Chris - Biscuit dunking duration was actually the subject of a proper scientific study in recent years. It was done by Len Fisher who is based at the University of Bristol. He published his findings in his book "How to dunk a biscuit". The reason the nation's favourite snack goes soft when you dunk it in anything is because biscuits are largely made of starch molecules (that’s the flour), which are long chains of molecules. Between them are sugar crystals that stick them together along with some fat as well.

When you put the biscuit in something hot like hot tea the heat melts the fat. Also the water soaks into the holes between the molecules and dissolves the sugar. This makes the whole structure become very weak and the biscuit falls apart.

Different biscuits with different physical properties and dimensions have different "dunking times" - in other words how long it takes before biscuit-meltdown occurs. For Rich Tea the dunking time is about four seconds. Digestives last longer, they can tolerate up to ten seconds of dunk before they start to fall apart. The only difference they found between the milky tea and non-milky tea was the flavour. They found that milky tea makes the biscuit flavour much more intense.

The reason, probably, is because milk has got a lot of fat in it unless you’re drinking liquid water (the white skimmed stuff). The fat intensifies the fat-soluble flavours in the biscuit, helps them to evaporate and go up your nose. You’ll get more flavour and more retro-aroma, as it’s called, from a biscuit dunked in milky tea than one dunked in black tea. The only possible exception I can think is that perhaps the fat in the milk is helping to liquefy the fat in the biscuit a little bit faster.

Another possibility is that it could be down to the surfactants in the milk. In order to keep the fat suspended, milk contains chemicals called surfactants. These behave a bit like washing-up liquid, which lifts fat off your washing-up by making oils dissolve. A consequence of surfactant action is that reduce the surface tension in the water so that could mean that the water can get into the biscuit quicker. If it’s absorbed faster it will have more time to dissolve the sugar. Therefore the dunking time for a given biscuit in a cup of tea made with full-fat milk might be lower!

Chris: That’s just not possible.

Dave: As far as we know, when the Big Bang happened everything was not only closer together but space was smaller. When we say the universe was really, really tiny - maybe less than the size of an atom - that means all the space is not just all the particles close together. All of space was smaller as well. In some senses we are, at the moment, where the Big Bang happened because this bit of space we’re in now was at the Big Bang – it’s just expanded hugely.

Victoria: Yes, as far as I understand it, that’s the case. Our ancestors needed wisdom teeth. They are, as many people will know through suffering, teeth that come through much later (between the ages of 18 and 25). That’s why they’re called wisdom teeth. You’re older and wiser when you get them. Allegedly. Our ancestors, when they used to eat raw meat and grub around and eat lots of roughage would grind down their existing teeth. They had to use very powerful jaws and chew a lot more. They then had a spare set of teeth that came in later on.

Chris: I’ve only got one and it hasn’t even come through. I went to the dentists about five years ago and he said let’s do an x-ray and see where your wisdom teeth are and there was one wisdom tooth. I asked him why he thought I only had one as most faces are set up symmetrically. There must be some kind of developmental thing – the cells that make that tooth didn’t turn up in that bit of my jaw.

Chris: The Geo4 paper came out this month and this is a big, multi-national report where scientists get together from every country in the world. They look at the raw data and work out where the Earth’s going and how it’s ‘powering’ itself. Their current calculations show that the current environmental demand, or how much land it takes to power each person on Earth, is about 22ha of land surface per person. How much can the Earth sustainably supply in the long-term? The Earth can only support humans sustainably on 15.7ha of land per person. We’re already using the land space, per person, of two Earths just in terms of land space. If you look at fishing the amount of exploitation of the oceans is thought to be 250% of sustainable levels of fishing in the long-term.

Victoria: That really puts into perspective how much extra land we’re going to need for biofuels as well.

Chris: The other point they make is that in about forty years time they think the Third World will need land space equivalent to the entire of South Africa for producing enough food just to support the extra people that the planet is sustaining by then.

Chris: In the last twelve months we’ve seen evidence that perhaps it can. The stumbling block at the moment is that perhaps we don’t have the stem cells necessarily, ethically, to do it. Scientists in University College London published a paper in the journal Nature about this time last year. They took mice which had been genetically programmed develop a disease like the human disease, macular degeneration, and they took stem cells from the retina of newborn mice. They implanted these stem cells into the eyes of the mice that had macular degeneration. They were able to show that the mice got back their ability to see. By following where the stem cells went in the eyes they found that they migrated to the right part of the retina and turned back into photo-receptors. These cells take the light and turn it into information that the brain can understand.

Dave: This is called a mirage. On a hot day the air above the road gets hotter than the air above that. When air gets hot it expands and becomes less dense. The less dense the air is the faster light goes through it. The light is going slower high up than it is really close to the road. The light then refracts as is comes down from the bright sky. It bends upwards and goes into your eye. What you’re seeing is an image of the sky in front of you.

Chris: When you have toast cooking in your toaster and you look at the air above it it’s all twisty and shimmery.

Dave: It’s the same phenomenon. You get hot air in swirly patterns above the toaster that bends the light which produces a distorted image behind.

Chris: You should always make sure things are fully-cooked. The reason for doing that is that bacteria may have settled on the food when it was being prepared. They may have only been there at very low levels when the food was being prepared. If it hasn’t been stored very well, those bacteria can persist. Bacteria can easily survive the temperatures in your freezer. Bacteria can survive being frozen down to -200 degrees. If you don’t warm food thoroughly to kill the bacteria you get some bits which are just warm enough to sustain a much better environment for the bacteria so they grow really fast. When they grow very fast they can either infect you, like salmonella, or they can produce toxins into the food like staphylococcus aureus. This produces a toxin which can cause diarrhoea and vomiting. That toxin is also stable so that if you thoroughly re-heat the food, unfortunately you can still get problems because the toxin is still in the food. The moral is to make sure you cook things absolutely thoroughly.

Chris: If you look at the back of the eye in animals that go out at night (nocturnal animals) or animals that are likely to be hunted at night they have this structure called a tapidum lucidum which is Latin for bright carpet. If you dissect a sheep’s eyeball you’ll see this surface that looks like mother of pearl. The back of the eyeball is highly reflective like a mirror.

The reason for having this is that if you’re under low light conditions, light comes into the eye, the retina sticks out into the jelly-like stuff in the back of the eye but any light that misses it will be soaked up by the back of the eyeball. By having the back of the eye a bit reflective then any light that missed the retina the first time can be bounced back onto the retina and you have a second chance of seeing it. The payoff is that you can see in low light. The downside is that the light gets altered in its path very slightly so the acuity, how well you can see, is lower with this structure.

Dogs, cats, sheep, cows and horses all have it. If you shine a torch at a dog in the dark its eyes look like they’re glowing (a bit like Tony Blair on those posters that you saw about ten years ago). It’s nothing to do with the pupil being open wider or smaller, although because it’s dark, the pupil will be open wider.

Because air is a good insulator the thing that limits how fast a normal oven can heat something up is basically how fast the energy is transferred from the hot air to your food. The oven is powerful enough to keep the air hot, so adding another cake will not slow it down much. A microwave on the other hand is very efficient at transferring energy from the magnetron (the thing which produces the microwaves) to the food. So the thing that limits the amount of energy getting to your food every second is basically how much energy you are converting to microwaves. If you have twice as much food the same amount of energy will be transferred every second but it will be shared out over twice as much food, so it will heat up slower.

In terms of microwaves killing bacteria, if you don’t heat food to the right extent there’s a danger of getting hotspots and colds spots. That’s why there’s a turntable in a microwave. Without a hot enough area in the food any bugs could persist so you could end up getting food poisoning. Microwaves are just radio waves and the reason they make food cook is that it absorbs the energy of the microwave, the molecules vibrate and this raises the temperature. They’re not doing anything special or zapping bugs by gamma irradiation or blasting DNA. They’re just heating them up. If you don’t make the food hot enough then you’re not going to kill anything. It’s all down to heat and nothing else.

Dave: The microwaves are a form of electromagnetic wave. When they hit something they try and make an electric current flow in it. If you’ve got two things with a gap in between them it can produce a big current. You get a large current running across this gap or through a tiny piece of skin in between. It’ll get hotter and hotter until eventually it burns out. At this point you have a big electric current trying to get between these two lumps of fruit which can jump through the air and create a spark. That will take the current and you’ll get a fireworks display.

Victoria: Yes it does because the ambient temperature makes it easier or less easy for your body to control the internal temperature. You have to use a certain amount of energy to keep your body at the right temperature and keep yourself healthy. It’s more to do with how many bugs are around. Bug such as the cold virus and the flu virus are extremely infectious and airborne. In the cold weather you have vulnerable people whose systems can’t get enough energy to maintain their core temperature and they’re having to keep themselves warm. They get bugs, the bugs are transmitted and then everyone comes down with it.

Dave: There’s also an effect that in the Winter everyone’s cramped together inside whereas in the summer they’re spread out. If few of the viruses are getting from one person to the next, they’re not going to spread as quickly.

Chris: The other big determinant that science has shown is really important to the spread of infections is the school year. Lots of people go away on holiday and then they come back and congregate in this thing called a school which is really a viral mixing pot where everyone exchanges viruses, takes them homes to their parents and brothers and sisters who then take them to their schools. School terms are really important in determining who gets what.

Dave: That’s because a bubble is made up of a very thin layer of water which has soap molecules on the outside and that has surface tension. It’s trying to minimise its area and get as small as possible. The best shape with the smallest surface for a certain volume of air inside is a sphere, so they’re round.

Victoria: I have no idea – I should have deferred to Mark Peplow on that one!