We’ve all experienced Internet black holes.  You send an email, it doesn’t bounce, but it never reaches the addressee.  Or maybe you can’t reach one of your web sites.  You know the site is operational, and the host server is online.  The cause in both cases could be an Internet black hole.  The good news is that the Hubble Project is monitoring Internet reachability in real-time.  You can read about the Hubble Project here.