One way of looking at it is that most mirrors are made out of something that conducts like a metal.  When the light, called an electromagnetic wave, that means that it had an electric field which is oscillating and vibrating.  When this light hits the metal – because it’s an electric field it means the electrons which are free to move inside a metal will start to vibrate backwards and forwards.  If electrons are moving backwards and forwards this means an electron moving backwards and forwards will create a vibrating magnetic field.  That’s how you create light in the first place.  You create another electromagnetic wave. The way in which they’re moving by the light hitting the metal will cause light to be emitted in the opposite direction.  It will reflect off in the way you’d expect light to reflect off a mirror.  Light comes in, causes electrons to move which then re-radiate the light out again as the reflected light comes off again.

Yes.  There’s a reason for saying that.  The reason is that Brian Fulton, who’s Professor of Astrophysics at York told me that.  So I know it’s right!

The reason is that the sun is so dense because it’s such a huge body with so much pressure in the middle that the photon effectively behaves like a gigantic game of pinball.  The photon gets banded around all over the place and finds it very difficult to escape.  If you extrapolate back to the reaction, the fusion reaction: four hydrogen atoms fusing together to make one helium and some energy.  The energy that came was probably made at least a million years ago to make that photon.  It’s just taken that long to filter its way to the surface.  If you took it to its logical conclusion if the sun suddenly stopped all its activity now you’d still probably have a million years of light locked away inside.

Baby teeth definitely do have roots and I have a painful personal experience to recount on this front.  When I was about 14 my dentist decided that I had too many of my milk teeth left and decided they needed pulling out.  He pulled them out and it was terrifically painful because they all had very long roots.  The ones that had fallen out didn’t have any roots.

The reason is that when you have secondary dentition, or adult teeth, they come up underneath where your baby teeth are and they erode the root away so this loosens the tooth and makes it fall out.  Only once there’s a secondary tooth to come in its place because evolutionarily speaking it wouldn’t do to have a period with no teeth.  If all your teeth just fall out then you’d have nothing to replace them with.  You might starve if you were back in ancient history and didn’t have the welfare start to look after you with pot noodles.  That’s why you have this dissolving of the root in order that the tooth can be replaced by secondary dentition.  What he’s seeing is nature in action.

Yes indeed.  Helium does strange things to your voice because it is much less dense than air.  In your throat it is acting a bit like a musical instrument.  You get sound waves vibrating backwards and forwards, up and down above your vocal cords.  That gives rich timbre to your voice.  It picks which frequencies of your voice to amplify.  Helium is a much lower density gas than air and that means that sound travels much faster in it.  Then your throat will vibrate at much higher frequencies.  It will amplify the sounds at much higher frequencies.

To reverse the helium effect you’ll need a much denser gas than air.  There are a couple of good ones.  Xenon would work beautifully, which is a noble gas, very safe.  Another good one to try is sulphur hexafluoride.  Both of these are much denser than air so you’ll amplify the much deeper sounds in your voice.

It’s all because bacteria have what’s called a tropism.  They are set up or they are specialised in order to survive in certain environments.  They might have, for instance, molecular grappling hooks which are called pili.  These are the bacterial equivalent of Velcro®.  It allows them to stick on to certain tissues.  Different tissues in our bodies have different chemical environments.  If you look at say, your bladder and the urethra people get urine infections because specialised forms of E. coli called uropathic E. coli can stick onto the wall of the bladder and also onto the urethra.  Then your body tries to prevent them from doing that by having this sort of anatomical Teflon® in the form of very slippery cells.  The E. coli have very strong Velcro® which enables them to stick.

Other bacteria would just be washed away. In the blood stream there are some bacteria that could cling onto the heart valves.  They can do that because they’ve developed an ability to recognise the surface of the heart valve, stick on and then secrete this thing which is called a biofilm: a protective layer which stops the immune system getting at it.  It’s not so much that they know where to go.  It’s more that by chance they find themselves in the right place and they have the ability to stick on and make a home there.  Different bacteria thrive in different environments because they’re specialised to exist in those particular places.

Not all wind turbines do have three blades.  I’ve seen some in Spain which have four and some older ones only have two.  Some old-fashioned windmills have up to six or eight.  Three seems to be the optimum for wind turbines.  There’s a few reasons behind that.  One of them is that if you have too many blades on a wind turbine each blade as it moves through the air leaves a vortex behind it.  It’s very like if you look at a plane taking off you can see swirling air behind to two wigs of the plane.  Wind turbine blades are very much like a plane’s wing.  You get a swirl left behind a moving blade.  If those interfere with one another that can cause big problems.

That’s similar to a boat propeller only having three blades.  If you had more blades you’d think you’d move more water but actually it would become self-demolishing in terms of the benefit.  That’s the optimum choice between weight and materials and efficiency.

If you have only two blades because the wind’s moving faster higher up than lower down then it tends to, if the blade’s pointing upwards, it puts a big twisting force on the bearings. It can damage the bearings with the horizontal force.

You can actually steer a boat that way.  With big boat propellers, really big propellers the water is denser at the bottom of the propeller than it is at the top.  The propeller as it turns round is creating more of a push to the side at the bottom of its run than at the top.  If you know which way your propeller rotates by giving the engine a big burst of power you can enable it to do what’s called prop walking.  It gives you an extra kick in one direction which can make it really easy.  That’s how these really clever people get their boats into really small spaces just because they’ve learned they can use that trick just to get some extra movement in one particular direction.

I’m not sure that it would go out of focus but something it will definitely do is affect the polarisation of the light.  Polarisation, if you imagine light’s a wave: if you imagine a wave on a tightrope -  vibrate it up and down that would be vertically polarised.  If I vibrate it from side-to–side and it would be horizontally polarised.  The light will hit the mirror as an electric current flow (see this question) – what magnets do to an electric current is cause them to bend and move in circles.  Because the magnetic field will cause the electrons to bend when the light hits it the reflection will have a slightly twisted polarisation to the one which came in.

One of the problems people with cerebral palsy have is very often a sort of ‘locked in’ syndrome.  They have preserved intellect and a very acute brain but the problem is it’s translating the messages of what they want to do down to the bits of the body that can make those things happen such as move the limbs or walk around.  That’s where they have the problem.  The device that you’re referring to is a piece of work that’s been done by Andrew Schwarz.  He’s in America and what he’s done is to produce a system, a computer that can decode the neurological chitchat that goes on in the brain’s motor-neurone areas and work out what sort of movement (at this stage a monkey) but a monkey’s brain works very similarly to how ours works.  He can decode the chit-chat between the cells and get the monkeys to move a robot arm which enables them to feed themselves so very fine and accurate movements just by listening to what the brain’s doing.  I don’t think there’s any doubt that it would be possible to use something similar for cerebral palsy.  There’s every reason to think that it might just work.

At the moment, no one’s actually doing it in humans although they are doing it in a very limited way they’re not actually doing it at the resolution that these people in America are. It’s very experimental.

The biggest effect is actually what colour something absorbs.  Different colours of light have different energies.  The bluer the light, and light comes in blobs called photons, the more energy the photon has.

The electrons inside atoms can only have certain energies so they have what are called energy levels.  Maybe they can absorb a certain amount of energy or twice that amount or two and a half times that amount, changing in discrete amounts.  They move up and down energy 'shells', between orbitals and energy levels.  A substance can only absorb light if the difference between one energy level and the next is equal to the energy of the photon.  It will gain the right amount of energy to absorb that photon of light.

This is also is why substances have that characteristic spectral fingerprint, an absorption pattern of certain frequencies of light that they absorb and certain lights that they reflect.

Fluorescence is a related effect.  This happens when you get high energy photons, for example ultraviolet light, which hit an atom.  The atom will absorb that energy and then instead of releasing it all in one big lump it releases it in two or three smaller lumps which will be a different colour to the UV, a lower frequencies that you can see.  Something can absorb ultraviolet light then emit blue light or green light and it looks like it’s glowing.

Another thing a lot of people don’t often realise is that most of the different colours in nature are flowers.  And these colours are actually created by the same molecule, a molecule called anthocyanine.  What the flower does is to make the petal more acidic or alkaline.  What this does is to add or remove hydrogen from the molecule and this changes the way the electrons whizz around in the molecule.  This changes the light wavelengths that they can soak up. The petals may be basically different colours but it’s all down to the same chemical, anthocyanine!

It’s called a solar radiometer, it turns in a circle and it’s amazing to think this thing can turn just by sunlight shining on it.  There’s no motor in there.  It’s just literally balanced on this tiny needle point and it spins round in the sun.  How does it do it?  If you look closely at those vanes, at those panels you’ll see that they have a light side and a dark side.  One side is soaking up the light, the other is reflecting it.  This is the best evidence there really is that light can be a particle and a wave.  Light can impact a punch or a kick when it hits something and it can push it along.  This is literally the light pushing this thing along. 

People are talking about building solar sails so you can make a craft, send it up to space, light will bounce off it and you’ll get a very tiny push by each photon of light bouncing and pushing it back

An alternative explaination is that the Crooke’s radiometer which you’ve got works in a slightly different way.  They’ve got two sides – one side shiny and one side’s black.  If the sunlight hits the black side it’s going to heat up more than when it hits the shiny side.  There’s a very low pressure gas inside the radiometer.  If the low pressure gas is near the hot side then it’s going to get hot and expand and get pushed away and therefore push the radiometer round a bit.  If it hits the shiny side it’s not going to be nearly as hot.  It doesn’t get nearly as much kick so the black side gets pushed back and the shiny side gets pushed forward and it spins round.

Firstly, the reason it floats up in the air is because helium is lighter than air.  It’s a bit light a boat floating on the water.  The balloon is pushing air out of the way that weighs more than the weight of the helium and the balloon together so the heavier air comes in underneath the balloon and the balloon is pushed up in the air.  That’s why the balloon goes up in the air and this process will carry on going until the helium filled balloon reaches a point or an altitude at which the air is the same density as the helium + balloon effectively is.  That is the maximum height which defines how high it can go.

As you get higher up the air pressure reduces so the balloon is going to try and expand.  Depending on how heavy the balloon is and how quickly it’s losing helium (it can get through the gaps in the rubber polymers quite easily) the balloon will keep on going upwards until either it gets heavy enough it can’t get any higher or the difference in pressure inside it and outside it is enough that it will explode.  I think if you just let go of a helium balloon it will just escape and will go up a few miles. But we couldn’t tell you exactly how many.

Recently, Michel Fournier was planning to do a parachute jump from the edge of space a couple of weeks ago and unfortunately his balloon took off without him.  His balloon would have got him to the edge of space because they use a material that can keep on expanding the farther up it goes, or by starting with the balloon almost entirely empty.  There’s just a tiny bit of helium in the top of them, so as they go up there’s lots of space for that helium to expand into.  They go up higher and higher.  I think the altitude record for an unmanned balloon is about 53km.