Archive for October, 2008

And the number of intelligent civilisations in our galaxy is…

Monday, October 20th, 2008


No really. At least according to Duncan Forgan at the Institute for Astronomy at the University of Edinburgh.

The Drake equation famously calculates the number of advanced civilisations that should populate our galaxy right now. The result is hugely sensitive to the assumptions you make about factors such as the number of planets that orbit a host star that are potentially habitable, how many of these actually develop life and what fraction of that goes onto become intelligent etc.

Disagreement (ie general ignorance) over these numbers leads to estimates of the number intelligent civilisations in our galaxy that range from 10^-5 to 10^6.  In other words, your best bet is to pick a number, double it….

So Forgan has attempted to inject a little more precision into the calculation. His idea is to actually simulate many times over, the number of civilisations that may have appeared in a galaxy like ours using reasonable, modern estimates for the values in the Drake equation.

With these statistics you can calculate an average value and a standard deviation for the number of advanced civilisations in our galaxy.

Better still, it allows you to compare the results of different models of civilisation creation.

Horgan has clearly had some fun comparing three models:

i. panspermia: if life forms on one planet, it can spread to others in a system

ii. the rare-life hypothesis: Earth-like planets are rare but life progresses pretty well on them when they occur

iii.  the tortoise and hare hypothesis: Earth-like plants are common but the steps towards civilisation are hard

And the results are:

i. panspermia predicts  37964.97 advanced civilisations in our galaxy with a standard deviation of 20.

ii. the rare life hypothesis predicts 361.2 advanced civilisations with an SD of 2

iii. the tortoise and hare hypothesis predicts 31573.52 with an SD of 20.

Those are fantastically precise numbers. But before you start broadcasting to your newfound friends with a flashlight, it’s worth considering their accuracy.

The results of simulations like this are no better than than the assumptions you make in developing them. And these, of course, are based on our manifestly imperfect but rapidly improving knowledge of the heavens.

The real question is whether we’ll ever have good enough data to plug in to a model like this to give us a decent answer, without actually discovering another intelligent civilisation. And the answer to that is almost certainly not.

Ref: A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence

Ways ‘n’ errors

Saturday, October 18th, 2008

The best of the rest from the physics arXiv:

Recent Results from Super-Kamiokande

Detection of Organic Materials by Spectrometric Radiography Method

Why Do Cosmological Perturbations Look Classical to Us?

Emergent Spacetime and The Origin of Gravity

“Fractal Expression” in Chinese Calligraphy

Entangled photons to produce better quantum images

Thursday, October 16th, 2008

A while back, we saw how quantum imaging had been put on a firmer theoretical footing, thanks to some new thinking by Seth Lloyd at MIT.

Quantum imaging involves sending one of a pair of entangled photons towards an object while holding on to the other.

For a long while nobody was quite sure what benefit you might get from this entanglement. Some physicists speculated that it could be possible to produce reflection-free images by measuring the entangled twin that you hang on to, even if the other photon never returns.

What Lloyd calculated was that illuminating an object with entangled photons can increase the signal to noise ratio of the reflected signal by a factor of 2^e, where e is the number of bits of entanglement. That’s an exponential improvement.

Now he and a few pals have filled in a few details in the scheme that make it more realistic. done the experiment and shown that Lloyd was right on the money. They sent photons towards an object and used the reflection to determine whether the object was present or absent.

When they used entangled photons, this process was much more efficient.

The result is effectively the first quantum image taken with entangled photons .

Now all we’re waiting for is experimental proof of the scheme which, if I’m not mistaken, won’t be long in coming. The work was part funded by DARPA’s Quantum Sensor Program so it’ll be interesting to see what plans the organisation has for this technique.

Ref: Quantum illumination with Gaussian states

How chemotherapy can make tumors bigger

Wednesday, October 15th, 2008


While our understanding and treatment of cancer has advanced significantly in recent years, most specialists would readily admit that the dynamics of tumor growth are poorly understood.

It’s easy to see why. Tumor growth is a multifaceted process  that involves complex interactions between many types of cells and their surrounding tissue.

So it’s interesting to see a multidisciplinary group of mathematicians, cell biologists, cancer specialists and chemists take on the task of modeling tumor growth and the effect that drug treatments have on it. Their results are startling, counterintuitive and frightening.
Such a model has to reproduce a number of important behaviors. For example, the availability of nutrients is the most important factor in tumor growth. When tumors reach 2 mm across, diffusion of oxygen and other nutrients is no longer enough to sustain them and so they enter a new phase in which they grow their own blood vessels to keep them nourished.

It is this that Peter Hinow at the University of Minnesota and buddies say they’ve captured in detail for the first time.

They also looked at the way in which drug treatments effect tumor growth. We know that endothelial cells that line blood vessels  play a dual role in tumor growth. On the one hand, blood vessels supply the tumour with the nutrients needed to help it grow. Many chemotherapy treatments target endothelial cells on the assumption that killing them will cut off the tumor’s lifeblood.

But on the other hand, blood vessels are also the channel along which cancer drugs must pass to reach the tumor.

So what is the effect of killing endothelial cells? That all depends on how they are applied, say Hinow and colleagues. Their frightening  conclusion is that, applied to the tumor in the right way, chemotherapy treatments can dramatically reduce the size of  a tumor.

But applied in the wrong way, without due consideration for the structure of the tumor, chemotherapy treatments can cut off the supply of cancer-fighting drugs to a tumor, causing it to grow.

So chemotherapy can end up making tumors bigger rather than smaller.

That’s a shocking and important result.

Ref: A Spatial Model of Tumor-Host Interaction: Application of Chemotherapy

The waves beneath the sea

Tuesday, October 14th, 2008


Dead water is the curious phenomenon when ships become sluggish and difficult to control in stratified waters in which a fresh layer sits on top of salty water. Such conditions often occur in arctic regions where water run off from melting glaciers or ice flows can float on top of denser salty water.

The effect was first noted by the Norwegian explorer Fridtjof Nansen in 1893 who noted that while his boat, Fram, could cruise easily at 7 knots in ordinary seas, in dead water she was unable to make 1.5 knots. “When caught in dead water Fram appeared to be held back, as if by some mysterious force,” he wrote.

Now Romain Vasseur and pals from the University of Lyon in France show how the effect is even more pronounced when three layers of water are involved: a fresh layer sitting on a salty layer sitting an even saltier layer.

They have even made a rather beautiful video showing how a toy boat is dramatically slowed by the effect.

The explanation is that movement of the boat causes a wave to form beneath the surface at the interface between the fresh and salty waters. This wave eventually catches up with the boat and breaks, dragging the boat to a halt.

What’ s fascinating is that while all this is going on beneath the water, the surface remains absolutely flat.

Presumably these guys have posted this paper in anticipation of the Gallery of Fluid Motion 2008 at the upcoming meeting of the APS Division of Fluid Dynamics in San Antonio in November.

Ref: Dead Waters: Large Amplitude Interfacial Waves Generated by a Boat in a Stratified Fluid


Solving the mouth-puckering mystery of tannins

Monday, October 13th, 2008


The distinctive sensation of tannins on the tongue will be familiar (overfamiliar, perhaps?) to many arXivblog readers.

And if you’ve ever wondered what causes that mouth-puckering dryness, you now have an answer thanks to the dedicated and selfless work of Drazen Zanchi and colleagues at the Laboratoire de Physique Théorique et Hautes Energies in Paris.

Tannins are large molecules with aromatic rings and OH groups which naturally bind to each other and to proteins, while repelling water. So the presence of tannins causes proteins to aggregate together. From the biological point of view, that makes good sense. Tannins are part of plants’ defence systems against the proteins that bacteria, viruses and higher herbivores secrete when invading. It takes these proteins out of action be forcing them to aggrgegate together.

Zanchi says exactly this process is responsible for the mouthfeel of tannins. Tannins bind to salivary proteins in the mouth making them aggregate and this causes a rapid and immediate drop in the viscosity of saliva. That’s why your mouth feels dry as you gulp sip your favourite oak-matured cab before after work every day.

Obviously, the strength of this effect and the size of the aggregates that form determine the mouthfeel of the wine.

So feel free to raise a glass to Zanchi and his pals next time you get a chance (which shouldn’t be too long now). Not least because this effect may turn out to have other uses.

The team say that attaching tannins to a surface could force proteins to aggregate at that site. Sounds handy. And they’re convinced they have only scratched the surface of a rich, untapped and largely undiscovered chemistry of tannin behaviour.

Ref: Colloidal Stability of Tannins: Astringency, Wine Tasting and Beyond

Cold ‘n’ cool

Saturday, October 11th, 2008

The best of the rest from the physics arXiv:

Clathration of Volatiles in the Solar Nebula and Implications for the Origin of Titan’s atmosphere

Why Do Cosmological Perturbations Look Classical To Us?

Hyper-Gratings: Nanophotonics in Planar Anisotropic Metamaterials

Fish Biomass Structure at Pristine Coral Reefs and Degradation by Fishing

The Decline in the Concentration of Citations, 1900-2007

The neglected puzzle of low energy nuclear reactions

Friday, October 10th, 2008


Cold fusion won’t go away and perhaps rightly so. Numerous groups have reported idiosyncratic behaviour of palladium hydrides sitting in heavy water when a current passes through them. Many of these experiments are said to be repeatable.

Of course, serious questions remain over what exactly is going on in these experiements. They may or may not involve fusion but either way, something interesting will have to be dreamt up to explain many of the results.

These days cold fusion goes by the name of LENR (low energy nuclear reactions). And Allan Widom from Northeastern University in Boston and a couple of mates have taken the trouble to spell out how they think the electroweak force may be behind one class of these reactions.

They say that the well known decay of a neutron into a proton and an electron is mediated by the electroweak force. And that the reaction can be reversed to turn electrons and protons into neutrons, a process that would also result in nuclear transmutation, which in turn my be responsible for the release of excess heat and of nuclear by-products. Both of these things are claimed to be seen in LENR experiments.

Surely it’s time we bury the hatchets on this one and start working out exactly what is going on in LENRs. No?

Ref: A Primer for Electro-Weak Induced Low Energy Nuclear Reactions

On the origin of Saturn’s rings

Thursday, October 9th, 2008


One of the outstanding mysteries of our Solar System is how Saturn’s rings formed.

We know they rings are made of water ice with very few contaminants. We know they are different to the rings around Jupiter, Neptune and Uranus which are much smaller and probably the result of the surface erosion of nearby moonlets.

But Saturn’s spectacular rings are different. They are far more massive, probably several times the mass of the Saturnian moon Mimas. So how did they get there?

There are three main theories, says Julien Salmon from the Université Paris Diderot in France and a couple of mates.

The first is that the rings are leftovers from the primordial cloud and never formed into a moon around Saturn. That seems unlikely say the researchers, because the rings have a different chemical composition to other Saturnian satellites which must have formed from the same cloud.

The next idea is that the rings formed when a comet collided with and destroyed an ancient Saturnian moon.

The final theory is that the rings formed when Saturn’s gravity captured one or more comets and tidal forces broke the comets apart.

These last two are much more difficult to tease apart because we know that about 4 billion years ago, the solar system was filled with comets which bombarded the planets and their moons. This period, known as the Late Heavy Bombardment, could have caused either scenario.

But a detailed analysis by Salmon and co cause them to lean towards the theory that a comet must have collided with an existing moon. Here’s why: if passing comets could be captured and torn apart by tidal forces, then all four gas giants ought to have Saturn-like rings. And Saturn’s ring system ought to be the smallest of the lot because of the planet’s low density and mass compared to Jupiter and its distance from the main body of comets compared to Uranus and Neptune.

So Saturn’s rings must have been formed by a collision between a comet and moon, say Salmon and buddies. And it turns out that only  Saturn (and possibly Jupiter) could have had a moon at the relatively close distance that the rings have formed. (At that distance, moons around the other gas giants would not have been stable because of tidal forces.)

So that settles it: Saturn’s rings formed about 4 billions years ago when  a number of comets smashed apart one of its moons.

Well, not quite. There are still a number of important outstanding details. For instance,  moons and comets are known to contain relatively high fractions of silicates. And yet the rings contain very little silicates. Nobody has adequately explained where these silicates have gone.

And then there is the annoying evidence that the rings may be much younger than 4 billion years old because we can see some of them darkening at a rate which cannot have been going on for too long without turning the rings black.

Salmon and co say that on balance, the late heavy bombardment is your best bet if you wnat to plump for a mechanism that created the rings.

But there’s no need to be hasty– there’s more mileage in this mystery yet.

Ref: Did Saturn’s Rings Form During The Late Heavy Bombardment?

How religions spread like viruses

Wednesday, October 8th, 2008


“Religions are sets of ideas, statements and prescriptions of whose validity and applicability individual humans can become convinced,” say Michael Doebeli  and Iaroslav Ispolatov at the University of Vancouver.

In other words, religions are memes, units of cultural inheritance just like songs, languages or political beliefs. Richard Dawkins proposed the idea that memes spread much in the same way that viruses do, using humans as hosts. Some get passed from person to person and can survive for many generations. Others die away and become rapidly extinct. The most successful adapt and thrive. Evolution acts on memes in the same way it acts on our genes.

That has given Doebeli and Ispolatov an idea: “We propose to model cultural diversification in religion using techniques from evolutionary theory to describe scenarios in which the reproducing units are religious memes.”

The model they use is relatively simple, including factors such as the rates of transmission of religious memes as well as the rate of loss,  but it generate some interesting results.

It predicts, for example, that new distinct religions should emerge as descendants of a single ancestor. Exactly this process has been observed many times in various religions such as the Catholic-Protestant split in the 16th century, and the ongoing fragmentation of a religious organisation in Papua New Guinea, which anthropologists are currently observing with interest.

This is an interesting piece of work and one that could lead to new detail in our  study of memes. Religious meme transmission rates are relatively easy to measure and change more quickly than other widespread memes such as languages. So there is plenty of data to play with.
But if ever an idea was likely to ruffle a few feathers, this is it. They’ll be spluttering over their coffee and donuts tomorrow morning in Dover, Pennsylvania.

Ref: A Model for the Evolutionary Diversification of Religions