How the future changes over time

Reading Mary Shelley's "The Last Man", what jumps out at me is the sheer ordinariness and unremarkableness of the early 19th Century conception of what the future might hold. The book was written in 1826, but its story begins in 2074, some two-hundred-and-fifty years into the future, and continues until 2100. Interestingly, though, Shelley's vision of the day-to-day world in 2074 looks like nothing so much as ... the world in 1826. Granted, then, an apocalyptic plague drastically changes the face of the world, but there is no sign of any grand, technological utopia (or dystopia) here. Even the geopolitical divisions and mechanisms of Europe seem to have weathered the two-and-a-half centuries with many a change. Plus ça change?
Sometimes called the first science fiction novel - and you can debate that one until the cows come home! - "The Last Man" was written eight years after "Frankenstein", but still some 60 or 70 years before the ground-breaking science fiction of H.G. Wells and Jules Verne. Quite honestly, there is little or no actual science in the novel, so perhaps speculative fiction or apocalyptic fiction would be a better label.
It seems to me that part of the point of science fiction (or speculative fiction, for that matter) is to imagine a world and a time that is very different from the world or time of the author's contemporary audience. But it is, by definition, impossible to imagine the unimaginable. An author's imagination appears to be circumscribed by their own, experience, knowledge and scientific understanding. Thus, the worlds envisioned by Isaac Asimov and Ray Bradbury in the early 1950s would have been literally inconceivable to Mary Shelley (or even H.G. Wells). By the same token, Isaac Asimov would probably have been unable to conceive of the kind of technical detail in Kim Stanley Robinson's Mars books, or the Culture universe of Ian M. Banks. Like it or not, we are, at least to some extent, a product of our times.
in 1826, big changes in science and technology were most definitely already afoot, and the well-educated Shelley was almost certainly aware of most of the developments. The Industrial Revolution was gathering steam (literally), Newtonian physics was well established, the first vaccines had been introduced, and the very early basis for modern chemistry, biology and geology were all in place. But, even so, the pace of innovation was positively glacial compared to what was to come.
When I think of what has come to pass in the fifty-odd years of my own lifetime - from near-Earth satellites to a man on the moon to probes approaching the edge of the Solar System and multi-spectrum photos from the edge of the observable universe; personal computers to the Internet to smartphones to virtual reality; genetically-modified crops to clones to whole genome sequencing and CRISPR gene editing; nuclear power to solar panels to hybrid cars; robotic assembly lines to 3-D printing to synthetic meat; the list could go on and on - and the speed of continuing development, envisioning two-hundred-and-fifty-years into the future seems all but impossible (or futile).
What we can be really sure of, though, is that the world in 2265 will look nothing like today's world.