Dark energy" is an invisible omnipresent prime mover and cause of cosmic expansion so it has some of the properties of God.
Travelers to the past or to other timelines might encounter dodos. This happens again in SM Stirling, Against The Tide Of Years (New York, 1999), Chapter Seven. A teacher shows children "...a live dodo in a wicker cage..." (p. 124)
I have speculated about Poul Anderson writing Superman and rationalizing Kryptonian powers. In fact, there are at least three popular sf series that I think need an overhaul:
Star Trek - the Vulcans should be not aliens but descendants of a small population of human colonists of an extrasolar planet;
Doctor Who - the Time Lords should be not aliens but our descendants;
Superman - there should be some explanation not only of Kryptonian powers but also of the Kryptonians' remarkable resemblance to white North Americans. (See here.)
Poul Anderson could have done all of these.
Star Trek has permeated our culture. To cite two examples -
when I told a friend of a "reality storm" in Neil Gaiman's The Sandman, he remarked, "That sounds like something out of Star Trek," and I replied, "One of the characters says, 'That sounds like something out of Star Trek.'" (People from different realities shelter from the storm and the different realities include ours);
when one of SM Stirling's Nantucketers meets the King of Babylon:
"'O King, live long and prosper,' he said solemnly, holding up his right hand with the fingers spread in a V. I always wanted to say that, he thought, then there was a sharp pain in his ankle as Doreen kicked him; she hadn't believed he would actually go through with it." (Chapter Eight, p. 131)
We were concerned when we read that strangers in big ships were bringing many gifts to the King of Babylon. Walker? We were relieved when we read that the strangers' king was called "'...Yhared-Koff'in...'" (p. 128) - the Nantucketers' Chief Executive Officer. Not military conquests but peaceful alliances will "...make all things new."