Back to the Future (BttF) was really good, both as science fiction and as comedy. It posited the invention of a new technology (time travel) and then explored one possible consequence of time travel (a version of the grandfather paradox). It managed to do so in an entertaining and lighthearted fashion, to boot.
The other two movies were not as good. Of them, I like the third one better, primarily because it doesn't struggle as hard to maintain the parallels that the second movie attempted, and failed.
But the second movie showed us a view of 2015 from about twenty-five years prior, starting with elements that were included in the first movie for comedic effect and to show that Doc had really been 30 years in the future.
First, if you look at Doc's clothing--the clear vinyl tie, the insane colors--some of that was popular wear for teens in the 1980s, some was speculation on the part of the production designers. Doc needed to look as if he'd been in the future, and no one would have bought it if he'd come back to 1985 wearing khakis, a polo, loafers, and maybe a light jacket against the early autumn chill, not even if he'd had an iPhone 6S plus in his hand. Fashion is always assumed to be ludicrous in the future; the reality is that it almost never is. A man's casual dress clothes from today would be passable in 1955, though people might wonder where he'd left his hat.
And on the reverse side, the scene at the high school in 1955--Doc's casual clothes would be almost perfectly acceptable in 2015.
Second, Mr. Fusion. In 1985, fusion was due any time now. There's been no change in that prediction; thirty years later we're still thirty years away from harnessing fusion power. Of all the advances we're shown in the BttF trilogy, this one would be the most important because it makes all the other technologies possible.
Like the oft-lamented flying cars. The reactionless thruster that is used to make them fly is approximately "magic" right now (though apparently we're working on it) but they won't do any good without some kind of power source, and a pretty dense one at that.
Just as an example: in his book Saucer: The Conquest Stephen Coonts has one of his protagonists attempt to use the alien antigravity technology in an old pickup truck, for yucks. To generate enough power to lift the truck, he has to run the engine flat out. (Note to self: there is now, finally, a third Saucer book, and I must read it. The first two are damned good books and I want to see what happens. Coonts never intended there to be a series.)
It takes a lot of power to support the mass of a car against gravity. Figure a ton of mass, and you have to provide enough thrust to counter an acceleration of 32 feet per second squared. That's a lot of energy just to hover. A reactionless thruster should convert power directly to kinetic energy, but the efficiency seems likely to be no better than a typical internal combustion engine (twenty to thirty percent).
I expect that innocuous-looking pink Barbie hoverboard Marty carries around during the latter two movies contains a tiny Mr. Fusion reactor, because we never see him plug that thing in and recharge it.
Which leads me quite naturally to the flying cars, of course. The second movie is full of things that float or fly or hover, like magic. The arrival in 2015 is on an airborne superhighway, delineated with floating lights and signs, full of flying cars and trucks.
The BttF version of 2015 doesn't include a lot of things we have, that the producers of the movie could not envision in 1985--and like most visions of the future it was based entirely on trends of the year in which it was made, extrapolated.
Soothsayers are usually wrong.
But the thing is, expecting new and radical changes in technology is actually correct. In 1985 no one thought people would routinely carry around, in their hip pockets, computers that could be used anywhere on the planet to communicate with people, watch movies, listen to music, or just look things up ("I know there's a Thai place around here somewhere; gimme a second to Google it.") and inexpensive enough that nearly everyone has one. Powerful computers, devices that eclipse all but the fastest computers available in 1985.
It was actually correct, in one sense, to expect flying cars and fusion power and-and-and by 2015. In 1955, no one expected things like the JVC GC-C1 camcorder Marty had in the first movie. No one thought computers would ever be personal (much less small enough to fit in a hip pocket and let you play "Angry Birds" between phone calls) and they certainly didn't think that we'd ever go to the moon half a dozen times and then just stop.
The expansion of technological knowledge is exponential--or, at least, it's supposed to be. Since the end of the space age we've put all our efforts into making circuits smaller and more efficient, with the result that we can now cram ten thousand transistors into the area once occupied by one, and wirelessly stream movies in HD, but still don't have a truly reusable rocket booster or a significant, permanent on-orbit manned presence.
Thirty years ago I was pretty certain the vision of 2015 in BttF 2 was incorrect. I just didn't know how; of all the technologies we saw in that movie Mr. Fusion seemed the most plausible.
Imagine how different things would be if fusion were commonplace and cheap like that, even if you had to use special fuel to run it rather than banana peels and stale beer (and the can it came in).
Thirty years from now, then? In 2045?
I'll be 78 years old, for crying out loud. I don't know. But I'm willing to take a stab at it.
Fusion power? I think so, at least I'd like to. It'd be nice if we'd finally crack that nut, because it's incredibly efficient and clean, even moreso on all fronts than fission power is. And there's literally unlimited fuel for it; even just within the bounds of the solar system there's enough deuterium for all of Man's energy needs ever. (And perhaps a century's worth of research into making fusion power more efficient will, I expect, crack the proton-proton fusion problem, freeing us from the need for deuterium.)
Flying cars--I doubt it. Maybe, but I doubt it. Flight adds an extra dimension of complexity to a vehicle, and the need to transition from ground travel to air travel adds weight and more shit to go wrong. And most people aren't smart enough to operate a car properly; how much worse would it be if they could fly, too? I expect us to continue to use one kind of vehicle for ground and another for air.
Clothing: clothes are going to evolve, just as they have for the entire history we've worn them. Our customs regarding nudity may change, but not drastically, and the clothes will look about the same in 2045 as they do now. Materials may change, patterns and features may be different, but I'd bet I could go to 2045 right now wearing what I wear to work, and not look too out of place.
Computers: There's a certain practical limit to miniturization, that we're rapidly approaching, though we're not quite sure where that limit is. I think we have perhaps a decade left in Moore's Law--I'm optimistic about that--but by the time we get to the end of it we won't need much more than we have when we're there. Following that, our understanding of nanoengineering will help us improve batteries to the point that your laptop will be able to run for a week on a charge, rather than a few hours.
Energy: better batteries will help a lot of things, but if we don't have portable fusion reactors we're still going to rely on power distribution grids. Vehicles may still require fossil fuels, or they'll be electric and require charging before use. Fusion power should help make electricity "too cheap to meter" which would be a huge boost towards making electric cars practical.
I expect us to be in the middle of a Maunder Minimum in 2045. It's going to be chilly. Climatologists will be claiming that unless we curb human pollution the Earth will enter an ice age before the end of the century. "Anthropogenic global warming" will be all but forgotten.
Socially--that's a tough one. I do expect a swing back to a moral, ethical society. I'm not sure how far we'll go towards "permissive" before then. I expect pedophilia to be legalized before things start to get better--it might even be the catalyst that turns things around--though I'm not sure how legal it will be. Will it be PC to celebrate it, as we must now celebrate homosexuality? Or will it remain in the ghetto, tolerated at best (as it was until only recently)? One can only hope things won't go that far, but right now I'm not seeing anything that can really stop the attempt.
I'm predicting a major war sometime between now and then. 2045 will be a post-war world similar to the 1950s or so.
Overall, I'm optimistic that the future will be better than today is. There will be rough spots; there always are. But we're pretty good at improving things. It's what we do.