Okay, this happens to me whenever I am reading about/working with non-causal systems. I start thinking a lot about time-travel. Wouldn't it be great if we could travel back in time and set right many of our wrongs? Or if we could travel to the future and see how our great-grand children would look? Practicalities aside, it is an amazing concept.
Time-travel has been a pet subject for sci-fi movie makers, for a long time, and it does not seem to get old at all! There used to be this series telecast on the Sci-fi channel. A man is tossed from one body to another body and another, all in different times, so that he can set right the wrongs done by other people, and finally return to his own body to the present. He has only one friend throughout this exercise - Al (I think), who appears to him as a hologram. It was an enjoyable series. Fi, yes, but Sci? I should think very little Science was involved :)
And there are those gadgets that have invited a lot of speculation but have always eluded serious research for practical reasons - the time machines. H.G. Well's book 'Time Machine' was even made into a movie starring Guy Pearce. I still have to read the book. A more famous movie and a personal favorite involving time machines, is the 'Back to the Future' trilogy. Who can not love the bungling 'Doc' and the spirited young Michael? And there is another good movie called 'Frequency', where a man communicates with his father from the past and saves his parents from fatal accidents. Even the famous 'Star Trek' has a few episodes on time travel. Coming to Indian cinema, we have 'Aditya 369' which is a pretty good movie too.
There is this theory about how time-machines may work. I had read it someplace, years ago. The events happening on the earth can be seen from the Sun eight minutes later, because the light from the earth takes eight minutes to reach the Sun. So, if you can travel faster than the speed of light (Ah, there is that limit again!), you can 'view' the events that happened eight minutes ago, first hand. There is no way of checking it because we still have not found a way to travel faster than light. And interfering with the past still cannot be explained.
Traveling to the future only gets trickier. There is absolutely no explanation that even remotely makes sense, of how one can travel into the future. Some argue that there are millions of futures etched out for you, and you just pick one each nanosecond of your life. Keep choosing futures one after another and - well, you can travel to the future! However, this argument is not even worth considering. There are just too many unknowns in the equation.
Theoretical physicist Kip Thorne suggests that wormholes, which are allowed by the laws of Theoretical Physics, can be used for traveling in time. Something that comes from an eminent physicist like him cannot be disregarded. But we have to continue being in the present, and see what direction research takes.
As far as I know, the concept of time-machines and time-travel is quite recent. I have not come across that in Indian or Western mythologies that I have read. From all practical observations, our conclusion is that Time flows only in one direction. That is what our ancients also seem to have thought.
That is the sensible thing to think, too. As a subhAShita goes -
गतशोकं न कुर्वीत भविष्यं नैव चिन्तयेत्
वर्तमानेषु कार्येषु प्रवर्तन्ति विचक्षणाः ।