In case you missed them, here’s a few pieces I’ve recently written and published in Aeon magazine, Scientific American, and Hakai magazine. Thanks as usual to my excellent editors! I’m only posting brief excerpts here, so if you’re interested, please check out the whole thing using the links below.
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Does dark matter exist?
Dark matter is the most ubiquitous thing physicists have never found: it’s time to consider alternative explanations.
In 1969, the American astronomer Vera Rubin puzzled over her observations of the sprawling Andromeda Galaxy, the Milky Way’s biggest neighbour. As she mapped out the rotating spiral arms of the stars through spectra that she and colleagues had carefully measured at the Kitt Peak National Observatory and the Lowell Observatory, both in Arizona, she noticed something strange: the stars in the galaxy’s outskirts seemed to be orbiting far too fast. So fast that she’d expect them to escape Andromeda and fling out into the heavens beyond. Yet the whirling stars stayed in place.
Rubin’s research, which she expanded to dozens of other spiral galaxies, led to a dramatic dilemma: either there was much more matter out there, dark and hidden from sight but holding the galaxies together with its gravitational pull, or gravity somehow works very differently on the vast scale of a galaxy than scientists previously thought…
Over the past half century, no one has ever directly detected a single particle of dark matter. Over and over again, dark matter has resisted being pinned down, like a fleeting shadow in the woods. Every time physicists have searched for dark matter particles with powerful and sensitive experiments in abandoned mines and in Antarctica, and whenever they’ve tried to produce them in particle accelerators, they’ve come back empty-handed. For a while, physicists hoped to find a theoretical type of matter called weakly interacting massive particles (WIMPs), but searches for them have repeatedly turned up nothing.
With the WIMP candidacy all but dead, dark matter is apparently the most ubiquitous thing physicists have never found. And as long as it’s not found, it’s still possible that there is no dark matter at all. An alternative remains: instead of huge amounts of hidden matter, some mysterious aspect of gravity could be warping the cosmos instead…
[Read the entire essay in Aeon magazine, published on 25 June.]
Planet Nine Could Be a Mirage
Mysterious patterns in orbits of small bodies in the outer solar system could arise from the gravity of a massive disk of icy debris rather than an undiscovered giant world.
Some four years ago, when Ann-Marie Madigan first encountered the idea that there might be an undetected massive planet lurking beyond Pluto’s orbit, she felt excited but skeptical. The evidence for such a world was then—and now remains—circumstantial: strange patterns in the orbits of small objects at the outskirts of the known solar system. Proponents of “Planet Nine” (Pluto no longer counts in the solar system’s planetary tally) say such patterns could be produced by that world’s hefty gravitational influence. But Madigan, an astrophysicist now at the University of Colorado Boulder, wondered whether some other, more prosaic explanation could suffice. At the time, she was studying how stars can jostle one another into different orbits as they whirl around supermassive black holes. And she saw no reason why her work could not also apply to tinier things orbiting our sun.
Today, from those modest beginnings, Madigan and a few of her collaborators have developed a totally different theory to explain the strangeness in the outer solar system: the “collective gravity” of a diffuse, sprawling disk of icy debris far beyond Pluto could alter the orbits of the far distant objects we readily see in a way that resembles the effect of a large planet. Such a disk would be composed of millions of small bodies, most of them left over from the solar system’s formation long ago.
“What we’re doing is taking the gravitational forces between all these small bodies into account,” Madigan says. “Including those gravitational forces turns out to be really important.” Provided the putative disk possessed sufficient mass—several times that of Earth—over a billion years or so, the tiny gravitational interactions between and from its constituent members could sculpt the trans-Plutonian outer solar system in ways otherwise explained by Planet Nine, she maintains. The effect would be a bit like the proverbial butterfly flapping its wings to eventually set a distant storm in motion….
[Read the entire piece in Scientific American, published on 5 May.]
What’s Bad for Bees Could Be Bad for Marine Life, Too
Preliminary research shows that a popular insecticide hampers arthropods in the ocean.
Over the past two decades, farmers hoping to ward off pests have increasingly turned to planting seeds that come straight from the supplier pre-coated in neonicotinoids, a controversial class of insecticide chemically related to nicotine. With the insecticide built into the seeds, farmers no longer have to spray their fields with toxic chemicals, theoretically reducing the risk to non-target species.
But as it turns out, neonics, as they’re also known, do impact other species—most famously honeybees, the steep decline of which has been linked to the insecticides. That discovery led the European Union to ban neonics in 2018. However, they remain widely used in the United States, as well as in Canada, though with some restrictions. Now, Haley Davis, an undergraduate student studying toxicology in marine ecosystems at Hollings Marine Laboratory in South Carolina, and her colleagues are raising yet another reason to be concerned about the insecticides. Neonics dissolve easily in water, they say, and could be harming marine life…
[Read the entire piece in Hakai magazine, published on 4 May.]