Itching to Travel to a Tiny World? Visit the Flea Circus : SCIENCE FILE / An exploration of issues and trends affecting science, medicine and the environment

“Alice in Wonderland.” “Honey, I Shrunk the Kids.” “Thumbelina.” “The BFG (Big Friendly Giant).” “Gulliver’s Travels.”

All these favorites take us on a kind of size-travel to universes where things are far beyond, or beneath, everyday human scale.

Luckily, one doesn’t need fictional devices to visit such fascinating realms.

The Cardoso flea circus, now on a series of tiny stages at San Francisco’s Exploratorium, features miniature players who perform superhuman feats made possible largely because of their puny size.

A human-sized critter could never pull 160,000 times its own weight. But Hercules, “the strongest flea on Earth,” can. Another flea jumps 100 times its height to make it through a hoop.

Of course, a flea circus depends on illusion as much as pilocology (the study of fleas), and Colombian-born, Yale-trained artist Maria Fernanda Cardoso is well versed in both. She gets her fleas (which she raises herself) to jump through hoops by breathing at them.

“It’s the CO2; they think I’m a cat and they want to jump on [me],” she said.

And they can lift relatively enormous weights because there’s no illusion to the strength of the very small. In fact, when it comes to physical forces, large and small things operate in very different universes.

Take a giant. How big could the biggest human-like creature be? According to J.B.S. Haldane in his classic essay, “On Being the Right Size,” a 60-foot giant would break his thigh bones every time he took a step.

The reason is simple geometry. Height increases only in one dimension, width in two, volume in three. If you doubled the height of a man, his muscle area would quadruple (2 times 2) and his weight would multiply by eight. If you made him 10 times taller, his weight would increase by 1,000 times, but the cross-section of bones and muscles to support him would increase by only 100 times.

Conversely, a pea-sized person would lose much more in weight than in muscle size--making Thumbelina a match for King Kong. In Cardoso’s circus, fleas take advantage of their small mass-to-length ratio to propel themselves to amazing heights.

For giant things, gravity is disastrous. If a tyrannosaurus fell, it would never get up again. The world of little things, however, is ruled by molecular forces. Bugs have no problem walking on the ceiling because the forces holding their feet are stronger than the puny weight pulling them down. The electrical pull of water, however, attracts them like a magnet.

As the fleas remind us, there’s a lot we take for granted about our own size--and a lot we miss because we perceive only things on our own scale.

Near the flea circus is a microscopic video camera that lets visitors explore the invisible worlds beneath their own skin. It is not a pretty sight.

Put the microscope on your arm, and the TV screen attached reveals a dizzy landscape of nicks, creases, folds and dewy transparent hairs that look like they are the size of redwood trees--all strewn with giant boulders of dirt.

I wait until I’m alone to check out my own face--and gasp at the globs of mascara encrusted on an eyelash like mud on a dog’s tail.

It is rather overwhelming to look through your own skin at blood cells coursing through capillaries. It’s like looking at yourself without clothes.

We forget the extent to which our view of the world is airbrushed, and that we see things through a shroud of size, a blissfully out-of-focus blur.

Realizing this truth sure does take the scales from your eyes.