In Greg Egan's The Clockwork Rocket (the first book in the "Orthogonal" series), Yalda argues that

If the cosmos were like the surface of the sphere, everything would be "absurdly predictable" and observing the light field in one speck of the cosmos would give you all the information about the entire field in all of four-space.

Still, later in The Arrows of Time (the third book),

Scientists agree that the cosmos actually has the topology of a 4-sphere (after ruling out the torus). The issue Yalda pondered in the first book is not brought up again.

Does this mean

that predictability does not matter so much after all (considering that it is even possible to send messages backwards in time)? I am slightly surprised that the issue that was discussed in great length in the first book does not surface again here.

(This is essentially a follow-up to Cosmic topology in Greg Egan's Orthogonal Universe, but I am not allowed to comment there.)

1 Answer 1


Read the last section of this page, on Cauchy Data and Predictions.

  • We prefer answers that are not link-only - if the link goes dead, the answer will become useless. Is it perhaps possible to provide a summary of the relevant section here? Apr 13, 2017 at 19:53

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