Invisibility, telepathy, limitless energy and antigravity are four of science fiction's oldest concepts - and, seemingly, four of its least plausible.

But scientists around the world are re-examining these phenomena: the reality of invisibility could be under 20 years away; the US Air Force is investigating antigravity; the secret services have studied telepathy; and a physicist has pioneered an experiment producing more energy than it consumes.

Hosted by Gillian Anderson.

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