NONISOMETRIC VACUUM EXTENSIONS OF VACUUM MAXIMAL GLOBALLY HYPERBOLIC SPACETIMES

We discuss a number of familes of maximal globally hyperbolic vacuum s pacetimes-Taub, Misner, and polarized Gowdy-and their nonglobally hype rbolic extensions. We show that many of the familiar extensions are is ometric, but we also show that in the Taub and Gowdy familes there are nonisometric maximal extensions. In the latter family, we show there are spacetimes that have an arbitrarily large number of nonisometric m aximal extensions.