Because of the way expansion will continue to work into the future, all the objects that are expanding away from us now will expand away increasingly faster in the future, and will eventually disappear from the part of the Universe we can reach.
MORE: http://scienceblogs.com/startswithabang/2012/12/28/the-universe-beyond-our-reach/
See also...
An Image Gallery Gift from NASA's Swift
http://www.sciencedaily.com/releases/2012/12/121228203202.htm
