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Postby mends » 01 Dec 2006, 09:19

Just How Precise
Is the Balancing Act
That Maintains Life?
December 1, 2006; Page B1
When you see the long list of everything that has to be just right for atoms, galaxies, planets and life to emerge in the universe, it's hard to avoid the conclusion that the fix was in. If the laws of physics and the fundamental constants of nature were the slightest bit different, the world would not exist, at least in the form we see it.
Such is the premise of the "anthropic principle." It asserts that the values of physical constants, such as the strength of gravity, are what they are because if they had other values there wouldn't be any scientists to marvel at it all.
If that seems like circular reasoning, well, so it seems to many astronomers and physicists. They recognize that nature has properties conducive to life, obviously, but still view the anthropic principle as a feeble answer to an age-old question, namely, whether a universe could exist if the laws of physics were different. (Or, as Einstein quipped, whether God had any choice in how He created the world.) Despite their discomfort with what felt like throwing in the towel, critics of anthropic reasoning have made little headway in coming up with a better explanation for why nature has properties so conducive to the emergence of life.
Some new studies may change that.
To get a sense of the challenge, consider how fine-tuned nature is. If gravity were stronger, then in the early universe hot spots of gas would have collapsed into black holes, rather than forming life-giving stars. If gravity were weaker, then our sun wouldn't have been able to hang on to its retinue of planets, which would spin off into space. Also bad for life. If the ghostly particles called neutrinos interacted differently, atoms heavier than helium wouldn't have blasted out of some exploding supernovas. A universe without carbon, oxygen and nitrogen isn't exactly lively.
Many of these quantities have to be precisely what they are for life to exist. Does that mean we're just really, really lucky?
Or maybe we're in this Goldilocks universe -- where nature's constants are not too big and not too small -- because "the" universe is actually only one neighborhood in a metropolis teeming with them. With so many universes, probability says that one will have life-giving values, so hey, why not ours? This idea has gotten a boost from string theory, which says there are oodles (10 raised to the 500th or so power) of universes. It could also be that our views about life are too parochial, and that weird life forms can exist in universes with no galaxies, shining stars or other things we assume life needs.
Maybe the anthropic principle is right: The universe is tuned for life because if it were not, no one would be here to notice.
For years, many scientists viewed anthropic reasoning as "the last refuge of scoundrels," says cosmologist Lawrence Krauss of Case Western Reserve University. "It was what you resorted to when you couldn't think of other explanations. But science has always tried to explain why the universe is the way it is. With the anthropic principle you're saying you can't explain why the fundamental constants have the values they do. It's giving up before you really get started."
That philosophical objection now has scientific company. Take the anthropic claim that atomic nuclei must have certain precise properties for helium to fuse into carbon and make our sun burn, and if they didn't the sun would fizzle and life wouldn't exist.
We gave up too soon, says Prof. Krauss, who makes this case in his book "Hiding in the Mirror," just out in paperback. It turns out that this property of atomic nuclei reflects something more basic, namely the strength and nature of the electromagnetic force. So the special traits of helium that let our sun shine do have a more fundamental explanation. There is no need to say "they have to be this way or we wouldn't be here to notice," as the anthropic camp does.
The anthropic principle was further undermined when scientists calculated what would happen if the universe lost one of its forces. There are four: gravity and electromagnetism, plus the strong force and weak force that act only at the subatomic level. The physicists erased the weak force and adjusted other physical parameters (all done mathematically), they reported in August in Physical Review D. Their calculations showed that the resulting pseudouniverse still made atoms, galaxies and stars that burned and cooked up elements like those in living beings, says Graham Kribs of the University of Oregon, Eugene.
This was surprising. It had been thought that in a "weakless universe" chemistry and nuclear physics would be so different from our real universe's that stars would not ignite and life (as we know it) would never emerge.
"But you get a universe that looks a lot like ours," says Prof. Kribs. The approach might work for other supposedly basic parameters of physics: although changing only one yields an uninhabitable cosmos, maybe you can change a few at once and, he says, "still get a universe with galaxies, stars and observers. I think it shows that we've been too parochial in our ideas about how to get a habitable universe."
If so, that lets out a lot of air from the anthropic balloon. Yes, our universe is fine-tuned for life, but other settings on the dial could also produce a cosmos of galaxies, stars and atoms -- and beings who wonder at it all.
• You can email me at sciencejournal@wsj.com.
"I used to be on an endless run.
Believe in miracles 'cause I'm one.
I have been blessed with the power to survive.
After all these years I'm still alive."

Joey Ramone, em uma das minhas músicas favoritas ("I Believe in Miracles")
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Postby mends » 11 Jan 2007, 18:12

Cosmology

I spy with my little gravitational lens

Jan 11th 2007
From The Economist print edition


How to map the invisible

SEVENTY years ago Fritz Zwicky, an astronomer at the California Institute of Technology, discovered that galaxies are not big enough. The visible matter they contain (stars, gas and so on) does not have enough gravity to hold them together. To explain this bewildering missing mass—a result verified independently by many of Zwicky's colleagues—he suggested that galaxies (and therefore, by extension, the universe) contain a lot of additional, invisible matter.

Dark matter, as the invisible stuff is now referred to, has turned out to be one of the most mysterious things around. Subsequent work has shown that it cannot be composed of the same particles (ie, protons, neutrons and electrons) as the visible stuff. But its gravity not only holds galaxies together, it controls their distribution in space—as a study announced in Seattle at this week's meeting of the American Astronomical Society, and published simultaneously in Nature, confirms.

The Cosmic Evolution Survey is the single largest project yet undertaken by the Hubble space telescope. It spent over 1,000 hours of the instrument's valuable observing time examining a section of the firmament about nine times the size of a full moon. Richard Massey, one of Zwicky's successors at Caltech, and his colleagues have used the data collected by the survey to draw the most extensive map of dark matter yet attempted.

They did so by employing a technique called gravitational lensing. This exploits one of the predictions of Einstein's general theory of relativity: that the path of a beam of light (which is a straight line in empty space) is bent inwards by the gravity of a massive object. The result is that such objects act as lenses, distorting the images of anything behind them.

Since dark matter is very massive indeed (there is about six times as much of it around as there is visible matter) it makes good gravitational lenses. Dr Massey and his colleagues were able to map the matter (both dark and visible) in the bit of the firmament covered by the Cosmic Evolution Survey by looking for characteristic distortions in the shape of distant galaxies that only Hubble, which is beyond the image-blurring effects of the atmosphere, can see. Regions rich in distorted galaxies were assumed to be places where large amounts of matter were present between the distorted galaxies and Earth.

That, however, only provided the researchers with a two-dimensional map of such concentrations of matter. Two further refinements were necessary: to work out the third dimension—distance from Earth—and to subtract the effect of visible matter in order to be left with the distribution of dark matter pure and simple.

The trick they used to perform the first refinement was a piece of basic optics. This is that a lens produces its biggest effect when it is halfway between source and observer. The most distorted galaxies, therefore, were those twice as far from Earth as the gravitational lens distorting them. And the distance of such galaxies from Earth can be measured.

That measurement uses another sort of optical distortion—this time of the wavelength of light. The expansion of the universe causes galaxies to recede from one another, and light from a receding object appears redder than that from a stationary object. The farther away a galaxy is, the faster it is receding and the bigger this red shift will be. Measure the distance to the most distorted galaxies and halve it, and you know roughly where your lenses are.

The result is a three-dimensional map of matter. To see which bits of it are dark matter simply requires superimposing the known pattern of visible matter.

Doing so is instructive, as Dr Massey's colleague Nick Scoville reported to the meeting. Dark and visible matter usually coincide. Their overlap confirms the hypothesis that dark matter is the skeleton upon which visible matter is supported, and also lends weight to a second idea—that galaxies form where dark matter accumulates at high densities, pulling visible matter with it. This study, then, has cast light on the darkest of matters and promises a far better understanding of the structure of the universe.
"I used to be on an endless run.
Believe in miracles 'cause I'm one.
I have been blessed with the power to survive.
After all these years I'm still alive."

Joey Ramone, em uma das minhas músicas favoritas ("I Believe in Miracles")
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Postby Danilo » 11 Jan 2007, 18:23

Only english written posts today... ow, I am with a preguiiiiiçççaaaaa...
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Postby junior » 11 Jan 2007, 18:40

Com relação a esse resultado...

http://ofteninerror.blogspot.com/2007/01/dark-matter.html

Jr, fazendo auto-propaganda :cool: :cool: :cool:
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Postby mends » 11 Jan 2007, 18:56

infelizmente não consigo mais ler seu blog. está bloqueado no selviço!! e como fico aqui 14 horas por dia... :lol:
"I used to be on an endless run.
Believe in miracles 'cause I'm one.
I have been blessed with the power to survive.
After all these years I'm still alive."

Joey Ramone, em uma das minhas músicas favoritas ("I Believe in Miracles")
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Postby mends » 22 Jun 2007, 14:26

Astrophysics

Spiralling in space
Jun 21st 2007
From The Economist print edition


A controversial suggestion that black holes cannot swallow information

BLACK holes have long aggravated astronomers and physicists. A consequence of Einstein's general theory of relativity—one of the pillars of modern physics—says that black holes formed by collapsing objects such as stars are so dense that nothing, not even light, can escape their gravitational pull. Unfortunately a second pillar—quantum mechanics—asserts that it is impossible for information to be lost. What happens, then, when information is dragged into a black hole? A team of physicists now proposes that such a scenario may never occur because the black hole actually disappears before it forms.
The team, led by Tanmay Vachaspati of the Case Western Reserve University in Ohio, decided to tackle what is known as the “information loss paradox” not by considering how a physicist might see the world as he fell into a black hole, as has often been done, but from the distant vantage point of a less foolhardy colleague.
According to classical theory, at the boundary of a black hole—the so-called event horizon—light can no longer escape. But this is not the complete picture. Some 35 years ago the British physicist Stephen Hawking argued that quantum effects would allow particles (including light) to escape from a black hole. The reason for this is that, according to Heisenberg's uncertainty principle, space is not entirely empty. At the quantum scale, virtual pairs consisting of a particle and its antimatter equivalent are constantly popping into existence. Normally, they quickly annihilate, but a black hole can peel such pairs apart by sucking in one of them and leaving the other to escape. This means that a black hole would not be truly black. Instead, it should glow.
The escaping particles would make the black hole evaporate with time, yet it was not thought possible that the particles could carry any information away from the black hole, so the proposal did not solve the paradox. (Although three years ago, Dr Hawking suggested that they might carry information after all.)
Dr Vachaspati and his colleagues go far further. Their calculations suggest that the event horizon for collapsing stars never quite comes into existence, at least, not for the colleague watching from far away. He sees the proto black hole evaporate marginally faster than information—including that wrapped up in the existence of his colleague—can fall into it. (The colleague, meanwhile, would never know whether he had crossed the event horizon.) The paper has been accepted for publication in Physical Review D.
If Dr Vachaspati and his colleagues are correct, then the many candidate black holes identified by astronomers to date must ultimately evaporate faster than they can suck in information. This could still be a leisurely process, prolonging the agony for astronomers and physicists who want to know exactly what is going on.
"I used to be on an endless run.
Believe in miracles 'cause I'm one.
I have been blessed with the power to survive.
After all these years I'm still alive."

Joey Ramone, em uma das minhas músicas favoritas ("I Believe in Miracles")
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Postby mends » 20 Nov 2007, 15:33

Image
"I used to be on an endless run.
Believe in miracles 'cause I'm one.
I have been blessed with the power to survive.
After all these years I'm still alive."

Joey Ramone, em uma das minhas músicas favoritas ("I Believe in Miracles")
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