KIRK.TYM@OFFICE-2.ARPA (04/13/84)
From: Kirk Kelley <KIRK.TYM@OFFICE-2.ARPA> An interesting mapping onto the surface of an expanding (pitted) balloon are the three spacial dimentions. Time is the dimention at right angles to the surface. The pits are locations of mass. Black holes make relatively deep pits. Concievably there might be some black holes that go all the way to the center of the balloon (though no further). I would expect to find the origin of a big bang somewhere near the center. Assuming a cycling universe, what would the completed solid of all of spacetime look like? Like a bowling ball with a few huge pits that represent the union of the last black holes? -- modeler of nothing
cramer%ti-csl.csnet@csnet-relay.arpa (04/13/84)
From: Nichael Cramer <cramer%ti-csl.csnet@csnet-relay.arpa> > An interesting mapping onto the surface of an expanding (pitted) balloon are > the three spacial dimentions. Time is the dimention at right angles to the > surface... I would expect to find the origin of a big bang somewhere near > the center... > -- modeler of nothing Your second point illustrates my point exactly. i.e. that there is no point IN the universe from which the primordial fireball expanded; keeping in mind the important distinction that it is the two dimensional surface that represents the model of expanding spacetime and not the interior space enclosed by the ballon. (In point of fact, the point in the center of the balloon is 'inside' the balloon only because we poor creatures are trapped in 3-space, just as a point inside a circle appears to 'contained' by a circle to a flatlander, a point of view that looks naive to us.) HOWEVER, and more importantly, the first point you raise is precisely the issue that prompted the original message. The 2-space of the surface of the expanding balloon does NOT represent our own 3-space (with one suppressed dimension) expanding out through time. Rather, it (with obvious limitations) models an expanding spacetime with TWO dimensions suppressed.
mclean%NRL-CSS@sri-unix.UUCP (04/13/84)
From: John McLean <mclean@NRL-CSS> I agree with Nichael Cramer that if SPACE is expanding it makes no sense to ask where the big bang occurred. However, if SPACETIME is expanding, it makes just as little sense to ask when it occurred. Nevertheless, it seems to me that dates for the big bang are given. How can this be? Thanks, John