In the Year 5555

If humanity hangs out for another few thousand years, it won't resemble itself.  Physically, there may be similarities, but mentally and emotionally, there will be very little linking future human to its past.  

Then again, humans may not look the same, either. That's a long shot, though.  It would take a very long time for any significant physical change.

Energy's riddle will be solved.  A new source is a prerequisite for survival.  Numbers or technology demand it.

Assessing space will be complete.  If possible, humanity will have at least partially moved on to other heavenly bodies.  If not, they'll spread out into space itself.