So, what is "dark matter?"
"Dark matter" or "missing mass" is an abstract concept that came out of the failure of gravitational cosmology to account for certain observations of objects in space.
"The idea of dark matter was born at Caltech in 1933 ... In observations of a nearby cluster of galaxies named the Coma cluster, Fritz Zwicky calculated that the collective mass of the galaxies was not nearly enough to hold them together in their orbits.
"He postulated that some other form of matter was present but undetected to account for this 'missing mass.' Later, in the 1970's and '80's, Vera Rubin similarly found that the arms of spiral galaxies should fly off their cores as they are orbiting much too quickly."
http://www.spacedaily.com/reports/How_We_See_Dark_Matter_999.html
Essentially dark matter is an error bar on the Standard Model of [Gravitational] Cosmology. We can calculate how much mass is needed, gravitationally speaking, to hold galaxies and such together. We can then observe galaxies and other objects in space across the range of the electromagnetic spectrum from radio up through gamma rays and assay whether or not the actually observable mass of the objects matches up with theoretical predictions.
Simply put: the observable matter in galaxies is insufficient to account for their characteristics.
There are, thus, two options:
- Consider the gravitational models falsified and move on to a different theory.
- Forgo falsification and invent a new theory or substance to salvage the gravitational model.
Don't worry, it gets weirder...
Not only is the stuff invisible, in order not to throw off other theories, it also only interacts gravitationally with other matter.
"Dark matter neither emits nor absorbs light or other electromagnetic radiation, and so cannot be seen directly with telescopes."
http://en.wikipedia.org/wiki/Dark_matter
That is, it doesn't emit electromagnetic radiation (the aforementioned EM spectrum, from radio up through gamma rays) and neither is it influenced by electric or magnetic fields. But, one supposes this shouldn't be surprising since it is, at its heart, only a mathematical kludge.
But wait, it gets weirder!
Despite dark matter not interacting with the known electromagnetic forces, some theorists want to shoehorn in some kind of electromagnetic-like force anyway, but one specific to dark matter.
"...just like ordinary matter couples to a long-range force known as 'electromagnetism' mediated by particles called photons,' dark matter [may couple] to a new long-range force known (henceforth) as 'dark electromagnetism,' mediated by particles known (from now on) as 'dark photons.'"It's difficult to tell whether these folks are just pulling our legs or they're actually serious. Though, the fact they've submitted a paper on the subject seems to imply the latter.
http://blogs.discovermagazine.com/cosmicvariance/2008/10/29/dark-photons/
So, okay, say for a moment that we accept the premise that dark matter exists. We don't. But let's say we did. This should be a testable theory.
And, testing it, some scientists are (in various ingeniously clever and indirect ways, keeping in mind we can't directly observe dark matter since it doesn't emit EM radiation or interact with electric or magnetic fields and we still have no idea how gravity itself actually works at the most basic physical level).
But, before dark matter has even been experimentally confirmed, scientists have already started incorporating it into other theories and applying this new tool to other fields of inquiry, building up a rickety structure of beliefs and assumptions all resting on this now load-bearing pillar. Reification is a dangerous thing. Once you start believing a thing is real, you stop questioning its reality and it becomes an unquestioned (even if also unproven) assumption, often mistaken for a "fact."
Recently, some scientists tried calculating how often WIMPs (Weakly-Interacting Massive Particles; one "dark matter" candidate particle) impact the human body. They predicted about "once a year," but in working through the problem they came up with something closer to "once a minute."
But, as such things go, their results have tons of assumptions, not least of which being that dark matter is abundant everywhere, including here. A reasonable assumption, considering that upwards of 23% of the mass/energy of the universe.
But, wait a minute... What's that? Breaking news! Two studies released in the past month have offered tentative refutations of dark matter based on actual observations of local space (in the Sun's and the Milky Way's neighborhoods). And one experiment here on Earth appears to be offering null results (that is, no evidence of "dark matter").
Earlier this week, scientists released the results of a survey of the Milky Way's local cosmic neighborhood. The press release had the following to say:
"'Once we had completed our analysis, a new picture of our cosmic neighbourhood emerged,' says Pawlowski.If the observations stand up to scrutiny, the Standard Model has a hard time explaining them with the current dark matter-centric theories. Team members put the situation thus:
"Team member Pavel Kroupa, professor for astronomy at the University of Bonn, adds 'We were baffled by how well the distributions of the different types of objects agreed with each other.' As the different companions move around the Milky Way, they lose material, stars and sometimes gas, which forms long streams along their paths. The new results show that this lost material is aligned with the plane of galaxies and clusters too. 'This illustrates that the objects are not only situated within this plane right now, but that they move within it,' says Pawlowski. 'The structure is stable.'
"''In the standard theories, the satellite galaxies would have formed as individual objects before being captured by the Milky Way,' explains Kroupa. 'As they would have come from many directions, it is next to impossible for them to end up distributed in such a thin plane structure.'"
http://www.ras.org.uk/news-and-press/219-news-2012/2118-do-the-milky-ways-companions-spell-trouble-for-dark-matter
"Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory. We see this as the beginning of a paradigm shift, one that will ultimately lead us to a new understanding of the universe we inhabit."
http://www.ras.org.uk/news-and-press/219-news-2012/2118-do-the-milky-ways-companions-spell-trouble-for-dark-matter
The question is, will the paradigm actually shift or will additional 'fixes' and 'patches' be added, order to save the oft-falsified theory?
A week or two ago, a different paper was released showing that observations of local objects in the Sun's neighborhood (stars, dust, gas) account well for their motions via gravity, with no room for any extra "dark matter."
The press release puts the implications bluntly:
“The amount of mass that we derive matches very well with what we see -- stars, dust and gas -- in the region around the Sun,” says team leader Christian Moni Bidin ... “But this leaves no room for the extra material -- dark matter -- that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!”That is, no mass is "missing" from our local neighborhood. Ergo, no dark matter is required to explain the motions of objects in local space, despite the Standard Model's expectations that it should be there. As they say, galaxies "certainly rotate faster than the visible matter alone can account for," gravitationally speaking. Their results "contradict the currently accepted models" and "a new solution ... must be found."
"Despite the new results, the Milky Way certainly rotates much faster than the visible matter alone can account for. So, if dark matter is not present where we expected it, a new solution for the missing mass problem must be found. Our results contradict the currently accepted models. The mystery of dark matter has just become even more mysterious."
http://www.eso.org/public/news/eso1217/
In fact, this revelation has implications for detection efforts here on Earth. Even if dark matter exists, if there is none in our local neighborhood, it'll be a lot harder to detect.
"The new results also mean that attempts to detect dark matter on Earth by trying to spot the rare interactions between dark matter particles and “normal” matter are unlikely to be successful."
http://www.eso.org/public/news/eso1217/
But more likely it won't be detected because, well, it's 'just not there.' It's a figment of the over-active imagination of astrophysical mathemagicians.
But, that brings us to the 'testability' requirement of theories and the experiment currently being run here on Earth to try to detect dark matter: Xenon 100.
It got some press back in the day (2012) when it released preliminary results from its first 11 days of operation.
"Now, a third experiment called Xenon 100, which its makers say is even more sensitive than the other two [DAMA & CDMS-II], has failed to detect the impact of any dark matter particles, casting doubt on the earlier results. 'Dark matter particles continue to escape our instruments,' says Xenon 100 spokesperson Elena Aprile of Columbia University in New York."However, there was a modicum of backlash against the Xenon 100 results, but the team has continued on undeterred, preferring their results to speak for themselves.
http://www.newscientist.com/article/dn18839
Appropriately enough, the team published a new paper in 2011 regarding the results of 100 days of Xenon 100 data. Their conclusion:
"In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found."So, at 100 days, the results are the same as they were at 11 days. "No evidence for dark matter is found."
http://arxiv.org/abs/1104.2549
In all, it seems that dark matter is on the shakiest of footings and current research is not bearing it out. The question, again, is whether the repeatedly falsified model will finally be thrown out... Time will tell.
It is suggested that researchers follow-up, embrace and extend the fully electrodynamic Particle-in-Cell (PIC) simulations carried out by Los Alamos plasma physicist Anthony Peratt back in the early 1980's, showing that galaxies can and should be explained in terms of the ubiquitous electrically conductive plasma permeating the universe. Starting from an electrodynamic point of view, galaxy rotation curves come directly out of the simulations, no dark matter required.
Astrophysicists need to move on from one of the weakest forces (gravity) to one of the strongest forces (electromagnetism), and acknowledge the electrodynamic nature of the universe as a whole.
We already know that we live in a so-called "magnetic universe." But, then again, we also know from whence springeth magnetic fields. Magnetic fields are generated by electric currents. Period.
"...steady electric and magnetic fields cannot generate themselves. Instead, they have to be generated by stationary charges and steady currents. So, if we come across a steady electric field we know that if we trace the field-lines back we shall eventually find a charge. Likewise, a steady magnetic field implies that there is a steady current flowing somewhere. All of these results follow from vector field theory (i.e., from the general properties of fields in three-dimensional space), prior to any investigation of electromagnetism."If we live in a magnetic universe, more fundamentally, we live in an electric universe. Live it, love it, deal with it.
http://farside.ph.utexas.edu/teaching/em/lectures/node37.html
"...all steady magnetic fields in the Universe are generated by circulating electric currents of some description."
http://farside.ph.utexas.edu/teaching/em/lectures/node35.html
So, lets dispense with the pixies and fairy dust and get down to the business of determining what actually runs the universe. Answers are at hand, if we're courageous enough to slaughter a few sacred cows in the process.
