Date published: 2005/03/11
The eighth and final lecture of the Darwin Lecture Series 2005 was by Paul Davies, a theoretical physicist who worked in Britain for many years before moving to Australia (currently at Macquarie University, Sidney).
Whereas previous lectures in this Darwin "Conflict" series were about conflicts between humans, this lecture was about "violent" events in the universe, so completely different. Cosmologists have a hard time justifying their existence these days, and one of their best angles is to talk about possible extraterrestial initiated catastrophes which could wipe out much life on Earth. These are low probability events, but ones which have occurred in the past. And low probability events have become all the rage in society because they cause such big effects. (Terrorism being the main current example, just look at all the hysteria politicians have created over that because they want to scare their citizens into submission.)
Davies talked about three types of catastrophe, in growing magnitude of disaster. First he mentioned the well discussed cosmic impacts, e.g. from a comet or asteroid hitting the Earth. The solar system is around 4.5 billion years old, and apparently for the first 700 odd million of those years the Earth was regularly pounded by objects up to several hundred kms across. Indeed it is believed that a Mars-sized object once hit the Earth and as a result enough matter was ejected to create the Moon. These kinds of impacts can cause mass extinctions. The last such mass extinction was around 65 million years ago and the current view is that an object around 20 km across was responsible for that catastrophe.
Perhaps once a century we have an impact by an object of 10s of meters across, the last one being in 1908 in Tunguska, Siberia, and that did some serious damage. Davies claimed that a 1 km object impact would possibly kill a billion people. Of course you can say just about anything you want when catastrophes get that big, for who is going to prove otherwise. Davies claimed that if you added up all the possible probabilities of collision by objects of various sizes, multiplied by the numbers killed in each case, and took the average, then there was around one in a million chance that any of us would die this month. That sounds high, and even if the calculation is theoretically correct, it is a bit meaningless since the frequency and impact of the low probability events are basically "finger in the air" jobs.
Of course Davies said that we would all be much better prepared if only government funded astronomers (and cosmologists) to look out for these deadly asteroids. Well, all scientists always want more money for their own field, and if you have to peddle scare stories to achieve that, then that is apparently a price worth paying.
He did at least mention that catastrophes may be bad for some species but they might be good for others. For example, the object that wiped out the dinosaurs created the environment in which mankind would eventually flourish. And Davies claimed that the Cambrian explosion around 580 million years ago, when the number of species shot up, might have been the result of the impact of an object which created just the right environment for life to take off.
He next talked about exploding stars (or supernovae) as a possible disaster for life on Earth. A supernova explosion can be of order 10^30 hydrogen bombs, so huge. If one happened close to Earth it would all be over (and fairly quickly). Apparently some scientists have recently claimed that there was a supernova explosion around 2.8 million years ago which was close enough to Earth that it left some detectable debris (with an iron-60 signature). But not close enough to cause serious problems. And a few weeks ago it was reported that there was a neutron star with a glitch in its magnetic field which spewed out as much energy in a tenth of a second as the Sun does in 100000 years. This would have been a problem if it had happened within 10 light years of Earth, but fortunately was around 50000 light years away.
Supernova also have their good points. For example, it is believed that the big bang created only hydrogen and helium, but carbon (generally believed to be crucial to life) can be created in the cores of stars, and supernova can spew this carbon into the interstellar medium.
Davies next talked about the big bang itself. Apparently this was equivalent to around 10^55 hydrogen bombs. Of course life would not exist at all without the big bang. Now the big bang created a largely uniform distribution of matter in the (observed) universe, with the fluctations being measured in the last few years to be of order 1 in 100000. These fluctuations led to the formation of galaxies, and apparently if the fluctuations were much bigger the universe would just have made monster black holes, and if the fluctuations were much smaller the universe would just have been boring nothingness. So it is a lucky "coincidence" that the fluctuations were of the size they were, otherwise we wouldn't be here. (And since we wouldn't be here it is obvious that the "coincidence" had to have happened.)
This led him on to state that there were ten or fifteen such "coincidences". (He specifically mentioned one first noticed by Hoyle, that to get carbon you need three heliums to collide in just the right way, and this just happens to work in stars because there is a resonance at just the right energy.) And what are the odds of all these coincidences? Well this is the kind of pseudo-philosophical question which has led cosmology to more and more resemble religion the last decade or two. Cosmologists can say whatever they want about these types of questions because there is no way to test the theories one way or the other. Apparently they are even talking about our universe being only one part of a vast "multiverse" (or "megaverse"). It's amazing that they can talk about this stuff with a straight face.
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