Reality

Based on the modern quantum mechanics, without any observation, questions such as "what has really happened" do not mean anything. We only know what has happened when we observe. In other words, observation tunes the possibilities into reality or reality only exists when observations occur.

Then the question becomes "what does observation really mean". Does human beings have the freewill to decide where, when and how to observe or so called observations are merely predetermined events between two or more groups of matters interact with each other.

Another question is what "really has happened" mean to us. We know that we can't tell what is going to happen in the future since we are part of the universe. However, if we were not part of the universe, then we can't even tell anything about it at all.