Okay.  In a very simple sense, they do stick to protons as much as they can.  They're attracted to protons and so, they form atoms.  So an atom is essentially an electron stuck to proton.  What you really ask is why don't they get any close than they do?  It’s all basically to do with the fact that electrons – in fact, everything- has wave properties.  And the electron’s wavelengths are about a  similar sort of size of atom and that’s the reason why atoms are that sort of size over the order of the wavelength in electron.  And so, you can't really compress a wave any smaller than one or few wavelengths.  And so, the electron can’t get any smaller than that without actually changing its properties entirely.  So, it can't actually get any closer to the proton in the centre of the nucleus than it does and so, it’s stuck as close as it can.  You can cause – if at very high pressures-, you can cause electrons essentially to react with protons and turn into neutrons and this is what happens in neutron stars.  A neutron actually isn’t stable just lying around, in the atmosphere or in a vacuum.  It decays in about 14 minutes into an electron and proton sort of forms into a hydrogen atom.

Dan -   I'm just wondering why car wheels sometimes appear to be going backwards when you view them under streetlights sometimes?

Chris -   I think I've seen it.  As you're driving along, the car next to you is accelerating away and it looks like their wheels are going backwards in the streetlights, illuminating the wheels of the car.

Dan -   Yeah, that’s right.

Chris -   Yeah.  It’s actually a stroboscopic effect.  If you've been a fan of Westerns, if you were a big John Wayne fan and you used to watch those early Westerns where the cart would pull away from the scene and the wheels would initially go forwards and then appear to start going backwards.  Did you see those?

Dan -   Yeah.  I've seen that before.

Chris -   Yeah.  It’s the same phenomenon.  In the case of the cart, it’s because the camera is taking X number of frames.  In other words, pictures every second.  In the case of the car driving down the road to where next to you, it’s the streetlight flashing on and off about 120 times a second because mains electricity is 60 hertz.  So the light goes on and off 60 times a second.  So as a result, you're seeing 60 flashes or illuminations of the car wheel per second. Now if the car is accelerating, if you imagine the – say you drew a line on the car wheel, a chalk mark and you watched that go around, it would go around in a circle.  But you only see it in the dark when it’s illuminated by the street light.  Now say, the street light flashes on, you see the chalk mark pointing straight upwards, the light goes off and the wheel turns around a bit, agree?

Dan -   Yes.

Chris -   Light comes back on, the chalk mark is now in the new position, agree?

Dan -   Okay.

Chris -   Now as the car wheel speeds up the distance of the chalk mark makes it around the wheel will change according to how fast the car is going, yeah?

Dan -   Yup.

Chris -   There will therefore be a speed at which the wheel will go when it doesn’t look like it’s moving at all because the chalk mark is starting going all the way around and finishing before the light comes back on again.

Dan -   Okay.

Chris -   Once it speeds up a bit more, the chalk mark will go right the way around and then a bit further.  So it will look like that it was going faster, faster and faster.  Eventually, you’ll get to a speed where it’s actually going right around and back on itself again.  So it looks like it’s actually going backwards a bit because it’s doing more than one complete revolution a bit more.  So it looks like it’s going backwards and it’s because of acceleration.  Once it reaches the constant speed, that effect would stop.  But it’s stroboscope, that you're seeing flashes of light, illuminating the wheel and your eyes sees it, doesn’t see it for a fraction of a second and then sees it in the new position.  And when the speed is right, it looks like it’s going backwards.

Catherine -   I just got a quick question for clarification really.  It has been discussed on your show about genes being turned on and off through things like genetic engineering and I’ve got a picture in my mind a sort of a big double helix with old-fashioned light switches sticking out the sides of it, which I seriously doubt is correct.  And I was just wondering what is actually meant by genes being turned on off.

Kat -   That is a great question and actually, your mental image is a fairly good analogy for it.  So, if you think about – imagine a long string of DNA.

Catherine -   Yes.

Kat -   Now, a bit of that will be the actual gene and genes are basically instructions that tell a cell to make a particular protein.  So you have kind of the recipe bit.  And then around that, you have sort of instruction bits.  So, these are regions of DNA that attract proteins that come and sit on them and tell the gene to be on or off.  So these are called transcription factors and they attract the kind of molecular machinery that actually churns through the instructions and tells a cell to make a particular protein.  So, you have all these different proteins sitting on different bits of the DNA and some protein’s transcription factors tell a gene to be switched off and some transcription factors tell a gene to be switched on.  So really, you do have these molecular switches.  You also have another aspect of that ,and Chris mentioned this a little bit earlier on the show, is that you have kind of things called epigenetic switches as well.  And these are things that are over and above what’s in the DNA.  You get little molecular, almost like post-it notes or tags stuck to the DNA and stuck to the proteins that are wrapped around the DNA that have more information about when a gene should be used, for example during development.  You know, you should turn on this gene for a bit while you're making hands and then turn it off again or should this gene be permanently switched off or permanently switched on.  So really, there’s this whole array of little molecular switches that are telling the DNA to be on or off in a particular cell at a particular time.

Catherine -   Very clever, isn’t it?

Kat -   Yes, it is.

Dave -   Can't you also get bits of DNA which are folded up so the chemistry can't get at it.

Kat -   Yes.  So, a lot of these sort of epigenetic factors.  When a cell has decided that this gene should be permanently off, that gene gets all compressed up and squished up so that the molecular machines can't actually get to it.  So we know that genes that are off are really compressed and wrapped up really tightly.  Whereas genes that are very actively used are much more open so all the machines can get into there and read the genes.

Well the answer is that some bacteria don't actually get to be bad for you because they infect you.  They actually put things into the food that are toxins and the toxins are not broken down by heat.  So, the bacteria multiplying in the food leads to the accumulation of toxins in the food which will then make you ill even though the bacteria may be long gone by reheating the food.  So if you keep cooling and warming the food, the food might spend enough time at a certain temperature which encourages the bacteria to grow and put toxins into the food whilst not themselves actually really posing much of a threat.  That’s one way.  Another way is that if you keep on warming up and cooling down food, some bacteria will just end up flourishing and they’ll go from being at very low level in the food, where they're not growing very fast because the temperature is low, to getting to a very high population in the food where that might be an infectious dose.  So to catch Salmonella for example, you actually need to eat about a million organisms, 106 particles of Salmonella.  That’s an infectious dose.  Other bacteria infect you at much lower doses.  So it really depends on what the pathogen is and what the way in which it makes you sick is – but the bottom line is, if food spends time at higher temperatures, there’s a higher chance that bacteria will grow and therefore, make you sick.  So, the best advice is to either cook it and eat it, cool it and eat it, but don't keep reheating it because that could be bad.

Temperature is basically a measure of how much energy each particle has got or each direction a particle moves in.  And so, you can pretty much all the energy away from something and you can't take any more energy away, and so, there’s a minimum temperature as an absolute zero.  But certainly, in any normal idea of physics, anything we know, definitely there’s no maximum amount of energy you can give particles.  So there’s no maximum temperature.  You can keep on giving more and more energy and the temperature will keep on going up. There could possibly be a maximum temperature.  You might find a maximum energy, you can give things due to some bizarre bit of quantum mechanics, but as far as we know, we haven’t found this solid one yet.

Chris - The answer is both yes and no actually.  When you give vaccines to people, what you're aiming to do is get the immune system to respond so that it can recognize that pathogen in the future and protect you either with antibodies or cells that kill viruses in cells.  Now, one way of vaccinating people is what’s called Live Attenuated Vaccine.  This is where you grow viruses in culture for many generations and through the effects of mutation, they lose the ability to make you ill, but they nonetheless remain infectious.  So, with the MMR, Measles, Mumps and Rubella, for example, you put the virus into the person.  It doesn’t cause severe disease, but what it does do is to display to the immune system the entire repertoire of viral genes, viral proteins.  And what that does is it makes a very broad immune response, involving making both antibodies and cells that can attack virally infected cells.  That way, your body is very powerfully primed to recognize and prevent you from getting that virus in the future.  The problem is that when you go into that state of infection, what it does is to release large amounts of a signalling hormone called interferon, Alpha interferon in fact.  And what that does is put all the cells in the body into this antiviral state where the cells are undergoing surveillance.  They increase the surface markers, they displace the immune system so that they're more likely to get killed if they’ve got a virus in them, they degrade genetic material that they think might be viral, and they become much harder to infect for viruses.  Now that means if you've had one virus, that’s attenuated vaccine, about a week or two before, your body makes load of this interferon.  If you then come along and then try and infect yourself with another attenuated virus, for instance another vaccine, it won't work very well because it doesn’t get into the cells, and the body kills it really quick before it has a chance to prime your immune system.  So live vaccines, if you don't have them at the same time, but you have them all together is a bad thing to do.  Having them all together is fine because the immune system works by discriminating very powerfully between different epitopes that different viruses display anyway.  So that’s not a problem.  For the present situation we’re in now though, people are asking me, “What about flu vaccines?”  Because lots of people had a seasonal flu vaccine but then they're also saying, “Well now, we need to have a swine flu vaccine.  Will the fact that I had the seasonal vaccine about two weeks ago make a difference for me having the swine flu vaccine now?”  And the answer is not in that circumstance.  No, because the flu vaccine is a killed vaccine.  You're just putting in bits of dead virus, shrapnel if you like which the immune system then learns to recognize.  This doesn’t trigger the same interferon response so it doesn’t make you feel ghastly in the same way.  It doesn’t actually prevent you getting infected with other viruses in the same way.

Dave -   Is this interferon response, the reason why I still feel really quite shattered now, two weeks after I had the flu?

Chris -   Yeah and the reason that flu makes you feel so rotten, despite the fact that the virus is only confined to your respiratory tract, nose and throat, and sometimes lungs if you get a very severe infection, you probably had symptoms that were nonetheless across your whole body.  Muscle aches and pains, tiredness, very bad headache, temperatures, just feeling ghastly.  That’s because  of these hormones, the interferons that the body produces in response to the infection which then turn all of your cells into this very antiviral prime state.  So, exactly right, yeah and that’s why after some vaccines that do provoke lots of interferons to be released, you have a day of feeling a bit rotten.  It’s not because you’re infected, although you might be.  It’s actually the interferons – it’s your body’s own hormones that are making you feel like that.

We have actually looked at this in the past and the answer is actually, yes.  Because  E=mc², Einstein’s famous equation, (E) energy equals (m) mass, times (c), the speed of light squared.  So, if you increase the energy in the system then the mass must also increase.  The Sun is adding energy to the Earth’s system in the form of chemical energy; this arrives as light and is converted into chemical energy by photosynthesis.  Therefore, the Earth is gaining a little bit of weight in the form of the entrapment of that energy within plant chemistry.  But, compared with the 40,000 tons of dust and material that rains in on Earth from space every year, it’s quite literally a drop in the ocean. So, on the whole, the Earth is gaining a bit of weight as plants in the biosphere capture energy coming from the Sun. 

I think that very much depends on the chemistry of your batteries.  A battery is essentially a chemical reaction which is split into two halves and the only way – and let’s say you got part half A and half B, the whole lot’s got to happen to be driven in any way that can happen is quite passing electron through your circuit.  And eventually, the battery runs out because you run out of all the chemicals you need for the chemical reaction.  Now, basically you're saying, if we apply a large voltage and carry on pushing electrons through the battery, what’s going to happen?  That would depend on what other the chemical reactions go on to move charge through the electrolyte in the battery.  Normally, that’s often quite inefficient.  If you’ve got have something like a lead acid battery which is symmetrical, it will just start up in the wrong direction.  Certainly a very simple that acid battery will – and so, it will turn into battery but pointing the wrong direction.  If you have other chemistries of batteries, it could cause all sorts of havoc and it will depend on the exact chemistry.  It will certainly become a very high resistance.  It will work for a bit but eventually, it’s going to run out of – it will either stop or it could do all sorts of strange things to your battery, it’s certainly going to damage a rechargeable battery.

The answer is yes.  It’s the death of the star.  The star’s gravity is what holds things in orbit around it and if the star blows itself to pieces, then it will completely decimate the material which is in that system and that would destroy unfortunately any planets.  Eventually, our sun will blow up like a red giant.  The one that should go supernova, I think it’s a bit too small but it will cook us but it won't blow apart.  But there are stars which do blow themselves to pieces and they could take things with them.

Chris - If you have a gas, which is, say, in an aerosol, says the contain you’re going to spray into your armpit with your deodorant, there’s a gas under pressure in there.  When you spray it in your armpit, it feels very, very cold.  What’s happened?  Well the gas has expanded.  I thought about simply if you imagine there’s some kind of piston, inside the aerosol can, when the gas expanded it effectively pushed on the piston, it’s done some work, let’s say.  If something has does some work, it must have less energy, after it’s done the work than before it did the work.  Since temperature is proportional to the energy in the particles, if somebody’s got less energy, is therefore going to lower the temperature so the temperature must fall and that’s why we think that when a gas expands, the temperature goes down.

Dave -   OK.  And now this is actually very related to why mountains are cold.  Okay.  The temperature of things on Earth is sort of balance between the amount of heat which is getting either from the sun or from heat moving around the world and the amount of heat it can lose by radiating into space or radiating anything at room temperature, radiating heat and infrared really quite well.  And so, basically the only things which can absorb sunlight very well tend to be at the ground.  The atmosphere is transparent so the heat is going into the ground and heating it up and then that heats up the air above it.  And now, the tops of mountains are very, very small.  So basically, what’s the temperature of the atmosphere at 30,000 feet?  10,000 meters, or 9,000 meters?  And the reason why that’s very cold is because if you have pockets of air which is being warmed up on the surface of the Earth and then it lifts up by convection, it’s moved upwards,  the pressure drops about half the pressure it was before, which means that gas expands and as gases expand, they get cold so the air gets very, very cold.  So, the air around the mountain is very, very cold and also anything which is pointy like a mountain has got lots – can emit infrared light in lots more directions and the flat thing has got more surface area compared to mountain sunlight which hits it.  So it cools down better during the night and emits light into the space very much better so it tends to be very cold. 

Okay.  There’s a secondary effect.  The world is far more complicated than you’d like to think.  That tends to be because cold air falls.  So, the valleys at low places on average are warmer.  But if you got somewhere which is high up and the air can cool down on the tops of mountains, it’s then denser around it and it falls downwards and if it’s not falling very far it doesn’t compress very much, doesn’t get very much hotter so you get, locally very cold air is in bottoms of valleys but globally it’s warmer low down and colder higher.

Why shouldn’t you be able to see the moon during the day?  The moon is orbiting around the Earth.  It takes the moon about 28 days to go right away around the Earth, come back to where it started.  The Earth turns.  Obviously, it does a complete evolution in one day, 24 hours, since so you would expect to see the moon go across the sky every day, pretty much.  At some point so it might not be visible on some occasions so much but it should be there.  So that’s not so unusual

The answer is they don’t.  It’s basically good old-fashioned quackery as far as we know.  There’s this idea that if you wear copper bracelets or magnetic bracelets in some way, it can help with things like arthritis.  Research has shown that this is absolute bunkem  There isn’t really any truth in there.  There’s some recent results published in October where they did a rigorously controlled trial looking at magnetic or copper bracelets compared to plastic bracelets so people didn’t know what it had, and really they found that it was just a placebo effect if you tell someone they’ve got a magnetic bracelet they think it’s doing them some good but there’s actually there’s no science supporting it.  But it’s a multimillion-pound industry so, you know, maybe worth it, if you’re making them.

Well, Les, if your kettle is open at the top than it would have evaporated a bit of water so it may have lost weight purely through evaporation but if the kettle is a sealed unit then E=MC² says, If you add energy to the kettle when it’s hot, therefore, it should weigh slightly more than the water’s hot than the water is cold.

You won’t see the same photons of light, the individual particles of light but the properties on either side of the earth are going to be very, very similar.

Kat -   I think you have to give up some socks as a sacrifice to the “God of Washing”.  I don’t know.  Maybe they didn’t end up as pairs in the washing machine when you put them in.

Chris -   I’ve got a theory of this actually.  I think what happens is that socks, very often, glue themselves to the inside of the machine so you remove the washing but you might leave one glued to the top so it gets separated from its counterpart.  You then go to the washing, hang washing up, process it, put it all back in your bedroom all ironed and stuff and now you got an oddsock.  You find the other one and that gets processed separately but by then you’ve got this odd sock in the bedroom and you think “Oh I must have forgotten to wash this one” so I put back in the wash.  Its counterpart is probably – or in the wash then the other one comes back from the wash having been found later but by then its counterpart is now in the wash and the two remain separate forever.  I think that’s what it is. 

Kat -   (Laughing) Yeah that’s the same circulating odd socks.

Chris - Actually I just got an email from Drew Merchant and he says 'I had to take apart my wasjing machine recently and I found 3 socks stuck in the drain tube, so this is where I think they end up'.