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Crafty_Dog:
Dark Energy
NY Times

Three days after learning that he won the 2006 Nobel Prize in Physics, George Smoot was talking about the universe. Sitting across from him in his office at the University of California, Berkeley, was Saul Perlmutter, a fellow cosmologist and a probable future Nobelist in Physics himself. Bearded, booming, eyes pinwheeling from adrenaline and lack of sleep, Smoot leaned back in his chair. Perlmutter, onetime acolyte, longtime colleague, now heir apparent, leaned forward in his.

“Time and time again,” Smoot shouted, “the universe has turned out to be really simple.”

Perlmutter nodded eagerly. “It’s like, why are we able to understand the universe at our level?”

“Right. Exactly. It’s a universe for beginners! ‘The Universe for Dummies’!”

But as Smoot and Perlmutter know, it is also inarguably a universe for Nobelists, and one that in the past decade has become exponentially more complicated. Since the invention of the telescope four centuries ago, astronomers have been able to figure out the workings of the universe simply by observing the heavens and applying some math, and vice versa. Take the discovery of moons, planets, stars and galaxies, apply Newton’s laws and you have a universe that runs like clockwork. Take Einstein’s modifications of Newton, apply the discovery of an expanding universe and you get the big bang. “It’s a ridiculously simple, intentionally cartoonish picture,” Perlmutter said. “We’re just incredibly lucky that that first try has matched so well.”

But is our luck about to run out? Smoot’s and Perlmutter’s work is part of a revolution that has forced their colleagues to confront a universe wholly unlike any they have ever known, one that is made of only 4 percent of the kind of matter we have always assumed it to be — the material that makes up you and me and this magazine and all the planets and stars in our galaxy and in all 125 billion galaxies beyond. The rest — 96 percent of the universe — is ... who knows?

“Dark,” cosmologists call it, in what could go down in history as the ultimate semantic surrender. This is not “dark” as in distant or invisible. This is “dark” as in unknown for now, and possibly forever.

If so, such a development would presumably not be without philosophical consequences of the civilization-altering variety. Cosmologists often refer to this possibility as “the ultimate Copernican revolution”: not only are we not at the center of anything; we’re not even made of the same stuff as most of the rest of everything. “We’re just a bit of pollution,” Lawrence M. Krauss, a theorist at Case Western Reserve, said not long ago at a public panel on cosmology in Chicago. “If you got rid of us, and all the stars and all the galaxies and all the planets and all the aliens and everybody, then the universe would be largely the same. We’re completely irrelevant.”

All well and good. Science is full of homo sapiens-humbling insights. But the trade-off for these lessons in insignificance has always been that at least now we would have a deeper — simpler — understanding of the universe. That the more we could observe, the more we would know. But what about the less we could observe? What happens to new knowledge then? It’s a question cosmologists have been asking themselves lately, and it might well be a question we’ll all be asking ourselves soon, because if they’re right, then the time has come to rethink a fundamental assumption: When we look up at the night sky, we’re seeing the universe.

Not so. Not even close.

In 1963, two scientists at Bell Labs in New Jersey discovered a microwave signal that came from every direction of the heavens. Theorists at nearby Princeton University soon realized that this signal might be the echo from the beginning of the universe, as predicted by the big-bang hypothesis. Take the idea of a cosmos born in a primordial fireball and cooling down ever since, apply the discovery of a microwave signal with a temperature that corresponded precisely to the one that was predicted by theorists — 2.7 degrees above absolute zero — and you have the universe as we know it. Not Newton’s universe, with its stately, eternal procession of benign objects, but Einstein’s universe, violent, evolving, full of births and deaths, with the grandest birth and, maybe, death belonging to the cosmos itself.

But then, in the 1970s, astronomers began noticing something that didn’t seem to fit with the laws of physics. They found that spiral galaxies like our own Milky Way were spinning at such a rate that they should have long ago wobbled out of control, shredding apart, shedding stars in every direction. Yet clearly they had done no such thing. They were living fast but not dying young. This seeming paradox led theorists to wonder if a halo of a hypothetical something else might be cocooning each galaxy, dwarfing each flat spiral disk of stars and gas at just the right mass ratio to keep it gravitationally intact. Borrowing a term from the astronomer Fritz Zwicky, who detected the same problem with the motions of a whole cluster of galaxies back in the 1930s, decades before anyone else took the situation seriously, astronomers called this mystery mass “dark matter.”

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So there was more to the universe than meets the eye. But how much more? This was the question Saul Perlmutter’s team at Lawrence Berkeley National Laboratory set out to answer in the late 1980s. Actually, they wanted to settle an issue that had been nagging astronomers ever since Edwin Hubble discovered in 1929 that the universe seems to be expanding. Gravity, astronomers figured, would be slowing the expansion, and the more matter the greater the gravitational effect. But was the amount of matter in the universe enough to slow the expansion until it eventually stopped, reversed course and collapsed in a backward big bang? Or was the amount of matter not quite enough to do this, in which case the universe would just go on expanding forever? Just how much was the expansion of the universe slowing down?

The tool the team would be using was a specific type of exploding star, or supernova, that reaches a roughly uniform brightness and so can serve as what astronomers call a standard candle. By comparing how bright supernovae appear and how much the expansion of the universe has shifted their light, cosmologists sought to determine the rate of the expansion. “I was trying to tell everybody that this is the measurement that everybody should be doing,” Perlmutter says. “I was trying to convince them that this is going to be the tool of the future.” Perlmutter talks like a microcassette on fast-forward, and he possesses the kind of psychological dexterity that allows him to walk into a room and instantly inhabit each person’s point of view. He can be as persuasive as any force of nature. “The next thing I know,” he says, “we’ve convinced people, and now they’re competing with us!”

By 1997, Perlmutter’s Supernova Cosmology Project and a rival team had amassed data from more than 50 supernovae between them — data that would reveal yet another oddity in the cosmos. Perlmutter noticed that the supernovae weren’t brighter than expected but dimmer. He wondered if he had made a mistake in his observations. A few months later, Adam Riess, a member of a rival international team, noticed the same general drift in his math and wondered the same thing. “I’m a postdoc,” he told himself. “I’m sure I’ve messed up in at least 10 different ways.” But Perlmutter double-checked for intergalactic dust that might have skewed his readings, and Riess cross-checked his math, calculation by calculation, with his team leader, Brian Schmidt. Early in 1998, the two teams announced that they had each independently reached the same conclusion, and it was the opposite of what either of them expected. The rate of the expansion of the universe was not slowing down. Instead, it seemed to be speeding up.

That same year, Michael Turner, the prominent University of Chicago theorist, delivered a paper in which he called this antigravitational force “dark energy.” The purpose of calling it “dark,” he explained recently, was to highlight the similarity to dark matter. The purpose of “energy” was to make a distinction. “It really is very different from dark matter,” Turner said. “It’s more energylike.”

More energylike how, exactly?

Turner raised his eyebrows. “I’m not embarrassed to say it’s the most profound mystery in all of science.”

Extraordinary claims,” Carl Sagan once said, “require extraordinary evidence.” Astronomers love that saying; they quote it all the time. In this case the claim could have hardly been more extraordinary: a new universe was dawning.

It wouldn’t be the first time. We once thought the night sky consisted of the several thousand objects we could see with the naked eye. But the invention of the telescope revealed that it didn’t, and that the farther we saw, the more we saw: planets, stars, galaxies. After that we thought the night sky consisted of only the objects the eye could see with the assistance of telescopes that reached all the way back to the first stars blinking to life. But the discovery of wavelengths beyond the optical revealed that it didn’t, and that the more we saw in the radio or infrared or X-ray parts of the electromagnetic spectrum, the more we discovered: evidence for black holes, the big bang and the distances of supernovae, for starters.

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The difference with “dark,” however, is that it lies not only outside the visible but also beyond the entire electromagnetic spectrum. By all indications, it consists of data that our five senses can’t detect other than indirectly. The motions of galaxies don’t make sense unless we infer the existence of dark matter. The brightness of supernovae doesn’t make sense unless we infer the existence of dark energy. It’s not that inference can’t be a powerful tool: an apple falls to the ground, and we infer gravity. But it can also be an incomplete tool: gravity is ... ?

Dark matter is ... ? In the three decades since most astronomers decisively, if reluctantly, accepted the existence of dark matter, observers have eliminated the obvious answer: that dark matter is made of normal matter that is so far away or so dim that it can’t be seen from earth. To account for the dark-matter deficit, this material would have to be so massive and so numerous that we couldn’t possibly miss it.

Which leaves abnormal matter, or what physicists call nonbaryonic matter, meaning that it doesn’t consist of the protons and neutrons of “normal” matter. What’s more (or, perhaps more accurately, less), it doesn’t interact at all with electricity or magnetism, which is why we wouldn’t be able to see it, and it can rarely interact even with protons and neutrons, which is why trillions of these particles might be passing through you every second without your knowing it. Theorists have narrowed the search for dark-matter particles to two hypothetical candidates: the axion and the neutralino. But so far efforts to create one of these ghostly particles in accelerators, which mimic the high levels of energy in the first fraction of a second after the birth of the universe, have come up empty. So have efforts to catch one in ultrasensitive detectors, which number in the dozens around the world.

For now, dark-matter physicists are hanging their hopes on the Large Hadron Collider, the latest-generation subatomic-particle accelerator, which goes online later this year at the European Center for Nuclear Research on the Franco-Swiss border. Many cosmologists think that the L.H.C. has made the creation of a dark-matter particle — as George Smoot said, holding up two fingers — “this close.” But one of the pioneer astronomers investigating dark matter in the 1970s, Vera Rubin, says that she has lived through plenty of this kind of optimism; she herself predicted in 1980 that dark matter would be identified within a decade. “I hope he’s right,” she says of Smoot’s assertion. “But I think it’s more a wish than a belief.” As one particle physicist commented at a “Dark Universe” symposium at the Space Telescope Science Institute in Baltimore a few years ago, “If we fail to see anything in the L.H.C., then I’m off to do something else,” adding, “Unfortunately, I’ll be off to do something else at the same time as hundreds of other physicists.”

Juan Collar might be among them. “I know I speak for a generation of people who have been looking for dark-matter particles since they were grad students,” he said one wintry afternoon in his University of Chicago office. “I doubt how many of us will remain in the field if the L.H.C. brings home bad news. I have been looking for dark-matter particles for more than 15 years. I’m 42. So most of my colleagues, my age, we are kind of going through a midlife crisis.” He laughed. “When we get together and we drink enough beer, we start howling at the moon.”

Although many scientists say that the existence of the axion will be proved or disproved within the next 10 years — as a result of work at Lawrence Livermore National Laboratory — the detection of a neutralino one way or the other is much less certain. A negative result from an experiment might mean only that theorists haven’t thought hard enough or that observers haven’t looked deep enough. “It could very well be that Mother Nature has decided that the neutralino is way down there,” Collar said, pointing not to a graph that he taped up in his office but to a point below the sheet of paper itself, at the blank wall. “If that is the case,” he went on to say, “we should retreat and worship Mother Nature. These particles maybe exist, but we will not see them, our sons will not see them and their sons won’t see them.”

Crafty_Dog:
(Page 4 of 6)

The challenge with dark energy, as opposed to dark matter, is even more difficult. Dark energy is whatever it is that’s making the expansion of the universe accelerate, but, for instance, does it change over time and space? If so, then cosmologists have a name for it: quintessence. Does it not change? In that case, they’ll call it the cosmological constant, a version of the mathematical fudge factor that Einstein originally inserted into the equations for relativity to explain why the universe had neither expanded nor contracted itself out of existence.

After the discovery of dark energy, Perlmutter concluded that the next generation of dark-energy telescopes would have to include a space-based observatory. But the search for financing for such an ambitious project can require as much forbearance as the search for dark energy itself. “I don’t think I’ve ever seen as much of Washington as I have in the last few years,” he says, sighing. Even if his Supernova Acceleration Probe didn’t now face competition from several other proposals for federal financing (including, perhaps inevitably, one involving his old rival Riess), delays have prevented it from being ready to launch until at least the middle of the next decade. “Ten years from now,” says Josh Frieman of the University of Chicago, “when we’re talking about spending on the order of a billion dollars to put something up in space — which I think we should do — you’re getting into that class where you’re spending real money.”

Even some cosmologists have begun to express reservations. At a conference at Durham University in England last summer, a “whither cosmology?” panel featuring some of the field’s most prominent names questioned the wisdom of concentrating so much money and manpower on one problem. They pointed to what happened when the government-sponsored Dark Energy Task Force solicited proposals for experiments a couple of years ago. The task force was expecting a dozen, according to one member. They got three dozen. Cosmology was choosing a “risky and not very cost-effective way of moving forward,” one Durham panelist told me later, summarizing the sentiment he heard there.

But even if somebody were to figure out whether or not dark energy changes across time and space, astronomers still wouldn’t know what dark energy itself is. “The term doesn’t mean anything,” said David Schlegel of Lawrence Berkeley National Laboratory this past fall. “It might not be dark. It might not be energy. The whole name is a placeholder. It’s a placeholder for the description that there’s something funny that was discovered eight years ago now that we don’t understand.” Not that theorists haven’t been trying. “It’s just nonstop,” Perlmutter told me. “There’s article after article after article.” He likes to begin public talks with a PowerPoint illustration: papers on dark energy piling up, one on top of the next, until the on-screen stack ascends into the dozens. All the more reason not to put all of cosmology’s eggs into one research basket, argued the Durham panelists. As one summarized the situation, “We don’t even have a hypothesis to test.”

Michael Turner won’t hear of it. “This is one of these godsend problems!” he says. “If you’re a scientist, you’d like to be around when there’s a great problem to work on and solve. The solution is not obvious, and you could imagine it being solved tomorrow, you could imagine it taking another 10 years or you could imagine it taking another 200 years.”

But you could also imagine it taking forever.

“Time to get serious.” The PowerPoint slide, teal letters popping off a black background, stared back at a hotel ballroom full of cosmologists. They gathered in Chicago last winter for a “New Views of the Universe” conference, and Sean Carroll, then at the University of Chicago, had taken it upon himself to give his theorist colleagues their marching orders.

“There was a heyday for talking out all sorts of crazy ideas,” Carroll, now at Caltech, recently explained. That heyday would have been the heady, post-1998 period when Michael Turner might stand up at a conference and turn to anyone voicing caution and say, “Can’t we be exuberant for a while?” But now has come the metaphorical morning after, and with it a sobering realization: Maybe the universe isn’t simple enough for dummies like us humans. Maybe it’s not just our powers of perception that aren’t up to the task but also our powers of conception. Extraordinary claims like the dawn of a new universe might require extraordinary evidence, but what if that evidence has to be literally beyond the ordinary? Astronomers now realize that dark matter probably involves matter that is nonbaryonic. And whatever it is that dark energy involves, we know it’s not “normal,” either. In that case, maybe this next round of evidence will have to be not only beyond anything we know but also beyond anything we know how to know.

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That possibility always gnaws at scientists — what Perlmutter calls “that sense of tentativeness, that we have gotten so far based on so little.” Cosmologists in particular have had to confront that possibility throughout the birth of their science. “At various times in the past 20 years it could have gotten to the point where there was no opportunity for advance,” Frieman says. What if, for instance, researchers couldn’t repeat the 1963 Bell Labs detection of the supposed echo from the big bang? Smoot and John C. Mather of NASA (who shared the Nobel in Physics with Smoot) designed the Cosmic Background Explorer satellite telescope to do just that. COBE looked for extremely subtle differences in temperature throughout all of space that carry the imprint of the universe when it was less than a second old. And in 1992, COBE found them: in effect, the quantum fluctuations that 13.7 billion years later would coalesce into a universe that is 22 percent dark matter, 74 percent dark energy and 4 percent the stuff of us.

And if the right ripples hadn’t shown up? As Frieman puts it: “You just would have thrown up your hands and said, ‘My God, we’ve got to go back to the drawing board!’ What’s remarkable to me is that so far that hasn’t happpened.”

Yet in a way it has. In the observation-and-theory, call-and-response system of investigating nature that scientists have refined over the past 400 years, the dark side of the universe represents a disruption. General relativity helped explain the observations of the expanding universe, which led to the idea of the big bang, which anticipated the observations of the cosmic-microwave background, which led to the revival of Einstein’s cosmological constant, which anticipated the observations of supernovae, which led to dark energy. And dark energy is ... ?

The difficulty in answering that question has led some cosmologists to ask an even deeper question: Does dark energy even exist? Or is it perhaps an inference too far? Cosmologists have another saying they like to cite: “You get to invoke the tooth fairy only once,” meaning dark matter, “but now we have to invoke the tooth fairy twice,” meaning dark energy.

One of the most compelling arguments that cosmologists have for the existence of dark energy (whatever it is) is that unlike earlier inferences that physicists eventually had to abandon — the ether that 19th-century physicists thought pervaded space, for instance — this inference makes mathematical sense. Take Perlmutter’s and Riess’s observations of supernovae, apply one cornerstone of 20th-century physics, general relativity, and you have a universe that does indeed consist of .26 matter, dark or otherwise, and .74 something that accelerates the expansion. Yet in another way, dark energy doesn’t add up. Take the observations of supernovae, apply the other cornerstone of 20th-century physics, quantum theory, and you get gibberish — you get an answer 120 orders of magnitude larger than .74.

Which doesn’t mean that dark energy is the ether of our age. But it does mean that its implications extend beyond cosmology to a problem Einstein spent the last 30 years of his life trying to reconcile: how to unify his new physics of the very large (general relativity) with the new physics of the very small (quantum mechanics). What makes the two incompatible — where the physics breaks down — is gravity.

In physics, gravity is the ur-inference. Even Newton admitted that he was making it up as he went along. That a force of attraction might exist between two distant objects, he once wrote in a letter, is “so great an Absurdity that I believe no Man who has in philosophical Matters a competent Faculty of thinking can ever fall into it.” Yet fall into it we all do on a daily basis, and physicists are no exception. “I don’t think we really understand what gravity is,” Vera Rubin says. “So in some sense we’re doing an awful lot on something we don’t know much about.”

It hasn’t escaped the notice of astronomers that both dark matter and dark energy involve gravity. Early this year 50 physicists gathered for a “Rethinking Gravity” conference at the University of Arizona to discuss variations on general relativity. “So far, Einstein is coming through with flying colors,” says Sean Carroll, who was one of the gravity-defying participants. “He’s always smarter than you think he was.”

But he’s not necessarily inviolate. “We’ve never tested gravity across the whole universe before,” Riess pointed out during a news conference last year. “It may be that there’s not really dark energy, that that’s a figment of our misperception about gravity, that gravity actually changes the way it operates on long ranges.”

The only way out, cosmologists and particle physicists agree, would be a “new physics” — a reconciliation of general relativity and quantum mechanics. “Understanding dark energy,” Riess says, “seems to really require understanding and using both of those theories at the same time.”

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“It’s been so hard that we’re even willing to consider listening to string theorists,” Perlmutter says, referring to work that posits numerous dimensions beyond the traditional (one of time and three of space). “They’re at least providing a language in which you can talk about both things at the same time.”

According to quantum theory, particles can pop into and out of existence. In that case, maybe the universe itself was born in one such quantum pop. And if one universe can pop into existence, then why not many universes? String theorists say that number could be 10 raised to the power of 500. Those are 10-with-500-zeros universes, give or take. In which case, our universe would just happen to be the one with an energy density of .74, a condition suitable for the existence of creatures that can contemplate their hyper-Copernican existence.

And this is just one of a number of theories that have been popping into existence, quantum-particle-like, in the past few years: parallel universes, intersecting universes or, in the case of Stephen Hawking and Thomas Hertog just last summer, a superposition of universes. But what evidence — extraordinary or otherwise — can anyone offer for such claims? The challenge is to devise an experiment that would do for a new physics what COBE did for the big bang. Predictions in string theory, as in the 10-to-the-power-of-500-universes hypothesis, depend on the existence of extra dimensions, a stipulation that just might put the burden back on particle physics — specifically, the hope that evidence of extra dimensions will emerge in the Large Hadron Collider, or perhaps in its proposed successor, the International Linear Collider, which might come online sometime around 2020, or maybe in the supercollider after that, if the industrial nations of 2030 decide they can afford it.

“You want your mind to be boggled,” Perlmutter says. “That is a pleasure in and of itself. And it’s more a pleasure if it’s boggled by something that you can then demonstrate is really, really true.”

And if you can’t demonstrate that it’s really, really true?

“If the brilliant idea doesn’t come along,” Riess says, “then we will say dark energy has exactly these properties, it acts exactly like this. And then” — a shrug — “we will put it in a box.” And there it will remain, residing perhaps not far from the box labeled “Dark Matter,” and the two of them bookending the biggest box of them all, “Gravity,” to await a future Newton or Einstein to open — or not.

ccp:
I was watching the
"Science" channel on cable the other night.  They had a show on supermassive black holes.  I didn't realize that present theory holds that there is a black hole in every galaxy and is in some way related to the clustering of the stars in that galaxy.  It is also theorized that quasars are also related to supermassive black holes.

I remember in my astronomy classes in the 70's (ugh!) that quasars were the farthests objects in the universe and there was absolutely no explanation as to what they were.  A lot of discovery has happened since then.  A lot of theories formulated.

Yet every time I read about space I am left with this empty feeling.   I feel like we will never be able to understand "where it all began".   It seems unanswerable.  It seems incomprehensible.  Should this thread be headed under religion or God?   But to me the concept of God doesn't really answer the great questions since the beginning of man.   But it is more comforting.

This link is not to the particular show but to another space site which came up today on a news link:

http://www.space.com/bestimg/index.php?guid=4499b3474b769&cat=strangest

 huh

Crafty_Dog:
The Shadow Goes
By MARGARET WERTHEIM
Published: June 20, 2007
NY Times


ON Thursday, on the summer solstice, the Sun will celebrate the year’s lazy months by resting on the horizon. The word solstice derives from the Latin “sol” (sun) and “sistere” (to stand still). The day marks the sun’s highest point in the sky, the moment when our shadows shrink to their shortest length of the year. How strange to think that these mundane friends, our ever-present familiars, can actually go faster than the sun’s rays.

I remarked on this recently to my husband as we sat on the porch with our shadows pooling by our chairs. Nothing can go faster than light, he insisted, expressing what is surely the most widely known law of physics, ingrained into us by a thousand “Nova” programs.

That is the point, I explained: Nothing can go faster than light. A shadow isn’t a thing. It’s a non-thing. It’s the absence of light.

Special relativity dictates that we cannot move anything more quickly than the particles of light known as photons, but no law says you can’t do nothing faster than light. Physicists have known this for a long time, even if they generally do not mention it on PBS documentaries.

My husband looked troubled, as did my sister and some friends I regaled with the story that evening. Like the warp drive on “Star Trek,” faster-than-light travel is supposed to be a science-fiction fantasy. Isn’t it?

They are right about the travel: According to relativity, no physical substance can exceed the speed of light because it would take infinite energy to accelerate anything to such a velocity.

Yet the laws of physics pertain only to that which is. That which isn’t is not bound by relativity’s restraint. From the point of view of relativity, a shadow (having no mass) is a non-thing, an existential void.

It’s quite easy to conjure up a faster-than-light shadow, at least in theory. Build a great klieg light, a superstrong version of the ones set up at the Academy Awards. Now paste a piece of black paper onto the klieg’s glass so there is a shadow in the middle of the beam, like the signal used to summon Batman. And we are going to mount our light in space and broadcast the Bat-call to the cosmos.

The key to our trick is to rotate the klieg. As the light turns, the bat shadow sweeps across the sky. Round and round it goes, projecting into the void. Just as the rim of a bicycle wheel moves faster than its hub, so too, away from the source our bat shadow will fly faster and faster, a consequence of the geometry that guarantees the rim of a really big wheel moves faster than a co-rotating small wheel.

At a great enough distance from the source, our shadow bat will go so fast it will exceed the speed of light. This does not violate relativity because a shadow carries no energy. Literally nothing is transferred. Our shadow bat can go 10 times the speed of light or 100 times faster without breaking any of physics’ sacred rules.

My sister leapt to the heart of this apparent paradox: Why isn’t the light itself traveling faster than the speed of light? Isn’t it also rotating in space? Actually, no. The bulbs that produce the light are spinning, but the light particles leave the source at 186,000 miles a second, the vaunted “speed of light.” Once emitted, the photons continue to travel at this speed directly away from the source. Only the shadow revolves around the great circle. The critical point is that no object, no substance, defies light.

My husband was right to object that you’d need one spectacular klieg to produce a detectable shadow thousands of miles out in space. Still, the theory is sound.

The anthropologist Mary Douglas noted that all systems of categorizing break down somewhere, unable to incorporate certain forms. By standing beyond relativity’s injunction, shadows suggest the limits of all classification schemes, a tension that even modern science cannot completely resolve.

In the terms recognized by relativity, shadows are non-things. Yet before the invention of clocks, shadows were the most important means for telling time. Weightless and without energy, shadows can nonetheless convey information — though they cannot, despite our giant klieg, be used for faster-than-light communication. That’s because the shadow’s location cannot be detected until the light, moving at its ponderous relativistic pace, arrives.

“Here there be monsters,” said the medieval maps, signaling the limits of reason’s reach. As a map of being, physics is flanked by the monsters of non-being whose outlines we glimpse in the paradoxes of quantum mechanics and in the zooming arc of a shadow bat going faster than light.

In Christian theology we are told, “God is that which nothing is greater than.” The scientific corollary might be, “Light is that which nothing is faster than” — a statement true both in spirit and fact.

Margaret Wertheim, the director of the Institute for Figuring, a science and mathematics education organization, is writing a book on physics and the imagination.

Body-by-Guinness:
For those needing a new unreasoned fear to latch on to. . . .

Aug 3, 2007
Fears over factoids

Recent TV programmes have claimed that the Earth could be destroyed by black holes created in particle accelerators and that helium-3 from the Moon could be used for fusion energy. Frank Close warns that these "factoids" must be stamped out before they become accepted as facts

Did you know that when the Large Hadron Collider (LHC) comes online at CERN next spring, it could end up creating mini black holes that destroy the Earth? This is not something from a Dan Brown novel, but from a TV documentary broadcast as part of the BBC's Horizon series in the UK on 1 May – a programme that has been running for 40 years and is supposedly the flagship of TV science in the country. Although the documentary itself was fairly measured, the producers began the programme with the black-hole claim and used it in their publicity for the show.


Unnecessary drama
Physicists who recall superb Horizon documentaries of the past – for example, on the discovery of the W and Z bosons – will have been disappointed that such a marvellous project as the LHC should have been sensationalized in this way. It was disheartening that the programme makers felt the need to rehash these unnecessary concerns over black holes being produced in particle accelerators, which physicists had already dismissed before the Relativistic Heavy Ion Collider (RHIC) came online at the Brookhaven National Laboratory in 2000 (Physics World July 2000 pp19–20, print edition only).

Meanwhile, another Horizon documentary, broadcast on 10 April, claimed that one reason for sending humans to the Moon is so that we can mine it for helium-3 as a fuel for fusion power back on Earth. The need to bring helium-3 back from the Moon has even been briefly referred to in Physics World (May 2007 pp12–13, print edition only) and, more worryingly, has been presented to US congressional committees, including the Science and Technology Committee of the House of Representatives in 2004.

As a particle physicist, I am of course interested in the LHC; and as the chair of a working group set up by the British National Space Centre to look into the future of UK space science – including the possibility of humans returning to the Moon – I am also intrigued by the helium-3 story. Both of the claims bother me and, on investigation, each is revealed as an example of what I call "factoid science" – myths of dubious provenance that propagate, become received wisdom and could even influence policy. So what is the reality and what can physicists do to correct such mis-information?

Strangelet statistics
The story of the LHC as an Armageddon machine would be laughable were it not so serious. Aficionados of Dan Brown – whose novel Angels and Demons was set partly at CERN – might believe that the Geneva lab produces antimatter capable of making weapons of mass destruction. But I did not expect to find similarly outlandish statements used to promote Horizon. As the programme's website puts it: "Some scientists argue that during a 10-year spell of operation there is a 1 in 50 million chance that experiments like the LHC could cause a catastrophe of epic proportions." The site then invites the public to take part in a poll on whether the LHC should be turned on or not, based on this "probability".

While the LHC will create the most energetic collisions ever seen on Earth, cosmic rays at these and even higher energies have been bombarding our and other planets for billions of years without mishap. When I asked the producers of Horizon where they had obtained the 1-in-50-million statistic, I was told it had been taken from a "reliable source": Our Final Century by Cambridge University cosmologist Martin Rees. But when I read his book, it became clear that the programme's research had sadly been incomplete. On page 124, Rees discusses a paper published in 1999 by CERN theorists Arnon Dar, Alvaro de Rújula and Ulrich Heinz that uses the fact that the Earth and the cosmos have survived for several billion years to estimate the probability of colliders producing hypothetical particles called "strangelets" that might destroy our planet (1999 Phys. Lett. B 470 142).

Rees fairly describes their conclusions as follows: "If the experiment were run for 10 years, the risk of catastrophe was no more than 1 in 50 million." In other words, the chance of disaster is one in at least 50 million (as no disaster has occurred); this is rather different from saying, as Horizon does, that there is a "1 in 50 million" probability of a catastrophe happening from the moment the LHC switches on.

Moreover, when Dar and colleagues wrote their 1999 paper, a committee of eminent physicists appointed by the Brookhaven lab was also investigating if RHIC could produce strangelets (arXiv:hep-ph/ 9910333v3). That study used not just information from cosmology but also data from collisions between heavy ions (albeit at lower energies than RHIC would obtain) to show that the chances of catastrophe are at least one part in 1019.

Furthermore, these figures refer specifically to strangelets being produced at RHIC, as Rees makes clear, and have nothing to do with the question of whether we should risk creating black holes. Indeed, why does Horizon talk about black holes at all? The only reason can be that a theory does exist that posits that mini black holes could be produced in a collider. But if one mentions this theory, then one must include the whole of it, which clearly states that mini black holes pose no hazard whatsoever because they do not grow but evaporate and die.

As if any more evidence was needed that colliders are safe, CERN also set up an "LHC safety-study group" to see if its new collider could create black holes or strangelets. It concluded – in an official CERN report published in 2003 (CERN-2003-001) – that there is "no basis for any conceivable threat" of either eventuality, which is as near as science can get to saying zero. Unfortunately, the Horizon programme made no mention of these serious and time-consuming enquiries even though CERN's press office gave the programme's researchers a copy of the lab's 2003 report. Instead, the public has been led to believe that scientists are prepared to embark on experiments that could spell the end of the planet.

Helium errors
Let me now turn to the helium-3 factoid. At most fusion experiments, such as the Joint European Torus (JET) in the UK, a fuel of deuterium and tritium nuclei is converted in a tokomak into helium-4 and a neutron, thereby releasing energy in the process. No helium-3 is involved, so where does the myth come from? Enter "helium-3 fusion" into Google and you will find numerous websites pointing out that the neutron produced in deuterium–tritium fusion makes the walls of the tokomak radioactive, but that fusion could be "clean" if only we reacted deuterium with helium-3 to produce helium-4 and a proton.

Given that the amount of helium-3 available on Earth is trifling, it has been proposed that we should go to the Moon to mine the isotope, which is produced in the Sun and might be blown onto the lunar surface via the solar wind. Apart from not even knowing for certain if there is any helium-3 on the Moon, there are two main problems with this idea – one obvious and one intriguingly subtle. The first problem is that, in a tokomak, deuterium reacts up to 100 times more slowly with helium-3 than it does with tritium. This is because fusion has to overcome the electrical repulsion between the protons in the fuel, which is much higher for deuterium– helium-3 reactions (the nuclei have one and two protons, respectively) than it is for deuterium– tritium reactions (one proton each).

Clearly, deuterium–helium-3 is a poor fusion process, but the irony is much greater as I shall now reveal. A tokomak is not like a particle accelerator where counter-rotating beams of deuterium and helium-3 collide and fuse. Instead, all of the nuclei in the fuel mingle together, which means that two deuterium nuclei can rapidly fuse to give a tritium nucleus and proton. The tritium can now fuse with the deuterium – again much faster than the deuterium can with helium-3 – to yield helium-4 and a neutron.

So by bringing helium-3 from the Moon, all we will end up doing is create a deuterium– tritium fusion machine, which is the very thing the helium aficionados wanted to avoid! Undeterred, some of these people even suggest that two helium-3 nuclei could be made to fuse with each other to produce deuterium, an alpha particle and energy. Unfortunately, this reaction occurs even more slowly than deuterium–tritium fusion and the fuel would have to be heated to impractically high temperatures that would be beyond the reach of a tokomak. And as not even the upcoming International Thermonuclear Experimental Reactor (ITER) will be able to generate electricity from the latter reaction, the lunar-helium-3 story – like the LHC as an Armageddon machine – is, to my mind, moonshine.

Rising pressure
Does any of this matter beyond raising the blood pressure of some physicists? All publicity is good publicity, some might say. But I believe we should all be concerned. The LHC factoid has now been repeated in the New Yorker and in various reviews of the Horizon documentary. Even some nonphysics colleagues are asking me to explain what it is all about. If Horizon claims to be the flagship TV science series on which the public rely to form their opinions, I would hope that their researchers do their research, and that the editors then take due account of it.

The factoids about mining the Moon for fusion fuel and of the LHC Armageddon make a cautionary tale. A decade from now it is possible that committees of well-informed scientists and rather less-well-informed politicians, with public opinion weighing on their minds, will be deciding on our involvement in mega-projects such as the next huge accelerator, human space exploration, or even a post-ITER commercial fusion plant.

Decision making driven by public opinion that is influenced by factoids already has a dire history in the bio-medical arena: the controversy over whether to give children a combined immunization against measles, mumps and rubella (MMR) being the most recent example. My advice is that if you see an error in the media, speak out, write to the editors and try to get corrections made. It is an opportunity to get good science in the news.

About the author
Frank Close is a theoretical physicist at the University of Oxford, UK

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