Will Dark Matter Hunters Ever Give Up?
The history of dark matter searches is a long string of non-detections. When does theory have to face reality?
The standard big-bang cosmology requires lots of mysterious unknown stuff labeled ‘dark matter.’ Cosmologists are convinced it exists, because otherwise galaxies and clusters of galaxies would quickly fall apart (quickly, that is, in moyboy cosmological terms). Theory requires that 85% of the universe is made up of this invisible matter that doesn’t emit electromagnetic radiation, but has gravity. Another 11% consists of dark energy, which is also completely unknown. That leaves only about 4% of reality accessible to observation.
Here are some of the most recent searches for dark matter and negative results.
The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations (Science Magazine). So much effort, so little return on investment looking at the decay of “stale neutrinos” as candidates for dark matter.
Dark matter may consist of previously unknown forms of subatomic particles. An unidentified astronomical x-ray emission line has been interpreted as being caused by the decay of a dark matter particle. If this is correct, then dark matter in the halo of the Milky Way Galaxy should produce a faint emission line across the whole sky. Dessert et al. tested this hypothesis using observations by the XMM-Newton (X-ray Multi-Mirror Mission) space telescope. Analyzing blank-sky regions with a total exposure time of about a year, they found no evidence for the predicted line and set upper limits on the decay rate that rule out the previously proposed dark matter interpretation.
Researchers look for dark matter close to home (University of Michigan). Sounds like a broken record: “Eighty-five percent of the universe is composed of dark matter, but we don’t know what, exactly, it is.” This is a press-release account of the Science paper mentioned above, showing off the guys who came back empty.
A new study from the University of Michigan, Lawrence Berkeley National Laboratory (Berkeley Lab) and University of California, Berkeley has ruled out dark matter being responsible for mysterious electromagnetic signals previously observed from nearby galaxies. Prior to this work there were high hopes that these signals would give physicists hard evidence to help identify dark matter.
Photograph of dark matter. White background provided for contrast.
First high-sensitivity dark matter axion hunting results from South Korea (Phys.org). South Koreans looked for the hypothetical ‘axion’ as a candidate for dark matter. Earlier searches turned up empty (30 May 2019, 31 October 2019–Halloween) but… (drum roll)… this one did, too!
In this experimental run, the team searched axions with a mass between 6.62 and 6.82 μeV, corresponding to the frequency between 1.6 and 1.65 GHz, a range that was selected by quantum chromodynamics. The researchers showed experimentally with a 90% confidence level, the most sensitive result in the mass range to date, that there is no axion dark matter or axion-like particle within that range.
The axion solves three mysteries of the universe (University of Michigan). UM believers are multi-tasking. The team looking for stale neutrinos fumbled (above), but maybe others will succeed in the axion hunt. They begin with high hopes: “A hypothetical particle called the axion could solve one of physics’ great mysteries: the excess of matter over antimatter, or why we’re here at all.” A good story begins with a conflict:
According to the Standard Model of particle physics, when our universe was born, the meeting of matter and antimatter should have annihilated each other. That means that nothing—no Earth, no sun, no galaxies, no humans—would exist. But we do.
“There’s a clear contradiction with the Standard Model,” said University of Michigan physicist and postdoctoral researcher Raymond Co. “Why is the whole universe filled with matter, and very, very little antimatter?”
That’s been a long-standing contradiction for decades now. The conflict now heats up to volcano temperature:
But there are a few contradictions within the Standard Model, one of them being the imbalance between matter and antimatter. The Standard Model also does not explain the existence of dark matter, nor does it explain an observed property of neutrons.
So does the axion solve these three contradictions? It might—if they could only find one. What is it?
The hypothetical particle axion is infinitesimally light—at least billions of times lighter than the proton, and almost does not interact with normal matter. This explains why they have not yet been detected, even with instrumentation that allows us to detect protons, neutrons and electrons.
Clever ploy: imagine a particle so small it cannot be detected. That explains why it hasn’t been detected. So do they deliver on the promise that an axion “solves three mysteries of the universe?” No. But it might if it were detected. Try that tactic with unicorns.
A new search for axion dark matter rules out past numerical predictions (Phys.org). A different team of hunters called the ADMX Collaboration looked for axions, too. Short answer: none found. But they keep trying. They compare it to scanning for a very weak radio station when you don’t know the frequency. That could keep someone busy for a long, long time. But take heart; they are improving the sophistication of their ignorance.
The search for dark matter axions has been ongoing for several decades now, and Du and his colleagues have already carried out a number of such searches using their cavity haloscope. While they were so far unable to detect invisible axions, the results of their recent experiment rule out a range of axion masses that were previously predicted by benchmark theoretical models of axion dark matter.
Graphic by David Coppedge
Why Not Change Course?
With the hunts always coming up empty, isn’t it time to try a different theory? Once in awhile, a team thinks outside the dark-matter box.
Galaxy formation simulated without dark matter (University of Bonn, via Phys.org). One alternative to the Standard Model is to ditch dark matter altogether, and try different assumptions. Maybe Newtonian dynamics acts differently at large scales. Using “MOdified Newtonian Dynamics” (MOND), the team from U of Bonn modeled galaxy formation without dark matter. Their results were “close to reality,” they say. MOND assumes that “the attraction of a body depends not only on its own mass, but also on whether other objects are in its vicinity.” Software built on this model was put into play.
The scientists then used this software to simulate the formation of stars and galaxies, starting from a gas cloud several hundred thousand years after the Big Bang. “In many aspects, our results are remarkably close to what we actually observe with telescopes,” explains Kroupa. For instance, the distribution and velocity of the stars in the computer-generated galaxies follow the same pattern that can be seen in the night sky. “Furthermore, our simulation resulted mostly in the formation of rotating disk galaxies like the Milky Way and almost all other large galaxies we know,” says the scientist. “Dark matter simulations, on the other hand, predominantly create galaxies without distinct matter disks—a discrepancy to the observations that is difficult to explain.”
Their approach is not without problems, but maybe they are on to something. Closeness to reality sure sounds more encouraging than repeated non-detection. And it doesn’t require believing that only 4% of reality is accessible to observation.
We’re watching a scientific community, obsessed with a theory (the big bang), refusing to give up. Dark matter is like the phlogiston of our time. Centuries ago, believers in phlogiston were convinced to their dying day that it must be there. It wasn’t. Only when other scientists changed the paradigm did chemists get out of their rut. Think how ludicrous the Dark Matter Myth is going to sound in future years if they don’t find it. ‘Scientists actually thought that 96% of the universe consisted of mysterious stuff they couldn’t find or describe. LOL!”
Dark matter is not a problem for a young universe. Certain creation models overcome the light-distance problem by various methods, allowing humans to see the distant universe even on the fourth day of a Biblical creation account. In that account, galaxies and clusters did not have time to spread out. (Recall, too, that secular cosmologists have their own light-distance problem, called the horizon problem). Creation also eliminates the antimatter problem, because it was the Creator’s purpose to make the universe habitable, and he is all-wise so as to get it right on the first try.
Creationists think that science should stick to what is observable. That’s why the multiverse is a bad idea; it is unobservable, even in principle. Dark matter needs to go into the waste bin of history, too, without spending any more money on it. Scientists should not waste any more time looking for mysterious, unknown stuff just because their pet theories require it. That sounds like the occult. Face reality, we say; look at the universe the way it really is: habitable, beautiful, declaring the glory of God.