I bet there were lots of people who predicted telephones, planes, and bombs way earlier than 1820.

For clarification, I didn't say it was impossible, I said to just imagine being a person trying to, and that they, the doubters, clearly can't imagine it. Also, if by "lots" you mean you could count them on one hand, then yes. But you are actually helping my point in a way. Do you think those few people got there by saying "nah we can't ever do it because of our current limitations of knowledge and technology" (aka, what the doubters in this thread are doing). And if they suggested it, the mass public would look at them and say "nice pipe dream idiot, that'll never happen". Did a few people have imaginations large enough to predict things and work towards them? Obviously - not every discovery or invention was an accident. Do you think those people are the equivalent of the doubters in this thread who don't believe anything will be possible because we can't do it now and they can't understand the technology involved (which has yet to be invented) will work? The answer should clearly be a "no", which is my point.

Your predictions aren't on the same scale as my examples because none of your predictions require a massive leap in technology that virtually everyone, outside of a few of the most brilliant minds in society, could accept or imagine.

Your 50 year is already well underway, 100 year is just a natural prediction of physical resource limitations (none of my examples were just a "natural progression" except maybe a nuclear bomb), 150 years is already well underway too, 250 years is a no brainer progression seeing as those are non-renewable but more importantly already have the technology to not require it, and 500 years is another progression by a likely limitation of our resources.