‘We are all star stuff’
So said astronomer Carl Sagan in his 1980’s television series, Cosmos, explaining that most of the atoms making up the human body, including carbon, nitrogen and oxygen, were likely to have been created in stars. This is an example of thermodynamics on a huge scale, involving nuclear reactions, violently exploding stars, and a process that takes billions of years. This is the type of process that people tend to think of when they hear the term ‘thermodynamics,’ forgetting, or unaware of, its everyday applications and the rich history behind the discovery of its laws.
The principles of thermodynamics developed due to a desire to make the steam engine more efficient. French physician, Nicolas Léonard Sadi Carnot, was the first to crack the mystery, later on becoming known as the Father of Thermodynamics. Previous engineers had tried and failed to improve the efficiency of the engine, which, at the time, was running at 3%. Working within the first law of thermodynamics — that energy cannot be created or destroyed, merely transformed from one type to another — Carnot developed a theoretical heat engine, calculating the maximum efficiency one can achieve when working between two temperatures. Carnot discovered that the hotter the heat source, the more efficient the engine can be, but that the process will always hit a limit; no engine will ever be 100% efficient due to friction and energy loss (for example, an exhaust pipe will heat up when an engine is running; this constitutes a loss of energy).
Carnot’s work is known as the Carnot Cycle and carries through until this day; engineers still bump into the Carnot Limit when attempting to improve on an existing design. Today, conventional steam engines can reach efficiencies of 25%, with car engines reaching about 20% of a 37% Carnot Limit. Conversely, despite appearing to have vast amounts of energy wasted through its nozzle, a rocket engine is almost capable of reaching its Carnot Limit of 60%, due to the high temperatures involved. Carnot’s perfect heat engine makes up the cornerstone of the second law of thermodynamics.
The third law of dynamics has little application in our everyday lives, unlike the first and second laws. The law predicts the behaviour of the properties of a system when it reaches the coldest temperature possible (known as absolute zero); something considered impossible and certainly not experienced in our day-to-day lives, unlike the first and second laws which are experienced by everyone, on an everyday basis.
Consider walking to the kitchen to get vegetables to chop and cook for dinner; expending calories both by walking and by changing the state of the vegetables, which cannot return to their original form. The vegetables are then cooked, requiring heat and energy expenditure, and eaten; our body metabolising the food, increasing its internal energy. Then you sit down to watch Formula One on the television, first turning on the light which converts electrical energy to electromagnetic radiation (light). The Formula One cars’ engines run at an efficiency of around 30%, not quite the Carnot Limit, with the energy converted into sound, heat and power. Much of its energy loss is due to the need to control the heat of the engine; without which it would explode due to the internal energy produced when accelerating at high speeds.
Had enough of watching Formula One? Perhaps it’s time for a hot drink before bed – boiling the water in a traditional kettle on the hob. Energy is transformed to heat and sound, causing the water to boil and the kettle to whistle. Drinking the hot drink again adds calories to your body, which metabolises the drink. Now it’s bed-time; walking up the stairs, brushing your teeth and getting into bed all converting energy. Even sleep — an activity which many assume uses zero energy (with the lucky amongst us feeling as though the activity creates energy) — uses energy, converting it into melatonin, cortisol and other crucial hormones.
Maybe you’ll dream of time travel; a concept which shatters the second law of thermodynamics[1] and is thus impossible. The very principles of thermodynamics cannot be broken, although some experiments appear to come close. Earlier this year scientists revealed that they are experimenting turning boiling water into ice without using any energy[2]. Initially this was referred to as ‘thermodynamic magic’ which challenged the very laws of thermodynamics, but which has since been revealed as possible without breaking any fundamental laws. The experiment, led by Professor Schilling of the University of Zurich, heated a piece of metal to over 100 degrees celsius, before cooling it to minus 2 degrees, without using energy. The stuff of dreams.
Sleep tight, keep warm.