Introducing Dark Watch

Okay, so as I've mentioned, it's hard to keep up with all of the amazing discoveries (or lack thereof) surrounding dark matter and dark energy, but the fact of the matter is that if you're interested in physics, they just can't be avoided. So how can I keep my readers up to date without going schizophrenic, reporting breakthrough evidence one day and contradictions the next?

Welcome to Dark Watch, my monthly update on all things dark matter-ish and dark energy-ish. Throughout the month, I'll keep a running tally of the major reports on these fronts, and will post one mega-post about all of them at the end of the month.

For example of what I mean, let's consider this month for an idea of why you could get whiplash trying to report all of these things as they come.

What is a Discovery?

One intriguing article that started the month off was Robert Crease's analysis of who should be credited with the discovery of dark matter, when (if) it finally does happen. (Discovering dark matter - June 2) Crease points out that the dark matter search affords a rare example where we can consider, before a discovery is made, who should get credit for it. (Discoveries that strike out of "nowhere," rarely afford this opportunity, because we didn't know beforehand that we were looking for the discovery.) In other words, what sort of evidence would be needed to be a discovery of dark matter? Who should get the credit for it? Consider this quote from the article:

Historians usually discuss credit after a discovery is made ... But thanks to the fact that WIMP search results will roll in with increasing data from different sources in the next few years, historians have a unique opportunity to assess a discovery as it happens, allowing them to test models and assumptions.

What happens if strong evidence comes in that contradicts the existing evidence? Is the current evidence, so compelling to many scientists, just thrown out as being statistical anomalies? Where is the line between statistics and evidence?

Given that experimental evidence of dark matter is almost guaranteed to earn a Nobel, the question of credit is no small one.

Videos of a Dark Matter Detector

Also from PhysicsWorld, we have some cool videos of the Boulby Underground Laboratory in Cleveland. (Assuming, of course, that you think dark matter searches in underground science labs are cool, but if you're reading this blog then I'm going to take that as a given.

In the first, we have an interview with physicist Sean Paling at the facility (Deep exploits - the quest for dark matter, June 7 - you can also access the video directly through YouTube). He provides a nice overview of what dark matter is and why physicists house their detectors in deep mines to search for it. The second is more of a detailed look at work inside the lab at the experiments ZEPLIN-III and DRIFT (Going underground - life inside the Boulby lab, June 7, or check out YouTube directly).

Two Varieties of Dark Matter?

This month also triggered a discussion of whether there may actually be two different types of dark matter. This comes out of work by a group of U.S. physicists (Daniel Feldman, Zuowei Lui, Pran Nath, & Gregory Peim) who sought to explain inconsistent and contradictory data from the PAMELA collaboration.

In 2008, PAMELA scientists announced that they'd found evidence of an increase in positrons, which they believed could be from collisions of weakly interacting massive particles (WIMPs), one of the leading dark matter candidates. Unfortunately, these particles should end up creating both positrons and also anti-protons through their annihilation and subsequent decay, and the PAMELA finding only caught the positrons. This can be explained, but only if the dark matter particles are slightly different from expectations ... and the particular differences that scientists predict would mean that ground-based detectors will be unsuccessful at locating them!

However, ground-based detectors such as the DAMA collaboration and Cryogenic Dark Matter Search II (CDSM-II) have indicated that they've gotten some data which, they hope, are early pieces of evidence in favor of dark matter. This all ties back into Crease's early contemplation of what represents evidence in this search, because neither of these can be completely correct ... or can they?

In the Feldman study, they explore the idea that the WIMPs are not the only form of dark matter. If there are two types of dark matter, then each set of detections could be valid without invalidating the other set. From PhysicsWorld on this topic:

One of these would be a conventional WIMP - a neutralino, predicted in supersymmetric extensions to the Standard Model of particle physics.... The other particle would be an unconventional, hidden-sector WIMP. The hidden sector is an addition to the Standard Model that involves different particles and forces to those known to exist today. The US group thinks that a hidden-sector "Dirac" particle (which has a separate anti-particle) would be able to decay into positrons after annihilation but not anti-protons, and would therefore explain the PAMELA signal.

The biggest benefit of this new analysis is that the new Planck Observatory should have enough resolution to detect possible evidence of this theory when it examines the cosmic microwave background (CMB) radiation. (The previous WMAP project didn't have the intensity to detect the variations predicted by the new model.)

• Physics Review D - Multicomponent Dark Matter in Supersymmetric Hidden Sector Extensions (or find the full preprint for free on arXiv.org), May 27
• PhysicsWorld - Does dark matter come in two types?, June 8

The End of Dark Matter and Dark Energy?

Of course, all of the above becomes a moot point if yet another analysis is correct. Published by the Monthly Notices of the Royal Astronomical Society, this study by Tom Shanks at Durham University brings into question the very basis of the evidence that's most often used in support of dark matter and dark energy.

The Wilkinson Microwave Anisotropy Probe (WMAP) provides the strongest evidence about the nature of the early universe and how it has since evolved, and the usual analysis of these results strongly support the idea that dark matter and dark energy both exist. (This research resulted in the 2006 Nobel Prize in Physics.) However, in order to analyze the data, the readings have to be calibrated ... and that is where Shanks and his graduate student Utane Sawangwit think they may have found a different result. According to MSNBC:

Instead of using Jupiter as a calibration source, the way the WMAP team did, Shanks and Sawangwit used distant astronomical objects in the WMAP data itself that were emitting radio light.

"When we checked radio sources in the WMAP background, we found more smoothing than the WMAP team expected," Shanks told SPACE.com. "That would have big implications for cosmology if we were proven right."

The results from Shanks indicate that the variations shown by the WMAP data is actually a lot less than currently believed, which means that exotic types of matter and energy may not be needed to explain the differences. As in other research areas related to dark matter and dark energy, the new Planck Observatory should help provide more information that can help distinguish between clear evidence and murky statistical anomalies.

• Space.com - Dark Energy and Dark Matter Might Not Exist, Scientists Allege, June 13
• MSNBC.com - Are dark energy and dark matter not real?, June 14
• Daily Mail - Dark energy and matter may not exist claim scientists, June 15 - Interestingly, this article's title was updated sometime between June 15 and June 21 to "Bang goes the theory: Scientists claim dark matter that makes up most of universe 'may not exist'"
• Scientific Computing - Universe's Dark Side Debated, June 16

Other Interesting Dark Energy/Dark Matter Articles:

• Daily Mail - Scientists use world's most powerful digital camera in hunt for dark matter, June 17
• PhysOrg.com - A Mine for Dark Matter, June 23