Scientists working in a hole 3,000 ft underground in Japan believe they have found something quite remarkable - a big chunk of the universe which had gone missing.
You would think something as large as the cosmos couldn't get lost but up to 90 per cent of it is unaccounted for, according to some theories. Astronomers refer to it as "dark matter", dust, lumps of rock and other space stuff which doesn't give off light, making it impossible for our telescopes to detect.
A team of Japanese and US physicists has caused quite a stir, however, with the announcement that they may have located all of that missing matter packed into tiny bits so small that they can hardly be detected, let alone seen.
Researchers from Boston University, the University of California at Irvine and the University of Tokyo were searching for one of the tiniest, most elusive of elemental particles, the neutrino. These particles are much smaller than atoms and are the components which assemble to make up atoms.
Neutrinos are remarkable in that they can pass through matter as though it is not there, even something as large and as dense as the Earth. They are detected by placing enormous tanks of purified water - the Japanese tank is 40 metres across, 40 metres deep and holds 12.5 million gallons - far underground.
If a neutrino passes by it causes a shock wave like a sonic boom in the water which, in turn, gives off a minute flash of light. These events can then be picked up by very sensitive cameras. There are 13,000 such devices mounted on the Japanese neutrino tank.
There are three neutrino "flavours" - electron, muon and tau. It is known they have no charge but there is debate among particle physicists about whether neutrinos have a tiny mass or none at all.
The scientists were using the Super-Kamiokande neutrino detector to try to understand why they were able to detect the predicted number of electron-neutrinos but only half the expected number of muon-neutrinos.
They concluded that the missing muon-neutrinos had "oscillated", changed into other types, including the undetectable tau-flavoured neutrino. According to Einstein's calculations, this could happen only if the neutrinos had mass.
This finding, if proven, is of tremendous importance to cosmologists who are trying to figure out how much mass the universe has. Muon-neutrinos are very plentiful and could make up most or all of the universe's missing dark matter, allowing accurate predictions of total mass.
Cosmologists want to know this figure because then they will be able to use gravity calculations to determine whether the universe will keep on spreading out into space forever or if it will eventually stop expanding, turn around and come crashing together in a Big Crunch.
"The major problem in physics for the last quarter century has been the problem of mass - where does it come from," according to Dr Lawrence Sulak, principal investigator on the Super-Kamiokande project.
"Until this observation, neutrinos were thought to be massless. Now we know that we have not missed a fundamental symmetry of nature that forbids a neutrino mass. On the contrary, that neutrinos do have mass provides a critical clue in the unification of the particles and forces of nature."