Dave -   This is a lovely problem and it’s one of my bugbears, primary colours.  The primary colours of light are pretty much red, green and blue.  That's nothing to do with physics, it’s all to do with biology.  In your eye, you've got three different types of cone cell, three different types of sensor:  Ones which absorb reddish light, ones which detect greenish light, and ones which detect bluish light.  Light is actually an incredible mixture of an infinite number of different colours, but your eyes approximate it to reddish, bluish and greenish.  So, if you mix red light and green light, you can actually confuse your eyes and make it look like it’s yellow light.  And so, by mixing red, green and blue light, you can make any colour of the rainbow.  It’s actually slightly more complicated but [you can convince your eyes that you're seeing] pretty much any colour of the rainbow.  That's how TVs work, using red, green and blue.  

But if you're dealing with printing or paints, you're doing something different.  You're adding colours together.  You're taking white light which has got all the colours of the rainbow in it and you're taking colours away.  So, if you've got red, green and blue shining down on a red piece of paper, all that comes back is red light and you see red.  

The primary colours in that sense aren't made by adding colours together, like with light, but actually subtracting, or taking colours away.  So the primary colours with pigments are:

• Taking red away; which actually emits a turquoise colour or cyan
• Taking green away, which is basically purple, and
• Taking blue away which is actually yellow.

So the primary colours of pigments are cyan, magenta, (purple) and yellow.  Red, yellow and blue are not any kind of primary colours at all and it’s just primary school teachers trying to confuse you.

Chris -   It’s quite intriguing isn't it, because it is literally down to what is going on on a surface in order to make a colour that you see.  White light hits the surface, all the other wavelengths get absorbed apart from the one that you see coming back to you.  Whereas, if I shine light at you, I'm making some coloured light that your eyes interpret as colour I shone at you.

Dave -   Yes, it’s to do with how you're getting those final colours which hit your eye.

Chris -   I think we’re very used to the fact that when we speak, you get sound coming at you from two different sources.  One is the vibrations coming out of your mouth through the air and into your ears, the other is that when you speak, or sing, or make noises, the vibrations go into your bones, and then into your inner ear via that route.

So you have these two sources of sound coming at you and I think we learn to control our speech patterns and our speech loudness, and the cadence of our speech (we make ourselves sound interesting) by listening to ourselves in real time.  You get used to that latency or the delay between you making the sound and then the stimulus coming back at you.

Obviously, when it’s coming through those two routes out of your mouth and into your ears again, the latency is incredibly short.  So the feedback route is optimised to work that way.  When you start using electronic equipment and you try to apply the same latency, of course it’s a much bigger delay so your brain gets confused because it’s trying to feedback and control what you're saying, but it’s listening out for information that it is receiving much later than it thought it would.  This confuses the brain, gets its interest going, and it says, “Right, I'm now listening for the sound.  It’s not there… Oh, there it is!” And that delay confuses you and you get sidetracked.  It’s that sidetracking that we find distracting until you learn to suppress it or ignore it.

I think that's basically what's going on.  I think if you spent your life living on video conferences, you probably find it a lot easier to cope with, but I wouldn’t advise it.

Hannah -   There is a paper that was published in 2010 by Martin Bootman at the Babraham Institute in Cambridge and they looked at rat hippocampal neurons, which are primary neurons that are quite susceptible to external environments while getting their neural circuitry together...

Chris -   These are brain cells.

Hannah -   These are brain cells in a Petri dish and they exposed these brain cells in a Petri dish to 900 megahertz electromagnetic radiation for 30 minutes.

Chris -   Dave, where does that sit in the spectrum of wavelengths?  A microwave oven will be around 2 ½ gigahertz.  That will be about 2 ½ times higher frequency than that.  So where is 900 MHz?

Dave -   900 megahertz, is still in the microwave region, but it’s at the bottom end of the microwave region.  Some mobile phones work on that, others are a bit higher.

Chris -   So it’s in the right sort of ballpark.  What did they find, Hannah?

Hannah -   Well they looked specifically at calcium signalling in these nerve cells and they looked by labelling, using a fluorescent dye to tag to calcium activity.  Calcium signalling is very important because it’s involved in neurotransmission and enzyme activity, and brain inflammation processing and transfer.

Chris -   So you use the calcium signal as an index of what the cells are doing, asking if we zap the cells with microwaves or not, if there's a difference?

Hannah -   Exactly.

Chris -   What did they find?

Hannah -   They didn’t find any difference at all.  They had a look at the baseline calcium levels after 30 minutes of 900 megahertz and they found no effect, no significant effect on the calcium signalling.  They also provoked a calcium response by adding in an agonist that caused a large calcium response and they found that the electromagnetic radiation had no effect on these cells in a Petri dish.

Chris -   And obviously, we’re interpreting this within the constraints that this is a certain frequency, we’re exposed to many others.  I mean, what do you think, Dave?  Are you happy with that piece of research or would there be other questions you'd like to ask?

Dave -   It’s not a kind of electromagnetic radiation which is likely to give you cancer directly.  The wavelength from mobile phones is several centimetres so it’s not going to interact strongly with anything which is a lot smaller than that.  So, the only conceivable effect I could imagine would be some very large scale thing, but there hasn’t been any big effect which people have noticed.  People haven’t suddenly all started keeling over and dying, so I'm not worried about it anyway.

Dave -   This is a really interesting one.  We did this as a Kitchen Science a couple of years ago.  If you blow with very pursed lips very quickly, it feels cold and then if you blow with an open mouth slowly on your hand, it feels warm. 

This is all to do with what's happening with the the air.  If you're blowing through very narrow pursed lips, the air is going very quickly and it tends to mix in very strongly with the air around it.  So, what's hitting your hand is mostly air from the room, it’s moving quite quickly and quick moving air tends to feel cold because it moves heat away from your hand quicker.  So mostly, what's hitting your hand is air from the room. Whereas if you breathe slowly with your mouth open, that's a much smoother jet of air, so it’s a much wider jet of air, it doesn’t mix in nearly as quickly.  So what hits your hand is mostly air from your lungs which is warm.

You can actually get the warm effect from the fast moving air by putting your finger right up close to your mouth when you blow, it still feels quite warm and it also gets quite damp. That's because it doesn’t have time to mix in with the air around it, so it’s still warm and you can feel it.

Hannah -   2012.02.26 - Q&A Show[In the Study I referred to earlier]they were specifically looking at calcium because calcium is such an important ion involved in signalling between nerve cells.  It’s important for building circuits and allowing passage of information from one nerve cell to another.  And it’s particularly important for developing brains and brain activity.  So they were using calcium as an indicator for the primary hippocampal cell health.

Chris -   Let’s poll the panel here.  Dave, would you pick up and eat something off the floor if it’s been there for fewer than 5 seconds?

Dave -   I'm not sure if 5 seconds is important.  It rather depends on the floor. If it’s a very clean floor then I would think it’s safe.

Chris -   Hannah, your view?

Hannah -   I think I'm a bit of a grotbag.  Mine is the 30-second rule.

Chris -   Oh, you go for as long as 30 seconds!  Well, Paul Dawson, who is a researcher at Clemson University has a very nice paper on this in the journal of Applied Microbiology.  He recruited his own students to do the experiment.  They tested things like Salmonella being placed on a surface to look at how long the Salmonella will remain viable after a surface is contaminated.  The answer is for 4 weeks.  So basically, if there's contamination on the surface, it remains viable for a long time so if you drop something on it, you could pick something up.

Then they did the experiment with food items being dropped on to a surface and removed within a certain threshold length of time, and the answer was that 99% of the bacteria that got transferred at any time all transferred instantaneously.  So, there is no 5-second, 2-second, 30-second rule even for grotbags like you Hannah, as you call yourself.  The answer is that instantaneous contact will transfer microorganisms and if there are pathogens there which can survive for a long time, they will end up on the food and depending upon how pathogenic they are and whether or not you then re-sterilise the food, perhaps with temperature for instance, then you could get something from it. 

So, if in doubt, throw it out – I think is the bottom line.

Dave -   Essentially, it’s by clever engineering.  If you look carefully at the toothpaste, instead of making those beautiful swooshes of toothpaste which they always show on adverts, if you chop the toothpaste straight across, you'll see that the colours are only just on the surface.  In the middle, it’s all just normal white toothpaste.  So, what they're actually doing is, in the nozzle, very close to nozzle which squirts the toothpaste out, there are other little nozzles attached to bags of colour – often several different nozzles attached to bags of colour.  So when you squeeze a tube of toothpaste, it squeezes both the main toothpaste bit and those little bags.  And so, as the main toothpaste comes out, the extra coloured bits get squeezed out on the outside and you end up with a white tube with little coloured bits around the outside.

Chris -   If you don't believe us, cut a tube up and you'll see this marvellous bit of engineering for yourself.  It was patented in America, I think, in the 1960s or the late ‘50s.  They actually introduced that as a major selling point.  I think Signal was one of the first brands to use it in this country.

Dave -   Probably, I think it’s based on a similar system for making icing.  So you can get coloured icing outside and the boring white icing inside.

Earwax is made in the outer canal of your ear.  Your outer ear is basically the bit that you can see.  It’s the bit that funnels all of the pressure – the sound wave pressure - and funnel it into your middle ear and your inner ear which then converts those sound wave pressures into electrical energy which you can then use to hear.  Earwax ,or cerumen, basically acts as a lubricant to help the sound waves to travel through, and it also protects against nasty bugs sitting in your ear and multiplying there and causing infections.  So, perhaps counter intuitively, it’s actually quite a cleansing thing to have as long as you don't have too much of it.  If there's too much of it then it can cause a blockage and prevent the sound waves from passing through into your middle ear and therefore cause impairments or problems with your hearing.

Dave -   It depends on the hands free system.  The problem that can happen, as someone discovered in a study a couple of years back, was that some of them were actually receiving the transmission which the mobile phone was making and funnelling them up the wires into your ears.

Chris -   Because the microwaves are making electrical current flow up and down the wires?

Dave -   Yes, that is exactly right.  Essentially you have a funnel into your ear which could actually cause similar, or if not higher, doses around your ears than you would get otherwise.

Chris -   How does is turn from electric current back into a microwave in your ear then?

Dave -   Any rapidly changing electrical current will produce electromagnetic radiation and therefore, it will be transmitting microwaves all the way up.  It should be electronically quite easy to stop that.  You just put in a filter which blocks the high frequency radiation, but not all headphones apparently had them.  So, it depends is the answer.

Chris -   He goes on to say, “Is a microwave oven which is shielded - it has all this protection to stop the microwaves coming out - therefore, less dangerous than a mobile phone?”

Dave -   That entirely depends on whether you're in the oven or not.  If you're actually in the oven...  The biggest problem you get from microwaves is heating.  The reason why a microwave oven could cause you damage, and how it cooks meat, is that it produces a huge amount of heat in there.  The amounts of heat which should be outside the microwave oven, or that coming from a mobile phone aren’t large enough to significantly change the temperature of your body.

Chris -   A microwave is running at say, a kilowatt whereas your phone is running at milliwatts, so the heating effect of your phone on the tissue that it’s irradiating, ie your brain, is going to be tiny in comparison.

The answer is that as the wavelength of radiation, light - EM radiation, gets shorter, in other words the frequency increases, then it packs a more energetic punch.  At long wavelengths like radio waves and microwaves, we regard this radiation as non-ionising.  In other words, when it impacts on something, it does not have enough energy to physically disrupt the bonds that connect atoms together.  For that reason, it means that when you are hit by this radiation, it will warm up your tissue because it will make the particles vibrate more and get hotter, but it will not physically break the bonds between them, so it should not trigger, for instance, mutations in DNA that could cause cancer. 

As you go into shorter and shorter wavelengths of radiation, so you go beyond UV and you're into x-rays and then gamma rays, this is light with a very high frequency, very short wavelength where the light has sufficient energy to physically disrupt chemical bonds.  It literally breaks the bonds between atoms.  This means you can introduce changes to your DNA, you can introduce damage to material in cells which can put stress on cells, damage tissue, and it can also introduce cancer causing mutations.  That's why we worry about ionising short wavelength radiation.  We’re less concerned about holding a mobile phone to our head because that's microwaves which are not said to be ionising.

Dave -   The interesting thing about this question is that it doesn’t particularly matter what the crust is made out of.  What's really important is how much power is coming out of the Earth every second.  The Earth is essentially a body sitting in a vacuum and there’s an equation which relates the temperature of that body to the amount of power it can lose per square metre.  The Earth is losing actually only about 0.1 watts per square metre from geothermal sources over the whole of the surface and this means that if it was just sitting in the middle of space with no Sun anywhere near it, you can work out the temperature it should be and it should be at about – 239ºC, but it’s not.  That's because the Sun is shining on it and heating it up all the time.  

Now you also asked how big the Sun would have to be, how thick a layer of crust it have to be over the Sun in order to get it down to the temperature we could walk on.  I used the same equations.  I said that you'd probably be able to walk on something at about 60ºC.  It might hurt but it’s just about possible.  A body at about 60ºC can lose about 664 watts per square metre in one direction.  If you work out the size the Sun would have to be to be losing heat about that rate, it’s about 213 million kilometres radius.

Chris -   That's way bigger in Sun is at the moment.  That’s outside well beyond the orbit of us!

Dave -   Yes, so the Sun would have to be enormous and actually, it doesn’t matter what insulation you put in there.  If you leave the Sun for long enough, it would be pumping out that heat all the time and that’ll get to the surface.  In fact, if you insulated the Sun, it would probably increase the rate of reaction and will get even hotter and increase the power released, so it will actually probably be even hotter and need to be even bigger.  So, yes rather inplausible I think!

Chris -   In Star Trek, they talk about a Dyson sphere where people create a structure around a star in order to capture all of the energy coming out of the star and do various nefarious things with it.  But that would mean you'd basically end up having to contain something that would be 200 million kilometres across then if you allowed it to expand?  You'd need something huge!

Dave -   Yes.  This was, I think invented by Freeman Dyson who was looking at if you took the limit of technology and you were staying in one solar system, what would you do to it?  How could you extract all the energy out of the star? If you want to collect all that heat, you then have to get rid of it at a sensible temperature so you would need something out at about the orbit of Mars, radiating outwards.  It would be absolutely immense, and an incredible technology needed to do it.

Chris -   I wonder how much material you would need to make a sphere as big as that in the first place.

Dave -   Immense amounts and just the physical strength of a hollow sphere that size is, I think completely implausible.

Well the best thing is thyroxin, the hormone that comes from your thyroid gland in your neck.  This binds to your DNA in different cells in the body and it turns on various genes to up your metabolic rate.  If you have too little thyroxin, you become hypothyroid and you get very cold, you tend to put on lots of weight, you can get your muscles feeling very weak, it’s hard to think straight, and have no energy.  Pretty much the reverse happens if you have too much thyroxin, hyperthyroidism.

Earwax production and characteristics vary genetically.  People who come from East Asia tend to have very dry earwax whereas people who come from the west tend to have genes that cause them to have wetter earwax.  You tend to increase the production of earwax if it’s got a job to do.  So if you're in a very dusty, dirty environment or if you have infections locally, you make more earwax in order to soak up the dirt and prevent the bugs from creating more of an ingress.  The downside is that the cerumen, the thick wax, can build up and block your ear canal. You sometimes have to soften it with something like olive oil so you can get it out easily.

Chris -   [Researchers have done] studies on laptops.  They did a study looking at men’s sperm counts and trouser temperatures and found that if you put your laptop on your lap, as nature intended you to use it, or at least the manufacturers intended you to use it, the elevation in temperature in the trouser area is of the order of several degrees.  This was sufficient to cause a decrement in sperm count because sperm gets made most optimally at a lower temperature, maybe 1 degree lower than other areas.

So, mobile phones do cause a heating effect because of the microwaves don’t they?

Dave -   But probably much less than a laptop.  Probably least a 10th as much, so I’d thought you'd have difficulty heating that particular region from your side pocket unless you have a very strange pocket.

Chris -   And also, the intensity must be lower.  The actual heating intensity of the microwaves coming out probably wouldn’t be enough to put the temperature up.

Dave -   The microwaves, even when it’s running and you're actually talking on the phone, are only a couple of watts whereas a laptop, just the heat which is coming straight out could be up to 100 watts which is far, far larger.