In 1949, mathematician Kurt Gödel, working alongside Einstein at the Institute for Advanced Study in Princeton, discovered a startling mathematical solution to the field equations of general relativity, describing a universe rotating at such a massive angular velocity that spacetime curves severely. According to this theoretical calculation, the gravitational pull from the rotation of immense mass bends light paths and the trajectories of matter so intensely that an object could travel forward through time and arrive back at its own past, creating what is known as a closed timelike curve. Gödel's solution required a global universe rotating in a way that modern astronomical observations prove our universe demonstrably does not, so it was never taken as a description of actual observational reality, but it proved a core point that Einstein's fundamental equations do not forbid this mathematically at all. Physically consistent solutions in which cause can follow effect in a closed loop still exist on paper.