This recent presentation from Kepler Airospace claims that Einstein was on the right track and a goes even further, stating that gravity can be manipulated through EM. I've graduated in Physics but not quite sure what to make of it.
If all major governments keep it secret, the conclusion would be that the phenomenon wants it that way. The US wouldn't be in charge. But apparently something changed.
There may not be much of a difference left then between machines and biologicals. Generations would alternate like a jellyfish does between polyp and medusa. No need for generation ships.