Q: What determines the speed at which fingernails grow? Do they continue grow even after we die? —Tom Gonzalez, Arlington, Texas

[Corel] An Egyptian mummy’s nails may look longer but they don’t grow.

A: A special growth area (called the matrix) at the base of the nail controls the speed. The matrix lies in a deep groove in the skin dermis (the thick inner layer alive with nerves and blood vessels) and makes nail material—a dead, hoof-like protein, called keratin. It makes nails constantly—from birth to death—at an average rate of 0.004 inches (0.1 mm) each day, or 1.5 inches (36.5 mm) in a year.

However, the matrix doesn’t make nails at a steady rate. Nails grow faster when it’s warm, when we’re young, when we apply pressure to the nails—like playing the piano or biting, cutting, filing, polishing, or scrubbing them. Nails grow slower when the matrix is short of blood, when the blood contains stuff that stunts growth (like chemotherapy material or cigarette byproducts), when we suffer malnutrition, or have a high fever.

Death stops growth. However, after death, skin dries and shrinks. When it shrinks back from nails, the fingernails (and toenails) appear to lengthen because more nail shows.

By the way, fingernails grow four times faster than toenails.

Further Surfing:

Louise Wright Robertson, Ed.D.: Did you know that?

Q: What part of the flower has the scent? —Karen, Richmond, Canada

[Purdue University, department of horticulture] Snapdragon scent brushes off on bumblebee.  She carries the scent back to the hive.

A: The flower petals make volatile oils and these oils contain the scent. Molecules boil off from the oils and waft the flower’s odor through the surrounding air.

The scent has several purposes: to ward off and kill harmful insects, to attract helpful pollinators, and to warn other plants of viral danger. Plants receiving the scent signal from infected neighbors fortify their own defenses against the virus.

Purdue U: Understanding floral scents

Q: Is there anything faster then the speed of light? Can anything travel along laser light? Maybe someday we could have space vehicles traveling by laser light at unheard of speeds. —Ron T, Lehighton, Pennsylvania

A: Sorry, no signal and no object travel faster than light in a vacuum. If any could, effects could happen before their causes. For example, a super-light-speed spacecraft could arrive before it started. Impossibilities would abound.

Suppose I could lope along at light speed, "c", and notice a light wave traveling beside me, of course, at speed "c", too. That light wave will look like it’s standing still, relative to me. Just like the car in the next lane looks stationary when it’s going at my speed.

But this is impossible, according to Einstein’s Theory of Special Relativity. The speed of light in a vacuum must be the same ("c") for every observer in a uniformly moving reference frame. It can’t be zero for me. Therefore, I can’t lope along at "c" nor, therefore, exceed "c".

What happens as an object approaches light speed? Suppose I’m the pilot of a spacecraft cruising at near light speeds. I decide to beat my headlight. Can I?

I push in the throttle and my velocity increases, slightly. So far, so good: give it the "gas" and it goes faster. However, as my velocity increases, so does my motion energy (called kinetic energy). Energy is equivalent to mass as Einstein discovered (E = mc²) and therefore also has inertia. As my energy increases, so does its inertia. It gets harder and harder to accelerate the spacecraft to greater speeds.

I shove in the thruster control all the way; the engine yields an enormous energy pulse—it’s best. But my speed remains much the same—near light speed—and the headlight shines merrily ahead of me.

Inertia increases without limit as the ship’s velocity approaches "c". Thus, it takes an infinite force and an infinite amount of energy to accelerate the spacecraft to "c" and that is impossible. Once again, since I can’t attain "c", I sure can’t pass the headlight.

I’m curious, though, as I watch the headlight skip ahead: What happens to the enormous thrust of energy? It no longer appreciably increases my speed. It can’t. My inertia’s too great. The energy squeezes into my mass! An outside observer sees me and my craft swell as I shove in the thruster. Soon we appear twice as large—good grief! As I hit 99.9997 % of "c", my craft and I loom 410 times bigger than when we started. "E" becomes "m" as Einstein predicted.

This really happens in the CERN or Fermilab particle accelerators. Protons accelerated to 99.9997 % of "c", appear enlarged by a factor of 410 times.

But, all is not lost. Our space vehicles may, someday, travel at unheard of speeds. Theoretically, they can travel as close to "c" as they please (and we can engineer the required propulsion energy). Remember, too, that spacemen traveling at near light speeds—age slowly.

Carl R. Nave, Georgia State University: Einstein velocity addition

Relativistic flight through Stonehenge

BBC: Faster than a speeding light wave

(Answered May 9, 2003)