The concept of changing the past and its consequences is often explored in science fiction and philosophical discussions. However, from our current understanding of physics, there is no empirical evidence or scientific theory that suggests the possibility of physically changing the past.
That being said, if we were to entertain the hypothetical scenario of changing the past, different theories propose different possibilities:
Altering a Single Timeline: Some theories suggest that if the past could be changed, it would create a single, altered timeline. This means that the changes made in the past would ripple forward, affecting the subsequent events and shaping a new future. In this view, there is no branching of alternate universes, but rather a single evolving timeline.
Branching Timelines or Parallel Universes: Another possibility, supported by certain interpretations of quantum mechanics and time travel theories, is that changing the past could lead to the creation of parallel timelines or alternate universes. In this scenario, each change in the past would result in a new timeline branching off from the original one, effectively creating a multitude of different universes with their own distinct histories.
Regarding time loops, they could arise in different ways depending on the theory or narrative. In some cases, changing the past may create a paradox or an inconsistency known as a "temporal loop" or "causal loop." This means that an event in the future causes changes in the past, which then leads to the future event occurring again, creating a self-perpetuating loop without a clear beginning or end. Temporal loops can be complex and can challenge notions of cause and effect.
It's important to note that all of these scenarios are purely speculative and remain in the realm of fiction and philosophical thought experiments. As of now, time travel and the ability to change the past are not scientifically established concepts, and our understanding of the nature of time and causality is still evolving.