Gravity, as Wikipedia tells us, is a natural phenomenon by which all physical bodies attract each other.
Most commonly it is experienced as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped.
Not unlike the jaws of author Tess Gerritsen's fans when they find out that the current box-office film smash "Gravity" is not based on the suspense drama of the same name penned by the bestselling writer who visited the Putnam County Public Library Monday afternoon.
"I've been receiving a number of emails from readers, congratulating me on the new movie 'Gravity,' which they believe is based on my book with the same title," she said.
"Yea, 'Gravity' is a great film, but it's not based on my book," Gerritsen said, noting that she saw the movie in Bloomington over the weekend.
But it could be.
Gerritsen's 1999 book "Gravity" follows the plight of astronaut Emma Watson, a research physician studying living things in space.
However, once at the International Space Station, things go horribly wrong and recovery efforts prove catastrophic as the space shuttle crashes and the space station is crippled by deadly multiplying organisms. Known as Archaerons, the organisms had been gathered from the deep sea to be monitored in the microgravity of space. And near zero-gravity brings them back to life.
The current film version of "Gravity" highlights the efforts of a female astronaut (Sandra Bullock) to return to Earth and her daughter after being stranded when satellite debris slams into the space station, wiping out the rest of the crew.
So, two stories titled "Gravity." Each focusing on a lone female astronaut. Each trapped aboard a space station, orbiting 400 miles above the Earth and fighting against all odds to get home.
Coincidences do happen and Gerritsen appears not to be bitter that people continually congratulate her erroneously on the novel being turned into a major motion picture with big-time Hollywood stars (also featuring George Clooney).
"Alas, the movie is not based on my book, despite the similarities," she concedes.
In "Gravity," Gerritsen said she set out to write a story so correct even a NASA engineer could not find fault with it.
She did hours upon hours of research, visited NASA, talked to scientists and downloaded hundreds of pages of NASA blueprints and information (remember, this was pre-9/11).
The author was extremely confident she had nailed it from both an astronaut and engineer's viewpoint.
Then came the anticipated telephone call. The guy on the other end was indeed a NASA engineer.
"He said, 'I read you book and you got something wrong,'" Gerritsen told the library audience.
"OK," she offered succinctly, "what?"
Gerritsen had written about the story's hero driving into the parking lot of a particular Johnson Space Center building, parking the car and going inside.
"I've worked here 30 years," the NASA caller said, "and there's never been an open spot in that parking lot."
Apparently to some people, there's no underestimating the gravity of a situation.