Chasing Rainbows: The Quest to Understand Light

Why Newton stuck a needle in his eye, how the brain sees and echoes of the Big Bang...
17 March 2015
Presented by Chris Smith, Kat Arney
Production by Graihagh Jackson.


People and Colour


Is it a particle? Or is it a wave? This week we're looking at light. From its earliest origins and what it can reveal about the Big Bang, to why Newton prodded his eye with a needle to probe the origins of colour, how the brain decodes the visual world and bionic implants to reverse blindness. Plus, in the news, a revelation in the remarkable colour-changing capabilities of chameleons, how an ultrasound can combat Alzheimer's Disease, and what people do with their fingers following a handshake...

In this episode


01:12 - Alzheimer's ultrasound breakthrough?

Using ultrasound, scientists have successfully treated Alzheimer's disease in mice...

Alzheimer's ultrasound breakthrough?
with Gerhard Leinenga, University of Queensland

On 12 March 2015, celebrated author Sir Terry Pratchett passed away after a Ultrasoundpublic eight-year battle with Alzheimer's Disease. This condition, which causes progressive loss of mental faculties, affects 40 million people around the world, and this number is expected to triple in the coming decades as the world population ages. But apart from symptomatic relief, there are currently no treatments that can actually halt the disease process. Now University of Queensland scientist Gerhard Leinenga has found that ultrasound waves can be used to remove from the brain the toxic chemical amyloid-beta, which, scientists think, causes Alzheimer's Disease. He spoke to Chris Smith...

Gerhard - You can think of the Alzheimer's disease brain as a toxic environment for the cells in the brain. One of the main creators of this toxic environment is this molecule called amyloid beta which stops nerve cells communicating with each other and also, impacts on their health and survival. So, we knew that there was a high concentration of amyloid beta in the brain and a low level in the bloodstream. We wondered whether we could remove or flush out some of this amyloid beta by making the blood-brain barrier leaky.

Chris - It would effectively ooze out of the nervous system and into the bloodstream.

Gerhard - Potentially, some mechanism like that.

Chris - How easy is it to temporarily make the blood-brain barrier leaky then?

Gerhard - Up until very recently, difficult or impossible to do this in the way that was safe and reversible. So, we used a new technology called ultrasound to open the blood-brain barrier. So ultrasound is basically just the application of soundwaves.

Chris - How does the ultrasound open up the blood-brain barrier?

Gerhard - So, it does this through an interaction with molecules injected into the bloodstream called microbubbles. These are little gas-filled shells that ultrasound makes them expand and contract. This affects the blood vessels of the brain so that it makes the barrier slightly leaky. You can think about it as little holes or slight leaks between the cells where molecules can squeeze past.

Chris - And how do you know that's actually working? How do you know that the blood-brain barrier is being dismantled albeit temporarily by this process?

Gerhard - You can inject the molecule that normally doesn't get into the brain when you inject it into the blood and what we found is that these molecules were present in the brain. We could detect them after the treatment.

Chris - What about when you repeat this and you do this with mice that have this mouse equivalent of Alzheimer's disease? What happens to them?

Gerhard - So, when we open the blood-brain barrier in these mice over a course of treatment, we found that the amyloid beta levels were reduced by about 50% and that the memory of the mice was improved.

Chris - So, how do you think it works?

Gerhard - One of our original hypothesis was that the amyloid beta could be flushed out into the bloodstream through a leaky blood-brain barrier. But we couldn't detect high amyloid beta levels in the bloodstream. So, I wanted to look after that what was going on actually inside the brain. Another way that the amyloid beta levels can be removed is through the actions of microglial cells in the brain. These cells have some ability to eat the amyloid beta and remove it. But what I found was that after the course of ultrasound treatments, the ability of the microglia to eat the amyloid beta was about doubled.

Chris - These cells were effectively consuming and removing the toxic protein that are built up and was that rendering it safe?

Gerhard - That's what we found within the microglial cells in compartments that normally degraded or chewed up and make it safe.

Chris - Could there not be a downside to albeit temporarily dismantling your blood-brain barrier presumably, it's there for a reason?

Gerhard - When we think about opening or making the blood-brain barrier slightly leaky, you need to think about it being made leaky to some molecules but not others. So, the size of the opening of the blood-brain barrier is enough say, for smaller molecules and proteins to get into the bloodstream but not large enough for say, bacteria or viruses to get into the brain. We didn't see any side effects in the mice that we treated. In fact, their behaviour was improved and there was no damage to their brains or the cells in their brains.

Chris - Would you regard this as a possible therapy for humans?

Gerhard - I think it is a possible therapy for humans. Once we can scale up and adapt the technique from treating a very small brain such as the mouse brain with a thin skull to a large brain like a human brain with a thick skull, I think that this could definitely be applied potentially in Alzheimer's Disease patients.


05:46 - 'Ouch zone' identified in the brain

Scientists have homed in on how the brain gauges pain intensity...

'Ouch zone' identified in the brain
with Dr Andrew Segerdahl, University of Oxford

We've all experienced the sensation of pain, from an annoying paper cut, to the Brainintense agony of breaking a bone. And scientists have long been looking for the part of the brain that decodes how much something hurts. Now Oxford University's Andrew Segerdahl thinks he's identified this human "ouch zone" which is catchily called the dorsal posterior insula, as he explained to Danielle Blackwell...

Andrew - Pain is a complex and multidimensional experience. Anyone who's suffered pain, either chronic or even just a bout of really bad headache can tell you that is the case. It involves not just features of how intense it is and where it is on your body but also, it often can involve memories of previous pain experiences or even more emotional types of experiences like anxiety, about when it will stop or why it's arising. So, pain becomes complex to study, because every time you put someone in pain, you have to deal with each of these variables.

Danielle - So, what is this new technique that you have used and how did it help you decipher the brain region that is involved in pain intensity?

Andrew -  So, the brain imaging approach that we used is ASL which stands for arterial spin labelling. What ASL does is, as your brain is working and you're thinking and you're using different parts of your brain, those different parts of the brain need oxygen to be active. And arterial blood is the main delivery system for oxygen. So, what this type of imaging approach does is it actually uses those principles and we can use that to actually tag the blood so that it actually becomes a signal that can be photographed with the imaging approach. We can actually start to make calculations about absolute amounts of blood that have flowed to a region A versus region B.

Danielle - What you were looking at then is the changes in blood flow and I guess the changes in blood flow or a marker of changes in how much brain activity is going on in that particular region.

Andrew - Exactly.

Danielle - So, how did you use this to look at changes in brain activity? Were you changing the pain intensity at the same time?

Andrew - Exactly. So, the subject will lie down on the scanner. We put them in and then we put a bit of capsaicin cream which is like a chilli pepper cream onto their leg. And gradually, that experience goes from being totally innocuous - you don't feel anything - to slightly warming. And then gradually over time, that warming starts to become painful. And it gradually habituates. So, that word means that essentially, the pain starts to go down a little bit. What you can then do is actually track how that pain intensity is changing by asking subjects to actually rate how much pain are you feeling at this moment and we're actually scanning them as well at the same time. and we do this for about a 2-hour period of time. And it's that which allowed us to actually zone in on the dorsal posterior insula as tracking that change of pain, the intensity at it unfolds.

Danielle - So, you were able to map the changes in pain intensity that the participants were reporting with the changes in activity and blood flow in this particular region of the brain.

Andrew - That's exactly how this type of approach works.

Danielle - How easy is this technique to do? Is it something that we could be using soon to understand if people are in pain? So for example, if people aren't able to communicate, could we still find out how much pain they might be in?

Andrew - The sure answer is that at the moment actually, we're at the stage where brain imaging is becoming really common clinically. So, we see really nice high-powered scanners being installed in hospitals globally. So, we very much are hopeful that this type of a result becomes potentially very helpful, as you say, to image those populations that don't have the capacity to communicate how much pain they may or may not be feeling. So, I'm thinking about people like infants, small children, those that may be in a comatose state or experiencing dementia, or we could really understand how much pain they may be experiencing. Or in another way, how much relief they may be experiencing with a new type of pain therapy.


10:34 - The real "Finding Nemo"

Why "Finding Nemo" would have been a very different film, if it had been true to science...

The real "Finding Nemo"
with Max Gray, University of Cambridge

FameLab is an international science communication competition where contestants take to the stage and talk to the public about science. During the last month or so, heats have been held in cities across the UK and we've been hearing from the finalists in Cambridgeshire over the past weeks. Kat Arney spoke with regional champion Max Gray, and asked how if felt to be in the finals...

Max - It feels great actually. I'm slightly surprised still. But no, it feels fantastic.

Kat - Now, your winning talk was about Nemo the clownfish. Is this what you actually work on as a researcher?

Max - No, it's not. I do work on the behaviour of fish in coral reefs but not on clownfish. I actually work on cleaner wrasses which are fish that you find throughout the Pacific.

Kat - Well, let's hear your price winning stuff. So, if you could give us your 3 minutes about Nemo, off you go.

Max - Yes, of course. So usually, when I introduce myself to new people, it's not on very larger scale, but what I tell people is that I'm a marine biologist. What I do is I study the behaviour of fish in coral reef communities and their reaction at that point is usually, "Oh! Something like Finding Nemo" which it's not quite. But regardless, that film isn't actually a bad portrayal of what a reef ecosystem looks like. People often follow this up with, it's a question like, "So, how accurate is the film?" And moreover, do the inaccuracies of which there are obviously some in the film, do they annoy me? Which is ridiculous! I mean, it would be like asking any other zoologist whether the inaccuracies in the Lion King would annoy them and as if anybody was going to go to the Savannah and expect to see an immaculately choreographed dance routine performed by giraffes and zebras so no, it doesn't annoy me.

That being said, what I am going to talk about is exactly those inaccuracies in Finding Nemo and why it will be a very different film indeed if it were biologically accurate. The reasons this is the case is because two very interesting details of how clownfish and anemone fish in general behave. First of is something called sequential hermaphroditism which is where the fish start off broadly speaking, sexless or ungendered if you will. And then as they grow and they become the second most dominant individual in their little anemone society, they become male. They develop testes. As they progress, they take over as the biggest most dominant individual in our society, they change sex to become a female.

So, if you remember the film in Finding Nemo, at the beginning of the film, you have a breeding pair of clownfish and they're happy, they've just created a nice large brood of eggs together and unfortunately, what happens next is that the female, the mother fish gets eaten by a barracuda.

So far, so accurate - that does happen.

However, what would've happened next would be that her death would've triggered Nemo's father to undergo a sex change and become a new mother which would make for an interesting film all that possibly more of an art house than a blockbuster flick.

Now, the second thing that's interesting about this fish is something called filial cannibalism and this is the process by which fish or any animal in fact will eat their offspring if something goes wrong and they find themselves in the disadvantaged situation. In the case of clownfish, new parents which they are in the film are even more likely to do this. They do this with alarming regularity. So, what's really likely to have happened in a sort of Finding Nemo situation is that the mother fish will have died, the father/ now, mother fish will have eaten all of the eggs including Nemo which would have produced a very different film indeed with her cannibalistic transsexual parent.

Cape Chameleon

14:13 - Chameleon colour-change breakthrough

Scientists have discovered how the kings of the colour-change, chameleons, alter their skin hue...

Chameleon colour-change breakthrough
with Professor Michel Milinkovitch, University of Geneva

Male chameleons have a well-deserved reputation as the colour-changing kings of the natural world, quickly switching their skin colour into a wonderful array of hues. But how do they do this?

It was previously thought that chameleons performed this quick change by shuffling pigment chemicals around cells in their skin, but there wasn't any actual evidence to support this idea. Now a team at the University of Geneva have taken a closer look, using a high-powered electron microscope. They've discovered that a special layer of colour cells in the chameleon's skin - called iridophores - contain tiny nano-crystals that bend light, and give the reptiles their colour-changing ability. Kat Arney caught up with Michel Milinkovitch to find out more...

Michel - We came up with this crazy hypothesis that given we didn't see how the animal could change colour, we thought that maybe, what is happening is that this animal was able to actually tune the distance between their nanocrystals because that would of course shift the light that is reflected. The photonic crystals act like a selective mirror. All light is going through except a specific wavelength that will be reflected with 100% efficiency. So, what you get is a very bright and very pure colour. But the wavelength that is reflected specifically is a function of the distance between the successive layers of materials. So, when the distance is very short, it would be blue light and when the crystals are more distant from each other it would be more yellow or red light.

Kat - Then when you shift the organisation of these layers of crystals then it basically goes a different colour. Were you surprised when you realised that this was happening?

Michel - Yes, we were. We never thought that actually this would be a possibility, for the animal to actively modify the geometry of the photonic crystal to change the distance among the nanocrystals.

Kat - How do you think that the chameleons are doing this?

Michel - Maybe they do it in the same way as we recapitulate the phenomenon ex vivo. We take a piece of skin, we put that in a Petri dish and then we change the concentration in salt basically, of the solution of which we keep the sample of skin. And therefore, the cells will shrink or swell depending on the amount of soil that you put in the system.

Kat - That will mean that the crystals get closer or further apart.

Michel - Exactly. That's what we were hoping for, is that by changing the geometry of the whole cell, you would force the lattice of nanocrystals to also shrink or swell. That's what is happening. We see exactly that. We see really single cells going from red to blue, passing by all the other wavelength of the spectrum.

Kat - It must be wonderful to work in your lab and see all these beautiful colours changing in front of you. It must make you think that nature and chameleons are just quite amazing.

Michel - These are amazing creatures. Actually, that's probably the reason why there is so much interest for these results. People really love chameleons because they have many different features that are spectacular. They have these protruding tongues that they can project at a distance to capture a prey. They have these weird feet and then they have these spectacular abilities to change colour which is really something unique in lizards. They have an amazing toolkit in their skin.

17:56 - Finger-sniffing good

Nice to sniff you? Scientists have shown that people sniff their fingers twice as often after a handshake...

Finger-sniffing good
with Idan Frumin, Weizmann Institute

The last time you greeted someone, did you shake their hand? Now a harder question: what did you do with your hand afterwards? You probably didn't realise it at the time but the likelihood is that you subconsciously brought it up to your face and sniffed it! Using hidden cameras, Israel's Weizmann Institute researcher Idan Frumin has found that we humans do the socially more acceptable equivalent of what two dogs do when they first meet, as he explained to Chris Smith.

A transcript of this interview with Idan Frumin about people sniffing their fingers after shaking hands is available.

People and Colour

21:38 - What is light?

Light continues to perplex scientists today, so we take a look back in history to try and understand what it is...

What is light?
with Scott Mandelbrote, University of Cambridge, Zephyr Penoyre, CHaOS

To most people, "light" refers to something that comes in a range of colours and isPeople and Colour something you can see. But visible light is actually part of a much larger "electromagnetic spectrum" that ranges from long-wavelength radiowaves at one end of the scale, to very short wavelength X-rays and gamma rays at the other. The part of this spectrum we can see sits roughly in the middle. And to complicate matters, sometimes light behaves as though it's a wave, while at other times, it behaves like a stream of tiny particles. One of the pioneers of the study of light was Isaac Newton. Graihagh Jackson went to meet historian Scott Mandelbrote at Cambridge University Library to see some Newton's original notebooks where he documented his attempts to understand this mysterious entity...

Graihagh - As we walk down these aisles, we've walked past Charles Darwin and now that we're in Newton's aisle, I can see Kelvin's papers and a bit further down, Ernest Rutherford's. It's a staggering collection of scientific manuscripts.

Scott - Yes, well the University library holds one of the finest collections of scientific manuscripts in the world and has held Newton's papers since the late 19th century.

Graihagh - The papers I had come to see had been especially laid out in the manuscript reading room. [I'm so excited!]. As you may be able to hear, I was just a tad amazed at the thought of seeing the original notebooks that Sir Isaac Newton himself had handwritten.

Scott - Well, we're now in a room which has a number of Newton's papers, a wonderful collection and some of the most important things that Newton wrote.

Graihagh - And they're in fantastic condition and I'm beginning to see why, because they're beautifully laid out on what looks like individual pillows for each and every single notebook! I wonder if we could focus on this one in particular because it's a sort of an A5 notebook and there's what looks like an eyeball with a stick pointing at it. What's he describing here?

Scott - Well, what he writes is, "I tooke a bodkine & put it betwixt my eye & [the] bone as neare to [the] backside of my eye as I could: & pressing my eye [with the] end of it there appeared severall white darke & coloured circles. Which circles were plainest when I continued to rub my eye [with the] point of [the] bodkine..."

Graihagh - Yes, you did hear that right. Newton peeled back his eyelid and stuck a bodkin or what we call them today, a giant needle, between his eyeball and cheekbone. He also stuck a brass plate in there too and later, stared directly at the sun until he went blind! Fortunately, Newton's eyesight recovered in all incidences. Why bother? You may wonder. Well, Newton was interested in the nature of light and how we see things around us. This particular experiment was designed to see if colour was the product of the outside world or created within the mind. Although sticking a needle in his eye didn't exactly determine this, it was one of many steps that led him to demonstrate how white light is made up of 7 individual colours. Prior to this revelation, it was widely believed that light was pure and that colours were created by the mixing of light and darkness. So, white light is 7 colours combined. But what physically is light? I met Zephyr Penoyre, a trainee physicist at Cambridge University, on the river to see if he could give me any answers.

Zephyr - Newton was one of the big supporters of the idea of light as a particle which he believed in because he saw how light reflected in straight lines off a surface, just like a ball bouncing off a surface.

Graihagh - Thomas Young came along and he said, "No Newton. You're wrong." What did he say?

Zephyr - He came up with a fantastic experiment where you take two small slits in a piece of material and shine light on them. If Newton was right, what we'd see is 2 dots of lights.

Graihagh - I can see that working.

Zephyr - It does seem to make sense but actually, if you do it, you don't see that, you see a series of white and dark bands.

Graihagh - A bit like a bar code then.

Zephyr - Yeah, it looks exactly like a bar code. This is a thing that only waves do. We've got here two poles and a river and I'm going to show what interference looks like.

Graihagh - Okay, let's go for it. We have two punt poles because we are on River Cam and you're going to dip them in and out of the water at the same time.

Zephyr - Yup! So, I'm going to dip them in and out. They're quite heavy.

Graihagh - And we're seeing a series of ripples from both of the poles as you'd expect, like you drop a stone in a pond, you see the ripples cast out. But actually, where the ripples meet, something quite interesting is happening.

Zephyr - What a ripple is, is a series of peaks and troughs moving outwards from a point. But where the two ripples meet, some places, the peaks are together and they add up; some places the troughs are together and add up. But some places, the peaks and troughs meet and they add up to nothing. Because waves have this property of adding up and cancelling out, this is exactly why we see the series of light and dark stripes on the wall. This is why Young's experiments proved that light must be a wave.

Graihagh - Problem solved! That's what I saw in my textbooks when I was 16, light is a wave, right?

Zephyr - Well yeah, light is a wave. But now, the next issue is, how light travels. So, we know that sound waves must move through a solid object or through air. Water waves must move through water. so, what does light move through?

Graihagh - Air? Is it not the same?

Zephyr - Well, we know that light does move through air, because we see light on Earth. But we also see light moving through space. And we know that space is a vacuum. Sound can't travel through space because there's nothing to transfer the vibrations in space. But somehow, light does and that was the next question which really puzzled scientists.

Graihagh - How does light travel then?

Zephyr - Someone called James Clerk Maxwell came along who showed that it's mathematically true that electric and magnetic fields can make waves. And he put this together to show that light is actually variations in electric and magnetic fields. This not only explains how light travels through a vacuum, but also explains things like how light comes in different colours and its different temperatures and energies.

Graihagh - Different wavelengths of light have different properties and that's where your radio waves, microwaves and x-rays come in. It's all light but just in different forms. Light then is a wave and we can all breathe one big sigh of relief. Well, sadly not. Einstein came along with photoelectric effect. He noticed more electrons were emitted from a metal when certain colours of light were shone on it. This is weird because well, waves shouldn't have that effect on electrons. Particles, on the other hand, do. So Einstein said, "Hey! You know what? Light comes in little packets or bundles and I hereby call them photons. Does that mean Newton was right all along when he said light was a particle. Well then Einstein developed his theory of special relativity and said light was a field of waves. Yeah, I know, confusing. So, this takes us right back to square one - what is light? A wave, a particle, or could it in fact be both?

Zephyr - In some ways, Newton was right. Light can behave like a particle, like a photon. But at the same time, Maxwell is completely right and Young, when they said that light behaved like a wave. Light behaves as both. We call this wave-particle duality. And it's something that we see a lot of evidence for in science, but we still can't really explain why light will behave as a particle sometimes and a wave with others.

Graihagh - Does this mean we still don't really know what light is?

Zephyr - It kind of does. We still might find that there's a better explanation for light or it may just be that light is going to remain this confusing thing that we don't quite understand.

An Eye

30:52 - Bionic eyes

Light is fundamental to how we see, but what happens if our eyes can no longer detect light? Could we make bionic eyes to treat blindness?

Bionic eyes
with Dr Patrick Degenaar, University of Newcastle

We depend on light more than you might realise - our eyes are completely An eyedependent on light to sense the world around us. Without light, we couldn't experience a beautiful sunset, see the faces of our loved ones, or view the natural marvels of the world. But how do we see? And what happens when this process stops working? Patrick Degenaar works in the groundbreaking field of neuro-prosthetics. These are devices or methods that can substitute motor, sensory or cognitive brain functions that might have been damaged as a result of an injury or a disease. Patrick explained to Chris Smith how these devices might work one day in the future...

Patrick - Fundamentally, light comes from objects. They go through the optics of the eye and get imaged to the back of the eye called the retina. When the light hits the back of the retina, we have some cells called rods and cones which act as photoreceptors. They sense the light. Once they've sensed the light then the signal goes through a series of processing. And then finally, the final stage of the eyes is cells called the retinal ganglion cells which project through something called the optic nerve towards the back of the brain. It's worth noting that the visual cortex, the part of the brain which processes our light that's at the very back, which is why boxers, when they get punched in the face see stars if you like because that's the visual cortex pressing against the back of the skull.

Chris - Sounds uncomfortable. So, when someone has a problem with their vision, it could be any part of that pathway which is damaged or breaks down but what are the common reasons why people lose the ability to see?

Patrick - The vast majority of people who lose sight in this planet are because of a condition known as cataracts. And that's where the lens in the eye basically becomes opaque and can no longer allow light to come through. But in terms of what I'm interested in which is in prosthetics, I'm much more interested in conditions which cause some damage but leave the remaining retina intact. One particular condition is called retinitis pigmentosa which has a prevalence of about 1 in 3,000 people. In this condition, the light sensing cells are destroyed. But this still leaves the rest of the eye intact. If that gives then the possibility that if we can communicate with those remaining cells, you can then communicate with the brain and therefore, restore some kind of visual signal.

Chris - So, because the rods and cones have degenerated or broken down, there's no cell there that can physically collect light and turn it into electrical signals that the retina can work on. But because the rest of the retina does still work, were you able to put new signals in, mimicking those missing rods and cones, you could potentially have a working visual system again.

Patrick - Correct.

Chris - But how might we be able to do what you're aspiring to achieve, Patrick?

Patrick - Well, for many years, people have looked at visual cortical prosthesis. It's actually dates way back to the 1920s in fact. But in 1992, people working on the retinitis pigmentosa disease discovered that the retinal ganglion cells were still intact. For the last 20 years, various groups around the world have looked at implanting various types of electrodes and using those electrodes to stimulate the remaining cells. They could bring back some flashes of light which when there was sufficient electrodes in place, you could make some kind of very basic type of image.

Chris - Is this working? Do we have devices that are capable of stimulating the right cells in the right place to create a visual image that makes sense?

Patrick - In basic theory, it shouldn't work at all. But it works to a very simple level, fundamentally mentioned before that the eye is really trying to process the world around us. What the eye does is it splits the signal into on and off pathways. These are kind of positive and negative. Fundamentally, this is about creating contrasts. Now, there's only information if there's a different between the plus and the minus pathways. So, if you stick a big electrode in and stimulate both simultaneously, it shouldn't actually work at all. It turns out that the off pathway is just a little bit slower than the on pathway. As a result, when you do the stimulus, you get a little bit of contrast. You still get to see something. But it's relatively weak.

Chris - So just very briefly Patrick, are we in a position where we can actually make devices that can stimulate the right bit of the eye to give people some kind of picture?

Patrick - There are no commercial devices in place which will give a very, very rudimentary vision. But the next generation of devices that are about to come out are based on a new technique called optogenetics. These can basically genetically engineer a new layer in the light eye to be light sensitive. This can then do that separation between on and off pathways much more accurately, much, much more stronger. And this should bring back some kind of vision - well, you'd still be legally blind but it would be significantly better than what is currently available.


36:02 - Do you see what I see?

Light is fundamental in how we see the world around us but how do we perceive it? Do you see something different to everyone else?

Do you see what I see?
with Dr Richard Clarke, UCL

Sir Isaac Newton was interested in whether colour is a product of the outside world,Glowing Eye or created within the mind. Prior to him, the Greek philosopher Empedocles thought light streamed out of eyes and bounced off objects and this what enabled us to see them. So is our perception of colour and everything else around us internal or external? Or could it be a mixture of the two? UCL physicist-come-neuroscientist Richard Clarke has been developing a series of tests especially for Kat Arney to find out...


43:34 - Unlocking the secrets of the universe

How do astronomers learn about the Big Bang? By studying fossilised photons in light left over from the origin of the Universe...

Unlocking the secrets of the universe
with Professor Anthony Lasenby, University of Cambridge

There's a vast amount of light we can't see. In fact, visible light only makes up a Spacetiny proportion of the total light spectrum. X-rays, gamma rays and radio waves are all examples of light we can't see. Since the 1930s, astronomers have known that the secrets of the Universe could be revealed with these types of invisible light. Graihagh Jackson spoke to cosmologist Anthony Lasenby about a particular kind of light emitted at the beginning of time...

Graihagh - A few kilometres west of Cambridge sits Mullard Radio Astronomy Observatory, a collection of what looks like huge satellite dishes that stare at the sky day in and day out. They're on the hunt for a different kind of light though - a type of light we can't see and that's radio waves.

Anthony - I started working on radio waves in 1978 and then I moved to Cambridge in 1984, been working here ever since.

Graihagh - That's Dr. Anthony Lasenby, a cosmologist at Cambridge University and that buzzing noise you can hear is AMI.

Anthony - The whole telescope we're standing in is called AMI and that's for arcminute microkelvin imager. So that noise we just heard is AMI moving to another source in the sky.

Graihagh - If we were to put on some magic glasses that enabled me to see radio waves, just like AMI can and I look up at the sky today, what would I see?

Anthony - Well, you'd see some really bright sources. The sun emits strongly and there's lots of individual radio sources which are being studied here for many years. But the thing that's behind them all would be a sort of pattern of stipples and little knots of what we call fluctuations in the background. You get hotter bits of the sky, less hot bits of the sky, and these are randomly arranged around us.

Graihagh - What would these blotches be?

Anthony - These are basically fossils. The actual photons we see today were emitted about 400,000 years after the big bang. They're extremely important because if you look at their properties, you can infer lots of extremely interesting things about the universe.

Graihagh - These fossilised photons were emitted shortly after the Big Bang and cosmologists refer to them collectively as the cosmic microwave background. But on discovery, Arno Penzias and Robert Wilson of the telecommunications company Bell Labs initially thought it was something rather different.

Anthony - They were at Bell telephone labs and Bell were interested in understanding whether sort of the cosmic dyes were possibly going to affect radio communication on Earth. And so, an experiment was set up to basically monitor and measure these cosmic sources of noise. One of the possible explanations for this noise was that it was much nearer to home. It was actually pigeon droppings in the antenna that they were using to look at the sky, because anything locally which is warm will emit radiation and be like some universal source of noise if it's sufficiently close to you. But they eliminated that. They moved the pigeons out of their nest.

Graihagh - And I'm imagining scraped all the pigeon poo off with it.

Anthony - Exactly and after that, they were put in touch with theorists at Princeton University and they could tell from their observations that it really was intrinsic, coming from the whole sky. At that moment then the microwave background had been discovered.

Graihagh - Given that this was discovered in '60s then why are we still looking at the cosmic microwave background today?

Anthony - Because it's got this amazing information imprinted on it. But to find that information, you have to study it at much higher resolution that was possible initially.

Graihagh - When Bell's team looked out to the universe, measurements of the cosmic background radiation were uniform across the sky. There were no hot patches or cold patches and this was strange because the universe today as we see it isn't one smooth temperature. It's full of stars and galaxies, what cosmologists refer to as structures. Bell's team should have been able to see footprints of these structures when they were first developing. AKA, they should've been able to see hotter patches and cooler patches imprinted on the sky. Baffling as this was, it turns out, it was just a matter of making our telescope see in higher resolution. In 1992, a satellite called COBE hit the jackpot. It found these imprints, these ripples, everyone had been searching for. But COBE followed by subsequent satellites like WMAP and Planck were only just beginning to uncover the secrets of the universe. And even today, there's still much more to be understood.

Anthony - What proportion is there a dark energy, how much dark matter is there, how much ordinary matter is there, is the universe open or closed or flat? All these things you can read off in great detail if you can get really precise measurements in the microwave background.

Graihagh - So the quest continues with AMI and other satellites across the world.

Anthony - Well with AMI, certainly, the quest continues. Satellites, that's another issue because Planck finished about 2 years ago and we don't have another satellite at the moment. Everyone is extremely keen that we have another mission which can map the whole sky which only a satellite can do. Continuing the study of the microwave background is incredibly important for moving our physics theory. So, we are hopeful that there will be another satellite but there isn't one yet.

Electric eel

49:37 - Eels: a source of electricity?

Can we harvest the power from eels as a source of electricity?

Eels: a source of electricity?

Bonga tweeted us asking if we could ever use eels as a source as electricity? Would it be efficient? And how would it compare to other energy sources? Khalil Thirlaway caught up with Dr David LaVan from the National Institute of Standards and Technology to find out...

Khalil - All organisms give off a weak electric field. But electric eels are one of a small number of fish species that can generate strong pulses of electricity with their body and they use them to great effect. But how do they do this? I spoke to Dr. David LaVan from the National Institute of Standards and Technology.

David - Electric eels produce electricity in brief spikes, in much the same way that humans do. When a human decides to move a muscle, an electric impulse called an action potential, fires in your brain, travels through neurons causing a muscle to contract. These individual signals carry very little power.

Khalil - The eels use a weak electric pulse to scan for the natural electric fields of smaller fish in the murky Amazonian waters, where they live. Once they find something tasty, they send out a stronger pulse that can paralyse or even kill their victim, making for an easy meal.

David - The cells that produce electricity in the eel, called electrocyte,s also create action potentials. But the electrocytes are stacked together to increase the total voltage in current. Large eels can produce up to 600 volts.

Khalil - Ouch! 600 volts is nearly three times the voltage of mains electricity in the UK and 5 times what you get in America. So can we harness this stunning power?

David - It is technically feasible to power human devices from eels or electrocyte cells but practically speaking, the electricity from eels is not very useful for us. First, it's important to recognise that eels convert energy from the food they eat to electricity. There's no free energy. Secondly, electric eels are just not very efficient in producing electricity. It turns out, they can convert about 15% of the energy in their food to electricity under ideal conditions in their natural environment. However, that value doesn't consider the energy needed to maintain them in an artificial habitat. Energy needed to heat and purify their water as well as the energy needed to grow and transport their food, all would reduce the efficiency even further if you were trying to domesticate them.

Khalil - This seems like a lot of effort. How does this compare to other renewable forms of energy?

David - Commercially available solar panels like you find on many roofs these days are about 15% efficient in converting sunlight into electricity. The newest solar materials coming out of research labs are about double that efficiency. So, for the most part, it would be better off using sunlight to make electricity using solar panels, rather than growing food, to feed to an eel, to make electricity.

Khalil - So, in answer to your question, yes, it is possible to harness the electricity of eels, but no, it isn't practical for our everyday electrical needs. There are some situations however, where eel electrocytes might conceivably be a useful power source. For example, to power disposable biodegradable electronics. Scientists like Dr LaVan are also suing what they've learned from electrocytes to inspire research into designing new, artificial power sources. Thanks to David LaVan for that electrifying answer. Next week, we'll be answering this cheesy question from Chris.

Chris - Is it true that cheese gives you nightmares?


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