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Published on 25 February

Why don鈥檛 we sneeze in our sleep?

鈥� A sneeze is a reflex reaction 鈥� an involuntary response to an internal or external stimulus. Reflex reactions shut down during sleep because of rapid eye movement (REM) atonia, a physiological state during which movement messages can鈥檛 get from the brain to the muscles, causing partial paralysis. This prevents sleepers from acting out their dreams to the detriment of themselves or their bed partners. A consequence is that reflex signals are not acted upon, so there鈥檚 no sneezing during sleep. If a sneeze is absolutely necessary, REM atonia ceases and the person wakes up before sneezing.

There have been cases of REM sleep behaviour disorder in which people acted out their dreams and ended up in court after injuring or killing their partner. Presumably, such people can sneeze in their sleep.

David Muir, Edinburgh, UK

鈥� It is a leading question, implying that 鈥渨e鈥� means all of us. I do sneeze during my sleep, frequently if I have a head cold. This wakes up my wife, who then awakens me and tells me that I have disturbed her sleep by sneezing yet again.

Presumably if I slept by myself, I would not have woken up. And the implication of this is that only couples are known to sneeze while they are asleep. Now, there is a PhD project.

Ron Pursell, Flookburgh, Cumbria, UK

Cloud cover

22 April

How much data does the World Wide Web hold?

鈥� Whatever the amount is in any one moment, it鈥檒l be quite a bit more in the next. A good estimate floating around is 1 yottabyte, or a trillion terabytes. Yet this figure is now almost a year old and, because the web is widely described as growing exponentially, it is reasonable to assume it could now have doubled to 2 or more yottabytes.

We should also consider the so-called deep web, which encompasses anything that is not found by a mainstream search engine. This includes many large databases for travel bookings, merchandise data for online shopping, any social media networks that do not put everything in the public domain, and so forth. Figures suggest that 80 per cent of the web is dark, so if that is true, the web comprised 5 yottabytes of data in 2014 and could now hold double that or even more.

It鈥檚 also important to add that many websites do not reveal how much data they store. Hosting sites hold several redundant copies of almost everything, in multiple locations on varying types of media. Should we count this as part of the web?

Similarly, much of the information on the web is duplicated. Years ago, I searched for a list of jokes and found a dozen copies of the same list with only minor differences, because every revised version was put on a new site and page. Who can guess how many copies of popular content exist?

It鈥檚 big, that鈥檚 for sure.

David Morton, Geeveston, Tasmania, Australia

Inside out

1 July

What effect would the accelerated particles in the Large Hadron Collider have if they hit a human body? And what would happen if particles aimed at each other collided inside you, or collided with one of your own particles?

鈥� At least one unfortunate person 鈥� Anatoli Bugorski 鈥� has already been struck by a high energy particle beam. In 1978, his head was briefly caught in the proton beam of a particle accelerator, the U-70 synchrotron in Russia. He reported seeing a flash of light 鈥渂righter than a 1000 suns鈥� but experienced no immediate pain.

The full extent of his injuries only became apparent over the next few days 鈥� he lost half of the skin on his face where the beam had burned a path through it and experienced various other complications. To the surprise of doctors, he survived, albeit with lifelong symptoms.

It isn鈥檛 clear whether the beam was operating at its full capacity of 70 gigaelectronvolts at the time of the accident. Presumably, if one did the same thing at the Large Hadron Collider, which has a beam energy of 6.5 teraelectronvolts 鈥� almost 1000 times greater, and double again at the point where the beams collide 鈥� the aftermath would not be pleasant.

There is also the experience of Ray Cox, one of the North American victims of the infamous Therac-25 radiation therapy machine in the mid-1980s.

As a result of poor hardware and software design, he was targeted with an electron beam that was more than 100 times the intended dose. In his own words, this felt like 鈥渁n intense electric shock鈥�, and he fled the treatment room screaming in pain.

Some victims of the defective equipment died of radiation poisoning. The beam energy of this machine was a mere 25 megaelectronvolts.

Richard Miller London, UK

Footloose

10 June

I sometimes notice that one of my shoes is loose, although the other is fine. When I tighten the laces on the loose shoe, the other shoe then feels loose. Is there an explanation for this peculiar effect?

鈥� Our senses are slaves to relative comparison. Place your left hand in hot water and your right in iced water, and then put both into the same tepid water. Now your left hand senses cold and your right feels warm, despite experiencing the same temperature.

When we walk from a sunlit area into a dimly illuminated room, we see next to nothing initially, yet within seconds our eyes compensate and we can discern subtle decor and different shades of grey. When loud, raucous music is switched off, silence prevails for a moment, until we perceive hitherto unnoticed sounds of far-off traffic or birdsong.

It can be irritating when the laces on one shoe loosen, so we retie them tight. The other then feels loose because, by comparison, it really is looser.

David Muir, Science Department, Portobello High School, Edinburgh, UK

Hisssssss

29 April

How long do I have to wait after dropping a beer bottle before I can safely present it to a guest, and how did its internal pressure build up if the system is in equilibrium?

鈥� The pressure inside a bottle of beer is unchanged after it has been dropped.

What has changed is the number of tiny bubbles that are distributed throughout the beer. These form when a bottle is dropped or shaken. When the bottle is opened, the bubbles act as nucleation points for the dissolved carbon dioxide, which comes out with such a rush that it takes a lot of the beer with it. This is a terrible waste: not only is good beer lost, but what remains is flat.

As the writer suggests, this doesn鈥檛 happen if you wait before opening the bottle. How long you must wait depends on a number of things: the size of the bubbles, how deep in the liquid they are and the viscosity of the beer. To be safe, one has to wait long enough for the last, smallest bubble to reach the surface and burst, before removing the cap.

鈥淲hen the bottle is opened the bubbles act as nucleation sites for dissolved carbon dioxide鈥�

In my experience about 10 minutes is normally enough. However, a 10-minute wait may be asking too much of a thirsty beer drinker, so it is far better to place the bottle at the back of the refrigerator and take out another 鈥� with greater care.

Andrew Carruthers, Quebec, Canada

Foaming mad

5 August

I have a handheld milk foamer for my coffee. I can foam milk to twice its volume when it is cold, out of the fridge, but it barely foams at all when heated. Why is that?

鈥� Creating a milk foam depends largely on the protein casein, which stabilises bubbles in the milk. The protein forms particles called micelles and the stronger the structure of these particles, the greater the volume and durability of the foam.

鈥淪kimmed milk makes a fuller foam, but the taste may leave something to be desired鈥�

Milk also contains many different fats in the form of long fatty acid chains attached to a glycerol backbone. Heating it increases the activity of an enzyme called lipase. This encourages lipolysis, a process by which fats break down into their constituent fatty acids and glycerol. The glycerol and free fatty acids can weaken casein鈥檚 structure, causing air bubbles to collapse more easily. If the milk has just been removed from the fridge, its fats are largely intact, so casein is able to stabilise any foam.

The freshness of the milk also has an effect on foaming, because the longer the milk is left to stand, the more of its fats will be broken down. To ensure a good froth, it helps to use milk with a low fat content, such as skimmed milk, so there are fewer fat breakdown products to weaken the casein. While this should help create a fuller foam, the taste may leave something to be desired.

Sam Buckton, Hertfordshire, UK

Perfect perch

28 October

Birds perch standing up, bats upside down. Are there any bird or bat exceptions to this? And why do the two perch differently?

鈥� There is a misconception that bats can鈥檛 take off from an upright position owing to their small leg bones and muscles, which have been reduced to make flight more efficient.

However, flapping their tail membrane allows bats to launch upwards. Granted, such an ungainly take-off would make them vulnerable to predation if they nested on the ground, which makes dropping into flight from a perch a better strategy.

It鈥檚 not just risk of predation that explains the difference, though. Bats also have superior aerobatic ability. These animals can invert and come to a virtual standstill in flight, which allows them to grasp a suitable roosting position from underneath. This means bats can monopolise the ceilings of caves and other inaccessible roosting sites.

鈥淭endons in bats and birds close the claws and lock the feet to the perch when they are relaxed鈥�

Bats are more manoeuvrable because their wings are larger relative to their body mass than is the case for birds. In addition, though wings have evolved from arms in both cases, the bone is limited to the front edge of a bird鈥檚 wing whereas in bats the fingers extend across and to the rear edge of the wing, giving bats finer control of the wing surface.

Conversely, birds鈥� lack of manoeuvrability might limit them to more accessible roosts. And this may help explain why birds don鈥檛 sleep as we understand the term 鈥� they rest each side of the brain in turn so that they stay alert to predators and possibly to avoid falling off their perches. However, there are a few birds, including the vernal hanging parrot (Loriculus vernalis), that roost upside down in trees.

The tendons in bats鈥� and birds鈥� feet are arranged to close the claws and lock the feet to the perch when the creature is relaxed, minimising energy expenditure. If a bat dies in its sleep, it doesn鈥檛 automatically fall to the ground, and needs to be knocked off its perch.

Mike Follows, Sutton Coldfield, West Midlands, UK

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