@Eorl,
Hm... Maybe the reason "there exists in this four dimensional structure [space-time] no longer any sections which represent "now" objectively" is that the concept "now" is invented by subjects that have the concepts of before and after. After all, without the concepts of past and future, the concept "now" is meaningless.
But think of it this way; nothing happens in the past. We cannot change what happened last year. Nor can anything happen in the future. Whatever you are anticipating will only happen when the changing circumstances we refer to as the present catch up to the predicted moment where future and present become one.
And even this is meaningless without specific events which function as manifestations of past and future. And these specific events are never more than memories (past) or expectations or predeictions (future).
So the concept of linear time is a metaphysical one, not physical. It exists in our minds right along side with god and santaclaus.