Every branch that grows out of the other you will no longer be contributing to this universe. So if I observe a spin that's in a superposition of spin up and spin down, and I see that it's spin up, do you think there's another version of me that saw spin down? Well, as an operational meaning, sure. But once the observation has unfolded, what happens to the other you? It's lost in a certain way.
Is there a multiverse, and if so, how should we think of ourselves within it? In many modern cosmological models, the universe includes more than one realm, with possibly different laws of physics, and these realms may or may not include intelligent observers. There is a longstanding puzzle about how, in such a scenario, we should calculate what we, as presumably intelligent observers ourselves, should expect to see. Today's guest, Thomas Hertog, is a physicist and longstanding collaborator of Stephen Hawking. They worked together (often with James Hartle) to address these questions, and the work is still ongoing.
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Thomas Hertog received his Ph.D. in physics from the University of Cambridge. He is currently a professor of theoretical physics at KU Leuven. His new book is On the Origin of Time: Stephen Hawking's Final Theory.
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