# What is behind recoherence?

I am quite familiar with the concept of decoherence, and I heard that a system that has decohered could recohere after that, I was wondering what could cause the the coherences that have leaked into the environment to come back to the system. I heard about thermal fluctuations for example, without being able to understand this argument.

Thanks.

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The bold and brilliant pioneer Susskind came up with the causal patch conjecture. The universe is accelerating and will approach de Sitter space. The universe right up to the cosmological horizon is all that exists. Nothing beyond exists. The Hilbert space of the universe is finite in dimensionality, approximately $e^{10^{123}}$ in size. A classical system this size will undergo Poincare recurrence at a timescale of the order of the number of states, but a quantum system with wave function components which can interfere will undergo a recurrence in about $\exp\{e^{10^{123}}\}$. Recoherence will happen by then. You can read up more about it in the brilliant conversations between Simplicio, Sagredo and Salviati at The Multiverse Interpretation of Quantum Mechanics. Check out their discussion on "unhappening".