Entropy

Chapter 1 - Our Worldview

Back to Book content or Previous page - Next page

Or directly to Main Page - Worldview

Welcome to the Entropy page

The only constant is change

In 1865, Clausius named the concept entropy after the Greek word for 'transformation'.

The second law of thermodynamics states that over time the disorder of energy, namely entropy, increases inexorably, and the usable ordered energy decreases.

In nearly all its meanings, entropy can be viewed as a measure of disorder and chaos, as long as, by order, one understands segregating things by their kind (e.g. by similar properties or parameter values). Chaos is the state of a system (physical or dynamical) in which elements of all kinds are mixed evenly throughout the space so that the space is homogeneous.

In common sense, the entropy tendency means a tendency towards disorder or chaos, meaning a decrease of usable energy and an increase in the uniform distribution of anything within the system. This last part may sound surprising, but:

Think about your home on a normal day. Clothes are in the wardrobe, dishes are neatly piled up in the kitchen, and food is stored in the fridge. This is a picture of low entropy with defined parts of high order within the total system.
Think about a horror scenario after a children's party at home: clothes everywhere in every chamber, food spread over the coaches and beds, glassware and dishes around. This is a picture of high entropy with no order and a high probability of finding anything anywhere.

.

Entropy is not the same as energy

Do not confuse energy with entropy. Let's consider fossil fuels, charcoal, oil even gas. They possess a high potential energy level and are in a low entropy state. They are the remaining of an even lower entropy state of the photons we receive from the sun. When we burn those fuels, we get heat. This is what we call energy because, for a short time, we can transform it into steam, electricity, motion etc. In the process, we decrease the usable energy (the global stock of oil) and pump heat and chaotic particles into the earth's atmosphere.

In practice, any self-sufficient system actually receives also energy from somewhere 'beyond' its system boundary. A simple real-world example is the rainfall cycle: water evaporates from the sea or land surface to form clouds, from which rain falls and returns to the sea via streams and rivers. It relies on energy from the sun to power the evaporation that drives the seemingly counter-entropy 'upward' part of the cycle.

.

Time

This unstoppable increase of unusable energy (entropy), postulated by classical thermodynamics, is the criterion for distinguishing between the past, the present and the future. Measuring the change in the amount of entropy tells you the order in which events occur: the lower-entropy state comes first, the higher-entropy state next, the total-entropy state last.

.

Entropy makes the world go round

There is a more profound puzzle underlying this spacetime confusion. At the deepest level of mathematical physics, time does not exist at all. There is, according to Rovelli, just one basic equation that points to an arrow of time: the second principle of thermodynamics, which says that entropy is always increasing, that the journey from order to disorder is down a one-way street. We observe this journey because heat flows towards the cold things and one day all the heat will have dissipated, and we will experience neither past nor future. “What makes the world go round is not energy, but sources of low entropy.” We don't live by inhaling heat but by eating food, a source of low entropy which releases its energy by digesting, meaning transforming into a higher state of entropy.


Content source
The Order of Time - Carlo Rovelli

.

Example: climat change

Climate change, more specifically human-induced climate change, is a surprisingly simple idea. The mathematician and philosopher, Bertrand Russell, summed up mankind’s activities as the rearrangement of matter on or near the Earth’s crust. Russell’s words need refining. The rearranging of matter is done in two different ways: by mechanical devices (such as levers), or by ‘heat-engines’ (such as muscle-power, or combustion engines). (Loosely speaking, anything that ‘farts’ is some sort of heat-engine.) A heat-engine consumes fuel and, by the Second Law of Thermodynamics, ‘always puts out some waste heat.’ Therefore, Russell’s summary should more accurately state: the activities of mankind can be summed up as the rearrangement of matter and the generation of heat. (By the way, ‘waste heat’ refers to direct heating and all other energy losses, not just the production of exhaust gases.) It would be very surprising if humans were not affecting the climate. Affecting it how? By increasing the amount of global warming – this is what the Second Law of Thermodynamics tells us. According to this Law, so long as our activities concern the planet in isolation, there is nothing whatsoever that we can do to stop global warming (we can merely reduce its rate). The only way to reverse global warming is to change the interactions between the Earth and its surroundings; and this can only be done by reducing the net flux of Solar energy received, by reducing greenhouse gases and/or increasing the Earth’s albedo.


Content source
Climate change – a very difficult, very simple idea - Jennifer Coopersmith - Oxford University Press's Academic Insights for the Thinking World - 2015

.