Incredible Shrinking Movies

One science theme that shows up in movies from time to time is the ability to shrink things down to a tiny size. The 1957 movie, The Incredible Shrinking Man, didn't use computer graphics because there were no computers at the time! In 1966, Fantastic Voyage told the story of medical professionals who were miniaturized and injected into the bloodstream of a patient so that they could perform surgery on a blood clot. More recently, in Honey, I Shrunk the Kids , a scientist invents a shrinking machine which puts his children, and his neighbor's children, in danger (although they're all OK in the end).

So, what about the science behind these movies? It's not so good - in fact the science is very wrong. It's true that, at normal size, there's a lot of space between the molecules of our bodies. But you can't actually make the molecules smaller; they'd just have to get closer together, and that would start to change the way our bodies work. In science, there's a Law of Conservation of Mass, which means that you wouldn't get any lighter, even if you could get smaller. So you would just become more dense. Just imagine a group of normal-weight people swimming through your blood vessels! These movies may be a lot of fun, but they really are incredible!