I read his book a year or so ago, so may be a bit hazy, but:

Pour Bruno: he definitely does not want to talk about space-time capsules. Partly this is motivated by his metaphysical ideas about time, partly by the technicalities of the 3+1 (i.e. space+time, not persons!) approach to GR and the Wheeler-De Witt equation which he advocates. This leads him into severe difficulties, and he has not successfully described how this can be reconciled with the relativity of simultaneity, which he also wants to assert. Barbour regards this as an open question within his theory; others regard it as a fatal objection.

Of course when Barbour says that "time is an illusion" he really means that the *flow* of time is an illusion, or rather a category error, which is a pretty standard position (e.g. forcefully argued by Deutch in his book). Although he sometimes speaks as though he denies it, I think if push came to shove he would have to admit that there is an identifiable, objective, structural feature in his (or anybody's) theory of physics which corresponds to time. Reminds me of the opening of a history book: "There was no such thing as the Scientific Revolution, and this is a book about it."

Paddy Leahy

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Dr J. P. Leahy, University of Manchester,
Jodrell Bank Observatory, School of Physics & Astronomy,
Macclesfield, Cheshire SK11 9DL, UK
Tel - +44 1477 572636, Fax - +44 1477 571618

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