Wednesday, January 24, 2007



Centauri Dreams points to a nice write up of retrocausality in the San Francisco Chronicle, which originally appeared in the pages of New Scientist. The piece talks a bit about the history of the idea back to Richard Feynman's proposal of positrons as electrons moving backwards in time, and concludes with a discussion of John Cramer's transactional interpretation of quantum mechanics, and his experiment to prove it.

The piece closes with a quote from Paul Davies, who extends the notion quite a bit farther.
Paul Davies, a theoretical physicist at the Australian Centre for Astrobiology at Macquarie University in Sydney, suggests another possibility: The universe might actually be able to fine-tune itself. If you assume the laws of physics do not reside outside the physical universe, but rather are part of it, they can only be as precise as can be calculated from the total information content of the universe. The universe's information content is limited by its size, so just after the Big Bang, while the universe was still infinitesimally small, there may have been wiggle room, or imprecision, in the laws of nature.

And room for retrocausality. If it exists, the presence of conscious observers later in history could exert an influence on those first moments, shaping the laws of physics to be favorable for life. This may seem circular: Life exists to make the universe suitable for life. If causality works both forward and backward, however, consistency between the past and the future is all that matters. "It offends our common-sense view of the world, but there's nothing to prevent causal influences from going both ways in time," Davies says. "If the conditions necessary for life are somehow written into the universe at the Big Bang, there must be some sort of two-way link."
At the heart of End of the Century is a bit of retrocausality very much in this vein (though not at this scale). That my admittedly wonky interpretation of physics is being echoed by Davies, at least in part, is very gratifying.

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