A 2012 poll shows that 45 percent of Americans say they believe in ghosts. More amazingly, in that same poll, 28 percent of the respondents said that they have personally seen a ghost before.

With such a widespread belief in ghosts, I was curious if there was actually any scientific evidence to fuel these beliefs.

I went to Buffalo, New York, to talk to Joe Nickell, a senior research fellow at the Committee for Skeptical Inquiry and allegedly the world’s only full-time paranormal investigator.

He told me that in his almost 50-year career of investigating all things paranormal, he’s never come across a single shred of evidence that would prove the existence of ghosts.

Instead, he points toward other scientifically explainable reasons for why people may think they’ve seen a ghost, including infrasound, sleep paralysis, and the traumatic grief of losing a loved one.

Watch the video above to learn more about the totally valid reasons you might experience a “ghostly encounter.”