Questions and answers

Over the past few months, through newspapers around Australia, Cosmos has asked readers to send us their secret science stumpers, to see how we go finding answers to your curliest questions. In this and coming issues, we present our findings, enlisting the insights and brainpower of Australia’s leading scientists along the way.

My 6-year-old son randomly asked me: How many people can fit into Australia? – Hannah

This is an interesting question because there are so many different approaches we can take to find an answer to it. Let’s try some different models.

The most efficient way to fit people into Australia – the way we might best fit people into a phone box, for example – is to make them all stand erect together, shoulder to shoulder, back to front, packed in like standing sardines.

According to the body proportions detailed by American sculptor Avard Fairbanks, the adult male has a shoulder width of around 45.7cm and an adult female of around 36.6cm.

 Because the dimensions of a male and female adult human differ slightly, we’ve based our calculations on a 50:50 ratio of males to females. Australia is 7.69 million square kilometres in area, so if we use the human sardine model we’d fit 39 trillion – 39,000,000,000,000! – people into Australia (as long as we build platforms over all the lakes and rivers).

But that’s not enough. What if we stacked people on shelves, on top of each other? If each shelf was 2 metres tall and we stacked them all the way up to the edge of the breathable atmosphere (which in itself is an interesting question, but which we’re going to decree as 6,000km above the surface), we could add 3000 times more flat-packed humans – and fit a 117 quadrillion people into the country (117 quadrillion seconds is the same as 31.7 million years; the earliest record of humans is around 5.7 million years ago).

You’ll have spotted the problem here: the sardine solution (single or stacked) won’t be acceptable under free-range chicken rules, where there can only be 10,000 hens per hectare. Based on this, we could only fit approximately 7.69 quadrillion humans and remain within legal free-range limits – but at least it’d be RSPCA sanctioned (and more likely to produce good-quality eggs).

But – getting to the important point – the issue is whether Australia could sustain all those people. People need resources – like food and water – so that’s a bigger limiting factor than space alone. Australians consume a lot of resources, even though Australia is very large.

“If everyone in the world started living and consuming and producing waste like an average Australian, then it would take the equivalent of four planet Earths to sustain them,” says Gour Dasvarma, Associate Professor of population studies at Flinders University. “But considering all possibilities it may be stated that about 40 million people could live in Australia.

“Of course, this does not mean Australians should go on consuming more and creating more waste; on the contrary, Australians should strive to reduce their ecological footprint in consideration of the worsening climate and food production crisis of the world.”

Just out of interest: what if Australia’s population was merely the equal of one of the world’s most population-dense places? The World Bank estimates Singapore has 8,019 people per square kilometre (let’s call it 8,000 – easier maths). That density would have Australia’s population at about 63.7 billion people: not as many as our sardine solution, but still more than eight times the Earth’s current population. Breathe in!

Deborah Devis

Why don’t people who snore wake themselves up with their snoring? – Sue

Ask any snorer why their sonorous rumblings don’t wake them up and they will almost inevitably give the same, simple response: “Why ask me? I don’t snore!”

A snorer’s blissful ignorance of their own sounds gives the impression that they must sleep soundly through them, while the rest of the household listens on in frustration or horror. But just because they don’t remember waking up doesn’t mean they sleep like a baby. To explain why, we need to look at why some of us snore in the first place. Let’s break it down.

Why do we only snore when we’re asleep?

Your mouth and throat are full of all sorts of soft, floppy bits, such as your uvula, tonsils, adenoids and other bits of tissue.

When we’re awake, your body holds all these bits in position, ready for action. But when we fall asleep, our muscles relax and everything is free to loosen up.

This relaxation is an important part of sleep. As well as allowing our bodies to rest and recuperate, partial muscle paralysis prevents us from acting out our dreams and walking. While a live action mime of our dreams could be an amusing insight to spectators, it could also be dangerous.

As well as keeping our limbs safely tucked in bed, sleep relaxation affects the muscles that hold everything in place. For some people, this relaxation is enough for the soft tissues in their mouths to flop into undesirable positions and partially block the flow of air as they breathe.

Snoring is the resulting sound of all the oral smooshy bits vibrating and slapping together as air forces its way through the obstruction when we breathe.

Evolution has set us up to be snorers

Those mouth parts that cause all the trouble are actually the result of human evolution. A perfect anti-snoring airway would be a long, straight tube with no soft parts at all. Unfortunately, a lot more is required of our airways than just unlaboured breathing. In order to vocalise beyond simple grunts, faces and throats have been shaped to accommodate more sophisticated sound apparatus – most of which is soft tissue. Our tongues have migrated back into our throats to shape different sounds. Compared to other mammals, our tongue rests precariously close to the back of our upper airway – the perfect place to become a blockage when we snooze.

Our upright posture has also had an effect, shifting throats underneath skulls and leaving less room in which to fit all those squishy bits – prime conditions for the airway obstruction that leads to snoring.

Loud sounds wake us up. Why not snores?

A loud crash from the kitchen in the middle of the night is almost certain to wake us up. Whether it’s a tree falling or a pet’s overly ambitious adventure, human bodies react to the sound by snapping speedily into a state of awareness.

This is because our ears are still taking in sound while we’re asleep, and our brain is still processing . Brains prioritise restfulness while we sleep, filtering out low-priority sounds and letting us snooze through unimportant background noise. 

Only high-priority signals trigger wakefulness: research has shown we’re more likely to respond to unusual sounds, especially loud sounds that could signal danger, and someone speaking our own names.

For the offending snorer, the brain interprets soft snores as innocuous background noise that needs no further attention. But what about the ones that rattle the roof shingles? In fact, very loud snores actually can wake the snorer, but only briefly. We usually need to be in a very deep sleep state for our muscles to be relaxed enough for snoring to start, and at that point our brains are shutting out all but the most important information. 

Even if a snore is thunderous enough to make it through this filter, the snorer slips right back to sleep within seconds. Brainwave research suggests that we can have up to 25 of these “microarousals” per hour without even noticing. 

Jamie Priest

How does popping candy work? – Jennifer

What causes that characteristic crackle?

If you’ve upped your lolly intake over recent months (we certainly have at Cosmos), you may have tried some popping candy. It’s a treat and a science experiment all in one, causing a tingling sensation on the tongue and a delightful crackle as you eat it.

But what causes that popping sensation?

You might think it’s a chemical reaction, but it’s actually a pretty cool combination of gases and heat. Precise recipes vary from brand to brand, but popping candy is typically a mixture of a few different types of sugar, and tiny pressurised bubbles of a gas, usually carbon dioxide. For this reason, it’s also referred to as “gasified candy” in some patent applications.

The gas is added to melted sugar at a high pressure – at least two or three times typical air pressure at sea level, and sometimes much higher. With the right combination of temperature and pressure, the sugar forms small crystals, each containing several gas bubbles roughly a tenth to a fifth of a millimetre in diameter. Sugar dissolves in water, so when the 

candy makes contact with your tongue, the water in your saliva breaks up these bubbles. The pressurised gas escapes, sometimes with enough force to crack the rest of the candy crystal. This is what causes the tingling, popping sensation.

Both the bubbles and the crystals are very small, so the amount of force involved in these cracks is unlikely to cause any problems. But in a small amount of bad news, at least one lab-based study has found that popping candy can have an effect on tooth enamel.

If you want to watch gasified candy pop but are concerned about your teeth, you can add it to plain water instead – this will also set it off.

This is particularly good news, because it means that popping candy can be used in chemical reactions. In 2021, a group of Chinese and Australian chemists used popping candy to extract some key molecules from vinegar and two alcoholic drinks: beer and baijiu, a liquor made from fermented grain. 

The carbon dioxide released by the popping candy proved to be the perfect way to agitate the mixtures and disperse the relevant substances. Because it uses edible sugars, the method is more environmentally conscious, and leaves the ingredients safe to ingest at the end.

This research paves the way for a range of potential applications in pharmaceutical or food additive manufacture.

Ellen Phiddian