World-building - where do we begin? For me it's a top-down, bottom-up, sideways-in, you-name-it accretion of (primarily visual) insights. The very word insight suggests visualization. (We're mixing physics and metacognition here.)
I like weird, abstract ideas on the edge of our understanding. Previously I mentioned the arrow of time and the transactional interpretation of quantum physics. When dreaming up that particular book, these concepts suggested to me the existence of oracles (experiencing time-flow backwards in parts of their brain, interfacing with their own future perceptions), whom I chose to treat as tools of the aristocracy. That suggests lots of potential detailed scenes, but let's stay with the big picture for now.
My perception of the arrow-of-time problem is that most people aren't aware it exists. So many people switch on a light without wondering where the power comes from (Faraday's observations being at the heart of it), or use a phone/computer/whatever without understanding its nature, that they are living in a world of Clarke's-Law magic. I'm driven by a desire to shake people's shoulders and say: "Wake up! Smell the roses! Understand the evolutionary process that produced petals and pleasing scent! Imagine the nuclear heart of the Sun that drives life and all Earth's far-from-equilibrium thermodynamic complexity!"
I restrain myself, and address the desire differently, by creating worlds. Call it controlled schizophrenia.
In the case of my fictional oracles, I was not satisfied with using backwards-in-time waves (from the transactional quantum thing) as a method of carrying information. But the power of symmetry has drawn me, ever since my A-level maths teacher, Mr G.A. Dickinson, showed us two ways of solving a tension-in-bridge-struts problem: the "normal" way that examiners would expect, and a one-line short-cut justified with two words: "by symmetry."
Huw Price wrote about the Sakharov-Gold conjecture, which ties the direction of the future with a larger cosmos, and the direction of the past with a smaller cosmos. Imagine you're outside a universe (!) that you can see collapsing. Its inhabitants think they're living their lives forward, because their arrow of time always points to the larger-volume universe; but you see them living in rewind mode.
So is our universe expanding or collapsing right now?
And by symmetry, if you can't tell the difference, perhaps every big crunch generates a big bang: a bouncing-universe cyclical model. (This is a viable model that can be reached in other ways - cosmic expansion is not guaranteed to continue, although it is the most favoured view.)
Let's stay playing at this level. Dark matter is a well-known concept: there's stuff out there and we don't know what it is. More precisely, we don't know what it's getting up to.
What else? I like Charlie's FTL idea (among his many others). If relativity continues to hold but FTL exists, a tremendously powerful being would want to prevent FTL travel on the basis that editing history becomes possible. Space-time is weird.
If FTL drives are possible, but limited in where or how fast you can travel, then the light-cone of causality spreading out from an event just sprouted filaments or tendrils, representing the place-times you can travel to and possibly edit history. (Sort of a light-Cthulhu, really.)
People talk about Einstein dreaming he was riding a photon. Let's do that in our imagination now, while knowing about relativity. We're in a photon generated in a gamma-ray burster event the far side of a cosmic void. We travel hundreds of millions of light-years without subjective time passing - we are in a timeless splinter of space - and "then" we encounter Earth's atmosphere at which point time begins to flow - very, very, very slowly - before impacting a retina and we're done.
I mean, how weird is that?
And now I play symmetry games with words. If you can have timeless splinters of space, what about space-less splinters of time?
OK, let's zoom in a bit. We're building a world, what about its ecology? I want to skate on the edges of understanding for a while longer, so I'm thinking of complexity, emergent phenomena and the beginning of life, perhaps with replicating molecules on clay substrates. Ah, replicating molecules, which mix logic and data (combining the process of building copies, perhaps among other processes, with the blueprint for making those copies).
DNA? What DNA? This isn't Earth...
We know that Earth life-forms could have turned out entirely RNA-based. What other possible replicating molecules exist? And why does it have to be one molecule? Symbiosis occurs throughout organisms; emergent phenomena in chemical reactions often occur because of feedback loops, such as autocatalytic reactions. Why not a trio of interacting molecules, for example?
Our native life-forms will surely exhibit predation and symbiosis, life and death, because those are emergent phenomena. Given that amino acids are flying around the cosmos, that's the probable common starting point for long, self-replicating molecules. But there may be other building blocks, and even with amino acids, other compounds that self-replicate.
And we haven't even touched non-biochemical analogues. Inside a star, plasma and magnetic flux are bound together, forming complex patterns. Remember, we're all built of different atoms than we were just a few years back. We are patterns, like tornadoes moving through the atmosphere.
(Stretch out a length of rope on the ground and flick one end up and down. The resulting wave moves along the rope, but the rope does not shift horizontally. The wave shape is built of different molecules from moment to moment.)
Staying with natural phenomena, how about bi-coloured patterned fog? A tiger's stripes are a form of Turing pattern, emerging from interesting but inherently simple interactions between two compounds. More emergent complexity.
And the unnatural, or rather the engineered... Sometimes I interrogate a mental scene. A party takes place in a high-tech society some centuries from now. People are drinking out of... what? Glasses? Cups? Something organic? Something that floats when you let go of it?
How about architecture? Specifically, how about morphing architecture? My linguistic short-cut says everything: how about buildings made of a substance I call quickglass?
It changes the shape of human experience when a room reconfigures at command, when tables and chairs rise from the floor or melt back into it, when that cup was an extruded goblet broken from the table, filled via capillaries in the quickglass. When packing your belongings largely consists of storing data in the "tu-ring" you wear on your finger.
When a city's towers can walk...
In the subterranean, stratified world of oracles-as-tools-of-aristocrats, palaces in the upper levels form doors at will, as the smart-membrane walls liquefy to allow passage. In the lower levels, the downtrodden poor live in simple chambers carved out of rock, privacy granted by hangings of rough fabric. There's a resonance between the two environments, but it arose naturally, not from clever planning.
I've a thing about doors. We all know about Heinlein's doors, so I'm in a competition with myself to discover how many ways doors can operate without irising. Or hinges. So far I'm most proud of "dissolved in a blizzard of Koch snowflakes" but the game's not over yet.
Of course, an interesting world is really built of people, but that's another topic...
Open question time...
1) What scientific weirdness makes you go: Huh? How can that be?
2) I sort of assumed that most people here know what the Arrow-of-time problem is. Should I have done so? Should I do so in a book?
3) Do you prefer books where weird concepts are explained, or just out of reach?
4) Any scientifically impossible pet hates in SF?
P.S. Yes, I believe SF is the bridge between the Two Cultures identified by C.P. Snow.
P.P.S. Not to mention that SF reveals how "magical" the universe really is - in the sense of vistas evoking awe, a form of mystical transport based on our best understanding of its nature, the kind Richard Dawkins experiences.
P.P.P.S. To postmodernists et al: Korzybski's oft-quoted "the map is not the territory" presupposes there is a territory. (And he went on to say that "a map's usefulness lies in its structural similarity to reality.") Maps are not arbitrary; they should be rational. We understand the universe through mental models - maps - but some maps are plain wrong, while others are the best we can make so far.
P.P.P.P.S. Does anybody still read van Vogt? (I'm not saying anyone should. Or shouldn't. Just wondering.)
P.P.P.P.P.S. "Insight" in German is practically the same: Einsicht. French is rather more tactile: pénétration. But shedding insight into something - clarifying it - is éclaircir.