My answer to the question : ”
Since time is a dimension in spacetime, could there anti-time/negative time on the other ‘side’ of the origin?
Time is an arrow, not a boomerang. This is one characteristic, among other things, that makes time stand apart from the other three dimensions.
But that does not mean that you cannot see time that has gone behind you. Look up in the sky, you see moon that was a couple of second before, our own neighbours – planets – in the same solar system at distances varying from a few seconds to several minutes or hours before, sun that existed 8 minutes in the past, Proxima Centauri as it was 3 million years ago (though you have no means to know if it it died last year or the year before), the twin stars ULAS J0744+25 and ULAS J0015+01 in our own galaxy as they existed some 900,000 light years ago – but with no hope of knowing if they still exist. If those stars had died before you were born, you would only know 900,000 years from now (when you won’t exist, and judging by what is happening around us – global warming and all, even your descendants might not exist!
The interesting thing is that you can speak of distance in terms of time and time in terms of distance (like, ‘the Town hall is ten minutes from here.”) Cosmologists measure time by means of colour – they call it red-shift. Haven’t you noticed that the rising and setting suns are orangish, but when the sun is closest to you right above, it is white?
You can slow down time by traveling at great speeds. To realize how slow Time gets, you’d need to travel very fast indeed. If you could travel at the speed of light – about 300,000 kilometers per second, time would stand still for you till the journey ends. Sadly, you may never attain that speed in your physical being.
Supposing you travel to Proximal Centauri at nearly (say 95%) speed of light after a bath and clean shave. You’d arrive there before you begin to feel a stubble on your chin. Send a signal to your wife, “Safely arrived.” She would receive it some 12-to 15 years (of her time) after you left mother earth, and would only be mildly excited if she hadn’t married again after she lost hope of hearing from you.
Figure that out. That is Time Relativity.
The sky is the best Time Machine you could get, though few of us are aware of it, and Einstein was the one who first told us about the magic of Time.