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)

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.

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.

Story continues at: newscientistspace.com