Employing exotic unobservable entities such as dark matter may be an escape from scientific rigor in more ways than one.
Recently, the notion that most of the universe is composed of dark matter took an evidential hit. Live Science said, “A sprawling collection of galaxies and star clusters surrounding our own Milky Way is challenging long-standing theories on the existence of dark matter, the mysterious substance thought to pervade the universe.” According to a survey of satellite galaxies of the Milky Way conducted at the University of Bonn, dark matter theories fail to account for the arrangement of matter in a region spanning 10 times our galaxy’s diameter. The astronomers extended the impact of their findings to the entire universe:
“Our model appears to rule out the presence of dark matter in the universe, threatening a central pillar of current cosmological theory,” said study team member Pavel Kroupa, a professor of astronomy at the University of Bonn. “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.”
The statement also implies that previous “understanding of the universe” was misguided or absent.
Last month Ker Than, reporting for National Geographic News, quoted an astronomer who said the finding of a huge structure of satellite galaxies surrounding the Milky Way puts cosmology “basically in a shambles.” He referred to his other National Geographic article two weeks earlier that also questioned the existence of dark matter because it wasn’t detected where needed to explain the Milky Way’s halo. That finding “could provide ammunition for skeptics who argue that the invisible substance is just an illusion,” he said. About the same time, though, another National Geographic reporter claimed that dark matter particles hit the average human once a minute.
Growing questions about dark matter’s existence may be giving rise to a proverb called the “dark matter argument.” In another context, Maggie McKee at New Scientist reported doubts that the star Fomalhaut has a planet. A bright spot imaged in a dust disk surrounding the star, imaged by the Hubble Telescope in 2004, had been hailed as a direct observation of an extrasolar planet. Astronomers were encouraged at the time by the fact that it appeared in a gap in the dust dusk, suggesting that the planet had cleared a path for itself.
Now, however, a new study from NASA’s Goddard Space Flight Center has shown that the bright spot might be a dust cloud, not a planet. Furthermore, simulations shown in a computer animation within the article indicate that gaps in dust disks – even with sharp edges – can form without the presence of a planet.
A JPL scientist used the occasion to joke about the escape hatch dark matter theories provide:
“I call it the dark matter argument,” says Wladimir Lyra at NASA’s Jet Propulsion Laboratory in Pasadena, California. “There is something you are seeing that you cannot explain, and you blame the gravity of something you cannot see.”
Dark energy has also come under scrutiny. National Geographic asked, is it a kind of “reverse gravity” as usually described? Perhaps not. The pressure leading to accelerated expansion of the universe might come from normal old antimatter, well characterized in earth-based detectors.
These appear to be dark days for dark matter theories.
Philosophers call appeals to unseen, unknown entities “occult phenomena.” Like spiritually occult things, they are placeholders for ignorance. But given a name, these placeholders take on a reality of their own, used by scientific shamans to tell the peasants why things are the way they are.
For too long, dark matter has been a rhetorical flubber to impress laypeople while escaping scientific rigor. It’s time to call astronomers to account. Account for dark matter, or turn on the light.