Kitoky brought this to my attention last night:
In the EE of ROTK Aragorn drops Arwen's evenstar necklace after confronting Sauron in the Palantir...and it breaks! *gasp!*
So how could we see Eldarion(Aragorn and Arwen's son) wear the evenstar necklace in the future?
-We see this vision when Arwen is walking in the woods. Elrond shows her the future, and also shows an old king aragorn, and their son wearing the necklace!
I think the keyword here is 'vision'... it's a vision, no blueprint of reality, just like the images in Galadriel's mirror.
They are not true, they can be, maybe they will be, maybe not, depending on how the recipient deals with the seen;
Their main purpose is to portray a possible situation or feeling; and the Evenstar is one of the basic symbols to underline and explain this situation.
Breaking, hope is lost, or thought to be lost, life fades, the Eldar are dying - etc, etc. And the point is - it isn't lost, and life saved, mainly through Arwen's future in this case - which is what's showed in the other vision. It's the hope Arwen sees, her own life, not faded but alive, more alive than ever, especially through her son, the reunion of human and elven power, against all pessimistic predictions, against what already seemed inevitable to everyone.
It perfectly paraphrases what the scenes were supposed to say I think
__________________ Life is complex: it has both real and imaginary components.
Elrond's vision to Arwen was one last glimpse of hope...before she sailed away forever, turning her back on what looked like the end of the world....but she sees hope...and so does elrond a little bit....