Imperfect Prolepsis

Poul Anderson's Time Patrollers know that World War II happened or will happen but cannot prevent it. Julian May's Atoning Unifex knows that the Metapsychic Rebellion will happen but cannot prevent it. However, the Patrollers, led by the Danellians based a million years hence, know the long term consequences and outcomes of WWII whereas Unifex lacks equivalent knowledge about the Rebellion because the leader of the defeated Rebellion will flee into Pliocene Exile and, five million years later, has become Unifex.

Thus, we see a definite limit to Unifex's knowledge. However, all knowledge is limited. We do not know the limits of the Danellians' knowledge.

Apparently, Godel somehow proved that omniscience is impossible. Here is my attempt at a proof:

if everything were known, then nothing would be unknown;

if nothing were unknown, then nothing would be future;

if nothing were future, then everything would be either past or present;

if everything were either past or present, then, at the next moment, everything would be past;

if everything were past, then everyone would be dead;

if everyone were dead, then nothing would be known;

therefore, if everything were known, then nothing would be known.

Reductio ad absurdum.