Some bubbles are boring

Rudi Sebastian/Plainpicture

THE curtain at the edge of the universe may be rippling, hinting that there’s more backstage. Data from the European Space Agency’s Planck telescope could be giving us our first glimpse of another universe, with different physics, bumping up against our own.

That’s the tentative conclusion of an analysis by Ranga-Ram Chary, a researcher at Planck’s US data centre in California. Armed with Planck’s painstaking map of the cosmic microwave background (CMB) – light lingering from the hot, soupy state of the early universe – Chary revealed an eerie glow that could be due to matter from aneighbouring universe leaking into ours.

This sort of collision should be possible, according to modern cosmological theories that suggest the universe we see is just one bubble among many. Such a multiverse may be a consequence of cosmic inflation, the widely accepted idea that the early universe expanded exponentially in the slimmest fraction of a second after the big bang.

Once it starts, inflation never quite stops, so a multitude of universes becomes nearly inevitable. “I would say most versions of inflation in fact lead to eternal inflation, producing a number of pocket universes,” says Alan Guth of the Massachusetts Institute of Technology, an architect of the theory.

Energy hidden in empty space drives inflation, and the amount that’s around could vary from place to place, so some regions would eventually settle down and stop expanding at such a manic pace. But the spots where inflation is going gangbusters would spawn inflating universes. And even areas within these new bubbles could balloon into pocket universes themselves.

“If two bubbles started out close enough that they touched, they could leave an imprint on each other”

Like compositions on the same theme, each universe produced this way would be likely to have its own spin on physics. The matter in some bubbles – the boring ones – would fly apart within 10^-40 seconds of their creation. Others would be full of particles and rules similar to ours, or even exactly like ours. In the multiverse of eternal inflation, everything that can happen has happened – and will probably happen again.

That notion could explain why the physical constants of our universe seem to be so exquisitely tuned to allow for galaxies, stars, planets and life (see “Just right for life?“).

Sadly, if they do exist, other bubbles are nigh on impossible to learn about. With the space between them and us always expanding, light is too slow to carry any information between different regions. “They could never even know about each other’s existence,” says Matthew Johnson of York University in Toronto, Canada. “It sounds like a fun idea but it seems like there’s no way to test it.”

Bubble trouble

However, if two bubbles started out close enough that they touched before expanding space pushed them apart forever, they could leave an imprint on each other. “You need to get lucky,” Johnson says.

In 2007, Johnson and his PhD adviser proposed that these clashing bubbles might show up as circular bruises on the CMB. They were looking for cosmic dance partners that resembled our own universe, but with more of everything. That would make a collision appear as a bright, hot ring of photons.

By 2011, they were able to search for them in data from NASA’s WMAP probe, the precursor to Planck. But they came up empty-handed.

“This signal is one of the fingerprints of our own universe. Others should leave a different mark”

Now Chary thinks he may have spotted a different signature of a clash with a foreign universe.

“There are two approaches, looking for different classes of pocket universes,” Johnson says. “They’re hunting for lions, and we’re hunting for polar bears.”

Instead of looking at the CMB itself, Chary subtracted a model of the CMB from Planck’s picture of the entire sky. Then he took away everything else, too: the stars, gas and dust.

With our universe scrubbed away, nothing should be left except noise. But in a certain frequency range, scattered patches on the sky look far brighter than they should. If they check out, these anomalous clumps could be caused by cosmic fist-bumps: our universe colliding with another part of the multiverse (arxiv.org/abs/1510.00126).

These patches look like they come from the era a few hundred thousand years after the big bang when electrons and protons first joined forces to create hydrogen, which emits light in a limited range of colours. We can see signs of that era, called recombination, in the light from that early hydrogen. Studying the light from recombination could be a unique signature of the matter in our universe – and potentially distinguish signs from beyond.

“This signal is one of the fingerprints of our own universe,” says Jens Chluba of the University of Cambridge. “Other universes should leave a different mark.”

Since this light is normally drowned out by the glow of the cosmic microwave background, recombination should have been tough for even Planck to spot. But Chary’s analysis revealed spots that were 4500 times as bright as theory predicts.

One exciting explanation for this is if a surplus of protons and electrons – or something a lot like them – got dumped in at the point of contact with another universe, making the light from recombination a lot brighter. Chary’s patches require the universe at the other end of the collision to have roughly 1000 times as many such particles as ours.

“To explain the signals that Dr Chary found with the cosmological recombination radiation, one needs a large enhancement in the number of [other particles] relative to photons,” Chluba says. “In the realm of alternative universes, this is entirely possible.”

Of course there are caveats, and recent history provides an important reality check. In 2014, a team using the BICEP2 telescope at the South Pole announced another faint signal with earth-shaking cosmological implications. The spirals of polarised light, spotted in the cosmic background, would have provided more observational evidence for the idea of inflation and helped us understand how inflation occurred. But it turned out that signal came from dust grains within our galaxy.

Princeton University’s David Spergel, who played a major role in debunking the BICEP2 finding, thinks dust may again be clouding our cosmological insights. “I suspect that it would be worth looking into alternative possibilities,” he says. “The dust properties are more complicated than we have been assuming, and I think that this is a more plausible explanation.”

Joseph Silk of Johns Hopkins University in Baltimore, Maryland, is even more pessimistic, calling claims of an alternate universe “completely implausible”. While he thinks the paper is a good analysis of anomalies in Planck data, Silk also believes something is getting in the way. “My view is that they are almost certainly due to foregrounds,” he says.

Chary acknowledges that his idea is as tentative as it is exciting. “Unusual claims like evidence for alternate universes require a very high burden of proof,” he writes.

He makes an effort to rule out more prosaic explanations. If it is dust, Chary argues, it would be the coldest dust we’ve ever seen. It’s probably not noise masquerading as a signal. It could be carbon monoxide moving toward us, but we don’t usually see that. It could be faraway carbon, but that emission is too weak.

“I am certain he made every effort to ensure that the analysis is solid,” says Chluba. Even so, foregrounds and poorly understood patterns could still be the source of the signals. “It will be important to carry out an independent analysis and confirm his finding,” Chluba says.

Sensitive solutions

One obstacle to checking is that we’re limited by the data itself. Planck was hyper-sensitive to the cosmic microwave background, but it wasn’t intended to measure the spectral distortions Chary is looking for. Johnson’s team also plans to use Planck to look for their own alternate universes, once the data they need is released to the public – but they estimate that Planck will only make them twice as sensitive to the bubble collisions they’re looking for as they were with WMAP.

An experiment that could help might be on its way. Scientists at NASA’s Goddard Space Flight Center plan to submitPIXIE, the Primordial Inflation Explorer, to be considered for funding at the end of 2016.

PIXIE’s spectral resolution could help characterise Chary’s signals if they really are there, Chluba says. But even if they aren’t, reconstructing how inflation happened could still lead us once again back to the multiverse – and tell us what kind of bubble collisions we should look for next (see diagram).

Just right for life?

If our universe is just one of many, that could explain why it seems so exquisitely tuned for our existence.

If dark energy, the repulsive influence hiding in empty space that speeds up the expansion of the universe, were just a little stronger, matter would be flung apart before galaxies could ever form. If it were attractive instead, the universe would collapse. But it is shockingly puny, and that’s weird, unless our universe is one of many in the multiverse.

Compared with what we might expect from quantum theory, dark energy is 120 orders of magnitude too small. So far, no compelling explanation for that discrepancy has emerged. But if the multiverse exists, and dark energy varies from bubble to bubble (see main story), that might not seem so strange.

That’s because our own universe might be an oddball compared to most bubbles. In many, dark energy would be too strong for galaxies, stars and planets to form, but not in all. “Plenty of them would have energies as small as what we observe,” says physicist Alan Guth of MIT.

That still leaves us struggling to explain why our universe is one of the special ones. Our best answer so far, Guth says, is a philosophical headache: our universe has to be special because we are alive in it. In a more average region, where dark energy is stronger, stars, planets, and life would never have evolved.

That could mean life only exists in a sliver of the multiverse, with any conscious beings convinced their own slice of space is special, too.

This article appeared in print under the headline “A brush with a universe next door”

{ https://www.newscientist.com/ }

Pluto's 'Unprecedented' Ice Provinces and Other Surprises from NASA's New Horizons — **View of Pluto's atmosphere captured by NASA's New Horizons spacecraft during its July 2015 flyby of the dwarf planet.**
**Credit: G.R. Gladstone et al./Science (2016)**

Pluto, known for more than eight decades as just a faint, fuzzy and faraway point of light, is shaping up to be one of the most complex and diverse worlds in the solar system.

Pluto's frigid surface varies tremendously from place to place, featuring provinces dominated by different types of ices — methane in one place, nitrogen in another and water in yet another, newly analyzed photos and measurements from NASA's New Horizons mission reveal.

"That is unprecedented," said New Horizons principal investigator Alan Stern, who's based at the Southwest Research Institute in Boulder, Colorado. [Photos of Pluto and Its Moons]

"I don't know any other place in the entirety of the outer solar system where you see anything like this," Stern told Space.com. "The closest analogy is the Earth, where we see water-rich surfaces and rock-rich surfaces that are completely different."

That's just one of the new Pluto results, which are presented in a set of five New Horizons papers published online today (March 17) in the journal Science. Taken together, the five studies paint the Pluto system in sharp detail, shedding new light on the dwarf planet's composition, geology and evolution over the past 4.6 billion years.

A distant world coming into focus

**New Horizons becomes the first probe to explore Pluto in mid-2015. See how the New Horizons mission to Pluto works in our full infographic here.**
**Credit: By Karl Tate, Infographics Artist**

Pluto was discovered in 1930 by American astronomer Clyde Tombaugh. The dwarf planet remained largely mysterious for many years thereafter, because it lies so far from Earth.

Pluto orbits in the Kuiper Belt, the icy realm beyond Neptune, at an average distance from the sun of about 40 astronomical units (AU). (One AU is the distance from the Earth to the sun — about 93 million miles, or 150 million kilometers.) That's so remote that even the best photo by NASA's famous Hubble Space Telescope portrays the dwarf planet as a mere blur of pixels.

But things began changing in a big way on July 14, 2015. On that day, New Horizons performed the first-ever flyby of Pluto, coming within just 7,800 miles (12,550 km) of its surface. The spacecraft saw towering water-ice mountains; flowing nitrogen-ice glaciers; pebbly "snakeskin" terrain; a vast, crater-free plain known as Sputnik Planum; and many other features that scientists are still trying to figure out.

One of the new papers dives deeply into the geology of these features, revealing new insights about their possible origin and evolution. The 620-mile-wide (1,000 km), nitrogen-ice-dominated Sputnik Planum, for example, apparently sits atop a huge and ancient impact basin, mission scientists say. [Sharpest Pluto Surface View Released by New Horizons Team (Video)]

Sputnik Planum is smooth and pristine, bearing no impact scars. This shows that the region was resurfaced extremely recently — 10 million years ago at most, and possibly much more recently than that, researchers said.

But other parts of Pluto harbor lots of visible craters, and some regions have a middling number, suggesting that the dwarf planet has been geologically active on a large scale over its entire history.

This finding came as a big surprise when it was first announced last year. Earth remains geologically active because it has a hot, molten core. Some icy satellites, such as Saturn's moon Enceladus and the Jovian moon Europa, also harbor substantial internal heat, which is generated by the powerful gravitational tug of their giant parent planets. But something else is likely happening at Pluto.

"I think we have to rethink our whole understanding of geophysics — how you keep small planets active over time," Stern said.

Stern isn't sure what exactly is going on, but he has a favorite hypothesis: that a subsurface Pluto ocean has been slowly freezing over the eons.

"As it freezes, it releases latent heat," he said. "It may be the freezing of this ocean that's powering all this geology."

These maps of water ice on Pluto's surface were created using measurements made by NASA's New Horizons spacecraft during its July 2015 flyby of the dwarf planet. The map at left is an early effort; the one at right used modeling techniques to achieve greater sensitivity.
**Credit: NASA/JHUIAPL/SwRI**

More geology insights

The new geology paper also discusses and interprets a number of other Pluto features, such as the huge, dark-red Cthulhu Regio — which appears to owe its color to hefty concentrations of tholins, complex organic molecules that drifted down out of the dwarf planet's atmosphere — and the towering peaks Wright Mons and Piccard Mons.

Wright Mons is perhaps 2.5 miles (4 km) high and 90 miles (150 km) wide. Piccard Mons is even bigger, rising about 3.7 miles into the Pluto sky and measuring 140 miles (225 km) across. Both of these peaks may have formed from cryovolcanic activity, the researchers said. [Ice Volcanoes on Pluto? New Imagery Points to It (Video)]

New Horizons also spotted long tectonic faults with very steep associated scarps — characteristics that suggest Pluto has a thick crust composed of water ice, mission team members said.

One of the other new Science papers maps out the distribution of various ices across Pluto's surface. This material — primarily frozen methane, nitrogen, carbon monoxide and water — is deposited in a curiously distinct way, researchers found; some Pluto provinces are dominated by nitrogen ice, others by methane and so on (though there are places, such as Sputnik Planum, where several different ices are found in abundance).

This pattern suggests that volatile material (nitrogen, methane and carbon monoxide) is being moved around by sublimation, condensation and glacial flows on both seasonal and geological time scales, the researchers said.

New Horizons’ Best View of Pluto’s Craters, Mountains and Icy Plains

https://youtu.be/0oXvYj2evzg

Surprising atmosphere

One of the other new Science papers focuses on Pluto's wispy atmosphere. This study also delivered some surprising results.

For example, New Horizons found that Pluto's upper atmosphere — the part that's more than 120 miles (200 km) above the surface — is a lot colder than pre-flyby modeling work had predicted, researchers said. In addition, the dwarf planet is losing its atmosphere at a much lower rate than scientists had thought.

Modeling studies had predicted that Pluto would be outgassing at cometary rates, losing lots of gas molecules to space every second. But New Horizons' measurements showed a mere leak rather than a gush — in fact, the model estimates were off by a factor of about 5,000.

"That shows the power of having a spacecraft there — actually going to see," Stern said.

These twin atmospheric surprises — the cold high-altitude temperatures and the low escape rate — are closely related, Stern added. Cold molecules are less energetic, and are therefore less likely to break free of Pluto's gravitational bonds.

Pluto's moons, too

**Dwarf planet Pluto has one giant moon, Charon, but now is known to have four more tiny satellites. See how Pluto's moons measure up in this SPACE.com infographic.**
**Credit: Karl Tate, SPACE.com Contributor**

Pluto does not cruise through space by itself. The dwarf planet has five moons — Charon, Nix, Hydra, Kerberos and Styx. The latter four are tiny, measuring just a few dozen miles wide at most, but Charon is 750 miles (1,200 km) across — more than half as wide as Pluto itself. Indeed, scientists regard Pluto and Charon as a binary system.

New Horizons studied these five satellites during its July 2015 flyby, and the new papers provide some insight into their origin and evolution as well.

For example, Charon and Pluto are very different worlds. The big moon shows no evidence of recent geological activity (though it boasts deep canyons, and was probably active until about 4 billion years ago), and its surface is dominated by water ice, with no sign of large-scale movement of volatile ices such as methane and nitrogen.

"Whether this is because Charon's near-surface volatile ices have sublimated and have been totally lost to space, owing to that body's lower gravity, or whether something more fundamental related to the origin of the binary and subsequent internal evolution is responsible, remains to be determined," study lead author Jeffrey Moore, of NASA's Ames Research Center in California, and his colleagues wrote in the Science paper.

In one of the other new studies, Pluto's four smaller moons are examined. These bodies are all quite reflective, suggesting that their surfaces are dominated by water ice, like Charon (but unlike Pluto). In addition, Nix, Hydra, Kerberos and Styx are all spinning quite fast, and their rotational axes are off-kilter compared to those of Pluto and Charon, the authors wrote.

In general, these characteristics bolster the hypothesis that a giant, long-ago impact created the Pluto-Charon binary system, the researchers said. The four small moons are basically shrapnel thrown off by that ancient impact, the thinking goes. (The small satellites are much brighter than typical Kuiper Belt objects, suggesting that they're not pre-existing bodies that were captured by the Pluto-Charon pair.)

Pluto Quiz: How Well Do You Know the Dwarf Planet?

Pluto, the most famous dwarf planet in our solar system, underwent a well-publicized (and somewhat controversial) reclassification that took away its title as the ninth and most distant planet from the sun. So, how well do you know this fascinating world?

Hubble Space Telescope photo of Pluto is most detailed ever seen.

More data coming

The five papers, which you can read for free on Science's website, don't represent New Horizons' last word on Pluto — far from it. For example, mission team members plan to present more new results next week at the 47th Lunar and Planetary Science Conference in The Woodlands, Texas.

And there's still a lot of flyby data left to analyze. New Horizons has beamed only half of the close-encounter images and measurements back to mission control, Stern said; the entire treasure trove likely won't be on the ground until October.

New Horizons may also perform another flyby that could help scientists better understand Pluto's neighborhood. The spacecraft is currently cruising toward a small Kuiper Belt object called 2014 MU69, which lies about 1 billion miles (1.6 billion km) beyond Pluto. If NASA approves and funds a proposed extended mission, New Horizons will study 2014 MU69 up close on Jan. 1, 2019.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

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