And dot your T’s

In the article about infinity (“Infinite Wisdom,” SN: 8/30/03, p. 139: Infinite Wisdom), the “stereoscopic” images of tiny squares on page 140 are too far apart to view in the conventional way. However, if the viewer holds the magazine at arm’s length and looks cross-eyed at the pair, the diagonal across the square becomes visible.

Robin Frost
Santa Barbara, Calif.

A shaky start?

“Long Ride West: Many western sediments came from Appalachians” (SN: 8/30/03, p. 131: Long Ride West: Many western sediments came from Appalachians) suggests that the most likely transportation system of the sandstone across the continent would have been a river system. Could it have been due to tectonic movement instead?

Edward B. Fan
Upper Marlboro, Md.

Both Utah and the Appalachians are on the North American plate, so there’s no tectonic boundary between them. Sediments from the East could have been deposited and then remobilized at innumerable locations on their way to Utah.–S. Perkins

Familiar ring

The idea of compensating tidal forces using a ring of compact matter (“Black Hole Life Preserver: Don’t get sucked in without one,” SN: 8/30/03, p. 132: Black Hole Life Preserver: Don’t get sucked in without one) isn’t quite “something no one has shown before.” A concept based on the same principles was analyzed 20 years ago by physicist Robert L. Forward, who published the details in a paper in Physical Review and his science-fiction novel Dragon’s Egg. Forward discussed using such tidal compensation to allow humans to explore the environment near a neutron star.

Geoffrey A. Landis
NASA John Glenn Research Center
Cleveland, Ohio

The article should have identified the size of the black hole in question. For a large-enough black hole, a person falling through the event horizon would feel just a gentle stretch-compression force. The real fun would begin as singularity were approached at the center.

David Marcus
Potomac, Md.


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