A traversable wormhole would allow an advanced civilization to travel back in time. This is because time progresses differently inside and outside the wormhole. As a result, synchronized clocks at either end of the wormhole remain synchronized for an observer passing through the wormhole. Imagine observers at one end of the wormhole that encountered time dilation and aged less by moving around or temporarily visiting a gravitational potential well. Such observers would be able to connect to the older end of the wormhole at the same time, thereby allowing the older version of themselves to meet their younger selves.

From the point of view of an outside observer, this constitutes what science fiction would recognize as a time machine.