Posted on 02/28/2005 6:29:00 PM PST by AntiGuv
WASHINGTON, D.C. - Scientists may not have to go over to the dark side to explain the fate of the universe. The theory that the accelerated expansion of the universe is caused by mysterious "dark energy" is being challenged by New York University physicist Georgi Dvali. He thinks there's just a gravity leak.
Scientists have known since the 1920s that the universe is expanding. In the late 1990s, they realized that it is expanding at an ever-increasing pace. At a loss to explain the stunning discovery, cosmologists blamed it on dark energy, a newly coined term to describe the mysterious antigravity force apparently pushing galaxies outward. This repulsive, unknown force is believed to make up more than 70 percent of the mass-energy budget of the universe. But the existence of dark energy is far from proven, and some researchers believe they and their colleagues simply don't understand gravity at larger scales. The gravitational pull between any two objects becomes less with distance. But in Dvali's view, it weakens more than standard theory predicts. Dvali would modify the theory of gravity so that the universe becomes self-accelerating, eliminating the need for dark energy. He presented his work here earlier this month at the annual meeting of the American Association for the Advancement of Science.
Dvali borrows from string theory, which states that there are extra, hidden dimensions beyond the four we are familiar with: three directions and time. String theory suggests that gravitons -- hypothetical elementary particles transmitting gravitational forces -- can escape to other dimensions. Dvali says this would cause "leaks" in gravity over cosmic proportions, reducing gravitational pull at larger distances more than expected. "The gravitons behave like sound in a metal sheet," says Dvali. "Hitting the sheet with a hammer creates a sound wave that travels along its surface. But the sound propagation is not exactly two-dimensional as part of the energy is lost into the surrounding air. Near the hammer, the loss of energy is small, but further away, it's more significant." The effect is to alter the space-time continuum, speeding up universal expansion. "Virtual gravitons exploit every possible route between the objects," Dvali said, "and the leakage opens up a huge number of multi-dimensional detours, which brings about a change in the law of gravity." The speeding up of the universe suggest that Einstein’s laws of General Relativity, describing the interaction of space and matter, must be modified at large cosmic distances. "It is this modification, and not dark energy, that is responsible for the accelerated expansion of the universe," Dvali concludes. The idea might be testable.
Gravity leakage should create minor deviations in the motion of planets and moons. Astronauts on the Apollo 11 mission installed mirrors on the lunar surface. By shooting lasers at the mirrors, a reflected beam can be monitored from Earth to measure tiny orbital fluctuations. Dvali said deviations in the Moon's path around Earth might reveal whether gravity is really leaking away. This article is part of SPACE.com's weekly Mystery Monday series.
Speaking from personal experience, I take it? ;^)>
The moon took lessons from Douglas Adams.
I have a simple explanation that, on the surface, explains everytthing without dark matter, leaking gravity, etc.
Consider that the light from the nearest objects being used for red-shift data left their sources long before the first red-shift measurments were made. Now, suppose that the expansion of the universe has already stopped, and the collapse has begun. Therefore, we are accelerating and receding from objects that appear to be spreading outward because, at the time the light left them, they still were receding from one another. The farther away the objects are, the faster they would seem to be moving away from us, since it would take longer for evidence of their slowing down to reach us. The nearer objects seem to be moving away more slowly because we see evidence of their deceleration sooner.
It's simple, it follows the laws, and it doesn't depend on any hidden matter or leaking gravity.
I am not an astronomer, but I did stay at a Holiday Inn Suites last night, so fire at wiil!!
Scientists have known since the 1920s that the universe is expanding.
Scientists have known no such thing. Scientists know that the universe appears to be expanding, not that it actually is.
As our deep space vehicles have shown, there is some unknown phenomenon that is slowing them down. Isn’t obvious that the same degradation happens to light. Older the light, farther it will have slowed and shifted toward the red.
Excellent point.
The universe is supposed to be 15 billion years old yet we can see well-defined galaxies 12 billions years old in any direction we look.
Excellent point.
How long does it take for a galaxy to form? Probably longer than 3 billion years for that much matter to gather (unless the gravity constant had changed in those early years).
There is no way we can know one way or the other.
Is Hubble such an icon in the astronomy community that the red shift can never be questioned even when new empirical evidence gives another explanation?
Yes, it is dogma. This has happened again and again throughout history. Like the guy a hundred years ago who advised some up and coming physicist to abandon the field because everything that could be known had already been discovered and it merely a matter of wrapping up the details. Then Einstein came along to wrap up the details and blew the whole field apart.
Nobody ever wants to admit to the Mystery. Nice post.
It's not really leaking into another parallel world. It's just having its effect in more than the three spatial dimensions. Since the extra spatial dimensions are coiled up tight, the gravity effect is more or less lost there in a dimension we cannot interact with.
Dr. Venkman may have found a new, corporate direction:
Universal Plumbing
But will the EPA Administrator allow him to turn gravity OFF while he changes valves & pipe connections?
Time will tell...film at eleven.
My perpetual motion machine uses duct tape -- lots of it -- to minimize the leakage. Very soon now, I shall astound the world!
Interesting idea. We once tried after many drinks to try to hit the Apollo mirrors with a laser (yes more powerful than a pointer). The results of the test are in dispute since we passed out before verification. Damn tequila. I still think we hit it and got a return.
Anti-gravity?
What if the universe were actually like the inside of sphere. Galaxies appear to be flying away from each other, but in reality all converge again on the far side of the sphere?
Dark matter is sucking the funds out of my bank account.
If that was the case , you would think that the close galaxies like Sagittarius ( at just 75,000 light years )would show some evidence of that. Presumably, if the expansion ended, the collapse would effect all bodies within the universe in a similar fashon, us and our nearby galatic neighbors included. We should need to see things beyond the redshift to know what direction things are heading in.
BTTT
'Cause it's going around in circles.
Me too, but I thought it was my ex.
I understand that. However, gravity is spreading out into the ten or eleven dimensions currently postulated by physicists (I've seen as many as 64 proposed, but most stick to the lower numbers). If the effects of gravity were concentrated in the first four, or conversely pushed more heavily into the other seven dimensions (reducing its presence in the first four), one wonders what might be possible.
Help me out here...
Is the universe expanding?
Is the "expansion" accelerating?
Whaddya mean..."slowing them down."?
"Since the extra spatial dimensions are coiled up tight, the gravity effect is more or less lost there in a dimension wecannot[don't know how to] interact with."
How powerful was your laser? (and more to the point, was it green?)
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