Ring of Dark Matter; A Two-Time Universe?
Date: Tuesday, May 15, 2007 @ 23:29:31 GMT
Topic: Science


Astronomers using NASA's Hubble Space Telescope have discovered a ghostly ring of dark matter that formed long ago during a titanic collision between two massive galaxy clusters. The ring's discovery is among the strongest evidence yet that dark matter exists. Astronomers have long suspected the existence of the invisible substance as the source of additional gravity that holds together galaxy clusters. Such clusters would fly apart if they relied only on the gravity from their visible stars. Although astronomers don't know what dark matter is made of, they hypothesize that it is a type of elementary particle that pervades the universe. Credit: NASA

Hubble Telescope Finds Ring of Dark Matter

US astronomers on Tuesday presented the most solid proof yet of the existence of dark matter, a mysterious substance believed to make up more than a quarter of the universe.

"This is the first time we have detected dark matter as having a unique structure that is different from both the gas and the galaxies in the cluster," said astronomer M. James Jee of Johns Hopkins University in Baltimore. Jee is a member of the team that spotted the dark matter ring.

The ring, which measures 2.6 million light-years across, was found in the cluster CL0024+17, located 5 billion light-years from Earth. The team unexpectedly found the ring while it was mapping the distribution of dark matter within the cluster. Although astronomers cannot see dark matter, they can infer its existence in galaxy clusters by observing how its gravity bends the light of more distant background galaxies. During the team's analysis, they noticed a ripple in the mysterious substance, somewhat like the ripples created in a pond from a stone plopping into the water.

Jee said, "Although the invisible matter has been found before in other galaxy clusters, it has never been detected to be so largely separated from the hot gas and the galaxies that make up galaxy clusters. By seeing a dark matter structure that is not traced by galaxies and hot gas, we can study how it behaves differently from normal matter."

Jee explained, "I was annoyed when I saw the ring because I thought it was an artifact, which would have implied a flaw in our data reduction. I couldn't believe my result. But the more I tried to remove the ring, the more it showed up. It took more than a year to convince myself that the ring was real. I have looked at a number of clusters, and I haven't seen anything like this."

Curious about why the ring was in the cluster and how it had formed, Jee found previous research that suggested the cluster had collided with another cluster 1 to 2 billion years ago. The research, published in 2002 by Oliver Czoske of the Argelander-Institute for Astronomy at the University of Bonn, was based on spectroscopic observations of the cluster's three-dimensional structure. The study revealed two distinct groupings of galaxies clusters, indicating a collision between two clusters.

Astronomers have a head-on view of the collision because it occurred along Earth's line of sight. From this perspective, the dark-matter structure looks like a ring.

The team created simulations showing what happens when galaxy clusters collide. As the two clusters smash together, the dark matter, as calculated in the simulations, falls to the center of the combined cluster and sloshes back out. As the dark matter moves outward, it begins to slow down under the pull of gravity and pile up, like cars bunched up on a freeway. ...

Full story: http://www.physorg.com/news98450367.html

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A Two-Time Universe? Physicist Explores How Second Dimension of Time Could Unify Physics Laws

For a long time, Itzhak Bars has been studying time. More than a decade ago, the USC College physicist began pondering the role time plays in the basic laws of physics — the equations describing matter, gravity and the other forces of nature.

Those laws are exquisitely accurate. Einstein mastered gravity with his theory of general relativity, and the equations of quantum theory capture every nuance of matter and other forces, from the attractive power of magnets to the subatomic glue that holds an atom’s nucleus together.

But the laws can’t be complete. Einstein’s theory of gravity and quantum theory don’t fit together. Some piece is missing in the picture puzzle of physical reality.

Bars thinks one of the missing pieces is a hidden dimension of time.

Bizarre is not a powerful enough word to describe this idea, but it is a powerful idea nevertheless. With two times, Bars believes, many of the mysteries of today’s laws of physics may disappear.

Of course, it’s not as simple as that. An extra dimension of time is not enough. You also need an additional dimension of space.

It sounds like a new episode of “The Twilight Zone,” but it’s a familiar idea to most physicists. In fact, extra dimensions of space have become a popular way of making gravity and quantum theory more compatible.

Extra space dimensions aren’t easy to imagine — in everyday life, nobody ever notices more than three. Any move you make can be described as the sum of movements in three directions — up-down, back and forth, or sideways. Similarly, any location can be described by three numbers (on Earth, latitude, longitude and altitude), corresponding to space’s three dimensions.

Other dimensions could exist, however, if they were curled up in little balls, too tiny to notice. If you moved through one of those dimensions, you’d get back to where you started so fast you’d never realize that you had moved.

“An extra dimension of space could really be there, it’s just so small that we don’t see it,” said Bars, a professor of physics and astronomy.

Something as tiny as a subatomic particle, though, might detect the presence of extra dimensions. In fact, Bars said, certain properties of matter’s basic particles, such as electric charge, may have something to do with how those particles interact with tiny invisible dimensions of space.

In this view, the Big Bang that started the baby universe growing 14 billion years ago blew up only three of space’s dimensions, leaving the rest tiny. Many theorists today believe that 6 or 7 such unseen dimensions await discovery.

Only a few, though, believe that more than one dimension of time exists. Bars pioneered efforts to discern how a second dimension of time could help physicists better explain nature.

“Itzhak Bars has a long history of finding new mathematical symmetries that might be useful in physics,” said Joe Polchinski, a physicist at the Kavli Institute for Theoretical Physics at UC Santa Barbara. “This two-time idea seems to have some interesting mathematical properties.”

If Bars is on the right track, some of the most basic processes in physics will need re-examination. Something as simple as how particles move, for example, could be viewed in a new way. In classical physics (before the days of quantum theory), a moving particle was completely described by its momentum (its mass times its velocity) and its position. But quantum physics says you can never know those two properties precisely at the same time.

Bars alters the laws describing motion even more, postulating that position and momentum are not distinguishable at a given instant of time. Technically, they can be related by a mathematical symmetry, meaning that swapping position for momentum leaves the underlying physics unchanged (just as a mirror switching left and right doesn’t change the appearance of a symmetrical face).

In ordinary physics, position and momentum differ because the equation for momentum involves velocity. Since velocity is distance divided by time, it requires the notion of a time dimension. If swapping the equations for position and momentum really doesn’t change anything, then position needs a time dimension too.

“If I make position and momentum indistinguishable from one another, then something is changing about the notion of time,” said Bars. “If I demand a symmetry like that, I must have an extra time dimension.” ...

Full story: http://www.physorg.com/news98468776.html







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