Actually, I am going to write someday a short post “time machine as existential risk”.
Technically, any time travel is possible only if timeline is branching, but it is ok in quantum multiverse. However, some changes in the past will be invariants: they will not change the future in the way that causes ground father paradox. Such invariants will be loopholes and have very high measure. UFO could be such invariants and this explains their strangeness: only strange thing are not changing future ti prevent their own existence.
Actually, I am going to write someday a short post “time machine as existential risk”.
Technically, any time travel is possible only if timeline is branching, but it is ok in quantum multiverse. However, some changes in the past will be invariants: they will not change the future in the way that causes ground father paradox. Such invariants will be loopholes and have very high measure. UFO could be such invariants and this explains their strangeness: only strange thing are not changing future ti prevent their own existence.