The question is, is GDP growth always going to trend upward, or will it trend downward at some point in the future. If the former, the bull market (with some crashes) can continue. If the latter, then nope. The stock market isn't the economy, but it certainly is a distorted reflection of the economy.
Look at the factors of production:
* land: not building any more of it (except the Chinese in the South China Sea :) ). Unless space travel becomes economical, then there's a ton of "land" available in terms of satellite habitats, the moon, etc.
* labor: human population looking to peak in 2050 last I checked. Not sure how climate change will affect this (could be a strong negative in 100 years).
* capital: lots and lots of capital and more efficient ways for it to move around the world.
* energy: fracking + renewables have changed the game and the west is far more able to control their energy supply than in the past (see "The Absent Superpower")
* intangibles (ideas, patents, etc). Lots of room to run here. The internet + youtube + google has made the cost of distribution close to zero. This means that new ideas (both inane, like dance fads, and useful, like new ways to organize teams) can spread far more quickly than in the past. (see "Capitalism without Capital")
I'm voting yes, the bull market will continue indefinitely. I'm long the human race :) .