Cosmologists Search for Gravity Waves to Prove Inflation Theory

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During the next decade, cosmologists will attempt to observe the first moments of the Universe, hoping to prove a popular theory. They’ll be searching for extremely weak gravity waves to measure primordial light, looking for convincing evidence for the Cosmic Inflation Theory, which proposes that a random, microscopic density fluctuation in the fabric of space and time gave birth to the Universe in a hot big bang approximately 13.7 billion years ago. A new instrument called a polarimeter is being attached to the South Pole Telescope (SPT), which operates at submillimeter wavelengths, between microwaves and the infrared on the electromagnetic spectrum. Einstein’s theory of general relativity predicts that Cosmic Inflation should produce the weak gravity waves.

Inflation Theory proposes a period of extremely rapid and exponential expansion of the Universe during its first few moments prior to the more gradual Big Bang expansion, during which time the energy density of the universe was dominated by a cosmological constant-type of vacuum energy that later decayed to produce the matter and radiation that fill the Universe today.

In 1979, physicist Alan Guth proposed the Cosmic Inflation Theory, which also predicts the existence of an infinite number of universes. Unfortunately, cosmologists have no way of testing that particular prediction.

“Since these are separate universes, by definition that means we can never have any contact with them. Nothing that happens there has any impact on us,” said Scott Dodelson, a scientist at Fermi National Accelerator Laboratory and a Professor in Astronomy & Astrophysics at the University of Chicago.

But there is a way to probe the validity of cosmic inflation. The phenomenon would have produced two classes of perturbations. The first, fluctuations in the density of subatomic particles happen continuously throughout the universe, and scientists have already observed them.

“Usually they’re just taking place on the atomic scale. We never even notice them,” Dodelson said. But inflation would instantaneously stretch these perturbations into cosmic proportions. “That picture actually works. We can calculate what those perturbations should look like, and it turns out they are exactly right to produce the galaxies we see in the universe.”

The second class of perturbations would be gravity waves—Einsteinian distortions in space and time. Gravity waves also would get promoted to cosmic proportions, perhaps even strong enough for cosmologists to detect them with sensitive telescopes tuned to the proper frequency of electromagnetic radiation.

If the new polarimeter is sensitive enough, scientists should be able to detect the waves.

“If you detect gravity waves, it tells you a whole lot about inflation for our universe,” said John Carlstrom from the University of Chicago, who developed the new instrument. Carlstrom said detecting the waves would rule out various competing ideas for the origin of the universe. “There are fewer than there used to be, but they don’t predict that you have such an extreme, hot big bang, this quantum fluctuation, to start with,” he said. Nor would they produce gravity waves at detectable levels.

A simulation at this link portrays the distortions in space and time at the subatomic scale, the result of quantum fluctuations occurring continuously throughout the universe. Near the end of the simulation, cosmic inflation begins to stretch space-time to the cosmic proportions of the universe.

Cosmologists also use the SPT in their quest to solve the mystery of dark energy. A repulsive force, dark energy pushes the universe apart and overwhelms gravity, the attractive force exerted by all matter.
Dark energy is invisible, but astronomers are able to see its influence on clusters of galaxies that formed within the last few billion years.

The SPT detects the cosmic microwave background (CMB) radiation, the afterglow of the big bang. Cosmologists have mined a fortune of data from the CMB, which represent the forceful drums and horns of the cosmic symphony. But now the scientific community has its ears cocked for the tones of a subtler instrument—gravitational waves—that underlay the CMB.

“We have these key components to our picture of the universe, but we really don’t know what physics produces any of them,” said Dodelson of inflation, dark energy and the equally mysterious dark matter. “The goal of the next decade is to identify the physics.”

Source: University of Chicago