Do we know everything about universe?
Short answer, no.
Some things like dark matter and dark energy, still remain undiscovered and not proven.
Some others include the actual existence of black holes and what is the singularity in them.
Also, are there any other universes besides ours?
Those are some unanswered questions, who knows when they will be answered...
Human knows just a fraction of the Universe..
Well, the space is keep expanding, due to which, slowly and gradually, galaxies, stars, planets are moving away from each other,
and the reason of this expansion is dark energy , which is the 90% or even more, part of the universe, which is
according to the recent research, a kind of repulsive gravity , which is the main cause of the expansion of our universe .
Also we don't know what currently is happening out there, right now at this exact moment, the reason is ,
we see things from which light reflects, as the speed of light is consider to be the fastest speed,
even this speed has to cover a lot of distance, which is like at the time, it reaches to our telescope,
a lot of time has passed already up there,and what we are seeing right now it's just the past of the universe,
so we are not even sure, what is happening right now.
If you are more interested, Be Sure to Check out this video...
Hope this Helps... :)