Searching for extra dimensions
Courtesy Northeastern University
and World Science staff
For years, scientists have seriously spoken of the possible existence of extra, unseen dimensions. The idea
resolves many questions in physics, but it’s unproven, and many researchers have called it untestable.
A group of researchers say that may be changing.
They claim they may soon get evidence for extra dimensions and other
bizarre predictions of a theory that proposes their existence, string theory—the closest thing science has to a “theory of everything.”
The evidence could come from a station at the South Pole set up to study ghostlike particles, neutrinos, from space, the researchers say.
Neutrinos are so hard to detect that most of them fly through the Earth in the blink of an eye without leaving a trace.
But early results from a neutrino
detector show the elusive particles could serve as probes to the unseen dimensions, say the researchers, from Northeastern University in Boston, Mass., and the University of California, Irvine.
They predict a bigger neutrino detector now under construction, called
IceCube, could provide the first evidence for string theory and other theories that attempt to explain the universe.
A paper describing the work appears in the current issue of Physical Review
The evidence, they say, would come from
the way neutrinos interact with material on Earth.
“To find clues to support string theory and other bold, new theories, we need to study how matter interacts at extreme energies,” said Northeastern’s Luis Anchordoqui.
That’s because scientists suspect the four forces of nature that physicists currently recognize—gravity,
electromagnetism and the strong and weak nuclear force—were unified as one when the Big Bang gave birth to the cosmos.
Then, everything was compressed into a
small space, and thus was extremely hot and high in energy. Physicists think that a proof of string theory would require studying the behavior of matter of such energies.
“Human-made particle accelerators on Earth cannot yet generate these energies, but nature can in the form of the highest-energy neutrinos,” Anchordoqui added.
String theory is a bid to resolve almost all the mysteries of physics at a blow by bridging the gap between the two most successful theories of the 20th century, general relativity and quantum mechanics. Each has been successful at explaining how the universe behaves over vast distances and in tiny spaces, respectively. But they conflict in some
ways; both can’t be right.
String theory claims all the particles of nature are actually different vibrations of unseen, tiny loops called “strings.” The theory mathematically fixes the major inconsistencies between the other two.
In the process, if it’s correct, it would show the underlying unity of
But it only works if the strings have several extra dimensions in which to vibrate beyond the dimensions we see. Different versions of string theory propose 10 or 26 dimensions, some of which are invisible because they are rolled up into tiny balls.
Since clues to test the theory lie at high energies, Anchordoqui’s
team says a good strategy is to exploit neutrinos from extragalactic sources
that serve as “cosmic accelerators,” producing high-energy neutrinos.
These could smack into protons, components of the atomic nucleus,
on Earth. In the process they would release energies in the realm where clues to string theory could be revealed.
Neutrinos are among the most common particles in the universe; billions pass through our bodies every second. Most of those reaching Earth are lower-energy particles generated in the sun.
A neutrino detector called AMANDA, buried in Antarctic ice, currently
works to detect neutrinos raining down from above as well as coming “up”
through the Earth. Its larger successor instrument, IceCube, is similar,
but has about six times more detecting devices.
A neutrino hitting atoms in the ice emits a
brief blue light. The detectors can tell scientists the direction where the neutrino came from and its energy.
The scientists plan to compare “down” to “up” detections to find any discrepancies in the detection rate, evidence of an exotic effect predicted by new theories.
“String theory and other possibilities can distort the relative numbers of ‘down’ and ‘up’ neutrinos,” explained Jonathan Feng of the University of California, Irvine, a member of the research team.
“For example, extra dimensions may cause neutrinos to create microscopic black holes, which instantly evaporate and create spectacular showers of particles in the Earth’s atmosphere and in the Antarctic ice cap. This increases the number of ‘down’ neutrinos
detected,” he continued.
“At the same time, the creation of black holes causes ‘up’ neutrinos to be caught in the Earth’s crust, reducing the number of ‘up’ neutrinos. The relative ‘up’ and ‘down’ rates provide evidence for distortions in neutrino properties that are predicted by new theories.”
The black holes would arise because
string theory predicts that at the tiny scales in which the extra
dimensions lie, gravity is much more powerful than we normally observe
it to be. Its immense strength within the confines of those dimensions
would crush matter into black holes.
AMANDA has detected no more than a dozen high-energy neutrinos so far, the researchers said, but the detection rate and energy range suggest IceCube
“The neutrinos accelerated in the cosmos to energies unattainable on Earth can detect the ‘footprint’ of new physics,” said Northeastern’s Haim Goldberg. “The ‘body’ responsible for the footprint can then emerge through complementary experiments at the new generation of human-made
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