If we look into the future projecting from what we have seen in most sci-fi movies we will see future cities that are crowded with people and tall buildings, filled with flying cars, plenty of devices on people, lots of large screens advertising stuff, etc. But lately, I have begun mentally picturing a completely different future after observing the real trends that govern technological development.
The deepest trend governing technology is progressive ephemeralization, this is the gradual shrinking of technological devices to the point of invisibility. The most noted example of this trend of progressive ephemeralization can be seen in microprocessor development.
Staring from the mechanical calculators of Babbage and others, we soon had vacuum-tube powered computational devices. Soon after, with the invention of the transistor, we moved to transistor powered computation. The transistors of this early post-1948 era were actual physical devices you could hold in your hand but with the advent of large scale integrated circuits, transistors were so miniaturized that you could not hold a single transistor in your hand but you could hold a VLSI chip containing millions and eventually later billions of transistors.
So we see that from large mechanical systems we moved to smaller and smaller systems until we now deal with transistors that are invisible to the naked eye, this is a clear example of progressive ephemeralization.
So what does the future hold? In my own opinion, the future high tech cities filled with stuff that we have been sold in sci-fi movies will not happen, rather in the future, if humanity actually survives to 2100 the kind of world we will have would be more of the kind of world you would find if you took some biodome used for the conservation of plant species and scale it up to cover the entire planet.
The population would be less either due to a massive die-off of most of the population in some natural or man-made disaster or just the fact that people will not want to have as many children any more, leading to a less populated world with people that age very slowly due to many advances in lifespan extension. I personally believe more in the latter case than the former.
Most of the advances in lifespan extension will come from augmenting our bodies will all kinds of nanotechnology, the cyborg era will not come with us stripping our brain-nervous systems off our bodies and mounting them in metallic frames like some predict, but will rather see us augment a lot of our biological functions with things that are too small for the eyes to see.
Programmable nanobots of all kinds will aid in our respiration, digestion, waste clearance and will even destroy tumours, viruses and all other kinds of pathogens. Will help correct errors in our gene-expression giving us longer lifespans. Death in most cases will be voluntary and due to boredom of physical existence
So what about the environment, how will it look like? Due to advances in synthetic biology, we will cover the earth with new flora and fauna of our own making, that act like the nanobots in our own bodies. Providing us food, and maintaining the biosphere by clearing off pollutants and providing oxygen.
You will have most of the earth look like the carboniferous era in earth's history. The majority of humanity will move to live in cities in the seas and sky and mars and an artificial planet orbiting the earth like the moon, leaving the land to fallow with vegetation because we will realize that plants are machines for maintaining the ecosystem of the earth.
As for technology like the internet, mobile communication, entertainment systems like TV, even health tracking will all move inside us. So you will not see someone using a fit bit because you will have access to all your health information mentally, heart rate, blood pressure, immune strength, etc.
If there is a need for any external thing then it will be beamed holographically like you would watch a movie with your family on a holographically projected screen of any size you want to fit in the space you have available and it will look so solid you will not be able to distinguish it from a physical TV set.
Before this full holography comes we will compress most of our devices into, first of all, Augmented reality glasses like the one in Westworld Season 3 and eventually, they will disappear into Augmented reality lenses placed directly on our eyeballs.
But as our bodies become synched with nanotechnology then everything we now do with some external device will be done internally, you could watch a movie, video call, look up stuff on the internet all inside your head using your mind's eye because you will have a second brain sandwiched between your original brain and communicating seamlessly with your original brain so much so that you will not know when you are using your real flesh and blood brain or your augmented nano brain.
With all the above-stated technologies I bet you can see that the future will look very different from what we have become used to in Science fiction works. That future world is a truly brave new world.