Metal Is Not Colder

Two spoons have been lying on the same worktop all night. One wooden, one steel. Touch the wooden one and nothing happens. Touch the steel one and you pull your hand back. Put a thermometer on both. Twenty degrees. Twenty degrees. They are the same temperature, and they have been all night. So what just happened to your hand? The nerve endings that respond to temperature are inside your skin, a few tenths of a millimetre down, under a layer of dead cells and tissue and fluid. They never touch the spoon. They never touch anything you touch. The only temperature they have ever been able to report is the temperature of the skin immediately around them. And heat only ever moves one way — from warmer to cooler. Your hand is at about thirty-three degrees, so the instant you make contact, heat starts leaving your finger. Not into the metal one. Into both of them. Nothing cold is coming back the other way, because there is no cold to come: it is not a substance, it is not stored anywhere, and it does not travel. What differs is how fast each one takes. Wood carries heat away slowly, so the wood touching your finger warms up almost to your own temperature and the draining nearly stops. Steel carries it off as fast as it arrives, into a piece of metal enormous compared with the patch of you that is touching it — so its surface never warms, the difference stays wide open, and your skin keeps losing. Same room, same twenty degrees: the skin against the wood settles near twenty-nine, and the skin against the steel drops to about twenty-two. That is nearly eight degrees, in you. Almost every explanation of this stops at "metal conducts better". That is half of it. A material has to carry the heat inwards AND have somewhere to put it — conductivity, times density, times how much each gram can swallow. Wood is four hundred and fifty. Steel is eight thousand. And the same rule, run hot, is why you can sit in a ninety-degree sauna for ten minutes and why ninety-degree water is