Well like I said it is beyond our science and technology to bring the dead back to life or even learn how a spirit works or how to encode or decode one. If we manage to figure out how to reverse time, it could be possible, though I doubt that would happen in our lifetimes.
In truth there is a lot about life and death that we do not fully understand yet. We can only speculate. When it comes to these sorts of things, we are still living in caves technology and science wise. I liken it to a Neanderthal who cannot figure out how to put a puzzle back together, but millions of years later and farther down the evolutionary path, one of his future relatives figures it out and solves the puzzle. Millions of years from now, who knows, maybe farther down the evolutionary path and one of our future relatives figures out how to put dead people back together?