Best science errors at the movies

Any idiot can make a science error, but the best movie errors give something of real value.  A good science blooper has pedagogic value.  It has some superficial plausibility, and in explaining to your students why it’s wrong, they really learn something.  Here are my three favorites:

  1. Movie:  Star Trek: Generations;  Mistake:  Evil Dr. Sauron fires Li_3 missle into star, which immediately stops all fusion in the core.  Star immediately dims and starts to collapse.  Why it’s wrong:  Being an astronomer, I’m partial to star mistakes.  It’s true that thermal pressure from fusion is what holds stars up against gravitational collapse.  However, if you turn off fusion, the thermal energy in the star won’t immediately disappear.  It only loses energy as fast as it radiates it away.  The timescale on which the star would lose an appreciable fraction of its heat is the Kelvin-Helmholtz timescale:  about 10 million years for a star like the sun.  More problems with this scenario:  Even if the star started collapsing right away, it should take several minutes for light from the star to reach the planet where Sauron and Picard are fighting, so even then, they shouldn’t see it right away.  Also, Sauron’s plan of moving the Nexus by changing the star’s gravitational field is flawed.  The star being very nearly spherical, its collapsing–even to a black hole–wouldn’t change the exterior gravitational field.  Also, since the star contracts quasi-statically, it obeys the virial theorem throughout:  E = T + W = -T.  So the star actually heats while contracting, even though it’s radiating energy, because it’s sinking deeper into its gravitational potential.  This really is a science mistake that keeps on giving.
  2. Movie: Mission to Mars; Mistake:  Human body exposed to vacuum immediately freezes.  Why it’s wrong:  This was a pretty forgettable movie, but I have a soft spot for it for all of the attention-grabbing science bloopers.  (“That looks like human DNA!”)  I expect one of the writers read somewhere that “space” has a temperature of 2.7K, which is really colde, so they thought “Hey, people in space should freeze.”  First of all, the vacuum itself has no temperature.  2.7K is the temp. of the cosmic microwave background, which is irrelevant to a body inside the solar system.  Such a body will cool (or heat) until it radiates away heat at the same rate that it absorbs it from the sun.  True, in Mars orbit this would be below freezing, but once again we must ask how long it would take for a human body to reach this equilibrium state.  The answer is a long time (hours) because the only way to lose heat in space is by radiation.  Like all hot bodies, a human emits blackbody radiation (about 100W, mostly in the infrared).  The cooling won’t be what kills you, though.  One exeption:  In a vacuum, the water in your eyes and mouth would boil off quickly (boiling temp. is a function of pressure; your blood, being pressurized, won’t freeze right away), and the latent heat the water carries away would quickly cool those parts.
  3. Movie: The Day after TomorrowMistake:  Air from the stratosphere descends quickly to Earth, “doesn’t have time to heat”, and so freezes the surface of the Earth.  Why it’s wrong:  I just love this mistake.  Whoever wrote this movie should get Al Gore’s Nobel Prize.    When a gas contracts or expands faster than it can heat or cool, its not the temperature that stays constant; it’s the specific entropy.  Thus, rapidly descending gas from the stratosphere would adiabatically heat.  Although the stratosphere has a lower temperature than the troposphere, it has a higher specific entropy.  (If it didn’t, the atmosphere would be convectively unstable and would quickly adjust itself.)  So descending air from it would actually heat us rather than cool us.

6 Responses

  1. Cute post.

  2. Thanks.

  3. Cool stuff. I like it when you delve into science; you should do it more often (I was actually fond of your suggestion for doing a global warming primer for rightists). I’d like to see you write something about quantum mechanics and its implications for traditional arguments for the existence of God, for instance.

  4. Hi Prof,

    Thanks. That’s all on the agenda. It’s all just a question of when I can get around to it.

  5. Fascinating

    Many years ago, I bought a Victorian reprint, in Latin, of “Somnium,” a sci-fi novel written by that ingenious (and eccentric) mathematician, Johannes Kepler. The Emperor Rudolph made him Imperial Wizard (Reichsmathematicus), the equivalent of the British Astronomer Royal. Nearly blind himself, he wrote an important treatise on optics.

    It is a rather dark little fable, but two episodes in it struck me very much. In the first, the Moon Daemons transport the hero, Duracotus, to a certain point between the Earth and Moon, where the Moon’s gravity takes over and then just leave him to fall to the surface. The idea of someone falling away from the Earth would have been a great challenge to the Aristotelian notions, then still prevalent.

    The other is a description of the Earth, as seen from the Moon – motionless in the sky, “as if it were nailed there,” he says. I was at Oxford at the time and this latter point struck me so much that I consulted Professor Blackwell, then the Savilian Professor of Astronomy, about it. He replied, in a charming little note, with a rough diagram and some cryptic formulae, that it was perfectly correct. This was in 1964, before the Moon landings, and I never thought to check, if he was right.

  6. […] and blood”.  Richardson doesn’t buy it, and neither do I, but the error involved is a pedagogically fruitful one; explaining why it is wrong illuminates key concepts of the conservative worldview.  In […]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: