Can you dehydrate in a bath?

In another question and answer edition of the show, the team get to grips with your questions - including can you dehydrate in a bath?
05 September 2013


Another special question and answer edition of the show where the team get to grips with your queries, including, cna you dehydrate in a bath? What is tinnitus? What chemicals leak from batteries? Why does water freeze from the top down? Are solar photons making the Earth more massive? And what causes deja vu?

In this episode

Why is water loudest just before it boils?

Dave - So, this is all to do with, if you think about what's happening before it actually boils properly, the heating element is over 100 degrees centigrade. Therefore, the water around it is going to be producing steam even quite early on when it's starting to boil. These bubbles are created and then if it's not quite boiling yet, they move up into a cooler area of water and they cool down. If a steam bubble cools down very quickly. It suddenly wants to disappear and it collapses and it forms in the cavity. If you imagine this bubble kind of collapsing symmetrically around each other, it kind of slaps into itself. This is known as cavitation and it's very, very noisy and it's actually, quite a destructive process. You get this in boat propellers and if the boat propeller goes too fast, you actually little bubbles of steam which collapse again and actually completely smash up the surface of the propeller and you can see horribly eaten up propellers. So therefore, going back to the kettle as it heats up, slowly these bubbles are getting bigger and bigger, and they're collapsing harder and harder, until eventually, they get hot enough that they get all the way up to the surface and they just pop gently.

Chris - So, the reason it gets louder just before the water boils is because that's when the bubbles are at their biggest to start with and therefore, they've got the biggest collapsing to do.

Dave - Yes, so it's the biggest bubbles which are collapsing and then they get to the point where they reach the surface, at which point, they just pop gently and then it gets much quieter.

Red sky at night, shepherd's delight

Why does the ozone layer float?

Laura - Obviously, the ozone layer is really important because it protects us from UV rays. But actually, that's one of the reasons why it actually is up there because it's continually being reformed. It needs to be up there, getting the UV rays, absorbing them, having that chemistry going on in the atmosphere. So, it is actually sort of heavier, but actually, it's because it's continually being reformed.

Dominic - I guess, another factor here is that because the ozone layer is absorbing all this ultraviolet radiation from the sun it's actually getting really quite hot. We think of temperatures decreasing with altitude, but when you get up to these quite high altitudes that air is getting hotter. Of course, hot air floats because it's less dense. That's how a hot air balloon flies. And so, this ozone is naturally quite buoyant because it's hot.

Inner ear

What is vertigo?

Ginny - So, vertigo is this sensation of dizziness or spinning and most people will have experienced it if not any other time when you've had a few too many drinks. But some people get it quite regularly and it's all to do with your inner ear. So, inside your ear, you have three semi-circular canals, little sort of loopy things which are filled with fluid and they're all at 90 degrees to each other. That's how you know which way up your head is and which way it's moving because the fluid inside them moves, knocks into these little sensor hairs and that tells you how you're moving. When you spin around, the fluid in them starts to spin as well, but after you stop, it keeps spinning for a while and that's what makes you feel dizzy after you've been spinning around. But lots of things can make you feel like you're moving even when you aren't, which is what is happening in vertigo. There's some circumstances when it can be caused by little pieces of debris that have found their way into the inner ear and they confuse the signals that are being sent to the brain. That type of vertigo tends to happen only when your head is in a certain angle so the debris is hitting the little cells. It can also be linked with migraines. In which case, the problem is probably actually not in your ear, but in the nerves or in the brain itself. But scientists still don't really understand migraines. They're a bit of a mystery to us. Chris - Do you know what is weird though? Why the body has evolved to make the decision that when you get motion sickness or vertigo or something to throw up? What's the point of that?

Ginny - Well, vomiting is a sensible response if you've eaten something bad and it seems that dizziness can sometimes be an indicator of poison. So, I think that's how that evolved, that in some circumstances it was very useful to throw up because you'd eaten something bad. And actually, if you throw up a few more times than you need to, that's better than not throwing up when you should.

Heat generated from the nuclear fusion in the Sun

Are solar photons making Earth more massive?

Dominic - Yes and I essentially think they do because you're probably familiar with Einstein's really famous equation e=mc2. This was the iconic equation of relativity and what that's saying is that energy has some mass associated with it. It's a very tiny mass, but when you're looking at really large amounts of energy like the power that the sun is delivering to the earth every day then that starts to become quite an appreciable mass. I actually sat down half an hour ago and was doing this calculation. I think it's about 7 kg of energy that the sun delivers to the Earth every second. But if you're then asking, is the energy of the Earth increasing is a result of that, well, the Earth's energy is not actually increasing as a result of the radiation from the sun. Because if it was, it would be getting hotter and we know that the Earth's climate has been fairly steady for millions of years. So, what that means is that the Earth is radiating to space, just about the same amounts of energy that it's receiving every day from the sun. It's in this thermal balance.

Dave - Though there have been a couple of NASA missions recently which have been actually attempting to measure that because if global warming is happening and the Earth is warming up, then the Earth should be re-emitting less energy than it's absorbing. And they reckon it was less than a Watt per square metre is disappearing somewhere into the Earth. So, some of that energy should be increasing the mass of the Earth very slightly by just heating it up.

Ice cubes

Why does water freeze from the top down?

Laura - So, this is a really brilliant question. It's all about how weird water is as a substance. Water, if you think about it, you know that ice floats. That's why your ice in your drink floats at the top. It's why we can ice skate on rivers although make sure the ice is fairly solid first.

Chris - Good job, you can ice skate on rivers rather than.

Laura - Rather than having to go down to the bottom. But I think probably, the wild life and the fish at the bottom of the lakes would quite like that as well. It's all to do with the way that hydrogen bonds. So water bonds and it forms these things called hydrogen bonds. So, you've got the oxygen in the middle of the water and then these two hydrogens coming off of it. And so, you're right. That as you heat water up, it becomes less dense and it floats. But then at about 4 degrees, there's this wonderful sort of turning point and actually, you're cooling it down, it gets denser and denser and then these hydrogen bonds come into play and it starts to make this structure, making it less dense. So, that's when the cold water floats to the top and then eventually freezes.

Dave - So, it's sort of almost starting to freeze in little lumps and they're non-freezing. So, more of it is in the ice structure, so it's bigger than it should be, so it starts to expand as it gets colder which is really, really strange.

Laura - Yeah, absolutely. The thing about temperature, you have to remember it's an average. So, things are going on at a different temperature.

Chris - There was an amazing episode of a David Attenborough programme where they were looking at life in the Antarctic and they show this very, very cold water coming down from the surface and then hitting the floor of the ocean, and then it just comes down and freezes in like a stalactite going down, hitting the ocean floor and then spreading as sheet of frozen water along the bottom. Because once it had enough ice there to start the freezing process, that then kick started the formation of a whole crystal and that whole nucleation process kicked in.

Laura - So, that's something called super cooled water which you can see and it's really cool. If you get water and leave it to stand, it can get colder than the freezing point without actually freezing. If you then pour out, it'll freeze in amazing structures.

Pinchas - Is water unique?

Laura - I wouldn't like to say definitely unique because there can always - but it's one of those really, really weird substances. You get different types of ice. So, in different temperatures and pressures, ice can form different crystals and there's all sorts of odd things that it can do.

Ginny - It's certainly very unusual amongst the kind of everyday things you'd see. So, if you had some oil and you froze that, oil ice would actually sink in oil. Now, we all think that would be really weird, but actually, solid should be denser than liquid so they should sink. We're just so used to water that we think ice floating is normal whereas actually, it's really quite strange.

Chris - Isn't there Dominic on some other planets? I mean, the people have said on Titan, Saturn's biggest moon, the pebbles that are made from the hydrocarbons that freeze on Titan would sink. They wouldn't float like the kind of ice that you get in the oceans here on earth.

Dominic - That's absolutely true. These moons of planets like Saturn, they have not water oceans, but oceans made of hydrocarbons, these materials like petrol and they behave in a way that most materials do. Their solid forms are more dense and they sink as compared to ice that floats.

Why doesn't my watch self-wind when I'm ill?

Ginny - Automatic wrist watches are really, really clever. So, you used to have to wind a watch because a watch needs energy in order to move the hands around. So, you used to have to wind up a little rotor inside that then drives the hands around. But what these kind of automatic watches have is there's a weighted bit inside that moves every time you move your arm. And you move your arm quite a lot during the day without even noticing it. So, that movement winds the spring that drives the hands. Watches vary in how much energy they can store. Most of them actually, you can take off over night or even if you leave them on, you're not moving over night and they'll store enough energy to still work perfectly well the next day. So, the only thing I can think here is that if you've been ill, you're probably not moving around as much. If you've got flu, you might be taking it a bit easy on the sofa. So, even if your watch is on, chances are, you're not moving your arms around quite as much. So, maybe if you're ill for a day, then it's gone a night and a day, and another night without much winding, that might be enough for it to stop.


What is tinnitus?

Chris - Well, the definition of tinnitus, I hope not in response to this programme Les of course, but the definition of tinnitus is when you have a sound experience in your ears or ear in the absence of any external presentation of sound. So in other words, you're hearing something that you know is not there. It's coming from inside your ear. There's a number of reasons why this can happen. The commonest is because of the ageing process and damage to your ears caused by degeneration of what are called hair cells and inside your inner ear are cells called hair cells that have tiny hairs projecting off of the cell. When vibrations from a membrane inside your ear are transmitted into those hairs, they make the hair cells fire off electrical impulses and they send the electrical impulses via a nerve to the brain stem and then onto the main part of your brain that does the hearing. If you are exposed to very loud sounds chronically, in other words, over long periods of time, we don't exactly know why, but it does damage these cells and eventually, they begin to be lost. This means that the sounds that they would've picked up and sent onto the brain no longer get transmitted to the brain. And it's a bit like if you're listening to the radio and you can't quite hear it loudly enough, you turn up the volume. That means that you don't only amplify the noises you do want. You also end up amplifying the hiss that you don't want. And so, we kind of regard tinnitus as a sort of hissing noise which is brought about by the brain increasing the amplitude or gain in the system, in order to try to make sense of the sounds that seem to now be missing. There are other things that can also cause tinnitus as well and one of them is probably infection. We know that some viruses can make a beeline into your inner ear and can irritate the nerves. In fact, there's been some viruses going around in the last few weeks called enteroviruses that can get into the nervous system. They tend to cause things like headaches and pain behind your eyes. Occasionally, you know you've got one because you can get ulcers in your mouth as well. They can sometimes also cause this tinnitus sensation. Also, don't forget drugs as well because there are certain drugs and medicines that can cause irritation of the cochlea - this is the hearing organ - and they include aspirin. If you take lots of aspirin, you can get ringing in your ears or a drug like aspirin called salicylic acid and also, some antibiotics can also do this as well. Ginny - Are those kinds of tinnitus reversible? So, if you take lots of aspirin, do you get it for a while and then it goes away again or are you stuck with it for life?

Chris - It depends. If you take a lot of aspirin or salicylic acid which is a chemical relative of aspirin, the stuff that's in willow bark, that tends to go away when the drug flushes out of your system. If you take certain antibiotics and this includes the antibiotic gentamycin which is sometimes given for certain deep rooted infections in the body, that is very toxic to the cochlea hair cells and if it damages them, it can sometimes cause tinnitus and ringing in the ear that unfortunately ends up being permanent.

Hot water tank

Turn off the immersion to save energy?

Dave - So essentially, with something like a hot water tank, the hotter it is, the more energy it's going to be losing. So, if it's not very well insulated, the effect is even bigger. Essentially, if you keep it hot all the time, then you'll be losing lots of electricity and lots of energy. You're going to have to put more electricity in there to keep it hot. If you turn off the electricity, it will cool down and the more it cools down, the less heat it will lose. Now, almost the best solution would be to improve the insulation but if you can't do that or that's expensive or difficult, turning it off will save energy. I can't say off the top of my head how much it's actually going to lose.

Dominic - It's interesting if you look at the typical electricity usage of a house. I think heating is one of really big costs you tend to have and that's water heating, but also, space heating. If you look at an airing cupboard where you've got a hot water tank in there and you feel it, it feels hot. So, that heat is leaking out of that tank into your house. So, if you've got that on all night then you're basically heating your house with your hot water tank all night.

fridge magnet

Can magnets on pipes soften water?

Laura - I have to say I'm pretty unconvinced by these claims. I have sort of looked at it. I've tried to work out what the magnets could be doing. We have to think about what hard water is. It's mainly calcium and other minerals dissolved. There's a tiny amount of iron in there that could be affected by the magnets, but I just can't quite see what could be happening there.

Dave - And even the iron is it in a form which is actually magnetic?

Laura - Yes, and most of it is in unmagnetic form so it's in one of the electronic configurations that isn't actually magnetically sort of active.

Chris - So we'll be giving that one the thumbs down.

Laura - We're giving that one the thumbs down. Water filters and things I think instead.

Ginny - There's probably an element of placebo effect here, in that, if you've bought a gadget and you've put it on your pipes and you drink the water.

Chris - Placebos for pipes.

Ginny - It probably does taste different to you or you possibly think, "Oh, yes! My kettle is not furring up as quickly as it used to", but it's likely to just be the placebo effect that you think because you've done something, something is going to happen.

Chris - But equally, you're hardly likely to cut into the water main, just to have a look and see if it's furred up, are you? So, I think it's very likely that most people just go, "Alright, I assume it's working." It's sort of as you say, you feel happy about it because you think you've done something when in fact, actually haven't probably done anything. So, the conclusion of the panel here, everybody, if I speak for you by saying, you're saying, don't waste your money. Would that be a reasonable summary?

Laura - I'd say, pretty much, yeah.

Hawker jet aeroplane

Does the spin of the earth affect flights?

Dominic - Well in fact, what's important is the plane's speed relative to the Earth's atmosphere - the air around it because that's what's giving it its lift up into the air and that's what is providing the the friction which is meaning it's having to thrust to keep going forward. The Earth's atmosphere is rotating with the surface of the Earth below it. The reason is, because it's got friction with the land masses beneath it and that means the air is always being pulled to rotate with the Earth. So in fact, because the air above us is rotating at the same speed as the land below, and what matters is your air speed - your speed versus the air - it doesn't matter whether you're going with or against the rotation of the Earth.

Dave - The one thing I would say with that is that there are some latitudes where the wind tends to blow in one direction. So, in our latitude, the prevailing winds from the west and they get even faster as you are higher up. So, it's a lot quicker to fly from the states to here than from us, back to the states. So, it's actually quicker to go against the direction of the spin of the Earth than with it, it just happens to be the way the air is moving. Other places, the wind is in opposite directions and they'll have the opposite effect.

Dominic - And I guess the other thing to say is that if you're going above the Earth's atmosphere into space then satellites all do go from east to west because there, you're above the Earth's atmosphere. You haven't got this drag from the air anymore and it is a lot easier to get into an orbit that goes with the Earth's rotation rather than against it.

Chris - A little bit of drag though isn't there because the International Space Station and some of the lower flying satellites have to be boosted every so often because they are experiencing a little tiny bit of drag from wisps of atmosphere out there.

Dominic - That's right. The International Space Station is in quite a low orbit, at about 130 or so kilometres up and it does have to thrust about once a month to maintain altitude.

Why do I feel I know what is going to happen?

Ginny - So, Déjà vu is a really common experience, but scientists really don't understand what causes it. The main reason for that is that it's very hard to predict when someone is going to have a déjà vu experience or to induce them. So, what we would love is to get someone in an MRI machine having déjà vu and look at what's going on in their brain, but it's really, really difficult to do. Some researchers at Colorado State University recently actually did manage to provoke déjà vu using a kind of immersive visual technology, sort of 3D.

Chris - Like virtual reality.

Ginny - Yeah, sort of virtual reality thing, but very immersive and they showed them various scenes. They found that déjà vu was provoked most regularly when the layout of a scene was similar to one they'd seen previously. So, the participants knew that the scene was new because they knew that they were only going to see the scene once. So, they have that feeling of, "I can't recognise this scene" because they haven't seen it before. But because the layout was similar, they got that déjà vu experience. So, that suggested that it might be that you get it when you've seen elements that are seen before, when there's something familiar about it, but you can't quite place where that familiarity is coming from and you know that the scene is new, that you shouldn't recognise it, and that's what gives you the weird feeling of déjà vu.

Dave - I once had a bike accident. I hit my head rather hard and for a while after, I got this kind of, "I've met this person before" someone I'd meet someone at a party or something. And after about 15 minutes, I was sure I've met them ages ago, but I wasn't sure whether it was Cambridge I probably them ages ago because Cambridge is a very small town or whether there was something. It was like my brain, my memory wasn't quite working properly.

Ginny - Well, we actually know a bit about what area of the brain is involved because some people who have epilepsy get déjà vu as part of their symptoms and that happens when you get epilepsy that occurs in your temporal lobe which is a bit sort of just above the ear. So, it could be that if you had a bit of damage going on there because you'd hit your head, that might make you more likely to have these feelings.

Chris - Has anyone else ever had déjà vu?

Dominic - I think I had it with sorts of memories sometimes, things that I don't remember perfectly and I think, why do I feel slightly familiar in this place and I think actually, when I was 5, maybe I was here.

Chris - It happens to me when I get sleep deprived and that, I think is interesting because also, sleep deprivation does trigger brain patterns of activity that we know also trigger epilepsy and people who are epileptic. So, it's interesting that you said epileptics get it but also sleep dep can do it, Ginny.

Ginny - Yeah, they've done quite a lot of sort of retrospective studies where they ask people, when do you get déjà vu? How often do you get it? So, they found that people do get it more often when they're tired and also, when they're stressed. But there was some other interesting things like it's more common in young people and it's more common in well-educated people which doesn't really seem to make that much sense. But also, people who travel a lot, which you can kind of understand a bit more because you're more likely to go to places that are new. And of course, you can only actually have déjà vu in a place that's new. You can't have it in your home because you know you've already been there. You know why it's familiar. So, that one kind of makes sense, but I can't get my head around why it's young, well-educated people who seem to get it more.

Spaceship One in Flight

How do they process body waste in space?

Dominic - Body waste in space, well in fact, a lot of it, you ship back to the earth now. If you're on the International Space Station then you have these what are called progress spacecraft that come every month or so and they'd leave new supplies, food, etc. And then once you've taken the food off those, you basically put the body waste back in there and then you send it back to the earth. Things like water, you don't really want to be transporting large masses of water around. So, there is actually a process on the space station where you take the wee from the astronauts and you can extract drinking water from that and then the other constituents of that pee, you just put back in that spacecraft and send back to earth. Historically, back in the Apollo era, you would just throw it overboard basically and you would have these ice crystals of human waste, flying off the side of these Apollo spacecraft. But the reason why they don't that anymore is because those ice crystals are moving incredibly quickly and if they collide with other satellite, they can be very damaging and they can smash very expensive spacecraft.

Chris - That would be rather ironic to be taken out by a blob of human excrement if you're a very expensive satellite or whatever.

Dominic - Ironic, but in fact, still a threat today because some of these stuff is still there from 40 years ago and it's still just whizzing around in orbit around the earth.

Will silver jewellery harm my health?

Laura - I would've thought mainly, silver jewellery would be fine first of all because silver is fairly unreactive and secondly, we've been wearing silver jewellery for many, many years. You can find it in archaeological sites all over the place. I think there would be potentially a little bit of a worry if there's something that he's allergic to in the alloy because no silver is 100% pure usually when you're wearing silver jewellery. So, that can be a problem. Some of the silver atoms will eventually - if you're wearing a ring, some of those atoms will move into your skin, but I wouldn't have thought there would be any kind of problem.

Chris - There was a gentleman, I think we discussed him here on the programme previously, who thought that silver was a good thing because it kills microorganisms and that kind of thing. So, he was drinking a solution of silver salts every day and he unfortunately went blue. This is a condition called argyria and he looks like a smurf honestly, bright blue and it's permanent because the silver goes into the skin and then reacts with sunlight, and you get this bluey grey gun metal sort of coloration. I've seen him on television. He's absolutely blue.

Laura - He is absolutely blue. What's even more astonishing is that he still drinks the colloidal silver because he still believes that it gives him these health giving properties. But I think there's a big, big difference between drinking what we call colloidal silver which is a large amount of it getting into your skin where it reacts and a couple of atoms occasionally getting into your skin. I mean, you eat probably more than you'll absorb from your jewellery.

What would a light speed camera be used for?

Dave - Okay, so the way that camera works - I saw this story a while ago - it's an actually incredible and I think it's brilliant is that essentially, it actually can only take one line of the picture. So, a picture is made of lots of different lines. It can only take one line of a picture in each burst of light. Basically, they send out lots and lots of bursts of light very, very quickly and they built up lots and lots of lines. And you take them exactly the same position of where the burst of light is, so you can build up the video that you've seen. The way they want to use it is because the really neat thing is if you can actually see light as it's traveling is that you can sort of use it a bit like radar on a really small scale. So, you can actually bounce it off just a normal wall and the light will bounce off the wall and then bounce around the room which you can't actually see and then bounce back again. If you can see exactly when all that light gets to you then if you can put that through a big computer you can actually work out what's around the corner. So, you can actually see around a completely normal corner with no mirror at all, just by being able to see the light as it comes back 1 nanosecond at a time. Dominic - So, what you're saying is if you see a pulse of light arrive at a certain time, you know that light must have travelled a certain distance. You know, the spped of light, so you know something in that room round that corner bounced that light back at such and such time. So, it must be such and such distance away.

Dave - And you've got some idea where it's coming from, so you can take all this information put it together and build a model of a room.

Ginny - Would you be able to tell what was in the room or would you just know that there was something?

Dave - Pictures I've seen ... it's quite early days.

Chris - It's amazing isn't it...

Dave - Yeah, they've actually built up a rough shape of an object and you can get some idea of the colour as well. If you've got a colour camera, you can tell what colour the light was which got there.

Chris - It was one of those mannequins, those artist's wooden mannequins, you know, the ones you put into funny postures and they had one of those. The pictures that it rendered afterwards were absolutely stunning. You could tell without a shadow of a doubt what it was, couldn't you?

Dave - Yeah.

A380 Airbus

What produces lift during a knife-edge pass?

Dave - So, the plane is basically flying on its side. The wings can't be doing anything because they're vertical. So, the lift must be coming from somewhere else. When you watch them doing it, they're actually quite a big angle. So, they're not flying horizontally. They're sort of flying at 20 or 30 degrees to the vertical. And so, you'll be getting some lift from the side of the body of the plane, from the side of the fuselage. Some from the tail plane itself will be giving you some lift and mostly, the kind of planes which do this have got very, very large propellers which can throw an awful lot of air backwards. So, because the plane is pointing upwards, that air is being thrown downwards, and so you get an equal opposite reaction and the plane gets pushed upwards.

Chris - Thanks, Dave. Similar to the sort of thing when planes fly upside down and people say, well, if the wings are generating lift in the right way up position, why should the plane be able to fly upside down? It's just that very high angle of attack, isn't it?

Dave - Yeah, wings are optimised to fly the right way up normally unless you've got a really stunt plane. But if you fly them upside down, as long as they've got enough angle attack, and you push them through the air hard enough, you will get enough lift to stay up.

Various batteries: two 9-volt, two \AAA\, two \AA\, and one each of \C\, \D\, a cordless phone battery, a camcorder battery, a 2-meter handheld ham radio battery, and a button battery.

What chemical leaks from batteries?

Laura - Okay, so what's actually happening here is the electrolyte from the battery is leaking out. So, you think of batteries, it's sort of school level chemistry that you've got a reaction going on between two metals and there's some sort of electrolyte in the middle that's allowing charge to be transferred between this two sides of the battery. That usually in your normal alkali batteries is potassium hydroxide usually or something like that. Eventually though, your batteries do keep reacting even if you've not connected them up. They react very slowly, but they do leech a little bit and there could be side reactions, and eventually, these things can just sort of pop open, at which point, your electrolyte comes out.

Chris - Is it nasty?

Laura - Potassium hydroxide is not very nice. It's an alkaline. It's quite caustic. However, it then reacts with carbon dioxide in the atmosphere. So actually, what you're seeing is those white crystals. That's actually potassium carbonate and that's actually potash. That's the main component in potash.

Chris - That's good for garden.

Laura - I wouldn't suggest necessarily knocking it off and putting it in your vegetable patch or anything. But probably, don't start licking at batteries or anything like that, but just dispose of them. If there's any on your contacts or things, you can start trying to wipe that off potentially with lemon juice or something.

Dominic - And I guess even if it's potash on the surface, underneath, you've still got the potassium hydroxide you don't really want to knock that surface off.

Laura - No, quite. So, that's why you want to use say, something like a weak acid to try and neutralise it as you're washing it off. The other thing of course is that these things can start creeping in to electronics and so, you can actually - if you've left your batteries in something for long enough, you can start really messing around with your circuits and degrading them.

A man having an ice bath

Can a person sitting in a bath dehydrate?

Ginny - The short answer is, no. Your skin is pretty waterproof. That's why we can go out in the rain and we don't get all soggy. Well, our clothes might, but our skin is actually pretty waterproof. Although, if you were in somewhere very, very hot, sitting in water might actually help stop you from dehydrating, just because it would keep you cool, so you'd sweat less. But you wouldn't actually be able to absorb it through your skin. Now, there's a group of researchers in Denmark who actually decided to test this, but rather than using water, they thought it would be a bit more fun to do it with vodka. So, they sat with their feet in a bath of vodka for a while and they tested their blood alcohol levels and they found that they didn't get drunk at all. So, that just shows that you're not absorbing things through your skin like that.

Chris - We did interview them on this programme, Ginny and they did say that although they didn't absorb any alcohol according to the blood test, they did all start talking very loudly and telling rather raucous jokes. So, it had a psychological effect if not a physiological one.

Ginny - Well, I wouldn't have been surprised if they'd inhaled some alcohol fumes and got drunk that way. I'd be quite interested to know though if their feet went wrinkly because we all know that our fingers and toes go wrinkly in the bath. People used to think that that was because you're absorbing water through your skin. But actually, some recent research at Newcastle suggests that it's evolved to help us grip objects when our hands are wet. They think it's actually down to your nerves because if you've got nerve damage, it doesn't happen. So, they found that people were much better at picking up marbles underwater when their hands had been in water for a while, so their fingers had gone wrinkly. So, it works a bit like the tread on tyres, but it's actually controlled by your nerves, not by you absorbing water through your skin.

Spherical mirror in Millennium Square, Bristol, England. The photographer is seen top right in the blue shirt. The mirror forms the side of the Explore-At-Bristol Planetarium sphere.

Would a spherical mirror trap light forever?

Dominic - So, you've got a perfectly spherical mirror, you've got a photon in the middle of this. I guess whatever direction that photon goes in, it will always hit the mirror and bounce off. The problem is going to making this 100% reflective mirror because any mirror that you make, it's got some small percentage chance that the light, rather than bouncing off that mirror, will hit a piece of dirt or just get absorbed as heat into that mirror. You know, for a piece of aluminium foil, about 70% of the light that hits that is reflected and if you make a really high class astronomical telescope mirror, you can get up to about 99% chance. But of course, this photon bouncing around at a speed of light it's bouncing off so many times, but eventually, it's going to get absorbed and just turn into heat.

Chris - So, is that a no.

Dominic - I think that's a no.

Vincent - Could I just ask one thing? If you could somehow associate this with the sort of solar panels, could it potentially provide energy forever?

Dominic - Well, of course unfortunately, to get energy out of sunlight, the solar panel has to absorb that sunlight and turn it into electrical energy. So in practice, in the process of absorbing that energy, that light has been destroyed. You can't use it again.

Chris - We also want solar panels that are as unreflective as possible so that they absorb as much energy and give away as much back out. That's why they're black, isn't it?

Dominic - Yeah, you want them black absorbing everything that hits them.

Old Fashioned Bakery

Why do I see things as I go to sleep?

Chris - Well, this is actually a sort of hallucination which is caused by often,

putting people into the dark. Ginny can probably comment on this in a second, but there are these things which are called float chambers and you put people in these experiences on purpose sometimes to do research studies. You effectively put someone in a very quiet, very calm, dark environment. It's a sensory deprivation experience and this has the effect of triggering all kinds of strange hallucinations. They do it with medical students sometimes in psychology studies and people will say, "I can hear voices" "I'm convinced the telephone is ringing" "I'm seeing things". And it's probably because in the same way as we were discussing earlier, when you have a tinnitus, this is the hearing part of the brain, failing to get a signal from the ear's cochlea, so it turns up or amplifies the signal a bit. And up comes the noise, the hiss, which is what you end up hearing as tinnitus. It seems like when you deprive the visual system of inputs and other parts of the brain, they start to invent signals or increase the amplitude of signals that are already there at low level and it makes them manifest a very real experience. Would you go along with that, Ginny?

Ginny - Yeah, I think that sounds right. I mean, our brains are quite incredible things and we don't fully understand them yet. One of the things we think is that we actually store more memories than we know we do. Actually, when we forget things, it's not that the information isn't there anymore. It's often just that we are unable to access it. So it maybe that this was a memory that you don't even know that you have, but that's there. And because it was dark and it was quiet, it came back to you.

Chris - Exactly and so, it was sort of playing out in the visual system, just because that part of the brain is already sort of seeing that experience.

Dave - I guess the other effect is certainly I get sometimes as I go to sleep, I start seeing random images and if you're kind of getting to bed and turning lights out, it might be something related to sort of starting to dream while still being awake.

Chris - That's certainly true. It could be sort of that weird phase between being awake and being asleep. You do have rather strange experiences. They're called hypnagogic experiences, aren't they?

Ginny - Yeah. There are even some people who can have lucid dreams where you can sort of control your dreaming and it's almost like you're awake, but you're dreaming, but you're asleep and we don't fully understand how they do it. But it could be something on those lines.

Why do mirrors reverse but not invert things?

Dominic - Well, in fact, it's a bit of a myth that mirrors reverse things because if you look in the mirror, you wave your left hand, you look in the mirror, the waving hand it's actually on the left. It's exactly the right side it should be. But if, let's say, I'm looking at Ginny and if I was sitting behind Ginny in a car and we stuck out our left hand, our right hand, we'd agree as to which side was which. But of course, to face me, Ginny is sitting on a swivel chair. She's turning around to see me. She has inverted her sense of left and right when she's turned around to look at me. Another that Ginny could turn around to face me will be to stand on her head. She is now trying to do that in the studio. I'm not sure that's going to end well, but of course, rather than inverting her sense of left and right, she's then inverted her sense of up and down. So, the inverse is in fact, when she turns around to look at me, rather than when I look in the mirror.

Chris - And so, the answer is.

Dominic - The answer is, that nothing is actually inverted when you look in the mirror, but things are inverted when we face each other in the studio.


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