10 Things You Thought Were Right That Are Wrong

In life we often take things such as "it is dangerous to wake a sleepwalker" as being the Gospel truth, but actually, most of these "facts" are more a case of deceived wisdom...
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It is dangerous to wake a sleepwalker

Somnambulists can occasionally hurt themselves and others, so the reverse is true. Waking a sleepwalker could save them from embarrassing situations or, worse, falling down the stairs. It may confuse the person if they are woken and find themselves out of bed, but that will cause them no physical harm.

Household dust is mostly skin

The precise composition of house dust depends on where you live, but it can be a mixture of dust from building materials, sand, soil, clothing fibres, plant fibres, fragments of hair (animal and human), pollen and insect faeces. Only a tiny fraction is formed from flakes of human skin.

You can see the Great Wall of China from the Moon

You can see the Great Wall, motorways and even office blocks from low-earth orbit. Astronauts have taken photos to prove it. However, the moon is about 370,000 kilometres from the earth. It does not matter how long the Wall is – at that distance a structure as narrow as the Great Wall (a mere five metres at its widest) is well below the resolution of the human eye. The moon buggy left behind on the Apollo mission is only a little less than five metre s long , but you can’ t se e it when you’re looking at the moon in the night sky. Even with the most powerful optical telescope, five metres is about ten times too small to discern from here on earth.

Hair and fingernails continue to grow after you die

Hair and fingernails require there to be living cells in the hair follicles and in the bed of the fingernails if they are to grow. As with all the other cells in a corpse, these cells die when the person dies. For several days after death, the skin and tissues of a body dry out and shrink, so largely dead tissues such as hair and nails may appear to protrude more from the follicles and fingers, but this is not actual growth.

Pigeons explode if they eat raw rice

Rice grains will eventually swell if placed in water. Luckily for cooks, the process occurs quite rapidly in a pan of boiling water, but luckily for a bird or any other animal, not in the stomach. Moreover, guts and gizzards are not solid vessels and pipes, and there is plenty of room for expansion should an animal eat the desiccated food and find the grains expanding within.


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Painting the Forth Bridge or the Golden Gate Bridge is a never-ending task

You might imagine workers beginning at one end of a bridge with pots of paint and big brushes and working their way towards the other end, and just as they finish the job it must be started all over again However, bridges are never painted in such a methodical but altogether inefficient manner. Also, specific areas of any given bridge weather at different rates, so one component will inevitably need to be replaced several times for another component between necessary paint jobs. In addition, modern paints and coatings will last at least twenty years, and it certainly doesn't take two decades to paint a bridge, even from end to end.

After five years of use, the contents of your pillow and duvet will have mostly been replaced by house dust mite faeces and carcasses

This is simply not true, as chemical analysis will testify, and so would estimates of the mass of house dust mites that might accrue over such a time period. My theory? This particular piece of deceived wisdom was fabricated simply to help manufacturers sell more new pillows and duvets.

Vertigo is a fear of heights

Despite the visual assertions of the eponymous Hitchcock movie, vertigo is not a fear of heights. It is a form of dizziness in which sufferers experience a feeling of movement even when entirely stationary. It is usually caused by a problem with the balance centres of the inner ear, and can cause nausea and vomiting.

Water always goes down the plughole anticlockwise in the northern hemisphere

It doesn't, nor does it always go down the plug hole clockwise in the southern. This particular piece of deceived wisdom presumably emerged from a simple misunderstanding of the Coriolis force. The Coriolis effect is a force caused by the rotation of the earth, which turns anticlockwise as you look down on it with the North Pole at the ‘top’. This force is tiny, though over vast distances and over long time periods it can pull on weather systems. However, sinks and baths tend to be smaller than weather systems, and the water drains down their plugholes relatively quickly – too quickly and over too short a distance for the Coriolis effect to influence the direction of flow. Experiments have shown that the shape of the sink or bath, together with any initial swirling control, is what determines the direction of flow down the plughole, and that the flow can be in either direction in either hemisphere, regardless of what the signs tell tourists at the equator.

If you die in a dream, you die in your sleep

How would anyone know what the recently departed were dreaming of before their demise?


Deceived Wisdom by David Bradley is published by Elliott & Thompson £11.99 hb/ebook available.

http://j.mp/Deceived-Wisdom - amazon and kindle

http://sciencebase.com/dw - ePub, PDF, mobi