. Image Credit: CfA
Shown here are the actual B-mode polarization patterns provided by the BICEP2 Telescope. Image Credit: Harvard-Smithsonian Center for Astrophysics

The team analyzed sections of the sky spanning one to five degrees (two to 10 times the size of the full moon) for more than three years. They created a unique array of 512 detectors, which collectively operate at a frosty 0.25 Kelvin. This new technology enabled them to make detections at a speed 10 times faster than before.

The results are surprisingly robust, with a 5.9 sigma detection. For comparison, when particle physicists announced the discovery of the Higgs Boson in July, 2012 they had to reach at least a 5 sigma result, or a confidence level of 99.9999 percent.  At this level, the chance that the result is erroneous due to random statistical fluctuations is only one in a million. Those are pretty good odds.

While the team was careful to rule out any errors, it will be crucial for another team to verify these results. The Planck spacecraft, which has been producing exquisite measurements of the CMB, will be reporting its own findings later this year. At least a dozen other teams have also been searching for this signature.

“This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin?” commented Harvard theorist Avi Loeb. “These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was.”

Not only does inflation succeed in explaining the origin of cosmic structure — how the cosmic web formed from the smooth aftermath of the big bang — but it makes wilder predictions as well. The model seems to produce not just one universe, but rather an ensemble of universes, otherwise known as a multiverse. This collection of universes has no end and no beginning, continuing to pop up eternally.

Today’s results provide a stronger case for “eternal inflation,” which gives a new perspective on our desolate place within the cosmos. Not only do we live on a small planet orbiting one star out of hundreds of billions, in one galaxy out of hundreds of billions, but our entire universe may just be one bubble out of a vast cosmic ocean of others.

The detailed paper may be found here.
The full set of papers are here.
An FAQ summarizing the data is here.

Cosmology 101: The Beginning

Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.
Representation of the timeline of the universe over 13.7 billion years, and the expansion in the universe that followed. Credit: NASA/WMAP Science Team.

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Editor’s note: The article “The Universe Could be 250 Times Bigger Than What is Observable” sparked a sizable discussion among our readers, with several suggesting UT should have a series of articles about cosmology — a Cosmology 101, if you will. Our newest writer, Vanessa D’Amico, who wrote the aforementioned article, begins the Cosmology 101 series today, starting at the very beginning.

How did the universe get its start? It’s one of the most pressing questions in cosmology, and likely one that will be around for a while. Here, I’ll begin by explaining what scientists think they know about the first formative seconds of the universe’s life. More than likely, the story isn’t quite what you might think.

In the beginning, there was… well, we don’t really know. One of the most prevalent misconceptions in cosmology is that the universe began as an immensely small, inconceivably dense collection of material that suddenly exploded, giving rise to space as we know it. There are a number of problems with this idea, not least of all the assumption implicit in an event termed the big “bang.” In truth, nothing “banged.” The notion of an explosion brings to mind an expanding tide of material, gradually filling the space around it; however, when our universe was born, there was no space. There was no time either. There was no vacuum. There was literally nothing.

Then the universe was born. Extremely high energies during the first 10-43 seconds of its life make it very difficult for scientists to determine anything conclusive about the origin of the cosmos. Of course, if cosmologists are correct about what they believe may have happened next, it doesn’t much matter. According to the theory of inflation, at about 10-36 seconds, the universe underwent a period of exponential expansion. In a matter of a few thousandths of a second, space inflated by a factor of about 1078, quickly separating what were once adjoining regions by unfathomable distances and blowing up tiny quantum fluctuations in the fabric of spacetime.

Inflation is an appealing theory for a number of reasons. First of all, it explains why we observe the universe to be homogeneous and isotropic on large scales – that is, it looks the same in all directions and to all observers. It also explains why the universe visually appears to be flat, rather than curved. Without inflation, a flat universe requires an extremely fine-tuned set of initial conditions; however, inflation turns this fine-tuning into a trick of scale. A familiar analogy: the ground under our feet appears to be flat (even though we know we live on a spherical planet) because we humans are so much smaller than the Earth. Likewise, the inflated universe is so enormous compared to our local field of view that it appears to be spatially flat.

As the theory goes, the end of inflation gave way to a universe that looked slightly more like the one we observe today. The vacuum energy that drove inflation suddenly transformed into a different kind of energy – the kind that could create elementary particles. At this point (only 10-32 seconds after the birth of the universe), the ambient temperature was still far too hot to build atoms or molecules from these particles; but as the seconds wore on, space expanded and cooled to the point where quarks could come together and form protons and neutrons. High-energy photons continued to dart around, continually striking and exciting charged protons and electrons.

So what happened next? How did this chaotic soup of matter and radiation become the vast expanse of organized structure that we see today? What’s going to happen to the universe in the future? And how do we know that this is the way the story unfolded? Make sure to check out the next few installments of Cosmology 101 for the answers to these questions and more!

First Observational Evidence Other Universes?

The signatures of a bubble collision at various stages in our analysis pipeline. A collision (top left) induces a temperature modulation in the CMB temperature map (top right). The "blob" associated with the collision is identi ed by a large needlet response (bottom left), and the presence of an edge is determined by a large response from the edge detection algorithm (bottom right). (Feeny, et al.)

In the realm of far out ideas in science, the notion of a multiverse is one of the stranger ones. Astronomers and physicists have considered the possibility that our universe may be one of many. The implications of this are somewhat more fuzzy. Nothing in physics prevents the possibilities of outside universes, but neither has it helped to constrain them, leaving scientists free to talk of branes and bubbles. Many of these ideas have been considered untestable, but a paper uploaded to arXiv last month considers the effects of two universes colliding and searches for fingerprints of such a collision of our own universe. Surprisingly, the team reports that they may have detected not one, but four collisional imprints.

Continue reading “First Observational Evidence Other Universes?”

How Can Galaxies Recede Faster than the Speed of Light?

Question: How Can Galaxies Move Away Faster Than Speed of Light?

Answer: Einstein’s Theory of Relativity says that the speed of light – 300,000 km/s – is the maximum speed that anything can travel in the Universe. It requires more and more energy to approach the speed of light. You could use up all the energy in the Universe and still not be traveling at light speed.

As you know, most of the galaxies in the Universe are expanding away from us because of the Big Bang, and the subsequent effects of dark energy, which is providing an additional accelerating force on the expansion of the Universe.

Galaxies, like our own Milky Way are carried along by the expansion of the Universe, and will move apart from every other galaxy, unless they’re close enough to hold together with gravity.

As you look at galaxies further and further away, they appear to be moving faster and faster away from us. And it is possible that they could eventually appear to be moving away from us faster than light. At that point, light leaving the distant galaxy would never reach us.

When that happens, the distant galaxy would just fade away as the last of the photons reached Earth, and then we would never know it was ever there.

This sounds like it breaks Einstein’s theories, but it doesn’t. The galaxies themselves aren’t actually moving very quickly through space, it’s the space itself which is expanding away, and the galaxy is being carried along with it. As long as the galaxy doesn’t try to move quickly through space, no physical laws are broken.

One sad side effect of this expansion is that most of the galaxies will have receded over this horizon in about 3 trillion years, and future cosmologists will never know there’s a great big Universe out there.

You can read more about this in an article I did called the End of Everything.

Method to Test String Theory Proposed

Image of 10 dimensional super strings. Credit: PBS.

What is the universe made of? While general relativity does a good job providing insights into the Big Bang and the evolution of stars, galaxies and black holes, the theory doesn’t help much when it gets down to the small stuff. There are several theories about the basic, fundamental building blocks of all that exists. Some quantum physicists propose string theory as a theory of “everything,” that at the elemental heart of all matter lie tiny one-dimensional filaments called strings. Unfortunately, however, according to the theory, strings should be about a millionth of a billionth of a billionth of a billionth of a centimeter in length. Strings are way too small to see with current particle physics technology, so string theorists will have to come up with more clever methods to test the theory than just looking for the strings.

Well, one cosmologist has an idea. And it’s a really big idea.

Benjamin Wandelt, a professor of physics and astronomy at the University of Illinois says that ancient light from the beginnings of our universe was absorbed by neutral hydrogen atoms. By studying these atoms, certain predictions of string theory could be tested. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon. And it would be really gigantic: Wandelt proposes an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt said, but would be prohibitively expensive.

So for now, both string theory and this method of testing are purely hypothetical.

According to Wandelt, what this huge array would be looking for are absorption features in the 21-centimeter spectrum of neutral hydrogen atoms.

“High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation — called brane inflation– into string theory,” said Wandelt. “If we embed brane inflation into string theory, a network of cosmic strings is predicted to form. We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe.”

About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background.

Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt said.

Cosmic strings are filaments of infinite length. Wandelt compared their composition to the boundaries of ice crystals in frozen water.

When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect.

Cosmic strings are defects in space. String theory predicts that a network of strings were produced in the early universe, but this has not been detected so far. Cosmic strings produce fluctuations in the gas density through which they move, a signature of which Wandelt says will be imprinted on the 21-centimeter radiation.

Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum.

If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt said. “And that would tell us about the energy scale at which quantum gravity begins to become important.”

But questions remain about the validity of this experiment. Also, could the array somehow be “shrunk” to search only a small area of the 21-centimeter radiation? Or possibily, could an instrument similar to WMAP (Wilkinson Microwave Anisotropy Probe) be constructed to look at the entire sky for this radiation?

Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters, and the paper is not yet available for public review.

Original News Source: University of Illinois Press Release