Fluid Dynamics

Call me crazy, but I don't see what kind of sense a ban on liquid travel on airplanes is. To be sure, letting people carry soda or shampoo onto an airplane could (apparently) allow them to conceal an explosive. And a bomb going off on an airplane would be a very bad thing. But by the same token, a bomb going off on a crowded Metro or Armtrak car would be quite bad. Hell, a bomb going off on a crowded airport security line snaking back and forth as everyone waits to have their bags searched for offending liquids woud be really point. At some point, common sense needs to kick in.

Banning firearms on airplanes is a very inconvenience that is very effective at halting what could otherwise be a very easy method of hijacking airplanes since guns are pretty easy to obtain. It's fairly clear, however, that permitting people to carry liquid aboard planes doesn't necessarily lead to a rash of airplane-bombings. It is, however, a huge inconvenience for travelers.

Worst of all, it's at best a minor inconvenience for terrorists. If you had a cell with some working liquid explosive devices ready to be set off, you could react to the ban by setting them off someplace other than an airplane. As outlined above, I would suggest a crowded rush hour Metro car. Try to position yourself near where the guy driving the train is located and blow it up on the Red Line between Gallery Place and Metro Center. That'd be a pretty good terrorist attack.

As James Fallows argues in his great "Declaring Victory" article, one of the main purposes of terrorist attacks is to provoke reactions to terrorism. In an ideal world, absolutely zero people would be trying to detonate liquid explosives on airplanes. Given that a certain number of people seemingly are trying to do so, you still have to ask yourself -- aren't we better off doing our best to find them and then taking our chances? A ban on liquids is a large price to pay in order to merely displace attacks from planes to things-that-aren't-planes.