Visa cards are printed with little holographic doves as forgery protection, and I’ve seen similar holographic images printed on things no thicker than a piece of construction paper. Soon there will be chocolate bars with holographic decorations etched on the surface (this according to Scientific American). How are these little holographic pictures made and how do they fool the eye into seeing depth where there really is none? –Susannah Faulhaber, Alameda, California
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As is often the case with technical subjects, Susannah, we are presented with an unfortunate choice: an explanation that is accurate but incomprehensible, or one that is comprehensible but wrong. Being a journalist and therefore shameless, we naturally opt for the latter. What follows is the Ollie North explanation of holography–it might get you past a congressional committee, but don’t try it on your PhD board.
L&O #1. There aren’t any mirrored balls. Actually each “mirrored ball” is a set of quasi-hyperboloidal interference fringes. Interference fringes reflect a percentage of the light that strikes them. Amounts to the same thing as mirrored balls, but they look a lot different, and from the standpoint of conceptual grabbiness they’re strictly to puke.
If she wants to splash in the pool, let her splash. From the 1930s through the 1950s there was a great fear that swimming after eating would lead to stomach cramps that would double you over in agony, causing you to sink like a stone. This was thought to be a leading cause of drowning. As late as 1956 the Red Cross water-safety manual devoted several pages to the topic complete with staged photo of a gasping “victim.” That same year, however, U. of Georgia swim coach B.W. Gabrielsen published a book called Facts on Drowning Accidents that revealed that swimming after eating was implicated in fewer than 1 percent of drownings. Thereafter the wait-an-hour hysteria began to subside. It’s now thought stomach cramps are rare. It still isn’t a good idea to do strenuous swimming right after eating lest you exhaust yourself. But a quick dip in the pool after dinner is harmless.
