Dark Energy's Fingerprint Found in Distant Galaxies

Scientists don't know much about the mysterious phenomenon known as dark energy, but they do have a picture of what it's doing to the universe, namely, driving it apart.

In what may be the clearest detection of dark energy to date, astronomers at the University of Hawaii looked at microwaves left over from the beginning of the universe some 13.7 billion years ago. The scientists grouped the rays depending on whether they had passed through massive clusters of galaxies or bee-lined to Earthly detectors through areas largely lacking galactic real estate.

The premise was that these "background" microwaves would pick up a little energy as they entered the clusters, urged on by the forces of gravity. But if gravity had a monopoly on the game, the rays would lose that snap as they pressed through the other side, rendering the energy gain a transitory phenomenon.

So how to explain that the microwaves passing through super-sized galaxy clusters got to keep a bit of unearned gain?

István Szapudi and colleagues believe it is because dark energy, which sometimes is referred to as anti-gravity or vacuum energy, had spread out the galaxy clusters, as it is doing to all space. By the time the microwaves exited, there was proportionally a bit less mass to deal with, leaving the rays with a slight energy advantage.

"It's kind of like if you have a car on a hill," explained Gary Hinshaw of NASA's Goddard Space Flight Center in Greenbelt, Md. "You pick up energy as you're going down, but you give it all back up again when you go up.

"What is happening here," he added, "is that the acceleration of the universe is forcing the gravity wells to be less strong...so over the time it takes for energy to cross the cluster, the strength of the cluster has diminished."

The measurements are difficult to make because tiny variations in the Big Bang remnant waves are larger than the observable effects of intervening galaxy clusters and voids. But by grouping together data from background radiation maps of the 50 largest galaxy clusters and the 50 largest voids, researchers were able to come up with a finding they say has only a one in 200,000 chance of being a statistical fluke.

The data was taken from Sloan Digital Sky Survey, which has mapped the distribution of galaxies in about 25 percent of the sky.

Previous dark energy studies have a one in 20 chance of being statistically coincidental, Szapudi said.

Dark energy was discovered about 10 years ago and is considered the leading outstanding puzzle in cosmology today.

"In the last six or seven billion years, the expansion of the universe has switched over from slowing down to speeding up, meaning that dark energy is becoming more dominant in controlling the growth of the universe," Hinshaw said. "As the universe expands, matter gets more and more dilute and dark energy gets more and more dominate."

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NASA shoots down Mars rumors: we're not sure what we've got

Over the weekend, rumors started rebounding around the Internet: initial work from the Mars Phoenix lander had found something that was evidence relevant to the possibility of life on Mars, and the President had been briefed. Before the jokes regarding the President and intelligent life had subsided, other rumors suggested that NASA had found a toxin that was incompatible with life. NASA decided to end the speculation, and dragged members of the Phoenix team into an early-afternoon press conference. Phoenix may have found an abundance of a specific chemical on Mars, but the researchers involved aren't even sure what it is yet.

NASA spokesman Duane Brown introduced the press conference by referencing what he called the "speculation and rumors," and described it as an attempt to set the record straight. The scientists, he said, were doing so reluctantly, as they are being forced to present the results before their instruments were even producing an unambiguous result, much less one that had passed peer review. Mike Meyer, the head of NASA's Mars efforts, said, "we're here today to announce a nonannouncement—more experiments and time are needed to resolve the results of the science experiments."

The project lead, Peter Smith, seemed a bit more accepting. Describing it as a "break with scientific tradition," he nevertheless said that it was a great opportunity that he likened to "opening a window to allow the public to see the scientific process in action." Although that process is still dealing with multiple, potentially contradictory, indications, the strongest one they have is that there are significant amounts of perchlorate on Mars.

Perchlorate's chemical formula is ClO₄^-, and is found naturally on earth, typically as part of a salt with a positive ion. It was once thought to be such a strong oxidizing agent that it was considered incompatible with organic compounds, leading to some of the rumors that circulated about findings of a chemical that could kill. Since then, however, it has not only been found in deposits with organic compounds, but microbes have been discovered that actually use it as the primary oxidizing agent in their metabolism.

The problem is that two instruments on the lander are providing somewhat contradictory results. Michael Hecht spoke about the MECA instrument, which runs wet chemistry experiments. The instrument contains a number of sensors that are tuned to pick up the presence of different classes of ions released as the sample heats up. The instrument that picks up perchlorate and (to a lesser extent, nitrates) registered a huge spike—so large, the scientists didn't trust it. Since then, however, a second sample and a test with an earth-bound version of MECA produced the same spike, so the MECA folks are feeling confident.

The Rosy Red sample on its way to MECA
NASA/JPL-Caltech/University of Arizona/Max Planck Institute

The people behind the TEGA instrument, represented by William Boynton, are less sure. TEGA probes the composition of gases released when samples are heated using a mass spectrometer, and it has seen large amounts of oxygen (consistent with perchlorate), but no chlorine. Only a number of perchlorate salts will decompose in a way that releases chlorine, so that's not a complete shock, but the team is now trying to figure out ways to detect some of the others.

Assuming the finding's right, what's it all mean? It's really hard to say. Different perchlorate salts can have very different properties, so nailing down precisely what's present in the soil will be critical. Once that's done, data from elsewhere on the planet can be reevaluated to determine whether its presence might be widespread. Given that some organisms use it as part of their basic biochemistry, it's clearly not incompatible with life, but it doesn't seem to make life—past or present—any more likely on Mars.

The researchers note that, because of its strong oxidizing properties, perchlorate was actually used in the propulsion system of one stage of the Delta rocket that got Phoenix to Mars in the first place. But dry runs with the instruments showed that they weren't contaminated, and the shovel has spent a month scraping itself clean on various soil samples, so any contamination there should have declined significantly. Amusingly, the scientists have been giving each soil sample brought on board a nickname, so the press conference was peppered with references to "wicked witch," "baby bear," "rosy red," and "sorceress."

So, as mentioned right at the start, this was a bit of a nonannouncement. We've got a strong indication that perchlorate is probably present, but we're not even positive yet, much less precisely the form it's in. About the clearest thing that can be said about the results came from Michael Hecht, who said, "they can potentially keep a lot of graduate students busy for a very long time."

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Rochester Physicist's Quantum-"Uncollapse" Hypothesis Verified

In 2006, Andrew Jordan, professor of physics and astronomy at the University of Rochester, together with Alexander Korotkov at the University of California, Riverside, spelled out how to exploit a quantum quirk to accomplish a feat long thought impossible, and this week a research team at the University of California at Santa Barbara has tested the theory, proving it correct.

Quantum particles behave in ways that from our everyday experience seem utterly impossible. For instance, quantum particles have wave-like properties and can exist in many places at once. Why the objects we see around us every day—in what physicists call the "classical" world—don't behave this way despite being made of these very same strange quantum particles is a deep question in modern physics.

Most scientists have believed that the instant a quantum object was measured it would "collapse" from being in all the locations it could be, to just one location like a classical object. Jordan proposed that it would be possible to weakly measure the particle continuously, partially collapsing the quantum state, and then "unmeasure" it, causing the particle to revert back to its original quantum form, before it collapsed.

Jordan's hypothesis suggests that the line between the quantum and classical worlds is not as sharply defined as had been long thought, but that it is rather a gray area that takes time to cross.

In the latest issue of Nature News, Postdoctoral Fellow Nadav Katz explains how his team put the idea to the test and found that, indeed, he is able to take a "weak" measurement of a quantum particle, which triggered a partial collapse. Katz then "undid the damage we'd done," altering certain properties of the particle and performing the same weak measurement again. The particle was returned to its original quantum state just as if no measurement had ever been taken.

Because theorists had believed since 1926 that a measurement of a quantum particle inevitably forced a collapse, it was said that in a way, measurements created reality as we understand it. Katz, however, says being able to reverse the collapse "tells us that we really can't assume that measurements create reality because it is possible to erase the effects of a measurement and start again."

Jordan is currently continuing to probe the differences between the quantum and everyday world. He's focusing on nanophysics, which addresses fundamental physical problems that occur on the mesoscopic level.

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