You've touched upon an interesting concept known as the "twin paradox" or the "reversal of causality" that arises from the hypothetical scenario of traveling faster than the speed of light. However, it's important to note that according to our current understanding of physics, traveling faster than light is not possible for objects with mass, as discussed earlier.
Nevertheless, let's explore the scenario you mentioned for the sake of understanding the implications. In this hypothetical situation, where an object or a person could travel faster than light and then decelerate to a stop, there are several ideas and speculations regarding what might occur:
Causality Paradox: If an object were to travel faster than light and exceed the speed of its own emitted light, it would lead to a violation of causality. The object's image or information would seemingly arrive at its destination before it actually left, creating a paradox where cause and effect are reversed. This challenges the fundamental principles of causality and leads to logical inconsistencies.
Time Travel and Paradoxes: The reversal of causality resulting from faster-than-light travel could potentially lead to time travel paradoxes, such as the famous "grandfather paradox." For instance, if you were to travel back in time and prevent your own birth, it would create a paradoxical situation with no consistent cause and effect.
Speculative Physics: In certain theoretical frameworks like the concept of wormholes or the existence of hypothetical particles called tachyons (which are thought to travel faster than light), attempts have been made to explore these scenarios. However, these concepts are highly speculative, and their practicality and feasibility are still subjects of active scientific inquiry and debate.
It's important to reiterate that our current understanding of physics, based on the theory of relativity, does not allow for objects with mass to travel faster than the speed of light. The implications and consequences of such travel are largely speculative and often lead to logical inconsistencies and paradoxes.