Dark hurricane

There are times that scientists use placeholder names for things they're pretty sure must exist, but haven't identified with sufficient clarity that they can say anything in detail about them.

One example -- that didn't end so well -- is the "ether."  The concept of the ether came about because once Christiaan Huygens, Augustin-Jean Fresnel, and Leonhard Euler made cogent arguments that light had many of the properties of waves, the next question was, "what medium is waving?"  In any familiar sort of wave, there's some sort of medium involved, the particles of which are moving as the wave propagates past.  So, not unreasonably, physicists proposed that there was some sort of medium permeating the universe through which light was propagating, and they called this substance the luminiferous ether.

The problem was, the ether didn't exist, as demonstrated by the Michelson-Morley experiment.  So scientists, scrambling about like mad to save their precious theory, proposed all sorts of convoluted dodges to explain why Michelson-Morley and the ether weren't mutually exclusive, but the whole thing came crashing to the ground when Albert Einstein came up with the Special Theory of Relativity -- which did away with the need for ether.

We have a similar situation right now in physics, except that (being in the middle of it) no one knows how it's going to end -- with a confirmation of an ether-like mysterious substance, or a 21st-century Einstein who proposes a shift in our understanding that makes the entire thing collapse.  I'm referring to dark matter, which was discovered in 1978 by Vera Rubin and Kent Ford because of its gravitational effects.  But this is no minor constituent of the universe; by Rubin and Ford's estimates -- which still hold -- dark matter comprises 85% of the mass of the universe.

The problem is, dark matter, whatever it is, is "non-baryonic" in nature.  Put simply, it does not interact with other matter, and has no effect on light except for the fact that its gravity warps the fabric of the universe and can deflect light's path (a phenomenon called gravitational lensing).

So at this point, we're pretty sure it's there, but no one knows anything about what it actually is.

But this may be about to change.  Last week a paper appeared in Physical Review D claiming that not only are we immersed in dark matter, we are currently in a stream of it (called "S1") that is blowing past us at an unimaginable 500 kilometers per second.  A team led by Ciaran O'Hare of the University of Zaragoza has been analyzing this matter stream, and have concluded that it was generated by the interaction between the Milky Way and a (now-defunct) dwarf galaxy the Milky Way devoured over a billion years ago.  But the remnants are still zooming past us, a dark hurricane light years wide in which we have been immersed without even knowing it until recently.

What the current study suggests is that we might use this to get some long-awaited hard data on dark matter.  Detectors are being set up to detect what are considered the two most likely constituents of dark matter -- WIMPs (weakly-interacting massive particles) and axions (which some theories say could exist in sufficient numbers to account for dark matter).

The problem is, there have been other attempts to find WIMPs and axions, and all have been completely unsuccessful.  In fact, the Wikipedia page on WIMPs (linked above) starts with the unpropitious words, "There exists no clear definition of a WIMP," which to my ears makes it sound like the 19th century physicists' "there's this stuff called ether, and we think it's there, but we can't tell you anything else about it."

The physicists, for their part, are hoping like hell something will come of all this, because if dark matter doesn't exist, it will punch a great big old hole not only in the General Theory of Relativity, but the Standard Model of Quantum Mechanics.  This isn't necessarily a bad thing; look at what the collapse of the ether theory led to.

Um.  The General Theory of Relativity and the Standard Model of Quantum Mechanics.  A little awkward, that.

Of course, I'm a layperson, despite my B.S. in physics.  Far smarter brains than I am are still taking the search for dark matter seriously.  If I was a betting man, though, I'd put money on the likelihood that there's something major we're missing, just as we did with Relativity.  This could lead to great things either way -- which is why this invisible storm is such an exciting discovery.

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If you are one of those people who thinks that science books are dry and boring, I'll give you a recommendation that will put that misconception to rest within the first few pages: Sam Kean's The Disappearing Spoon: And Other True Tales of Madness, Love, and the History of the World from the Periodic Table of Elements.

Kean undertook to explain, from a human perspective, that most iconic of all images from the realm of chemistry -- the Periodic Table, the organized chart of elements from the simplest (hydrogen, atomic number 1) to largest and most complex (oganesson, atomic number 118).  Kean's sparkling prose shows us the personalities behind the science, including the notoriously cranky Dmitri Mendeleev; tragic, brilliant Henry Moseley, a victim of World War I; and shy, self-effacing Glenn T. Seaborg, one of only two individuals to have an element named after them while they were still alive.

It's a fun read, even if you're not a science geek -- maybe especially if you're not a science geek.  Because it allows you to peer behind the curtain, and see that the scientists are just like the rest of us, with rivalries, jealousies, odd and misplaced loyalty, and all the rest of the faults the human race is subject to.

[If you purchase the book from Amazon using the image/link below, part of the proceeds goes to supporting Skeptophilia!]

The dark side

I love science, but sometimes scientists can be their own worst enemies.

The reason I say this is that scientists sometimes have a tendency to throw caution to the wind and engage in speculation, which then gets reported by the media as "scientific fact."  When said speculation turns out to be false, or is superseded by other models for which there is more evidence, laypeople get the wrong idea that scientists sit around all day making shit up, and when it turns out to be wrong, they just make more shit up, and on and on it goes.

So media bears a large share of the blame for this, as usual.  But that said, it would be nice if there was some way for scientists to identify in their academic papers when they're engaging in tentative hypothesis, and when they're elaborating on a well-established and rock-solid theoretical model.

Amongst the latter would be evolution and anthropogenic climate change.  Just had to throw that in there.

But as an example of the former, let's look at a paper by Michael Rampino, professor of biology at New York University, who recently published a paper in Monthly Notices of the Royal Astronomical Society proposing that the periodic mass extinctions that have occurred on Earth might be caused by the interaction between the Solar System and a thin layer of dark matter along the galactic plane.  Rampino writes:

A cycle in the range of 26–30 Myr has been reported in mass extinctions, and terrestrial impact cratering may exhibit a similar cycle of 31 ± 5 Myr. These cycles have been attributed to the Sun's vertical oscillations through the Galactic disc, estimated to take from ∼30 to 42 Myr between Galactic plane crossings. Near the Galactic mid-plane, the Solar system's Oort Cloud comets could be perturbed by Galactic tidal forces, and possibly a thin dark matter (DM) disc, which might produce periodic comet showers and extinctions on the Earth. Passage of the Earth through especially dense clumps of DM, composed of Weakly Interacting Massive Particles (WIMPs) in the Galactic plane, could also lead to heating in the core of the planet through capture and subsequent annihilation of DM particles. This new source of periodic heating in the Earth's interior might explain a similar ∼30 Myr periodicity observed in terrestrial geologic activity, which may also be involved in extinctions. These results suggest that cycles of geological and biological evolution on the Earth may be partly controlled by the rhythms of Galactic dynamics.

The difficulty, of course, is that dark matter is still yet to be detected, despite years of search.  We can observe that there's something out there that, from its gravitational effects, seems to make up most of the universe's mass.  But what it's made of, and what its properties are, are completely unknown.  "WIMPs" -- the Weakly Interacting Massive Particles Rampino references in his paper -- are one candidate for the constituents of dark matter.  But they, too, are yet to be confirmed to exist, despite multiple experiments designed to detect them at the Large Hadron Collider.

So Rampino is proposing that a 31 ± 5 million year mass extinction cycle (5 million years representing a 15% variability either way) links to a 30 to 42 million year galactic-plane-crossing cycle (which represents a 16% variability either way) via a mechanism connected to a type of matter we've never seen and whose properties can only be guessed at.

Map of the "dark matter halo" surrounding a galaxy [image courtesy of the Wikimedia Commons]

Now, don't get me wrong.  Thinking outside the box is the way great discoveries are made.  For example, it was Einstein's decision to throw away the "problem of the constancy of the speed of light" that led to the discovery of the Theory of Relativity.  Einstein's contemporaries had spent decades trying furiously to explain away the fact that in a vacuum, light seemed to move at the same speed in all reference frames, something that couldn't happen according to classical mechanics.  All sorts of wild ideas were proposed -- for example, a universal "ether" that permeated the universe, and through which light moved -- and one by one they were knocked down.

Einstein, however, decided to take the "problem of the constancy of the speed of light" and turn it into the "law of the constancy of the speed of light" and see what mathematical predictions came out of that assumption.  And then, run experiments to see if those predictions worked.  Lo: the Theory of Relativity, with its wild time dilation and Lorenz Contraction weirdness.

All of which is a long-winded way of saying that there's nothing wrong with speculation.  I just wish there was some way for scientists to differentiate between when they're proposing a speculative hypothesis and reporting on an experimentally-supported theory.

Maybe they should write speculative articles in "Comic Sans."  I dunno.

I say this because I'm seeing stories come up all over the place, just in the last couple of weeks, claiming that "dark matter killed the dinosaurs."  Which Rampino himself would admit is not justified at this time (note in the passage I quoted how many times he uses the words "could," "might," and "may").  And when someone else proposes a different mechanism to explain the periodicity of extinctions, it'll also get reported as fact, and laypeople will have further evidence that all scientists do is come up with wild tales all day long.

So I really should revise my initial statement.  It's not that scientists are their own worst enemies.  It's that popular media are the scientists' worst enemies.  That, and the fact that the public still doesn't really understand how science is done (look at the ongoing confusion about what the word "theory" means).

And given the fact that a significant proportion of the public still doesn't accept the findings of science that aren't speculative, the last thing we need is to sow more doubt in people's minds by misrepresenting the parts of science that are still only conjecture.