Picture this.

I predict that in possibly less than a hundred years, reality as we know it will have no meaning.

There is a nanotechnology concept called "Utility Fog". It was first put forth by Dr. J. Storrs Hall some few years ago. Utility Fog is a cloud of cell-sized nanos that each have 12 eensy teensy arms. The nanos can grab onto each other's arms to form objects and exert forces -- nearly anything, real or imagined, can be simulated in this way. You can also levitate things, fly, and appear to teleport since someone else could essentially call your utility fog and have it create an image of the person to interact with you. You, of course, could do the same. Utility Fog could display images, produce sounds, push and pull things... you name it. One wonders if this is the stuff that all these cartoon characters have had all these years, with their ability to produce anvils, carrots, etc. out of thin air.

Moreover when our attempts at AI get closer to the mark of sentience then an AI could also use the Fog to project and inhabit images that it may find or create for itself. And we wouldn't be able to tell the difference.

It looks like a person. It behaves like a person. It can interact with others and with objects in its environment. But unless something happened to the Fog to make it discorporate you would never know if it was an AI.

And even outside of the AIs you wouldn't be able to tell if the environment itself was real or not. The Fog would create and project a total immersion environment. Every object you see or touch could be mutable Fog. All the normal sensory tests you could do would tell you that it was real.

If somebody got control of your Fog they could make you do or believe literally anything. They could drive you quite handily insane.

And then there's this. What if, a hundred years from now, this kind of environment becomes all we know?

It's taken only 2 generations for computers to worm their way into our every moment.

It bears thought.