ADVERTISEMENT
See Inside June 2008

Mailbag: Yes, Earth's Crust Moves 25 Centimeters with Every High Tide

Land "Tides" -- Polar Ice Sheets -- Market Morality

Tidal Terra Firma
Is Graham P. Collins correct in stating in “The Discovery Machine” [Special Report: The Future of Physics] that the land near Geneva rises 25 centimeters when the moon is full? A shift that large should damage considerable infrastructure.

Charlie Gotschalk
Sequim, Wash.

COLLINS REPLIES: Because the tidal forces from the sun and moon deform the entire earth, all the land in the vicinity of Switzerland is raised by very nearly the same amount at “high tide.” Consequently, at the scale of buildings and towns nothing is displaced enough from anything else to damage infrastructure or even to be particularly noticeable—unless you happen to be running an 8.6-kilometer-diameter accelerator and need to know its circumference to an accuracy of a millimeter. You would have to travel about a quarter of the way around the world (10,000 kilometers as the crow flies) to go from the location of the land’s “high tide” to that of the land’s “low tide,” so it is only over distances of thousands of kilometers that the relative movement is as large as
25 centimeters.

A 1992 talk on this issue by Gerhard E. Fischer of the Stanford Linear Accelerator Center is available at http://tinyurl.com/2ncx2o. Slides from a 2000 talk by Jorg Wenninger of CERN (pdf file at http://tinyurl.com/2vnpth) show how the effect of the tides on the beam energy of CERN’s Large Electron-Positron (LEP) collider was first measured in 1992.

Free-Market Fairness?
After detailing research on the desire for fairness in humans and other primates in “The Mind of the Market” [Skeptic], Michael Shermer concludes that market economies are driven primarily by fairness. His assertion is supported neither by the research discussed nor by history and economics.

Shermer conflates the behavior of markets with that of humans, but corporations, whose only legal and structural motive is profit, conduct the majority of market activity. He also generalizes the results of studies of a presumably random sampling of humans to those who exert a disproportionate influence on the market. Systemic factors may have selected these individuals for ruthlessness. Moreover, Shermer ignores real-world factors: A person may not be able to turn down an unfair deal if the alternative is starvation or homelessness. And an executive may be prevented from offering a better deal by the profit motive of his or her corporation.

Shermer claims that if morality were not the rule, “market capitalism would have imploded long ago,” which falsely assumes that an immoral market cannot be stable. (The transatlantic slave market thrived for hundreds of years.) Further, markets implode with great frequency—in crashes and depressions. When such crises occur, it is humans, not markets, that use their political will and governmental agencies to impose regulations and provide social services that restore some degree of justice to their society.

Delano Lopez
Appleton, Wis.

Good-bye, Ice?
“The Unquiet Ice,” by Robin E. Bell, describes the effects of the ice sheets of Greenland and Antarctica collapsing completely, but currently there is no evidence that they will fully disappear. Furthermore, Bell’s model does not take into account the rebound effect that would take place if those landmasses were free of ice, which would offset some of the sea-level rise. She also does not consider the possibility that there would be a greater movement of water vapor from the ocean to the atmosphere.

Raphael Ketani
Sunnyside, N.Y.

BELL REPLIES: Ice sheets have come and gone throughout the history of our planet. The recent news of a large part of the Wilkins ice shelf collapsing reminds us of this flux. The results of the ice sheets changing are global and complex. The land underneath a disappearing ice sheet will rebound (today the Nordic countries and northern Canada bounce back almost one centimeter per year from the load of an ice sheet that disappeared more than 15,000 years ago), and the sea level will rise differentially depending on the water temperature and the source of the water. These complexities aside, we will likely continue to see increasing sea-level change from the polar ice sheets. It is difficult to transfer continental-scale ice to a framework we can apply to our own experience. The scientific community certainly does not anticipate a complete collapse of the polar ice sheets, but changing ice will increasingly be a theme of the coming decades.

Rights & Permissions
Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Scientific American Back To School

Back to School Sale!

12 Digital Issues + 4 Years of Archive Access just $19.99

Order Now >

X

Email this Article

X