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Bridging to superconductors. In charged superfluids (superconductors), entropy waves couple to electromagnetic fields, but the underlying entropy transport remains central. Seeing where heat behaves ballistically versus diffusively clarifies the hydrodynamic window relevant to high- Tc T c ​ materials. M

Recently pulsar timing arrays have detected and thus reported evidence of stochastic gravitational wave background in the field of nHz frequency orders. Super-cooled transition MeV-scale first-order wave transitions seem to be open as an or the proposition of an explaination for the NANOGrav signal and the pulsar timing arrays in general. However some claim that such first-order wave transitions fail complete the relevant time scales and thus fail to be physically viable. In…

First sound is the everyday sound you know: a pressure/density wave. In a superfluid, Landau’s two-fluid model says the liquid behaves as two interpenetrating components: a normal part (viscous, carries entropy) and a superfluid part (inviscid, carries no entropy). Small oscillations in this coupled fluid admit two propagating modes. The second, in which entropy and temperature oscillate while total density barely moves, is called second sound, literally a wave of heat.

"Second Sound" Made Visual In 2024–2025, physicists directly imaged “second sound” — heat moving as a wave rather than diffusing — inside an ultracold superfluid of lithium-6 atoms. Using a new, radio-frequency–based thermography method with sub-nanokelvin sensitivity, the team watched a hotspot sloshing back and forth through the gas, cleanly crossing from ordinary diffusive heat flow to a bona-fide entropy wave predicted by Landau’s two-fluid theory. Beyond being a…

"Second Sound" Made Visible Executive summary In 2024–2025, physicists directly **imaged** “second sound” — heat moving as a **wave** rather than diffusing — inside an ultracold superfluid of lithium-6 atoms. Using a new, radio-frequency–based **thermography** method with sub-nanokelvin sensitivity, the team watched a hotspot **sloshing back and forth** through the gas, cleanly crossing from ordinary diffusive heat flow to a bona-fide **entropy wave** predicted by Landau’s…