A normal star is a big ball of gas, its gravity is pulling it together, trying to make it collapse. It’s actually held up because it’s really, really hot. In the same way that when a gas is hot it expands the star’s temperature allows it to expand and stay fairly big. When the star gets really old it can explode and eventually it has burn most of its fuel and it cools down a bit. It starts to collapse under its own gravity.

Stars which are massive enough start to crush the protons and electrons to form neutrons. These form a huge star-sized atomic nucleus, basically just neutrons, a neutron star is. A normal star can collapse into a neutron star. If a neutron star slowly gathered more and more mass then it could collapse again whereby the neutrons couldn’t support themselves.

It would start to get crushed together and it would get so heavy and dense that it would turn into a black hole. A black hole is where you get so much mass in one place it stretches space so much that even light can't escape, this will happen whatever the internal structure of the black hole. We don't know anything about the internals of black holes, and in fact they won't affect anyone outside the black hole, so as far as we can tell a black hole is as far as anything can collapse.

Birds are quite adaptive when it comes to people and the kinds of foods we give them. Here in the UK there’s a wonderful phenomenon that happened. Since 1921 a thing which we no-longer have, glass bottles of milk sitting on our doorsteps with milk that wasn’t homogenised, had this wonderful creamy chunks floating up to the top. For the first time in 1921 someone saw a blue tit pecking at that top, the silver foil top of the milk bottle to drink the cream. If that isn’t a more unnatural food-source for birds, I don’t know what is. What actually happened, and people studied how this behaviour spread around England, by the 50s and 60s birds all the way around England had learned how to do it. It always seems like it came to a new area and all the birds in that area would learn how to do it. It’s this phenomenon that spread around. I think birds do know how to adapt very much to different types of food that we give them. Suet, I think, is actually meant to be a very good type of food for birds, especially in winter. The RSPB here in the UK – the Royal Society for the Protection of Birds – on their website they do recommend putting out suet. I don’t think that’s a problem. I think birds can eat other animals, it’s all right but I understand your concern. I think birds really are quite adaptable. They’ll have a go and if it tastes good they’ll realise it’s got nutrients and energy in it then they’ll take it and they’ll eat it.

That’s quite a deep question, If you go back to the big bang, if you look in any direction, you’ll see something. If you look in any direction far enough and there’s no stars in the way, you’ll see a big soup of atoms which were created after the big bang. This light was emitted when electrons were collected by hydrogen atoms. When they did that they released lots of energy and photons, very high energy light. This is well into the gamma rays. Because the universe has expanded so much and these gamma ray photons which are incredibly hot, thousands and thousands of degrees centigrade, have slowly been stretched as the universe has stretched. Their wavelength has got longer and longer. With that they’ve got colder and colder because longer wavelengths are lower energies. They’ve got stretched so much that their temperature is about 2 or 3 degrees above absolute zero. It’s about -270 degrees centigrade.

This is a really good observation and it’s absolutely true. Your ice cubes will lose volume in your freezer over time. The reason is, although they’re frozen, literally the water molecules have been joined together to form ice, what actually is going on (if you could zoom in with a very powerful microscope and watch the energy in ice) is that the ice is sharing out all the energy -even though there’s a lot less of it because it’s cold - amongst all the water molecules. And it’s random. Every so often there’ll be some water molecules that have enough energy to vibrate or escape free from the surface of the ice. At the same time others will rejoin onto the ice and this is what’s called a dynamic equilibrium. Every so often you’ll get a molecule of water which will gain enough energy to spring off of an ice cube and it might well form some ice elsewhere in the freezer or just fall out of the door. Over time we’ve got a lot of something, water as ice, it will slowly diminish and shrink. It will slowly disappear. It will deposit round the inside of the freezer but because the freezer has the door open from time to time you’re going to be loosing water as well that way. Some water goes in from time to time if you open the door and you’re got a stuffy room. Basically it’s because there’s a dynamic equilibrium going on with some of the ice losing water molecules as they gain bits of energy.

The same process actually happens in reverse to form snow flakes. The snow flake is actually formed by this process known as sublimation. Water vapour sublimates to form ice crystals directly without going through a liquid otherwise it would be little balls. It goes straight to form ice crystals and you get the beautiful crystals in snow flakes.

No, I don’t think flies do go on holiday, they don’t migrate. Flies only live for a maximum of two months but usually only about 15-24 days. There’s a possibility that some of them might hang on until winter but they generally do much better when it’s warmer. They can survive over winter and that’s actually another stage in their lifecycle which is as larvae or pupae. What happens with flies is they will lay eggs which hatch into larvae, otherwise known as maggots, which is lovely. They will be alright when the temperature drops and they’ll hang around in food and faeces and things like that. Lovely. If you’ve got a pile of horse manure in your garden they might hang out there.

The larvae grow and then they will pupate so they will wrap themselves up in a tight little packet which will then sit around and survive the winter. That hatches into an adult. So the ones you’ve seen in winter you’ve notice are quite slow. They don’t fly so quickly – much easier to swat. They’re really the ones from the tail-end of the summer population waiting to regrow again in the spring time.

No one actually knows what preceded the Big Bang. All we know is that when the Big Bang happened there was this massive amount of energy in a tiny amount of space. It appears that space itself has been expanding since the big bang so before then as far as we know there was no space. So we have no idea what was going on before the big bang.

Whether all of the mass all in one place at the big big should have created a black hole, or whether we would know if it did, I'm not sure.

It’s a very good question and you‘re absolutely right and there are pigments that animals use to attract mates. That’s generally what it’s all about. These are molecules that are quite costly to create. Not to mention the fact that you also look more obvious to things like predators. This was a question that someone, a guy called Geoffrey Hill looked at. He’s from the University in Alabama. He looked at house finches that grow colourful feathers in yellows and orange and reds using carotenoid pigments. Similar to what Dave was talking about earlier. What he did was he actually fed a bunch of house finches with these types of pigments in water. He fed half of these birds lots of food so they were nice and happy and were doing great. The other half he restricted their diets, which wasn’t very nice. Basically he wanted to know what the difference was when they did and didn’t have enough food to eat. As you might imagine, the ones that didn’t get enough food were much more drab than the ones that had lots of food who grew lots of night, shiny colourful feathers. That’s a really good way of showing to us that yes, producing pigments is expensive in food and if you haven’t got enough food to do that then you tend to not be able to produce such brightly coloured feathers.

That kind of image was probably from a scanning-tunnelling electron microscope on which you get a very sharp point where it’s so sharp it’s probably only got one or two atoms on the end. They scan that very slowly across the surface of a material. With a scanning-tunnelling electron microscope you measure the amount of electric current going between that and the material. You apply a tiny voltage, measure the current between that tip and the surface. You’re actually measuring the resistance of the surface.

There are other similar images where you can measure the force on that tip. You’re basically measuring the force between the end of the tip and the surface at the bottom. If the atoms are higher up the force will go up and vice versa.

Aeroplanes suddenly drop and you feel weightless. You are almost becoming weightless, normally your stomach is being held up by your body, but if your body is falling at the same rate as your stomach wants to fall under gravity all of a sudden the supporting tissues can relax, pulling your guts upwards.

Your guts and your viscera are quite heavy. They’re also hanging inside you so your stomach hangs down below your diaphragm and it’s connected to your guts. Everything is pretty much mobile. If you do an operation on a patient it’s always amazing to think that when we used to open people up for appendicitis or something you can see the guts writhing around themselves. It’s not dramatically fast like a snake pit or something but you can actually see them moving. Everything is mobile, it’s gotta be like that to enable things to move. The guts have to be able to stretch to take in things and shrink again when things move through them. Because it’s all not fixed inside you if you go over a bump when the car or aeroplane drops on the other side of the bump your body is a bit left behind for a little while. There’s enormous number of stretch receptors and vibrations sensors in your guts. That’s why people talk about having a gut feeling for something. It’s very true. A lot of the frequencies that we get from the world around us, the low frequency vibrations are felt in your abdomen and you think you’re sensing them from your abdomen but enormous amounts of that information comes from your gut. It’s a gut feeling, quite literally. Because those stretch receptors get excited when your guts literally fly up in the air with your body moving down around them. As a result it does feel like you have a sort of sinking feeling.

The other reason you get a sinking feeling is because you might get a bit frightened. When an aeroplane suddenly drops you can have that moment of terror, ‘Oh my god, is the aeroplane gonna drop out of the sky?’ What happens then is you get a little surge of adrenaline. Your sympathetic nerve system kicks-in in a very big way. That’s the part of the nerve system that gears you up if you’re going to run away or have a big fight with someone. That produces lots of adrenaline and adrenaline powerfully switches off your guts because the one thing you don’t want to be doing when you’re trying to run away is wasting your blood supply feeding your guts. You want your blood going to your muscles and your lungs every other part of your body when you need to run away of fight. So you turn off your guts and that turn-ff signal gives you that sinking feeling or the butterflies you get in your stomach so it could be possible a combination of the two effects, I reckon.

If the sides are just made of solid ice then it will behave just like a box made of anything else or made of stone or anything. Slowly over time it will cool down to the same temperature as the air around it. However if you had a box of ice filled with water then instead of the water cooling down when heat is taken out of it from the cold environment outside it will create ice. Slowly the water inside it will freeze and as long as there’s water in there that water can’t be much below 0 degrees centigrade. If you had a box of ice full of water then it would be zero and as soon as it freezes then it could get below that.

I don’t think so. I think the point is they’re not doing so well anyway because they’ve got less food. In nature I suppose if they did want to live longer by not having such fancy feathers it might give you a bit of a helping hand. That’s something I think we need to study as well because I think that guy was keeping those creatures a bit hungry. I don’t suppose they would have lived as long!

It’s possible that these stingrays were after food because they do tend to get fed a lot and they could have been sniffing around for that but there’s also been thoughts that similar creatures to the stingrays which are the sharks, because they’re quite closely related, might possibly have the ability to sniff the air. There was a study in Russia in 1994 about oceanic white tips which are quite dangerous sharks, not very dangerous but quite dangerous that go through open ocean. They were seen to sniff above the surface of the water, a similar thing in great white sharks. The scientists looked at this sensory part of their snouts and they think there is a possibility they were actually detecting scents in the air that would move more quickly in the air than in water. Volatile chemicals will disperse much more quickly so perhaps they were doing much better than their competitors at smelling things like dead whale carcasses that wouldn’t be so smelly underwater.

There are a number of reasons for this. One of them is that carbon dioxide dissolves really quite well compared with nitrogen. Nitrogen will not dissolve. It’s very insoluble, you have to make nitrogen work quite hard to dissolve and that’s why when you get the bends after you surface quickly from diving it’s the nitrogen that bubbles out of your blood and causes the bends because it just doesn’t want to dissolve. Carbon dioxide does. The other thing that carbon dioxide does when it goes into water and one of the reasons it dissolves quite well is it reacts with water to make carbonic acid. So CO₂ plus H₂O goes to H₂CO₃, that’s carbonic acid and that dissociates into H+ (that’s the acid bit, the hydrogen ions) plus HCO₃^- bicarbonate. When you have acids in a liquid acids taste liquidy. So you get this very nice lemony flavour added to the drink so the carbon dioxide not only dissolves well so you can get your drinks really fizzy and get your gasses in it also means it tastes nicer and you can get lots of gas dissolving so it comes out gently in the drink. It stays fizzier for longer. Also it’s free. You can get it from the brewing industry, yeast produces it and you don’t even have to purify it. You can just get it off the yeast.