The simple answer would be that it's not impossible. I believe the dead can visit us, but maybe it's hard. Maybe it gets easier as time goes on. My great grandfather passed away a few years ago. A day or two later, a radio that hadn't worked in years turned on for my grandma (his daughter) at a time she usually talked to him in the morning. My cat passed away last year. A few days later, her food dish rattled - nothing and no one else was nearby. I'd also "felt" she was nearby, and I have had brief dreams where she appeared as if to say she's still with me. My cousin passed a few days ago, and I heard footsteps in the hall while I was in the kitchen. I called out to my husband but he was in a completely different room. Then my mom told me our bathroom scale used to be his. I think we just can't explain it yet, but humanity will learn the science of it someday.