You should meet me and my colleagues the Winchesters, I guarantee you'd change your opinion.

Yes they are

If you can prove that ghosts are real claim your Noble Prize, you either proved a spectral form of life, or proved an afterlife. There's no scientific evidence of ghosts, they are not real.

No one has proof for ghosts existing, no one has proof for ghosts not existing. Either one is possible. Don't argue about it if you have no facts.

You're all forgetting about burden of proof. Specifically, burden of proof is on the positive claim, not the negative. Ergo, ghosts are not real until proven otherwise, not the other way around.

Aka "theory" ... Ghosts are theories!