The concept of time travel is a subject of speculation and exploration within both physics and philosophy. In the context of four-dimensionalism and impossible worlds, there are differing viewpoints and interpretations. Let's consider these concepts:
Four-Dimensionalism: Four-dimensionalism is a philosophical position that suggests objects, including individuals, exist not only at a particular moment in time but also have temporal extension. According to this view, entities are considered to be four-dimensional "worms" or "time-slices" that span across different moments of time. Four-dimensionalism is often invoked in discussions about time travel to provide a framework for understanding the temporal aspects of such journeys.
Impossible Worlds: Impossible worlds are hypothetical constructs used in philosophy to analyze counterfactual and metaphysical possibilities. They are alternative "worlds" that do not conform to the laws of physics as we understand them in our actual world. Impossible worlds can be employed to explore the logical consequences of propositions that contradict our actual world's laws.
When it comes to time travel, the involvement of four-dimensionalism and impossible worlds can depend on the specific theoretical framework or interpretation being considered. Here are two perspectives:
a. Novikov's Self-Consistency Principle: Novikov's self-consistency principle is a concept proposed within the framework of general relativity and quantum field theory. It suggests that any time travel scenario that involves closed timelike curves (CTCs) must be consistent with the laws of physics and avoid logical contradictions. According to this view, time travel events cannot create paradoxes or violate causality. Therefore, the concept of impossible worlds may not necessarily be invoked.
b. Branching Universes and Multiverse Theories: In some interpretations of time travel, branching universes or multiverse theories are considered. These theories propose that when time travel occurs, it leads to the creation of alternative timelines or parallel universes. Within this context, impossible worlds or non-actualized possibilities may be invoked to describe the different branches of the multiverse.
It's important to note that the nature and implications of time travel are still highly speculative and subject to ongoing scientific and philosophical discussions. The concept of four-dimensionalism and the use of impossible worlds are tools employed in different approaches to analyze and explore the possibilities and implications of time travel, but they are not universally agreed upon or essential for all interpretations of time travel.