It may be the season for vampires, ghosts and zombies. Just remember, they're not real, warns physicist Costas Efthimiou.
Obviously, you might say.
But Efthimiou, a professor at the University of Central Florida, points to surveys that show American gullibility for the supernatural.
Using science and math, Efthimiou explains why it is ghosts can't walk among us while also gliding through walls, like Patrick Swayze in the movie "Ghost."
That violates Newton's law of action and reaction.
If ghosts walk, their feet apply force to the floor, but if they go through walls they are without substance, the professor says.
"So which is it? Are ghosts material or material-less?" he asks.
Zombies and vampires fare even worse under Efthimiou's skeptical microscope.
Efthimiou looked at the most prominent child-turned-zombie case that zombie aficionados cite: the 1989 case of a Haitian 17-year-old who was declared dead and then rose from the grave a day after the funeral and was considered a zombie.
Efthimiou takes out the calculator to prove that if a vampire sucked one person's blood each month — turning each victim into an equally hungry vampire — after a couple of years there would be no people left, just vampires.
He started his calculations with just one vampire and 537 million humans on Jan. 1, 1600, and shows that the human population would be down to zero by July 1602.
Take that Casper, Dracula and creepy friends.
All this may seem obvious, but to Efthimiou and other scientists, the public often isn't as skeptical as you might think.
More than 1 in 3 Americans believe houses can be haunted, a 2005 Gallup poll showed. More than 20 percent of Americans believe in witches and that people can communicate with the dead. TV shows such as "Medium" and "Ghost Whisperer" are popular.
"We're talking about a large fraction of the public that believes in subjects that scientists believe are out of the question," said Efthimiou.
University of Maryland physics professor Bob Park, author of the book "Voodoo Science," said scientists have to keep telling the public what seems all-too-obvious.
"There are things that we need to point out that are crap," Park said.
It's gotten so bad, Park has a hard time watching movies these days. Not Efthimiou, who liked the horror movie "The Ring."
"I have nothing against movies," he said. "I have nothing against people who like them, as long as they don't mix reality with fiction."
And Halloween? Both physicists will suspend disbelief when vampires, ghosts and zombies come to their doors.
"I give them candy and I feign fright," Park said. "They enjoy it, what the hell. The problem is the ones that never get over it."