Quantum theory is said to have started a revolution in Physics since the first days of its existence. The reason is that it introduced a completely new thinking over the idea of reality;
People that are not familiar with Physics they have the idea that Science is a simple process that is based in a basic theory and by following some rules it produces new knowledge. They tend to think that new knowledge is coherent to the old one. So when they here about quantum physics or quantum reality they bring in the mind the -for the most non so pleasant- “school” ideas of forces, wheels and vectors (not to mention silly ideas about apples…) These were the ideas of what Scientists call “Classical Physics”.
This kind of physics was based to well established notions of reality -that were examined by Philosophers at least in the Renaissance (not to say maybe even before the time of Classical Greece). Classical reality is based in the idea that space exists independent of matter and time (which is are completely different ideas) and it is independent of our existence as observers.²
Physics though is not one theory, it is actually a set of different theories that describe different aspects of “reality”. Quantum physics theory (and with quantum physics theory the problem of quantum reality) did not appear as a theory that evolved naturally from the ideas of previous Physics. It developed in order to cope with experimental results (for the same reason that the Theory of Relativity was developed by Albert Einstein) . Quantum physics sounds odd because the experimental results that it does explain are odd!
In quantum reality³ reality itself does not exist before we observe it. Actually we cannot know if reality exists before we try to observe it and even worse the question itself does not have a meaning. The experimental result that led to this interpretation is that matter was observed to behave both as particle and a wave. The final answer of the theory³ is that matter is neither a wave nor a particle; what we observe depends how we observe it. If your experimental apparatus detects waves then you will detect waves! Before the observation it is believed that matter is in what we call superposition of both states both particle and wave, actually is something that we cannot understand and experience since we are only built to understand particles or waves.
² We cannot resist to the comment that the ideas of absolute time and absolute space, that is completely independent of out presence in it, reminds us the idea of God that exists before the creation and after the Armageddon, God of the monotheistic religions.
³ According to what is called the “Copenhagen interpretation”