According to our current understanding of physics, specifically within the framework of theories like general relativity and quantum mechanics, time travel to the past in a way that allows for changing the future is considered highly unlikely, if not outright impossible. The laws of physics and thermodynamics as we currently understand them impose significant constraints on the concept of time travel.
There are several reasons why changing the future through backward time travel is generally regarded as implausible:
Causality and Paradoxes: Time travel to the past raises concerns about causality and paradoxes. For example, the grandfather paradox suggests that if you were to travel back in time and prevent your own grandparents from meeting, it would create a contradiction because it would imply that you were never born to travel back in time in the first place. Resolving such paradoxes is challenging and requires speculative solutions like the Novikov self-consistency principle or the idea of parallel universes.
Conservation Laws: The laws of physics, such as the conservation of energy and momentum, pose constraints on the possibility of altering events in the past. Changing the past would require violating these fundamental principles, which are strongly supported by empirical evidence.
Grand Unification and Quantum Gravity: Our understanding of the laws of physics is not yet complete, especially when it comes to reconciling general relativity (describing gravity on large scales) with quantum mechanics (describing physics on tiny scales). A consistent theory of quantum gravity that could potentially address time travel paradoxes is still a subject of ongoing scientific research.
It's important to note that while time travel to the past as commonly depicted in science fiction appears to be highly unlikely, theoretical physicists continue to explore and investigate the nature of time and the possibilities that exist within the framework of our current understanding. It's an active area of research and subject to ongoing scientific inquiry and refinement.