General Warning: this is emphatically not a spoiler-free Forum! Hence all of the text all of the contributions will be safely below the fold, and only the identifying information for the author of the contribution will be here for even causal browsers to see.
Iver B. Neumann is Montague Burton Professor of International Relations at the London School of Economics. For some reason he doesn’t have a personal page at the LSE, so here’s his Wikipedia page instead.
If we are to begin with author intentionality, The Hydrogen Sonata is about ‘the subliming business’. In the Western tradition (which is rather less Western than we sometimes imagine it), the concept of the sublime may be traced back to a work that surfaced in Byzantium during the tenth century, but that probably hails from the first century A. D. It is called Peri hupsous, which is traditionally translated as on the sublime, but hupsos simply means height. In this work, the sublime is seen as an effect of deeds. The deeds must be pristine, for ‘[T]hose whose thoughts and habits all their lives are trivial and servile cannot possibly produce anything admirable or worthy of eternity’ . The effect of the deeds are about being teleported into another state of mind. To draw on the vernacular, the deeds knock you out. Far out, man. Into another dimension, actually. So, when Banks conceptualises the sublime as a space — in his case, the ninth to eleventh dimensions of the metaverse inhabited by, amongst others, the Culture — he is seemingly on classical ground.
The sublime returned in the 18th century. At that point in time, people like Immanuel Kant were interested not so much in how deeds could produce a sublime or knock-out effect, but in how simple vastness could have the same effect. The mere quantity of, say, seas or mountains, could knock out an individual. This aspect of the sublime is also thoroughly present in Banks’ metaverse. When some society decides to sublime (as a non-native speaker, I take particular pleasure in the verbing of the sublime here), a big something appears out of nowhere and just hangs in the air. When the time that society has allotted to the move draws near, somethings appear across vast areas and you just have to go through a little quotidian ritual to fly away into the sublime.
There is a third chapter to the conceptual history of the sublime. From the 1980s onwards, theorists like Lyotard and Derrida conceptualised the knock-out effect of the new and of the eternal. Once again, Banks’ usage comprises these meanings, for subliming definitely means a new start for a society. Furthermore, the possibility of subliming – Banks the evolutionist stresses how society somehow has to qualify for it – is an eternal concern, and the subliming itself, from what little that is known of it, seems to involve being forever changed.
Seemingly, then, Banks’ conceptualisation of the sublime dovetails nicely with the Tradition. When I write seemingly, it is because Banks thinks of the sublime as something from which one cannot meaningfully return. I write ‘meaningfully’, for while there are a number of examples of Minds returning from the sublime physically, none of them is able to find any meaning in existence as we know it here in our dimension any more. That is at loggerheads with the tradition, where the entire point of being knocked out is that the very experience of having been knocked out will be something to treasure in the here and now from that point onwards. Traditionally, the sublime is exactly the effect, the experience, of having been teleported to some realm and then back. It is supposed to be about a round trip, as distinct from the one-way run that Banks describes.
I fasten on this difference for a reason, and the reason is not Banks’ conceptualisation of the sublime, but of the religious. Banks himself bunches them together, by observing in The Hydrogen Sonata that once the society known as the Gzilt had decided to sublime, interest in religion increased markedly. This seems immediately logical not only to Banks, but also to the reader, at least to this reader. The reason lies close to hand. Religion is to do with the relationship between the sacred and the profane, with the sacred being conceptualised as a privileged realm – or dimension(s) – and the profane being the here and now. There is only a small step, then, from saying ‘the sublime’ to saying ‘the sacred’. After all, in Look to Windward, the Chelgrian’s antechamber to the Sublime is called ‘heaven’.
Banks is not exactly big on the sacred. He is, rather, a militant atheist. Every time, and I mean every time, organised religion crops up in the Culture metaverse, there is something fishy about it. It is a misunderstanding, as in Matter. It is a focus for confused individuals, as in the short story “The State of the Art.” Or it is simply a fraud, as it hinted at in passing in so many different settings. As to spiritual concerns, Banks is equally dismissive. To him, the real miracles are technological in nature. The last Culture novel but one was called Matter for a reason.
In light of Banks’s avowed materialism, then, his conceptualisation of the Sublime as a place from which one cannot go back makes sense. To me, this is one of the key themes of the novel. This theme is at loggerheads with what seems to be happening globally, where religion is becoming more pronounced as a societal force, rather than less. Voltaire, Weber and Banks seem to be empirically wrong when they predict religion’s demise. But that is neither here nor there. Let’s stick to the spirit of the genre and focus on conceptual issues.
The classical definition of religion, and Banks seems to stick with it, is that of Edward Burnett Tylor. It dates from 1871 and has it that religion is belief in spiritual beings. Banks has no problem with spiritual beings. Actually, he himself has put them into a metaverse that is of his own making. More precisely, we are told that they occupy its ninth through eleventh dimensions. Furthermore, they know of what happens in the rest of the dimensions, and they make themselves known to the inhabitants of those dimensions. Actually, in the high Western tradition, we have to go back way before 1871, to the early 1700s, to find this kind of interventionist theology. But no matter. Banks’ key problem is not with the existence of spiritual beings, but with the belief in them. In sci-fi, we know this basic stance from places like Star Trek, where every god turns out simply to be another material species with superior technological capability, or, alternatively, some kind of energy being. Either way, they are not sacred beings, only more and different species.
The problem with this conceptualisation of religion, be it in Tylor’s or Banks’ version, is that it at loggerheads with developments within the anthropology of religion, where the religious is tied not so much to belief as to experience. The locus classicus is Clifford Geertz’s essay on religion as a social system:
The religious perspective differs from the common-sensical in that […] it moves beyond the realities of everyday life to wider ones which correct and complete them […] It differs from the scientific perspective in that it questions the realities of everyday life not out of an institutionalized skepticism which dissolves the world’s givenness into a swirl of probabilistic hypotheses, but in terms of what it takes to be wider, nonhypothetical truths. Rather than detachment, its watchword is commitment; rather than analysis, encounter. […] Having ritually ’leapt’ (the image is perhaps a bit too athletic for the actual facts – ‘slipped’ might be more accurate) into the framework of meaning which religious conceptions define, and the ritual ended, returned again to the common-sensical world, a man is – unless, as sometimes happens, the experience fails to register – changed. And as he is changed, so also is the common-sense world, for it is now seen as but the partial form of a wider reality which corrects and completes it. 
If we follow this understanding of the religious, then all debates about the sacred, and here we may include debates about the sublime, have a religious character. So, incidentally, has writing science fiction, for it is a defining aspect of doing so that one imagines how things could be different in order to invite readers to dip into this other world and come back to their own with a changed perspective. Actually, in Geertz’s sense, all kinds of utopian thinking have a religious aspect.
My conclusion is that there is something self-contradictory in Banks’s treatment of religion. Banks seemingly tackles the issue head on, by creating sublime beings and then refusing to give them much play. Subliming comes across as a bit of a joke. We should not believe in spiritual beings, even when they exist. However, the willing suspension of disbelief is a necessary precondition for reading a piece of science fiction in the first place. Banks is still fighting yesterday’s battles between believers and non-believers, between cultists and atheists, where the issue that is increasingly at the heart of debates about religion concern a much wider and much more interesting issue, namely the place of the sublime and the sacred in our everyday lives. What about giving us a planet that challenges the Culture with something like that in the next novel?
 D. A. Russell (1964) ‘Introduction’ in Longinus Peri hupsus [On the Sublime], pp. ix–l, Oxford: Clarendon, on pp. ix-x.
 Clifford Geertz ( 1973) ’Religion as a Cultural System’ pp. 87-125 in The Interpretation of Cultures: Selected Essays New York, NY: Basic, on pp. 112,122.