The Tipler cylinder (also known as a Tipler time machine) is a hypothetical object predicted by Einstein's theory of general relativity that could theoretically allow for time travel into the past. While the mathematical foundation for a rotating cylinder of dense matter was first discovered by Kornel Lanczos in 1924 and independently by Willem Jacob van Stockum in 1936, it was American physicist Frank Tipler who demonstrated in 1974 that this configuration could create closed timelike curves (loops in time). The underlying physics relies on the extreme warping of spacetime through a phenomenon known as frame-dragging. If an ultra-dense material — such as the matter found inside a neutron star — were shaped into a massive, infinitely long cylinder and spun along its longitudinal axis at speeds approaching the speed of light, it would literally drag the fabric of spacetime along with it. This intense rotation tilts the light cones of objects nearby, causing the spatial and temporal coordinates to swap. A spacecraft approaching this spinning cylinder and following a precisely calculated spiral trajectory around it would enter a time loop. From the crew's perspective, time would continue to move forward normally, but within the broader framework of the universe, the ship would be traveling backward through time, potentially arriving back at its starting point before it ever left. In practice, however, building a Tipler cylinder is widely considered impossible due to fundamental physical constraints. Renowned theoretical physicist Stephen Hawking proved that a time machine based on this mechanism can only function if the cylinder is infinitely long. If one attempts to construct a cylinder of finite length, its immense gravitational pull would cause it to collapse into a singularity (a black hole), or the violent centrifugal forces of its near-light-speed rotation would tear it apart. To stabilize a finite cylinder and prevent this collapse, it would require "exotic matter" possessing negative mass and energy — a substance that has never been observed in the macro-universe. Consequently, the Tipler cylinder remains a purely mathematical model and a popular concept in science fiction, notably featuring in the plot of the anime Steins;Gate. #scientists #Science #astro #engineering - @holvek