TALK about a cure that’s worse than the disease. A proposed quantum field can account for the universe’s ever-quickening expansion, but it would also trigger the universe’s death in a catastrophic collapse.

In 1998, astronomers discovered that the universe has been ballooning at ever-faster rates for the past few billion years. They dubbed the mysterious entity responsible “dark energy” and have been striving to identify it ever since.

The simplest explanation is that particles briefly bubbling into and out of existence imbue every cupful of space with the energy needed to accelerate the universe’s growth. But this quantum stew, known as vacuum energy, is no panacea.

Energy, like matter, causes space to curve, according to Einstein’s general theory of relativity. Calculations suggest that this vacuum energy is so strong that it would make the universe curve in on itself until it spans less than the distance from Earth to the moon – and clearly it’s bigger.

To get around this discrepancy, of the University of California, Davis, and of the University of Nottingham in the UK attempted to cancel out the curvature caused by the quantum instabilities by modifying the equations of general relativity on the largest scale possible: the whole of space-time.

Last year, they found a way to do this that , leaving just enough to explain the acceleration we observe (Physical Review Letters, ). But their method requires space-time to be finite, which implies that cosmic expansion must eventually stop and reverse, causing time to end when the universe collapses. “The universe returns back to where it banged from,” says Kaloper.

“Cosmic expansion must eventually reverse… the universe returns back to where it banged from”

Now the researchers have proposed a trigger for that collapse: a new quantum field that permeates the universe. The field’s energy would drop slowly over time, eventually becoming negative and setting off the cosmos’s contraction. Before the contraction begins, however, the field would cause the universe’s initial expansion to accelerate, just as it is doing now. “It’s as if the dark energy is the harbinger of doom,” says Padilla (, ).

“It’s an interesting approach, but it’s still incomplete,” says of the Perimeter Institute in Waterloo, Canada. “What is the underlying theory that tells you that this is how you should write down your equations?”

The researchers are now working on a generalisation of their proposal that should help address these concerns, says Kaloper. They are also calculating when the universe’s contraction may begin, though they suspect it wouldn’t start for another few tens of billions of years, says Padilla.

“We’re pretty safe,” says Arvanitaki. “I’m not going to lose any sleep over it.”

This article appeared in print under the headline “Dark energy, the harbinger of doom”

“Planck showed BICEP2’s entire signal could be due to dust. The final nail in the coffin came last week”

This article appeared in print under the headline “Big bang discovery crumbles to dust”

NASA called on aerospace engineer Owen Morris to consult on its latest spacecraft – he’s also dreaming of a space station on the far side of the moon

What inspired you to get into space travel?
I’ve been interested in things that fly since I was a kid. I got degrees in aerospace engineering, applied to NASA and stayed there for my entire career.

What did you work on at NASA?
During Apollo, when we started the lunar module project, I was the chief engineer. Later, I managed the entire Apollo spacecraft programme. In the shuttle programme, I was manager of systems integration and systems engineering.

NASA summoned you back as a consultant on their next spacecraft, Orion. Why did they call on you?
NASA has not developed a big new vehicle since the shuttle. Most of the people that worked on the shuttle are now retired, so those starting the Orion programme didn’t have the shuttle people to advise them. That’s what I’ve been trying to help a bit on.

Does it matter that NASA lacks recent experience in designing a spaceship?
With the tools they have now, the people conducting the Orion programme are much more technically capable than we were back in the Apollo and shuttle days. For example, we knew what the aerodynamics equations for Apollo were, but we could not solve them in any detail with the computers we had at the time. Now they can.

No human has left low Earth orbit for more than 40 years. Where can Orion take us?
The big capability of Orion and its rocket, the Space Launch System, will be to let us do things in deeper space again. It’s good for trips that would last three weeks or so, depending on the size of the crew or the details of the mission. You can go to a captured asteroid. To get to Mars, however, you would need a habitation module in addition to Orion, because of the duration of the trip.

If it were up to you, where would you send future astronaut missions?
It’s not in the present space programme, but I would like to establish a space station on the far side of the moon. At that location you’re shielded from a lot of radio interference originating on Earth, so it would be good for radio astronomy.

Looking back, what is your most vivid memory of your career at NASA?
The one that always comes to mind is Apollo 13. The service module exploded on the way to the moon, so the lunar module basically had to support the crew all the way to and around the moon. We had to use it to do things it had never done before. I was at NASA for about 85 hours straight. It was a very exciting time.

Would you have gone to space if they had asked you to?
Yes, but I didn’t have the chance. For me, though, the fun is in being part of the crew that is designing and developing the vehicles.

This article appeared in print under the headline “Back to making people fly”

Rebel planets that orbit their parent stars backwards may be the result of turbulent pregnancies.

In the last five years, a of exoplanets have been found orbiting their stars in the opposite direction to the stars’ spins. Astronomers have proposed various explanations for their deviance, including .

Now at the University of Vienna in Austria and colleagues say chaotic conditions in the solar systems’ gaseous wombs may be to blame.

Solar system genesis is often described as an isolated sphere of gas and dust neatly pancaking into a planet-forming disc as it rotates. But observations reveal that stars and planets are born in turbulent nurseries, where star-studded knots of matter fly through a larger gas cloud “like bees within a hive”, Vorobyov says. A star-filled knot that forms spinning in one direction can later find itself in a different spot where the surrounding gas swirls the other way.

Nature vs nurture

Vorobyov and colleagues ran simulations that show the clouds of gas collapsing into counter-rotating discs. A gap opens up at the boundary between the discs, whose opposing motions “sort of cancel each other out”, Vorobyov says. The inner disc goes on to fall onto the central star, and the outer disc can then fragment to form planets.

“Environment tends to be quite important,” Vorobyov says. “Nurture can completely change the nature of star- and planet-forming gas clouds.”

“It’s an important piece of work,” says of the University of Bonn in Germany. He previously showed that gas flowing onto a planet-forming disc from the location of a nearby star could lead to backwards planets. In many cases, a combination of effects may lead to wonky planetary orbits, he says.

Journal reference: Astronomy & Astrophysics, accepted (arxiv.org/abs/1410.1743)

The man in the moon may still have some fire in his belly. A new study argues that magma erupted onto the lunar surface less than 100 million years ago – nearly a billion years later than previously thought. If confirmed, the finding suggests that radioactive elements may be keeping the moon’s innards toasty even today.

The moon is thought to have formed from the debris of a collision between Earth and a Mars-sized body about 4.5 billion years ago. Its fiery birth kept its surface molten for a few hundred million years. But even after its crust solidified, magma regularly erupted onto the moon’s surface until about 3 billion years ago, creating vast basaltic plains known as maria. After that, the eruptions largely stopped, with the most recent volcanic features dating to about a billion years ago.

Now at Arizona State University in Tempe and colleagues say that dozens of small rocky formations spotted by NASA’s eagle-eyed were laid down by lava no more than 100 million years ago – a geological eye-blink.

The spacecraft, which has been orbiting the moon since 2009, can make out , providing the best orbital view yet of the moon’s surface. Scouring the images, Braden and her team found 70 regions that stood out from their surroundings, most of which were new to science.

Called irregular mare patches, or IMPs, the features measure less than 5 kilometres across, and are sprinkled over the moon’s near side within the larger maria. They have two-toned textures, with smooth, usually dark, rock lying over rougher, blockier rock. That may be because the first lava to emerge during an eruption formed a rough crust that was then overlaid by smoother flows, Braden says.

Fresh-faced IMPs

The IMPs appear relatively fresh-faced compared with their surroundings, suggesting they have experienced no more than 100 million years of impacts from space rocks, the team say. If so, “the moon was more active in recent history than previously thought possible”, says Braden.

“Young volcanism indicates possibly more magma, or magma at higher temperatures, or magma at shallower depths, or all of the above,” she says. The heat powering this activity may come from or the decay of radioactive elements beneath the moon’s surface.

“This paper demonstrates how much we don’t know about the moon,” says at Brown University in Providence, Rhode Island, who wasn’t involved with the work.

But he has another explanation: he believes magma lying deep within the moon produces gas that seeps up through cracks and occasionally bursts through the surface. In 2006, he suggested such bursts could explain the few IMPs known at the time. He also believes that this “degassing” has occurred even more recently than Braden’s estimate for volcanism, with a 3-kilometre-wide IMP named Ina forming no more than 10 million years ago.

Both explanations suggest that “the moon isn’t dead”, he says. “We need to visit such sites to understand what happened – or could still be happening.”

Journal reference: , DOI: 10.1038/ngeo2252

IT HAS been called a bruise on the sky – a curious cold spot in the afterglow of the big bang that has sparked wild cosmic theories attributing it to a run-in with another universe or a wrinkle in space-time.

Now it seems the answer may be a little more mundane: the biggest known hole in the universe.

The cold spot appears in maps of the cosmic microwave background (CMB), the earliest light emitted in the universe. Temperature variations in the light show up as a mottled pattern in the maps, which can be explained if quantum fluctuations at the universe’s birth were stretched out by a brief but spectacular cosmic growth spurt known as inflation.

But some features in the maps don’t fit into the leading models of inflation. For example, the relatively even pattern of the CMB is marred by an unusually large cold region. Scientists have struggled to explain it, suggesting a number of ideas that require exotic physics or even evidence for a multiverse.

A much simpler explanation is that the cold spot is caused by a giant void in the universe. The cosmos consists of a web of bright galaxies and clusters surrounded by dark pockets that contain little matter. Radiation loses energy when it crosses these empty regions, so a large void could cause a cold spot in our CMB maps. But most surveys haven’t looked at a wide enough region of the sky to be able to find such a void relatively close to Earth. One study that claimed to have discovered one in 2007 was later disputed.

at the University of Hawaii in Honolulu and his colleagues analysed an all-sky survey made by NASA’s WISE satellite to conduct their own hunt for a giant void. In May, they reported finding one about 2.8 billion light years away, in the direction of the cold spot. It stretches some 1.8 billion light years across, making it about twice the size of the previous largest known void, says Szapudi.

Now the team has studied the properties of the so-called supervoid, including its alignment with the cold spot and its apparent depth. A number of techniques all yielded similar results, which the team says bolsters the case linking the void to the cold spot ().

“This would be the simplest explanation requiring no exotic physics,” says Szapudi. He adds that similarly simple causes may lie at the heart of other CMB mysteries, such as temperature differences that seem to be aligned along a preferred direction, dubbed the “axis of evil“.

at the University of Michigan in Ann Arbor questioned the 2007 claim, but he thinks Szapudi’s team makes a good case for their void. “This is a very exciting finding,” he says.

This article appeared in print under the headline “Biggest hole in universe solves cosmic cold case”

The world’s largest particle smasher may be sleeping, but the hunt for fresh physics continues.

Hints of what may be a brand new particle have appeared in data generated by the Large Hadron Collider at CERN near Geneva, Switzerland, before it shut down for upgrades at the start of 2013.

The standard model of particle physics says that a particle called a Z boson should decay into electrons and muons – particles with the same electric charge but about 200 times as much mass. Both particles should appear at about the same rate, aside from a small, predictable disparity due to their different masses.

Particle popper

Now at the National Institute for Subatomic Physics in Amsterdam, the Netherlands, and his colleagues have looked at data produced by the and spotted that Z bosons seem to decay into electrons 25 per cent more often than muons. This suggests some unknown particle may have popped up and skewed the rate.

One possible culprit is a heavier type of Z boson, dubbed a Z’ (pronounced “Z prime”). This hypothetical particle might not be democratic in its treatment of electrons and muons, says Koppenburg. Preliminary hints of the Z’ were seen at the LHCb experiment last year, when the decay products of another particle called a B meson were .

“There could be a whole hidden sector of nature that’s hidden because of the rareness of the events,” says at the University of Victoria in British Columbia, Canada. But he cautions that signs of the imbalance could vanish with further data.

Up the odds

Koppenburg is also cautious, warning that the result right now shows a relatively high level of uncertainty. There is a 1 in 100 chance that normal particle interactions could produce the same signature – that chance would have to be closer to one in a million to make physicists really sit up and take notice. And previous hints of novel physics at the LHCb have gotten less likely with further scrutiny. “This is the reason why we’re not getting too excited,” he says.

Still, Koppenburg says the aim of the LHCb experiment is to follow any possible leads. “We need more data to figure out whether it’s a statistical fluke or whether there is something real going on there.” For that, the team will have to wait for the LHC to restart in April 2015.

An imprint left on ancient cosmic light that was attributed to ripples in spacetime – and hailed by some as the discovery of the century – may have been caused by ashes from an exploding star.

In the most extreme scenario, the finding could suggest that what looked like a groundbreaking result was only a false alarm. Another possibility is that the stellar ashes could help bring the result in line with other cosmic observations. We should know which it is later this year, when researchers report new results from the European Space Agency’s Planck satellite.

On 17 March, researchers led by of Harvard University announced that gravitational waves from the early universe had been found by a telescope called at the South Pole.

The waves were said to be the “smoking gun” evidence for the theory of inflation, which suggests that space expanded faster than the speed of light in the first moments after the universe’s birth. The announcement sent shock waves through the physics world. “I was so excited,” recalls of Stanford University in California.

Dust damper

But soon it dawned on him that his own research on galactic dust might put a damper on the result. That is because BICEP2 identified the waves based on how they appeared to polarise, or align, the electromagnetic fields of photons they came into contact with in the infant universe.

Those photons, which have been travelling through space ever since, appear in every direction in the sky as the cosmic microwave background (CMB) radiation. But other things apart from gravitational waves, such as dust, can emit polarised photons.

To minimise the chances of this effect causing a false signal, the BICEP 2 team pointed their telescope at a patch of sky far away from the Milky Way’s dusty disc. Then they used models of the dust in that part of the sky to estimate its effect on the polarisation. They found that this could account for no more than about 20 per cent of the signal that they attributed to gravitational waves last month.

Giant loops

But Mertsch says the models they used didn’t account for dust shells produced as the expanding remnants of supernovae slam into surrounding gas and dust. Magnetic field lines threading through those shells should get compressed and aligned, causing some of the material to line up as well. If the aligned dust contains iron, the particles’ slight vibrations due to their own heat would produce polarised microwave radiation, says Mertsch.

A handful of nearby dust shells can be seen by radio telescopes, appearing as giant loops looming above the Milky Way’s galactic disc. Mertsch and his colleagues, led by at the University of Copenhagen in Denmark, plotted the positions of these loops. They , Mertsch says. This shows the patch of the sky that BICEP2 observed (multicolored patch) and the giant loops detected by radio telescopes (blue lines).

The effect of this finding on the BICEP2 result is not clear, because no thorough measurements have yet been made of how much polarised light the dust in our galaxy produces. But of Princeton University says that if you take the dust into account, along with emissions from charged particles in the galaxy – which he says the BICEP2 team probably underestimated – it might make the gravitational wave signal disappear entirely.

“It is important to explore the possibility that the galactic signal could account for all of the signal seen by BICEP,” he says. “Given its importance, the BICEP2 team needs to make a more convincing case.”

Pressure on Planck

Another upshot of the finding could be that dust doesn’t account for all of the polarisation that BICEP2 attributed to gravitational waves – just some of it. That would help bring the BICEP2 result in line with more preliminary measurements taken by the Planck satellite last year, which hinted at weaker ripples than BICEP2 reported.

The BICEP2 team leaders did not respond to requests for comment on the new research, but upcoming observations by Planck should help settle the matter. The Planck team is currently measuring the polarisation of the CMB and is expected to report its findings in October. Unlike BICEP2, Planck observes at a range of different wavelengths. Because emissions from dust vary with wavelength, this should allow researchers to better separate out the contributions to polarised light from dust.

“For sure, this BICEP2 result will put even more pressure on Planck’s next release,” says , a Planck team leader at Italy’s National Institute for Astrophysics in Bologna.

Journal reference:

Quarks are subatomic particles that are the fundamental building blocks of matter. They are known to exist either in groups of two, forming short-lived mesons, or in threes, forming the protons and neutrons that make up atomic nuclei. Researchers have suspected for decades that quarks might also bind together in quartets, forming tetraquarks, but they have not been able to do the complicated quantum calculations necessary to test the idea.

“Our computers aren’t yet big enough to solve the theory from first principles,” says at the University of Maryland in College Park. That means no one knows if the laws of physics should allow matter to clump together to form the still hypothetical tetraquark. But the latest sighting at the LHC means we are closer than ever to finding out.

“The main argument about Z(4430) was, does it exist or not?” says at Syracuse University in New York, who is a member of the team that carried out the latest work. “We came and said Z(4430) is real.”

Belle v Babar

The newly nabbed Z(4430) is one of a handful of suspected tetraquarks that have been found in recent years. It was by the detector at the KEKB accelerator in Tsukuba, Japan, in 2008. But the particle’s existence was questioned after the detector at the SLAC accelerator in Menlo Park, California, .

Now the , which sits at the LHC along with the experiments that spotted the Higgs boson, has analysed 10 times as much data as either Belle or BaBar and says it .

“It’s a very good piece of work,” says BaBar spokesman Michael Roney. It seems that the particular way BaBar searched for the particle reduced its chances of a sighting. “We didn’t have enough data to have the full sensitivity,” he says.

Meson molecules

Now that Z(4430)’s existence is confirmed, the next challenge is to work out whether it really is a tetraquark.

There is at least one reason why physicists can be hopeful. The other suspected tetraquarks might simply be loosely bound pairs of mesons, says , a theorist at Tel Aviv University in Israel, who was not part of the team. Z(4430) is different because its mass does not seem to allow for this.

“There aren’t any mesons at the right masses to make such a thing,” says Karliner. This points to a bona fide particle quartet, says Skwarnicki: “It does make it more likely that it’s a tetraquark.”

However, one puzzling aspect remains: Z(4430) decays at least 10 times as fast as previous suspects, which doesn’t fit with simple models of tetraquark behaviour, says Karliner.

Gathering more data on how this particle decays could help shed light on whether it is a tetraquark or something else. And that could help researchers get to grips with how matter behaves at the most basic scales. Could quarks bind together in even larger groups, for example? Previous hints of five-quark groupings, called pentaquarks, have mostly disappeared in recent years, but they have not been fully ruled out, says Karliner.

“What determines who can bind together and who can’t?” he asks. “It’s completely uncharted territory.”

Reference:

The next Russian-style meteor strike may come as a complete surprise, and maybe that’s OK. A study of a potential early-warning system has found that it will miss more than half of incoming space rocks the size of the one that burst apart above Chelyabinsk, Russia, a year ago. However, the chances of such a meteor causing a dangerous impact are so low that catch-all warning systems are not worth the cost.

The Chelyabinsk meteor was a 20-metre rock that unexpectedly hurtled into the Earth’s atmosphere on 15 February 2013. It exploded with the force of about 600 kilotonnes of TNT, creating a shock wave that shattered windows and knocked people off their feet. The event sparked increased global interest in meteor warning systems.

Millions of smallish rocks are thought to swing near Earth as they orbit the sun. They are tough to find and study because they reflect very little sunlight and can only be spotted when they are close. Even then, there might not be a telescope trained on that part of the sky at the right time.

Rocky forecast

Wide-field telescopes that sweep the whole sky several times a night would show up more of the potential impactors. From late 2015, the in Hawaii will start searching for Chelyabinsk-sized rocks and bigger coming near Earth. The system should be able to find the smaller objects in time to give as much as a two-day warning of a possible collision, says project leader John Tonry at the University of Hawaii in Honolulu.

Meanwhile, the European Space Agency is considering a plan to build a bigger, global array that would more than double that warning time, says Andrea Milani at the University of Pisa in Italy.

Warning times of a few days could lower casualty counts, says , an astronomer retired from NASA’s Jet Propulsion Laboratory in Pasadena, California. “In the case of Chelyabinsk, even a couple of hours to alert people not to run to the windows would have prevented at least 90 per cent of the injuries,” he says.

But such surveys would have missed the Chelyabinsk meteor. Ground-based surveys can only see rocks that appear in the night-time part of the sky, and that one, like about half of all potential impactors, came from the daytime sky. In fact, a survey like ATLAS would spot just one-third of the smaller objects heading for Earth, a recent simulation suggests. “The only way you can get around that problem is having a spacecraft,” says team member Robert Jedicke of the University of Hawaii at Manoa.

Prepared enough

There are no plans to build such dedicated spacecraft. But Tim Spahr, director of the in Cambridge, Massachusetts, is not worried: Chelyabinsk-sized meteors hit the planet only once or twice a century, and most fall over the ocean or unpopulated areas. A spacecraft that could find these dim bodies a few days before impact would need a large, sensitive telescope and could cost more than $1 billion.

For less money, we could launch missions that would spot larger, brighter objects, at least 100 metres across, that have greater potential for devastation – and we would see them coming decades in advance.

Two space missions targeting these larger asteroids are in development. One private project, called Sentinel, is looking for philanthropic donations to place a telescope near Venus.

Another, , is hoping for NASA funding to place a telescope closer to Earth. Space telescopes like these are needed to meet a US congressional mandate of finding 90 per cent of all near-Earth asteroids larger than 140 metres by 2020, says Spahr. At the moment, that figure stands at only 25 to 30 per cent, notes NASA’s Amy Mainzer.

But even projects like these may not be worth the cost, says Harris. Ground-based surveys should provide shorter, but still sufficient, warning times. Earth may not be fully prepared for another impact, but perhaps we’re prepared enough, he says.

Journal reference: