Time Dilation Effects

As you approach a black hole, gravitational time dilation becomes extreme. Clocks near the event horizon tick far slower than clocks far away. At the horizon itself, time effectively stops relative to an outside observer — a real physical effect predicted by general relativity, not an illusion.

Orbit just outside a supermassive black hole's horizon and return to Earth, and you might find that centuries had passed while you aged only hours. That is genuine time travel into the future — possible in principle, but only this close to a black hole, where survival is another matter.