Pretend, for a moment, that heat is visible, that our naked eyes can see the infrared rays shedding from objects all around. At closest range, we observe the incessant buzzing of molecules—vibrating at 1,100miles per hour in the air of a room at a pleasant 72 degrees Fahrenheit. Pull back, and whole masses of molecules are churning and drifting, always in flux. There’s no substance to heat; it is not contained in a cup of coffee or a warm breeze. The temperature scale measures how much motion, or kinetic energy, lives inside an object, and “heat” refers to the way this energy passes from one place to another—from hot to cold—in streams and swirls and currents. If we can look at heat, we see a world constantly in motion.
Start with our very own bodies. Under a microscope, we see warmth in cells, in tissues, molecules set atwitter passing heat ...
