By Maggie McKee | newscientistspace.com
An exotic theory, which attempts to unify the laws of physics by proposing the existence of an extra fourth spatial dimension, could be tested using a satellite to be launched in 2007.
Bursts of high-energy gamma-rays from the deaths of massive stars may reveal whether the universe contains extra dimensions (Illustration: Dana Berry, SkyWorks Digital)
Such theories are notoriously difficult to test. But a new study suggests that such hidden dimensions could give rise to thousands of mini-black holes within our own solar system – and the theory could be tested within Pluto’s orbit in just a few years.
Black holes of various masses are thought to have sprung into existence within 1 second of the big bang, as elementary particles clumped together at extreme energies. But Einstein's theory of general relativity predicts the smallest of these "primordial" black holes should have already evaporated, through a quantum process called Hawking radiation.
But according to some alternative theories that attempt to unify gravity with quantum mechanics, such as string theory, small black holes could still exist. That is because these theories propose extra spatial dimensions, which alter the way gravity behaves on small scales. The theory of general relativity holds that there are three spatial dimensions plus time.
"That [extra spatial dimension] changes the rate at which black holes radiate, so you can slow down the evaporation quite substantially," says Charles Keeton, a physicist at Rutgers University in New Jersey, US.
Now, Keeton and colleague Arlie Petters at Duke University in North Carolina, US, have calculated how many of these tiny black holes should exist – and how they might be detected – according to an offshoot of string theory.
The theory they use, called the Randall-Sundrum braneworld model, proposes that the 3D universe we live in is floating within a larger universe with an extra spatial dimension.
They based their calculations on black holes that each contain only the mass of a small asteroid. Assuming these objects make up 1% of the mass of nearby dark matter – whose existence can only be detected through its gravitational effects on normal matter – the team says there could be several thousand black holes in the solar system. And not only that: "The nearest ones would lie well inside Pluto's orbit," says Keeton.
And the researchers say these black holes may soon be detected. Their gravity should bend light passing nearby, so that light passing on one side of a black hole should take a different amount of time to go by than light passing on the other side. This time delay should be small, so the only chance of detecting it would come from light waves with a period (the time taken for light to travel one wavelength) shorter than the delay, says the team.
They say fleeting cosmic explosions called gamma-ray bursts (GRBs) have just the right period to provide such a test. GRBs are volleys of energetic gamma-ray photons that are thought to be caused by the violent deaths of massive stars, or the collisions of dense stellar corpses.
Light taking different paths around the black hole would later recombine, producing an interference pattern. This would create a telltale signal in observations of how many photons of different energies were emitted in the burst, says the team.
"The lensing would cause wiggles in the energy spectrum, so in some places there would be an excess of photons and in others, a dearth of photons," Keeton told New Scientist.
Below the limit
Current telescopes do not probe the high-energy gamma rays required to test the theory. But a NASA satellite called the Gamma Ray Large Area Space Telescope (GLAST), due for launch in August 2007, will. "If we do see the signal, then the strongest conclusion we can draw is that primordial black holes exist," says Keeton.
Then, researchers would have to analyse the data to measure the mass of the black hole. "If it is below some limit, you could say such a black hole cannot exist in general relativity because it would have evaporated by now," says Keeton.
"What we think is exciting is that we can make a specific prediction for an astronomical measurement that would open the door to studying the fourth dimension," he says.
Neil Gehrels, deputy project scientist for GLAST and a GRB researcher at NASA's Goddard Space Flight Center in Maryland, US, says identifying such "wiggles" will not be easy. "It's difficult to pick out small features in the energy spectrum," he told New Scientist. "But it's an interesting suggestion and definitely worth pursuing."
Journal reference: Physical Review D
Article from: http://www.newscientistspace.com/article/dn9240-
Related: The Search for the God particle
God Particle...or God Himself?
Stargates, Ancient Rituals, And Those Invited Through The Portal (Pt. 1)
There Is No More Firmament
Astronomers shed light on mystery of 'dark matter'
Astronomers find the gate into parallel worlds
How does the Universe work and What is Reality?
Holographic Reality & Spritual Science