The concept of time travel and its implications for alternate universes is largely speculative and subject to various interpretations in science fiction and theoretical physics. While it's difficult to provide a definitive answer, I can describe a few different theories and ideas that have been explored:
Many-Worlds Interpretation: This interpretation of quantum mechanics suggests that every possible outcome of a quantum event spawns a new universe. If time travel were possible, it could potentially create branching timelines or parallel universes, each representing a different outcome resulting from the time traveler's actions. This theory implies an infinite number of alternate universes resulting from every possible choice or event.
Novikov's Self-Consistency Principle: This principle, proposed by physicist Igor Novikov, suggests that time travel is only possible in a way that maintains self-consistency. According to this view, any actions performed by a time traveler would be inherently consistent with the timeline they came from, ensuring that no alternate universes or paradoxes are created. Essentially, the time traveler's actions would already be part of the timeline's history.
Bootstrap Paradox: The bootstrap paradox is a time travel scenario in which an object or information is sent back in time, creating a loop without a clear origin. For example, imagine a person traveling back in time to give a famous musician a song that becomes their greatest hit. The question arises: where did the song originate if the time traveler brought it from the future? In such cases, there is no clear explanation for the origin of the object or information, leading to a paradox.
It's important to note that time travel is still purely theoretical, and there is currently no scientific evidence supporting its existence. Consequently, the nature and extent of alternate universes resulting from time travel remain purely speculative and open to interpretation.