Leaking Gravity May Explain Cosmic Puzzle

SPACE.com ^ | February 28, 2005 | Sara Goudarzi

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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.

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[AntiGuv]

puzzle ping!

[PatrickHenry]

Science Ping!

An elite subset of the Evolution list.

See list's description in my freeper homepage. Then FReepmail to be added/dropped.

[TC Rider]

I think the gravity is leaking into my gut.

[RightWhale]

Yes, this may be testable. There was a different name associated with this idea, but I don't recall who it was, another physicist, a woman, I think.

[Mr Ramsbotham]

I'm reminded of paleoanthropologists who create a new subspecies every time a bone pops up.

[Strategerist]

Yes this doesn't seem new; the idea of gravity leaking into other dimensions (and the possibility this could be tested experimentally) was mentioned in Brian Greene's superstring book.

[lafroste]

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.

Interesting theory. I would like an experiment of very accurate measurements of the Earth's gravitational field at different points in its solar orbit. Unfortunately, the hypothosis behind the experiment dictates that those measurements cannot be made on Earth or near Earth, making execution just a bit of a challenge.

I bet you would find variations on the order of 10E-13 at different orbital positions.

[GloriaJane]

I don't understand this. What happened to the big bang they have been telling us was the reason for our creation? Are they going away from that one new?

That one I could at least wrap my mind around because it worked in the same way shooting a shot gun worked. The shot in the shell expands outward as it travels. The further the shot travels the wider the separation of the pellets when they hit their target. That I can see. These new idea's just befuddle me.

[AntiGuv]

This avenue of inquiry is not meant to account for the expansion of the universe (which is what the Big Bang does) but rather to account for why the expansion of the universe is accelerating.

[GloriaJane]

Oh, I got cha. Thanks

[RightWhale]

This may also be related to why the strength of gravity is so much smaller than the other basic forces. All four should be roughly the same, but gravity is next to nothing by comparison. If most of the gravity is leaking, what we see is the small amount remaining in our universe.

[GloriaJane]

Ok, now I'm going to ask a really dumb question then I'm going to go run away and hide LOL!!

Is there such a thing as up or down in space? Like if bird shot were shot up, if there is such a thing as up in space, would it continue up for all time or would it reach a point where it began to fall? And if it did begin to fall how would it react? Would it, being in a vacume, travle at the same speed on it's way down?

[sourcery]

This story could have been titled: "When Gravity Take A Leak, Physicists Find It Repuslive." :-)

[Wisconsin155]

up or down would be relative.

An object thrown from space would continue on into forever. Unless it were dragged into a gravity well. Otherwise even if it were to collide with a rock it would still have momentum. Think of billiards on ice. It would not go up and then fall back. That would only happen from the bottom of a gravity well, ie a planet surface, etc

[ValerieUSA]

Why doesn't the moon crash into the earth?

[grey_whiskers]

This may also be related to why the strength of gravity is so much smaller than the other basic forces. All four should be roughly the same, but gravity is next to nothing by comparison. If most of the gravity is leaking, what we see is the small amount remaining in our universe.

Does the theory cover why it is only *gravity* that leaks?

Or is it that gravity is the only one of the four forces for which we can observe significant macroscopic effects on other massive bodies (i.e. galaxies) over astronomical distances?

I.e. strong and electroweak I wouldn't expect to notice affecting things however many gazillion light years away...

Full Disclosure: Whiskey Tango Foxtrot?

[GloriaJane]

Thank You!! :)

[Alamo-Girl]

Thanks for the ping!

[redheadtoo]

Gravity is leaking? No wonder my gravity bill is so high. I'll call the Gravity company to come out tomorrow and fix it.