=== Other approaches based on general relativity ===Another approach involves a dense spinning cylinder usually referred to as a Tipler cylinder, a GR solution discovered by Willem Jacob van Stockum in 1936 and Kornel Lanczos in 1924, but not recognized as allowing closed timelike curves until an analysis by Frank Tipler in 1974.
Čeprav so starejši računi nakazovali, da bi bila potrebna velika količina negativne energije, so kasnejši izračuni pokazali, da je lahko poljubno majhna.