I will argue that if we want to believe that physics of today can explain everything, we have to accept existence of parallel worlds in our Universe. I will explain how to see an object without light and why an attempt to prove, without light, that an object is absent, fails. This will demonstrate that Wheeler's approach to the past of a quantum particles does not explain the weak trace it leaves and that the proper description of the past of a quantum particles requires addition of a quantum state evolving backward in time.