Who has no regrets about things done in the past? Wouldn't it be nice if, somehow, we could go back to change a couple of bad decisions? This sounds like science fiction.
The laws of physics prohibit traveling back in time for many reasons. If we did travel back in time and changed the course of events, we would be altering the course of history. An example often cited is the grandfather's paradox (悖论): If your grandfather died when he was still a high school student, he wouldn't have met your grandmother and your father and you wouldn't exist.
Putting humans or consciousness traveling back in time aside for the moment, is there anything in science even similar? Surprisingly, yes. At the level of quantum particles (量子粒子), there is something called Wheeler's delayed-choice experiments that show that actions in the present can influence the past. The experiments use something called the wave-particle duality (波粒二象性) of light and of matter. The fact that the physical nature of quantum objects is undetermined until it is measured. In other words, this means that a particle of light or of matter can behave either as a wave (spreading out in space) or as a particle (staying together) depending on the measuring devices. Long and ongoing discussions about the nature of quantum physics are still trying to work out what this actually means. Do our minds determine the nature of physical reality?
Should we offer food for thought for the future or the past? Unfortunately, these experiments say very little about how we could interfere with the past in events relevant to the human scale. Better to think carefully about decisions than to try to fix them backwards.
