In the long run, the sky going dark is not such an unlikely scenario. Big asteroid impact or a large volcanic eruption would be enough. Or some big war, sadly

In the long run, the sky going dark is not such an unlikely scenario. Big asteroid impact or a large volcanic eruption would be enough. Or some big war, sadly we tend to have them quite frequently. I forgot that was the background story to The Matrix... :-) I agree that fusion power would also be great for travelling into deep space. In the reeeally long run, there is no other choice for mankind.