Chris: -  The reason we get cold sores is because of a virus.  It’s a virus called Herpes Simplex Virus, HSV.  It’s one of the commonest human viruses.  In fact, about 80% of adults have antibodies to this virus, indicating they've been infected.  James Bond said, “Diamonds are forever.”  Well Herpes is for life.  Once you've got it, you have it for the rest of your life and the reason for that is that the virus exists as what’s called a latent state inside the cells of your nervous system.

Herpes simplex goes into the sensory nerves, the ones that supply the skin for example, and after you’re infected, the virus goes along inside the nerve fibre to the cell body which is a structure where the nucleus of the cell is, and inside that nucleus is the DNA of the cell, and the virus adds its DNA alongside your own cell’s DNA.  So it just sits there inside the cell and periodically, and in response to various stimuli, the virus can come back out again. 

So if you get sun burned, if you get trauma to the skin, if you get rundown, or ill for some other reason, this can all prompt the virus or provoke the virus to switch on the DNA.  In that DNA there are genes that tell it how to make new virus particles and they come back out down the nerve cell to the patch of skin that that nerve supplies, and the virus particles bud off from the end of the nerve, and infects the overlying skin, and you get a cold sore.  That’s got lots of virus particles, millions of virus particles in it, and they're infectious. 

You can then – if you get close to someone else, as in kissing close, you can pass the virus on.

Caroline: -  Oh right.  Okay.

Chris: -   So I guess you want to know why do some people get it, some don't?

Caroline: -   Yes.

Chris: -   We don't know  - because if you do this test, although you can find 80% of people have got it, only about 15% of people have regular so-called “reactivations.”  In other words, the virus only comes back periodically in about 15% of the people who’ve got it, and in an even bigger proportion, it can come back asymptomatically.  You can shed the virus without realising it, in saliva.  So it looks like there’s either something about the virus that makes it come back in some people - there might be some genes that are slightly different in the virus or more likely, is that there’s something different about the people that reactivate the virus much more frequently, and maybe they carry a gene or something that makes them more likely to reactivate it.  But the bottom line is that it’s normally getting rundown or sunburnt, or trauma to the skin that discloses the virus.

Helen: -    Wow!  It’s really good question and you've hit on the right point that it’s not just about our taste in our mouths.  It’s also our nose that leads to a sensation of flavour and taste, and we have two things going on.

We have our tongues which have taste buds on them, in little ridges and valleys called papillae, and these are responsible for picking up the four and some people think five main tastes which are bitter, sweet, sour, salty, and savoury or ‘umami’.

There’s not much nuance to those different flavours, but we do pick those up in our tongue, and the rest of the taste that we have comes from smelling the food, from the odour molecules that come off it.  They waft up our nose and essentially, fire nerves signals from somewhere called the olfactory mucosa inside your nose which has receptor neurons and they will tell your brain when you've picked up certain different chemicals in the food.

But interestingly, it’s not all the smell that comes up your nose that is responsible for the taste.  So the reason you can't smell when you have a cold is because your olfactory mucosa gets covered in goo and those receptor neurons really don't get anywhere near to those molecules of odour that they're interested in.  But if you hold your nose, you might have noticed you can still taste quite well when you're eating, and that’s because some of those molecules also go from your mouth through the internal passages, and still find their way to the olfactory mucosa. 

So it’s no good just holding your nose if you don't like the taste of your medicine.

Chris: -   I used to do that.  The medicine for Brussels sprouts actually.

Helen: -   It does help and interestingly, in a 2005 study in the journal Neuron, Dana Small from Yale University led a study where they put tubes up volunteers’ noses.  (I hope they did pay these people well because it does sound like a fairly nasty study.)  One of the tubes went just to the nose.  The other one went back into the mouth and they wafted smells up these different tubes.

They put the people inside an MRI scanner, and showed that different parts of the brain were activated depending on if the smell went to their olfactory mucosa directly or whether it went into the mouth and then sort of wafted back up there. 

It makes sense that essentially, if you're smelling something from a distance, it’s more like, “Oh goodie, there’s some chocolate on the way.  Perhaps I should go find myself some of that.”  Whereas if you're eating the chocolate, you're actually doing other things like preparing your body for a nice hit of fat and sugar that’s going to come along with this chocolate that you're eating.  So it seems something quite interesting is going on in your nose and your mouth to lead to the sensation of taste.

Chris: -   Terrific.  I still say holding your nose works well for Brussels sprouts.  It did for me.

Andrew -   North would generally be determined, I would say, in terms of the rotation of a planet.  So when we talk about North here on Earth, what we really mean is that you can look at the way that the Earth’s rotating.  There are two fixed points.  There are two points on the Earth which never actually move at all and that’s what defines where the poles are on earth.  Now which one’s North and which one’s South is going to be determined by say, you look from the top and you see it going around clockwise, then that tells you which one you’d call North and which one you'd call South.  So that’s going to apply to any planet regardless of whether there’s a magnetic field.  Now of course here on Earth, we do have a magnetic field.  It’s actually not perfectly aligned with the rotation of the planet and as I think you're hinting, sometimes it even flips around.  So the naming of the North and South poles in terms of magnetic fields of course, does come about historically because it was roughly lined up with the way that the Earth rotated, but it’s not a direct physical link, if you like.

Chris -   And this is slightly more speculative on his part, “Would there serious cartographical stress if the earth’s polarity flips around?”  I guess not really, would it?

Andrew -   Well, not for cartographers exactly, but it would have really serious consequences.  I'm by no means an expert, but from my geology courses way back when, I remember that you can find certainly records of these flips and they correlate very well with mass extinctions.  One of the reasons people think this might be is that the Earth’s magnetic field protects us from an awful lot of nasty particles streaming through space.  At the point at which it reverses, [the magnetic field] probably shrinks down to more or less nothing, and then all these particles can bombard the organisms living on the earth and...

Chris -   This is solar radiation.  It’s that solar wind, isn’t it?

Andrew -   It’s the solar wind and other cosmic rays in fact from other sources, and clearly causes major problems for Earth, so we really don't want that to happen and we don't know how much warning we’d get either if it was about to happen.

Chris -   Historically, looking at the records written geologically in rocks, it’s every 100,000 years or so.  But it hasn’t happened for 800,000 years, leading people to suggest that we’re overdue.  There is an anomaly over the Southern Ocean or the southern Atlantic isn’t there, and the satellite ironically was put up to study the earth’s magnetic field and it ended up floating across this anomaly, and got bombarded and it actually got messed up by the very solar radiation, that we’re worried about basting the earth, so yes, a point well made.  Thank you, Andrew.

Chris -  Okay.  What do we think here in the studio?  Helen?

Helen -   My guess is that you should not squeeze the air out because at least that by having the air, the carbon dioxide that’s already been released when you first close it that somehow must help stop more carbon dioxide coming out too.  Otherwise, you've got a sort of vacuum to fill and that the carbon dioxide will quickly come out of your drink if there’s nothing for it to push against.

Andrew -   Yes, I absolutely agree with Helen actually...

Chris -   You sound surprised!

Helen - I am only a biologist!

Andrew -   Yes, exactly.  We can't have biologists answering physics questions!  I absolutely agree.  Basically, there’s loads of carbon dioxide dissolved in these drinks and the fizzing happens when the carbon dioxide is coming out of solution and turning back into a gas, and the rate at which that happens is determined by the pressure against which it’s pushing.  So, you want as high pressure as possible in the vicinity of the liquid to stop the gas coming out of solution.

Chris -   Because you can buy those gadgets that will pump up the bottle again and put some pressure above the liquid.  Some people have said this won't work because it’s putting in air, not carbon dioxide.  But the point is that air is 80% nitrogen.  Nitrogen is really poorly soluble in water.  So for the carbon dioxide to come out and go into the air above the bottle, it’s got to increase the pressure because hardly any nitrogen is going to dissolve.  So if you pump up the pressure even higher above the liquid, it’ll make it even harder for the CO₂ to come out, so I reckon that’s the reasonable strategy.

Andrew -   Yes, that’s right.  You just want the pressure to be as much as possible to stop it coming out of the solution.

...

Chris -   The biggest determinant of keeping the drink fizzy actually is putting it in the fridge, because as the temperature of the liquid rises, it’s ability to dissolve a gas like CO₂ or oxygen for that matter drops.  And therefore, the colder the liquid is the easier it’s going to hang on to its CO₂, so whacking it back in the fridge is absolutely what you’ve got to do.

Helen -   This is particularly relevant because I think there’s been a hatching of spiders in Cambridge very recently.  If I sit in my garden for more than about 5 minutes, I get turned into a spider web.  So, they're doing it at the moment.

Chris -   Turned into a spider web?

Helen -   Okay.  One gets made around me.  So they're definitely out there doing this but how are they doing it?

Chris -   Hopefully, it’s a money spider.  Yes, a good question, isn’t it?  because you think, “I see this web.  It goes from one tree over there to one tree over there.  did the spider go all the way down, walk along the ground, up the other tree, and then string this piece of thread across the two?”  The answer is no, of course. It’s too small to know these places exist relative to each other.

The way the spiders do this actually is that they sit on the end of one twig or something, and they stream out this very long but very light thread of silk which gets picked up on air currents and it floats away from the spider, and the spider is continuously testing the tension in the thread.  When it feels it goes taut, it realises it must have snagged on something.  So it will then fix that end and go across counting steps - because the spiders measure distance by counting their steps, and it therefore knows how far away it is.  It then counts back halfway, knows that it’s halfway back across and then drops a perpendicular.  So it goes down to the ground and that’s the middle of its web in a sort of T-shape, and fixes the bottom thread, and then after that, it’s got the three points it needs to start making the web. So that’s how it does it, ingenious stuff.

Helen -  What’s the point of eyebrows?  To look lovely so we can paint them in and be very beautiful.  No.  The main theory is, the eyebrows rather muckily stop sweat from dropping into our eyes.  In fact, the prominent brow that we have and our ancestors had is to help to stop us having to mop our brows quite so much.  If you watch hot tennis players at the moment in Wimbledon, you might see that having eyebrows does help, and I think that people have said that if you lose an eyebrow or if you shave it off – or if your friends do perhaps – then you will get more sweat in your eyes.  I think it does seem to actually work especially if you've got big bushy eyebrows.  That really does help to mop things up. So don't pluck all your eyebrows out, unless you want to be impairing your vision on hot days!

Chris -  They don't.  Spiders have a compound eyes, so they have lots, and lots of individual lenses that then filter down through this lens material, onto a photo receptor, a light-sensitive plate underneath so they don't have a call for having any kind of eyelid type structure.  Their eyes are open all the time, so they'll keep an eye on you because they've got plenty of them.

Andrew -  The strength of gravity on Earth is measured in terms of how fast it accelerates things and roughly speaking, it’s about 10 metres per second every second.  That’s how fast it accelerates things.  And you're absolutely right that it differs slightly depending on whether you're at the equator or at the poles, and there are basically two effects that are contributing to that.  The first is actually the rotation of the Earth itself.  We were saying earlier on that if you're standing on the poles, that point is fixed so you're not moving at all whereas if you're at the equator, you're moving very fast around it in a circle, and that reduces the gravity that you feel by what’s actually 3.4 centimetres per second per second.  So that’s about a 0.3% effect.  It reduces the weight by 0.3%.  You also said correctly that the Earth actually bulges around the equator and I think if I'm getting this right, that’s going to make it up into about a 0.5% effect.  So it’s going to have a 0.5% effect on the weight that’s measured of your Boeing 747 which is not really a huge amount in terms of the uncertainties involved in aviation.

Chris -   [With aviation] they've also taken into account extra things in terms of safety factors before those kind of take offs anyway.  So it’s already been taken account of.

Chris -   Well actually, there is quite a bit of science behind this and in fact, your mates, Rick, are probably right it turns out. If you look at how footballs behave when they spin through the air as they fly, when they fly at slow speeds, what they are doing is parting the air stream and the air forms a nice even layer on either side of the football.  It forms what’s called laminar flow around the football and because the air is sticking to the surface of the ball, it’s applying a drag to it.  But if you speed the ball up even more, so you go past a threshold point at which the air flowing past the ball is no longer in this lamina configuration.  It becomes so called turbulent.  Suddenly, people have found, the drag on the football plummets and becomes much, much lower, even though you've increased the speed and the increase would be only at small amount, you suddenly got a very, very low level of drag, and it then begins to increase again gently.  

So when footballers are doing these incredible, sort of ‘banana’ shots, what they're doing is cannoning the ball away at about 30 metres a second, 70 miles an hour, and at that speed, the air is travelling in a turbulent way past the ball.  So the amount of drag is actually quite low, but as the ball slows down, it then goes into the ‘high drag regime’ as it’s known.  In other words, the speed becomes such that instead of the air being turbulent around the ball, it begins to stick to the surface of the ball again and that increases the drag very markedly, and this abruptly decelerates the ball, and it can also make a changed direction which is why the ball can slew into the goal in this bizarre way that we sometimes see.  So, speed is of the essence and therefore, the amount of that’s sticking to the ball is important.  So if you look at what’s going on in Jo-burg, that stadium is at about 4,000 feet.  There’s an index that people use on aeroplanes which is called the indicated air speed.  This is a record of how fast the air is apparently going past the aeroplane, and we know by rule of thumb that it’s about 2% wrong for every thousand feet in height you go up.  So in other words, at 4,000 feet, it would be 4 times 2% which is an 8% error.  In other words, the ball will be feeling drag as though it were going about 8% more slowly than it really is.  So when your footy player is booting the ball, having trained at sea level, knowing how the ball performs in air of the density you're going to get at sea level, actually the speeds they're booting it at to make these effects happen are going to be all wrong because the ball is actually travelling and experiencing drag about 8% lower than it ought to at sea level. Therefore, this will if you're a highly seasoned, highly practiced footballer, unless you have an opportunity to realise this is what’s happening, there could be an error in the way that you're going to boot the ball.  It’s amazing to think how much there is going on in physics in football, isn’t it?

Andrew -   Yeah, well that Wayne Rooney is well-known for his love of physics.

Chris -   But not for his knowledge of it nor his ability to score goals this year unfortunately.

Helen -  Well, yes.  All you have to really do is look at a peacock’s tail to see just how important the colour blue is for birds and in fact, birds have really extraordinary vision because they have four cones.  As well as the three that we have as mammals and humans have, they can also see UV and near UV light, and the reason they do this is for all sorts of things.  We think it plays a really important role in sexual signals if you cut out the UV part of feathers, it really kind of interferes with how birds can communicate with each other.  And it’s also quite important for them in their ability to find prey and to forage and find other food.  So UV light is very important and they have great colour vision too.  So birds are really quite championing the world of colour vision actually, and can see much more than we can.

Helen -   There are plenty of accounts.  They're all on the internet and I should think they are all untrue because there are all sorts of reasons why I don't think it’s likely that anyone’s really going to survive - at least not for very long - inside any of these animals.  We could look at it if you like.

Which of the whales could physically swallow us?  That’s the first question.  Can we actually get into their gullet, down their oesophagus?  If you're talking about Baleen whales with baleen plates that filter tiny plankton and creatures from the sea, like a blue whale, the answer is no because their oesophagus’ are very tiny thin things, a couple of inches across.  Even a blue whale’s oesophagus only reaches about 10 inches if you stretch it.  So I don't think that’s going to be enough for us to get through.  Maybe a child, but let’s not try that. 

So that really leaves the toothed whales, the other part of the whale group, things like killer whales and sperm whales.  Yes, they can swallow large prey.  They can swallow large seals whole.  We know sperm whales can swallow giant squid whole, so chances are, they could swallow a human whole.  If you can survive the being swallowed part of it and get past all those teeth, you then will find yourself in a complex digestive system.  They have up to four stomach chambers, like a cow.  Find your way through those if you can while also dodging all those nasty digestive enzymes that are going to start corroding your skin.

Chris -   Well not least the lack of oxygen, sure it is.

Helen -   Absolutely.  That was my final point – was there really isn’t any air in there.  If there is any gas inside a whale, it’s probably methane, and that’s not going to help you out very much.  We do know that whales can be flatulent, so there is some gas.  They do have gassy pockets, but it’s not air, not good to breath.  Certainly, no air inside a fish, so I think that’s really what’s going to get you in the end.  So I'm afraid no.

But there are lovely stories.  I like Rudyard Kipling’s, “How the Whale Got it’s Throat” which tells of a shipwrecked mariner who was swallowed by a whale and he caused such a fuss that the beast agrees to release him, but the mariner, to prevent this ever happening again, forces a wooden grate into the mouth of the whale so that it won't swallow anymore people, and all it can do is swallow little fish.  So he got that half right -  that’s half of the whales, the Baleen whales.  So, no, I don't think there’s any chance.  I think all the stories of people surviving being inside a whale are made up.  Sorry about that.

Andrew -   In fact, it would just carry on accelerating forever until it ran out of fuel because the reason that it’s accelerating is not so much to do with measuring particular speeds.  It’s more just to do with the fact that it’s throwing out lots of mass out of its rear end, to put it nicely, and when it does that, it feels a little push.  This is one of Newton’s laws – every force must have an equal and opposite force.  It receives that equal and opposite force, and as a result, it accelerates.

Chris -   This reminds me of a question we had in the Naked Scientists awhile back which was, how hard would you have to pee to push yourself over.  I think the answer we’ve worked out was, you would have to be able to pee and produce a fountain, more than 20 metres high in order to achieve sufficient force that would have any kind of backward propulsion, assuming a modestly weighted man.  Similar physics, Different situation.

Andrew -   Okay.  Let’s tell this stuff one bit at a time.  First of all, if space really were completely empty then a fan would be useless to try and propel you through it.  Although the conservation of angular momentum is important here, what it would actually mean is that if you weren’t very careful about how you constructed this, you would switch a fan on, and you would find that this spacecraft started rotating very fast in the opposite direction.

Chris -   This could be uncomfortable for the people inside.

Andrew -   But actually, space isn’t completely empty.  So if you could get over this conservation of angular momentum problem perhaps by having two fans which were counter rotating then you could use the – if you’re near the Sun – something like 5 to 10 protons in every centimetre cubed of space or if you're a bit further away from the sun, somewhere else in the galaxy, something like half a proton on average every centimetre cubed.  If you got a really big fan, you could in principle use those protons to thrust against, but I've been just scribbling away, doing a really rough calculation here, and I've made some pretty generous assumptions and I wouldn’t swear by this if NASA were asking me, but this is what I reckon.  If you could take a really well designed spacecraft, say it was 10 tons.  That’s fairly light and it had a 100 metre radius fan and blades that were 1 metre deep, then I reckon you would get sufficient acceleration to get from 0 to 60 miles per hour in the age of the universe, so in about 14 billion years.

Chris -   It’s a pretty efficient system then.

Andrew -   Well I think we should certainly be funding, looking into this to see what the possibilities are, yeah.

Chris -   And this assuming that you had overcome, although you presumably wouldn’t have overcome with one fan, the spacecraft spinning around the opposite way for the hectic ride for the people aboard.

Andrew -   No.  I think you need counter rotating blades definitely.

Andrew: - You would absolutely fall out the other end.  So you'd accelerate all the way until you got to the centre and then you’d decelerate all the way until you got to the other end and then you would come to a graceful stop, just as you got to the hole in Australia if you jumped in in the UK, and that would be that.

Chris: -   And you then oscillate presumably?

Andrew: -   If you didn’t actually manage to stop yourself when you got to the other end, and hopefully be prepared and you would, you would oscillate backwards and forwards forever.

Chris: -   Some people say with the same rate as if you had a satellite doing an orbit around the earth.

Andrew: -   Well it depends slightly on exactly what orbit you put it into.  If I remember correctly, it’s about 42 minutes, the period of oscillation.