日本語訳お願いします。
Time travel poses, however, all sorts of problems, logical, social, and technical. The most difficult one is the so-called“grandfather paradox”:what happens if we travel back in time and kill our own grandparents or parents before we are born? This is a logical impossibility because it implies that we would not have been born and thus could not have gone back in time to commit the murder. Difficult as it may sound, there are, however, ways to resolve this paradox.
First, perhaps, you simply repeat past history when you go back in time, therefore fulfilling the past. In this case, you have absolutely no free will and are forced to complete the past as you know it.
Second, you have free will, so you can change the past but within limits. Your free will is not allowed to create a time paradox. Whenever you try to kill your parents before you are born, a mysterious force prevents you from actually doing this.
Third, the universe splits into two universes. On one time line, the people whom you killed look just like your parents, but they are different because you are now in a parallel universe. This latter possibility, which is also explored in the famous Hollywood movie Back to the Future, seems to be consistent with the quantum theory.
