A bewildering variety of planets have been found by the Kepler spacecraft. This illustration is based on best guesses about what those planets are like. Further study almost guarantees more surprises. (Credit: C. Pulliam & D. Aguilar/CfA)

The Kepler project is typically described in terms of raw numbers. As of the last official announcement, it had found 2,740 likely new planets–including 1,200 Neptune-size planets, 350 Earth-size planets, and at least 4 planets that orbit within the “habitable zone” where liquid water can exist. All of those numbers are sure to increase, as more observations are confirmed and as mission scientists continue to dig through a trove of archived data. But spirit, not statistics, is what really defines Kepler. It is a modern version of the expedition of Lewis and Clark, or the great voyages of Vasco da Gama and Ferdinand Magellan. It is a headlong plunge into the unknown cosmic territory around us.

Extrapolating from Kepler’s results, astronomers now estimate there are at least 17 billion Earth-size planets in our galaxy. That is another number, yes, but one with a powerful message: Another age of exploration awaits, one that may very well lead to the discovery that humanity is not alone in the universe. 

There could hardly be a sharper contrast between Kepler’s grandiose mission and the humble mechanical failure that threatens to end it. The fault lies in one of the telescope’s gyroscopic reaction wheels, a key component of its pointing system. Kepler needs three reaction wheels running at all times to maintain a stable position. Think of it like a stool: Two legs are just not enough to keep things balanced.

Extreme stability is essential because of the way that Kepler finds planets around other stars. It points a 0.95-meter (3-foot) light-collecting mirror toward the constellation Cygnus, watching approximately 150,000 stars and monitoring the tiny dimming that happens whenever a planet passes in front of one of them. And by tiny I mean tiny; Kepler seeks out brightness changes as slight as 0.01 percent. Since all the stars in Kepler’s field of view are quite close together in the sky, and since the shadows of passing planets are exceedingly subtle, there is little room for error.

Kepler started out with four functional reaction wheels, allowing for one to go bad without harming the mission. Last July, wheel #2 failed and was switched off. On May 12, wheel #4 apparently failed as well, leaving only two working wheels and sending Kepler into an automatic “safe” mode.

That is not necessarily the end of the line for the hardy telescope, which has been operating nonstop for 1,532 days. Scott Hubbard, former director of NASA’s Ames Research Center, notes that it might be possible to restart wheel #2 and see if it is now functional, which is possible if its lubrication shifted in the interim. Kepler has thruster rockets that could be used to stand in for the third reaction wheel, at least for a few months until the propellant runs out. NASA mission planners have also discussed trying to run wheel #4 backward or otherwise getting it somewhat operational again.

Kepler’s results show that about one in six stars has one or more Earth-sized planets in a fast orbit. That translates to at least 17 billion such planets in our galaxy, and many more planets in slower, Earth-like orbits. Credit: F. Fressin (CfA)

So a requiem for Kepler is somewhat premature. It is also not the right tone. If this is the end of the mission, there is far more to celebrate than there is to mourn. The Kepler team just posted an upbeat assessment of what comes next: “Even if data collection were to end, the mission has substantial quantities of data on the ground yet to be fully analyzed, and the string of scientific discoveries is expected to continue for years to come.” William Borucki, the principal investigator for Kepler, is optimistic that more Earth-like planets lurk within that trove.

Last week, an international team used Kepler data to identify a new planet, nicknamed “Einstein’s planet,” using a novel technique based on the effects of relativity. Multiple ground-based efforts will carry on the search for planets around other stars, and NASA recently approved a successor mission, TESS, that will specifically seek nearby Earthlike worlds.

This is also a good time to recall how extraordinary it is that the Kepler mission happened at all. Last year Borucki gave an in-depth interview with Andrew Grant, an associate editor at DISCOVER, describing the hurdles that he and his collaborators overcame to make the mission happen–a process that at times seemed more Sisyphean than Herculean.

In the 1970s, when Borucki began thinking about searching for extrasolar planets, nobody knew if such planets even existed. In the 1980s, when Borucki began sketching out the starlight-dimming search technique that Kepler uses, most of his colleagues scoffed. “The reviewers quickly rejected it,” he recalls. “They said there were no detectors that could make such precise measurements.”

I clearly remember the mood at that time, because I too was obsessed with the idea of planets around other stars back when it was more science fiction than fact. In the 1950s an 1960s, Dutch astronomer Peter van de Kamp reported evidence of planets around Barnard’s Star and 61 Cygni–but these claims were later debunked. In his book The Cosmic Connection, Carl Sagan showcased some elegant simulations of what other planetary systems might look like–but these were only theoretical models.

For years, Canadian astronomer Bruce Campbell championed the idea of watching the back-and-forth motions of stars to search for the gravitational pull of unseen planets. That technique eventually turned out to be spectacularly successful, but it required a level of precision beyond what Campbell could attain.

Campbell is a forgotten hero in the quest to find to find new worlds beyond our solar system. His pioneering work made possible the series of spectacular planetary finds that began with the discovery of a searing-hot, Jupiter-size planet around 51 Pegasi in 1995. Seven years before that, Campbell (along with Gordon Walker and Stephenson Yang) published a paper presenting evidence for a planet around the star Gamma Cephei. He admitted that the detection was tentative, since it was right at the limits of what his equipment could do.

The report received little attention, and Campbell’s name is missing from most stories about the discovery of exoplanets. He barely registers in a Google search (even after you weed out the other Bruce Campbell, the one who stars in Burn Notice). But the Gamma Cephei planet was eventually confirmed, and the 1988 paper by Campbell, Walker, and Stephenson is the very first verified detection of a planet around another star.

The 2,740 planets detected by Kepler as they passed in front of their stars are depicted here as black dots. View the image full size to appreciate the true avolume of data. (Credit: Kepler/NASA)

Whether or not this is the end of the Kepler spacecraft, Kepler’s mission–and the mission of Campbell, Borucki, and the many many others who made it possible–goes on. The next great moment in the age of planetary discovery lies just ahead.

Follow me on Twitter: @coreyspowell

OUR COSMIC FATE hangs in the balance, depending on the behavior of dark energy. If dark energy increases, everything will be torn apart; if it changes direction, the cosmos could end in a big crunch. (Credit: NASA/CXC/M.Weiss)

Small wonder, then, that our recent DISCOVER magazine cover story about the mystery of dark energy (Confronting the Dark by Zeeya Merali) produced such an outpouring of curious reader mail. In a previous post, I addressed some of the key cosmological questions submitted by our readers. But really, that first set of responses only scratched the surface. For every letter writer who asked broadly about the nature of the Big Bang, someone else who wanted to know more about dark energy itself.

So as promised, here is a second installment addressing how scientists came to realize that energy, not matter, rules the universe.

As before, I need to put out a disclaimer up front. The answers I give here are not just my own. They are distilled from the dedicated efforts of astronomers and physicists around the world—although some of the more philosophical questions inevitably trigger more personal answers. I should also acknowledge that there is a lot we still do not know about the universe. But over the past 15 years, scientists have put together a convincing case that dark energy is real. At this point, it would require revolutionary new discoveries to disprove that.

That said, let’s move on to Cosmic Questions II: The Dark Universe.

What the scientists studying dark energy are doing is just speculation that leads nowhere. It is obvious that they have no idea what it’s all about. –Dick and Linda C.

There is a powerful question embedded in that statement. Cosmologists talk all the time about how little they understand about dark energy, about how enigmatic it is. Can they be sure that it exists at all?

To paraphrase a certain president: Yes they can.

Let me back that answer with a quick review of how dark energy was discovered in the first place. Ever since the Big Bang theory became widely accepted in the 1960s, researchers have been trying to measure a number called the “deceleration parameter.” That number describes the rate at which the universe is slowing down due to the mutual attraction of all the matter in the universe.

The rate of deceleration is significant for several reasons. It tells you the total mass of the observable universe. It tells you the fate of the universe, by showing if things are slowing down enough that they will eventually come to a halt and reverse. And it is crucial for determining the age of the universe, since it tells you how the rate of cosmic expansion has been changing since the time of the Big Bang.

To measure the deceleration, you need to compare how the universe is expanding now with the way it was expanding in the distant past. Fortunately, the finite speed of light acts like a visual time machine. A galaxy located one million light years away appears to us as it was a million years ago. A galaxy a billion light years ago appears as it was a billion years ago, and so on.

SUPERNOVA 2005ke, the bright star at upper left, is a Type 1a supernova–the kind used to discover dark energy. The images show it in light (left), UV (center), and X-rays. (Credit: NASA/Swift/S. Immler)

In the 1990s, a few researchers—most notably, Saul Perlmutter, Brian Schmidt, and Adam Riess, who eventually shared a Nobel prize—developed a novel way to measure the deceleration parameter by looking at very distant, extremely bright exploding stars called Type 1a supernovas. As the data rolled in, the deduced number they were getting for the deceleration parameter kept getting smaller and smaller, until it hit zero. That corresponds to a universe with no mass at all. “I guess we’re not here!” Perlmutter joked with his team. Then the number started going to less than zero. That meant the universe was speeding up, not slowing down, and some outward force, not the inward pull of gravity, was the dominant actor. Cosmologist Michael Turner proposed the name dark energy for this unknown repulsive agent.

When the first supernova papers came out in 1998, many scientists were skeptical. Since then, however, studies of cosmic acceleration have been repeated over and over, always with the same result. Dark energy is also supported by studies of the radiation left over from the Big Bang, and by studies of how clusters of galaxies have evolved over time.

Dark energy is not speculation. It is a description of the observed behavior of the universe.

Dogma be damned: I have a different idea about dark energy…

We got a lot of letters that began like that. DISCOVER readers clearly were not satisfied with the prevailing scientific view that space itself is filled with invisible energy—so much energy that its mass is far exceeds that of all the stars, planets, and gas put together. (Remember that mass and energy are equivalent: e=mc²)

It does seem counterintuitive that the universe as a whole is so different than the world we live in. On earth, everything you touch consists of atoms made of protons, neutrons, and electrons. On the cosmic scale, though, such “ordinary” matter is not ordinary at all. According to the latest cosmic measurements, it accounts for just 4.9 percent of the total. Dark matter is 26.8 percent. (For more about dark matter, see my primer on the shadow universe.) Dark energy is 68.3 percent. More than two thirds of the universe is completely immaterial.

Even cosmologists have a hard time wrapping their head around these ideas. So it is important to keep in mind that they have embraced the idea of dark energy not because it sounds cool, but because observational evidence has forced them to do it.

Scientists’ uncomfortable relationship with dark energy began with none other than Albert Einstein. In 1917 he examined the cosmic implications of his new theory of gravity (the general theory of relativity), and ran into a problem: On very large scales, gravity would tend to cause the universe to collapse. Einstein therefore invoked a possible repulsive force that could balance out gravity and allow the universe to remain static—as he and most astronomers believed it was at the time. He called it Lambda but that was, in essence, just an earlier name for dark energy.

The key point is that Einstein invoked dark energy because it was the simplest, most consistent way to explain the observed behavior of the universe. After the 1929 discovery that the universe is expanding, Einstein realized that the outward motion of the galaxies alone could explain why things are not collapsing, and he abandoned the idea of Lambda.

[An interesting historical note. Contrary to many claims in the popular press, there’s no compelling evidence that Einstein ever called Lambda his “biggest blunder.” Astronomer Mario Livio has recently found that the “blunder” story is probably a myth. Einstein always recognized that something like dark energy was a theoretical possibility—and now it looks like that possibility is a reality.]

Could dark energy be…

• …a crystallization that produced points of compressed space?
•  …a cosmic electrostatic effect?
• …a 3-dimensional bubble moving as a point on the time axis in a 5-dimensional “real” universe”?
• …a “big suck” pulling on our cosmos?
• …energy expelled by stars when they go nova?
• …mass that is too far away to ever see?

In their letters, DISCOVER’s readers offered many creative way to explain dark energy. A credible theory of dark matter requires more than creativity, however. It must adhere to the known physical laws. It must offer specific, testable descriptions. And it must match all known observations about the behavior of the universe.

PUSH AND PULL between gravity and dark energy caused the universe to slow down, then speed up, according to the latest observations. This schematic of cosmic history was assembled using data from the Hubble Space Telescope. (Credit; NASA/HST)

One of the oddest things about the expanding universe is that it has not always been expanding the same way. Until about 5 billion years ago—roughly the time when the Earth formed, give or take—it was slowing down. Then ago things turned around and the expansion started speeding up. Because we look back in time as we look out into space, this cosmic switcherooo shows up in a strange way. The most distant (long ago) parts of the universe are decelerating, while the more nearby (recent) parts of the universe are accelerating. Astronomers can actually see that pattern and map it, again using supernovas as milemarkers in deep space.

That slowing-then-speeding universe makes sense if there is a repulsive energy embedded in the structure of space. When the universe was young, small, and dense, gravity dominated. As the universe got bigger, its density dropped and the volume of space (and energy) increased. About 5 billion years ago, dark energy finally overwhelmed gravity.

Now it’s easy to see the problems with some of the reader ideas about dark energy.

A “big suck” implies that cosmic acceleration should be most intense at the greatest distances, but in fact we see the opposite. Mass that is too far away to see likewise could affect only the farthest parts of the universe; anything that lies beyond the edge of the visible universe from our vantage point cannot physically influence us here. Likewise, dark energy cannot be the effect of mass that is too far away to see.

Some other reader ideas fail because they apply commonsense ideas to cosmic questions—and human intuition simply is not a valid guide on such unfamiliar scales. For instance, matter and energy expelled by novas or supernovas does not change the density of the universe and so cannot influence its expansion. The universe is electrically neutral overall, so it cannot be under the influence of a cosmic electrostatic effect.

Finally, some of the more exotic reader ideas are too vague to evaluate. Terms like “compressed space” or “a 5-dimensional real universe” make sense only if they are precisely defined and connected to other, well-supported physical concepts.

The important lesson here: Anyone who is serious about developing a new theory of the universe first needs to engage in a thorough study of the current theories and to talk seriously with the people who have developed them. I strongly encourage that. The more perspectives brought to bear on cosmology, the more progress it will make.

Scientists say the Big Bang should have produced as much antimatter as matter. I believe that dark matter could be antimatter. Maybe matter and antimatter repel each other, like the north poles of two magnets, and this repelling force could account for the dark energy that is mysteriously expanding our universe. – Harry P.

This letter raises a fascinating and very concrete question: Does antimatter experience antigravity?

Amazingly, nobody knows. Current theory says that antimatter and matter should react to gravity exactly the same way. But what you really want to do is run a test: Assemble a clump of antimatter, let it go, and see if it falls down or up.

A large team of physicists working on the ALPHA experiment at CERN (the European physics consortium that brought you the Large Hadron Collider) recently did just that. They created atoms of antihyrdogen, trapped them, and then let them go. The results, published last month in the journal Nature, will disappoint anyone who enjoys answers like “yes” or “no.” The experiment is so difficult that the researchers can say only that the antihydrogen atoms didn’t move much; both gravity and antigravity are compatible with the results. Still, the ALPHA results show that the measurement is possible, and a much more sensitive project called AEgISwill follow up in a couple years.

TWO WEIGHTS dropped from the Leaning Tower of Pisa fall at the same rate regardless of their mass. Does antimatter likewise fall just like matter? Three new experiments will investigate. (Credit: Aegis/CERN)

(Since matter attracts matter, it’s not clear why antimatter would repel antimatter, as the reader suggests. At any rate, running that experiment in the lab would require holding and measuring two large lumps of antimatter, something that is far beyond our current technological capabilities.)

Antimatter probably cannot solve the dark energy problem. Balloon- and space-based detectors suggest that antimatter is rare in the universe. Even if the antimatter is hidden in distant locations, its influence should decrease as the universe expands—the opposite of the observed pattern of cosmic acceleration. Still, if antimatter and matter react differently to gravity, that would require some serious tinkering with both general relativity and quantum physics.

Your “Guide to the Dark Side” didn’t account for light energy. Surely, all that electromagnetic radiation, that would fry us to a crisp if it were not for Earth’s atmosphere, must count for something. — Gregg D

Now here’s an intriguing thought. Light and other forms of electromagnetic radiation contain mass in the form of energy. Perhaps that mass helps pull things together, or perhaps the pressure of radiation helps push things apart. It almost sounds like a zen koan: Could light energy be dark energy?

Measuring the total amount of radiant energy in the universe is quite easy, actually, because this is the stuff we can see. It turns out that radiation accounts for less than 0.01% of the mass of the universe (once again using special relativity to convert energy into its equivalent mass). That is too small to have a substantial effect on cosmic expansion, and the net effect is to slow things down, not speed them up.

There is that humbling lesson again: The things we see in the night sky—both the stars and the light by which they shine—make up a very small portion of what is out there.

The article made no mention of the Higgs boson. If I understand it correctly the Higgs creates a field; does that energy affect gravitational pull? –Roger

Let’s break this question into two parts. Does the Higgs field affect gravity? Most definitely, since the Higgs field is what gives other particles their mass, and without mass they would have no gravitational attraction. (At least, that’s what last year’s discovery seems to confirm.) So in that sense, the Higgs field is a central player in our whole cosmic drama.

Now the second part. Does the Higgs field have anything to do with dark energy? Very different question. Dark energy may be related to vacuum energy, the residual energy of all the fields that exist in empty space. Vacuum energy includes familiar things like the electromagnetic field (the one that allows light to exist) along with all the other known fields…including the Higgs field. So the Higgs could be one component of the energy that makes up dark energy. But we are deep into speculative territory here, since nobody yet has a well-established model of where dark energy comes from.

The cosmic expansion, we are told in this DISCOVER article, is happening only at large scales and is having no impact on smaller things like the Milky Way, planets, and atoms.  Yet, one of the projected results of the expansion is the ripping apart of planets, atoms, and other small-scale things.  How are the two reconciled? – D. V. Thompsop

It all comes down to timescales. Right now, dark energy makes itself felt only at the largest cosmic scales. Wait a while—and by a while I mean anywhere from tens to hundreds of billions of years—and the story may change. Recall that the balance between the inward pull of gravity and the outward push of dark energy seems to be steadily shifting in dark energy’s direction as the universe keeps expanding, creating more space and diluting the existing matter.

If the essential nature of dark energy stays constant, space will keep expanding faster and faster. As that happens, it will be harder and harder for gravity to hold things together. At the same time, the visible edge of the universe—the distance at which space moves away from us at the speed of light—will keep migrating closer and closer. Eventually the expansion of space will overwhelm the gravity that loosely holds clusters of galaxies together. In about a trillion years (about 100 times the current age of the universe) all other galaxies will disappear from view and we will live in our own pocket of isolation. “It’s going out in the bleakest fashion I can think of,” says Brian Schmidt. “It’s eternity, but it’s nothingness at the same time.”

Unless it isn’t. Nobody knows if dark energy stays the same over time. It could get stronger, in which case things get even worse. In this scenario, the expansion of space will become so rapid that it will start to disassemble our own galaxy, the Milky Way. Then things will keep going, until the accelerating expansion of space starts pulling apart stars, planets, people, atoms–everything–in a final Big Rip. The Big Rip might come as soon as 100 billion years from now (still long after the sun will have burned out, in case you are keen on long-range planning). Then again, dark energy might decay or even flip around, causing the universe to stop expanding and fall back in on itself. Some cosmological theories even suggest that a new Big Bang will happen after the current universe empties out.

The moral: Don’t count on a gloomy fate. There are so many theories on the table right now that you can pretty much pick the way you want the story to end…for now.

If space exploded out of nothingness to create the universe we inhabit now, this begs the question–Did the universe create God? –Gail S.

This is a completely unanswerable question, so forgive me for attempting anyway.

If you believe in a personal God—the kind of God who answers prayers, performs miracles, and speaks directly to people—then science has nothing to say on the matter. Such a God exists out of space and time and does not live within the laws of physics, so cosmological discoveries are irrelevant.

ROOM FOR GOD, yes, but maybe not this particular one.

Einstein had a different view of God, one that is widely shared in one form or another by many other scientists who study the universe. “I believe in Spinoza’s God who reveals himself in the orderly harmony of what exists, not in a God who concerns himself with fates and actions of human beings,” Einstein told Rabbi Herbert Goldstein in 1921. When George Smoot called his map of the cosmic microwave background “the face of God,” or when Leon Lederman refers to the “God particle,” they are speaking roughly in this context. Insofar as the laws of physics emerged at the time of the Big Bang, you could say that the God we know appeared then too. Then the question of “what came before the Big Bang?” becomes equivalent to the question of whether there is a deeper, more timeless form of God.

Recent theories about multiple universes that exist in infinite time (also described in my previous post) provide a place for God to exist before our universe—and after, if there is an after–if you choose to interpret them that way. Those theories could also explain how our universe began, and what came before the Big Bang. As yet these theories are untestable, though, so they still live in the realm of metaphysics as much as physics.

Follow me on Twitter: @coreyspowell

In Stephan’s Quintet, the ruddy galaxies are 8 times as far away as the bluish one at upper left. Astronomer deduce distances by measuring how light is affected by the expansion of the universe. (Credit: NASA, ESA and the Hubble SM4 ERO Team)

The May cover story in DISCOVER magazine (Confronting the Dark by Zeeya Merali) chronicles that game-changing discovery, and lays out the latest thinking about what dark energy is and how it affects the fate of the universe. As soon as the article was published, DISCOVER’s inbox began to fill with letters from curious readers wanting to know more. Here I will address sweeping, big-picture questions about cosmology. I’ll consider more specific queries about dark energy and dark matter in a following post.

Before I dive in, an important pieces of context. The answers I give here are not my own. They are distilled from the dedicated efforts of astronomers and physicists around the world, working with the greatest telescopes and instruments ever built. There is a lot we still do not know about how the universe began and how it will end. Some widely held ideas will, very likely, again be overturned. But the past century of research has yielded an amazingly detailed understanding about the overall structure and workings of the universe. OK then, on to the questions!

I have seen maps of the universe, but I never saw where it started. Is there some way we could plot the direction of all the galaxies to reverse engineer the starting point?  –Roger D.

This question, and several other similar ones we received, gets at one of the most confounding yet fundamental ideas in modern cosmology. The Big Bang was not an explosion in space—it was an explosion of space. Put another way, the Big Bang took place everywhere at once because space itself emerged at the same time as matter and energy. There was no outside space that the universe expanded into (at least not in the familiar three-dimensional sense), and there is no one location we can point to that is the place where the Big Bang began.

Wherever you are sitting now, you can think of that as the center of the Big Bang. It is as accurate as picking any other location. Sorry, but that’s the real answer.

From our perspective, galaxies appear to be flying away in all directions. Observers elsewhere in the universe would see the exact same thing. There’s nothing special about our spot, because every location in a uniformly expanding universe appears to be at the center of the expansion. Plotting the direction of galaxies cannot reverse engineer the starting point; again, it will only lead right back to where you are.

You might wonder, how can galaxies all be flying through space in such neat formation? The answer again requires discarding the notion of “space” as a fixed, immutable thing. In the overall expansion of the universe, galaxies are not flying at tremendous speeds through space; space itself is expanding, increasing the total scale of the universe.

What is the shape of the universe? Is it a hollow sphere? The balloon analogy seems to suggest it is, but it can’t be that simple. –Howard L.

The balloon analogy is a visual tool that that cosmologists often use to help explain the expansion of the universe. Imagine you are sitting on the surface of an enormous balloon that is marked with dots. If the balloon is inflated, the dots appear to move away from your location in all directions. The same is true for any other observer at any other location on the balloon. Furthermore, the speed at which the dots move away is proportional to their distance. Imagine the balloon doubles in size after a minute. Dots that were an inch away are now two inches away; dots that were two inches away are now four inches away (ie, they have moved twice as far); and so on.

Another way to look at the shape of the universe: a plot of the changing radius of the visible part of universe over time. By far the most extreme expansion happened in the first fraction of a second–and this diagram is very much not to scale. (Credit: NASA/WMAP Science Team)

The problem with the balloon analogy is that it is just an analogy. On a local scale the surface of the balloon is essentially a two-dimensional membrane, but the universe is a three-dimensional space. The balloon has a geometric center in three dimensions, whereas the universe does not. “The interior of the balloon is analogous to the 4th dimension,” explains Brian Schmidt, who shared the Nobel prize for the discovery of the accelerating universe. In that sense, he argues, you really can think of the universe as a higher-dimensional sphere. I don’t know about you, but I that pretty hard to visualize.

Cosmologists do talk about the overall “shape” of space in the universe. This is a way of describing what would happen to a beam of light traveling an extremely long distance through space: Would it curve or move in a straight line? (The shape of the universe is influenced by its overall density.) A widely accepted cosmological model called “inflation,” developed in the 1980s, predicted that the universe should be almost perfectly flat. At the time, there was no way to tell, but now we know that the prediction was correct: By studying microwave radiation emitted shortly after the Big Bang, NASA’s WMAP satellite has found that the universe is flat to within a 0.4% margin of error.

How about that. The world is flat after all.

What existed 10 minutes before the Big Bang? What caused the Big Bang to occur? How many other Big Bang universes are there? – Joseph T.

The simplest and most honest answer to this question is, “nobody knows.”

Oh, but plenty of people are wiling to theorize. There are many ideas out there in the scientific literature. In the 1920s and 1930s a number of scientists, including Albert Einstein, considered the possibility of an eternal, cyclic universe that expands, contracts, and rebounds over and over. Those original models failed because they violated the second law of thermodynamics; essentially, the universe would keep running down instead of resetting. But the idea of endless rebirth is so appealing that it keeps coming back.

One form is the ekpyrotic cosmology co-developed by Paul Steinhardt at Princeton University. In this model, the Big Bang was sparked by the collision of two “branes”—three dimensional worlds moving through higher-dimensional space. Picture two crinkled pieces of paper banging into each other and you have the right idea, within the limits of visualization. When the branes hit, our universe was born and the two branes moved apart. After a trillion years or so they will collide again, triggering a new Big Bang and a new universe, and then again and again. According to Steinhardt’s calculations, the cycle could keep going essentially forever without violating thermodynamics.

Another type of eternal cosmological model emerges from the theory of inflation—the same one that predicted that the universe is flat. Cosmologists Andre Linde and Alan Guth, two of the creators of inflation theory, realized that this model could allow not just a single Big Bang but endless Big Bangs, each giving rise to new universes. In this model of eternal inflation, our universe is just one of a multitude—a multiverse—which could be infinite in extent and duration. Each universe is born from a quantum fluctuation in an energy field, which rapidly buds off and expands into a new universe. The inflation field can be thought of as the trigger that made the Big Bang go bang. Guth once called this “the ultimate free lunch.”

And things get weirder. Each universe could have its own laws of physics, meaning that some would be almost exactly like ours and some would be completely different. String theory (which attempts to build a single set of rules to explain all particles and forces) predicts there could be 10⁵⁰⁰ different types of universes. For now this is pure speculation, however.

The underlying theory of inflation, on the other hand, accurately matches many of the observed properties of the universe, and it has received impressive empirical support. Inflation predicts a specific pattern in the cosmic microwave background, the radiation left over from the Big Bang. The WMAP and Planck satellites have observed just such a pattern. That does not prove that inflation is correct, but it sure does make the theory look more credible.

If the Big Bang initially expanded the universe faster light, doesn’t that violate Einstein’s belief that nothing can exceed the speed of light? –Rick B.

If inflationary model of cosmology is correct, the universe expanded faster than light—much, much faster than light—in the first 10^-30 second of existence. At first blush that sure seems like a violation of Einstein’s special theory of relativity, which states that nothing can go faster than light. More specifically, though, special relativity states that no object with mass can match (or exceed) the speed of light. In the early universe, objects were not moving through space faster than light; space itself was moving faster than light, which does not violate Einstein at all.

Sounds like cheating, doesn’t it? But this concept is completely true both to the letter and the spirit of Einstein’s theory. Special relativity explains the behavior of light and moving objects, and accounts for why the laws of physics look the same to all observers. The hyper-expansion of space would not affect the local laws of physics, and any objects receding faster than light would be fundamentally unobservable and hence irrelevant.

Once again, the key is dispensing with the idea of objects moving through space and getting used to the idea that space itself can stretch. That is also essential to understanding the current thinking about dark energy and the accelerating expansion of the universe.

The author refers to the redshift related stretching of light as arising from the Doppler Effect, but this is not true. It is from space stretching which is distinctly different from the elongation of wavelength from the Doppler Effect. –Tom M.

The writer is correct. As distant galaxies move away from Earth, their light gets stretched and reddened. The resulting “redshift” is how Edwin Hubble (drawing on data from unsung astronomer Vesto Slipher) deduced the apparent expansion of the universe in 1929. Many scientists—including Hubble himself—have attributed that reddening to the Doppler effect, even though that explanation is not technically accurate.

The Doppler effect causes waves to pile up if they are moving toward you and to stretch out if they are moving away. The classic example is the siren of a fire engine, which shifts to a higher note as the engine approaches you and suddenly shifts to a lower note as it passes by and begins to recede. Astronomers observe Doppler shifts all the time, measuring how various objects are moving toward or away from their telescopes. This is one of the primary ways that scientists have identified planets around other stars.

But as I keep saying (and please bear with me), the expansion of the universe is due to an expansion of space itself, not to the motion of galaxies through space. As light waves move through expanding space, they themselves get expanded and shifted to the red. (The balloon analogy is useful again: Think what would happen if you drew a wave on the balloon and then blew it up.) The result is essentially equivalent to a Doppler shift, but the root cause is very different. For this reason, the redshifts of distant galaxies are properly known as cosmological redshifts. A tip of the hat to Tom M. for catching a subtle but important error.

Follow me on Twitter: @coreyspowell

Scientific illustrations of recently discovered, potentially habitable worlds. Left to right: Kepler-22b, Kepler-69c, Kepler-62e, and Kepler-62f, compared with Earth at far right. (Credit: NASA/Ames/JPL-Caltech)

Alan Stern, a former NASA associate administrator and founder of a startup called Uwingu, thinks these newfound worlds should have real names, and that the general public should be able to have a say. The International Astronomical Union–the organization the organization that officially validates astronomical nomenclature–strongly objects to Uwingu’s approach, and has effectively thwarted it. After the IAU’s blistering April 12 press release attacking Uwingu, submissions to Uwingu’s fee-based online planetary naming database plummeted. Stern calls it a “torpedo attack.”

I am not a neutral party in this dispute. Uwingu has partnered with DISCOVER and its sister publication, Astronomy, to help promote Stern’s efforts to raise funds for various astronomical exploration projects. And as I noted in a previous post, I am also inherently sympathetic to Stern’s position. I do understand the IAU’s concern about allowing private companies to hijack to process of naming celestial objects–but that is not what Uwingu is doing, and several of the IAU’s statements about Uwingu (which the IAU never mentions by name, even though the identity is obvious) are highly misleading.

I am pleased to see that I’m not the only one coming to the defense of Uwingu and, more generally, to the idea that the public should have some say in the naming of new planets. On the Physics Today web site, Charles Day provides a thoughtful post on the value of getting ordinary people involved. At Universe Today (no relation), Nancy Atkinson does a great reporting job on the controversy and quotes several professional astronomers who disagree with the IAU arguments against Uwingu. Carolyn Collins, who calls herself TheSpacewriter, digs much more deeply into the flaws with the IAU approach.

The dust-up between Uwingu and the IAU would be a tempest in a teapot outside of the astronomical community, except that there is actually a lot at stake here for anyone who cares about cosmic exploration and science literacy. Uwingu is trying to perform two important services: getting the public to participate in one of the greatest discoveries of modern times, and raising money for very worthy but underfunded research and education projects. The idea the a professional bureaucracy with the stated goal of advancing astronomy and astronomical education would stand in the way of Uwingu’s efforts is both odd and unsettling.

There is still time to participate in Uwingu’s call to nominate a real name for Alpha Centauri Bb, the nearest known planet outside our solar system. In response to the slow-down that followed the IAU press release, Stern has extended his deadline to April 22. More important, Uwingu’s broader planet-name nomination process is ongoing. And the broader issue here is not going away. Having more of the general public invested in scientific discovery is a win for everyone.

MORE UPDATE (5/1): The winning name for Alpha Centauri Bb is Albertus Alauda.

Follow me on Twitter: @coreyspowell

Illustration of the Earth-size planet orbiting Alpha Centauri B, part of the closest star system to home. The planet is currently known only as Alpha Centauri Bb. (Credit: ESO/L. Calçada/Nick Risinger)

Uwingu’s name-that-planet project has a noble aim. Alan Stern–the founder of the company, lead scientist for the New Horizons mission to Pluto, and a former associate administrator at NASA–is using the money raised by the contest to restore funding to NASA’s education and outreach efforts, which have been hit hard by sequester-related budget cuts. [Full disclosure: DISCOVER magazine and its sister publication, Astronomy, have partnered with Uwingu on its efforts to raise private funds for astronomical research.] But as one side effect, Stern has found himself embroiled in a battle with the International Astronomical Union (IAU), the self-described arbiter of “unambiguous astronomical nomenclature.” In a testy statement released on April 12, the IAU declared that private competitions (the union never cites Uwingu by name) will “have no bearing on the official naming process.”

All of which raises a big question for the rest of us: Who gets to name new astronomical objects, and how exactly do they get that right?

The IAU was born in 1919, during an era of post-war international collaboration. Operating as kind of United Nations for astronomy, the IAU today includes nearly 11,000 astronomers from 93 countries, giving it broad authority and legitimacy in setting standards for the field. One of the most prominent powers it wields is the authority to issue official names. But that process is complicated and often controversial–as the union itself acknowledges up top.

The abbreviated public summary of the IAU’s naming procedures runs nearly 4,000 words because of its complexity. Comets, for instance, all have two separate designations: a compound alphanumeric tag that indicates the date of discovery and the type of comet, and a separate name that recognizes the people, instrument, or spacecraft that made the actual discovery. That’s how we ended up with two very odd comet names this year. Comet PanSTARRS is named after a telescope array in Hawaii; Comet ISON, which may make a spectacular appearance later this year, is named after a Russian-based astronomical network.

If you discover an asteroid, a whole other kind of bureaucracy awaits. First, its orbit must be well established, a process that can take many years. Then it receives a formal number by the IAU, which buys the asteroid’s discoverer a 10-year window to select a name. The name can be anything (there are asteroids named Zappafrank and Misterrogers), provided it meets a lengthy list of conditions. For instance, it cannot be longer than 16 characters, and names of pets are “discouraged” (whatever that means). The rules for dwarf planets, Kuiper Belt Objects, new satellites, and specific features (craters, mountains, etc) on other worlds all have their own IAU methodology. It’s a bit overwhelming; take a look for yourself.

The situation for giving names to planets around other stars is particularly obscure, because for now there is no official procedure whatsoever. Although the first exoplanet (the technical term for a planet outside of our solar system) was discovered in 1995, the IAU didn’t even consider the possibility of naming these worlds until fourteen years later. At that point, the IAU general assembly punted, failing to reach any consensus and generally opposing the whole idea of giving names to new planets. Given all the excitement about exoplanets these days–and the hundreds new worlds that have been discovered–the IAU plans to revisit the issue this year. The IAU committee considering the issue is called the “IAU Division F Commission 53 Extrasolar Planets (WGESP).” It has, as yet, delivered no official decision.

New planets found by NASA’s Kepler space observatory: So many worlds, so few names. (Credit: NASA/Kepler Mission/Wendy Stenzel)

Nevertheless, when Uwingu recently launched its planet-naming contest, IAU officials were clearly not pleased about being bypassed by a private organization. In a widely circulated statement, the IAU wrote: “Recently, an organization has invited the public to purchase both nomination proposals for exoplanets, and rights to vote for the suggested names. In return, the purchaser receives a certificate commemorating the validity and credibility of the nomination. Such certificates are misleading, as these campaigns have no bearing on the official naming process…”

No doubt a large part of the reason for that indignation is that the IAU, and professional astronomers in general, have spent years fighting shady companies that would offer to “sell” star names and place them in an official-looking registry. These schemes clearly were intended to mislead customers into thinking that they were purchasing an official scientific name, and the proceeds of the sale were used for nothing but the enrichment of the sellers. But what Alan Stern is doing here is fundamentally different in several ways.

Stern points out that he never said his names would be official–although he says that “of course” he hopes the names that emerge from his campaigns will eventually be the widely used ones. The Uwingu campaign is dedicated to aiding astronomy education, a mission that dovetails with the IAU’s own goals. Some of the funds raised so far by Uwingu have gone to support Astronomers Without Borders, the Galileo Teacher Training Program, and the Allen Telescope Array, which searches for signals from extraterrestrial civilizations. “All of it is with the purpose of fueling The Uwingu Fund for space research and space education grants,” Stern says. Uwingu’s team works without pay. And this kind of voting contest bears far more resemblance to a crowdsourcing campaign than it does to the single-sale model of the old star-registry hustlers.

New Worlds, New Challenges

To Stern, his dust-up with the IAU partly comes down to a philosophical battle between a bottom-up and top-down approach to astronomy. The IAU’s position is that only a professional organization should bestow names on new planets. Stern responds that “a model more like the Internet domain registry, with many providers, would be better than a monopoly. There’s no confusion when that’s done properly, as the Internet shows.” He’s also a big fan in public participation, which is essentially the opposite of the professional model on which the IAU was founded.

On April 15, three days after the IAU statement, Uwingu responded with a press release of its own. In it, Uwingu notes that many astronomical objects have multiple names. (One example: In different contexts and different catalogues, the star Polaris is known as the North Star, Alpha Ursae Minoris, HD 8890, HIP 11767, SAO 308, ADS 1477, FK5 907, etc.) At the same time, many colloquial names (again, North Star is one such example) long predate the IAU, while others emerge directly from scientists’ nicknames and informal terminology. Press notices from the Hubble Space Telescope and the European Southern Observatory are rife with such coinages–the “Pillars of Creation” is one of the most famous. Researchers working with NASA’s Curiosity rover give informal but widely recognized names to new Mars features all the time.

Uwingu says that the IAU is both overreaching and mischaracterizing Uwingu’s contest. From the Uwingu release: “Uwingu affirms the IAU’s right to create naming systems for astronomers. But we know that the IAU has no purview–informal or official–to control popular naming of bodies in the sky or features on them, just as geographers have no purview to control people’s naming of features along hiking trails.”

For both Uwingu and the International Astronomical Union, the deeper issue here is that the discovery of planets around other stars presents a truly novel naming challenge. Unlike galaxies or stars, these are tangible worlds–places that people want to see, to study, to search for signs of habitability or even signs of life. They feel personal in a way that other astronomical objects do not. And there are a lot of them. From the invention of the telescope to 1995, astronomers had uncovered only three new planets (and one the three, Pluto, has been partially revoked). Since then, they have found roughly 700 confirmed worlds, and thousands more likely planetary candidates. NASA’s Kepler mission has just revealed three more, potentially life-friendly worlds, including the most Earth-like planet yet.

Giving all of that new cosmic real estate nothing but zip codes seems cold, and also wasteful. This is an extraordinary opportunity to tap into the romance of cosmic exploration and to get the public excited about science. After 18 years, the IAU is still pondering the concept. Uwingu is taking action right now–and the IAU can always consider those contest-winning names later as candidates for the “official” naming process. In the end, it is hard to find fault with Stern’s motivating philosophy: “It’s a big universe, and one that all people can enjoy connecting to through naming.”

Follow me on Twitter: @coreyspowell

America’s Science Idol cast: Gillian Bowser; judge Corey S. Powell; host Chris Mooney; judge Indre Viskontas; Joshua Schroeder; winner Tom DiLiberto; Maura Hahnenberger; and runner-up Jenna Jadin. (Not pictured: Dan Gareau and judge Jennifer Bogo.)

Or maybe I just thought it would be a lot of fun.

At any rate, a few weeks ago I teamed up with Popular Science editor Jennifer Bogo,  neurscientist Indre Viskontas, and journalist Chris Mooney to riff on the American Idol format at the annual meeting of the American Association for the Advancement of Science in Boston. The result was “America’s Science Idol,” a science-communication competition sponsored by the National Science Foundation, and the video of our event has just been posted online:

If you don’t have 41 minutes of free time to watch the whole thing (what, you’re busy?), I’ll cut to the chase and share a few conclusions. First, the six scientists who participated were not only good sports, they all brought a lot of passion and sincerity to their performances. There are few nobler things in life than dedicating yourself to a deeper understanding of the world, sharing that knowledge, and finding ways to apply it to make people happier, healthier, safer, and more aware of their place in the larger order. Science produces fabulous stories, but the general public often does not get to hear them–at least, not in a form they can relate to. All six of these contestants reached out with great conviction and good humor.

Despite that, some succeeded much better than others. We set a taxing challenge for our contestants, explaining their work in 3 minutes or less, in an entertaining but meaningful way, using only language that the average layperson could understand. That is not how science typically works. Normally scientists are encouraged to use jargon that helps them communicate with other researchers in their fields; normally they labor over papers and grant proposals rather than having to spit out ideas at the pace of a music video. I listened to hear who could most clearly articulate the nature, excitement, and relevance of his or her work. It is a useful exercise for any working scientist to be able to articulate those things. In fact, it is a useful exercise for all of us, regardless of profession, to occasionally step back and ask what we do and why we do it.

Although 3-minute public performance may not be a part of the regular practice of science, clear communication is an increasingly essential skill in every profession. In the age of Twitter, Facebook, and blogs (this one included), the public is exposed to an unprecedented flow of information. That gives scientists an amazing new opportunity to share ideas, but that also makes it easier than ever for their message to get drowned out. The contestants who fared the best were those who understood that it does not pay to talk down to the public, or to be too cute, or to assume that other people automatically understand your own interests and motivations. Honesty, transparency, and specificity pay huge dividends–as our winner, Tom DiLiberto, ably demonstrated.

America’s Science Idol itself may have suffered from a touch too much cuteness, but to a very deliberate end. By its nature, science is open to new ideas. It allows open debate, and encourages a change of opinion when the facts point that way. Scientists are routinely thrilled to have to modify their theories or discard them entirely in the face of new evidence. At a time of too much petty political polarization, those are incredibly important values to spread. I’m glad to say that America’s Science Idol brought out the competitiveness in our contestants, and in the process helped make sure that their bigger message does not get lost.

Follow me on Twitter: @coreyspowell

Color-coded, composite of the galaxy cluster Abell 520. Green denotes hot gas; orange highlights starlight from galaxies; blue shows the inferred location of dark matter. (Credit: NASA, ESA, CFHT, CXO, M.J. Jee, and A. Mahdavi)

And yet scientists have assembled a nearly airtight case that the majority of the matter in the universe consists dark matter, a substance which is both intrinsically invisible and fundamentally different in composition than the familiar atoms that make up stars and planets. In the face of staggering difficulties, researchers like Samuel Ting of MIT are even making progress in figuring out what dark matter is, as evidence by teasing headlines from last week. Time to come to terms, then, with the new reality about our place in the universe. Here are seven key things every informed citizen of the cosmos should know.

1 Dark matter is real. The evidence for dark matter goes all the way back to a paper published by visionary Swiss astronomer Fritz Zwicky in 1933–less than a decade after Edwin Hubble definitively proved the existence of other galaxies. Zwicky noticed that galaxies in clusters were moving so quickly that the clusters should be flying apart, and yet the clusters remain intact. He concluded that there must be dunkle Materie (dark matter) scattered through the clusters, providing the extra gravitational pull that holds everything together. At the time, most of Zwicky’s colleagues considered the evidence too tentative, and the idea too weird, to believe. In the 1970s, American astronomer Vera Rubin changed their minds with the same kind of observations carried out in much greater detail. She found that galaxies systematically rotate so quickly that they should fly apart unless bound together by dark matter–or unless our understanding of the laws of gravity are wrong. More recently, astrophysicists have run elaborate computer models of how galaxies form. These models beautifully fit the observed structure of the universe, but only if they include dark matter into their equations.

Stars in the outer regions of spiral galaxy M74 move much more quickly than expected if they were held in orbit only by the visible matter. The best explanation is that they are being pulled by a large halo of unseen, dark matter. (Credit: Gemini Observatory/GMOS Team)

Two other lines of evidence strongly support dark matter. One comes from observations of gravitational lensing, the bending of light due to gravity. Astronomers can make crude maps of where the matter is in galaxy clusters by observing how they distort the light of more distant galaxies. These maps not only confirm the presence of huge amounts of dark matter, they also show that the dark stuff moves independently from hot gas in the cluster, something that alternate theories of gravity cannot easily explain. Another, completely independent line of evidence comes from studies of the cosmic microwave background, radiation left over from the Big Bang. The distribution of that radiation on the sky is very sensitive to the exact composition of the early universe. The observed pattern allows a very precise measurement of the makeup of the universe, as I described recently, in which dark matter outweighs visible matter by a factor of 5.5 to 1. All three types of observations not only show evidence of dark matter, they also show the same amount of dark matter. That’s awfully persuasive.

2. Dark matter can be visible…sometimes. That sounds like a contradiction of all that I’ve just said, so bear with me. Dark matter seems not to interact with light or any other form of electromagnetic radiation (radio, x-rays, etc), but it may be able to interact with itself. One of the leading theories of dark matter holds that it consists of fundamental particles called WIMPs (weakly interacting massive particles) that can destroy each other if they happen to smack into each other. In the vastness of space, particles don’t collide very often but it will inevitably happen occasionally. If two WIMPs annihilate each other, they might create visible radiation in the form of gamma rays; or they might give rise to more familiar types of particles, such as electrons and their antimatter partners, positrons.

In fact, two space-based experiments are currently looking for both signals, and both see some intriguing signs of something strange going on in the depths of space. NASA’s Fermi Gamma-Ray Space Telescope has picked up an extremely faint but unusual glow of gamma rays having a very specific energy: 130 giga-electron volts (GeV), or about 60 billion times the energy of visible light. That looks a lot like the breakdown of a dark-matter particle, but Christoph Weniger of the Max-Planck Institute for Physics cautions that the evidence right now “is as ambiguous as it can be.” Further hints of dark matter come from Samuel Ting and the $2 billion Alpha Magnetic Spectrometer, or AMS, experiment aboard the International Space Station. That’s the one that just made headlines last week. (New York Times: “Tantalizing New Clues into the Mysteries of Dark Matter”.) AMS is picking up a slight excess of positrons from all directions of the sky, which is again consistent with the presence of dark matter but not yet at all conclusive. Stay tuned for more results; Ting says it will take “several more years” before he has enough data to say for sure.

The Alpha Magnetic Spectrometer experiment (top left) aboard the International Space Station. (Credit: NASA/AMS)

3. Dark matter might show up here on Earth. In theory, we are swimming in dark matter all the time. It should be passing through you right now. Because dark matter is so unreactive, most of the time it keeps going and nobody here is any the wiser for it. But starting in the 1990s, a few hardy (or foolhardy, depending on your perspective) physicists decided to try to sense dark matter particles as they pass. The idea is that on very rare occasions, a dark matter particle might strike an atom of ordinary matter, giving it a kick. That could potentially be detected as a thermal signal: a minuscule dose of heat. Several experiments along these lines have claimed tentative sightings of dark matter signals. The most celebrated results have come from the detector known as DAMA, short simply for DArk MAtter. Beyond a core of true believers, nobody considers these results convincing, however. A new experiment called LUX should clarify the situation. “The sensitivity is significantly better than previous direct detection experiments,” promises LUX principle investigator Richard Gaitskell of Brown University. By the time LUX finishes its first full run in 2015 it will be, he hopes, “a very definitive experiment.”

4. We might be able to create our own dark matter. That is one of the great goals for the ambitious Large Hadron Collider: making dark matter in the lab so that scientists can study it. The core concept of the LHC is that the mad smashing of particles into other particles will shake loose all kinds of things that do not show up in the calm and quiet of everyday physics. In essence, the huge amounts of energy created at the LHC can be spontaneously transformed into various particles (mass and energy being equivalent–remember your e=mc²?). That is how the physicists at the LHC (probably) found the Higgs Boson. If WIMPs have the kinds of masses that theorists expect, the LHC should create them too. Such dark matter particles will be hard to track down, because of their elusive nature. They tend to fly right out of the detectors, unseen, and so would initially show up as missing energy in the LHC reactions: One more shadow to chase. Still, if the WIMPs really are there, the crafty researchers and enormous computers that sift through data from the LHC should be able to find them when the collider restarts in 2015.

5. Dark matter is a totally different thing than dark energy. In 1998, two competing teams of cosmologists discovered that the expansion of the universe is speeding up. The force behind that cosmic expansion is now known as “dark energy,” a term that was coined by Michael Turner at the University of Chicago as a deliberate (if sometimes confusing) counterpoint to dark matter. Both are dark in the sense that they are unseen, and both are dark in the sense that they are mysterious. But dark matter seems to consist of some sort of particles, and it exerts a gravitational pull that tends to bring things together: it glues together galaxies and galaxy clusters, and may have provided the extra attraction that allowed these structures to form in the first place. Dark energy, on the other hand, is even less well understood but it seems to be a form of energy that is embedded into the fabric of space itself, and it exerts a repulsive force–almost like antigravity–over extremely long distances. To add further confusion, dark energy has the equivalent of mass (if you didn’t remember your e=mc² before, try remembering it now) and when you total up all that mass, dark energy is the dominant component of the universe.

6. The dark stuff really dominates. Based on the latest observations from the Planck observatory, the universe consists of 68.3 percent dark energy, 26.8 percent dark matter, and 4.9 percent ordinary matter. A little perspective: More than 95 percent of the universe is dark and fundamentally unobservable, most of the universe does not consist of matter, and most of the matter does not consist of atoms like the ones that make up you and me. Feeling insignificant yet?

7. The dark universe might have a life of its own. A few years back, Savas Dimopoulos of Stanford University postulated that dark matter could form dark atoms that create their own dark chemistry. Neal Weiner at NYU has kicked around the thought problem of how a hypothetical scientist composed of dark matter might be able to find the visible universe (which of course would be invisible to him or her). The answer: It wouldn’t be easy. And just recently a group of Harvard University physicists led by JiJi Fan and Lisa Randall have theorized that some dark matter might be able to cool and collapse just the way ordinary hydrogen gas does, leading to the possibility of dark galaxies, perhaps even dark stars and dark planets.

Right now nobody knows. Perhaps these ideas are just flights of fantasy, but they are fantasies that are consistent with what we currently understand about how the universe works. In fact, they are supported by some of the best available current observations. Douglas Finkbeiner, an astrophysicist at Harvard, neatly sums up the wonder and uncertainty of this kind of research: “We should all be lying in bed awake wondering what dark matter is.”

Follow me on Twitter: @coreyspowell

Victor Hess (center) rode up in a balloon in 1912 to prove that Earth is bombarded by radiation from outer space. Astronomers are only now making sense of those enigmatic “cosmic rays.” (Credit: American Physical Society)

Physicists have been wrestling with that question for a century now, but the past couple months have seen remarkable progress toward a meaningful answer. It’s taken so long because researchers have had to overcome a lot of obstacles along the way. Even the name of the thing they are studying is confusing. The particles are formally known as cosmic rays even though they are not rays at all, but fragments of atoms that are moving at extremely high velocities. And those fragments are extremely difficult to study, because cosmic rays do not move in straight lines. They are electrically charged, so they bend to the will of the magnetic fields that snake almost everywhere through deep space. By the time a particular cosmic ray reaches Earth, its path may have nothing to do with the place where it started out. Looking at cosmic rays is like pointing a telescope into a set of funhouse mirrors.

But cosmic rays exciting things, because they provide a direct record of what is happening in some of the wildest, most energetic, most violent parts of the universe. They get kicked around by massive young stars, supernova explosions, pulsars, and black holes. The most potent cosmic rays are so energetic that they challenge the limits of physics to explain how they came to be. All of which explains why a small, hardy group of researchers continues to obsess cosmic rays so long after Victor Hess‘s 1912 balloon flight that first proved the existence of mysterious radiation coming down from the sky in all directions.

Some of the progress has come from the aggressively named Super-TIGER experiment, which flew up to the stratosphere over Antarctica and circled the south pole for over 55 days in December and January. That mission watched the skies from 25 miles up, lofted by a 39-million-cubic-foot helium balloon. Its detectors scanned specifically for heavy cosmic rays: atoms heavier than zinc, which come from highly evolved “Wolf-Rayet” stars heading toward their demise. The results of the latest experiment are still under study. (I will discuss them in greater detail in next month’s Out There column in DISCOVER magazine.) But data from TIGER, a smaller precursor mission, have made it pretty clear that the high-drama Wolf-Rayet stars are intimately linked with the origin of cosmic rays.

The Super-TIGER experiment prepares for lunch in Antarctica in December, 2012, setting out to make sense of cosmic rays once and for all. Credit: Ryan Murphy/Washington University

Robert Binns of Washington University in St. Louis filled me in on some of the details. “The Wolf-Rayet phase is an evolutionary phase of a massive star’s life when very high-velocity winds occur, and they drive off huge amounts of material in a very short time. The lifetime of this phase is only about 100,000 years; then at the end of that phase, the massive star core collapses and either undergoes a supernova or collapses to a black hole,” he says. “We believe the primary accelerator of cosmic rays is the magnetic fields in the shockwave from these supernovas.  And the source of the material, we think, is partly the wind material that’s blown off before the explosion that is then picked up by the expanding shock, and also just ordinary interstellar medium, gas and dust that’s laying around in that region.”

If Binns is correct, the atomic particles he is studying are the very ones swept up by distant supernovas–explosions that briefly flare up a billion times as bright as the sun–which then traveled across hundreds of light years of space before hitting Super-TIGER’s detectors. Two other recent studies strongly bolster this view.

One comes from NASA’s Fermi space telescope. Unlike Super-TIGER, Fermi cannot detect cosmic rays directly. Instead it picks up gamma rays (similar to visble light, but millions to billions of times as energetic) that are produced by a chain reaction that occurs when the cosmic rays randomly slam into surrounding hydrogen atoms that are floating quietly in space. The resulting gamma-ray glow is like a tracer that points back to the locations where atoms are getting energized. Put another way, Fermi makes it possible to take away the funhouse mirror and see where cosmic rays are born.

A large team headed by Stefan Funk of Stanford University and the Kavli Institute used the Fermi telescope to track the origin of cosmic rays back to two unusual nebulas, named the Jellyfish Nebula (IC 443) and W44. Both of these have previously been identified as the remains of supernova explosions; both remnants are associated with massive stars like the ones that pass through a Wolf-Rayet phase. Finding that the trail of cosmic rays leads right back to these locations clinches the conclusion by Binns and others that supernovas are, in fact, stirring up atoms and flinging them across the galaxys. Funk, unable to resist the inevitable cry of the scientist trying to explain a successful piece of detective work, calls this discovery the “smoking gun.”

If the Fermi data are the smoking gun, then another, parallel piece of research has just turned up the fingerprints as well. Serbian astronomer Sladjana Nikolic, a Ph.D. student at the Max-Planck Institute for Astronomy in Heidelberg, Germany, and her colleagues sought out another visual clue about where and how the cosmic rays are getting energized. Using the Very Large Telescope in Chile (one of the largest telescopes in the world and an amazing instrument, despite its prosaic name), she zeroed in on another supernova relic, known as SN 1006. At the outer edge of the fast-expanding cloud of gas she–right where the shock front should be–she detected hot, energized hydrogen nuclei. They are almost surely the precursors of the kinds of cosmic rays that Super-TIGER and other experiments detect when they reach the Earth millions of years later.

SN 1006, the remains of a stellar explosion seen a thousand years ago, has been fingered as a source of cosmic rays. This view is a composite of radio, light, and x-ray images. (Credit: NASA, NOAO, NRAO.)

It’s been a slow, painstaking process getting to this level of understanding of cosmic rays, but the implications are profound. Before, when I looked up at the night sky I  perceived it as something chilly and remote. The stars were things fundamentally cut off from my life, both in space and in time. Now I know that I was wrong. Fragments of distant stars are striking Earth’s atmosphere all the time. They mix with the air. I am breathing them in at this very moment, and so are you.

Other atoms, born in earlier generations of stars, also made the journey across space. They mingled with a gas cloud that, 5 billion years ago, collapsed to form the sun, the Earth, and the other planets. As Carl Sagan memorably put it in his landmark series Cosmos, “The nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of starstuff.” Cosmic rays may seem esoteric, but each one is a reminder of who we are and where we came from.

Follow me on Twitter: @coreyspowell

Lopsided universe: Planck’s new skymap shows that one half of the microwave background is brighter than the other, and the universe has a large cold spot. Credit: ESA and the Planck Collaboration

So let’s step back for a moment, look at how this image came to be, and consider some of the more surprising details hidden within it.

The map started out as static. Planck didn’t just turn on its microwave cameras and take this picture. Planck’s detectors pull in 9 different microwave bands, at frequencies ranging from 30 gigaherz to 857 gigahertz. Most of the radiation it picks up is noise: spurious signals from the detectors themselves, emission from within our galaxy, emission from all the other objects beyond our galaxy. Planck scientists had to remove all of that to unmask the extremely faint background signal of the “cosmic microwave background”–the afterglow of the big bang that you see in the picture. (If you have an old-style TV around, you can tune it to an empty UHF station and watch the static flickering on the screen. TV static is, in part, the noise of the cosmic microwave background.)

Human brains cannot make sense of all the data from Planck. If this kind of research seems almost beyond human comprehension–it is. The spacecraft has made a trillion observations of a billion points on the sky, looking at each pixel in this image an average of 1,000 times. In order to make sense of all those data points, and to weed out the noise I just described, Planck scientists had to rely on a series of computer simulations. Most of these were done on a Cray XE6 supercomputer known as the Hopper, located at Lawrence Berkeley National Laboratory. Those simulations made it possible to mimic and subtract the unwanted signals from foreground objects and from within the detectors. According to NASA, the current cosmic snapshot required 10 million processor-hours of time on the Hopper–time spent looking at a fake universe, in essence, in order to make sense of the real one.

The universe is darker, lighter, slower, and older than we thought. Strange as it may sound, Planck shows that the universe contains both more ordinary visible matter (4.9 percent of the total mass) and more dark matter (26.8 percent) than previously estimated. The loser in the new cosmic census is dark energy, now estimated at 68.3 percent, down from 73.8 percent in the earlier estimate. That doesn’t change the fundamental picture of the universe, but it does show the importance of recognizing false certainty. Those earlier numbers looked very precise, but turned out to contain bigger unknowns in them than the impressive looking decimal points would indicate. Put it all together and we get a new picture that the universe is just a hair under 13.8 billion years old–about 100 million years older than previously estimated–and expanding a little more slowly than thought. Those who have been following cosmology research for a long time will recall that the cosmic expansion rate was once the subject of heated, intensely personal disputes; the two sides disagreed by a factor of two. Now we know the answer (67.15 kilometers/second/megaparsec, in case you are counting) to within 2 percent.

What we’re made of: A breakdown of the composition of the universe based on earlier data (left) and based on the new Planck results (right). Credit: Planck/ESA.

The universe is lopsided. This is certainly the biggest surprise buried within the Planck news. Ever since Albert Einstein created the first truly physical model of the universe in 1917, scientists have adhered to the “cosmological principle” that overall the universe looks the same in all locations, and in all directions. There is a lot of  local variation of course (a galaxy here, a cluster there) but on the whole the universe should be the same everywhere because the physical laws governing its formation and expansion operate the same way everywhere. Except–that is not what Planck sees. The cosmic microwave background is distinctly stronger in one half of the sky than in the other. There is also a large “cold” spot where the effective temperature of the microwaves is below average. Current theory cannot account for either of these features. They are brand new mysteries to be solved.

But the fact that there are mysteries within this incredible cosmic map is not unexpected. The unexpected thing is that such a map is possible. And that certainly counts as the fifth and most wonderful surprise of all.  Follow me on Twitter: @coreyspowell

Is this the real Mars? A mosaic from NASA’s Curiosity rover shows Mount Sharp in raw color. NASA describes raw color as the way the scene would look “in a typical smart-phone camera photo.” (Credit: NASA/JPL-Caltech/MSSS)

The very first Viking images from the surface of Mars in July, 1976 showed blue skies, largely because that’s what people were expecting and so that is how the imaging experts initially set the color balance. They quickly realized their error and reissued the image with tangerine skies.

Or is this the real Mars? The scene has been given a white-balanced color adjustment that turns the sky blue. That change simulates Earth-like lighting, making it easier to interpret the geology. (Credit: NASA/JPL-Caltech/MSSS)

The Martian atmosphere is fully of orange tinted dust that dominates the color of the sky, it turns out. Changing the color balance to reflect that unexpected reality was a fairly straightforward adjustment, and yet even today images of the same scene on Mars often seem to take on different tones. Sometimes the landscape looks ruddy and rusty, sometimes tangerine, sometimes butterscotch, sometimes a drab brownish yellow.

Different magazines and web sites make their own color adjustments, of course, and there are plenty of amateurs out there doing their own corrections and distortions. But NASA itself still seems confused at times about what Mars really looks like. Consider three images of Mars from space. The first two are from the Hubble Space Telescope. The third is from the Mars Global Surveyor. You’ll notice that they don’t match up very well, even though Mars is very much the same planet and two of the images even come from the exact same telescope.

Mars as seen by the Hubble Space Telescope in July, 2001. (Credit: Credit: NASA and The Hubble Heritage Team)

Mars as seen by the Hubble Space Telescope in March, 1997. (Credit: David Crisp; the WFPC2 Science Team; NASA)

Mars as seen by the Mars Global Surveyor in February, 2006. Say, that planet doesn’t look red at all. (Credit: NASA/JPL/Malin Space Science Systems)

The short explanation is that color balance is a highly subjective thing. No two spacecraft use the exact same filters; even two instruments on the same telescope can use different filters and channels. Once the data come in from the digital detectors, then the imaging specialists process the data to make the most meaningful kind of picture. Sometimes they highlight what seems most scientifically significant. Sometimes they try to simulate what the human eye would see–what most people mean when they ask, “What does it really look like?” But even then, the color receptors of the human eye do not match up exactly with any of our instruments, so creating a color balance that resembles human vision is itself something of a subjective art.

And the problem of authenticity gets worse, because not all people perceive color the exact same way. You probably do not even perceive color exactly the same way in your two eyes. (Stare at a monochrome wall or a blue sky. Cover one eye, then the other. Is it exactly the same?) Perhaps the biggest challenge of all: The way the eye registers color changes depending on the amount of light. That is why deep-space photos of nebulas have all those amazing pinks and purples that you never see in the sky. You could look at the Orion Nebula through the best telescope in the world and you would only see gray-green. The human eye just cannot pick up the extremely faint reds.

Keep that in mind when looking at images from deep space. In fact, the nature of true color is a problem for any kind of unfamiliar imagery. You know exactly what to expect from local landscapes. But did the photographer bump up the greens in the Amazon rainforest, or make a sunset more colorful? Are Emma Stone’s eyes really that color? The confusions and the lies are as old as photography itself, and digital imaging only makes the manipulations easier and the subjectivity more evident.

At least there is a solid scientific motivation for NASA’s latest color manipulations. The white-balanced color adjustment that turns the sky blue in the latest Curiosity panoramas from Mars’s Gale Crater are designed to make the surface rocks look the way they would under normal terrestrial illumination. That makes life easier for planetary geologists who are used to looking at rock formation on Earth, and so simplifies the process of understanding the exotic setting where Curiosity is exploring.

And it is an exotic setting. The current location, called Yellowknife Bay, appears to be an ancient river or lakebed. It contains sedimentary rocks. It has a benign chemistry that would have been favorable to life, if it ever took hold there. It contains many of the elements used by microorganisms on Earth. From here, Curiosity will slowly make its way up Mount Sharp, testing chemicals and looking around as it goes. If you want to know whether Mars ever could have supported life–or might still today–this will be our best shot at getting an answer.

But if you want to know what color Mars really is, my advice to you is to wait until it comes into view later this year, take a look up, and decide for yourself.

Follow me on Twitter: @coreyspowell