Eddies and currents in this metallic outer ocean produce Earth's magnetic field. "At least we believe that, though we don't understand exactly what the mechanism is," said Richard Terrile, a planetary astronomer at the Jet Propulsion Laboratory in Pasadena, California, and a science consultant for the film.
So can the magnetic field really shutdown?
"In fact it has happened many times in the Earth's history," says Terrile. "The Earth's magnetic field is not a stable solid thing like a bar magnet—it actually changes, it moves directions, it goes up and down, and it actually reverses."
Don't throw away your compasses just yet. These shifts only occur every few hundred thousand years or so. But that's still enough to make the idea of a magnetic field shutdown at least plausible.
What would happen next is debatable even in scientific circles. In The Core, radioactive particles and microwave radiation literally cooks the planet. In one scene they even slice the Golden Gate Bridge in half.
"I don't want to diminish enthusiasm for the movie, but I don't think anybody would notice if the magnetic field disappeared," said Jack Connerney, a planetary scientist at Goddard Space Flight Center, in Greenbelt, Maryland.
"The ionosphere and atmosphere would keep out much of the solar wind and radiation," said Connerney, so although the radiation would increase slightly, life on Earth would not fry.
Connerney also doubts that huge electrical storms would be instantly generated. Both Venus and Mars lack global magnetic fields, he said. "We don't see strange electrical phenomena happening there."