QUANTUM STABILITY OF THE TIME MACHINE

In a number of papers it has been claimed that the time machine is qua ntum unstable, which manifests itself in the divergence of the vacuum expectation value of the stress-energy tensor [T] near the Cauchy hori zon. The expression for [T] was found in these papers on the basis of some specific approach. We show that this approach is untenable in tha t the above expression, first, is not derived from some more fundament al and undeniable premises, as is claimed, but rather postulated, and second, contains undefined terms, so that one can neither use nor chec k it. From this we conclude that at the moment there is not a grain of evidence to suggest that the time machine must be unstable. As an ill ustration we cite a few cases of (two-dimensional) spacetimes containi ng time machines with [T] bounded near the Cauchy horizon.