Zeroing in on the Mystery of Dark Matter --"We are on the Verge of Detecting a New Particle of Nature"
Dark matter makes up about 23 percent of the mass-energy content of the universe, even though we don’t know what it is or have yet to directly see it (which is why it’s called “dark”).
"Figuring out what is dark matter has become a problem that astrophysicists, cosmologists and particle physicists all want to solve, because dark matter is central to our understanding of the universe," says Michael S. Turner – Rauner Distinguished Service Professor and Director of the Kavli Institute for Cosmological Physics at the University of Chicago.
"We now have a compelling hypothesis, namely that dark matter is comprised of WIMPs (Weakly Interacting Massive Particle), particles that don’t radiate light and interact rarely with ordinary matter. After decades of trying to figure out how to test the idea that dark matter is made up of WIMPs, we have three ways to test this hypothesis. Best of all, all three methods are closing in on being able to either confirm or falsify the WIMP. So the stars have truly aligned."
A theoretical cosmologist trained in both particle physics and astrophysics, Michael Turner coined the term “dark energy” and helped establish the interdisciplinary field that combines cosmology and elementary particle physics.
"Ten years ago," Turner says, "I don't think you would've found astronomers, cosmologists, and particle physicists all agreeing that dark matter was really important. And now, they do. And all of them believe we can solve the problem soon. It's wonderful listening to particle physicists explain the evidence for dark matter, and vice versa –astronomers explaining WIMPs as dark matter. "
"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) 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."
Answering the observation that the dark matter particle might not be detectable, Turner 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.'
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
Image Credit: NASA/JPL-Caltech/ESA/Institute of Astrophysics of Andalusia, University of Basque Country/JHU