Analysis: Science & Technology — 30 October 2026
UC Davis mathematicians find Friedmann spacetimes unstable, challenging dark energy
A UC Davis team reports in Proceedings of the Royal Society A that Friedmann spacetimes, the backbone of the Lambda-CDM expansion model, are unstable to radial perturbations at both small and large scales. Blake Temple and colleagues recast the Einstein–Euler system so the standard cosmology appears as a rest point, then show that disturbances grow rather than decay. Fact: they conclude that accelerated expansion can emerge from Einstein’s original gravity without a cosmological constant. Analysis: that is a mathematical claim about solution stability, not a new astronomical measurement of the expansion rate.
Dark energy entered the standard picture after 1990s supernova data showed acceleration, reviving Einstein’s cosmological constant as a placeholder for unknown energy density. Friedmann models assume a homogeneous, isotropic universe whose scale factor evolves under that framework. The Davis group previously explored shockwave and self-similar solutions in the radiation era; the new paper extends the instability argument into the matter-dominated epoch.
The result does not yet replace Lambda-CDM as an observational fit. A spherically symmetric alternative introduces a center of symmetry, which sits uneasily with the Copernican assumption that no location is special. Temple notes that Lambda-CDM also privileges a vantage point if it is to match data. Open questions are whether the unstable modes produce the observed Hubble history, baryon acoustic oscillations, and cosmic microwave background, and how far from any “center” an observer could sit without contradicting isotropy.
Juno finds Jupiter’s bow shock uses multi-harmonic plasma waves and shocklets
University of Iowa researchers using NASA’s Juno spacecraft report in Nature Communications the most detailed view yet of Jupiter’s bow shock, the boundary where the solar wind meets the planet’s magnetosphere. Juno’s Waves instrument, sampling in December 2024, shows plasma waves with multiple frequency harmonics that heat and slow incoming particles more broadly than Earth’s typically single-frequency shock. Upstream “shocklets” further decelerate the flow before the main shock. Fact: Jupiter’s defense against the solar wind is structurally richer than Earth’s.
A bow shock forms when supersonic solar-wind plasma hits a magnetized obstacle. Earth mainly uses one shock surface; Jupiter’s larger magnetosphere and stronger field allow a cascade of wave modes. The Iowa team, including Jayasri Joseph and Bill Kurth, argues that extra harmonics couple energy into a wider particle population.
The paper is a local plasma measurement, not a complete magnetospheric model. Whether the same multi-harmonic plus shocklet pattern holds at all solar-wind speeds and Juno orbital phases remains open. The authors treat Jupiter as a nearby laboratory for stronger astrophysical shocks, including supernova remnants, but scaling from a planetary bow shock to a stellar explosion is an analogy, not a demonstrated mapping.
Delft researchers flip a single atom’s nuclear spin with radio waves
Delft University of Technology reports in Nature Communications that a scanning tunneling microscope can drive nuclear magnetic resonance on one atom. Hester Vennema, Sander Otte and colleagues sent simultaneous signals to an electron spin and a nuclear spin and found they could reverse the nucleus even when the two were largely disentangled. Fact: textbook expectation was that STM electrical signals would not couple directly to the shielded nuclear moment.
Nuclear spin is weaker than electron spin but better isolated, which is why it is a candidate quantum memory. The group adapted double magnetic resonance so electron and nuclear “notes” could be addressed separately; nuclear frequencies sit two to three orders of magnitude lower. Hyperfine coupling had previously revealed the nucleus only indirectly.
The coupling mechanism is unexplained: Otte says a simple picture forbids the observed drive. Until that channel is identified, it is unclear how general the effect is across elements, substrates, and temperatures, or whether it can be used for coherent storage and readout rather than a one-shot flip.
Sources: ScienceDaily; Phys.org; University of California, Davis; University of Iowa/NASA Juno; Delft University of Technology; Proceedings of the Royal Society A; *Nature Communications.