Radiation from early universe found key to answer major questions in physics

May 13, 2014
Radiation from early universe found key to answer major questions in physics
The UC San Diego astrophysicists employed the HuanTran Telescope in Chile to measure the polarization of the cosmic microwave background. Credit: POLARBEAR

(Phys.org) —Astrophysicists at UC San Diego have measured the minute gravitational distortions in polarized radiation from the early universe and discovered that these ancient microwaves can provide an important cosmological test of Einstein's theory of general relativity. These measurements have the potential to narrow down the estimates for the mass of ghostly subatomic particles known as neutrinos.

The radiation could even provide physicists with clues to another outstanding problem about our universe: how the invisible "dark matter" and "," which has been undetectable through modern telescopes, may be distributed throughout the universe.

The scientists are publishing details of their achievement in the June issue of the journal Physical Review Letters, the most prestigious journal in physics, which highlighted their paper as an "editor's suggestion" because of its importance and significance to the discipline.

The UC San Diego scientists measured variations in the of microwaves emanating from the Cosmic Microwave Background—or CMB—of the . Like polarized light (which vibrates in one direction and is produced by the scattering of visible light off the surface of the ocean, for example), the polarized "B-mode" microwaves the scientists discovered were produced when CMB radiation from the early universe scattered off electrons 380,000 years after the Big Bang, when the cosmos cooled enough to allow protons and electrons to combine into atoms.

Astronomers had hoped the unique B-mode polarization signature from the early cosmos would allow them to effective "see" portions of the universe that are invisible to optical telescopes as gravity from denser portions of the universe tug on the polarized light, slightly deflecting its passage through the cosmos during its 13.8 billion year trip to Earth. Through a process called "weak gravitational lensing," the distortions in the B-mode polarization pattern, they hoped, would allow astronomers to map regions of the universe filled with invisible "dark matter" and "dark energy" and well as provide a test for general relativity on cosmological scales.

The recent discovery confirms both hunches. By measuring the CMB polarization data provided by POLARBEAR, a collaboration of astronomers working on a telescope in the high-altitude desert of northern Chile designed specifically to detect "B-mode" polarization, the UC San Diego astrophysicists discovered weak gravitational lensing in their data that, they conclude, permit astronomers to make detailed maps of the structure of the universe, constrain estimates of neutrino mass and provide a firm test for general relativity.

"This is the first time we've made these kinds of measurements using CMB polarization data," said Chang Feng, the lead author of the paper and a physics graduate student at UC San Diego who conducted his study with Brian Keating, an associate professor of physics at the university and a co-leader of the POLARBEAR experiment. "This was the first direct measurement of CMB polarization lensing. And the amazing thing is that the amount of lensing that we found through these calculations is consistent with what Einstein's general relativity theory predicted. So we now have a way to verify general relativity on cosmological scales."

The POLARBEAR experiment examined a small (30 degree square) region of the sky to produce high resolution maps of B-mode polarization, which enabled the team to determine that the amplitude of gravitational fluctuations they measured was consistent with the leading theoretical model of the universe, known as the Lambda Cold Dark Matter cosmological model. Another team Keating's group collaborates with, based at the Harvard-Smithsonian Center for Astrophysics, called BICEP2, used a telescope at the South Pole to examine B-mode polarization across wide swaths of the sky. In March, it announced it had found evidence for a brief and very rapid expansion of the early universe, called inflation.

One of the most important questions in physics that can be addressed from these data is the mass of the weakly interacting neutrino, which was thought to have no mass, but current limits indicate that neutrinos have masses below 1.5 electron volts. Feng said the B-mode polarization data in his study, while consistent with the predictions of , are not statistically significant enough yet to make any firm claims about neutrino masses. But over the next year, he and Keating hope to analyze enough data from POLARBEAR, and its successor instrument—the Simons Array— to provide more certainty about the masses of neutrinos.

"This study is a first step toward using polarization lensing as a probe to measure the mass of neutrinos, using the whole universe as a laboratory," Feng said.

"Eventually we will be able to put enough neutrinos on a 'scale' to weigh them—precisely measuring their mass," Keating says. "Using the tools Chang has developed, it's only a matter of time before we can weigh the neutrino, the only fundamental elementary particle whose mass is unknown. That would be an astounding achievement for astronomy, cosmology and physics itself."

Explore further: Researchers detect B-mode polarization in cosmic microwave background

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5 / 5 (1) May 14, 2014
A question to people educated in physics: Since the article suggests that the mass of neutrinoes isn't well known, could neutrinoes actually be the mysterious "dark matter"?
5 / 5 (3) May 14, 2014
The mass of neutrino isn't known yet, but it's upper limit is already determined better - so "we" can say rather safely, that the neutrinos itself aren't sufficient for explanation of all dark matter mass (up to 5% of dark matter mass can be formed with neutrinos, but no more). In addition, the dark matter has a more complex behavior (we're distinguishing so-called the "cold", "warm" and "hot" dark matter), than the neutrinos alone could explain.
5 / 5 (1) May 14, 2014
Thanks for the info. I just googled about the subject and found a Wikipedia article of a hypothetical particle named "sterile neutrino", which might account for part of the dark matter. What I'm wondering is that is the sterile neutrino included in the 5% estimation you mentioned or is that reserved for the neutrino types whose existence is confirmed?
5 / 5 (2) May 14, 2014
The sterile neutrino is supposed to be a part of normal neutrino oscillations and quite rare in addition. So that the sterile neutrino will definitely form very rare component of dark matter. But there were many other particles proposed, which do behave in similar way, like the sterile neutrino and they could be a much more frequent (but similarly difficult to find in detectors).

For to give an illustrative analogy of all of it, you can imagine the space-time like the water surface and then the dark matter will be formed with all possible turbulence at the water surface. The neutrinos will be Falaco solitons (i.e. well developed underwater vortices with helicity) and the sterile neutrino will be Falaco solitons without helicity.
not rated yet May 19, 2014
Gravity does not "tug on light". Electromagnetic waves pass through one another without distortion or degradation. If there is an effect on light, it would have to be a reflection or diffraction due to a change in the medium.
Whydening Gyre
not rated yet May 19, 2014
Gravity does not "tug on light". Electromagnetic waves pass through one another without distortion or degradation. If there is an effect on light, it would have to be a reflection or diffraction due to a change in the medium.

Another article here mentions a "matter from light interaction" scenario. Perhaps regions with sufficient gravitational "charge" form a cavity of sorts and creates a sort of medium from all the light crashing around inside it, starting with virtual particles and cascading down into solid matter...
Or not.
not rated yet May 19, 2014
make detailed maps of the structure of the universe, constrain estimates of neutrino mass and provide a firm test for general relativity.

Sounds like a triple whammy right there.

light, it would have to be a reflection or diffraction due to a change in the medium.

Diffraction would be different for different frequencies. The observed bending does not.
The 'tugging on light' is only a metaphor as there is no force involved (light moves along a geodesic - which is always a straight line from its point of view). It is only from an 'outside' perspective that the path looks bent.

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