7 things that science cannot explain

Science is a beautiful thing. It explains the world to us and allows us to continue educating ourselves. But there are a few things that scientists have had trouble explaining until now. Here are seven:

The ancient Greeks were already familiar with this phenomenon: there are people who sneeze when they suddenly step from a dark environment into the light. And – with a few unfortunate exceptions – a maximum of three times. Depending on the severity, 17 to 35 percent of people, including slightly more women, know this sun sneezing from their own experience. To date, there is no clinical diagnosis for the photic sneeze reflex – also known in English by the onomatopoeic acronym “ACHOO syndrome” (from Autosomal Dominant Compelling Helio-Ophthalmic Outbursts of Sneezing).

The syndrome, which has nothing to do with a sun allergy, is probably hereditary. Until now, science has not been able to fully elucidate the causes of the photic sneeze reflex. After all, there is a theory that is currently considered the most likely explanation: in those affected, the optic nerve and the triplet nerve, which comes from the nasal mucosa, are too close to each other. If a strong stimulus is sent over the optic nerve, the triplet nerve also responds and signals to the brain that there is no irritation in the nasal mucosa.

However, it is also possible that the visual cortex in the brains of ‘photic sneezers’ responds more sensitively to light stimuli, whereby brain areas responsible for the sense of touch are also stimulated. In this case, the phenomenon would be more than just a reflex occurring exclusively at the level of the brain stem and spinal cord. By the way, sneezing reflexes also exist in combination with other stimuli – for example, there are people who sneeze during an orgasm or just at the thought of sex.

Anyone who has learned to ride a bike knows that it is not always easy to maintain balance on a bike. When the bicycle is in motion it is not particularly difficult, but at very low speeds or even at a standstill the balancing exercise can only be performed by experts. However, it is not so easy to answer why a bicycle does not simply fall over even if it only touches the ground at two points. If a driver is involved, the bicycle’s behavior can be explained by steering towards the side where the bicycle is in danger of tipping over. This means that the contact point – where the tires touch the ground – is again below the center of mass.

But even riderless bicycles that are pushed will wobble back and forth for a moment, but then stabilize and move forward a certain distance. For a long time, the gyroscopic effect – the resistance of a rotating wheel to inclination – was considered the explanation for this. However, this theory was refuted in 1970.

The substitution theory postulated that the so-called ‘lag’ provides stability. The front wheel touches the ground a few centimeters behind the so-called track point, where the imaginary extended steering axis touches; this leads to a kind of caster effect. But this theory also had no better fate. It was also declared invalid in 2011.

What could be more comforting than the rich purr of a contented cat? The strange vocalizations of our domestic cats – by the way, lynxes, servals and even cheetahs also purr – is apparently innate, because even very small kittens purr when they nurse for the first time. In this situation, purring probably serves as a means of communication; it shows the mother cat that the kittens are comfortable.

In general, spinning seems to serve as a signal of peace. However, cats that are alone also purr. And they also do it in stressful situations, such as when they are hungry, scared or injured – possibly to calm themselves down.

Not only is the question of why cats purr unresolved, but also how they do it. There are several hypotheses about how cats generate vibrations in the range of 20 to a maximum of 150 Hertz. There should be rhythmic vibrations of the vocal cords that are amplified by resonance spaces.

But the so-called false vocal cords – two folds of skin that lie behind the actual vocal cords – can also be responsible for purring. Or cat sounds can be converted into purrs by the hyoid bone, aorta or by blood flow in the lungs. Currently, the most plausible theory is that rapid twitching of the laryngeal muscles and diaphragm causes purring.

We yawn in different situations – not only when we are tired, but also when we are bored or stressed. Although yawning is an everyday and common occurrence, science still has no conclusive explanation for why we do it in the first place. Yawning is apparently highly contagious; it can be caused not only by observing it, but also by just thinking about it.

There is also evidence, although not uncontroversial, that empathetic people become infected more quickly than others. For this reason, many scientists suspect that yawning has something to do with empathy, especially since emotional closeness appears to facilitate infection. This apparently applies even to dogs infected by human yawning, and the better they know the person, the better.

The previously popular theory that yawning has anything to do with oxygen supply to the brain has long been disproved. The often made assumption that it wakes you up is not scientifically substantiated. Brain activity does not change when you yawn. But it could possibly have something to do with the regulation of temperature in the brain. Rats yawn when the temperature in their brains rises. In fact, it then drops again through deep breathing of cooler air. However, this approach is also just a hypothesis: yawning still remains a mystery.

Anyone who has visited a medieval castle and climbed a spiral staircase in the keep may have noticed that it turns to the right. The reason for this is that the defender standing above it can better extend his hand while carrying the sword during an attack. This preference for right-handed people is understandable because the clear majority of people are right-handed.

Although the proportion of left-handers among men is slightly higher than among women, in total only 10 to 15 percent probably prefer the left hand – exact figures do not exist. However, it is certain that the share of left-handers has increased in recent decades. This is probably mainly because left-handed people are no longer re-educated these days.

The reasons for the dominance of right-handers are not clear. What is certain is that genes play a role: while purely right-handed parents only have a left-handed child in 2 percent of all cases, the chance increases to 17 percent if one parent is left-handed. And with two left-handed parents that is almost 50 percent. However, it is still unclear whether a single gene is responsible for handedness and which gene it is.

Research with identical twins also shows that not only genes influence dexterity, but also the environment. In addition to upbringing, these can also be influences during embryonic development, for example an increased testosterone level, which leads to dominance of the right hemisphere and therefore to left-handedness.

We all dream – but no one knows exactly why. This is mainly due to a methodological problem: only awake people can provide information about their dream experiences; but when they are awake they do not dream. This is how the waking self always filters and interprets the dream events. The land of dreams is a sometimes bizarre parallel world – to which esotericism attributes a kind of higher reality – to which logic and conceptual thinking have only limited access.

However, the physiological processes in the dreaming brain can be investigated. For example, it turns out that parts of the brain in the motor cortex responsible for movement are active when we move in dreams. However, the impulses that go from these areas to the muscle cells are blocked, preventing the body from performing the movement.

The function of dreams is particularly controversial. There are several theories, some of which are mutually exclusive: there are scientists who see dreams as a meaningless product of a storm of neurons in certain parts of the brain. Others see the function of dreams in the fact that when we dream, the brain processes and consolidates the things we have learned during the day – mixing and storing new and old information. On the contrary, dreams can also serve to forget things after they have been clarified in the dream.

A similar theory states that dreams train us to deal with fearful situations, especially nightmares. The brain then processes fearful content. Yet another hypothesis holds that we find more creative approaches to solving problems when we dream. There are even examples of artists who had creative ideas in dreams – such as Paul McCartney, who says he dreamed the melody from ‘Yesterday’.

The total length of the banks of the Swiss lakes is about 2000 kilometers, we read here. And Great Britain has 12,500 kilometers of coastline. Such information is ideal for pesky guess questions in a geography quiz – but is it correct? Well, that depends. The coastline paradox states that finer measurements lead to greater length. You can imagine this with a ruler: the shorter it is, the more accurately it represents the irregular coastline – until eventually, in theory, every molecule is measured. And the length goes to infinity.

Structures with a limited area but an infinite perimeter are reminiscent of fractal curves in mathematics, such as Koch’s snowflake. However, fractals often look similar, meaning that their structure repeats itself over and over as the size increases. This happens only approximately on coastlines – here the similarity of structures occurs only to a limited extent and does not extend to the infinitesimally small. Be that as it may, measuring coastlines is only of practical use up to a certain scale.