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Kerri Smith: Coming up this week. Confused by quantum physics, you'll be even more baffled after this.

Nicholas Gisin: The quantum correlations are indeed coming from outside space-time in the sense that there is no story inside space-time that can describe them.

Kerri Smith: We try to explain the incomprehensible.

Adam Rutherford: The importance of silent infections in cholera epidemics.

Aaron A. King: If you focus only the most severe cases then you may miss a big part of the picture. You may get a very misleading picture of what's going on in the population as a whole.

Kerri Smith: And how researchers prob the most remote parts of our planet.

James Vicky: We know less about the Earth's inner core than we do about other planets and even other stars simply by the fact that we can't see it and we have no direct way of sampling the material there.

Kerri Smith: This is the Nature Podcast. I'm Kerri Smith.

Adam Rutherford: And I'm Adam Rutherford. Of the great challenges facing humanity at the beginning of the 21st Century, few are more pressing than Global Warming. Electricity generation is responsible for 10 Giga tons worth of carbon dioxide but despite the acknowledged need to reduce carbon emissions, we show no signs of reducing our energy consumption. So in this week's Nature, we turn to electricity without carbon. We've got a special feature analyzing the future of energy generation from geothermal to wind power. Chief News Editor Oliver Morton masterminded the article and is here with us in the studio. Oli, how bad is the problem, 10 Giga tons of carbon sounds like a terrifying amount. Published online 13 August 2008, Nature 454, 816–823 (2008)

Oliver Morton: Yeah, it certainly is. Electricity generation is the biggest single source of green house gases in the atmosphere. Electricity generation is becoming more of a proportionate source of carbon and that, you know, the amount of carbon per watt for the global system is going up and not down and this is the one we have to turn around and we also have to turn around transportation, but this is a bigger thing, and also it's in some ways more tractable.

Adam Rutherford: And the suggested solutions include renewables such as wind, power, solar, geothermal. How much energy is currently supplied by renewables?

Oliver Morton: Not that much, I mean at the moment following the way of the biggest source of renewable electricity is hydropower. There are a lot of dams on a lot of continents; we have more than two times the area of Italy as under water providing us with electricity and the only our carbon-free source of energy that's similar in scope is nuclear. Dams in nuclear are roughly the same sort of size around the world. Then you come down a long way towards the other renewables which include biomass. You can burn biomass for electricity, wind, geothermal, solar and even oceans and we are looking at those in order.

Adam Rutherford: So going through some of those renewable power sources, tell us a little bit about the disadvantages.

Oliver Morton: Yeah that's a good question. We actually decided to focus on this to some extent because it is easy to say what something's absolute capacity is that not noticed the disadvantages. So as mentioned, dams have a lot of different disadvantages, including the fact that you often have to move a large numbers of people, the dams themselves, the reservoirs can give off greenhouse gases. It's almost unnecessary to point out the disadvantages of nuclear, but they include the fact that no one has found a long term politically viable storage method for the waste and that to keep going with nuclear really high rates, you've to start looking at breeder reactors which may, you start putting more plutonium atom into the world and that's something that many of us have misgivings about. Geothermal has the disadvantage that we don't know how to do it in most of the world yet, might be we can work out how to do it at deeper levels with in hotter geological settings but no one has put that much money into that yet and that's it. It's not that much money you need to find out about that sort of thing. Solar cells have the obvious problem of night time, wind has the problem that it is very intermittent. Although, people who want to put wind or wind turbines on big heights and you get a lot more constant power that way, but again and that's a technology we haven't quite got to yet. And the problems with Ocean technology we could just be here all day..

Adam Rutherford: So we will come on to nuclear in just a minute, but what is the likelihood of one or many of these renewable energy sources being developed sufficiently to actually meet are needs, what are the barriers?

Oliver Morton: Well the barriers are probably easier to find. The likelihood of the barrier is that although these are huge investments, they are not in fact that huge compared to what's been done in the past. I mean, over the last 25 years or so, we've put in about 6 Terra Watts of generating capacity around the world. What's needed now is to put in 11 Terra Watts of generating capacity to both replaced stuff that's falling out of use and also to allow for growth and also to get rid off the carbon stuff. The problem is that these new Terra Watts you do use technologies that have not been deployed on scale, so among the things that you need to do, is make sure that companies have incentives to develop these things. One way of doing that is with subsidies and if you look at Germany, Germany has built a great solar power industry of the bases of subsidies. It's possibly unfortunate that is in a rather cloudy country where solar power is not displayed to its best advantage, but still a huge achievement. You can also do a few things like just mandating the use of renewable energies in your belt or you could just say, "I am the government of Morocco. I have a lot of desert and I'm now going to start building a lot of solar power plants". The real barriers are barriers that we, kind of, know how to deal with enough will. The real problem is that people see the feasible level of shift as marginal. The level of shift that's actually needed is huge. That doesn't mean that it's not doable, but it does mean that just going for the little incremental things is not necessarily going in the right direction.

Adam Rutherford: Okay, and then there is nuclear power. So we know that nuclear fission has got a quite bad rep in some western countries. Surely what is needed is a wartime strategy on developing nuclear fusion.

Oliver Morton: Well we have a nuclear fusion program, a global nuclear fusion program which the physicists' community has signed off on fairly happily, but following through that, you still don't get commercial fusion plants till about 2040 and that's just too late. We can't go on burning fossil fuels until 2040. There is a phrase people use in the business that nuclear fusion is either 50 years in the future or 8 minutes in the past. Because what that means is that sunlight takes 8 minutes to get from us. It's the biggest fusion reactor we'll ever have access to. It's turning out energy at a quite astronomical rate and I mean astronomical literally. We just need to be able to find ways to use that solar energy. It's going to help us in the short term far more than fusion can.

Adam Rutherford: Thanks Oli, that feature and a host of related material is all on the web at

Kerri Smith: Coming up later in the show, we find out how a drug that usually turns down the immune response can counter-intuitively be used to defeat a virus.

Adam Rutherford: But first here's Charlotte Stoddart with an update on the structure of the innermost part of our planet.

Charlotte Stoddart: On last week's show, we discovered that the Earth's inner core is lopsided. To explain the asymmetry, a team at the institute of geophysics in Paris developed a model in which liquidy outer regions influence the structure of a solid in a core. Here's Julien Aubert talking to Geoff on last week's pod.

Julien Aubert: We like to understand the Earth as a system of layers, so the inner core, the outer core, the mantle, the crust. This model was challenged by this observations and I am sure this is not going to be the only paper on this question, there are probably a few more to come.

Charlotte Stoddart: Well we didn't have to wait long for the next paper. Because in this week's Nature, James Wookey and George Helffrich published the results of their seismic wave survey. The researchers from the University of Bristol in the UK, used data from an earthquake in Mozambique to probe the structure of the inner core and with more of these measurements, they'll be able to put Aubert's model to the test as James explained to me. Nature 454, 873–876 (14 August 2008)

James Wookey: Aubert and his colleagues talk about how the mantle imposes its will on the inner core by imposing a variation base at temperature at the top of the liquid outer core, causes patterns to be caused in the texture of the iron there. Now what our paper does is we detected a seismic phase, which is very hard to detect. Seismic wave through the inner core which happens to be one that's very sensitive to this kind of texturing and that ours is only one detection so far. We think that because it is done with a new generation of seismic array that these phases will be detected much more and we will be able to build up a big database of this kind of observation. Now we can use these kind of observations to start to test some of the ideas that Aubert and his colleagues have in their model. So potentially with our seismic waves, we can actually look at how these patterns have changed in the core through time.

Charlotte Stoddart: Now this seismic phase that you're talking about, this was caused by an earthquake, was it?

James Wookey: That's right, yes, we looked at an earthquake in Mozambique actually which happened in 2006 in February and it's quite a large earthquake of magnitude of 7 and we recorded the waves that were generated on a seismic array in Japan.

Charlotte Stoddart: This is one way that you can go about sort of measuring what the Earth's inner core is like I guess because it must be very, very difficult to make measurements in what's a really remote part of the Earth and more difficult to get at than the moon or the surface of Mars.

James Wookey: That's right absolutely. We know less about the Earth's inner core than we do about other planets and even other stars simply by the fact that we can't see it and we have no direct way of sampling the material there. So seismology really is the main way that we have of understanding what the construction of the inner part of the Earth is like and because when you've a powerful earthquake or explosion, the vibration from that travel throughout the Earth, we can use the properties of those vibrations by how long they take to get to us and how strong they are. It's really sort of tough pick apart the structure of the Earth.

Charlotte Stoddart: What kind of earthquake is it that makes it a good earthquake for making these measurements of the inner core?

James Wookey: Well the earthquake we used for is actually rather unusual in the sense that it has what we call a very short source time function and what that means is that when the earthquake happens, it releases all of its energy very, very quickly. So what that translates to, in seismology terms is a very high amplitude short duration wave. The other approach is to look for very deep earthquakes, because most of the energy from an earthquake is dissipated by the shallow part of the Earth. So if you can get earthquakes at convergent margins like subduction zones, you can get earthquakes that are very deep in the Earth up to about 600 to 700 kilometres. These are really the ideal ones to look at very deep Earth like the inner core.

Charlotte Stoddart: With these more sophisticated ways of measuring what's going on then in the inner most part of our planet, what were your findings together with this paper by Julien Aubert tell us about the structure of our planet.

James Wookey: I think what Aubert's model shows is that our, sort of, previously rather simplistic way of thinking about the Earth, that's sort of being divided into the separate layers that interact in fairly limited ways is too simple and we aren't really able to use it to explain the nature of the structures we see. And using these new seismic observations as a guide to be able to tell us whether the models we run are right or not, it is pretty good to improve our knowledge of how the whole Earth works as a system and probably challenge few of our previously held assumption.

Kerri Smith: James Wookey there, talking to Charlotte.


Kerri Smith: Prepared to get tangled up over quantum entanglement later in the show.

Adam Rutherford: But before that two features on the world of infectious disease. First James Morgan reports on how knowing about hidden infections could help us fight cholera epidemics.

James Morgan: The threat of epidemic cholera remains in every developing country according to the World Health Organization. The struggle to eradicate the water borne bacteria is made harder by the many thousands of symptoms-less carriers, who act as a hidden reservoir of the disease. To help us understand how cholera is spread and how we can tackle it better, researchers from the University of Michigan looked back over public health records from 1890 to look for clues of how we can refine our models of how cholera spreads. I spoke to Aaron King to find out more. Nature 454, 877–880 (14 August 2008)

Aaron A. King: In the case of infectious diseases probably more than in any other area of ecology, we have a pretty good understanding of the basic rules by which diseases are transmitted and these rules can be formalized as mathematical models.

James Morgan: Take us right to the beginning then Aaron. Where did you find your data on cholera?

Aaron A. King: My colleague, Menno Bouma who is at the London School of Hygiene and Tropical Medicine made a painstaking study of some of the records the British India office kept on the number of cholera deaths that were taking place in each district and so we were able to develop new statistical methods that allowed us to use these data in conjunction with mathematical models to estimate some of the key parameters.

James Morgan: And what did you find?

Aaron A. King: What we found was that we could only explain the patterns in the data by assuming that lots and lots of individuals were being affected by the disease, whether or not they were actually carriers. They were being exposed to the pathogen in some way or other and their exposure was resulting in some from of immune protection that prevented them from being infected immediately following. So it was this protection that they derived that prevented the epidemic from spreading further than it did.

James Morgan: And how is this picture different from our previous understanding of cholera epidemics?

Aaron A. King: Well essentially earlier studies had concluded that relatively small number of individuals are actually being affected by the disease that the patterns of outbreaks were being driven by some sort of external driver so that there is essentially a season when cholera could spread. It would spread and than that season would come to an end and with it the epidemic. What we find is that, although, there are still some seasons when cholera is more actively spread than others. The disease essentially spreads like wild fire until there is nobody left to spread to or not enough people left to spread to and then of course the epidemic comes down and the rapidly weaning immunity allows the disease to then reappear the following year.

James Morgan: And how is this going to help us?

Aaron A. King: So if in fact we are correct that the disease has been controlled historically by immunity in the population, then prospects are good for control of the disease even by means of some of the cheap and relatively inefficacious vaccines that are available. What our results suggest is that if those vaccines are applied to significant fraction of the population, they could forestall cholera outbreaks. On a related note from the other parameters that we estimated in our model, suggest that the fraction of the population you would have to immunize with such vaccines may be quite small and may be in fact less than half the individuals total need to be immunized every year in order to prevent the outbreak from spreading at all.

James Morgan: We have a situation now in places like Baghdad and Sudan where cholera epidemics are threatened. Do you think that the data that you find which looks back to cholera back at the turn of the last century, do you think that those lessons apply to cholera epidemics in the cities of the world today?

Aaron A. King: Well it's not entirely clear. A number of things have changed with cholera epidemiology. The strains of cholera which are circulating in the world now are different in some ways from the ones that were prevalent in the first half of the last century. There are other predictions that our results make that might help deal with cholera epidemics better going on now or forestall cholera epidemics that might take hold, but all of them basically stem from the idea that if you focus only on the most severe cases, then you may miss a big part of the picture. You may get a very misleading picture of what's going on in the population as a whole. So our results suggest that more generally if we focus our efforts on understanding disease at the population level, specifically studying people who may have very mild infections or may not be symptomatic at all that we may actually see a picture that's very, very different.

Adam Rutherford: Aaron King there, talking to James Morgan.

Kerri Smith: Now a bit like the world of celebrities, some infections persist for ages while others come and go. Researchers have been puzzled as to what makes certain strains turn into chronic infections, the Paris Hiltons or Britney Spears of the viral realm. So, Emory University's John Altman and his team took two different versions of a virus called lymphocytic choriomeningitis virus catching bug not so catchy title and found that they provoke the immune system in different ways. One strain called Armstrong forces lymphocytes, members of the body's army of white blood cells to be sequestrated in the lymph nodes, whereas the other strain that turns chronic called clone 13 doesn't. By using a drug that artificially induces the lymphocytes to head for the nodes, the usually chronic clone 13 can be cleared as quickly as Armstrong, but what strange is that this drug usually acts as an immunosuppressant. Here's John Altman. Nature 454, 894–898 (14 August 2008)

John D. Altman: We work with a virus called lymphocytic choriomeningitis virus. It's a virus that will infect both mice and humans and the major reason that lots of us work with it is that it's a model for what I have taken to call it a high level persisting viruses. Viruses that persist at a high level in a host versus those that persist at a lower level or that are latent and periodically reacting. And a key distinction between high level persisting viruses and those that persist at lower level is the amount that they actually continually stimulate the immune system. Assume there is a model for what happens in people that might be infected, say with hepatitis B and C viruses or HIV, which also persist at high levels in many patients.

Kerri Smith: And so in the mice that you use, they have two different forms of this virus and the response of the immune system as you were just mentioning there differs in those cases, doesn't it?

John D. Altman: Yes.

Kerri Smith: And that difference is down to the lymph nodes, what's their importance here?

John D. Altman: The lymph nodes are where responses get started, where T-cell responses get started and it's there that they meet up with cells that come into the lymph node from remote sites carrying the viral infection or the by-products of the viral infection and they meet up with the T-cells. And so one metaphor that I use is this sequestration is kind of like sending a bunch of people to a party and taking away their keys so they can't leave and they've got sort of mixed up and find a partner and in this case the partner is a T-cell with a cell that pairs an appropriate antigen. In that metaphor what's going on in a normal immune response might be that the system is optimized to promote those chance encounters. The Armstrong strain of the virus is cleared within about the first week of infection and in contrast the clone 13 strain which actually differs from the Armstrong strain by only two amino acids persist at a high level for a long time.

Kerri Smith: And so given that these virus strains don't differ very much, was that the result you expected?

John D. Altman: The sequestration that we saw with Armstrong was not really a surprise. What was the surprise was that we saw significantly less sequestration following infection with a clone 13 strain and, you know, that was just a chance observation. It wasn't what we set out to do, but we noticed that and then we followed that.

Kerri Smith: And you followed that then by testing that if you artificially, sort of, sequestrate the lymphocytes in the lymph nodes in the case of the clone 13, using a particular drug then it acts as if it's the Armstrong strain and it clears the infection very well.

John D. Altman: Yes, it does clear the infection completely.

Kerri Smith: Now from what I understand as well that the drug is already used as an immunosuppressant for various conditions like multiple sclerosis or to prevent the immune system rejecting a transplanted organ for example. So, it seems to me quite counter-intuitive that in this particular case, it's to boost the immune system.

John D. Altman: Yes, so as you point out the drug has been used successfully as an immunosuppressive agent and it's currently in phase III clinical trials for treating of multiple sclerosis, we are in the midst of trying to discover exactly what the mode of action of the drug is.

Kerri Smith: So, I know it's early days for this kind of the next question that I am going to ask, but what might this mean, the sort of counter-intuitive effect of this drug for people taking this drug for conditions like MS, you know, if it also has this reboosting capacity.

John D. Altman: Well, one of the concerns that the developers of the drug for MS have is that by treating people with the drug that you might render them less capable of, for example, controlling latent infections and so there's a concern that the drug might have similar effects, it would, you know, be manifested in the inability of the immune system to do what it normally does which is to keep this latent infections in check.

Kerri Smith: And on the flip side then as a benefit, a possible benefit of this drug could we use it to treat chronic infections in humans as you've used it here in the mice?

John D. Altman: Well, that is certainly a reasonable extension of our work and how we think and why we think our work is potentially important but a lot of basic ground work has to be done in order to translate our findings that far.

Kerri Smith: That was John Altman of Emory University.

Adam Rutherford: Now it might be counter-intuitive that a drug that usually suppresses the immune system can fight infection in other circumstances but the word counter-intuitive doesn't really do justice to the topic of our final article this week. Geoff Brumfiel has been discovering just how little we know about quantum entanglement.

Geoff Brumfiel: The field of quantum mechanics is littered with all kinds of weirdness, but one of the weirdest things is called spooky action at a distance. The basic idea is this; start with two particles that are entangled that means they are connected through quantum mechanics. If you separate them and measure one of them then you'll instantly know what the other one is doing. Einstein called this spooky, because he found it unsettling that two particles could communicate so quickly from far apart, but as it turns out he was wrong. A paper in this week's Nature shows that though the particles are apparently connected they're not talking to each other in any sort of way we can think of, confused? So was I. And to try and straighten it all out I called Nicolas Gisin from Geneva University. We started with the easy stuff, how do two things communicate in the normal world. Nature 454, 861–864 (14 August 2008)

Nicolas Gisin: You've to imagine that there are two parties that are at a certain distance from each other, so they're separated in space. Let's say they behave in a similar way and there is a typical example for instance, you watch a football game and the left and the right wing player both stop running at the same time and why is it that they stop running, may be because the umpire has whistled. So there is a cause and that cause goes to both of these players and the two players react in a coordinated that we would say a correlated way. Another way would also be that one person talks for instance to another, what I am now doing with you and of course in this way, we will also get correlated of course what I say is correlated to what you hear. Now in quantum physics, there also are situations where we observe correlations, but these correlations are very peculiar in the sense that we do not follow neither the first example with one common source, this umpire nor is it that one is influencing or talking to the other one. It's a different kind of correlation.

Geoff Brumfiel: One of the most common examples of this is with two photons, may be you can just describe that very simple experiment.

Nicolas Gisin: So, the idea in this example is to create a pair of photon in a very specific way but something we can do today and then to send one photon to one place and the other photon to another place and since in our example, we send these photons via optical fibres to two villages that are near by Geneva and then they are clearly well separated in space and then we like to ask a question to a photon. Now how do you ask a question to a photon, actually you give the photon a certain choice in some interferometer with some beam data and things like that and then you have two detectors and so the photon can decide which detector will fire. And you can ask then the same question to both photons, so one in one village and the other photon in the other village. And for instance the answer to the same question is always the same; we would say these photons are correlated.

Geoff Brumfiel: Now couldn't the photons just be agreeing on the answer before they left wherever the light source is, their little bulb.

Nicolas Gisin: Okay, so that would be exactly the kind of example which my umpire. So if there is a cause, a common cause in the past and so in the example of the photon the past would be when they were together at the source. So this is clearly a natural assumption and there are ways of testing this assumption and very surprising fact is that quantum correlations are such that this explanation in terms of common cause is impossible.

Geoff Brumfiel: So, I suppose then the other classical option would be that somehow one of the photons is telling the other one which answer it's giving.

Nicolas Gisin: Exactly, so that would be the communication, but then what you could do is to arrange that you ask the question precisely at the same time and also you decide at the last moment which question to ask and then you ask the question and then later you'll see that sometimes it happens that you've asked the same question and you notice that in all these cases where you have asked the same question you got the same answer. If you ask the questions at precisely the same time there is just no time for these two photons to communicate.

Geoff Brumfiel: How fast were these photons have to be communicating with each other according to your measurements that you have made.

Nicolas Gisin: We estimate that the speed of this hypothetical spooky action at a distance would have to be at least 100,000 times the speed of light.

Geoff Brumfiel: At least a 100,000 times the speed of light. So that's pretty fast.

Nicolas Gisin: Well, that's so fast that let's say for most physicists would agree I guess our conclusion that there is no hidden communication that would be too fast and so the conclusion is that there is actually no way to tell a story in space-time that describes how these photons manage to get their correlated answers.

Geoff Brumfiel: Most scientific experiments you sort of expect them to clarify something. It sounds like you've actually made quantum physics less clear and less intuitive.

Nicolas Gisin: This was known and that was actually even Einstein already realized all that and that's the reason he didn't believe in the existence of these correlations. Now it seems, that time many experiments have confirmed that the correlation, this quantum correlation exists and I guess, we could say that I will experiment and just put the finger right here in some sense, because I guess most physicists still have the kind of intuitive understanding that there is one measurement that influences the other and this experiment shows that actually such a kind of naïve picture does not work. We just clarified that the quantum correlation are indeed coming from outside space-time in the sense that there is no story inside space-time that can describe them.

Geoff Brumfiel: If there is no story in space-time, where could the story be?

Nicolas Gisin: But I think this is a very good question and I think it is a very fascinating question, we understand more and more about it but I don't think we can today claim that we have a good story to tell how these all happens.

Kerri Smith: Nicolas Gisin, that's all from us. Tune in again in a week's time when we will be taking a look at research on survivors of the 1918 flu virus and doing some gold based chemistry. I'm Kerri Smith.

Adam Rutherford: And I'm Adam Rutherford. Always believe in your soul.


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