The search for dark matter opens up to new horizons after decades without conclusive findings

The MIT Technology Review article, written by Dan Garisto, offers a broad and well-documented overview of the current state of the search for dark matter, one of the greatest open mysteries of fundamental physics. The text is not a paywall teaser: it is a complete report with statements from several experimental and theoretical physicists, as well as concrete technical details about ongoing experiments.

The starting point is revealing: underground liquid xenon detectors—such as LZ in the Homestake mine (South Dakota), PandaX-4T in China and XENONnT at the Gran Sasso laboratory (Italy)—have spent years searching for WIMPs (weakly interacting massive particles), the favored dark matter candidate since the 1980s. However, these detectors have begun to record signals that come not from dark matter, but from solar neutrinos, ordinary particles that pass through the Earth without difficulty. This phenomenon, called the "neutrino fog," represents an almost insurmountable physical limit: the larger and more sensitive the detectors become in hunting WIMPs, the more neutrinos they detect, and these end up masking any possible signal of real dark matter.

This implies that the next generation of xenon detectors—the XLZD project, which would require between 60 and 80 metric tons of liquid xenon (practically the entire annual global production of the element)—could be the last serious attempt with this technology. And its future is uncertain: in December 2025, the U.S. Department of Energy announced that it would neither host the project nor co-finance its cost, estimated at more than 300 million dollars, which according to one of the scientists cited (Hugh Lippincott, of the University of California, Santa Barbara) could mean that the project may never materialize.

Faced with this outlook, the particle physics community is drastically broadening the range of candidates and search strategies. The article explains that, in addition to WIMPs, there are other theoretical candidates spanning an enormous range of masses—on the order of 50 orders of magnitude of difference—from primordial black holes (hypothetical asteroid-sized objects formed after the Big Bang) to axions, ultralight particles that were also originally proposed to resolve another problem in particle physics (the so-called "strong CP problem" of the strong nuclear force).

The search for axions is carried out using "haloscopes," ultracold chambers with intense magnetic fields that function as a kind of tunable radio, with names as curious as MADMAX or ABRACADABRA. According to the report, so far only 10% to 20% of the parameter space where an axion that resolves the strong CP problem might be found has been explored, which leaves much ground still to investigate. Gray Rybka, a physicist at the University of Washington, provides a nice anecdote: at one point in the experiment they detected a signal they jokingly called "a message from God," which turned out to be a religious radio station picked up by mistake.

Another research front is so-called "low-mass dark matter," situated between the weight of an electron and a proton. Here the detectors use crystals, semiconductors and even superfluid liquid helium to capture minimal vibrations or ionizations. The article mentions that in 2020 "excess events" were recorded in several experiments that made people think, for a moment, of a possible dark matter signal, but that they were ultimately explained by background noise (impurities in the materials, cosmic rays, and even a detector that vibrated because it was too tightly fastened in its mount). This illustrates how delicate and prone to false positives this branch of research is.

The report also gathers more unusual, large-scale proposals: searching for ultraviolet auroras in planetary atmospheres caused by the annihilation of dark matter particles, precisely measuring the temperature of the Earth's core, or even examining the icy surface of Ganymede (a moon of Jupiter) in search of anomalous craters that could have been caused by asteroid-sized primordial black holes.

Theoretical physicist Kathryn Zurek, of Caltech, proposes a radically different approach: focusing exclusively on the gravitational interaction of dark matter, the only property of which we have certainty, instead of assuming hypotheses about its specific nature. However, she herself acknowledges that this path could take up to a hundred years to bear fruit, and that she probably will not live to see results in her own lifetime.

The article closes with an illuminating comparison regarding the discovery of the Higgs boson: before the LHC came online, physicists already knew, thanks to robust theoretical calculations, that the Higgs should weigh between 120 and 150 times the mass of a proton, and indeed it appeared in the data with a value of 133. With dark matter, by contrast, scientists do not even know the shape of the "hat" from which they are trying to pull the correct number, in Rybka's words. Even so, researchers such as Rouven Essig (Stony Brook University) insist that, despite the uncertainty and the risk of finding nothing, the only sensible option is to keep searching on many different fronts at once.

Overall, the article conveys a clear message: after decades of fruitless searching with a relatively narrow approach centered on WIMPs, particle physics is entering a much more exploratory, diverse and experimental phase, with multiple technologies, scales and disciplines—from tabletop detectors to astronomical observation of icy moons—competing to solve one of the universe's most persistent enigmas.