“Why did that happen?” he asked the audience, some of whom were relaxing their brain cells with a mixed drink called a Bunsen Burner.

“The heat seeped out of it,” someone yelled.

“You get an A,” he said.

The spirit of “Mr. Wizard’s World” has now reached an audience that can legally drink. The same late-night revelers who spent their high school and college years plodding through mandatory science classes are now gathering voluntarily to listen to presentations on principles of string theory or how orbitofrontal cortexes work  as long as it takes place far from the fluorescent lights of classroom.

Science groups for young professionals who don’t wear white coats, like the year-old Secret Science Club at Union Hall, are cropping up in bars and bookstores all over the country, from Massachusetts to Montana.

“If you have a certain type of job, after a while that part of your brain starts to deteriorate,” said Amy Lee, 25, who works at an Internet startup and was attending her second Secret Science Club meeting. “You want to use it again. Plus, there’s alcohol.”

About 50 groups, with names like Science on Tap and Ask a Scientist, have formed in the last four years. There are three in New York City alone. Each month, they invite scientists, usually professors at nearby universities, to lecture on topics as varied as mass extinctions and frog mating calls. Anywhere from 50 to 100 people, none of whom wear pocket protectors, show up for an evening of imbibing hard science along with hard liquor.