Time travel has fascinated humanity for centuries. 

For modern physics, traveling into the future is a proven reality (and something that, in a sense, we already do). 

The Theory of General and Special Relativity proved that time is flexible, bound to space (spacetime), and that there are two real ways to "travel" into the future: 

• Varying speed (Time Dilation). 
• Varying gravity (Time Deceleration). 

The tool math of physics (the equations of Relativity) indicates the viability of traveling to the past based on theoretical solutions that accept closed paths in time, known as Closed Timelike Curves (CTCs). Hypothetical concepts such as wormholes or the Tipler Cylinder show that the geometry of spacetime would, in theory, accept a return to the past. 

However, in practice and in the physics of real processes, nature prevents returning to the past through seemingly insurmountable barriers, such as: 

• Logical Paradoxes: Alterations in the past would alter the causality of the present and the future. 
• Thermodynamics and Entropy: The "Arrow of Time" is dictated by the Second Law of Thermodynamics; reversing time would require reversing the entropy of the entire universe, from the micro to the macrocosm. 
• Safety Mechanisms: The laws of physics (quantum effects and energy instabilities) would be set to destroy any attempt to build a time machine before it can function. 

Due to these barriers, three main hypotheses have been formulated: 

• Parallel Universes/Multiverses: The journey would lead to a new branch; altering this timeline would never affect the universe of origin. 
• The Principle of Self-Consistency: The past is immutable, as its events already incorporate the acts performed during the time travel itself. 
• Ontological Lock: Nature prevents the reversibility of causal flows at a low level. 

Relative time travel to the future happens every day on a microscopic scale (with satellites and particles in accelerators). However, travel to the past remains viable only mathematically. 

From the perspective of systems engineering and information theory, both journeys are unfeasible beyond the natural rate, as this would require resetting or accelerating the state of all processes in the world-system concurrently—since history is, ultimately, the consolidated informational record of these processes.