Answering the observation that the dark matter particle might not be detectable at a colloquium organized by the Kavli Institute for Cosmological Physics at the University of Chicago, Michael Turner, a theoretical cosmologist trained in both particle physics and astrophysics who coined the term “dark energy,” said that for 20 to 30 years, this idea that dark matter is part of a unified theory has been our Holy Grail and has led to the WIMP hypothesis and the belief that the dark matter particle is detectable. "But there’s a new generation of physicists that is saying, 'Well, there's an alternative view. Dark matter is actually just the tip of an iceberg of another world that is unrelated to our world. And I cannot even tell you about that world. There are no rules for that other world, at least that we know of yet.
"As cosmologists," said Rocky Kolb, who studies the application of elementary-particle physics to the very early Universe, and is the co-author with Michael Turner of The Early Universe, the standard textbook on particle physics and cosmology, "one of our jobs is to understand what the universe is made of. To a good approximation, the galaxies and other structures we see in the universe are made predominantly of dark matter. We have concluded this from a tremendous body of evidence, and now we need to discover what exactly is dark matter. The excitement now is that we are closing in on an answer, and only once in the history of humans will someone discover it. "
"Nothing in cosmology makes sense without dark matter, says Turner. "We needed it to form galaxies, stars and other structures in the Universe. And so it's absolutely central to cosmology. We also know that none of the particles known to exist can be the dark matter particle. So it has to be a new particle of nature. Remarkably, our most conservative hypothesis right now is that the dark matter is a new form of matter – out there to be discovered and to teach us about particle physics."
"Dark matter is absolutely central to cosmology, said Turner, "and the evidence for it comes from many different measurements: the amount of deuterium produced in the big bang, the cosmic microwave background, the formation of structure in the Universe, galaxy rotation curves, gravitational lensing, and on and on."
"There is five times more dark matter than ordinary matter, and its existence allows us to understand the history of the universe beginning from a formless particle soup until where we are today," said Turner. "If you said, 'You no longer have dark matter,' our current cosmological model would collapse. We would be back to square one."
"Dark matter particles, or WIMPs," said Turner, "don’t interact with ordinary matter often. It's taken 25 years to improve the sensitivity of our detectors by a factor of a million, and now they have a good shot at detecting the dark matter particles. Because of the technological developments, we think we are on the cusp of a direct detection.
"Likewise for indirect detection. We now have instruments like the Fermi satellite (the Fermi Gamma-ray Space Telescope) and the IceCube detector (the IceCube Neutrino Observatory at the South Pole, above) that can detect the ordinary particles (positrons, gamma rays or neutrinos) that are produced when dark matter particles annihilate, indirectly allowing dark matter to be detected. IceCube is big enough to detect neutrinos that are produced by dark matter annihilations in the sun."
Sadly, this point of view could be correct and might mean the solution to the dark matter problem is still very far away, that discovering what dark matter actually is could be 100 years away.
The Daily Galaxy via http://www.kavlifoundation.org and AFP 2013