It is a legitimate goal of SF to boggle the reader with huge ideas, colossal magnitudes, stupefyingly immense distances. Inconveniently, human powers of apprehension tend to blow a fuse long before assimilating mere Ringworlds, Orbitsvilles, the long haul to Proxima Centauri – the petty doldrums of the merely finite.
Infinity is a different country, and they even do addition differently there. Rudy Rucker took the full range of infinities beyond infinities as a fantasy geography in White Light, complete with plans for mathematical vehicles to take you there (cries of delighted recognition from those who'd already glimpsed the foothills of Cantor's set-theoretic immensities, and of frustrated bafflement from everyone else). Christopher Priest presented his infinite Inverted World with more canny circumspection as perhaps a function of one's point of view... a wise stratagem, since the unstable Ringworld's embarrassing tendency to fall into the sun is as nothing to the Priest hyperboloid's perpetual feat of intersecting its own hyperboloid primary in more than one place.
In Eon (1985), Greg Bear offered an ingenious example of spatial infinity fitting neatly into the pocket; actually, into a smallish chamber of a 250km asteroid. This is the "Way", which extends forever along one dimension only and seems sort of comfortably feasible, a never-ending tunnel not unlike the Circle Line. One's feelings that rather a lot of energy would be required are countered with reassurances about the hugeness and incomprehensibility of the space/time generators which maintain the Way, while philosophical worries about how an infinity "fits" into our relativistic universe are not so much met as subverted into a justification for the temporal slippage whereby the asteroid end of the Way heaves into sight of Earth some centuries before its construction.
The Way, in fact, is an ambitious and involving creation which is the real hero of Eon. Bear leads up to it tantalizingly and unveils its secrets with effective timing (for example, the original architects are still in residence, a billion or so kilometres along the tunnel – one has grown tired of super-engineers who construct wonders of the universe and then bugger enigmatically off to spare the author the trouble of fitting them into the plot). On the debit side, the human characters are less successfully drawn, and the politics of 2005 seem designed not so much for plausibility as to provide an excuse for exciting free-fall battles while Earth burns.
Finally, the infinite curate's egg of Eon breaks open and fragments of plot fly in various directions, including one exhilarating trajectory along the Way itself: ever-opening horizons, the shades of Arthur C.Clarke falling fast, "Excelsior!" and "Sail on! sail on!"
All this background is needed to tackle Eternity, a sequel which tells us at considerable length what happened next. Gosh, Greg Bear is a destructive chap. We have had the transformation of Earth's biosphere in Blood Music, nuclear holocaust by way of mere colourful background to Eon, and the smashing of Earth itself in The Forge of God. There remain the universe and the Way; the end of the former provides a minor flash-forward early in Eternity, whose climax is the annihilation of the latter.
Oh dear, it's like this. A character last seen heading off beyond infinity returns to describe (in italics) the end of the universe; the way he and his mates were left without amusements and became gods; how they weren't very good at this; how they were bailed out by some altogether more experienced gods who'd been practising longer; and how he comes to have returned with a portentous message. The message is that the Way is a bad thing. By, as it were, being an infinite open-cast mine stretching through the lush green fields of futurity, it's mucking up the orderly closure of the universe. The god-intellects request the prompt removal of this obstacle to a tidy decommissioning. As you might imagine, there is much debate about this request, along the traditional lines of "What has posterity ever done for us?"
A philosophical question not answered nor as far as I can see even considered in the book goes as follows. If the infinite Way's disfiguring extension through space/time means that it "is" once blocking the plumbing at the far end of time, what good can its "subsequent" destruction do?
Further delaying excitement is provided by the Jarts, a culture of authentically creepy aliens last seen being wiped out by the superspatial shockwave produced by that final, epic and just a trifle genocidal journey up the Way in Eon. There still seem to be a lot of Jarts around, however, including a computer-stored specimen which has fallen into human hands and which with unbelievable idiocy a character decides to upload into his own mind. Naturally the Jart is soon in control, after a mental tussle about which Bear is inartistically reticent:
"How did you break through my barriers?"
"Your understanding of certain algorithms is incomplete."Happily it turns out that the Jarts – who like the Pnume of Jack Vance's Tschai sequence are great believers in gathering and stasis-preserving any and all information, artifacts and people – have identified that final god-mind as the appropriate authority to which their data-harvests should be delivered. Hence the Jart Problem is solved in the great and groan-making tradition of SF, by discovering that all along they and we were secretly on the same side, tra la.
All digressions past, the Way is cataclysmically closed down and the nicer characters nicely if not always plausibly pensioned off. And despite Bear's solid narrative skill ... what a sour taste it leaves in the mouth. For all Eon's flaws, that book ended on a high note of outward seeking: to follow knowledge like a sinking star beyond the utmost bounds of human thought (and then, given infinity, further still). In Eternity the ultimate reaches of space/time are glimpsed and shown as dead boring, the domain of a tiresome gestalt whose chief interest – as though this were the tail end of a science fiction convention – is the organization of a nice, smooth-running closing ceremony.
Meanwhile, back on Earth, it is made clear that there are things with which twenty-first century humanity is not to meddle. The Way was the hero; Bear has finished with the Way; bye-bye to it and all its symbolic weight. The gates to infinity have been slammed forever shut. Ambition should be made of sterner stuff.