Recycling Humans?

Chemistry as it applies to the human population.

Recent bush fires in Australia have had me thinking down some very black roads.  Some related to politics, capitalism and how the world could have been better if we had taken advantage of different “sliding door” moments.

I have reflected on climate change, sustainability, the death of native animals, destruction of houses and communities. I thought about the moments in history which have led us here to this time and place.

…And then I got to thinking about thermodynamics. About available energy and matter.  The fact that there is a finite number of atoms on this Earth.

The big question in my mind then became “How many people could live on this planet without ruining it?”

As a chemist, I have studied closed system reactions. Our earth is essentially a closed system.  A closed system only has a certain number of atoms available so once you use them up the reactions have to stop. Rearranging atoms usually uses up energy. Energy is also limited.

These limited atoms are used to make up all the things on Earth including humans. There are an estimated 7,656 million people on the planet. Let’s say the average mass of a human is around 80kg. That’s 612,480 million kilograms of humans. (1 kilo = 2.2 lbs)

If we wind back the clock just 300 years to the 1700s, the estimated upper limit[1] of the human population was 680 million. That means there is an extra 558,080 million (558,080,000,000) kg of human flesh on the planet now compared to then.

Most of those extra kilograms have come from other living things in our closed system because we eat them.  There has to be a time when we simply run out of atoms and energy to keep making more humans. The majority of the energy we are using now has come from the stored energy of ancient living things – a.k.a fossil fuel.

While some of the atoms in current humans may have come from recycled humans (i.e. the return of nutrients to the soil through decomposition) most of the time we don’t generally “recycle” humans. We put them in sealed boxes in burial grounds off-limits to agriculture where the nutrients can not be returned to the system. Cremation adds to the carbon in the air.

We waste and misuse so many resources. As consumers, we salve our conscious with the catch-cry,  reduce-reuse-recycle, but that is unlikely to be enough to stop or reverse climate change.

Is it time to stop being humans who recycle to humans who are recycled?

Is it time to start thinking about burial practices so the nutrients in humans are available for other uses? I’m of course not the only one thinking about this sort of thing; burial trees pods have been mooted for a while.

It’s all sounding like Soylent Green may not be such a bad idea after all! By the way, that movie, where people were recycled to make food for other humans was set in 2022.

I also believe that those of us in developed economies, who use a lot of resources, have a moral imperative to reduce the number of children we have. We need to seriously consider limiting our population through natural attrition so that some of the atoms can be returned to make other things.

Instead of “one [child] for mum, one for dad and one for the country” how about just one for the planet?


Note to Self: The day job pays the bills!

Photo 21-06-2015 23 01 19-55
When physics was easy – Newton’s Principia Mathematica

I have a list of reminders on my fridge. Number 7 says

“Don’t forget the day job pays the bills!”

Sometimes when I get so caught up with writing stories, editing photos and fooling around with my creative side I don’t pay enough attention to my day job – being a high school teacher. I need to remind myself that this aspect of my life needs attention too. I need to calibrate my work-life balance, otherwise I won’t be able to do the other stuff!

University of Applied Physics in Prague.

One thing I can say about teaching is that it is NEVER boring. Often frustrating, sometimes amusing, rarely profound, it is never boring. I teach science and it’s a joy to open kid’s eyes to the complexity of the universe and the the beauty of the subatomic intricacies of matter. To see students understand the impact humans are having on the planet and listen to their strategies to solve problems.


The best part though is when we can go outside the classroom. A few years ago, I was lucky enough to take a small group of Year 11 students to France, Switzerland and the Czech Republic to visit a number of scientific institutions including the Large Hadron Collider at CERN. A rare opportunity, I learnt a lot – more than the students I think.  This post is not to share the science but the scenery!

The Old City in Bern – Switzerland

The old fashion museum exhibit in Geneva
Amazing blown glass models used before plastic

Yoga on a bus

The bus was crowded with no empty seats. I logged into the free on-board wi-fi and got ready for a relaxing trip. Four hours north and I would be in the mystical city of Tsfat, headquarters of the Kabbalah movement. My quietude was shattered when I noticed the young conscript across the aisle. He was kitted out in his khaki uniform and like all conscripts in Israel, he carried a rather large gun. The rather large gun was draped across his knee and the barrel was pointed straight at me. He had fallen asleep very soon after he had sat down. I can’t say I blamed him. The sun was shining through the window; it was warm and cosy. If I didn’t have a gun pointed at my right knee I would have been asleep too! His hands were on rifle butt and his finger was on the trigger.  I don’t know much about guns but I knew enough to know that at this distance, if it did go off, it would not end well for me.

As a high school science teacher, I often hear the bored taunt of students asking, “Are we ever going to use this in real life?” My standard answer – “You never know what you need to know!” was suddenly vindicated

A wooden block with mass M = 3 kg is lying on a horizontal table. It is hit by a bullet with mass m = 5 g which moves horizontally. The bullet remains in the block after colliding with it. The block moves on the table a distance d = 25 cm. The coefficient of kinetic friction μk = 0.2. Find the starting speed of the bullet.

Scrap that…Let’s change it a little to make it more relevant to today’s problem.

A woman with mass M = 60kg is sitting 0.5 m from a rifle which fires a 5.00g bullet moving at an angle of 32o. The bullet remains in the woman after colliding with her.

Calculate (to the correct number of significant figures) the following:

a) the amplitude and duration of the woman’s scream and

b) Will her travel insurance cover the medivac?

(Include all units and working out.)

As a problem-solver, I quickly developed a strategy to avoid being knee-capped and arranged myself in a very elegant yoga pose which I estimated would avoid the straight shot. Half-squatting elephant with sideward fold would describe it nicely. The man sitting next to me looked on with quiet amusement and buried his face in his book. I smiled sheepishly but held my position. I began to feel a little sorry for the person in front of me who would end up with a bullet in the backside when it ripped through the back of their chair.

I had been sitting like this for about an hour. My back was beginning to cramp. Thankfully soldier-boy moved a little, slumping further into his seat with a very casual attitude. Too casual for my liking! I quickly shifted my limbs into the more advanced position of seated mallard.

Another thirty minutes passed.  He opened his eyes and looked sleepily out the window, all the while keeping his finger at the ready. I reasoned this must be part of their training, to be ever alert, even when asleep. After all, attacks on buses by terrorists are common in Israel.

20170113-P1660503With his next sleepy move, the barrel pointed a little upwards – now in line with my heart. I stopped breathing. It was then I noticed the small, red plastic plug that was filling the end of the barrel. The air escaped from my lungs with the same force as the bullet I had been trying to avoid. The gun was not operable. It was a training weapon.


For the remainder of the journey, I adopted a new pose – embarrassed reclining puppy.