Someone asked how a block universe "comes to exist" and if it comes into
existence "all at once, or a bit at a time" (or something like that).
I wish I could find the original question, to make sure exactly what it
was. But I haven't managed to find it, and I can't spend all night trawling
the forum for it, so I will just put my take on the matter here.
Assuming I've got it right, this seems to me a rather odd question. Asking
how a block universe comes into existence presupposes that this is a
process that must happen within a time stream. This would presumably be
external to the 4D manifold, so it would require a 5D "space-time-time"
manifold in which to operate. This seems like a crypto-religious viewpoint.
The assumption is that a universe has to be created, and even created /
sustained at every moment of its existence - rather as Newton imagined God
keeping the planets in their orbits (he worked out that they were unstable
over the long term, I believe). In this view a 4D space-time can't simply
exist due to some logically prior cause. Yet assuming it has to "come into
existence" within some external time merely pushes the question back a step
- the time within which the BU is created can also be viewed as a BU, with
one more time dimension, so one then has to ask how *that* BU came into
existence - and so ad infinitum.
This worked rather nicely in Isaac Asimov's novel "The End of Eternity" (in
which he posited a multiverse and an external time running across it, so
his "Eternals" could change history and effectively move across the
multiverse to a new history in their search for a perfect society). But it
seems unnecessary from a scientific viewpoint, and of course runs foul of
Occam's razor. It's possible, of course, but there is no evidence for it
(and I can't offhand imagine what such evidence would be). It seems to me
more sensible to try to explain the existence of space-time by positing
something simpler, from which space-time emerges. Most current approaches
to quantum gravity use this approach, I believe.
Otherwise, one is just explaining space-time in a circular manner, by
requiring the existence of what you're trying to explain - another time
dimension - and, in fact, an infinite number of them, if one takes this
idea to its logical conclusion ("It's time-tles all the way down...")
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