The anecdote you mentioned about Stephen Hawking's party for time travelers was a playful way to illustrate a point about the feasibility of time travel, but it's important to understand the context and limitations of the situation.
Firstly, the party was a lighthearted gesture proposed by Stephen Hawking in 2009, and it was not intended as a scientific experiment or a rigorous test of time travel. It was meant to highlight the absence of time travelers up to that point, based on the assumption that if time travel were possible, individuals from the future might visit the party. However, the lack of attendees does not provide conclusive evidence about the impossibility of time travel.
The concept of changing the past through time travel is a subject of debate and speculation in physics. While it is an intriguing idea, it raises significant questions and paradoxes, such as the grandfather paradox. The grandfather paradox suggests that if one were to go back in time and change an event in a way that prevents their own existence, it creates a logical inconsistency. This and other paradoxes challenge the logical consistency of altering the past.
Our current understanding of physics, including the laws of causality, suggests that the past is fixed and cannot be changed. However, it's worth noting that the study of time travel is primarily theoretical at this stage, and there are ongoing scientific discussions and research exploring its potential implications and constraints.
In summary, the absence of time travelers at Stephen Hawking's party does not definitively prove or disprove the possibility of time travel. The idea of altering the past raises logical and theoretical challenges, and the subject is still an area of active scientific investigation.