I think people have a hard time imagining it because they don't understand how technology advances. It's predicted that with our current rate or progress in technology, we'll see 100 years worth of growth, in the span of only 25 years. That's what's important to understand. And that was about 10 years ago. By 2025, it's not unreasonable to assume that we'll have seen a rate of progress that takes us to this level of technology.
It's difficult to explain in just one paragraph post, but I'd recommend doing a little reading if you really think it's too far-fetched. I found one such article that talks about something known as The Law of Accelerating Returns. Here's a little excerpt from it:
http://www.kurzweilai.net/the-law-of-accelerating-returns
An analysis of the history of technology shows that technological change is exponential, contrary to the common-sense “intuitive linear” view. So we won’t experience 100 years of progress in the 21st century — it will be more like 20,000 years of progress (at today’s rate). The “returns,” such as chip speed and cost-effectiveness, also increase exponentially. There’s even exponential growth in the rate of exponential growth. Within a few decades, machine intelligence will surpass human intelligence, leading to The Singularity — technological change so rapid and profound it represents a rupture in the fabric of human history. The implications include the merger of biological and nonbiological intelligence, immortal software-based humans, and ultra-high levels of intelligence that expand outward in the universe at the speed of light.
And here's a wikipedia article explaining a little more about this:
http://en.wikipedia.org/wiki/Accelerating_change
