1 . 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.

1. What’s the purpose of mentioning the paradox?

A．To show it is interesting.

B．To explain Wheeler’s tests.

C．To demonstrate time is different from what we have known.

D．To show it’s impossible to travel back in time.

2. What can we infer from paragraph 3?

A．Consciousness traveling back in time was tried in the experiments.

B．Different measuring devices have the same result.

C．More research is needed in the future.

D．These experiments can determine the nature of matter.

3. Which can best summarize the last paragraph?

A．We should focus on the present.

B．The future food is more nutritious.

C．We can change the past from the experiments.

D．It is never too late to make up for mistakes.

4. Which can be a suitable title for the text?

A．Is changing the past wise?

B．Can we change the past?

C．Do our minds determine the future?

D．Do the laws of physics ban traveling back?