we can breakthrough the constant of time ( that means we can travel past or future ) as well
It is sometimes interesting to look back to see where discussions like this started. An important point here seems to be the possibility (or otherwise) of time travel; with past-directed TT being particularly relevant in view of recent experimental results with the speed of light.
In the course of thinking about TT, I found myself going round in circles, so I took my wife's advice and wrote everything down. The following is something I wrote a couple of years ago, which seems relevant here.
Think about other people! This is not an exhortation to indulge in charitable thoughts, laudable as such a practice might be, it is, rather, an invitation to think about the people who would be left behind by someone who travelled through time. Suppose you were to travel back a hundred years, what would become of your family and friends? Indeed, what would become of all the people who were living on Earth at the time from which you departed? The simple answer is that they have not yet been born. This is true in your frame of reference, but what of theirs? Suppose for a moment that it was not you who frisked off into the past; suppose it was your friend, or your neighbour, or even someone you did not know. What would happen to you? Nothing, I suspect! Life for you would not change. If you go back in time, your family and friends have to get on with their lives without you. They do not cease to be – in their frame of reference – only in yours.
What does this tell us about the nature of time? Intuitively, we think of only the present as being present. We reason, like St Augustine, that the past no longer exists and the future has not yet happened, so only the present is real; but if you travel to the past, then the past becomes your present, while the present which you left behind still exists for those who did not travel with you. This must raise questions about how you could have gone to the past, if the past were not real, and how your loved ones could still be living in the future, when the future has not yet happened. It begins to look as though time, past, present and future, are all relative: as though time might be a static entity, of which we are able to experience only an “infinitesimal point” as we progress through it. If time really is static, and we are moving through it, then surely we have overcome the first hurdle in our quest for time travel. We are already travelling through time, all we have to do is find some way to change the direction or speed at which we travel. If that sounds easy – think again!
