Why Are Cucumbers Cool and Are They Really Twenty Degrees Cooler Than Their Surroundings?

Twenty degrees, eh? Well, let’s just see about that. (We’ll assume that we’re dealing with Fahrenheit cucumbers, rather than Celsius.)

If cucumbers are always twenty degrees cooler than their surroundings, let’s put a cucumber into a barrel with a whole bunch of other cucumbers and wait to see what happens. Will they fight it out, each one trying to be twenty degrees cooler than its neighbors? Have you ever seen a bushel of cucumbers suddenly freeze itself solid for no apparent reason?

Or, how about this: If cucumbers are always twenty degrees cooler than their surroundings, let’s build a big box out of cucumbers and keep all of our wine nice and cool in it, at maybe fifty-five degrees Fahrenheit. And why stop there?

Let’s build a smaller cucumber box and put it inside the first one, thereby lowering the temperature by another twenty degrees and we’ll keep our beer in it at a nice thirty-five degrees. And no ice required, thank you, because with one more box we can get down to a temperature well below freezing and make our own. With enough boxes-within-boxes, we could build a refrigerator that would freeze Hell itself. And all without even having to plug it in.

We have just violated the most basic law of physics: the First Law of Thermodynamics, more familiarly known as the Law of Conservation of Energy. For here we have a substance, cucumber flesh, that must be constantly shooting off heat energy into its surroundings. That’s the only way an object would be able to stay cool: by constantly throwing off any heat that might flow naturally into it from nearby objects. Since heat is energy, the cucumber flesh is, in effect, an inexhaustible fountain of energy.

Free of charge. No need to burn coal or oil or to put up with the problems of nuclear energy. Why, we can use cucumber energy to generate electricity, to propel smog-free automobiles, to irrigate the deserts to grow more and more cucumbers! Why, we can . . .   The only thing we can’t do is stop people from putting silly things in books.

And of course, the totally fabricated number of twenty degrees is irrelevant. Automatically cold cucumbers, or automatically cold anything else, simply can’t exist. Nothing can permanently maintain even a slightly different temperature, colder or hotter, from its surroundings, unless we supply or remove energy to or from somewhere else. That’s why we have to plug in our kitchen appliances; we use electrical energy from the local power plant to pump heat energy out of our refrigerators and to pump heat energy into our ovens.

But you say you picked up a cucumber that hasn’t been in the refrigerator and placed it against your forehead it really did feel cool. It most certainly did. But that’s because the cuke is cooler than your ninety-eight-degree skin, not because it’s cooler than the seventy-degree room.

Leave an unrefrigerated cucumber and a potato in the same location for several hours. Cut them and hold the cut surfaces against your forehead. They’ll feel equally cool. Prove that they’re really the same temperature by thrusting a meat thermometer into each.

Except for variations due to such things as air currents and sunshine streaming through a window, every object in a room is the same temperature. Unless you’ve turned the thermostat up to ninety-eight-point-six degrees, they’ll all feel cool compared with your skin.

When any two objects are in contact, heat will flow spontaneously from the warmer one to the cooler one. So when the cuke, or any other room-temperature object, sucks out some of your hard-earned forehead heat, you feel the loss as a cool sensation.

Scientifically speaking, of course, there’s no such thing as coldness; there are only various degrees of heat. The words “cool” and “cold” are mere linguistic conveniences. And so is the expression “cool as a cucumber.” It’s so much more fun to say than “cool as a rutabaga.”

A cucumber isn’t one bit cooler than a potato.