Q Say an aeroplane is flying at 500mph and I run forwards inside the aeroplane at 10mph. I’m travelling at 510mph. If we replicate this on a larger scale, an aeroplane flying inside another aeroplane, inside another and so on, could we eventually break the speed of light?” asks Paul Dunny

A The short answer is no. Indeed although the scenario might sound plausible, as Dr Ed Daw from the University of Sheffield explains: “Sometimes common sense is just wrong, or perhaps different common sense ideas conflict with each other, and something has to give.” Another thought experiment provides a good illustration of such limitations. “It is ‘common sense’ to say that a car moving on top of another car has a total speed of the sum of their speedometer readings relative to the ground.

“However, what happens if instead of doing this with cars, you do it with light beams?” asks Daw. “Suppose I have a trolley travelling along a road at almost the speed of light, and I shine a light backwards off it. How fast is the backwards travelling light going with respect to the road?”

Following the apparent “logic” of the argument brings you to a bizarre conclusion: “The so-called ‘common sense’ above suggests that if the trolley is travelling fast enough, the light can be stationary,” says Daw. “That’s just nonsense! Stationary light? Well, at least, Einstein thought it was nonsense.”

Unfazed, the great man of physics understood that one aspect of the scenario must be awry. “He realised that the common sense notion of light as somehow NOT like particles, and of light always travelling fast with respect to anyone looking, meant that the idea of adding speeds together to get a resultant speed [that is] the sum of its parts just can’t be right for light, and therefore it isn’t right for other objects moving at speeds close to the speed of light either,” says Daw.

Q “Why does movement on the water surface lead to dark shadows on the floor of a pool?”

asks Chris H

A “When a breeze runs across the surface of a pool you get ripples, and if you are lucky enough to have a clear day then you will see that the bottom of the pool becomes covered in bright patterns of light,” explains Professor Richard Templer from Imperial College London. “David Hockney’s Bigger Splash pictures show these light patterns,” he reveals. “They occur because rays of light are refracted or bent when they go from travelling in air to travelling in water.”

Ripples, however, change the geometry of surface. “Since the water surface is not flat but undulating, this leads to the rays of light becoming focused. The beautiful patterns you see are a product of the undulating water surface,” Templer explains. “This surface generally looks like the one you will find in an egg box, so you might guess (correctly) that it will not focus an image of the sun like a camera lens would. Instead you get that wonderful mesh of intersecting lines and lobes, and the dark space in between, where the light rays are not focused.”

It’s a phenomenon that has intrigued sunseekers and physicists alike. “The technical name for these wonderful patterns is caustic surfaces and in the 1980s Professor Michael Berry, FRS of Bristol University demonstrated that these caustics could be described using catastrophe theory,” Templer reveals.

Q “There is a saying something like ‘ontogeny follows phylogeny’, so that, for example, a human foetus passes through a fishlike stage. How does this apply to, for example, butterflies, bluebottles and the other creatures that go through larval, pupal and imago stages? What stage of development does the pupal stage represent? asks AM Wooster

A “Your reader is referring to the theory of recapitulation and Ernst Haeckel’s phrase ‘ontogeny recapitulates phylogeny’,” Dr Andrew Peel from the University of Leeds reveals. “The idea was that animal embryos start off looking quite similar to each other, and as embryo development proceeds they look increasingly different in a manner that reflects their different evolutionary histories – the idea was that they pass through the different forms that they had taken during their evolution (eg a fishlike stage), with more primitive forms early in embryogenesis.”

But appearances can be deceiving. “There is a stage during animal embryogenesis when the embryos of quite unrelated animals are considered relatively similar to each other, however, it must be noted this is quite a subjective comparison, depends a lot on the animal species being compared, and at this stage the animal embryos are far from identical!” he says. “This probably reflects the existence of key steps in the development of an animal body plan that all animals [with bilateral symmetry] have to go through (eg the formation of internal tissues). If any of these events ‘go wrong’ it would be catastrophic/terminal for the animal, meaning that [such] stages during animal embryogenesis have remained relatively unchanged during evolution.”

In fact, bugs come rather a cropper in the theory of recapitulation. “Insects that undergo a life cycle involving egg, larva, pupae and adult [holometabolous insects] almost certainly do not represent the ancestral insect condition,” Peel explains. “In other words, the common ancestor of all insects would not have passed through a larval and pupal stage. [Some] insect orders have retained a more ancestral mode of development: hemimetabolous insects (such as grasshoppers ) hatch looking quite similar to the adult, and then pass through a series of nymphal stages looking progressively more like the adult.”

Instead the evidence supports a rather different theory. “We now realise that the earliest events during embryogenesis can happen in very different ways, even between very closely related species,” Peel explains. “Thus, in animal development, embryos of different species usually begin from a very different starting point (in terms of the characteristics of the egg at fertilisation), they obviously end up at a very different finishing points (ie a distinct adult body form typical of the species in question), but must undergo some quite similar ancient embryonic processes along the way. This has led to the ‘hour glass’ model for the evolution of animal development, which has replaced the older recapitulation model.”

Q How can my shirts end up whiter than white when I wash them? asks Christopher

A If a material reflects all wavelengths of visible light equally well it will appear white, however ‘white’ fabrics often suffer from a yellowish tint (corresponding to the absorption of blue light). Optical brightners in laundry products provide a solution. These chemicals cling to the fabric and their alternative name – fluorescent whitening agents – gives a clue as to their action.

Optical brightners absorb UV light, gaining energy to become “excited”. However, they don’t hold on to this energy for long – most of it is released again as light. But as some of the energy is lost in other processes this emitted light is of a longer wavelength than that absorbed, and falls in the blue region of the visible spectrum. Since the blue light emitted more than compensates for the yellowing effect, brightners not only make your shirts seem whiter, but more dazzling too.