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The dark side of the universe

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Author Topic: The dark side of the universe  (Read 61 times)
Deborah Valkenburg
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« on: May 04, 2008, 11:03:11 pm »

The dark side of the universe
We can see about 4 per cent of the cosmos. These guys are looking for the other 96

Oct 23, 2005 01:00 AM
Peter Calamai
National Science Reporter
Unusual people and even more unusual ideas jostle for space in the modest lounge/lunch room on the 12th floor of the McLennan Building at the University of Toronto's downtown campus.

Balancing paper plates of Jamaican chicken and salad are two dozen or so individuals, mostly male in their mid-20s to mid-30s and mostly somewhat scruffy. A few chat about commonplace matters, like soaring gas prices and the rain forecast that scuppered a planned September outing to Toronto Island for this picnic.

But most of the conversation features words like cosmic web, dark energy, first light, baryons, superstrings, dark matter, microwave background, weak lensing, cosmological constant, power spectrums and anthropic, as well as numbers that are very, very big or very, very small.

Welcome to The House that Einstein Built, the cramped, frenetic and very successful Canadian Institute for Theoretical Astrophysics or, as the coffee mugs advertise, CITA. Wending through this intellectual feeding frenzy is CITA's director, John Richard ("Dick") Bond, a cherubic cosmologist incapable of speaking for more than a minute without describing some recent development as either exciting, ambitious or spectacular often all three.

Usually the adjectives are justified. The 30 U of T faculty and researchers here at CITA, along with others across the country linked by a virtual network, rank among the most daring Canadian explorers of Einstein's legacy, their minds constantly probing the deepest mysteries of the universe.

"We're in an era of discovery, learning from detailed observations how all the structure of the universe arose," Bond says.

"It doesn't mean that the questions are going to cease. They aren't. They'll get more and more precise, more and more difficult to get the answers for. It's an amazing ride."

At CITA, that ride includes:

using the microwave equivalent of Polaroid sunglasses to probe the universe as a toddler, a mere 270,000 years into its 13.7 billion year existence, so far;

unravelling the structure of the "cosmic web," the name cosmologists have given the pattern of voids and spidery filaments created as gravity tugs matter, both visible and invisible, into clumps;

seeking clues to the expansion of the universe in the largest-ever survey of supernovae, now being carried out by the Canada-France-Hawaii telescope on Mauna Kea;

and using computer simulations of the evolution of the universe to recreate moments like "first light," the instant when the original opaque soup of superheated particles then permeating space cooled enough to become transparent and allow starlight through.

This ride began in 1915 when Albert Einstein unveiled his General Theory of Relativity, with its revolutionary view of gravity as a warping of space and time.

Gravity underpins cosmology, which is the study of the birth, structure and dynamics of the universe. (By contrast, astronomy is the study of celestial bodies, especially stars.)

So, since CITA focuses mainly on cosmological mysteries, senior researcher Lev Kofman can declare confidentially: "You're in the right place for Einstein."

CITA's ride became truly amazing just as it was created in the mid-1980s, with the first of two enigmatic developments that have turned physics, and particularly cosmology, upside down.

Put simply, most scientists now believe that almost 96 per cent of the universe is composed of mysterious ingredients called dark matter and dark energy and their best theories can't explain either.

This means there is much more to the universe than meets the eye. Consider all the stars you see overhead on the darkest night, all those stunning photographs of distant galaxies taken by the Hubble space telescope and from giant scopes perched on mountain tops: all that amounts to about 4 per cent of what's really out there. And science didn't have much of a clue that was the case until a couple of decades ago.

"We all missed it. It's absolutely a scandalous situation," says the 48-year-old Russian-born Kofman in mock horror.

The horror is mock, because dark matter and dark energy are actually good news for many scientists. Their manifold mysteries have sparked a worldwide firestorm of theorizing and experimenting, and also loosened the public purse strings for costly detectors on Earth and out in space.

As well, there's the tantalizing prospect of being among the first to succeed in deciphering the true nature of the universe. Spend time among cosmologists and astrophysicists and you can sniff the Nobel yearnings. Such high stakes help explain why differing theories in the field resemble religious wars, with an explosive mixture of faith and fact.

Many Canadians would be surprised to learn that their country is home to a small cadre who rank in the major leagues of such high-powered cosmology and astrophysics researchers. The United States dominates, as expected, and the U.K. comes second. Yet based on how often scientific papers by researchers living here are cited in other papers, Canada vies with Germany for third.

Among the most highly cited of cosmologists worldwide is the 55-year-old Bond, who seems to exist in a state of perpetual anticipation of yet another scientific upheaval.

"It all looks very robust now," he says. "But one of the exciting things is that maybe it isn't at all what we're thinking. It's just really wide open."

There's the rub. If 96 per cent of the universe is composed of dark matter and dark energy, then ordinary mortals would like to know what that is and how it got there. Yet cosmologists barely finish laying out one explanation before they point out its shortcomings and offer up another.

So here's the current thinking, likely valid only until the next big set of cosmic observations sparks new interpretations.

First, remember that because energy and matter are interchangeable (E = mc{+2}), we're really talking about total matter/energy in the universe. Dark matter is the stuff, so far invisible, whose gravitational attraction stops rapidly rotating galaxies from flying apart. It makes up about 23 per cent of the universe (six times more abundant than ordinary matter) and accounts for more than 90 per cent of the gravity out there

Dark energy supposedly constitutes about 73 per cent of the universe. It is the anti-gravity force, so far undetected, that is causing galaxies in the universe to fly apart faster than originally supposed.

`The biggest blunder of Einstein was to call the cosmological constant the biggest blunder'

Lev Kofman

CITA senior researcher


No one has yet managed to fill a jar with either dark matter or dark energy. But their existence can be inferred from extremely precise observations by spaceborne detectors and telescopes on Earth, including some in which CITA plays an active role.

Both were initially postulated by scientists to account for astronomical observations that existing theory couldn't explain. That's a normal process in science, although usually for fine-tuning an idea rather than accounting for 96 per cent of the universe.

Dark matter had been lurking around the fringes of astrophysics since the 1960s, but it moved into the mainstream in the 1980s as the most appealing explanation of why the Milky Way galaxy holds together in such a tight disc, and why galaxies form clusters across the universe. With typical puckishness, the astronomers dubbed the two leading dark matter candidates WIMPs and MACHOs, for "weakly interacting massive particles" and "massive astronomical compact halo objects."

The science community was still coming to grips with dark matter when, in 1998, astronomers reported that the light from one kind of distant supernova explosion was a lot dimmer than predicted.

The most appealing explanation was that the universe was not only expanding a well established fact but the expansion was speeding up. So these Type-1a supernovae would actually be farther away than originally assumed and therefore dimmer than predicted.

The unknown cause of this accelerated expansion was dubbed dark energy.

In 1917, Alberta Einstein had called it "the cosmological constant." It was a fudge factor he introduced after his calculations based on general relativity produced a universe that was either contracting or expanding, but not stable.

Unfortunately, astronomers of the day insisted the universe was static, based on observations of the only galaxy they knew, the Milky Way. Faced with a clash between his theory and observation, Einstein invented the cosmological constant, a repulsive force that exactly balanced the pull of gravity and made the universe static, essentially by fiat.

When American astronomer Edwin Hubble showed conclusively in 1929 that the universe was, in fact, expanding, Einstein reportedly said the cosmological constant was his "greatest blunder."

Says Kofman, recalling an anonymous bon mot: "The biggest blunder of Einstein was to call the cosmological constant the biggest blunder."

Bond contends that someone else used the words "biggest blunder," not Einstein himself. Both men agree, however, that dark energy, a.k.a. the cosmological constant, is the hottest topic in cosmology right now.

To make matters more interesting, dark energy likely isn't constant, with the anti-gravity pull probably varying throughout time, and maybe even being weaker or stronger in different parts of the universe.

"The way I like to think of it is that it's a measure of one of the greatest, powerful things in physics, but it isn't so easy to explain," Bond says, seated at a desk where any minute he could disappear under an avalanche loosed from teetering paper mountains.

"There is something called the vacuum, which sounds like it's nothing. But in fact the vacuum is totally alive, and that's one of the fundamental aspects of physics, that there is all of this virtual bubbling activity associated with nothing."

After a soft chuckle he continues, "There is apparently an energy associated with that nothing, which is this energy of the vacuum. So calling it a cosmological constant is a bit mundane, when in fact it's such a powerful physical phenomenon."

Not only powerful, but decidedly weird. The dominant idea is that dark energy lurks in the vacuum of space at the quantum level, a bouillabaisse of short-lived particles that pop in and out of existence (Kofman calls them "mosquitoes").

One itsy-bitsy problem with this explanation is that the dark energy predicted by the standard model of particle physics is so intense that all matter would be shredded in an instant. In fact, it's too intense by a factor of 10{+1}{+2}{+0} 10 followed by 119 zeros.

Asked what accounts for this huge difference, Bond replies, "Just our lack of understanding. Somehow the universe has decided that it's not there. This is arguably the biggest puzzle in physics the nature of this vacuum energy and why it's such a low value now."

CITA researchers are bringing an arsenal of cosmological weapons to bear on the dark energy puzzle, starting with the one Stephen Hawking called "the scientific discovery of the century, if not all time" when it was originally announced in April 1992.

A NASA satellite had found the equivalent of a cosmic fossil tiny ripples in the sea of microwave radiation left over from when the universe was about 270,000 years old.

That finding not only provided the ultimate triumph of the Big Bang theory but also nailed the existence back at the dawn of time of gas clouds that would eventually clump together under their own gravity and collapse to form galaxies and stars.

The cosmic fossil discoveries continue today. A successor satellite, called WMAP, is now mapping that cosmic microwave background in even greater detail. So far those measurements have firmly established the age of the universe at 13.7 billion years and also provided the 73-23-4 breakdown for dark energy, dark matter and ordinary matter.

There's more to come, says Bond, tossing an inflated globe splashed with colourful blobs and swirls. The patterns trace fluctuations in the microwave background across the universe as minute as one-hundred-thousandth of a degree Celsius.

"It turns out that, if you had Polaroid glasses, you can also see polarized patterns in this," he says. Even though those polarized signals are a hundred times smaller than the microwave variations, WMAP investigators have recently succeeded in teasing them out.

CITA researchers have also deployed other weapons from the 12th floor of the McLennan Building: the computer simulations of First Light; the supernova survey with the Canada-France-Hawaii telescope; and recording the gravitational tugs on light from distant galaxies as it travels through space-time on its way to Earth.

And underway or in the offing around the world are a whole slew of new experiments to tackle the unanswered questions in Einstein's cosmological legacy, with names like the Large Synoptic Survey Telescope, the Joint Dark Energy Mission, the Planck spacecraft, the Large Hadron Collider, the Gamma Ray Large Area Space Telescope and Cryogenic Dark Matter Search II.

Amidst all this optimism and exuberance, look to Lev Kofman's son for a reality check. Talking to a Grade 5 class at his children's school, Kofman asked if the pupils knew anything about the expanding universe or things like dark energy.

His son Sergei, then 8, replied:

"Daddy, no one knows what dark matter is."
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Skepticism is good, but when you reach a certain level where
you're grasping at straws and making little sense... it's not
called skepticism.  It's called ignorance.

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« Reply #1 on: May 11, 2008, 05:03:09 pm »

I've seen alot of specials and movies on this subject and opinions about dark matter still only makes up about another 20% of the stuff that holds our universe together.

Ofcourse understanding gravity could explain everything if we had a way to see it!

Dark Energy is an interesting side of the argument of what our universe is composed of. I have no ideas about what could increase itself without more being put into it.
Yet the evidence of this is in the way the universe is expanding faster and faster.

« Last Edit: May 11, 2008, 05:10:39 pm by HereForNow » Report Spam   Logged

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