Le 01-juin-05, à 18:49, Patrick Leahy a écrit :

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.

Thanks. Very clear.

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).

I agree with Deutsch. Note that I don't like to much the word "illusion". A more relevant word would be phenomenological (but then that's ugly). Perhaps "appearance" or "first person appearance" would be more precise and less misleading than illusion.

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.

I hope for him!



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