Diamond Melting Resolved at Extreme Pressures
Lawrence Livermore National Laboratory researchers used laser-driven shock compression at the Omega facility to measure diamond’s atomic structure, temperature, density and reflectivity at pressures exceeding those inside Neptune and Uranus, and hotter than the Sun’s surface. Published in Nature Physics on 20 August, the work ends a 20-year mismatch between experiment and quantum simulations on diamond’s melting curve. The data confirm diamond floats in metallic liquid carbon, analogous to ice in water, with direct relevance to inertial confinement fusion capsules and models of ice-giant interiors.
Earlier experiments indicated denser liquid carbon upon melting but reported temperatures ~20% off theory; Sandia Z-machine data had also hinted at an intermediate crystalline phase. New X-ray diffraction during the nanosecond-scale shocks showed diamond retains its structure until melting, with no intermediate phase under single-shock conditions, and temperatures now match advanced simulations. The improved diagnostics resolved faint carbon scattering signals that previously limited precision.
Key uncertainties remain in multi-shock pathways relevant to full fusion implosions and whether slower initial shocks can fully melt diamond capsules without degrading uniformity. Models suggest slower shocks could triple fusion energy gain by increasing fuel compressibility, but only if other performance losses stay controlled. Planetary applications depend on how well laboratory single-shock results scale to the longer timescales inside ice giants.
Sources: ScienceDaily/LLNL, Nature Physics.
Dark Energy Linked to Quantum Gravity Uncertainty
A theoretical proposal published in Physical Review D argues that dark energy, the driver of cosmic acceleration, emerges as a macroscopic consequence of quantum gravity rather than a separate field or particle. Physicist Savvas Koushiappas of Brown University applies a cosmological uncertainty relation: the size and expansion rate of the universe cannot be known simultaneously with arbitrary precision. This imprints an accelerating term on the Friedmann equations that matches late-universe observations.
Standard cosmology treats dark energy as a cosmological constant or exotic component, while quantum gravity remains untested at accessible scales. The new approach unifies the two by letting quantum uncertainty act on spacetime geometry itself. It can also replace the Big Bang singularity with a bounce from a prior contracting phase, avoiding infinite density.
Open questions include the precise mathematical form of the uncertainty relation and whether it fully reproduces the observed expansion history without additional parameters. Upcoming data from DESI, Euclid and the Vera C. Rubin Observatory will provide sharper tests of the predicted residuals relative to ΛCDM. Confirmation would eliminate the need for new particles while remaining consistent with existing precision measurements of both gravity and quantum mechanics.
Sources: Phys.org, Physical Review D/arXiv.
Programmable Photonic Chip for Optical Computing
Researchers at Seoul National University and the University of Seoul have designed a reconfigurable photonic integrated circuit that dynamically tunes the delay, bandwidth and frequency response of light pulses on a single chip. Reported 19 August, the architecture uses tunable loop couplers in a coupled-resonator-induced transparency network, allowing post-fabrication control of optical timing without fixed hardware delays.
Optical computing promises high bandwidth and low heat compared with electronic interconnects, yet synchronizing signals has required custom delay lines for each function. Conventional CRIT devices lock delay and transmission characteristics at fabrication. Electromagnetic simulations on a silicon-nitride platform, including realistic losses, fabrication variations and thermal crosstalk, show the design remains functional and can adjust delay while operating.
The work is currently theoretical and simulation-based; experimental fabrication and validation are still required. Practical challenges include scaling to larger circuits, managing residual phase errors, and integrating with existing photonic platforms for AI processors or high-speed communications. Success would enable flexible buffering, filtering and frequency conversion in light-based systems where precise arrival timing is essential.
Sources: New Atlas, Advanced Science.