Dark Matter Universe Part 2: Dark Worlds

Posted by: Mike Pallante on December 7, 2010 at 11:27PM
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Dark Matter Universe Part 2: Dark Worlds

Dark Matter Universe Part 1 explained the origins of theoretical Dark Matter. Fritz Zwicky, while observing effects of mass in galaxy clusters, was puzzled by the lack of light to the mass observed. Because there appeared to be more mass than the light to mass ratio expected, this inferred the existence of lightness or "dark" matter."
A theoretical particle called a WIMP (Weakly Interacting Massive Particle) that carry great mass but do not interact with the strong atomic force or electromagnetism seem a likely candidate for dark matter. So far no observations suggest dark matter does anything but clump together forming gravitational mass; however, bold new theories suggest possible dark matter worlds coexisting with our own.

Beyond WIMPs: Dark Matter May Not Be Inert

One theory suggests unstable WIMPS created during the first nanosecond of the Big Bang decayed into not-so-subtly named “Super WIMPs” which interact only with gravitational forces, compared to weak atomic forces plus gravity. In a WIMP model of the universe, WIMPs created at the Big Bang settled into dark matter halos producing gravitational mass and drawing in “normal” matter forming galaxies. In the Super-WIMP model much the same happened except WIMP decay resulted in a delay in the creation of galaxies. The delay allowed for greater expansion of matter post Big Bang. The resulting difference in galactic densities could indicate which scenario is more likely.

Dark matter, whether made of WIMPS or Super-WIMPs may not simply sit around in space collecting gravitational mass. A paper by Lotty Ackerman, Matthew Buckley, Sean Caroll and Marc Kamionkowski titled "Dark Photons" explores other dark forces at play.

Dark Forces and Dark Worlds

In 1871 Lewis Caroll published Through the Looking Glass, a sequel to Alice's Adventures in Wonderland, where Alice steps through a mirror and finds a world similar in structure to her own but governed by strange forces unique to the “other side”. Similarly, on our side of the looking glass matter collides and annihilates. Dark matter, however, fails to annihilate. Dark matter annihilation would change the gravitational mass in galaxies and no evidence of such changes have been observed. What does influence dark matter? It is speculated that forces too weak to cause annihilation but strong enough to cause relevant reactions among dark particles affect dark matter. "Dark Photons" suggests a “dark electromagnetism” similar to our own but working, differently, as if through Alice's looking glass. Specifically the authors posit a long range weak force mediated by a masses particle (dark photon) which couples only to non-baryonic matter (Baryons comprise quarks which form protons and neutrons which provide the basis for atomic nuclei and thus atomic matter. All atomic matter interacts with the four known fundamental forces therefore dark matter should necessarily contain non baryonic particles). A mass-less dark photon mediating dark electromagnetism over a vast distance, yet still too weak to cause collisions, allows some interesting physics in dark sectors. Consider a dark electromagnetism, mediating dark electric fields, dark magnetism and dark radiation.

Work by physicist Jonathan Feng demonstrates a possible scenario in which non-baryonic particles (dark matter particles) decay from a variety of baryonic matter (Ordinary matter). If dark matter decayed from baryonic matter then a range of dark matter particles may exist in the universe- presumably decayed from the plethora of matter existing at the moment of the Big Bang. Given discrete particles of dark matter with a charge provided by dark electromagnetism, dark nuclei and thus atoms reasonably follow. With a variety of dark atoms theorists could begin describing dark chemistry. Cautiously, theorists might then step into dark biology, or life.

Is science on the cusp of staring through the looking glass of physics into the Imaginarium of Dr. Zwicky? Not quite yet. For one, dark matter appears six times more massive than baryonic matter to theorists and may interact differently. Further, according to the paper "Relics in Hidden Sectors" by Jonathan Feng not all forces at play in a dark universe are simply mirror our own; rather, like Alice's mirror they retain a strange and unique flavor. Any life developing in the dark matter world would be as different from our own as a Jabberwock to Alice. However, these facts don't drive a vorpal blade snickersnack into the heart of the dark universe.

The Real Dark Universe

Scientists estimate 95% of the universe is actually dark matter. This unobserved majority may hold particles, forces and physics all its own. Theorist Sean Carroll write, “...it's important for we theorists to propose specific, testable models of non minimal dark sectors, so that observers have targets to shoot for when we try to constrain just how interesting the darkness really is.” When we only observe 5%, discovering the nature of the rest of the universe brings us closer to understanding our place in creation. For example "Relics in Hidden Sectors" suggests the moments just after the Bing Bang may have played out quite differently than currently thought but still result in the same world we observe. In Lewis Carroll's story, Alice discovers the world is much larger, stranger than she ever imagined before she stepped through the looking glass. The dark matter universe may wait on the other side of the experiments of the Large Hadron Collider at CERN which recently succeeded in creating a miniature Big Bang. Or, as Alice once said, it may be, “nothing but a deck of cards.”