31573.52

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: http://arxiv.org/abs/0810.2222: A Numerical Testbed for Hypotheses of Extraterrestrial Life and Intelligence

The many worlds interpretation of quantum mechanics holds that before a measurement is made, identical copies of the observer exist in parallel universes and that all possible results of a measurement actually take place in these universes.

Until now there has been no way to distinguish between this and the Born interpretation. This holds that each outcome of a measurement has a specific probability and that, while an ensemble of measurements will match that distribution, there is no way to determine the outcome of specific measurement.

Now Frank Tipler, a physicist at Tulane University in New Orleans says he has hit upon a way in which these interpretations must produce different experimental results.

His idea is to measure how quickly individual photons hitting a screen build into a pattern. According to the many worlds interpretation, this pattern should build more quickly, says Tipler.

And he points out that an experiment to test this idea would be easy to perform. Simply send photons through a double slit, onto a screen and measure where each one hits. Once the experiment is over, a simple mathematical test of the data tells you how quickly the pattern formed.

This experiment is almost trivial so we should find out pretty quickly which interpretation of quantum mechanics Tipler’s test tells us is right.

Then it boils down to whether you believe his reasoning.

(And not everybody does. When Tipler published his book The Physics of Immortality one reviewer described it as ” a masterpiece of pseudoscience”.)

Let’s hope this paper is received a little more positively than his books.

Ref: arxiv.org/abs/0809.4422: Testing Many-Worlds Quantum Theory By Measuring Pattern Convergence Rates

The Pioneer anomaly grows ever more fascinating.

Here’s the background: Pioneer 10 and 11 were launched in 1972 and 1973 respectively and, after sweeping past a number of the outer gas giants, have been heading out of the solar system ever since.

NASA has been accurately tracking their position and speed using Doppler tracking measurements of radio signals from the craft. But this data has thrown up a problem. Both probes appear to be decelerating faster than can be explained by the Sun’s gravity. All that has been widely discussed and numerous explanations have been put forward to explain this discrepancy.

What isn’t so well known is that there is a periodic component to the anomaly. The team at the NASA’s Jet Propulsion Lab who have been collecting the data say that it’s unlikely that this variation is a from the spacecraft. Instead, they think probably the result of something at our end such as a tiny variation in Earth’s orbit.

Now Bruno Christophe and pals from the French aerospace lab, ONERA, near Paris and various other French institutions, have carried the most detailed analysis yet on these periodic variations and raise another interesting possibility.

A number of people have suggested modifications to general relativity that would explain the Pioneer anomaly. But there has never been a way to test these modifications.

Now Christophe and co say that the periodic variations are compatible with the effects on radio signals that some of these modifications might cause.

That’s an extraordinary claim. Obviously, more analysis is needed and it always pays to be cautious with these kinds of ideas. But could it really be possible that the Pioneer anomaly is the first evidence of physics beyond Einstein’s version of general relativity?

Ref: arxiv.org/abs/0809.2682: Pioneer Doppler Data Analysis: Study of Periodic Anomalies

About 444 million years ago, more than half of all marine invertebrates were wiped out at the end of the Ordovician era in the third worst mass extinction in history.

A couple of years ago, Brian Thomas at the University of Kansas pointed out that this holocaust could have been caused by a nearby supernova zapping the Earth with gamma rays. A 10 second burst of gamma rays, they said, would have done for about half Earth’s ozone layer, leaving life here more or less unprotected from the Sun’s harmful UV rays for 10 years or more.

Organisms living deep beneath the waves would, of course, have been protected from UV rays anyway but those nearer the surface would have been wiped out within that time. What makes Thomas’ idea interesting is that the geological record seems to indicate that species living nearer the surface were hardest hit in the Ordovician extinction.

Today, Thomas and a pal give us an update based on more detailed simulations. They say the geological data is consistent with a gamma ray burst somewhere over the South Pole.

And this also allows them to predict that any large land mass well above the equator would have been shielded from the burst and so the geological record there ought to be different. Thomas suggests that northern China would be as good a place as any to start looking.

Better get digging.

Ref: arxiv.org/abs/0809.0899: Late Ordovician Geographic Patterns of Extinction Compared with Simulations of Astrophysical Ionizing Radiation Damage