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 nature’s forces. 

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.”