The Straight Dope | The Straight Dope | Chicago Reader

# The Straight Dope

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Since people living close to the poles are moving much more slowly than people living at the equator, isn't it true that a person near the pole will age faster than someone at the equator due to the effects of the theory of relativity? --Jim Uschold, Washington, D.C.

Jim, you sound like a guy with a lot of spare time on his hands. But what the hell, this is one of those questions that'll bring a boring physics class to a complete halt, so consider the following a public service. As near as I can figure, people age the same at the pole and at the equator, mainly because of relativistic effects that cancel each other out. Here's how it works: (1) Due to the rotation of the earth, people at the equator are moving at about 1,000 miles an hour, while those at the poles are more or less stationary. (2) Special relativity tells us that for any inertial (i.e., nonaccelerating) observer, moving objects seem to age more slowly. (3) Objects at the equator of a rotating sphere are not inertial, since they undergo continual acceleration toward the center of the earth. If they didn't, they would fly off on a straight line into space. (Think about it.) (4) Ergo, a person at the pole may legitimately consider that a person at the equator is aging more slowly, but not vice versa. (This may seem like an odd way of putting it, but the theoretical physicists out there will know what I mean.)

However, (5) the earth bulges at the equator due to centrifugal force, and (6) the pull of gravity decreases the farther you get from the center of the earth. (7) Furthermore, general (as opposed to special) relativity tells us the farther you are from the point of max gravity (i.e., the center of the earth), the more quickly you age. Thus you age faster on a mountaintop than in a valley (which serves all those rich bastards in Beverly Hills right). (8) Therefore, since people at the equator are farther from the center of the earth, they age faster. (9) The special relativistic effect in #4 exactly cancels the general relativistic effect in #8. In other words, people at the pole and at the equator age at the same rate. A lot of work to arrive at a result the average bozo would have guessed in a second, but at least we're right for the right reason.

I read somewhere that ordinary water has a peculiar characteristic that makes life on this planet possible. When most materials cool off they become denser and heavier, including water--except near the freezing point. It seems ice is less dense than water, so it floats. If it didn't and sank instead, lakes and rivers would freeze solid in winter, killing all the fish and triggering a terrible ice age. Is this true? Do any other materials exhibit this abnormality or is water unique? --William Kay, Burke, Virginia

If you already know all this stuff, what are you asking me for? Water isn't the only thing that expands when it freezes; so do cast iron and type metal, the lead alloy used in linotype machines. But the phenomenon isn't very common.

Like most things, water contracts as the temperature drops--until the mercury reads 40 degrees. Then it starts to expand again. When water freezes, in fact, its volume increases about 10 percent. Since ice is less dense than water, it floats, forming a crust over lakes and streams and enabling life to go on below. A very convenient coincidence, in which some see the hand of a benevolent Creator. I say we just got lucky.

What the hell is toejam, anyway? --Goofy Gholson, west suburbs, Chicago

The grotty stuff that collects between your toes, of course. A "toejam football" is the odious ellipsoid that forms when you rub it with your finger. What Freudian significance it had for the Beatles (cf "Come Together") I think I'd just as soon not know.

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