In condensed matter physics, a class of strongly correlated systems share three remarkable transport properties simultaneously. Strange metals, quantum spin liquids, and Sachdev-Ye-Kitaev (SYK) models all exhibit (i) a shear-viscosity-to-entropy ratio at or near the conjectured KSS minimum $\eta/s = \hbar/(4\pi k_B)$, (ii) a Lyapunov exponent saturating the Maldacena-Shenker-Stanford (MSS) chaos bound $\lambda_L = 2\pi k_B T/\hbar$, and (iii) a Planckian dissipation time $\tau = \hbar/(k_BT)$ governing all transport. These systems have no quasiparticle description. Their low-energy physics is instead captured, in known cases, by a gravitational dual via holography. This post argues that the cosmological horizon of a de Sitter (dS) universe belongs to this same universality class, with every quantitative bound matched, provided one applies the correspondence to the horizon membrane rather than the bulk spacetime. The membrane paradigm as the physical basis Th...
An easy-to-read journey spanning 100+ years of geometric algebra, quantum mechanics and relativity, right up to some of the biggest questions (and solutions) of present-day physics. Many giant shoulders stood upon.