Based on our current understanding of physics, time travel, especially in the conventional sense depicted in science fiction, is still purely speculative and has not been achieved or proven to be possible. Therefore, discussing the relative difficulty of time travel into the past versus the future is purely hypothetical.
However, it is worth noting that there are some concepts in theoretical physics that explore the possibility of time travel, such as certain solutions within general relativity, the study of wormholes, and theories like the Alcubierre drive. These concepts, however, are highly theoretical and come with numerous challenges and limitations.
That being said, if time travel were to become possible in the future, it is difficult to speculate on whether traveling to the past or the future would be more challenging. Both directions of time travel would likely present significant scientific and technological obstacles.
Traveling into the past could potentially involve dealing with issues like causality violations, paradoxes, and the violation of known physical laws. Theoretical frameworks, such as the Novikov self-consistency principle, propose that any actions taken in the past would be predetermined and consistent with the observed present, thus avoiding paradoxes.
Traveling into the future could involve overcoming challenges related to manipulating spacetime, surpassing the speed of light, or accessing regions of spacetime with significant gravitational forces.
Ultimately, until a scientific breakthrough occurs and a robust theory of time travel is established, it remains speculative to discuss the relative difficulty of traveling into the past versus the future.