Since it was first proposed way back in the 1930s, scientists have wondered about whether the matter we know of — atoms, their constituents, and other subatomic particles — represent all the matter that exists in the Universe, or whether there’s an unseen form of matter making up the majority of the cosmic mass budget: dark matter. Although the evidence for it has been largely indirect and astrophysical in nature, the cumulative case for dark matter is incredibly strong, coming from many different independent lines of evidence and all pointing towards the same cosmic picture. However, the ultimate hope is that we’ll be able to detect it directly: through particle interactions in a laboratory-based detector. Today’s leading efforts, all of which have yet to bear definitive fruit, include the LUX-ZEPLIN and XENON experiments.

In early September of 2026, the LUX-ZEPLIN experiment announced the appearance of an unprecedented, single event in their detector: an event that points towards a dark matter particle, albeit at a meager 2.6σ statistical significance. The event itself is already the single most compelling data point in the quest to directly detect dark matter, and deserves a large amount of follow-up interest. However, no matter how good the data is for this one single event, that isn’t sufficient to claim that we’ve detected dark matter. A similar experimental lesson arose historically: from 1982’s even more compelling detection of what appeared to be a magnetic monopole.

Here’s what the two experiments have in common, and why anyone hoping that this detection really does signal dark matter should remain appropriately skeptical.

Above, you can see an image of the LUX-ZEPLIN detector: one of the most modern, sophisticated apparatuses designed to search for dark matter. The idea behind most direct detection setups is similar:

• you design a controlled target: a collection of atomic nuclei held under conditions with specific properties,
• you wait for an incoming particle to collide with one of those atomic nuclei,
• as a result of that recoil, at least one particle gets kicked off at relativistic speeds, where it moves faster than the speed of light through the medium in which the target is embedded,
• which means that particle produces a cone of blue light in the form of Cherenkov radiation, which can be detected by surrounding your target with photomultiplier tubes,
• and the relativistic particle then also produces an ionization trail, leading to a “line” of electrons within the target region,
• and an external set of electromagnetic fields causes those electrons to “drift” up to the top of the chamber (a time-projection chamber),
• and then, by correlating the drifting electron signature with the Cherenkov light signature, physicists can reconstruct the type of event that occurred.

LUX-ZEPLIN is just one of many dark matter direct detection efforts to leverage this setup, alongside XENON, SuperCDMS, and CoGeNT, among several others. The differences between the experiments largely arise from the size/mass of the targets, the types of atomic nuclei chosen as the target for the experiment, the types of shielding used to winnow out background events, and so on.

This photograph shows the XENON detector and target, wrapped in the ~700 tonnes Cherenkov water detector (left), with the supporting instrumentation in the LNGS hall (right).

It’s a tricky game, of course. In addition to the signals that could be caused by a dark matter particle colliding with atomic nuclei, there are many other less exotic, better understood particles that can produce similar signatures. When radioactive particles, found in the natural environment of the surrounding Earth, undergo decays, one of the products they can produce is neutrons of varying speeds. When a neutron collides with an atomic nucleus in the target area, it can produce a similar signature to what dark matter would produce.

The same thing applies to neutrinos: particles produced by the Sun, by atmospheric cosmic rays, and by the background of supernovae all across the Universe. The XENON experiment recently achieved sufficient sensitivity that the majority of their events-of-interest now come from this neutrino fog, which makes efforts towards the direct detection of dark matter within that parameter space even more difficult.

And there are also rare events that can occur where two signals are produced independently: a cone of Cherenkov light (picked up by the photomultiplier tubes) and an ionization signature (picked up by the time projection chamber), but that happen to be coincident in time.

This two-panel illustration of the LUX-ZEPLIN detector shows the anatomy of the apparatus on the left, where the target material (at center) is surrounded by photomultiplier tubes that can pick up the signal of any Cherenkov light generated within the detector, while an applied electromagnetic field causes the subsequently generated ionization trail of electrons to drift upwards as shown at right, creating a second signal at the top as part of the time projection chamber. Coordinating these two signals together is what signifies a detection event.

Although there are legitimate reasons to argue against the likelihood of any (or all) of these interpretations, these are indeed all things that do happen inside every such detector that one can build, and measures need to be taken to understand these backgrounds very well. Even so, outlier events occur, and a single outlier event can indeed mimic what a true “dark matter signal” would look like. This is not intended to diminish how interesting the new LUX-ZEPLIN event is, but rather to serve as a cautionary voice: there are mechanisms that exist by which currently understood physics, without invoking any form of particle-based dark matter, can create the exact signals that were seen inside the LUX-ZEPLIN detector.

If we can collect more data and continue to see additional events that are consistent with the one outlier event that was seen already, then we can start to build a case for the direct detection of dark matter, albeit with these highly unusual, unexpected properties. While most dark matter detectors, including LUX-ZEPLIN, were designed to search for specific classes of particles:

• rather heavy WIMPs, with expected (energy-equivalent) masses in the GeV to hundreds-of-GeV range, more massive than an individual proton,
• or rather light axions, with expected (energy-equivalent) masses in the sub-eV range, making them less than a millionth the mass of a single electron and closer to the mass of a neutrino,

this novel event instead suggests a mass of between 10,000 and 300,000 eV, which is only somewhat lighter than an electron but much heavier than a neutrino.

This graph shows the signals generated in the LUX-ZEPLIN detector after 2.84 tonne-years of exposure time. The two axes represent the Cherenkov radiation signal and the time projection chamber signal, both of which must be correlated to the same event. Most of the events are background events, clustered along the curve, with the one event just below the red lines representing the outlier event: a candidate dark matter signal.

Because this is a first-of-its-kind event, it’s only natural that a plethora of theorists and experimentalists are pursuing it further: concocting potential explanations and mechanisms for what could be going on, and motivating further follow-up apparatuses that could explicitly attempt to expose a dark matter particle with the properties that could create such a signal. But with one event only, we must demand high levels of both skepticism and care, as single, outlier events in the direct detection space have arisen before, only to fail the reproducibility test when larger, more expensive, more sophisticated experiments were built and conducted.

Back in the early 1980s, largely motivated by compelling theoretical reasons surrounding grand unified theories, there was a widespread expectation that in addition to the “electric monopoles” known to exist — particles with fundamental positive and negative electric charges — there ought to exist fundamental magnetic charges as well: isolated north magnetic poles and south magnetic poles: magnetic monopoles. In our conventional understanding of the world, we have only fundamental electric charges, and the way you create a magnetic field is by having an electric charge in motion. The motion of the electric charge induces a magnetic field, and by having a charge move back-and-forth or in a loop, you can create a north and south magnetic “pole” in tandem: the existence of a magnetic dipole.

It’s possible to write down a variety of equations, like Maxwell’s equations, that describe the Universe. We can write them down in a variety of ways, but only by comparing their predictions with physical observations can we draw any conclusion about their validity. It’s why the version of Maxwell’s equations with magnetic monopoles (right) doesn’t correspond to reality, while the ones without (left) do. The displacement current term (the second term in the fourth equation) arose from Maxwell’s attempt to fix the incompleteness in electricity and magnetism that existed prior to his work: an important theoretical leap that turned out to accurately reflect reality.

However, if you extend our currently understood physics in a variety of ways, including:

• by making Maxwell’s equations symmetric between electric and magnetic fields,
• by allowing the existence of even a single magnetic charge to explain why electric charges are quantized,
• or by embedding the Standard Model’s gauge group, SU(3) ⊗ SU(2) ⊗ U(1), within a larger gauge group, such as SU(5) or SO(10), in a grand unification scenario,

then the Universe would also have fundamental magnetic charges within it in addition to electric ones: magnetic monopoles. These are mere theoretical motivations to consider their existence, however. If we want to determine whether magnetic monopoles actually exist or not, we need experimental evidence to support it.

One method for doing this is very simple. If you take one end of a bar magnet (i.e., part of a magnetic dipole) and pass it through the middle of a loop of conducting wire, or move it in-and-out of that loop, the changing magnetic field inside that loop will induce an electric current in the wire: a consequence of Faraday’s law of induction. However, because bar magnets always have both a north and a south pole, the current that gets induced is symmetric between one pole of the magnet entering the loop and the other pole of the magnet exiting the loop. You don’t get a net flux of magnetic charge through the loop: for every north pole (or “positive” magnetic charge), you get a south pole (or “negative” magnetic charge) that must also go through the loop.

When you move a magnet into (or out of) a loop or coil of wire, it causes the field to change around the conductor, which causes a force on charged particles and induces their motion, creating a current. The phenomena are very different if the magnet is stationary and the coil is moved, but the currents generated are the same. By changing the magnetic field inside a conductor, you induce an electric current. If we had magnetic monopoles, in addition to the magnetic dipoles we know we have, it would be possible to generate a unique signal as a monopole passed through that coil of wire.

Therefore, if you want to look for magnetic monopoles, what you can do is set up a very sensitive loop of wire, and look for any changes in the net flux of magnetic charges that went through that loop. If you made the loop of wire superconducting, you could have a low enough noise floor that you could conceivably detect even a single fundamental “unit” of magnetic charge — a Bohr magneton (or some fraction thereof, depending on how magnetic charges were quantized) — that passed through the loop. And if you made multiple loops of wire all superimposed atop one another, i.e., a coil of wire, you could then amplify the signal you saw by a factor of N, where N is the number of loops in your coil of wire.

This is not just something you can do in principle, but has been within experimental reach for many decades now. Back in 1981, partially motivated by the 1974 work of t’Hooft and Polyakov and the across-the-board interest in Grand Unified Theories, experimental physicist Blas Cabrera built precisely such a device. He built a coil of wire with exactly 8 loops in it, allowing him to differentiate between a spurious signal that only affected one or two of the loops. He cryogenically cooled and isolated his experiment, allowing him to precisely measure any signal of electric induction that affected the coil of wire. And he knew exactly what to search for: an electric current that corresponded to a single magnetic charge, of one Bohr magneton (resulting in a signal of either +8 or -8 in the detector), passing through the loops.

In 1982, an experiment running under the leadership of Blas Cabrera, one with eight turns of wire, detected a flux change of eight magnetons: indications that were consistent with a single magnetic monopole having passed through the coil of wire. Unfortunately, no one was present at the time of detection, and no one has ever reproduced this result or found a second monopole. Still, if string theory, grand unification, and/or a whole host of other scenarios are correct, then magnetic monopoles, being not forbidden by any law, must exist at some level.

If there were a standard dipole magnet passing through the coil instead of a true magnetic monopole, you wouldn’t observe an overall net electric induction signal. In the dipole scenario, a signal of either +8 or -8 would be swiftly followed by the equal-and-opposite signal, of -8 or +8, bringing the total net signal back to zero. While small fluctuations were routinely seen in the experiment, likely corresponding to expected low levels of thermal noise or the addition of more cryogenic coolant to the system, no such signal was observed for the first few months that the experiment was run.

Then, on February 14, 1982 — Valentine’s Day, which happened to be a Sunday that year — a transfer of liquid nitrogen occurred at around 9 AM: a routine event. Afterwards, everyone left for the remainder of the day. While there was nobody around in the office, the experiment continued to run. The next morning, on Monday, Blas Cabrera returned to the office, and was absolutely shocked by what he saw. Waiting there for him was the experiment’s recorded data. At right around 2 PM on the previous day, a signal, consistent with precisely +8 Bohr magnetons, appeared in the data. The new baseline was stable, having shifted upwards by exactly the amount that a theorized magnetic monopole would have caused.

Prior to the event of February 14, 1982, the only events registered in Cabrera’s detector were of 2 magnetons or less. The one event of 8 magnetons was unprecedented, and was consistent with a magnetic monopole of the predicted (Dirac) charge passing through it. Unlike all other events observed by the experiment, this one was entirely consistent with a magnetic monopole event.

Had his team done it? Had they detected the first magnetic monopole in history?

The data was certainly consistent with exactly that interpretation. However, there are all sorts of errors and uncertainties that can be induced in an experiment by a variety of factors: some easily explainable by backgrounds, others by faulty equipment, and others by human error. (I myself once worked with an experimental physicist who installed a sensitive cable backwards by mistake, leading to a very expensive short-circuit and a subsequent fire; the data from the experiment from the time of installation to the time of the short-circuit was similarly unreliable.)

The only way to be certain you aren’t fooling yourself is to obtain independent verification of what it seems that you saw. Emboldened by Cabrera’s positive result, several teams of physicists set out to build similar apparatuses. Many had:

• larger surface areas, increasing the likelihood of a magnetic monopole passing through them,
• more loops in their coils of wire, increasing the magnitude of any signal that would arise,
• and more sensitive “veto” channels, where any spurious signal even one single loop within the coil would be detected.

And yet, no other similar signal was ever seen: not in any experiment or upgrade since. On Valentine’s Day of the next year, 1983, Nobel Laureate Stephen Weinberg composed a poem to Blas Cabrera, stating:

“Roses are red,
Violets are blue,
It’s time for monopole
Number TWO!”

These are the modern constraints available, from a variety of experiments largely driven from neutrino astrophysics, that place the tightest bounds on the existence and abundance of magnetic monopoles in the Universe. The current bound is many orders of magnitude below the expected abundance if Cabrera’s 1982 detection was to be expected within the parameters (duration, cross-section, and sensitivity) of the experiment, rather than a single outlier event.

In fact, as of 2026, the bounds from a wide variety of experiments that would have been sensitive to magnetic monopoles are many orders of magnitude more stringent than the expected abundance of them would have been based on the observed 1982 event. Although we don’t know what the underlying cause was behind the signal — an experimental error, an actual monopole, a prank played by a graduate student, a trick involving two connected (and then disconnected) horseshoe magnets — the fact remains that without independent confirmation, we simply can’t state with any confidence that we have discovered something remarkable from one event alone.

Cabrera himself eventually abandoned the search for magnetic monopoles, and went on to become a senior figure in the experimental search for dark matter via direct detection, participating in and taking a leadership role for the CDMS and SuperCDMS collaborations.

Now, some 44 years after that legendary event, we have a new “one-of-a-kind” event to puzzle over: one that could indicate dark matter, or be an unlikely outlier of a background event, or be a hitherto unexplained experimental error of an unknown variety. One thing is certain, however: this single event — an unexpected “blip” in the data — isn’t sufficient, on its own, to lead to the conclusion that we’ve directly detected dark matter. For that, additional data points, and independent confirmation, is needed. What we’ve seen so far is fascinating and suggestive, but only time, and more data, will ultimately point the way to what nature is telling us about itself.

This article One blip isn’t enough to declare “dark matter has been detected” is featured on Big Think.

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