Lightning strikes, purring cats and how bicycles work; we are surrounded by things that are mysterious. Here are 8 everyday things that can't be explained.
What Causes Lightning Strikes?
There are 44 000 thunderstorms on earth every day, generating 100 lightning strikes every second. It is one of the commonest natural phenomena known to us. So it is surprising to learn that scientists are not sure what actually causes lightning.
What is known is the mechanics of the lightning strike itself.
Cumulonimbus clouds are towering masses of water vapor that form in warm, humid conditions. Inside theses clouds is a swirling mass of particles - water, ice, other gasses – that carry electric charges. Positively charged particles concentrate at the top of the cloud, and negatively charged at the bottom. This negatively charged part of the cloud has an electrical attraction to the ground, which carries a positive charge; and lightning is the mechanism that allows the two areas to equalize.
While this is still pretty amazing, it seems reasonably straightforward. And this is where the mysterious elements arise.
For starters, scientists are not sure what mechanism causes the charged particles in the cloud to separate the way they do; there is no known reason why they would group themselves into positively and negatively charged areas. Studies have shown that the inside of a thunder cloud is chaotic; a whirling maelstrom of different elements, thrown around by air currents.
How do they arrange themselves in the way required to generate lightning?
One theory is that cosmic rays, radiation created by stars across the universe that hit the earth’s atmosphere, interact with clouds and somehow alter their electrical composition. But this theory is controversial, and has not been proven.
This brings us to the second mystery: air is a natural insulator. It does not conduct electricity well, and has an enormous resistance to doing so at all. So once the cloud has, somehow, separated its charged particles into positive and negative groups, for the lightning to ‘spark’ there needs to be a high enough negative charge to overcome the air’s electrical resistance.
Analysis of thunder clouds has shown that the charge detected in the negative part of the cloud is much lower than what is thought to be needed, by a factor of about ten. Bearing in mind that a lightning bolt is enormously powerful; it contains around a billion volts of electricity, that flares at a temperature of 28 000 degrees centigrade, or six times hotter than the surface of the sun.
Where does all this energy come from? It is not being detected in the cloud itself.
Again, there are theories – that the lightning at its instigation is briefly powerful enough in a way hard to observe, or that the air’s resistance to electricity is somehow lowered – but no evidence.
How Do Bicycles Stay Upright?
Bicycles, originally called ‘Velocipedes’, were first patented in 1818.
The first designs were discovered by trial and error, and the same method was then used to improve them. A hundred years after their discovery, by the early twentieth century, bicycles looked much as they do today; two wheels, handle bars, spokes and pedals.
But despite their apparent simplicity, every time someone rides a bike, something strange is happening.
The easiest way to think of this, is via the riderless bike problem. If you take a bike, without a rider, and give it a shove, it will travel a fair distance before it runs out of momentum and falls over. As engineers, and then mathematicians, began to analyse this, they realised it could not be explained; with the amount of energy given to the bike through the initial push, it should fall over sooner than it does.
The same thing happens, in a less pronounced fashion, when someone is riding a bike; the amount of effort the rider applies when pushing the pedals is less than what should be required, according to physics, to keep the bike going forward in a stable way.
How to explain this?
Many scientists, many of them cycling enthusiasts, have tried to crack this riddle over the past 100 years. One widely accepted theory, proposed in 1910, was that bikes were kept upright through the ‘gyroscopic force’ of their wheels; ‘gyroscopic force’, a proven concept in physics, holds that once a wheel is spinning, it becomes more stable and less resistant to redirection. But this was subsequently disproven, in relation to bikes, in a series of experiments.
Another theory, proposed in 1970, was that the bike’s ‘trail’ is responsible for its stability. The ‘trail’ is the distance between the line of the steering axis, and where the bike’s front tire meets the road; shorten the tail, and the bike becomes unstable, lengthen it, and it becomes difficult to move. Somehow the bike’s original inventors had lucked onto the right ratio between these two elements.
But this has also, subsequently, been disproven. And the internet remains full of cycling enthusiast scientists, trying out their pet theories.
Why Do Cats Purr?
One of the great things about owning a cat, is when they climb up on your lap for a cuddle. You can pat them, and, if you do this well, the cat may favour you with a purr. It is one of the great things in life, actually.
But the reason why the cat purrs, is uncertain.
In fact, it even took scientists a long time to agree on how a cat purrs, in the first place. But this debate now seems to be settled: muscles around the cat’s larynx restrict, and as the cat breaths in or out the tightened muscles cause the animal’s vocal chords to vibrate, which generates the purring sound. The muscle tightening is triggered by a neural oscillator in the cat’s brain, which otherwise has no function (yes, there are people whose job it is to study this).
So now we have the mechanics understood, the question becomes: why? What causes this neural oscillator to switch on in the first place?
The most obvious answer is that the cat purrs when it is happy, as noted in the example at the beginning of this section; you pat your cat, the cat is pleased, it purrs. But studies of feline behaviour have shown that they will also purr at other times; when they are hungry, sleepy, frightened or anxious. They will even purr when they are by themselves.
So while cats do purr when they are happy, this is not the complete picture.
One radical theory is that purring is a type of physical therapy. A cat’s purr resonates at a frequency of about 26 hertz; a frequency that has been shown will also promote tissue regeneration. So as the cat lies around purring, it is also exercising its muscles in a subtle way, a technique that would have been useful before cats were domesticated and were required to hunt.
But a simpler explanation may be more likely; cats purr to reflect a range of emotional states, similar to how a human being can laugh to indicate amusement, happiness, nervousness or just to release tension. Cats, are complicated little beings.
One final mystery; not every cat can purr. Lions, leopards, and tigers do not purr, while other big cats like cheetahs and cougars do. Again, no one is sure why.
And Why Do We Yawn?
But it is not just our cat friends who demonstrate inexplicable, everyday behaviour. The reason why people yawn is not understood either.
Similar to purring, this one also seems to have a simple explanation: people yawn when they are tired. Well, yes and no.
While people do yawn when they are tired, why this happens is not clear. Yawning has been studied in detail over the past thirty years, and many scientists think that it has no detectable physiological effect on your body. You yawn, and your body’s physical state does not change at all. Basically, you yawn for no reason.
Scientists had originally thought that yawning was designed to provide an oxygen spike to your body’s vascular system, which would wake you up a little; this was its connection to tiredness. But this has been disproven through experimentation.
One current theory holds that yawning is designed to cool your brain; the sharp intake of air that comes as part of a yawn sends cooler blood to your head. But this has not been proven and is not widely accepted.
An additional mystery surrounds yawning; it is wildly contagious. Studies of groups of people have shown conclusively that if one person yawns, the people around them are very likely to follow suit. This behaviour has also been demonstrated in groups of apes, and rats, and dogs. If you own a dog, and your dog sees you yawn, it will likely yawn as well.
Why this happens is not known. Although it is likely something to do with the built in desire of animals with complex brains to mimic other animals around them. Mimicking behaviour can be useful from an evolutionary perspective; if you fit in, you are less likely to be singled out.
Where Did the Word ‘Dog’ Come From?
Speaking of dogs, the greatest unsolved mystery of the English language is associated with our four legged friends. Why are they called ‘dogs’ at all?
English is a great assimilator of words from other languages. It has borrowed heavily from French, Spanish, Latin, Arabic and many others. Most words in modern English can either be traced to Old English, a modified type of German spoken by the Anglo-Saxons, or from these other common languages elsewhere in the world.
But there are exceptions. And one of the most commonly used words without a clear origin is ‘dog’. In his book ‘Mother Tongue’, author Bill Bryson puts it like this:
‘For centuries in English, the word used was hound (or hund). Then suddenly in the Middle Ages the word dog – a word etymologically unrelated to any other known word – displaced it. No one has any idea why.’
This displacement happened rapidly, certainly in less than a hundred years and probably in more like fifty, sometime in the 12th century. While linguists do not know what caused this to occur, and due to the lengthy time period since may never know, there are theories.
One is that ‘dog’ was originally a term for a group of breeds, mostly types of mastiff, that became popular. As their popularity grew, so did the use of the word. Another theory, listed in the Oxford English Dictionary, is that dog was a local slang term for the animal, that caught on. Slang words are regularly created out of thin air, and to this day often find their way into common usage (think of recently coined words like fomo, or bae).
But even if either of these theories can be proven, it just shifts the mystery down the road; what caused the dog breeds to become popular, or what caused the new slang term to catch on? We will probably never know.
As a footnote, the word dog has also become one of the most versatile words in English. You can refer to someone you don’t like as a dog. People say things have gone downhill when they have gone to the dogs. A dog’s life is used in a variety of contexts. Your feet can be dogs (my dogs are barking), and so can a sausage in bread (a hot dog) and so can a book page with the corner turned over (dog eared). The phrase ‘the dog days of summer’ comes to us from Ancient Greece, and its origin story is a wild ride.
The list of dog usages is almost endless.
How Does Gravity Work?
Well, we know the answer to this one… right? Gravity is the thing that keeps you attached to planet earth, and that means when you drop an egg it hits the ground and breaks.
And yes, gravity is these things. The questions are… why and how?
Gravity is associated with mass; the larger the object, the greater its gravitational footprint. This is not a new concept, the Ancient Greeks knew about it thousands of years ago, and Sir Isaac Newton described it mathematically in the 1600s. But after all of that time, and the dedicated study of some of history’s greatest minds, we still do not understand why mass creates gravity, nor do we really understand how one object gravitationally influences another.
In his famous paper on ‘General Relativity’ in 1915, Albert Einstein came up with a new way to describe gravity; as a curvature of spacetime. Think of the universe as a rubber sheet, and the stars and planets as weighted balls. Place a ball on the sheet, and it will sink into it and curve the surrounding area. Roll another, smaller, ball towards this one, and the curvature made by the first object will influence the rolling balls trajectory, directing it towards the larger ball.
On a high level, this is a reasonable description of how gravity operates.
But this does not tell us why it works that way; what quality of mass produces this space-time curvature? No one knows. Particle physicists suspect a subatomic, short lived particle, dubbed a ‘graviton’, is responsible, but none have ever been detected. Sophisticated experiments to try and find gravitons, using particle accelerators, are ongoing.
The other mystery about gravity is how weak it is, compared to other natural forces.
Consider this simple experiment. Place a paperclip on your coffee table; it will sit there, held in place by the gravity of planet earth. Make a mental note of planet earth’s size and weight; it has a circumference of about 40 000 kms, and weighs about 6,000,000, 000,000,000,000,000,000 kilograms (i.e. it is big and heavy). Now get a fridge magnet from your fridge door, and hold it over the paperclip; the clip will leap into the air and connect itself to the magnet.
That is how weak gravity is comparatively; the magnetic force from this tiny magnet can overpower the gravitational force of a planet.
Why Are There So Many Right Handed People?
Favouring one hand over the other is a physical trait found only in primates. From an evolutionary perspective, scientists think this relates to our ability to use complex tools; as the tools we made became more sophisticated, and were used for more intricate work, it became an advantage to have one hand specialise in their use.
But there is no reason why being a right hander or a left hander would be more advantageous, so you would expect to see an even spread of each. And this is what we see in other primates; apes and monkey populations both show roughly a 50-50 split between righties and lefties.
But in humans, the ratio is heavily slanted in favour of right handers; 90% of people are right handed, and only 10% left.
What hand you favour is genetic. So now that the right handers are in the majority, this is likely to continue; they are passing on their right handed genes to their kids. What is unknown is how this imbalance arose in the first place.
There is some tentative evidence that suggests a connection between left-handedness and certain neurological conditions. People with Down Syndrome and autism have been shown, in some studies, to be more likely to be left handed. While left handedness does not cause these conditions, it may be an indicator of unusual brain development. But what the connection between these conditions and being a leftie is, is not known. And the subject is controversial within the scientific community, with the majority of scientists denying there is a link.
But another explanation has proved elusive.
The comparative rarity of left-handers has lead to some unusual consequences; the scarcity of left handers in earlier times caused them to be singled out, and viewed with suspicion. The Latin word for left handedness, 'sinistra', came to be associated with bad luck, and finally with evil, and is where we get the modern English word 'sinister.'
Why Does Anaesthesia Knock You Out?
Something you may find alarming next time you need to go to hospital: science cannot explain why anaesthesia knocks you out.
Anaesthetics were discovered in the 1840s, and their initial means were crude; patients would inhale potentially toxic amounts of either, or chloroform, until they passed out. In modern times, anaesthesiologists administer complex chemical compounds that can render someone unconscious for a few minutes, or a few hours, depending on the length of the procedure.
People who have been under a ‘general’ anaesthetic describe a feeling almost like lost time; no dreams, no awareness, and no memory of what has happened to them. But scientists are not sure how the anaesthetics that are administered have this impact.
The human brain is a small, squishy bundle of nerve cells called neurons; approximately 86 billion of these, each connected to about 10 000 others, creating a neural network of 1 000 trillion different possible connections in our cerebral cortex.
MRI imaging shows how anaesthetics affect this fantastically complex network, and this does show impairment of neurological function. Unfortunately, these images also show a wide impact across the brain, including in areas that are known to be not associated with consciousness, that this does not really help solve the question. What areas of brain activity need to be reduced for us to lose consciousness?
Another mystery: a large number of anaesthetics have been discovered, and these are completely dissimilar. Everything from large complex molecules like barbiturates, to xenon gas, which exists at an atomic level, will produce an anaesthetic effect. How could these very different substances produce the same effect?
Ultimately, this mystery simply points to another, deeper one: what is consciousness, in the first place?