Do you think you can tell the temperature of something just by touching it? I’ll bet you can’t. Here’s why:
As was hopefully clear from the video above, what we typically perceive as a relative temperature difference between two objects can actually be a difference in thermal conductivity. This is not to say that you can’t tell whether an ice-cube is cold or a stove is hot, but that we can misjudge the temperature of things that are objectively the same temperature.
In physics, the thermal conductivity of a material is the ability of that material to transfer heat. Heat transfer across materials of high thermal conductivity occurs at a higher rate than across materials of low thermal conductivity. This is why the ice-cube in the video above melted faster on the aluminum (higher conductivity) than on the plastic (lower conductivity), even though both were at the same temperature.
So why would our body be sensitive enough to thermal conductivity that we could mistake the temperature of two similarly heated objects? To speculate, perhaps it was evolutionarily beneficial for our ancestors to be able to tell how fast they were losing heat. As we branched out from Africa and lost our fur (relatively speaking), the conservation of heat would become very important in less hospitable environments. Being able to sense how much heat your body is losing then becomes an advantage. Today, this results in us hopping off a bathroom floor and onto a floor mat after a shower because the floor seems “colder.” Or, at a day at the local pool, 70 degree water on a 70 degree day still feels colder because spending any amount of time in the water will sap our precious heat. Or maybe our sensitivity to thermal conductivity is simply a quirk of our tactile senses and how our brain interprets relative temperature. But again, this is speculation on my part.
Even though my evolutionary explanation could certainly be wrong, it still stands that we are not very accurate reporters of reality. It takes something objective, like science, to shake us free of this subjectivity. And it is always fascinating.
I love smashing through our common sense with science.