True/False looks at commmonly held beliefs with a scientific mindset and tries to find out if they are, well, true or false. Sometimes the answer is clear, sometimes things are quite murky, and there are often some surprises.

Bad things happen in threes: true or false?

According to some people good things happen in threes, too, but there is nothing magic about the number three. Things do sometimes come in clusters but it isn’t fate or a higher power taking control, it’s just the counter-intuitive nature of randomness.

When explaining randomness a fruitcake is usually wheeled out — not, alas, for the purposes of refreshment, but as an illustration. Imagine a fruitcake (imaginary fruitcake is usually employed, as it leaves less crumbs, but feel free to verify with a real one) and think about the way the bits of fruit are distributed throughout. There are solitary sultanas scattered about, but in some places there are clumps of fruit and in others wide expanses of uninterrupted cake. That is what randomness looks like.

Our brains, on the other hand, seem to prefer a notion of randomness that spreads everything perfectly evenly. We imagine a random fruitcake to be one where all the sultanas and cherries and so on are arranged in a neat pattern.

But random things are unpredictable things. If you ponder the matter you will come to realise that for the position of fruit in a cake to be random — unpredictable — then occasionally they have to be in clumps. If they were spread out uniformly in an evenly-spaced grid then from the position of one sultana you could predict where all the others were. And if they aren’t spaced evenly then some must be closer together than others — in other words there must be clumps.

Now imagine events scattered through your life like the fruit scattered through a cake. Many of them are also unpredictable and so, while they sometimes come one at a time, they often clump together in twos, threes, even fours and beyond.

It is true that sometimes a cluster of things go wrong all at once. In a way it’s just the price we must pay for having interesting and varied lives. If you live life not knowing what tomorrow will bring, you just have to accept that sometimes it will bring far more than you bargained for.

Knuckle cracking causes arthritis: true or false?

If you’re like me and rate the sound of cracked knuckles as an irritation second only to nails on a blackboard then this common warning seems like poetic justice. Yet, in a further sign of the unfairness of nature, arthritic hands do not come about because of cracked knuckles.

Arthritis isn’t even associated with knuckle cracking: there just isn’t any evidence that the two are related. When you look under the bonnet of each phenomenon it’s easy to see why. Osteoarthritis is caused by loss of cartilage in the joints which leads to bone damage and joint swelling. The other kind of arthritis, rheumatoid arthritis, is caused by a faulty immune system leading to joint inflammation. The bone-crunching noise of a cracked knuckle certainly sounds like it’s damaging something crucial, and it definitely inflames tempers, so why not joints? Yet the ghastly noise doesn’t signal cartilage damage and doesn’t trigger inflammation.

The sound of a cracked knuckle comes from the creation and sudden collapse of gas bubbles inside the synovium, the liquid-filled capsule that protects and nourishes the joint. As the knuckle is pulled apart the pressure inside this capsule is lowered and gases which have been dissolved in the liquid spring out of solution and form bubbles, just as happens when you open a bottle of fizz. When the knuckle snaps back the capsule is compressed and the bubble bursts with a bang.

So we have two unrelated processes. Joint cracking is about the fluid in between the joints, not the cartilage or other parts of the joint that are involved in arthritis.

That doesn’t mean knuckle cracking is harmless. It can lead to loss of hand function. There is some justice after all — though if you ask me the crackers are getting off easy.

If you’ve been cracking your knuckles to your heart’s desire without thought of the consequences then consider your bubble burst. You won’t get arthritis, but you can still expect problems. And just watch out if you start cracking around me — or you may find a knuckle sandwich heading your way.

Grape seeds cause appendicitis: true or false?

I’m sure I’m not the only one to have wasted the odd youthful hour worrying about the consequences after swallowing a fruit seed. While my concerns centred on unrealistic (though alarming) scenarios such as finding a sapling inching its way up my throat, Linda Caradus has queried a more reasonable fear, that of appendicitis. While more likely than the impossible seedling-in-the-stomach, seeds of any kind are such an infrequent cause of appendicitis that it isn’t generally worth worrying about.

The appendix is a curious worm-like organ that hangs out near the start of the colon. Its function, if it has one, is far from clear. It appears to have no purpose, though some experts think otherwise.

Hardly less mysterious is appendicitis, the disease that occurs when the appendix becomes inflamed. It is very hard to diagnose from the outside, so the treatment for acute appendicitis generally precedes a firm diagnosis. The upshot is that the appendix is quite often removed only to find that acute appendicitis wasn’t the problem. At least that can only be a once in a lifetime experience.

There is still some dispute over the cause of acute appendicitis, because it isn’t clear whether some signs typical of the disease are causes of it or caused by it. What is fairly clear, though, is that fruit seeds are hardly ever found in a removed, diseased appendix. Seeds are the culprit less than one percent of the time, according to one reckoning. So while fruit seeds can cause appendicitis, most cases arise from some other cause and — given how many seeds must be swallowed every day — it is likely that most seeds travel through our intestines without stopping at the appendix to cause trouble.

Seeds are a common cause of some intestinal problems but appendicitis is not one of those. So if you do feel a grape seed — or any seed — slip down your throat (and your appendix is still inside your abdomen rather than a jar), just relax and don’t even give fear a chance to take root.

Head lice like clean hair: true or false?

I remember overhearing this when I was knee-high to a grasshopper and thinking that, at last, I had the excuse I needed to banish bathing once and for all. Parental authority had other ideas, for which I am thankful — not just because the advantages of clean habits dawn on you with the arrival of adulthood, but because it turns out head lice aren’t as picky as I had heard.

At least as far as I can tell. Head lice are one of those medical curiosities that, while widespread and irritating, aren’t dangerous or interesting enough to attract a lot of scientific scrutiny. Your typical medical researcher doesn’t dream of holding in their hand the cure for lice, they set their sights on cancer, Alzheimer’s and other big hitters — and probably rightly so. Lice and the nits they leave behind are annoying but not life-threatening. But the lack of scientific interest does allow all kinds of nit-wit claims and lousy ideas to spread.

Head lice aren’t very good with curly hair, probably because the cross-section of naturally curly hair is challenging for them to get a grip on. That doesn’t stop them trying, though.

As for cleanliness, there isn’t any evidence that head lice prefer clean or dirty hair. They just don’t care what kind of hair they grab on to: as long as it is hair they will get their hooks into it and do their best to stay put. These critters are after blood, after all. How picky are they going to be about whether you shampooed in the last 24 hours?

Mind you, it isn’t a crazy idea. Some infectious diseases really do spread better among cleaner populations than dirty ones. And one could imagine that the accumulation of grime and oil on dirty hair might make it hard for the little bloodsuckers to hold on. But it just isn’t so.

Head lice aren’t all that fussy about their accommodation. Dirty hair is no protection and clean hair isn’t an open invitation. You don’t need to worry that your lustrous locks will leave you lousy.

The sun is yellow: true or false?

Every four year old knows that the sun is yellow. Ask one to draw a house and there, smiling down on the four windows, door and smoking chimney is the sun, rendered in golden hues with a chipper expression on his face. It’s a good thing we don’t trust four year olds with major policy decisions because not only does the sun not have an expression — happy or otherwise — but it isn’t really yellow.

If you rely on the evidence of your eyes you may agree with the preschoolers. From down here, at the bottom of the thick atmospheric fug, the sun does look yellow, but looks can be deceiving. It’s often hard to pin down the colour of even everyday objects. We’ve all seen clothes that look one colour in daylight and another in the harsh glare of fluorescent lights. The perceived colour of an object depends not just on the object itself but also the viewing conditions. The sun is no different.

Clothes change colour because perceived colour is a combination of pigment and the colour of the illuminating light. Though the sun’s light comes from within rather than being reflected from some other source the viewing conditions can still alter our perception of its colour.

The sun glows with a white heat but looks yellow because of the atmosphere. Different coloured light is scattered differently in the air. Blue light is scattered a lot, and so ends up spread far from the direct beam of sunlight all over the sky. Red light, by contrast, is relatively unaffected by its journey through the air and streams straight down. The result is that most of the sky looks blue, while the sun’s disc turns a yellow orange. This is most pronounced at sunset and sunrise when the sun is a much deeper colour than at midday.

In space the sun looks white — perhaps a mere mention of yellow but nothing like we see from down here on the surface of the earth. Despite appearances and rumours to the contrary, the sun just ain’t yeller, y’hear?

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