For example: there is no way to objectively demonstrate that the universe you see, hear, smell, touch, and taste actually exists in any real way. Your subjective senses tell you it does, but subjective sense experiences are not objectively verifiable; the senses are often fooled. In dreams, for example: from the point of view of the dreamer, it's impossible to objectively distinguish the things one sees in the dream from the things one sees in so-called reality. We may assume that the world we experience when we are awake is in fact the Real World, but we cannot demonstrate that assumption to be true.
That is where faith comes in -- and it is that faith that lies at the root of all scientific reasoning. If you choose to believe that the Universe is real, then that is your business -- but don't kid yourself into thinking that you know it to be so, because you cannot. As Descartes pointed out, the only thing we can know to be objectively true is that which we perceive directly, without the medium of our subjective senses -- in other words, our objectively experienced self-awareness.
Each of us can know that he or she exists because we constantly and objectively experience ourselves existing: cogito ergo sum.
Think about that before deciding what's real and what isn't.