I would say we don't know much—or at least mainstream science doesn't. Our accepted models of physics are riddled with assumptions and falsehoods so we can pretend we know more than we do.
I sometimes think about all we could learn from a civilization that's thousands or millions of years older than us. When I was writing Alarm Clock Dawn I constantly thought about how the universe might have a way of limiting the technological evolution of those who aren't spiritually advanced enough to handle the responsibility and implications of that tech.
I think humans, as a whole, might just not be responsible enough quite yet to be accepted into the fold of those other advanced civilizations zipping around the cosmos—especially the sociopaths that run our world. I'd say a lot of ordinary folks are already "there" or almost. I was curious about the disclosure documents but wasn't holding my breath. Most documentaries or any release of information on this topic ends up being a huge build up and then an even larger disappointment.