In this talk I will give a common-sense introduction to the topic of strange metals. First observed in copper oxide high-temperature superconductors, the strange metal state is now seen in a wide variety of materials, ranging from organic molecular crystals to cold atom simulators to twisted bilayer graphene. The key feature is Planckian dissipation, where the scattering rate  is determined only by fundamental constants, representing a conjectured universal bound on the degree of quantum entanglement possible in a many-body system. I will review the history of this strange metals, starting with the marginal Fermi liquid theory of the late 1980’s to the development of the SYK model by Sachdev and Ye in 1993, which Kitaev showed in 2014 could be “derived” using holographic duality via the AdS-CFT correspondence, drawing intriguing parallels to black holes.

Additionally, I will present our latest data* on density fluctuations in the strange metal Bi₂Sr₂CaCu₂O_8+x, which show the system to be quantum critical and conformally invariant, the latter meaning the system behaves as if the dynamics occur on a circle of radius 1/T in imaginary time. I will provide evidence for an excitation that may be related to Kitaev’s “scramblon,” which he argued is a generic feature of the extreme dissipative nature of the strange metal state.