Thought of something, I would consider this similar to Malthusianism if it was more modern and applicable and not gay and stupid. Basically in the future the amount of energy we produce from one plant will have an average or a set amount. For every new power plant the only change in our output will be linear as we are just increasing the value of x while the amount of energy produced is the slope. The amount of energy we need to traverse solar systems, then galaxies, then clusters, etc. is exponential, and eventually the simply linearity of our energy production will limit our progress, so we need to figure out how to make our energy output exponentially increase for every new plant built to combat the challenges of traveling deep space. Just as in malthusianism the population growth was exponential but the resource gathering was linear, but human ingenuity made this not an issue any more, so we can do it with this too(maybe)