Where Grey Matter meets Dark Matter

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Episode 12 - 17 May 2009

Dr. Phil Plait is the self-declared Bad Astronomer, and president of the James Randi Educational Foundation. He writes the Bad Astronomy web log, one of the most popular science blogs on Mr. Internet. But he also writes on ye olde paper, and that's what we wanted to talk to him about: Death from the Skies!

Book cover, courtesy of Phil Plait

It's pretty much what you expect: the stuff in space that can destroy we humans. Here's some examples:

Asteroids colliding into us

Ida and her moon. Courtesy of nasaimages.org

Ida is a huge asteroid, 56 kms long, big enough to have its own moon (the small thing to the right, which is 1.5 kms across) and big enough to wipe out a sizable portion of the human population. Don't worry, this one's not likely to hit us - soon.

Our sun going nova

Nova Cygni 1992. Taken by Hubble Space Telescope. Credit: Francesco Parasce, ESA and NASA.

This is the star Nova Cygni 1992, located in the constellation Cygnus, about 10,000 light years away. It blew up (ie. became a nova) in 1992, hence the name. The ring is a huge cloud of hot gas surrounding the star - roughly 400 times the width of our solar system. This will happen to our sun in about 4 or 5 billion years. It will expand to about the orbit of Mars (ie. burning the earth to dust) like this star did.

A gamma-ray burst

Artist's impression (the best pictures always are, aren't they?). Courtesy of nasaimages.org

This is where a giant star collapses and sprays out 2 beams of gamma rays, which could easily cook the entire earth.

This star, called Eta Carinae (below), exploded in1841. The big gas clouds coming off it are huge: each is roughly the size of the solar system. When it finally collapses it could generate a gamma ray burst.

Eta Carinae . Courtesy of nasaimages.org.
Credit: J. Hester/Arizona state University NASA


This is not the walking, talking, anal-probing X-Files aliens. This is alien invasion by poisonous tiny microbes that come from somewhere else. It has a disturbing, Wellsian fittingness.

These little things were found in a rock that came from Mars in the form of the meteorite ALH 84001.

Possible Martian microbe in the meteorite ALH84001. Courtesy of nasaimages.org.
Credit: D. McKay, K. Thomas-Keprta, R. Zare, NASA.

These probably weren't martian critters (they were probably just rock formations), but if they had been biological then they might have caused some serious problems for the beasts already here.




The Foundation Series - which is a sequence of 7 science fiction novels (with about 8 others that are sort of related) written between 1942 and 1988 by Isaac Asimov (who died in 1992).

Isaac Asimov. Source: The Asimov Wikia

The series got a stack of awards including: The one-time Hugo Award for "Best All-Time Series" in 1966. It is a true Science Fiction (not a space fantasy like Star Wars, which was basically spaceships, aliens and magic) - there are some really good science ideas in here. You need two things in science: hard work and creativity - makes you wonder how much creative influence writers like Asimov gave to the scientific community.

The key plot device of the series is the fictional science called "Psychohistory", which is basically a statistical study of societies. In Asimov's future, the human species has spread from the end of one spiral arm of our galaxy to the other. It is also populated by quintillions of humans (a quintillion is 1 with 18 zeroes).

Now, the complexity of humanity is the bane of the sociologist - who is essentially someone who tries to put patterns on masses of people. An empirical, statistical and objective study of societies remains out of reach. In the book, rather than try to predict the actions of individuals or even small groups, mathematician Hari Seldon instead treats humanity, as a whole, as a system of particles following certain rules, similar to the present theory of Statistical Mechanics.

Statistical mechanics (or Stat Mech to those in the know) takes a large group of particles and treats them statistically. You can predict what one particle will do when it is by itself. If you increase the number of particles just a little bit, say about 10, then you've no idea what each particle will do. But increase the number a whole lot (and we mean a really big lot, say 1,000,000,000,000,000,000,000,000), then you can work out what most of the particles will do. It can seem totally counter-intuitive that adding more particles would make a system more predictable, but it works in the same way that the more times you toss a coin the more you can depend on there being around 50% heads and 50% tails. This is essentially Asimov's premise in Foundation. With heaps of people in the universe, then maybe we can apply the same techniques.

But a quintillion people isn't very many. It falls short of the magic number by about 6 zeros. This may not be such a big problem though, because for smaller numbers the probabilities just become a bit more lax. The main problem lies in the individual particles themselves. The following is a list of things that are true of subatomic particles but not of humans:

  • The rules for a group of particles don't change over time - that's one of the assumptions the whole business of physics is based on.
  • A single particle follows a fairly basic set of rules - when in a certain type of field it acts a certain way, near another particle it acts another way, if unacted on by a force it will continue doing whatever it was doing.
  • You can study a particle on its own and introduce one variable at a time (such as another particle), and get a picture of how it acts under certain conditions.
  • Particles of the same type are essentially clones. They have the same effect on each other, and on other things, as any other particle of the type.

If Seldon's psychohistory can be made to work, and the computing power is ever available, then in addition to the principles of statistical mechanics, a whole bunch of other things will need to be included: general equilibrium theory of economics, game theory, anthropology and sociology, evolutionary psychology (if the theory is valid), and maybe even things like military strategy and diplomacy. If all this could be codified into mathematics, then we're in business - the business of prophesy.



  • Here's what started it all: Asimov, Isaac (1951), Foundation, Gnome Press, New York.
  • In the spirit of this modern age of audio recordings, here's an interview with Asimov.
  • A good description of how psycho history might work: http://www.zompist.com/psihist.html
  • Here's a serious article about applying network theory to sociology, from the most useful resource on the internet.
  • Another attempt in the same vein is the idea of econophysics
  • Some lecture notes from a course in statistical mechanics at New York University:
  • The webpage of John J. Xenakis, who claims that he has all the powers of Hari Seldon, today!
  • There's a whole field of study, unrelated to Asimov's idea, already called psycho history. It seems like it largely reduces to the claim that people who were abused as children grow up to become warlords.



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