6 hours of the sun's energy, or 15 billion years worth of current human energy use (or only a few trillion years human energy use in the early first millennium, it really was not exponential until the 19th/20th century and these days its more linear). The only way you get energy levels that high is with truly enormous stellar-scale engineering projects like Dyson clouds, which we see no evidence of when we look out into the universe in infrared - those are something we would actually be able to see. Again, if things of that sheer scale are something that intelligent systems don't get around to doing for one reason or another, then this sort of project would never happen.

Additionally, the papers referenced there have 'seed' masses sent to other GALAXIES massing grams with black-box arbitrary control over matter and the capacity to last megayears in the awful environment of space. Pardon me if I don't take that possibility very seriously, and adjust the energy figures up accordingly.