On the 22 Sept 2011, news hit that a bunch of neutrinos (subatomic particles) were suspected of breaking the speed of light limitation. After four weeks of relentless efforts the media managed to spread the idea that such discovery could challenge Einstein’s Theory of Relativity. But who would guess that the existence of faster than light travel may have a dramatic impact on the fate of the entire human race? This week, Figure it Out, using simple calculations and logic, looks to establish a link between these “superlight neutrinos”, extraterrestrial life and the estimate of the date of the Apocalypse.
In order to do this, we need to consider what we already know about life on this our planet, and potentially, other planets. Let’s first think about the chances of us meeting an Alien.
First, let us consider what Enrico Fermi (Nobel Prize 1938) was thinking about one’s chance of meeting an alien. There are approximately 200 billion stars in our galaxy, half of which are surrounded with planets, which means that there are 100 billion stars with planets. In addition, scientists estimate that on average 2 planets per star are likely to support life. Therefore, follows that there are 200 billion potential cradles of life in our galaxy only! And for the entire visible universe this number grows to 7*1022.
But what is the chance that a suitable planets breed’s intelligent life, capable of space travel? If we take the example of Solar System, considering the Earth and Mars as capable of supporting life, intelligent civilization developed in 50% of occurrences. But of course the only example of the Solar System is not enough to reach any sound conclusion. The odds may be much smaller than 50%. But even if the chance of breeding intelligent life was as small as 1/1,000,000, we would still end up with 200 000 alien races sharing the Milky Way. If this is the case, shouldn’t we have met at least one alien species already?
Indeed, even if some of the alien nations might have some ethical issues or paranoid tendencies regards colonising the galaxy, there is no doubt that at least one civilization would decide to make the best all of the galactic resources. And considering that the average diameter of the Milky Way is around 100 000 light years, it would take around 10 million years to colonise the galaxy while moving at 1% of light speed only. Given the age of our galaxy, 13.7 billion years, 10 million years is nothing at all in comparison; it’s practically a flash. It follows that the galaxy should have been colonised long ago before first humans walked on the earth.
So where are they?
A number of speculations have been made around this so called “Fermi’s Paradox”, but one interesting scenario has been advocated by astrophysicist Carl Sagan. He advanced that the reason Earth is not presently under control of some extraterrestrial life form is simply because no civilisation lasts forever. Looking at Earth’s history, it appears indeed that civilisations are constantly under the threat of decline if not massive extinction, as both Romans and Dinosaurs would probably testify.
In this case the lack of flying saucers on the sky of London would be the proof no civilisation has lived long enough to conquer the galaxy. Indeed, if an alien race had colonised the whole universe at some stage, the galaxy would certainly be filled with remarkable markings of its culture. But so far, we haven’t found any. This would suggest that no civilisation has lived longer than 10 million years (time it takes to colonize the Milky Way as calculated earlier). If this figure is true, humanity should not worry about watching the sun getting old, our civilization would have perished in a nuclear war or a cosmic cataclysm long before the sun runs out of fuel in some 9.7 billion years
The average lifespan of a galactic civilisation could be actually very short.
Figure 1: The alien races could have expanded in different locations, thus populating the whole galaxy with the evidences of their cultures. The size of each colony in this case is relatively small compared to the size of the galaxy.
Time left for humanity may be even shorter than 10 million years. Indeed, if one alien race could fill the Milky Way with its relics by colonising it, the same result would be achieved with several distinct civilisations developing in different parts of the universe. In the latter case, no civilisation needs to exist long enough to conquer the whole galaxy, just long enough to overtake a few of its surrounding planets. Yet, there is still no evidence of that. So it is seems clear that the average life span for a species is less than 10 years, but how much less?
To Figure it Out, it suffices to find the maximum time (denoted T) that a galactic civilisations is develop, in other words, when the Human Race enters in the space era and it finds its neighbourhood (still) empty. Thanks to the magic of mathematics and especially the Theory of the Probability, this problem has an answer.
After solving some nasty equations[i], we have reached the conclusion that T is at most 20 000 years! Bu this answer is only valid when the expansion rate is bounded by the speed of light limit. And here is where those ‘super neutrinos’ intervene. If it is possible to travel faster than the speed of light, that would mean that T is even smaller than that. Legends say that Maya’s priests have forecasted the End of the World for the 21st December 2012. So all we can do is to hope that the CERN scientists and their neutrinos are wrong, otherwise it’s the Maya’s priest who may turn up to be right!
Wesson, Paul (1990). "Cosmology, extraterrestrial intelligence, and a resolution of the Fermi-Hart paradox". Royal Astronomical Society, Quarterly Journal 31: 161–170.
Crawford, I.A., "Where are They? Maybe we are alone in the galaxy after all", Scientific American, July 2000, 38–43, (2000).
Amir Alexander (23 March 2004). "Can a Star's Glow Reveal an Advanced Civilization?". Planetary Society. http://www.planetary.org/news/2004/0323_Can_a_Stars_Glow_Reveal_an_Advanced.html.
Bostrom, Nick. "Existential Risks Analyzing Human Extinction Scenarios and Related Hazards". http://www.nickbostrom.com/existential/risks.html. Retrieved October 4, 2009.
[i] The approach undertaken is to approximate the galaxy to a 2D square shaped surface and to allocate a zone to each developing species. We end up by calculating how many zones there should be so that to galaxy could be entirely filled in 13.7 billion years with 90% confidence. The filling of a zone is considered to be a Bernoulli trial. The number of the zones n can be found solving the following equation: . T is the age of the universe and p the probability of appearance of intelligent life on a given year. Once n is known, it is easy to obtain T knowing the size of the galaxy and the speed of extension of the civilizations.