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To talk of many things: of octopuses and energies and...

Q: Is an octopus a reptile, mammal, or amphibian? Or is it just a fish? (Christine, Chardon, Ohio)

Q: How do blue-ringed octopuses breathe? (Priscilla, Tootgarook, Victoria, Australia)

A: An octopus is not a reptile, a mammal, or an amphibian (though it can live short periods of time out of water — long enough to climb out of a tank at night and eat shell fish from other tanks). It is not even a fish.

A provoked greater blue-ringed octopus. When disturbed, the octopus switches from its normal drab brown/yellow color to bright yellow with bold blue rings. [Courtesy of Roy L. Caldwell © Used with permission.]

The ancestors of octopuses branched off from the ancestors of vertebrates more than 550 to 600 million years ago. Annelids (for example, earthworms and leeches) and arthropods (insects, lobsters, and the like) may be their closest major related groups, says biologist Roy Caldwell, a professor at the University of California.

Octopuses are in the mollusk group — muscular slimy creatures such as slugs, snails, mussels, oysters, squids, and cuttlefish.

Although not fishes, all octopuses (including the blue-ringed octopus Reader Priscilla asked about) breathe like fish with gills. They suck water through two internal gills, just behind two of their three hearts. The gills extract oxygen and blow the water out through a tube, called a "siphon" or "funnel". The octopus can shoot through the sea — in reaction to the expelled water jet — although he usually walks or crawls.

When attacking prey, an octopus gets close, leaps forward by spurting a water jet backwards, and grabs his lunch — perhaps a crab or fish.

By the way, all octopuses have poisonous bites. The golf-ball size blue-ringed octopus of Australia, however, is the only octopus whose bite is known to kill humans. The poison can stop a person’s heart and breathing in several minutes. Without medical care, this can kill the victim. We have no antidote. With medical aid to maintain ventilation, though, victims usually recover.

There is another species, called Octopus mototi, whose name on the Rapa Island in the South Pacific, literally means "poisonous octopus," says Caldwell. We don’t know if this creature is deadly, "but I would not let one bite me."

Further Reading:

Roy Caldwell, "Death in a Pretty Package: The Blue-Ringed Octopuses." Freshwater and Marine Aquarium Magazine, 23 (3): 8-18.

BBC: Octopuses

Q: What is energy? (Mc, Cebu, Philippines)

A: Energy? Examples spring to mind. The Sun’s thermonuclear furnace blasting forth a fiery spectrum of electromagnetic waves. White water thundering over Niagara Falls.  A swirling cyclone of white clouds verging on the golden peninsula of Florida.

Such an intuitive commonplace concept. Yet the idea was unknown to Sir Isaac Newton, the founder of classical mechanics in the 1680s.

A fire dancer displays heat, light, and kinetic energy. [Courtesy of Wikipedia, photo taken at Wesleyan University]

"Energy is defined as the amount of work required to change the state of a physical system," say many textbooks in a typical circular definition. What is energy or work, though?

More helpful: "The combination of energy and matter makes up the Universe: matter is substance, and energy is the mover of substance," writes Paul G. Hewitt in his Conceptual Physics (sidestepping the issue of dark matter).

"All forms of energy are associated with motion," says the Encyclopedia Britannica. Anything moving has kinetic energy, from a supernova-exploding star to a gas molecule bopping around. A pulled bow or a coiled spring has potential for motion. As do chemical bonds in molecules and nuclear bonds in atoms.

As alluring as this concept is — that energy is somehow motion — we must relinquish it. "It is important to realize that in physics today," says Richard P. Feynman, "we have no knowledge of what energy is."

Feynman was one of the three recipients for the Nobel Prize in Physics in 1965 for his contributions to quantum electrodynamics and was one of the most influential physicists of the 20^th century.

We only know that energy is conserved, says Feynman.

Energy has many forms: motion, gravitational, heat, elastic, electrical, chemical, radiant, nuclear, and mass. Energy, however, is simply a mathematical quantity that we can calculate but, so far, do not understand.

The energy form can switch but the energy quantity is always the same. That is the law of the conservation of energy and the only exact thing we know about energy. There is no known exception to this law.

What is energy? You know what it is. I know what it is. But, we don’t, really.

Further Reading:

Paul G. Hewitt, Conceptual Physics, Ninth ed. New York: Pearson, Addison Wesley, 2002.

HyperPhysics by Rod Nave: Energy

(Answered Sep. 30, 2005)