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Having received email for some time from general relativists who have been working on the Warp-Drive I can summarise their current thoughts as virtually total scepticism. Most have given up on making the Alcubierre style warp-bubble work within physics as we know it. A recent analysis by Visser and Lobo has nailed the lid on the coffin so to speak, the chief problem being that the mass-energy of the warp-ring needed, even for sub-light travel, is a fraction approaching unity of the ship's rest mass - and is over unity for v > c. In otherwords it needs immense amounts of "negative mass" to work and no one is sure that's even physically possible.