This story was updated 9/25 at 5 p.m. ET.

In his latest gaffe, Republican presidential candidate Mitt Romney lamented the fact that airplane windows don't roll down.

Romney's wife Ann's plane had to make an emergency landing Friday (Sept. 21) because of an electrical malfunction. Discussing the incident at a fundraiser the next day, he said: "When you have a fire in an aircraft, there's no place to go, exactly, there's no — and you can't find any oxygen from outside the aircraft to get in the aircraft, because the windows don't open. I don't know why they don't do that. It's a real problem. So it's very dangerous."

Here's why they don't do that.

Gravity tends to keep air molecules concentrated near the ground, so the atmosphere thins out as you go up. The air becomes so thin at 10,000 feet (3,000 meters) or so that airplane cabins must be pressurized above that altitude to prevent occupants from suffering from hypoxia, or lack of oxygen. Because temperature and pressure go hand-in-hand (i.e. low-pressure air feels cold), pressurization is also necessary to keep cabins sufficiently warm.

At 35,000 ft. (11,000 m), the typical altitude of a commercial jet, the air pressure drops to less than a quarter of its value at sea level, and the outside temperature drops below negative 60 degrees Fahrenheit (negative 51 degrees Celsius), according to The Engineering Toolbox. Exposed to such conditions, you would quickly die.

Pressurization is normally achieved by pumping the cabin with "bleed air," or compressed air sucked in and heated up by the plane's turbine engines. Pressurization only works in an airtight fuselage. Were you to open a plane window, the compressed air inside would rapidly rush out, atmospheric conditions inside and outside the plane would equalize, and everybody would die.

Plane windows that roll down would therefore be, to borrow Romney's words, "a real problem."

In the context of expressing concern for his wife's wellbeing, there was no indication that Romney's statement was a joke, but one can't know for sure.

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Update: Romney was joking. The New York Times' Ashley Parker, who wrote the original report about the Beverly Hills fundraiser that quickly got spread around the Web, told New York Magazine today that Romney had been joking. Parker said that while her report didn’t explicitly indicate Romney was joking, “it was clear from the context” that he was.

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