The Physics of "Gravity" and "Interstellar"

Hanukkah is a Jewish holiday celebrating a miracle whereby oil sufficient for just one day burned for eight.  Over this past week, an entirely different miracle took place: I, a father of two young girls watched two movies, none of which contained a single princess.

I really got my nerd on: I rented "Gravity" and then went to the theater to see "Interstellar".  Both films feature a lot of physics, but they could not be more different.  "Gravity" is a ninety minute expedition featuring orbital mechanics, while general relativity weaves its way through the three hours of "Interstellar".

You are probably expecting me to dissect these two films and expose all of their scientific inaccuracies.  In truth, I enjoyed both of them immensely, but would like to address one major problem with each one.

Hollywood Films Get Space Travel Wrong

As the space ship in the 1986 film Aliens moves towards a mysterious planet, the cosmonauts aboard gaze suspiciously at the foreign body with their feet firmly pressed against the ship’s floor.  The sci-fi adventure has barely begun, and already, the laws of physics have been ignored due to a common imbalance in Hollywood: too much fi, too little sci.

I want to be clear about something: I am an avid fan of science fiction movies, whether or not they are set in space.  In fact, I was thoroughly entertained by Aliens, the sequel to Alien - so much so that I watched it recently for the second time. 

As the film is set in the distant future, it is sensible that several technological leaps have been made by mankind.  I am comfortable with the intelligent robot that is a part of the crew.  I am intrigued by the sensitive motion detection equipment that they use.  What makes me queasy is when the most basic law of motion is inexplicably defied.

When advances in technology occur, they lead to more robust tools.  However, these tools, no matter how fantastic they are, must operate within the constraints of the universe.  Otherwise put, technology is dynamic, but exists within an operational framework that is static.

When a space travelling Sigourney Weaver stands up on the surface of a ship, this implies that there is a set of contact forces between her feet and the surface.  A force, commonly referred to as the normal force, is pushing up onto her feet.  Unless you are currently undergoing a vertical loop on a jet airplane, or happen to be reading this article while in a space orbit, the normal force is currently acting on you.