Nature Podcast

This is a transcript of the 8th January edition of the weekly Nature Podcast. Audio files for the current show and archive episodes can be accessed from the Nature Podcast index page (, which also contains details on how to subscribe to the Nature Podcast for FREE, and has troubleshooting top-tips. Send us your feedback to

Adam Rutherford: Coming up in our first show of 2009, what the year ahead has in store for science.

Oliver Morton: This is the year that many of us expect, when Craig Venter and his colleagues will be producing a creature for the first time using a genome that's entirely synthetic. This is of course the big Darwin anniversary year, and it would be nice to originate a whole new species to celebrate.

Kerri Smith: And squeezing photons makes measurements better.

Krister Shalm: We can start from a completely unsqueezed state and then squeeze and squeeze and squeeze until we reach the most squeezed state that you could possibly make. And we found some rather surprising results.

Adam Rutherford: Plus we mark the beginning of the international year of astronomy, with two papers from our special astronomy issue. This is the Nature Podcast, I'm Adam Rutherford.

Kerri Smith: And I'm Kerri Smith. We'll be getting stuck into some of that Astro shortly, with a pair of Antarctic meteorites and some star formation, but first Natasha Gilbert has been finding out how to squeeze as much as possible out of photons.

Natasha Gilbert: Measurement lies at the heart of experimental science, but there is a problem. On very small scales, the more precisely you try and measure one property, a particle's position for example, the more uncertain its related property, momentum, becomes. This is Heisenberg's uncertainty principle. By using a quantum trick called squeezing, scientists are able to push the uncertainty of the property they want to measure onto its counterpart, greatly improving the accuracy of the measurements. Krister Shalm from the University of Toronto has found a way to squeeze photons, the particles in light further than anyone has done before. Krister told me the discovery could make measurements up to 1 million times more sensitive, which could have huge potential for improving biomedical imaging. Nature 457, 67–70 (1 January 2009)

Krister Shalm: Currently, we use light to make most of our precise measurements and using light you can study some absolutely phenomenally precise and exquisitely sensitive phenomena, for example, there is a gravitational wave observatory that's using light to try and detect gravity waves and using light, they can make measurements that are far more precise than even the size of a single atom, but despite this all of our measurements have some uncertainty that's inherent in them, no matter what we try and do, no matter how accurate the instrument is, there will always be some uncertainty that's there as a fundamental limit.

Natasha Gilbert: So by squeezing, you can increase the certainty in one property, but that obviously reduces the uncertainty in another property.

Krister Shalm: That's absolutely correct. So you can think of uncertainty as being a bit like a balloon and so if you squeeze it in one direction, you make it narrower, but the consequence is you increase the uncertainty in the other direction and so as long as you only care about measuring say, the position of something, then you don't care how much you squeeze it in the other direction, you can increasingly just measure that one property.

Natasha Gilbert: And you squeezed photons more than anyone else has ever squeezed them before.

Krister Shalm: That's correct, at least in a manner of speaking. We wanted see what would happen with the approaching the limits of squeezing. So in other experiments that have occurred, people have achieved absolutely incredible precision with the types of measurements that they have used, but they haven't been able to probe these absolute limits of squeezing. Current techniques leave us about a factor of million away from what quantum mechanics dictates that we can achieve, because these experiments deal with very large numbers of photons, more photons than there stars in the universe, so instead we decided to take a different approach and it worked from the ground up and so we build up our squeeze states photon by photon. In our case, we take three photons, we put them together and we engineer a special type of quantum state we call it a triphoton and because we have absolute control over it, we can start from a completely unsqueezed state and then squeeze and squeeze and squeeze until we reach the most squeezed state that you could possibly make and we found some rather surprising results.

Natasha Gilbert: What did you find?

Krister Shalm: So you would ordinarily think that as you continue to squeeze that your measurement precision would continue to increase, so more squeezing leads to better measurement results, but we found there's a certain point where if you continue to squeeze, your measurement result actually become worse and so we call this regime over-squeezing. but we found a way out of this so-called paradox and that is we realize that as we continue to squeeze, our photons were becoming entangled and entanglement is what Einstein called Spooky Action and this is where the photons as they become more and more entangled start to loose this individual identity and begin to work cooperatively with one another. And what we realized is that current detectors that people use for squeezing to make their measurements, are not sensitive to this cooperative effect with the photons, but if we are able to go to a detection system that is sensitive to this cooperative behaviour of photons, then we are able recover most of the measurement precision, so squeezing leads to better results, and this is what we did in our experiment; we employed these special detectors that are sensitive to this cooperative effect and we were then able to recover all of the precision and squeezing does lead to better measurement results.

Natasha Gilbert: So basically kind of overall, you have found the point at which you could most accurately measure photons that's pretty cool.

Krister Shalm: We think so. Yes, so it's the absolute limit to what you can measure with and if we are able to scale this up to much larger numbers of photons, then it would open up completely new rounds. We would be able to measure things at, you know, a million times higher sensitivity than anything we can today.

Natasha Gilbert: And what kind of practical applications could that have?

Krister Shalm: May be you have a sample that you want to measure very precisely, but you do want to damage. Ordinarily if you send a large number of photons through, then you can get a very precise measurement, because the more photons you send through, the more information you can get out; but there is a problem with this and if you send too many in, you can actually destroy the sample, you can heat it up too much and cause damage. So, there is a lot of applications where you need a very low level of light. So if I say you only have a 1000 photons to make a measurement with, you want to do the smartest thing that you can with them and that would involve having the photons act cooperatively, like we were able to make with three photons do in which case you can get much higher precision and sensitivity.

Natasha Gilbert: Krister Shalm, who has been putting some certainty into uncertain measurements.


Adam Rutherford: Coming up, what to watch out for in 2009. First though gravity: it always wins, but here's Geoff Brumfiel with how it helps create stars.

Geoff Brumfiel: Gravity plays a key role in the formation of stars that much is clear; what's a lot less clear is exactly when gravity becomes important. Some theorists argue that, early on at least, the dust cloud could eventually form stars are swirled by other forces like cosmic winds and they even go so far as to argue that gravity can be completely ignored in simulations of those early days, but not so fast says Alyssa Goodman, an astronomer at the Harvard Smithsonian Center for Astrophysics. Her team's new simulation shows that gravity plays a role at every stage of a star's birth. I called her to learn more about how this self-gravity works and why it matters. Nature 457, 63–66 (1 January 2009)

Alyssa A. Goodman: Most people on earth think of the gravity of the earth and they don't realize that they themselves have gravity too and that you know gravity is actually a force between two things but that the force that you get from gravity depends on the mass of the object. And so self-gravity is always present and it's just the gravity between any two things and so it could be two molecules or could be earth and you and it could be a particular machine and a computer. It's anything but it is negligible unless it's the only thing around.

Geoff Brumfiel: So what about clouds in space then, what about the star forming regions of space? Is gravity powerful enough there to play a role in making actual stars form?

Alyssa A. Goodman: Right well we know that in the end gravity is absolutely what makes actual stars form. So the only thing that can make material collapse all on to one place is gravity which is what's called the radial force. So we know that that's the end of the story. What our work was about is more about the beginning of the story and how do the pieces that are ultimately going to collapse like that under their own weight, had a little form.

Geoff Brumfiel: And you found that the gravity actually plays a role on all these at all times, right, which I guess not everyone, had agreed on.

Alyssa A. Goodman: Right I think if you ask people to be really honest, they would admit that gravity has some role on all scales but it turns out to be very difficult to do numerical simulations where you include many different spatial scales because you have to include a lot of different physics that's important on those different scales. and so what people have been doing and I should say that people include me and colleagues of mine is pretending that turbulence which is generated by all sorts of other forces in the interstellar medium, so by supernova explosions, winds from stars, magnetic fields, all kinds of other forces even gravity on very large scales of spiral density waves, but basically the stirring of the gas causes it to have a sort of swirly structure that you can see in one of the figures in the paper and the idea is that that swirly structure would randomly create higher density areas, more concentrated areas and that then you could sort of turn on gravity in a simulation when you got to that high concentration and watch that particular region collapse and so it is kind of cost efficient to ignore gravity until the very end but it turns out that if you do this based on observations and what we did was we were able to calculate the gravity of the pieces, little clumps of what we saw would be self-gravitating on each other, turns out that they have an important gravitational effect on each other, so they essentially can orbit each other and they can even if they come close enough steal mass from each other in a process that's called competitive accretion. These results suggest that it may play some role, this kind of trading back and forth between these clumps as they are forming stars.

Geoff Brumfiel: So then I mean how would this really change our view on how stars and planets and all these different structures form?

Alyssa A. Goodman: With a much more exciting process, you know, there's one analogy that you can make of people growing up and you know, they can grow up in cities or they can grow up in the country and in the country, it's a really long distance to the next house, you can really grow up in a very isolated way and you can treat the process differently than if you live in a city and you come into contact with all sorts of other influences that are going to change your life and so that kind of city side view of star formation is one that's like living in a city where people have to compete with resources and even kids as they are growing up, so stars as they are born are exposed to many more environmental influences and so this picture of competitive accretion that I talked about earlier makes it very hard to model star formation, because you don't really know what these influences are going to be on a star as it's collapsing.

Geoff Brumfiel: So we have this sort of exciting dynamic, what you sort of call a, citified view of star formation which sounds very exciting, but sounds it's also kind of a pain in the neck you modellers.

Alyssa A. Goodman: Yeah, it's a huge pain in the neck and there are some theorists who think that no self-respecting theorists would work on star formation, because it's such a messy problem and what we have done is actually make it a little bit more messy but thankfully computers are getting better and better all the time and so what we have to tell people is that they basically have to turn on the gravity switch a little bit sooner than they would have otherwise in the simulation.

Geoff Brumfiel: So we now understand one of the reasons you're excited about this paper, actually the paper itself and something that people who pick up the print issue won't see, but if you go online what are you going to find?

Alyssa A. Goodman: Right, in the print issue, there is a little marker suggesting that if you do go online, you can see the key figure in the paper that shows the internal three-dimensional structure of the cloud, essentially in 3-dimensions. You can click on the figure and rotate it and turn certain surfaces on and off and this allows people who are interested in the subject to really investigate what we are saying and see if they believe it for themselves and it's a way to literally interact with the real data within the published paper and I really think that that's the future of sort of e-science and that this is one of the first demonstrations of it.

Adam Rutherford: Alyssa Goodman of the Harvard Smithsonian Center for Astrophysics and that 3-D figure is available on Just use your star charts to navigate to the international year of astronomy collection.

Kerri Smith: Next up, we are concerned not with how stars form, but how a peculiar piece of crust got to be how it is. Here's Charlotte Stoddart with the story.

Charlotte Stoddart: We are all familiar with plate tectonics and the earth's crusty covering, but what about the outer layer of other planetary bodies? It is an interesting question, because the chemical nature of a crust tells you how its parent body formed, developed and cooled and by cataloguing the crusts of planets and asteroids in our solar system we can learn more about the whole systems' evolution. So when geologist James Day came across two newly discovered meteoroids with crust that looks just like earth's he was rightly intrigued. These meteoroids probably came from an asteroid several billion years ago, but as James told me, they were only discovered in 2006. Nature 457, 179–182 (8 January 2009)

James M. D. Day: These meteoroids were found in Antarctica by the United States Antarctic search for meteorites field team who search the ice every year and this was in 2006-2007 and they were in the Graves Nunatak ice field region.

Charlotte Stoddart: And how did you come across them James?

James M. D. Day: One of the nice things about the program is that all of those meteoroids are free for study by people around the world and obviously when they showed these meteorites in their newsletter, we immediately realized that they were unusual because they contained large amounts of a feldspar called plagioclase which we don't normally see in meteorites, so we requested the samples from them.

Charlotte Stoddart: And how old are these meteorites?

James M. D. Day: We have dated these rocks using a method where we hooked a laser to a mass spectrometer and measured the lead isotope compositions and these tell us that the meteorites are at least 4.5 billion years old.

Charlotte Stoddart: And so that's about the age of the earth in that case.

James M. D. Day: It's about the age of the solar system in fact. The age does probably represent last heating event on the parent body when it was floating around in space, it gets hit by other impactors and there's lots of heat surround early on and so these age is probably a minimum age, so they are probably as old as the very beginnings of the solar system.

Charlotte Stoddart: And in that case, can the meteorites themselves tell you something about the very early history of our solar system.

James M. D. Day: Absolutely and that's why we studied them, obviously these rocks with these unusual compositions that we've never seen before in meteorites, will tell us a great deal because they are representing something that happened at the very earlier stages when the solar system was just being birthed.

Charlotte Stoddart: So when you looked into the unusual chemical make up of these meteorites what did you find?

James M. D. Day: First and foremost, the amount of feldspar in these rocks and other constituents given them compositions like earth's continental crust. That piece of crust that is beneath our feet right now and that rock type is called andesite, so this was obviously an unusual feature because these have not been seen in meteoroids before.

Charlotte Stoddart: So these meteorites have sort of an earth-like crust to them and did this crust form in a similar way to the earth's crust?

James M. D. Day: No it's unlikely it formed in a similar way. On earth what happens is to generate this andesite composition, you require plate tectonics where rocky portions of earth's crust and mantle try together and they subduct material and they push it down into the mantle of the earth and replenish the mantle with water and this generates melting which forms volcanoes such as the pacific ring of fire. Whereas with these meteorites what happened is that the asteroid formed and there was volatile water perhaps trapped inside it and that enhanced the melting, so this opens the possibility that perhaps in an earlier time before plate tectonics and when there was more water present in earth's mantle a similar mechanism could have occurred on earth.

Charlotte Stoddart: So these meteoroids can actually give you clues perhaps to the very early history of our own planet.

James M. D. Day: That's what we think might be the case. Obviously, these are very new meteorites in the sense that we found them two years ago, but clearly they're telling us something about what was happening on the small bodies and may be this could be brought to understanding our own planet, yes.

Charlotte Stoddart: What's your next step then James? Do you expect to find more of these earth-like meteorites?

James M. D. Day: Actually the big question for us is where do they come from and one of the next steps in our work is to look for possible asteroids, these meteorites are likely to come from asteroids rather than from a planet and look at, I think with their spectra, what they look like in the near infrared spectrum and also in the visible spectrum of light.

Charlotte Stoddart: And so I guess to go out and look for these asteroids you're going to have to collaborate with other groups of astronomers.

James M. D. Day: That's right, we're actually collaborating with some astronomers at the University of Maryland, so one of the questions we are going to answer in the next, hopefully, couple of weeks is what the spectra of these meteorites looks like and begin trying to match them with asteroids out there in the asteroid belt.

Kerri Smith: James Day there on the line from the University of Maryland.

Adam Rutherford: Now a big shout out to all you raccoons, robots, and other virtual beings listening to the show in second life, every Thursday the Nature Podcast is played to an audience of avatars on Nature's Islands. If you want to joint in just create yourself a second life alter ego or tell about your existing one to the Elucian Islands at 11 AM SLT that's 7 PM GMT for those of you unfamiliar with Second Life Time may we see you there.


Kerri Smith: Finally this week in lieu of our regular news chats we thought we will have a go at predicting 2009's biggest science headlines. Chief news and features editor Oliver Morton has joined us in the studio to help out. Hi Olli.

Oliver Morton: Hi.

Kerri Smith: Now let's start with biology first of all.

Oliver Morton: Well for biology, almost every year recently, the story is more and more genomes and certainly 2009 is going to be no exception to that. The current generation of really fast genome sequencing material is now in the big genome centres and so they're churning out product and we're expecting fairly early in the new year, we are going to start seeing even faster genome sequencing mechanisms going into, suddenly coming out of the lab, might be not going into so widespread use and so the cost of doing genome sequencing is going to fall further and further and further.

Kerri Smith: And these are individual human genomes or other types?

Oliver Morton: There's a 1000-genomes project that's going on and that will certainly have churned to a few hundred. I think particularly interesting is we are going to see a lot of plant genomes next year. I think, we are expecting maize and soy beans and millet and various fruits and things and that's interesting because at the same time, we have the new techniques under development that allow much more precise genetic engineering in plants and what would there still being global food crisis and all, I think, we might see quite a lot of plant science with some real focus on agricultural needs.

Kerri Smith: So last year of course everyone was pretty excited in November about the woolly mammoth, please tell me that's going to be some more ancient genomes?

Oliver Morton: Well people are quite widely expecting a good chunk of if not all of the Neanderthal genome. There's also of course the possibility of seeing genomes that nature hasn't naturally provided it us that this is the year that many of us expect when Craig Venter and his colleagues will be producing a creature for the first time using a genome that's entirely synthetic. They've already synthesized the genome, they haven't yet published anything about how they can actually get the genome into a little genome-free cell, but I think there is widespread expectation that that's going to happen this year and that might even try, and well at least in Craig Venter's mind, with the fact that this is of course the big Darwin Anniversary year and it would be nice to originate a whole new species to celebrate.

Kerri Smith: So it is going to scoop the unscoopable and...

Oliver Morton: And eff the ineffable, yes it's going to be great.

Kerri Smith: So that's the basic biological blueprint level. If we go up a level to cells, what's getting people excited there?

Oliver Morton: I think what people are excited about at the moment is this new abilities to actually watch cells doing specific things both on their own absolutely in isolation in organisms. I know that are neuroscientists are very excited about the new techniques for looking at cells as they function, but also using light to turn specific types of cell on and off by building light sensitive switches into the genes of animals and then looking literally through their skulls in order to see what goes on when you turn this and that off and so, I think, those sorts of ideas where you can see cells really doing that stuff in large numbers but with very fine precision is definitely something that a lot of biologists are excited about.

Kerri Smith: So let's turn are thoughts to physics then. I know that again at the end of last year there were some hints that we may have a bit more of an idea what dark matter is, where it is.

Oliver Morton: Yes people are very excited about and there were some hints from a couple of space missions that something is going on that could be described in terms that it gave some exotic form of dark matter. There is possibly more data on that this year there were also searches for dark matter on earth, in mines on earth seeing it passing through which are becoming more sensitive year by year and so they are beginning to start ruling out whole areas of possibility. So we could see something there. It had been hoped that if the LHC at CERN had been working the vast particle accelerator outside Geneva, we might actually be making some dark matter, but as it stands it looks unlikely that the LHC will be doing a huge amount of science before certainly the tail end of 2009, but this is of course good news for the LHC's competitors the Tevatron in Fermi Lab in America now has an extra year to try and find the much badly hoed Higgs Boson.

Kerri Smith: So the first of January issue our special astronomy issue contains a round up of the findings of the Hubble Telescope.

Oliver Morton: It is remarkable how fond people are of the Hubble telescope. There are lots of spy satellites that work almost exactly the same but no one cares about them.

Kerri Smith: Which space telescope should we be caring about in the future?

Oliver Morton: Oh! Three exciting space telescopes next year. There's Herschel which is doing long-wave infrared which is not something that people have done anything like this in detail before. That's going up sometime in the spring and it's sharing a ride with Planck which is a telescope that will provide us with images of the echoes of the Big Bang and a never before seen granularity and then as well as that those are both European missions. The Americans are launching Kepler which is a smallish mission but with quite big ambitions and that it is designed to be the first machine that could really reliably discover quite a lot of planets no larger than the earth. So it can find earth-like planets around distant stars. There's already an international mission led by the French that's doing something along these lines, but Kepler is I think everyone agrees, significantly more capable.

Kerri Smith: So closer to home then Obama soon to be sworn in as president of the US, what kinds of effects will that have on science, there are some larger effects we expect to see on energy.

Oliver Morton: Yes, well on the Obama campaign was very strong on the idea of energy research and energy investment. Steve Chu who runs Lawrence Berkeley Labs at the moment has a Nobel Prize. He is very, very interested in energy. He made that a central mission of the Lawrence Berkeley labs and he is now going to be secretary of energy and other aspect of the new Obama presidency I mean which is linked to energy research is that we are expecting to see a lot of movement on climate politics and that is going to feed into the big UN meeting in Copenhagen next year. It's not clear how that's going to plan yet because once the economy gets bad it becomes harder to focus on what's going on in the climate, but there is definitely the fact that the new administration has such a different view from the old administration will make climate politics and will climate science different this year.

Kerri Smith: Okay Oli thanks for stopping by.

Adam Rutherford: That's it for our first show of 2009. We are back to our usual schedule now, so tune in next week for more of the best from Nature. Till then, I'm Adam Rutherford.

Kerri Smith: And I'm Kerri Smith. Happy New Year science fans.