Communication

In the Haertel overdrive futures:

telepathy unites the Central Empire;

the Lithians have a Message Tree and the CirCon radio is instantaneous;

the Dirac transmitter will unite an expanding intergalactic civilization although, in an intermediate period, High Earth may or may not be Old Earth, the Traitors' Guild motto is "Mundus vult decipi," "the world wishes to be deceived," and the Green Exarch is served by shape-shifters;

the Angels communicate on a universal scale -

"Like sparks in a column of smoke, the discussion whirled and danced away throughout the galaxy and throughout the universe..."
-James Blish, Mission To The Heart Stars (London, 1980), p. 127.

In Cities In Flight, the Web of Hercules leaves a record that is read in a subsequent universe.

In The Seedling Stars, many original human beings remain prejudiced against Adapted Men, i.e., in this case, a lack of communication.