Time travel, as commonly depicted in science fiction, poses numerous challenges and contradictions that make it highly problematic from a scientific perspective. Here are some of the key difficulties associated with time travel:
Causality and Paradoxes: Time travel to the past introduces the potential for causal paradoxes, such as the famous "grandfather paradox." If one were to travel back in time and somehow prevent their own birth or cause an event that would prevent their journey back in time, it leads to logical contradictions. These paradoxes create inconsistencies where cause and effect become ambiguous or self-contradictory.
Conservation Laws: Time travel to the past could violate fundamental conservation laws, such as the conservation of energy or the conservation of mass. Interactions between time travelers and the past could potentially create situations where the total energy or mass in the universe becomes unbalanced or infinite, which is incompatible with our current understanding of physics.
Time as a Dimension: Time is often treated as a dimension in physics, similar to spatial dimensions. However, there are fundamental differences between time and spatial dimensions. Time has a unidirectional nature, with events occurring in a particular order, while spatial dimensions allow movement in multiple directions. This distinction makes it challenging to conceive of time travel in the same way we think of spatial travel.
Time as a Local Phenomenon: Time is experienced differently depending on the observer's relative motion and gravitational field. This concept, known as time dilation, is a consequence of Einstein's theory of relativity. As a result, time travel to the past would require the manipulation of spacetime on a scale that exceeds our current technological capabilities and theoretical understanding.
Lack of Empirical Evidence: So far, we have no empirical evidence or scientific observations that demonstrate the existence or possibility of time travel. While certain phenomena, such as time dilation, have been experimentally confirmed, they are limited to small-scale effects and do not enable practical time travel.
In terms of why traveling forward in time is considered relatively more feasible, it's because the time dilation effects predicted by Einstein's theory of relativity have been experimentally confirmed. By traveling at high speeds relative to others or experiencing intense gravitational fields, it is possible to experience time passing more slowly compared to those in different reference frames. However, this is still limited to relative time dilation and does not involve jumping to specific points in the future.
Overall, time travel to the past remains highly speculative and faces significant conceptual and theoretical challenges that are yet to be resolved within the framework of our current scientific understanding.