Around this time of the year, a single question preoccupies the minds of many people: Why is it so cold? Unfortunately, while many people ask this question out of either pragmatic concern or faux existential grief, many also fail to see how profound just such a question is. This is due in part, I imagine, to their misunderstanding of how the whole process of “feeling cold” works.

When pressed for an answer for “why winters are cold,” many people often hem and haw about the earth being farther away from the sun in the “winter,” thus receiving less light and becoming colder. This is wrong. This line of thinking exposes a bit of northern hemisphere bias, since the southern hemisphere experiences summer while we have winter. If we consider that the variation in the orbital distance between the earth and the sun is approximately 3,110,000 miles — which is nearly 800 times greater than the radius of the earth — we can see that all regions of the earth are affected pretty much equally by this variation. Therefore, it’s not the cause of seasonal changes

However, that seasons are hemisphere dependent suggests an answer, namely that the tilt of the earth is the reason for the seasons. And this is true as far as it goes. Since the tilt of the earth remains constant during the northern hemisphere’s winter, the northern hemisphere points away from the sun. This angle causes the sun to be lower in the sky, heats the ground less efficiently and shortens the days to bring on the cold. But the “tilt of the earth” answer always seemed a bit shallow to me, as it fails to answer the more interesting question: Why do we feel cold? And as with most “why”-based questions, there are both proximate and ultimate answers.

The proximate, or most direct, answer is that we don’t feel cold. In fact, human beings and other animals do not feel temperature at all. What we actually sense is the flow of heat caused by temperature differences. We feel “heat transfer.” This is not a trivial distinction. Everything in a heated oven is at the same temperature, but a cake pan will hurt more to touch than the surrounding air because the heat transfer from the pan is rapid and intense, while that from the air is slow and inefficient. Heat transfer is the answer to more questions than many could have hoped to ask, and it tells us why we feel cold.

In general, there are three main types of heat transfer. The first, and most intuitive, is known as conduction. Conductive heat transfer occurs when two objects of different temperatures physically contact one another. Heat energy from the object with the higher temperature will flow into the colder object until the two are at equilibrium. This happens when two people hold hands or when a significant other asks to have their cold feet warmed up.

The second type of heat transfer is known as convection and is essentially the same process as conduction, except instead of two solids interfacing, one solid interfaces with a fluid — either a liquid or a gas. Fans feel good in the summer because they push air across our skin and wick away heat — in conjunction with evaporation, another type of heat transfer — and why they would feel so bad to us in the winter.

Conduction and convection are the primary causes of the answer to why we feel cold. These are the two modes that have shaped our physiology and guided our evolution. They are why the ears of rabbits are long, why noses get cold to insure that the rest of the body remains warm, and why the genitalia of human males are kept outside of their torsos. The forces of evolution are mindful of thermodynamics, if for no other reason than that it is the law. We feel warmth and coldness because there is a higher evolutionary pressure to determine differences in temperature rather than absolute temperatures to ensure survival.

Perhaps the least intuitive but most important of the three modes of heat transfer is radiation, the process by which energy is transferred in the form of electromagnetic waves. While conduction and convection require a physical medium to move heat about, all things, at all times, are taking in and giving off this radiative energy, with “hotter” objects giving off more radiation than they take in and “colder” objects taking in more radiation than they give off. This is the reason we can feel the sun’s warmth at all.

If we consider this fact, we can come to our revelation: we feel cold because space is cold. When you step outside in the morning on those winter days, you are feeling outer space suck away your heat. Every chill, every shiver, every breath hanging in the air is directly attributable to the cosmos’s cold, unfeeling nature. With an average temperature of approximately -450 degrees Fahrenheit (roughly -270 Celsius), space does not seem particularly suited for the lives we enjoy. Coldness is the rule, not the exception.

In fact, instead of asking ourselves why it gets so cold, maybe we should ask, “why does it ever get warm?”

Barry Belmont can be reached at belmont@umich.edu.

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