Blog Post 8 — Time Travel

Cody S
2 min readMar 9, 2021


Is time travel possible? Most would answer no, a perfectly rational conclusion. But yes, isn’t far from rational either.

Most of this paper will be conducted from the study by Kip S Thorne, a theoretical astrophysicist, and the main summary of their paper.

Most of this lecture is based on closed-timelike curves, this paper theoretically attempts to answer the questions like if the laws of physics prevent closed-timelike curves from ever forming in the classical spacetime and if so, by what physical mechanism are they prevented.

This paper delves into the deeper topics of quantum gravity.

Much of the forefront of theoretical physics deals with situations so extreme that there is no hope to probe them experimentally, sadly. Thorne wanted to create these experiments to the best of his ability in an attempt to quantize gravity.

Hawking has given the name chronology protection to the conjecture that there is such a mechanism that can bring a person back in time, no matter how hard advanced civilization may try.

However, the combination of general relativity laws in curved spacetime may well provide a chronology protection mechanism — thought we might not be sure of this until we understand the laws of quantum gravity.

The earliest example of space-time with CTCs is Van Stockum’s 1937 solution of the Einstein field equation, which represents an infinitely long cylinder made of rigidly and rapidly rotating dust. The dust particles are held out against their own gravity by centrifugal forces, and their rotation drags internal frames so strongly that the light cones tilt over in the circumferential direction in the manner shown in the picture above. This causes a dashed circle in the figure to be a CTC.

A second old example of spacetime with CTCs is Godel’s solution of the Einstein equation, which describes a stationary, homogeneous cosmological model with a nonzero cosmological constant, filled with rotating dust. The tilts come from light cones, creating CTCs, and due to spacetime being homogeneous and stationary CTC’s pass through every event. Although this seems more probable, physicists have generally dismissed this conclusion