Entropy is hardly a household word.

It certainly wasn’t one I knew much about until 2020, when I began to develop the library series, “Physics: The Camelot Period 1900-1930.”

As a prologue for that series, I needed to look back to the 1800s. Most of us are familiar with the fathers of evolutionary theory, Wallace and Darwin and less so Faraday and Maxwell – pioneers in electromagnetism.

But it’s a rare person, outside of physicists and engineers, who is familiar with thermodynamics – the science of heat and energy.

Thermodynamics began with the Industrial Revolution, especially the development and efficiency of the steam engine. Today’s column focuses on the second law of thermodynamics.

This law states that energy comes in two forms: one is usable and the other disorderly and more important, inaccessible, or in the language of thermodynamics, entropic.

Beginning with the Big Bang, moving forward to the present and trillions of years into the future, the fraction of the universe’s energy which is unusable, has and will continue to increase. However, the net sum of the energy, usable and not usable, will remain the same.

That’s what the first law of thermodynamics says – no overall loss of energy even if, as the second law states, the fraction of the universe’s energy (which is entropic) increases with time.

Take stars for example. The intense gravitational forces that create stars in the first place create enormous pressures and temperatures, which, working together in the star’s core, are sufficient to fuse trillions and trillions of hydrogen nuclei into helium nuclei per second.

In the process, tiny bits of matter are transformed into enormous amounts of energy, known as nuclear fusion. The reason? Remember Albert Einstein’s most iconic equation: E (energy) = m (mass) x c2 (the speed of light squared).

Most of the latter energy comes in the form of photons of energy generated in the star’s core from which they eventually reach the surface of the star and create the light that baths surrounding space including in our case, Earth.

Without this light, there would be no photosynthesis, no plants and no us.

The synthesis of more complex, heavier elements continues through to iron beyond which synthesis of heavier elements requires the far more intense pressures and temperatures typical of supernovas, or other horrendous events such as collisions of neutron stars, for their creation.

Nucleosynthesis and the creation of more complex elements reduce entropy somewhat, but there’s a net loss. Why?

An enormous amount of the energy released by stars, including our sun, is dispersed – wasted if you like – and no longer accessible, meaning an increase in entropy.

In like fashion, the creation of life and the increasing complexity of life (analogous to the increasing complexity of atoms through nucleosynthesis) requires a lot of energy that becomes less accessible with use and hence, increases entropy.

For the long term – possibly trillions of years in the future – the energy economy of the universe will continue to provide enough low-entropic energy to sustain the formation of stars and thus light and heat to keep the universe and, anthropomorphically speaking, life humming.

But eventually, the math and probabilities of the second law of thermodynamics will catch up with the universe.

The result, sometime in the very distant future, will be not enough accessible – and therefore usable – energy to keep stars forming and for those present, all will run down, this time with no replacements.

That’s when the lights will go out in the universe.

That is unless there’s another cycle of creation – a new Big Bang with a new injection of energy into the system.

Perhaps that’s what happened when our universe began. It may have signalled the end of a previous universe.

Perhaps an infusion of energy might come from other universes with which ours coexists, but which are out of reach of any tools we now possess to see them.

I used to think the whole idea of multiverses was crazy, but like Einstein, who couldn’t accept an expanding universe until the evidence was overwhelming, we could be wrong about multiverses.

If Einstein could be wrong, we’re in good company.

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the InfoHealth series at the Niagara-on-the-Lake Public Library.