Damghan University Press Journal of Holography Applications in Physics 2783-4778 6 4 2026 05 30 More About the Spontaneous Breaking of Time Reversal in de Sitter Space 1 15 2089 10.22128/jhap.2026.3250.1192 EN Leonard Susskind LITP and Department of Physics, Stanford University, Stanford, CA 94305-4060, USA; Google, Mountain View, CA, USA Journal Article 2026 02 10 It is widely thought that the quantum theory of de Sitter space requires the existence of a physical observer in the static patch. What exactly is meant by an observer is unclear; it could be anything from a few photons with energy just above the Gibbons-Hawking temperature to a gravitationally bound cluster of galaxies. In a recent note,  I explained that one way the need for observers can arise is from the spontaneous breaking of time-reversal symmetry. This longer paper expands on the subject,  filling in conceptual arguments that were implicit but not explicitly stated in the earlier paper.  https://jhap.du.ac.ir/article_2089_b9e8901dad506f591a8d3500735b55bd.pdf