Let’s be reductive and say science fiction refers only to those subgenres which occupy what is generally considered the genre’s heartland – hard sf, space opera, soft sf, first landing, first contact, military sf, etc. Let’s call all the rest “speculative fiction”, a term I dislike, but since they seem not to bother with the science aspect it is perhaps more appropriate.

Let’s say there are two types of science fiction as defined above. There is the type of science fiction that appeals to people who would happily read supplements for a role-playing game. And there is the type for people who would prefer to read a physics text, or a book about the engineering involved in building the Saturn V. Both types, at heart, operate by adjusting a reader’s sense of scale and turning that which cannot be conceived into something which can. Or vice versa. For example…

Look at the photograph above. That’s the surface of Titan, a moon of Saturn. The photo was taken by Cassini-Huygens, a space probe which launched in 1997, and the Huygens part of which descended to Titan’s surface in 2005. Saturn orbits between 1.3 billion and 1.5 billion kilometres from the Sun. Earth orbits between 147 million and 152 million kilometres from the Sun. If you could travel to Titan in a straight line (which you can’t), it’d be a journey of around 1.2 billion kilometres… That’s equivalent to flying from London to New York and back over 108,000  times, or 6.5 million circuits of the M25 (at an average speed of 120 kph, that would take you about 1,150 years).

Numbers. They define our world – what we can directly see and experience, and what we can’t see or experience. As those numbers increase in size, so our sense of place in our world is increasingly diminished. Using science we can investigate, and gain an intellectual understanding of, this feeling of diminution. Science fiction, however, postulates situations in which we can experience it directly. It also gifts us with agency in this new world being explored. It is a visceral, albeit vicarious, manifestation of what science can show us.

Science fiction is scale, its uses and abuses. It can take something huge and beyond direct human experience, and by giving it the purpose of something within the reader’s real-world frame of reference, render it unfamiliar:

Planets. Seven of them. Armed and powered as only a planet can be armed and powered; with fixed-mount weapons impossible of mounting upon a lesser mobile base, with fixed-mount intakes and generators which only planetary resources could excite or feed. (p 40, Second Stage Lensman, EE ‘Doc’ Smith (1953))

It can directly manipulate the human frame of reference, and make of it something which would otherwise be strange and impossible to fathom:

It was not clear what had happened to the man for the next million years or so. One line of argument held that he had expanded himself to encompass a massive swathe of galactic space – swallowing hundreds of thousands of systems, across thousands of lights. (p 239, House of Suns, Alastair Reynolds (2008))

Or, it can simply map parts of the real world we cannot experience, and allow us to compare the scale of our frame of reference with that being described:

It took an effort to remember that the distance to the horizon was more than ten times that on Earth. That the storm was two thousand kilometres across. That the sky was hydrogen and helium a thousand kilometres deep, with cloud layers of ammonium ice above and decks of ammonium hydrosulphide and ammonium-rich water-ice and water-droplet clouds below, endlessly blowing around this vast world. (p 215, The Quiet War, Paul McAuley (2008))

There are a number of rhetorical tools and literary devices science fiction uses to manipulate scale and the reader’s perception of it. Analogy is a particularly common one – by directly referencing something known, and of a size encompassable by the reader’s mind, the sf text can make manageable the scale of something normally beyond comprehension. This is not always a good thing, as it can have a trivialising effect.

There is a great deal of implication in the findings of science. The photograph earlier in this post does not in and of itself present a particularly impressive-looking picture. It’s a stretch of orange ground littered with pebbles. But it’s on Titan. Which means… the launch of the space probe, the journey there, the distance the probe travelled, the mechanisms which comprise the probe and the science behind them, the descent into Titan’s atmosphere, Titan’s surface conditions… the real and true fact that it is an alien world.

Science fiction not only gives us the orange photograph, but it also shows us how it was achieved. It makes explicit the wonder. And since wonder is central to science fiction, then to define wonder is to define science fiction:

…where:
W = wonder
l_g = greatest distance mentioned in the text
t_g = greatest length of time mentioned in the text
N_n = number of ideas/nova in the text
N_f = number of ideas/nova reader has encountered previously
i_r = closeness of the viewpoint character to the reader as a function of background, worldview, attitudes, etc – ie, an indicator of their ability to identify with the character
j_n = number of situations of jeopardy for point-of-view character(s)
j_a = amplitude of situations of jeopardy for point-of-view character(s), where 1 is fatal
C_n = size of cast in the text
B_r = bandwidth of the reader (calculated from educational level, number of books read, age)
D_r = willingness of the reader to suspend disbelief