I can't see any plausible reason to predict that Microsoft will last longer than Google or that Britain will last longer than the USA.

In general, I tend to assume that recent history is more relevant to future prediction than older history, a sort of generalized informal Markov assumption if you wish, therefore trying to predict how long things will last based only on their age is likely to yield incorrect results.

These don't seem unreasonable.

I'd give Less Wrong and e-mail substantially more than 25% chance of surviving to 2020 and 2135 respectively in some form, and the US a bit less than 25% chance of surviving to 2732. (But still within the same ballpark -- not bad for such a crude heuristic.)

I think it should work if we see clear effort to create something physically possible. In case of Emdrive it may be proved that it is impossible. (But NASA just claimed that its new version of Emdrive seems to work :) In case of seasteding I think it is quite possible and most likely will be created during 21 century.

We could also use this logic to estimate next time nuclear weapons will be used in war, based on 1945 date. It gives 75 per cent for the next 105 years.

But if we use 75 per cent interval, it also means that 1 of 4 predictions will be false. So Lesswrong may survive )))