The Liberty Bell, with its famous crack, hasn't been rung in 180 years, but that hasn't stopped scientists from pondering what the bell might have sounded like when tolling. In honor of the nation's 250th anniversary, researchers at Penn State University have modeled its acoustic properties, drawing on data collected from one of the bell's replicas. The work was first presented at a meeting of the Acoustical Society of America in Philadelphia earlier this year, followed by an article in Physics Today.

Historians aren't sure exactly when the Liberty Bell acquired its distinctive crack, just that it occurred sometime between 1817 and 1846. An 1846 account in the Public Ledger described the ringing of the bell on February 23 that year and mentioned that the bell had developed a crack, which someone had attempted to fix by filing the sides down. But it didn't work: The February 23 ringing extended the crack even more, so much so that "the old Independence Bell ... now hangs in the great steeple irreparably cracked and forever dumb." Nobody has heard it ring since.

This wasn't the first time the bell had cracked; the rim cracked shortly after it arrived in Philadelphia in 1752, the first time the clapper struck while testing the sound. It was recast by two local foundry workers, John Pass and John Stow, not once but twice, because the first recast produced a sound that one bystander likened to coal scuttles banging together.

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Writing about quantum entanglement is always a challenge. There are so many clichés to avoid: It’s mysterious, ghostly, spooky, and weird. Entanglement is none of those things, and yet it is also all of those things—a superposition of clichés, you might say. So, having gotten all of my clichés out of the way in the second sentence, let’s take a look at how a group of researchers managed to entangle a light beam with a glass bead, which is, frankly, quite an achievement.

Cliché-free entanglement

Quantum entanglement is nothing more or less than the idea that if two objects are linked, then their behavior will, in some ways, be correlated. To take a terrible example: My upper and lower arm are very strongly correlated in terms of relative position because they are connected at the elbow. No one is surprised by this because we can see that they are actually a single object called an arm.

Two photons can be, in a sense, joined together, meaning that they have correlations, too. In this case, we are (naively) surprised for three reasons. First, we think of photons as separate objects that cannot be joined—this is a mistake of understanding. Second, when we connect two photons, we only connect them in limited ways: The two photons may be wholly uncorrelated in terms of polarization, but strongly correlated in terms of energy.

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Francis Halzen, a physicist at the University of Wisconsin, Madison, has won the 2026 Nobel Prize in Physics "for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin.” Halzen spearheaded the development and construction of the IceCube Neutrino Observatory in Antarctica, enabling physicists to capture high-energy neutrinos created in the distant universe.

“It was a great surprise, and I obviously didn’t expect it,” Halzen said during a news conference in Stockholm, Sweden, speaking by phone from Italy. While the Nobel was awarded to Halzen, he emphasized that his work was the result of a “large collaboration” with other researchers.

“This reflects on the really courageous people who joined me in this project when really no respectable conservative physicist would have joined me. But many talented people did, and that’s why I’m here,” he said.

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It’s a regrettable reality that there is never enough time to cover all the interesting scientific stories we come across. So every month, we highlight a handful of the best stories that nearly slipped through the cracks. September’s list includes a tantalizing hint of the elusive dark matter at the LUX-ZEPLIN detector; entangled Z bosons at the Large Hadron Collider; possible use of psychoactive substances in the Late Pleistocene; and an intriguing technical description of a telescope attributed to Galileo.

A hint of dark matter?

Physicists believe dark matter makes up roughly 85 percent of matter in our universe, with the strongest (but not only) candidate being so-called weakly interacting massive particles (WIMPs). But directly detecting WIMPs, or other alternative hypothetical dark matter particles, has eluded physicists for decades. We might have our first glimpse, however, courtesy of the LUX-ZEPLIN detector buried deep in a gold mine in South Dakota. Those potentially exciting results were presented in a scientific talk at the 2026 TeV Particle Astrophysics conference in Japan, with a preprint available on the arXiv. (It has been submitted to Physical Review Letters for peer review.)

The announcement came with strong caveats: the signal is just a hint, well below the threshold needed to confirm discovery, and might just be a statistical fluke. Anyone who regularly follows dark matter news knows that past tantalizing anomalies evaporated as more data came in. But the LUX-ZEPLIN team was unable to account for this event and decided to report their result to the broader physics community. They are still collecting data, as is the XENONnT at the Gran Sasso National Laboratory in Italy. And China's PandaX detector is currently being built.

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An attempt to save NASA's $500 million Neil Gehrels Swift Observatory from dropping out of orbit fell short, but the behind-the-scenes machinations required just to make a rescue possible deserve recognition, government and commercial space officials said in a recounting of the mission.

The rescue mission was developed by Katalyst Space Technologies, working under a $30 million contract awarded by NASA last September. NASA gave Katalyst nine months to build and launch a satellite to capture Swift flying some 200 miles above the Earth and boost it into a higher orbit.

Katalyst's rescue spacecraft, known as Link, successfully launched July 3 and completed some of its initial checkouts before a malfunction caused it to spin out of control a few weeks later. NASA announced in August that Link would not be able to reach Swift as intended, and the rescue mission was aborted.

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