Preheating a pan does minimize food sticking but not for the reasons claimed by this myth.
What is This Theory?
Most cooks know that you should start with a hot pan to prevent or minimize food sticking. You may hear a theory that goes something like this: food sticks to pans because it seeps into tiny cracks and pits in the surface of the pan and then solidifies when heated, becoming stuck. If you heat the pan before adding the food, the metal expands and fills in the microscopic cracks and holes in the pan's surface or at least makes them smaller. With fewer or smaller surface defects for the food to grab onto it is less likely to stick. This theory is, shall we say, cracked!
Heating Metal Does Not Shrink Defects
Unfortunately whoever came up with this idea knew nothing about the physical properties of metals. When metal expands due to heating, each individual atom vibrates faster and faster and thus takes up more space. The result is the same as if each atom simply got a bit bigger, and the result is that the entire piece of metal, defects, holes and all, gets bigger. Thus, if you heat a donut-shaped piece of metal, the outer diameter gets bigger and so does the diameter of the hole. You have probably used this fact yourself when trying to get a metal screw lid off a glass jar. Running hot water over the lid expands the entire lid and loosens its grip on the jar, making it easier to remove. So, we can see that heating a pan will cause these hypothetical surface cracks to get larger, not smaller.
Why Does Preheating Prevent Food From Sticking?
When meat is put in a cold pan which is then heated, the proteins that are in contact with the pan slowly denature and during this process can form bonds with the pan including with those microscopic cracks and pits that are always present. If the pan is already hot when the meat is added, the denaturing process happens almost instantly—a crust forms—and there is very little time for the proteins to bond to the surface of the pan. So we can see that microscopic scratches and pits in the pan are in fact involved in sticking, but changes in their size during heating are not the reason why preheating reduces sticking. When there is a thin layer of oil between the meat and the pan, as is usually the case, there is even less contact and sticking is further reduced or completely eliminated.
Adding one wrinkle to a post I think is right. The expansion argument does kill the “heat closes the cracks” idea, and your denaturing-and-crust explanation is the real mechanism.
But for cast iron and carbon steel, the surface pits and pores really do get filled, just not by heat. They fill with seasoning: oil polymerized in a hot oven over several rounds into a film bonded to the metal (C&EN, “The chemistry of cast-iron cookware,” 102/9, which describes the polymerized oil layer smoothing the surface). So “fills in the cracks” is half-true, it just credits heat instead of oil.
My read, not a sourced line: on bare stainless there is no seasoning to do that, so on that pan your crust-timing point carries all of the weight.