Wormholes: the concept that a shortcut through space-time could be created by connecting two points in space with a tunnel.

The Grandfather Paradox: the idea that going back in time and changing an event could create a paradox that could erase one's own existence.

Time Dilation: the theory that time can be warped and slowed down by gravity and velocity.

Multiple Universes: the idea that time travel would create new timelines and alternate realities, resulting in multiple versions of history.

Closed Timelike Curves: the notion that it's possible to travel back in time along a path that loops back into the past, but this theory is highly debated.

Tipler Cylinders: hypothetical cylinders that could be used to create a stable time loop, but they would require enormous amounts of mass and energy.

Time Travel Paradoxes: various paradoxes that arise when contemplating the consequences of traveling back in time, such as the Bootstrap Paradox or the Predestination Paradox.

Special Relativity: Einstein's theory that time and space are relative and interconnected, and time can be affected by speed and gravity.

Quantum Entanglement: the idea that particles can be linked across space and time, and manipulating them could allow for communication across time.

 Causality Violation: the concept that time travel could lead to causal loops or changes to the timeline, potentially causing unintended consequences or catastrophic events.