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No. 2276:
The Cascade Effect

Today, we try to sort out science. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

All science eventually snares us in epistemology -- the question of how we know things to be true. Most of us have some notion of scientific method -- the means by which scientists arrive at new knowledge of our world. But almost all of what you and I know of that world is given to us. It's knowledge we have not, ourselves, obtained by scientific means. 

Now and then we check facts scientifically, but not often. I checked the law of gravitation in a physics lab; but I've never checked the diameter of the moon. Economists tell us that incomes are more nearly equal to one another in good times. I believe that because I once found a way to derive that fact myself, using methods of molecular thermodynamics. But I rely on others to tell me that I can safely drink water if it has less than 500 parts of salt per million. 

Now: I've just cited four scientific conclusions. And I ask you, which of these can I claim to know? That's a troubling question in our complex world. For we have to act upon so much that we've never tested. We're at the mercy of others. 

CascadeScience writer John Tierney talks about cascade effects. They work like this: I don't know what's true about, say, eating fatty foods. So I listen to a person I trust and form the opinion that I should avoid fat. Now two of us agree, and it' s a lot easier to convince a third. Pretty soon it's common knowledge that fatty foods lead to cancer, stroke, and heart failure. 

The scientific business of erecting conclusions consistent with facts must often be done when facts are incomplete. What happens when we can't table a question? I can't put off eating until I know what's good for me. For twenty years I've faced dire warnings about fatty foods -- claims we now take as gospel. I try to turn away, but my baked potato cries out for butter and sour cream.

Now we have the result of a huge government-sponsored eight-year study of 49,000 women. Disease, it turns out, and even weight, were virtually unaffected by diet. This study, for all its solidity, is kicking up a storm. And far be it from me to try to start a new cascade effect. Doubters point out that the study didn't sort good fat from bad, it was limited to older women, and so on. Still, it now does seem that our genetic formation (and maybe our mental condition) are bigger factors than diet. 

I suspect the science of nutrition is particularly vulnerable to cascade effects since it's an arena where we might actually influence our destinies. But so many choices also lie outside our bodies. Think about how the intense hurricanes of 2005 provided a flurry of evidence in favor of global warming. Then the dearth of hurricanes a year later was evidence for global-warming nay-sayers.

That's how cascade effects work. Incomplete evidence is coupled with a need to believe what our friends do. In the end, it seems, we have to rely on people less well-tuned to the minds of those around them -- if we're to be saved from ourselves.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)

J. Tierney, Diet and Fat: A Severe Case of Mistaken Consensus. Science Times, The New York Times, Tuesday, October 9, 2007, pp. D1-D2.

For more on the economic calculation I mention above, see: J. H. Lienhard and L. B. Davis, Jr., An Extension of Statistìcal Mechanics to the Description of a Broad Class of Macroscopic Systems. Zeitschrift für Ang. Math. und Mech. (ZAMP) Vol. 22, No. 1, 1971, p. 85 et seq.

These two websites relate new ideas about the consumption of fat: New York Times, Feb. 8, 2006
New York Times, Feb. 14, 2006

Another cascade

(photos by JHL)