Black holes: the inside story...

Have you ever dreamt of climbing up the outside of a building like Spiderman? Making that dream a reality would require specially adapted adhesive feet that can take advantage of weak molecular forces of attraction between your body surface and the wall, much like a gecko. Felicity Bedford spoke to David Labonte from Cambridge University who has been investigating whether there's a good reason that this wouldn't work for humans...

David - There's only a certain range in sizes that actually use a sticky pad.  So you find  you find tiny mites, you find big geckos, you find frogs and spiders and many different insects in between, and the question that we were interested in is whether there's actually a limit, or what is the limit to the size you can grow to where you can still use adhesive pads.  And there's an interesting problem hidden in trying to stick to surfaces because as they grow in size, the amount of surface area that they have per body volume, goes down, and  it's probably easiest to illustrate that problem if you think of a tiny ant.  If you look at the ant you mostly see surface area and there's a tiny bit of volume, and if you look at an elephant you see a lot of volume but there's really not much surface area.

Felicity - It's difficult to imagine and elephant climbing with sticky feet.  You mentioned quite a diversity of different animals there, from insects all the way through to reptiles.  Are the sticky pads and the mechanisms that they use to climb the same across those groups?

David - From all the evidence we have, they're surprisingly similar and, in fact, adhesive pads in climbing animals have been a prime example of what evolutionary biologists call 'convergence,' where you find the same solution appearing in very different animal groups.  So, if you think, for example, of spiders and geckos - so they are really, really different animals in terms of their evolutionary history but, if you look at their feet, they just look almost identical.  And this, of course, hints at the possibility that these structures are really good in what they do and, therefore, they have evolved multiple since then.

Felicity - So what do these structures look like?

David - So on the feet of geckos, and spiders, beetles, and flies, you would find what we call 'hairy pads' and they are essentially dense arrays of tiny little hairs and on the feet of many ants, and cockroaches, and tree frogs, you would find what we call 'smooth pads' that are essentially unstructured, at least on a microscopic level so you can best think of them as a soft cushion.

Felicity - In front of me we have an array of different machines...

David - Yes, so what you're seeing here is one of the devices that we can actually use to get an idea of how well animals can actually stick, and what you see is a centrifuge here.  So we can essentially spin it around at different speeds and we can put tiny little insects on the centrifuge so that they're spun around and at some point they start to slide outwards and, using very simple physics, we can calculate how much force is actually acting on these animals and is pulling them outward.

Felicity - So it's a bit like a merry-go-round in a play park, except insects not children.

David - Exactly, and that for insects it's not very dangerous because they're small enough to not be harmed at all by these techniques.

Felicity - Can we switch it on?

David - Yes, of course you can.  If we look at the ant here, right now, and we switch it on and it slowly increases in speed... You can see, at some point, the ant slowly starts sliding outward.  So that's the point at which it starts to slide and, if we go faster, and faster, and faster, suddenly it's of the surface.

Felicity - That's quite impressive really.  That's certainly not something I would be able to do if this was scaled up.

David - No.  Some of the ants can, actually, withstand forces up to 1,000 times it's own body weight so it's really, really impressive what they can do with their adhesive pads.

Felicity - We're all familiar with the Hollywood version of sticky pads in the form Spiderman.  How accurate is their representation of him clinging by his fingertips?

David - So, I mean of course, there's a large number of issues if you talk about the scientific accuracy of Spiderman, but if you phrased the question differently and say, well why are there no larger animals with adhesive pads?  Then we can start saying something about this because if we scale up our calculations with our data that we have then we find if you go to the size of a human, you probably end up with an unrealistically large fraction of your surface area that needs to be covered in sticky pads and what we calculated it somewhere in the area of something like 40% of your total body area or 80% of your frontal area, which I think is UK size 89.

Felicity - That's going to make it difficult to climb.

David - Exactly, and that's just to illustrate the problem that you face if you grow bigger and bigger.  It comes from very simple physical laws that effectively put constraints on what evolution can do.

Felicity - Larger animals - many of them do climb...

David - So, if you go larger than a gecko say, for example, or if you go to a certain size, then what starts to happen is that suddenly the world doesn't look flat to you any more.  If you think again of an ant and it climbs on a twig, the twig is effectively flat for the ant, but if you think of a monkey, the monkey can actually grasp around the twig and that's why you start to see a departure from these clinging pads, or adhesive pads, going to something like hands or massive claws, or so on and so forth.

Recent building works in Oakington, near Cambridge, have uncovered an Anglo Saxon burial site. With the help of DNA experts in Australia, archaeologists have used the human remains recovered from the site to build an Anglo Saxon genetic profile that they've been able to compare with modern Britons. This is revealing how these European immigrants - a thousand years ago - mixed with the general population. Graihagh Jackson went to meet archaeologist Richard Mortimer at the Museum of Archaeology and Anthropology to see what the research has been turning up...

Richard - The Anglo Saxons are the formation of England as we now know it.  Because by the end of the early Anglo Saxon period, by about  700 AD, England has become physically what it looks like today in the fact that all of our villages and most of our towns is formed or is forming by about 700.

Graihagh - There's a collection of about 20 objects here.  They all look like gold but I'm sure they're probably not.  People would have been buried with these things - talk me through, what are these?

Richard - Well they are gold, they're gold gilt. Bronze underneath and then gold gilt on top and they are, quite frankly, one of the most beautiful things you'll ever find, as an archeologist.  These on the right, these large ones, they'd be for ladies to wear and they'd be to hold, with a pin, hold your dress together.

Graihagh - They're brooches then?  They actually are massive.  Some of them are bigger than my hand; they almost look like door knockers, to be honest.

Richard - Yes they do.  I can't deny it.

Graihagh - And I can see necklaces and combs.  They look like little keys on keyrings but I assume they're not that.

Richard -   Yes, they are, they're girdle hangers - formalised key sets.  One of the women at Oakington buried, oddly enough with a cow; that's not only unusual, it's a first in Britain, it's a first in Anglo Saxon Europe. Nobody's ever been buried with a cow before.  And she, the cow lady, got the keys to every lock, and every latch, and every box in that settlement.

Graihagh - Why on earth would you be buried with a cow?

Richard - Absolutely no idea whatsoever.  Because it's a first, you just have try and make up our own reasons, you know.  Archaeologists just do it anyway.  We're telling stories half the time, not telling truths.

Graihagh - Women buried with cows and made up stories aside, this site is extremely important in our quest to understand our British heritage.  Over a hundred people were buried at Oakington and they were in good enough condition for scientists, like Dr Richard Durbin, to extract DNA and find out just how Anglo Saxon we really are.

Richard - So what we do is we take a bone, in fact, in our case we took the teeth which are kind of protected by the enamel.  We sent those to an expert laboratory in South Australia where they purified, removed all the DNA from the outside so as to get rid of any contaminated material, and then ground it up and isolated a very small amount of DNA and, very sensitively, we brought that back and because it's been degraded, it's in small pieces.  So technically this is a hard thing to do but it's become feasible over the last five years or so, and there have been a number of studies but this is the first study of British samples from more than a thousand years ago.

Graihagh - And what, you compared that data with modern humans?

Richard - Yes, what we did is we looked at some of those places where there were clear differences, which were rare and recent, which could tell us a lot about where people came from and then we looked in the ancient samples to see who they shared most with and where they fell in that spectrum of modern variation.

Graihagh - And so, how Anglo Saxon are we?

Richard - Well.  It turns out that modern English are about, in the east of England, are about 38%, but if we go further west, Cornwall or to Wales, that fraction drops.  So we're all a mixture of the people who were here before, and the people who came in the Dark Ages.

Graihagh - But why is it that modern Welsh are only 30% Anglo Saxon versus east of England being 38% Anglo Saxon?

Richard - I would presume that that is because people coming into the country, you know, predominantly settle in the east, and only progressively moved further afield into the west of England.

Graihagh - So it sort of matches the migration pattern.  The Anglo Saxons came over from Europe and landed in the east of England and then migrated west and north, and that's why you see less of this genetic influence on the Scottish, and the Welsh, and people from Cornwall.

Richard - Yes.

Graihagh - It's said quite often, you share, what 50% of your genes with a banana and within species, the human race, it's something like 99.9% or whatever it is.  So surely, given that Europeans and these local inhabitants from the Iron Age would have shared a lot of their DNA, what sort of mutations were you looking for to distinguish these populations.

Richard -    We're all North West Europeans; we're all genetically quite similar to each other so the differences are subtle.  Although we only differ from each other one in a thousand places across three billion bases, that amounts to several million differences.  Sometimes new mutations happen, that's what gives rise to differences and ones that happen within a country, within say Denmark, will only be found in the Danes, or in people who mate with them. So we were looking for those, very rare, mutations as traces of identity.

Graihagh - And you say us in the East are 38% Anglo Saxon, often you hear you're 2% Neanderthal!  So what's the remaining 60% of us?

Richard - Modern humans left Africa about 50 000 years ago, and that point they met other human species and Neanderthals who had left several hundred thousand years ago, and there was a little bit of intermixing at this point which contributed about 2% we think. And then in Europe there were the hunter gatherer peoples who did the cave paintings that one finds in France and Spain. And then after the ice age the farmers came in and moved across Europe from Turkey, and then there was a later movement of peoples bringing metalworking from Russia. So all of these things have left genetic traces we know other people have been studying. We know people from Britain are a mix of all of those.

Graihagh - An area of further research then?

Richard - I think this is just beginning now, alongside the medical advances we obtained from understanding how the genome works in the body, it will tell us about our history as people and evolution. It's a very exciting time to be a genome scientist.

Supermassive black holes, which sit at the centres of galaxies, can have masses ten billion times greater than the Sun,. And despite being black holes capable of locking in light, they've actually been linked to some of the brightest lights in the Universe: quasars. Manda Banerji, who is from the Institute of Astronomy at Cambridge University, tells Chris Smith about these shining lights... 

Manda - Quasars,  these are the brightest lights that we see in the universe and, basically, what they are are powerful, very energetic emissions but they're coming from the immediate vicinity of these supermassive black holes.

Chris - Are they visible light that I could see with my own eyes, or would I need a fancy telescope to see this sort of light?

Manda - Quasars do emit in visible light, but they also emit in all parts of the electromagnetic spectrum, so all the way from x rays to radio waves.

Chris - And is that the clue that this is not just a star we're dealing with here because the fact that you're seeing all these different ranges of colours of light - all these different wavelengths - and stars don't do that?

Manda - Yes, absolutely.  So that is one of the biggest clues; all of this emission and all parts of the electromagnetic spectrum that we're dealing with something very powerful, very energetic.

Chris - And what do you think's going on then to do this?

Manda - So what you need to do to power a quasar is to basically dump a whole load of material, a whole load of matter, onto these supermassive black holes at the centres of galaxies.  So, when you have lots of material, lots of gas, dust, stars being funneled into these central regions, all of that material gets heated up and it shines very brightly as a quasar.

Chris - So this is sort of like a black hole with indigestion.  It's lots of material trying to pile in very, very fast?

Manda - Yes.  It's a feeding monster of a black hole, so quasars are really the feeding phase of a black hole.  We're seeing them as they are devouring all the material up around them.

Chris - Do they have any effect on the galaxy on which they sit, by virtue of just existing?

Manda - Yes.  So this is one of the main reasons that we study quasars is because we now know that they have a very profound impact on their host galaxies.  So we now know that there's a supermassive black hole living at the centres of most galaxies in our universe and when these supermassive black holes feed during this quasar stage, all of this energy that they're outputting into their host galaxy, that can have a very dramatic impact that can blow gas, dust, stars out of the whole galaxy and so in that way it can actually control how big a galaxy will eventually get.

Chris - So it does have an important modelling effect on the ultimate structure of the galaxy.  Can you also look at it the other way, which is to say, if I look at the structure of the quasar and its behaviour, can I deduce something about the black hole that is giving rise to it by studying it, and that tell me something about what the black hole is doing itself?

Manda - Yes, absolutely.  So, we look at this quasar emission and by looking at the gas and dust that's being eaten up by this black hole, we can infer lots of interesting things about the black hole like, how big it is, how massive it's going to get.

Black holes are so far removed from what we can see and test, that they are the playground of mathematicians and theoretical physicists. This month Stephen Hawking, the king of black hole physics, published a paper stating that black holes have "hairs". This challenges the notion that blackholes destroy everything that enters them completely, leaving a shadow of what might have entered at the event horizon. Andrew Pontzen, a cosmologist from University College London, explains this idea to Kat Arney...

Andrew - I do occasionally wish that some of my physicists colleagues would be better at naming things.  This is possibly the least useful name anyone's ever come up with, but the point is supposed to be that if you look at Einstein's theory of general relativity, which is what underlies everything we've been talking about today, about black holes.  It makes a very firm prediction that everything about a single black hole, you're looking at a single black hole, it is completely summarised by just three numbers and those three numbers are: it's mass, so how much stuff is in there; it's charge, so if you throw something in that's got static electricity on it it can keep that, and also it's spin, how much it's spinning.  And according to general relativity that's all there is to know about a black hole, absolutely nothing else to know about it, and when we talk about hair, what we're saying is, actually maybe there's complications.  Every theoretical physicist knows having hair is a real nuisance, it's difficult to make it look any good and so, when we say a black hole has hair we just mean it has extra things that you need to worry about, as well as just those three numbers.

Kat - Okay.  So they're not actually like a hairy hole at the middle of the Universe?

Andrew - No, sadly not.

Kat - Okay.  Well that's shot down my idea anyway.  So how does Stephen Hawking come into this?  

Andrew - The whole question was originally posed by Stephen Hawking in a way, because I think earlier on Matt Middleton was mentioning Hawking radiation and that's the one mechanisms we know of by which you can get rid of a black hole.  That very slowly a black hole will throw off bits and pieces and then, eventually, it loses all its mass and it actually disappears if you wait a very, very, very long time and that was really one of Stephen Hawking's great discoveries in theoretical physics.  But he immediately realised that it poses a kind of strange question, which is that in physics, we normally think that information can't be lost.  So, say I chuck something into my black hole so, I mean. I think earlier on Georgia was threatening to throw herself into a black hole so, let's suppose she does that and let's suppose she weighs 60 kg or something - something like that, then the black hole has grown by 60 kg.  

Now equally well, we could get it to do that by throwing in sack of potatoes that weighed 60 kg and really then the black hole wouldn't then know any different because, as I was saying earlier on, it's just got these three numbers so all that's happened is it's matters gone up a bit.  Then, according the Stephen Hawking's 'Hawking radiation' idea, the black hole disappears and, somehow, all the complexity about Georgia that makes her different from a sack of potatoes, has been completely lost.  That sits very uncomfortably with our normal idea that in physics that you can't lose information.  If you have a complicated thing sitting there you can't just get rid of all that complexity.  So, this poses the question, how can it be that you lose information?

Kat - Sort of what things were, what things were like?

Andrew - Exactly.  And where's it gone and so for a long time Stephen Hawking said "well you know, tough, deal with it.  The informations lost, it's a new law of physics." But...

Kat - I love physicists...

Andrew - Theoretical physicists...

Kat - We'll just make up another equation just to explain it...

Andrew - Well, you know, when you're stuck you sort of have to.  But, he changed his mind.  He said "well maybe, looking at the way things are going, looking at new ideas people have about how black holes really work. Maybe somehow or other that information isn't completely lost,"  and now what he's saying is the information is somehow stored.  And it's stored in a very subtle way so that you couldn't really look at a black hole and tell that Georgia had fallen into it but, in a very, very subtle way, on the event horizon itself, it's stored a faint imprint of the fact that it was Georgia and not a sack of potatoes that fell into that black hole.

Kat - And so, presumably, this is the metaphorical hair, the sort of fringe round the edge that has all this information in it.

Andrew - Exactly.  You've turned Georgia into hair.

Kat -   But if black holes do actually record this, what does this mean for our understanding of black holes, of the Universe, of the theory of physics that we have?

Andrew - If you can make sense of the way that a black hole behaves without losing information, then it really points us towards the next level of understanding black holes and, in particular, what we really want to bring in is what we call a 'quantum theory of gravity.'  That's combining Einstein's ideas about warping space and time with the other great development in the 20th century, which was this idea of quantum mechanics. Historically it's been very hard to fit those things together and, perhaps, as we begin to understand these very extreme objects, we'll slowly begin to understand, actually, how should these things fit and together and what does a better theory of physics actually look like.

Kat - And sort of very briefly, obviously, the theoreticians come up with their theories and all of that kind of stuff but, to find out if that is how the universe is working, you need to test it.  So, could you explain how could we actually test whether this information is stored?

Andrew - Oh dear, yes, that's pretty hard. I mean there's a reason why theoretical physicists are called 'theoretical physicists.'  You know they really try and push the boundaries of theory for, but don't necessarily come up with the tests so, typically, tests are a long way behind.  But, if you look at what's happened with black holes, it was thought that the whole idea of black holes was untestable but now we're thinking about things like the Event Horizon Telescope, so maybe one day.