Along with stem-cell research, cloning and artificial intelligence, scientists are struggling with the search for the "heaviest" heavy metal band.

You didn't read that in Scientific American, but it's true. They're keeping it a secret. A Nobel Prize in Heavy Metal awaits whoever can find the heaviest heavy metal band whose career half-life can be measured in more than a few nanoseconds. The problem is twofold: The biggest heavy metal bands often earn their success with heavy metal ballads - an oxymoron if there ever was one. On the other hand, brave attempts to be heavier-than-thou often result in noisy nonsense with gravel-pit-from-hell vocals and no translator available. Was the guy from Cannibal Corpse singing, "Satan rules" or "Me want cookie?"

However, as Fear Factory singer Burton Bell points out, there is more to "heavy" than guitars distorted to amp-blowing levels, tempos faster than a frightened gerbil's heart rate and the Cookie Monster on lead vocals.

"It's all relative," he says. "Heavy isn't just necessarily sound. Heavy is also an attitude, lyrical content. A real light tune could be really heavy if the lyrics say something deep, meaningful, and it shocks people."

Combine heavy sound with heavy lyrics and you have Fear Factory. The band, which hosts an evening of extreme heaviness at Red's tonight, doesn't just make concept albums. The entire band is a concept - about the continuing relationship between man and machine. Bell would probably be a science fiction writer if he weren't the singer in a heavy metal band.

He says the idea behind Fear Factory's new album, Digimortal, is an "evolution" of the concept he had when the band formed 10 years ago. The first record was "the birth of the machine." The second was a rebellious teenager fighting the machine. The last album, Obsolete, was where the machine begins to question its existence. And on Digimortal, "instead of fighting the machine, you're starting to understand it and work with it. The constant evolution of humanity is still going on. And whatever new element comes into it, we're going to evolve with it."

Bell admits the concept is sometimes lost on audiences during the frenzy of the live show.

"I don't take it personally," he says. "Not everyone's going to get it. But that just makes me challenge myself even further. If the person wants to get more involved in it, they have that opportunity. If not, hey, at least they're getting some interesting music."

Opening for Fear Factory tonight are Puya, Primer 55 and Dry Kill Logic. Tickets are $24.50.