Imagine that you’re in ancient China. You’ve been accused of a crime, but you swear you didn’t do it. And now you’ve got a mouth full of dry rice. Why?
You’re being given one of the earliest known lie detector tests.
Lie detector tests have been used throughout history to try to solve crimes. This early one in China was based on the simple idea that lying makes you nervous, which makes your mouth dry. If you spit out the rice and it was dry, you were guilty. Not surprisingly, it didn’t always work.
Lie detectors have improved over time. The modern lie detector, invented in 1921, is a machine called a polygraph. Basically, it measures your blood pressure, heart rate, breathing, and sweat.
An examiner may begin by asking you simple questions—such as What’s your name? and What year is it?—that have only one right answer. This shows the examiner how your body responds when you’re more comfortable with the answer. Then, they ask what they really want to know, such as Did you do it? It’s up to the examiner to interpret the results and decide whether you’re lying or not.
Obviously, there are problems with this. A polygraph measures your stress level, not whether you’re lying—and being accused of a crime would make anyone feel stressed! Plus, if you Google “how to beat a lie detector,” you’ll learn that it’s very possible.
Fortunately, polygraphs are almost never used as evidence anymore. But a few decades ago, a failed polygraph test could put you in jail.
It all makes you wonder: How will we be solving crimes 100 years from now?