From: LARRY KLAES (ljk4_at_msn.com)
Date: Tue Feb 17 2004 - 06:54:59 PST
>From Space, a New View of Doomsday
>
>February 17, 2004
> By DENNIS OVERBYE
>
>
>
>
>
>Once upon a time, if you wanted to talk about the end of
>the universe you had a choice, as Robert Frost put it,
>between fire and ice.
>
>Either the universe would collapse under its own weight one
>day, in a fiery "big crunch," or the galaxies, now flying
>outward from each other, would go on coasting outward
>forever, forever slowing, but never stopping while the
>cosmos grew darker and darker, colder and colder, as the
>stars gradually burned out like tired bulbs.
>
>Now there is the Big Rip.
>
>Recent astronomical
>measurements, scientists say, cannot rule out the
>possibility that in a few billion years a mysterious force
>permeating space-time will be strong enough to blow
>everything apart, shred rocks, animals, molecules and
>finally even atoms in a last seemingly mad instant of
>cosmic self-abnegation.
>
>"In some ways it sounds more like science fiction than
>fact," said Dr. Robert Caldwell, a Dartmouth physicist who
>described this apocalyptic possibility in a paper with Dr.
>Marc Kamionkowski and Dr. Nevin Weinberg, from the
>California Institute of Technology, last year.
>
>The Big Rip is only one of a constellation of doomsday
>possibilities resulting from the discovery by two teams of
>astronomers six years ago that a mysterious force called
>dark energy seems to be wrenching the universe apart.
>
>Instead of slowing down from cosmic gravity, as
>cosmologists had presumed for a century, the galaxies
>started speeding up about five billion years ago, like a
>driver hitting the gas pedal after passing a tollbooth.
>
>Dark energy sounded crazy at the time, but in the
>intervening years a cascade of observations have
>strengthened the case that something truly weird is going
>on in the sky. It has a name, but that belies the fact that
>nobody really knows what dark energy is.
>
>In six years it has become one of the central and
>apparently unavoidable features of the cosmos, the surprise
>question mark at the top of everybody's list, undermining
>what physicists presumed they understood about space, time,
>gravity and the future of the universe.
>
>"In five years we've gone from saying it looks like a
>mistake to something that everyone is claiming evidence
>for," said Dr. Robert Kirshner of the Harvard-Smithsonian
>Center for Astrophysics, who was part of the original
>discovery.
>
>Dr. Saul Perlmutter, a physicist from the Lawrence Berkeley
>Laboratory who was a leader of one of the 1998 teams, said
>he thought astronomers had even gotten comfortable with the
>idea - "or as comfortable as you can be with something as
>bizarre as dark energy."
>
>Now, armies of astronomers are fanning out into the night,
>enlisting telescopes, large and small, from Chile to Hawaii
>to Arizona to outer space, in a quest to take the measure
>of dark energy by tracing the history of the universe with
>unprecedented precision.
>
>Some of them are following the trail blazed by the first
>two groups six years ago, searching out a kind of exploding
>star known as Type 1a the supernova. Those stars serve as
>markers in space, enabling scientists to plumb the size of
>the universe and how it grew over time. Where the first
>groups based their conclusions on observing a few dozen
>supernovas, the new efforts intend to harvest hundreds or
>thousands of them.
>
>Others are seeking to gain leverage by investigating how
>the antigravitational force of dark energy has retarded the
>growth of conglomerations of matter like galaxies. In one
>ambitious project, a team led by Dr. John Carlstrom of the
>University of Chicago is building an array of radio
>telescopes at the South Pole to count and study clusters of
>galaxies deep in space-time. Others are already probing the
>internal dynamics of galaxies by the thousands, or building
>giant cameras that use the light-bending powers of gravity
>itself as lenses to map invisible dark matter in space and
>compile a growth chart of cosmic structures.
>
>Dr. Anthony Tyson, now at Bell Laboratories, is head of a
>project to build a "dark matter telescope" known as the
>Large Synoptic Survey Telescope. "High energy physicists
>have been marching into our project," he said. "This is not
>just another telescope. It's a physics experiment, like a
>particle accelerator."
>
>After all, the fate of the universe is at stake. If the
>dark energy is virulent enough, then that fate "is quite
>fantastic and completely different than the possibilities
>previously discussed," Dr. Caldwell and his colleagues
>wrote last year.
>
>The Search for One Number
>
>The idea of an antigravitational force pervading the cosmos
>does sound like science fiction, but theorists have long
>known that certain energy fields would exert negative
>pressure that would in turn, according to Einstein's
>equations, produce negative gravity. Indeed, some kind of
>brief and violent antigravitational boost, called
>inflation, is thought by theorists to have fueled the Big
>Bang.
>
>As they try to figure out how this strange behavior could
>be happening to the universe today, astronomers say the
>ultimate prize from all the new observing projects could be
>as simple as a single number.
>
>That number, known as w, is the ratio between the pressure
>and density of dark energy. Knowing this number and how it
>changes with time - if it does - might help scientists pick
>through different explanations of dark energy and thus the
>future of the universe - "whether it's gonna lead to a Big
>Rip, a Big Collapse or just a Big Fizzle," as Dr. Adam
>Riess of the Space Telescope Science Institute in Baltimore
>put it in an e-mail message.
>
>One possible explanation for dark energy, perhaps the
>sentimental favorite among astronomers, is a force known as
>the cosmological constant, caused by the energy residing in
>empty space. It was first postulated back by Einstein in
>1917. A universe under its influence would accelerate
>forever.
>
>While the density of energy in space would remain the same
>over the eons, as the universe grows there would be more
>space and thus more repulsion. Within a few billion years,
>most galaxies would be moving away from our own faster than
>the speed of light and so would disappear from the sky; the
>edge of the observable universe would shrink around our
>descendants like a black hole.
>
>But attempts to calculate the cosmological constant using
>the most high-powered modern theories of gravity and
>particle physics result in numbers 1060 times as great as
>the dark energy astronomers have observed - big enough, in
>fact, to have blown the universe apart in the first second,
>long before even atoms had time for form. Theorists admit
>they are at a loss. Perhaps, some of them now say,
>Einstein's theory of gravity, the general theory of
>relativity, needs to be modified.
>
>Another possibility comes from string theory, the putative
>theory of everything, which allows that space could be
>laced with other energy fields, associated with particles
>or forces as yet undiscovered. Those fields, collectively
>called quintessence, could have an antigravity effect.
>Quintessence could change with time - for example, getting
>weaker and eventually disappearing as the universe expanded
>and diluted the field - or could even change from a
>repulsive force to an attractive one, which could set off a
>big crunch.
>
>Recently, in a variation on the quintessence idea, Dr.
>Leonard Parker of the University of Wisconsin at Milwaukee
>and various colleagues, including Dr. Caldwell, have
>suggested that the field associated with some unknown very
>light particle could get tangled up with gravity and cause
>the universe to accelerate. That would alter Einstein's
>equations, said Dr. Caldwell. He added, "Our calculations
>show, however, that galaxies reside in a bubble of
>old-fashioned Einstein gravity, whereas gravity has changed
>outside and between galaxies."
>
>A Weird Idea Gets Weirder
>
>But the strangest notion is what Dr. Caldwell has called
>phantom energy, the dark energy that could lead to the Big
>Rip.
>
>"It's weird negative pressure," said Dr. Lawrence M.
>Krauss, an astrophysicist at Case Western Reserve
>University in Cleveland.
>
>While the density of the energy in Einstein's cosmological
>constant stays the same as the universe expands, the
>density of phantom energy would go up and up, eventually
>becoming infinite. Such would be the case if the parameter
>w turned out to be less than minus 1, say physicists, who
>admit they are stunned by the possibility and until
>recently simply refused to consider it.
>
>"It crosses a boundary of good taste," Dr. Caldwell said,
>calling phantom energy "bad news stuff." Phantom energy
>violates physicists' intuitions about how the universe
>should behave. A chunk of it could be used to prop open
>wormholes in space and time - and thus create time
>machines, for example.
>
>"It could lead to such bizarre effects as negative kinetic
>energy," Dr. Krauss said. As a result, objects like atoms
>would be able to lose energy by speeding up.
>
>Nevertheless, a recent analysis by Dr. Caldwell and his
>Dartmouth colleague Dr. Michael Doran of the supernova
>measurements to date, combined with other cosmological
>data, suggest that w could lie anywhere from minus 0.8 to
>minus 1.25, leaving open the possibility of phantom energy.
>The cosmological constant would give a value of minus 1.0,
>and anything higher would be a sign of quintessence.
>
>Dr. Kirshner said phantom energy had been dismissed as "too
>strange" when his group was doing calculations of dark
>energy back in 1998. In retrospect, he said, that was not
>the right thing to do.
>
>"It sounds wacky," he said, referring to phantom energy,
>"but I think we're in a situation where we're going to need
>a really new idea. We're in trouble; the way out is going
>to be new imaginative things. It might be our ideas are not
>wild enough, they don't question fundamentals enough."
>
>Dr. Chris Pritchet of the University of Victoria, who is
>part of a collaboration using the Canada-France-Hawaii
>telescope on Mauna Kea to search for supernovas, said, "In
>many ways phantom energy is unphysical, but we're not
>ruling it out."
>
>Counting Down to the Big Rip
>
>This version of doomsday would start slowly. Then, billions
>of years from now, as phantom energy increased its push and
>the cosmic expansion accelerated, more and more galaxies
>would start to disappear from the sky as their speeds
>reached the speed of light.
>
>But things would not stop there. Some billions of years
>from now, depending on the exact value of w, the phantom
>force from the phantom energy will be enough to overcome
>gravity and break up clusters of galaxies. That will happen
>about a billion years before the Big Rip itself.
>
>After that the apocalypse speeds up. About 900 million
>years later, about 60 million years before the end, our own
>Milky Way galaxy will be torn apart. Three months before
>the rip, the solar system will fly apart. The Earth will
>explode when there is half an hour left on the cosmic
>clock.
>
>The last item on Dr. Caldwell's doomsday agenda is the
>dissolution of atoms, 10-19, a tenth of a billionth of a
>billionth of a second before the Big Rip ends everything.
>
>"After the rip is like before the Big Bang," Dr. Caldwell
>said. "General relativity says: "The end. Time can't
>evolve."
>
>The cosmos probably still has a lot of life in it,
>according to recent calculations by Dr. Krauss. Based on
>the current age of the universe, some 14 billion years, and
>other data, w cannot be less than about minus 1.2, he said,
>putting the Big Rip about 55 billion years in the future.
>
>"It can't be very phantom," Dr. Krauss said.
>
>The dark
>energy surveys now under way hope to be able to measure w
>to an accuracy of 5 percent, but even if that can be done,
>it may not be sufficient to eliminate the nightmare of
>phantom energy.
>
>"It's hard to measure anything in astronomy to a few
>percent," said Dr. Sandra Faber of the University of
>California at Santa Cruz, who directs one of the dark
>energy surveys. Variations in the atmosphere and gaps in
>astronomers' understanding of supernova explosions add
>uncertainty to the dark energy measurements.
>
>As a result some astronomers fear that the results may
>leave us on the razor's edge unable to decide between a
>cosmological constant and the other possibilities -
>quintessence or a Big Rip. Cosmologists could then be stuck
>with a "standard model" of the universe that fits all the
>data, but which they have no hope of understanding.
>
>If the parameter w comes out to be something other than
>minus 1, Dr. Krauss said, it will at least give some
>direction to physicists.
>
>One encouraging sign - "a tantalizing bit of hope," in Dr.
>Krauss's words - that the data will distinguish between a
>cosmological constant and the other possibilities came last
>fall when Dr. Riess, of Baltimore, reported, based on new
>observations of distant supernovas, that the "cosmic jerk"
>when dark energy took over the universe happened only five
>billion years ago.
>
>In the standard cosmological constant model, said Dr.
>Riess, the turnaround should have come one or two billion
>years earlier.
>
>Dr. Tyson was more sanguine. "Dark energy is crazy, right?"
>he said. "It's going to be exciting no matter what we
>find."
>
>Dark Future for Dark Energy?
>
>The work of the dark energy hunters has been complicated by
>the impending loss of the Hubble Space Telescope, which can
>see far enough out in space and time to measure how and if
>the dark energy parameter w is changing over the eons.
>
>Last month, citing safety, NASA canceled all future shuttle
>maintenance missions to the telescope, dooming it to die in
>orbit, probably within three years, according to
>astronomers. "The Hubble shutdown will slow us all down,"
>Dr. Perlmutter said.
>
>At the same time, as a result of the agency's
>presidentially ordered shift toward the Moon and Mars,
>plans for a special satellite that was to have been jointly
>sponsored by NASA and the Department of Energy have at
>least temporarily disappeared from NASA's five-year budget
>plan.
>
>Dr. Perlmutter, who has devoted much of his time in the
>last six years to the proposed satellite experiment, said
>he hoped that a way would be found to keep the project on
>track to be launched in the next decade.
>
>"When you have the most exciting scientific problem of the
>day, you don't want to wait around," he said.
>
>http://www.nytimes.com/2004/02/17/science/space/17DARK.html?ex=1078023766&ei=1&en=ba66bb02e261b870
>
>
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