Perhaps a useful way to restate some of the above is to notice that we all have developed a sense of our
own "past", "present", and "future", based on an ordering that relates to what can cause or influence what. What we dreamed we'd be when we grow up affected what we did become, but what we did become never affected what we dreamed about as kids! And as
@PeroK was saying, these concepts all apply to the
location we were "present"
at, at the time-- that means the concept of "present" is not just a time-related concept, it is
also a position-related concept. So our "present" is a location in both space and time, as
@PeroK was also saying about the awareness of a child. Children are not so dumb after all-- it turns out that is actually the
correct meaning of "present" in relativity! It was something of a mistake for us to try to extend that concept of "present" to other places around us-- not a mistake because it doesn't work well (it works very well in our lives), but a mistake because it is not exactly true, and starts to show serious flaws when you try to extend to distances too far away.
What this also means is that your current "present," the one you are experiencing as you read this, can be connected to all the "past" events that could have affected it, and all the "future" events that it could affect, at all the other places around you that you were not, nor will be, at. So we can say that your present has its own kind of past and future, which is not just about your location in your life, but drawing in all the things you care about and can affect you or you can affect. But the big surprise of relativity is, since there is a fastest possible speed of any kind of influence (the speed of light), once you've grouped all the events that could affect your present and all the events that you could now affect, it does
not include
all the events that are happening around you-- there is a
third category that many events fall into: they cannot affect your present, and your present cannot affect them.
If the speed of light were infinite, that would be what we mean by "now", an infinitesmally short duration containing this narrow slice of events spreading through space from your own present. But because influences cannot exceed a finite speed, the farther away you consider, the more events are in this third group, and it is not an infinitesmally short slice at all-- it's a lot of events! Any of them could be considered to be in your "now" without contradiction, so any language that regards an infinitesmally short subset of those events to be your "now" would be a
valid, but not
unique, way to talk about those events. So "now" just doesn't pick out a specific set of events, unless we extend the word to mean all those events that could not affect your present and your present could not affect. (We don't usually do that, instead we choose a convention for saying what "now" means, but it's just a convention because other events could be labeled as that without any contradictions in causality).
This should help with the "Andromeda paradox," because it only seems paradoxical if you think that your present can be matched up to their present in a fundamental way, such that if you experience 10 sequential presents as you ride a bicycle, you can ride the bicycle so erratically that it justifies you, in some standard coordinate system, in matching your 10 presents to only 2 distinct presents in Andromeda that get repeated 5 times each. Then you might think they actually experience those presents 5 times each. But of course they only
