Man, I'm rarely spooked by posts on reddit. But, these are EXACTLY my biggest mind fuck things about space.

When I first learned about gamma ray bursts, I remember it being described as a beam of light, essentially appearing from nowhere that could essentially melt all forms of advanced life off of the surface of the earth. It could happen tomorrow or never. Like the aneurysm of interstellar proportions.

Dark matter is also fucked. Likely responsible for the continuous expansion of the universe and yet it is still basically unknown. This is one of those things that, because its essentially everywhere, we will undoubtedly know so much more about in 1000 years. I expect this is something future humans will understand like gravity, but to us its essentially magic.

And the Fermi thing is just another way to marvel at the vastness of space. We can reasonably assume there have been millions if not billions of civilizations that have already well surpassed earths technology and destroyed themselves and there is a 99.9999999999999% chance we learn about a single one of them.

The only other one I'd add is the varied potential for alien lifeforms that operate on totally different chemistry than the traditional carbon/oxygen organisms we are used to. Hydrogen breathing aliens on planets with extreme gravity or even nitrogen based organisms living on frozen planets.

Space is the most amazingly wonderful concept that is also existential crisis enducing.