If ghosts aren't real, where does the energy go from someone who has passed away?

I am not a scientist. At all. I claim to know nothing about science past the fact that caterpillars turn into butterflies and that fat floats to the top.

But I have always liked the idea of ghosts. So a few weeks ago I was reading a book.. just fiction.. and in it was a character who majored in paranormal research or something, and I can’t remember verbatim, but in the book he explained that “ghosts” are just energy; energy can’t just disappear or be destroyed so when someone passes on, their energy has to become something else.

As a science-stupid person, that sounds logical to me. For you science geniuses and non-believers, can you elaborate on why it is or isn’t horsehockey?

I think there was more of an explanation… I am trying to dig through the book a little but I’m at work