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Monday, March 13, 2006
Physics: George Ellis on Messages from the Megaverse
In my recent review of Leonard Susskind's The Cosmic Landscape, I stated that observational evidence for the existence of the multiple universes supposed to make up the megaverse was “barring some conceptual breakthrough equivalent to looking inside a black hole, forever hidden from science by an impenetrable horizon”. This is an allusion to chapter 12, “The Black Hole War”, which suggests that Stephen Hawking's throwing in the towel and conceding that black holes do not cause loss of quantum state information means that it may be possible (at least in theory) to obtain information about other parallel universes encoded in radiation emanating from the cosmic horizon which delimits the observable universe. George Ellis, who, along with Stephen Hawking, literally wrote the book about The Large Scale Structure of Space-Time has now posted a brief comment on ArXiv, “On Horizons and the Cosmic Landscape”, which says that this is all nonsense, based on Susskind's confusing event horizons such as those which surround black holes with particle horizons, which are observer- and time-dependent, and simply specify the volume of space-time from which light has had sufficient time to reach an observer; your own horizon, which is slightly different from everyone else's, expands in every direction by one light-year from one birthday to the next. Ellis also observes, as did I, that the visual horizon due to the cosmic background radiation further reduces the volume accessible to observation and concludes, “The ESA-NASA Planck Surveyor data will not have coded into it the nature of multiverse regions enormously more distant from us than a Hubble radius. An application for a grant to decipher information about far distant regions of a megaverse that may be hidden in the data will not succeed.”Posted at March 13, 2006 15:51