Why do Cats Have Vertical Pupils?

We put Allan's question to physics expert Caroline Steel... Caroline - So, in a kettle, you have a heating element at the bottom and that heats up quickly to actually above one hundred degrees. So the first thing to heat up in a kettle is the water around the heating element. This hot water around the heating element forms tiny little bubbles which then rise up through the kettle, but as these bubbles rise, they rise into an area of colder water. So the bubbles cool down and condense and kind of implode, and the bubbles sort of slaps against itself making a really loud noise.

But as the kettle heats up throughout so all the water inside the kettle is one temperature. As these bubbles form and rise through the water they don't reach an area of colder water, so they actually make it all the way to the surface and then they pop on the surface. But this popping sound on the surface is a lot more gentle and quiet than the sound of the bubbles kind of imploding on themselves within the kettle.

So, if you watch your kettle boil, as it's making a loud sound and coming up to boil you'll see lots of tiny little bubbles in the main body of the water, but you won't see them reach the surface. And then once the kettle has reached boiling point and these bubbles make it to the surface, you'll see them expand and pop but that popping noise is actually quieter than the imploding bubbles in the main body of the water.

We put Omkar's question to Judith Croston... Judith - Well the answer to that is yes. So the questioner is right. If we think about aliens that were say living in the Andromeda galaxy. So the Andromeda galaxy is our nearest galaxy and it is a few million light years away. And so what that means is that any signal that those aliens could measure, it would have to travel at the speed of light to get there. So it would have taken some number of millions of years to get there so what they would be seeing would be prehistoric creatures wandering around on the Earth.

Chris - Doesn't that presuppose that the light hasn't spread out so far that they wouldn't be able to see a dinosaur?

Judith - There are a couple of problems with that. One of them is that, obviously, the sorts of telescopes we have are nothing like good enough to be able to see the prehistoric creatures on planets in the Andromeda galaxy - so that's one problem.

And so when we think about trying to hunt for aliens, we try to think about the sorts of radio signals, we think about technological society. So the earth has been only sending out signals that are likely to be detectable for sort of a hundred years so that's one thing and that's if we think about aliens in a different galaxy.

But I think perhaps what the questioner has missed, or at least isn't in the question, is whether the aliens would have to millions of light years away. Because, in fact, we know of plenty of planets that are a lot closer than that. There are actually, I think, about seventy five known planets within fifty light years. So if there were aliens on one of those planets, then maybe they would be listening in to signals we were sending out, fifty light years away they might be listening to the Beatles on the BBC or something.

Chris - They've got reasonable taste then?

Judith - We don't really know. This light travel time thing is a really important thing to take into account if you're trying to figure out what we can see from alien civilizations and what they might be watching.

Chris - So in summary: the light is spreading out, it's spreading out at the speed of light and, in theory, they could pick up that light, they could interpret what that light came from and the would, effectively, be seeing prehistoric Earth, if they were that far away. But they may be much closer and they may even be watching Neighbours?

Judith - Yes, absolutely.

Chris Smith answered Martin's question... Chris - Well the answer is that the way your body develops when you're an embryo, it starts off as a flat sheet of cells and then another flat sheet of cells forms underneath that, and then the whole thing rolls up rather like a tube. So you get a tube inside a tube. If you imagine two plastic plates laying on top of each other and then the edges curving round to meet in the front, the inner tube is your gut tube, and the outer tube is you skin. And along that length the body divides itself up into segments - a bit like a millipede - and those segments are running different genetic instructions and they also have different spinal nerves coming out of the central nervous system that's developing that supply them.

So your body has a pattern and the inputs from those nerves therefore signal where on the body surface and, to a lesser extent, where on the body insides a signal is coming from, so the body can localise pain reasonably well. It's much better at doing it on the outside surface of the body a) because there are more nerves there, and b) because it's more helpful to you to be able, for instance, put your hand in your pocket, feel around and found a two pence coin than being able to do that level of precision with your innards.

But it is useful to know when things are upset inside because, obviously, if you're uncomfortable or if you have stomach ache or something like that, knowing where the pain is it can give you help as to how to make it better. So you do have the ability to do that but you don't do it with the same level of precision.

And a good example of this is when people classically have a heart attack, or angina chest pain because of cardiac pain, they don't just feel the pain where the heart is, they may feel the pain in their neck, they may complain of pain down their left arm. Or, if they're one of the rare individuals in the population who have their heart on the opposite side of the body, they may actually complain of pain going down their right hand side.

Caroline - So I understand that we need to feel where pain is coming from inside us and that helps but why can't we feel any pressure at all because when we digest food we don't feel that at all?

Chris - We do a bit when your tummy rumbles, and you get nervous and you have butterflies in your stomach. That sinking feeling, a bit like before you come on this programme, is because your 'fight or flight' response, your sympathetic nervous system, kicks in and it suppresses the parasympathetic nervous system which is part of your nervous system which makes you rest and digest and it strongly deactivates your intestines. And that shuts down your stomach and shuts down your guts and all the muscles relax, and that sinking feeling is everything going 'urrgh' as it turns off in order to prepare you to run off. So you do have a degree of sensation but your brain is also very good at subtracting from the signals being presented to your consciousness everything which you have got used to. Which is why you put your cloths on this morning and are probably aware of pulling your jumper over your head but then pretty quickly you stop noticing "I'm wearing a jumper." But if your bring it to mind, suddenly you'll start noticing it again. And you think 'ahh' because your brain is mentally subtracting in order to prevent information overload.

We put Paul's question to Judith Croston...

Judith - Okay, so to the answer to this is no, but it's quite interesting why. So I should start perhaps by briefly explaining what a neutron star is. So, just as a reminder, a neutron star is one of these really strange stars. You take an ordinary star, so you could say take all of the matter in our solar system and squash it down to an incredibly high density so you could fit our solar system inside the M25, basically. Neutron stars are about ten kilometers in size but they all the matter inside them that an entire solar system could have.

Chris - Like one teaspoon full weighs millions of tons?

Judith - Yes. A teaspoon full could weigh the same as Mount Everest or something so they're very strange. The physics of them is really weird. They have very strong gravity but the important thing is the density and the pressure in the centre of neutron star is so incredibly high we just don't understand how physics work in those conditions, we can't do experiments in the lab.

So there are quite a lot of exotic theories about what could happen in the centre of a neutron star, but one thing that couldn't happen is the creation of a new chemical element similar to the sorts of things we have on the periodic table because chemical elements have protons and neutrons bound together and then they have orbits of electrons spinning around. And what happens in a neutron star is that as, when the star forms the protons and the electrons that were there, and the nuclei from the star, they combine together so the electrons and the protons combine together to make neutrons. So there's no space to have these orbitals of electrons spinning around so you couldn't make a new element like that.

On the other hand, there are theories about all sorts of weird things that could go on in the centre of neutron stars because the neutrons themselves might break down into quarks, which are the little particles that you get inside neutrons and protons. And then those quarks can do quite strange things and then combine together in various ways. So people are quite interested in trying to figure out the physics of neutron stars because it might tell us something interesting about those sorts of exotic states.

We put this to zoologist Max Gray... Max - So there's a whole bunch of things you could do: making sure you've turned your lights off; don't leave the fridge door open too long when you're looking in the fridge; spend less time in the shower. There's lots of things that will make a tiny difference but the small things that won't necessarily change your life that much but that could make the biggest difference is what you choose to eat. The amount of meat you eat is probably on an individual basis, per person, the biggest single contribution to how much environmental impact you, as a person, have. I'm not saying everybody needs to go vegetarian or, indeed, needs to give up meat but just eating less meat. Loads of people eat meat for two meals a day, particularly will have meat during lunch and during dinner.

Chris - Why is meat so bad Max?

Max - It's because of the amount of energy that is required to produce meat compared to producing vegetables, for example. Energy initially comes from the Sun and gets absorbed by plants through photosynthesis. They create proteins and sugars and that's where you get the food from. The efficiency is better going from sunlight to plants than if it has to go from sunlight to plants and then be fed to an animal. The energy isn't transferred a hundred per cent efficiently and so it takes a lot more energy to get to a plant. And it's factored into the amount of water that is required to keep cattle, the amount of energy that goes to growing the crops to produce cattle feed, and that's before you even count the amount of methane that cows burp into the atmosphere.

Chris - But not all meats are equivalently bad are they?

Max - No.

Chris - I think beef is the worst culprit.

Max - Beef is by far and away the worst - followed by lamb, followed by pork.

Chris - So what's best - what can I eat with less.

Max - Chicken is roughly on a par with hard cheese. So cheese.

Chris - It tastes better though!

Max - Well, I don't know. I'd pick cheese over chicken most days, myself.

Chris - You prefer cheese?

Max - Who doesn't! If you're lactose intolerant, I suppose, they get a pass.

We put Lucille's question to neuroscientists Heidi Solberg Ã~kland... Heidi - I think there are lots of advantages to being raised bilingually. I'm a bilingual myself. I was born and raised in Norway but I learned English in school and now I'm a Norwegian English bilingual. But imagine if I was born in England and I had an English dad say, then I would be able to talk to my family members. If I knew Norwegian I would be able to visit Norway to talk to people, to engage with that culture. I would be able to work there. I couldn't really do my work now if I didn't know English I couldn't be doing science. These are things that are kind of a bit more common sense.

But if we think about what the disadvantages and advantages is in terms of the brain. For you Chris - you're a monolingual English speaker?

Chris - Yes. Heidi - So if you think of a thing that you usually put on bread. It's usually made of fruit or berries and sugar - what would you call that?

Chris - Jam.

Heidi - Jam, exactly. So you just have one word for that thing. So in your brain, when you think about that concept, if you want to say what that concept is then you say jam and that's it, that's easy. For me, if I think about this thing, I have to choose been two different words. So I could either say "Jam" or I could say "syltetøy," which is the Norwegian equivalent of that. So we know that actually when I was speaking English, my Norwegian is still running in the background so this creates some kind of a conflict, interference.

Chris - Conflict, yeah. Is there a latency effect as in if I record how quickly I get the word for jam and how quickly you get the word for jam. The more languages you learn if you've got to pick through more, does it take longer for your brain to sort through and say right, I need the English one?

Heidi - I would think yes, but I would have to go and l look that up. But I do think that that's the case. And also, what happens is - well this is something I notice a lot of the time - is I find it more difficult sometimes to think of the words. I have the word at the tip of my tongue but I can't access it.

Chris - What language do you dream in?

Heidi - Since I live in Cambridge now and I'm speaking English all the time, I probably dream a bit in English as well.

Chris - With what accent? No it's funny because this person wrote to us and said he downloaded, from America, the entire back catalogue of the Naked Scientist and we've got something like a thousand episodes of the programme now. And he said he did the podcast equivalent of a binge - sort of doing many episodes per day - and he said I knew I'd overdone it when I began to dream with an English accent. So I just wondered if.?

Heidi - Well, given that I'm mostly using the British accent when I'm speaking in English, I probably would dream in a British accent.

Chris - Jolly good!

Heidi - Yeah, jolly good.

We put this question to space scientist Judith Croston...

Judith - Okay, yes. So the questioner is right. There is a black hole in the centre of our galaxy and black holes are these very strange places in space where, essentially, no light and no matter, nothing can escape. An awful lot of matter has been squashed down - a bit like the neutron stars I was talking about before but even worse. Everything gets squashed down really, really far so there is a lot of gravity to do with a black hole.

But what's interesting really is that black holes are only weird if you get close the them. Once you're a little bit further away from the black hole, they just behave like any other star that had the same amount of mass. So actually, although in our galaxy we have stars spiralling around, we have these sort of beautiful spiral arms. But it's not the black hole at the centre that's actually controlling that, it's actually the gravity from everything else in the galaxy. So the things that the stars are orbiting around is not really the black hole, it's all the stuff in the galaxy. And there's actually much more stuff in the stars, and even more stuff in the dark matter. So it's actually ninety-five per cent of the mass in the galaxy is this strange, invisible dark matter and that's actually what controls everything moving around.

So going to the bigger picture - talking about could there be a really monster black hole and all the galaxies were spiralling around a really monstrous black hole. Well firstly, the biggest black holes we know about are about a billion suns and that's still a lot less matter than in one single galaxy. So when you think about how much gravitational pull that will have, even the biggest black holes we know about couldn't make an entire galaxy move around.

So again, when you think about what's happening and the way that galaxies are moving in the universe, which is something we can actually measure quite a lot - we can do lots of different observations - in fact again, it's the dark matter that's out there that's really controlling everything - it's not the black holes. It's pretty impossible to imagine a black hole that would be big enough to be able to control the movement of whole galaxies.

We put Martin's question to Caroline Steel...

Caroline - Black is just the absence of light really. It sort of seems to be a colour to us because we can differentiate it from other colours, but a black object is actually an object that absorbs all colours of the visible spectrum, that's all frequencies of light. So say this black microphone absorbs red, blue green, all of the colors, so to us it just looks like the absence of colour, which is black. So when we shut our eyes we see black as no light's getting in.

The opposite of this would be white. A white object reflects all light and when we can see all frequencies of visible light, they combine to make sort of a white colour, although colour would be a slightly misleading word.

Chris - We had Pulickel Ajayan on the programme about 2008, I think it was. And he published this paper that said the new black, and said that he'd made the blackest substance ever made. And he sent me a picture of it and I actually had this disc of this stuff and the industry standard of what we call black. And his stuff, he says, is thirty times blacker than black. It seems paradoxical that something could be blacker than black, but it really was dramatically darker.

And their technique was exactly as you say Caroline. The reason something has a colour is because it's reflecting light off it's surface. His approach was well if we want to stop light being reflected off a surface - how do we do it. They made a layer of carbon and had this bamboo like forest of carbon nanotubes sticking up like bristles off of the surface. And their rationale was any photons of light that go in there will ricochet around and just get lost in these carbon nanotubes and never come out. It just basically turns the light into heat in the surface, and that's why it's so black. But no, an amazing discovery.

We put this question to Max Gray...

Max - Yes, yes the do. Any single individual of any species is going to have the same DNA throughout its entire lifespan. What changes in butterflies is, particularly between a caterpillar and an adult butterfly, is they go through metamorphosis. And during this process there's a hormone which is found in most insects as they change from a larvae into an adult, which is called ecdysone, and that hormone triggers metamorphosis and it changes how DNA expression works.

So all of the cells within the caterpillar will start to produce different proteins and slowly that will cause a mass physiological change because the DNA is being expressed differently. It's creating different proteins and all of the cells will change, and what triggers that, what starts the processes of hormone being released is often an environmental factor. And a lot of caterpillars, as you might know from everybody's favourite text book "The hungry, hungry caterpillar," it'll happen when they're well fed. They'll will eat, and eat, and eat, and eat until they have enough food to be butterflies, which are basically just there to breed. The butterflies tend to live very short periods of time and most of the butterfly's lifespan is a caterpillar.

Chris - And so the bottom line is that the DNA remains constant but, under environmental and hormonal influences, you change which genes are turned on, to what extent, and where. And that's what drives the metamorphosis and also drives the behaviour?

Max - Yes, absolutely. And it's true in all manner of insects. It's not just caterpillars and butterflies.

Caroline Steel had a breeze answering this question...

Caroline - So the short answer is yes you can. When the wind turns a blade of a wind turbine it does in fact lose speed because of the sheer effort it takes to turn those blades. Now this isn't something we really need to worry about. I know there's been some speculation that this could change climate and this would have vastly terrible implications but, realistically, with the number of wind turbines we have at the moment, that decrease in wind speed is actually, completely, negligibly, unimportantly, small. Unless you're in a wind farm, in which case you don't want to put wind turbines downwind of wind turbines.

But, anyway, we can work out an efficiency for them by looking at how much energy they get out of the wind, so how much does the wind slow down versus how much energy they can output. And it actually turns out that wind turbines are relatively inefficient because there's a lot of friction between the blades and the rotor in the middle. So they have an efficiency of. it changes hugely but about forty per cent would be an okay guess. So, yes, in comparison to other energy formats wind turbines are fairly inefficient but, luckily, we've got a lot of wind so it doesn't really matter.

Chris - But a solar panel's only what twenty/twenty-five percent efficient?

Caroline - Yeah. So solar panels are fairly inefficient as well. That's something we have to live with when we're using forces to power things really.