Stripping Down Science (11 page)

This fits with the findings of Geoffrey Miller's lap dancer study (see previous chapter), in which scientists showed that lap dancers earn over 200% more in tips during their most fertile days. At the time of this earlier study, it wasn't clear whether the fiscal boost was just because the lap dancers were making themselves look more appealing or had sexier-sounding voices when they were at their most fertile. Now it looks like it was at least partly down to smell.

From an evolutionary standpoint, the results are exactly what we would expect: women exude some sort of pheromonal smell signal to broadcast their fertility to men who, in turn, as Miller and Maner put it, manifest ‘mating-related behaviour'. By which, presumably, they mean a sudden inability to speak coherently coupled with the urge to drink too much, turn up the stereo to ‘11' and perform outlandish macho displays and skateboard stunts. And that's just the over-60s …

Most people assume, correctly, that flowers look the way they do to attract insects that pollinate them. But that's not the whole story. Scientists have now discovered that plants have another ‘trick up their leaves' to make themselves irresistible to even the most choosy insect – solar power.

Cambridge University's Beverley Glover and her colleagues
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recently set up some fake flowers filled with a sugar solution, which they kept at different temperatures. Unleashing a team of bumblebees on their floral offerings, they watched as the insects visited the flowers to drink the surrogate ‘nectar'. Very quickly, it became obvious that the bees were concentrating on the flowers with the warmest nectar. Just in case it was something to do with the colour of the fake flowers, the scientists also tried a different colour combination – and got the same result.

This proved that bees like their nectar hot, irrespective of the colour of the cup it's served in. But can flowers dish up hot beverages? ‘Yes,' say the scientists, who have found that the surfaces of
over 80% of flowers are covered with tiny conical-shaped cells which behave like microscopic lenses. These focus sunlight, warming up the flower and its nectar by several degrees. As the sun moves across the sky, the flower head moves too, keeping a fix on the sun like the dish of a radar tracking station.

But why would bees be interested in a warm drink anyway? Well, flight is an energy-hungry business, and by drinking hotter nectar the bee keeps warm for nothing. As Beverley Glover points out, ‘For a bumblebee, we think it's about metabolic reward. They need the sugar from the flower to make energy to fly but they, like you on a cold day, might get more energy more quickly from a warm drink than a cold drink. It saves them from using their own energy to warm that nectar up if the flower's already providing it at a warmer temperature. The effect's also strongest at dawn and dusk and we know that bumblebees need extra help at these times of day when it's hard for them to get that big fat body off the ground.'

In the grand scheme of things, it's a clever way to save energy. And besides bees, other insects have also been spotted taking advantage of
this natural plant solarium effect by basking in flowers to warm themselves up first thing in the morning. But hot nectar turns out not to be the whole of the story. The team suspected that the conical cells might also be giving bees a helping hand to clamber into flowers.

To test this idea,
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they looked at how bees responded to a mutant snapdragon (
Antirrhinum
) plant which lacks these conical solar cells but looks and smells identical to a normal plant in all other respects. The lack of conical cells in these plants turns the flower surfaces into the floral equivalent of an icerink, making it hard to get a grip. Predictably, the bees universally turned their noses up at visiting the blooms, preferring the normal flowers instead. To prove that it was this genetic Teflon-effect that the bees were objecting to, the team then made casts of both the normal and the mutant petal surfaces using epoxy resin. These plastic flowers were then loaded with sugar solutions at identical temperatures and offered to the bees.

Incredibly, when these epoxy casts were presented horizontally, with the flowers lying
flat and pointing upwards, the bees showed no preference in favour of either, but as soon as the epoxy blooms were hung vertically, so that the bees had to cling to the surface in order to drink the sugar solution, the bees showed a strong preference for the petal casts taken from the plants with conical cells. ‘This is like bee velcro,' says Beverley Glover. ‘Flowers have evolved these cells so that pollinators can get a grip on them.'

So flowers have killed two birds with one stone: by coming up with a conical cell covering, their petal surfaces can capture sunlight and serve up warm nectar, making the plant more metabolically attractive than a trip to the gym. But at the same time, these floral solar panels provide convenient stepping stones to help would-be pollinators get a grip.

A simple soul like me could be forgiven for thinking that black does exactly what it says on the tin: it's black. But not anymore it seems, because scientists have recently shattered the myth that black is black by producing a substance 30 times darker. This new coating, which is the brainchild of Rensselaer Polytechnic researcher Pulickel Ajayan and his team,
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consists of a sheet of nanotubes. These are very tiny but extraordinarily long molecular straws of carbon atoms, each about 5000 times thinner in diameter than a human hair.

They're grown as a film using a process called vapour deposition and the result resembles the nanoscale equivalent of a bamboo forest with the carbon tubes standing vertically, side by side, their tops entangled to make the surface appear irregularly corrugated. The individual nanotube
bamboos also vary in height and can be up to one millimetre tall. Prepared in this way, the result, says Ajayan, is a material that's very good at absorbing light but also very bad at reflecting it again, which is why it looks so dark. ‘An ideal black material absorbs light at all wavelengths and all angles, basically.' The new material achieves this by allowing light to penetrate into the spaces between the nanotubes before being absorbed by the carbon in their walls. Even if a light ray manages to ricochet off one nanotube, it will still be absorbed by an adjacent one. ‘So basically, light enters this material and it gets trapped.'

Compared with black paint or graphite, which reflect about 5–10% of the light that lands on
them, this new nanosurface soaks up over 99.9% of the light that hits it, right across the visible spectrum, making it at least 100 times darker than even the average teenager's bedroom wall. The surface is also three times blacker than a nickel-phosphorus compound previously crowned the ‘world's blackest substance', and 30 times darker than the carbon-based ‘gold-standard black' held by the US National Institute of Standards and Technology.

But why is it useful? Apart from being an academic curiosity, and deserving of another entry in the
Guinness World Records
for the creator (his first was in 2007 for the ‘world's smallest broom', a nanobrush with bristles 30-billionths of a metre in diameter), the discovery does have some potential spin-offs: it could, for instance, hold the key to invisibility cloaks to conceal the next generation of stealth bombers, or be used to create highly efficient solar cells that are capable of harvesting significantly more of the sun's energy than the 15–30% achieved by today's technology.

To pursue this, the Rensselaer team are now testing the substance to see whether it can soak up some of the other wavelengths of light beyond
the visible spectrum, such as infrared, microwaves or possibly even X-rays and gamma rays. ‘If you could make materials that would block these radiations, it could have serious applications for stealth and defence,' Ajayan points out, although it will be a little while yet before he can shed light on whether it actually works.

‘BLACK' BOX

Another black myth is the name of the so-called ‘black box' flight recorder carried on aeroplanes. Despite the misleading moniker, these devices, the first modern forms of which were developed in Australia in the 1960s and known as ‘Red Eggs', aren't black at all but instead are painted bright orange to make them easy to locate in the event of a crash.

Although they are normally housed in an aircraft's tail section to maximise their chances of surviving an impact, today's flight recorders are nonetheless capable of withstanding head-on smashes at over 300 miles per hour
and immersion in water to depths of over 6000 metres. To help crash detectives to recover them, they also fire off locator beacons to announce their positions.

Surprisingly, the idea for the flight data recorder first took off as early as the 1930s, in Europe. Two French aviation engineers eager to work out how to make their planes fly better, Francois Hussenot and Paul Beaudouin, developed a system that used mirrors to beam thin rays of light onto strips of slowly advancing photographic film. By adjusting the angle of the mirror, the light beam position could be altered to record parameters like altitude and speed. Developing the film would then reveal a line charting the course of a flight. Although no one knows for sure, this could be the origin of the name ‘black box', because it would have been necessary to keep the film in the dark to avoid accidental exposure and hence loss of the flight recording.

These days, rather than the eight metres of film used in Hussenot and Beaudouin's recorders, modern devices use solid state
electronic systems to log up to 25 hours of flight data, including any movements or adjustments of the aircraft controls, the performance of the major systems as well as communications amongst the flight crew and with air traffic controllers. This provides a forensic record to help investigators trace the causes of crashes but, increasingly, the information is also being used by manufacturers and developers to work out how to fly planes at maximum efficiency to minimise fuel costs and reduce greenhouse gas emissions.