This article is classified "Real"
On some occasions -- such as the ushering in of a new era with the most
significant digit of the year being incremented -- a few people start to get
a bit worried (a condition dubbed by some as PMT; pre-millennial tension).
What they exercise their paranoia on is one of those oldest of science
fiction chestnuts: that of alien invasion.
If you just sit down and think rationally for a few minutes (assuming that
you are capable of this), you should come to the conclusion that it isn't
very likely, now is it? [1]
Astronomer Dr Carl Sagan worked out from some rather dubious estimates
that there ought to be around 10,000,000 advanced technological
civilisations in our galaxy, the Milky Way [2]. From equally dubious
assumptions we can also work out the likelihood of aliens invading, say, in
the next century, in a worst-case scenario. If we assume:
1) That the Earth hasn't been invaded by an alien race yet.
2) That the Earth has been around for approximately 4.5 billion
years (that figure may have to be updated as this article gets
older).
3) That the probability of aliens invading Earth has remained
constant throughout the Earth's history.
Then, as a worst case scenario, presume that aliens invade tomorrow (or some
time in the next century, if they're held up by bad weather, traffic
congestion, or the wrong type of interstellar hydrogen). From a total of 45
million and one centuries, we will then only have been invaded in one
century. Thus the probability of being invaded in the next century is
vanishingly small, at only one in 45 million [3].
The chance of an alien invasion commencing in the very minute that the year
2000 starts [4] is therefore even smaller, at about one in
2,368,000,000,000,000. [5]
Sceptics might point out that the three assumptions I made earlier are
wrong, which would make my estimate equally wrong. (What am I talking
about? Real sceptics would be arguing the same as me!) However, I can
justify these three premises.
For (1), there is no proof, as yet, that the Earth has ever, in its history,
been invaded by outsiders (notwithstanding Nazca plain figures). That also
means ignoring, for the time being, any theories that say life on Earth was
of extraterrestrial origin (which might count as an invasion of sorts).
However, it is probably impossible to prove that the Earth hasn't been
invaded at all, only that is has (which it probably hasn't). Remember:
absence of proof doesn't mean proof of absence.
As for (2), this is an estimate made by people with more geological,
astronomical and cosmological knowledge than I (say that with your false
teeth in). This can't be proven absolutely either, without being able to
travel faster than light, which is impossible (although its impossibility
cannot be proven, only extrapolated) [6]. Anyway, even if this estimate is
out by several orders of magnitude, the chances of invasion are still slim.
You might say that point (3) is the weak point in my argument; that the
probability of an alien invasion hasn't been constant throughout our
planet's life. Firstly you might point out that as any hypothetical alien
race becomes more technologically advanced, the chance of them invading
increases. This is true... well, probably: the aliens might become more
benevolent and wise over time, but since we don't know if there are any
aliens out there, their existence and frame of mind are effectively random
-- their quantum wave function hasn't collapsed yet, you might say.
Besides, aliens aren't really going to want to invade a planet just for us
(what would give you that idea?). They wouldn't need to enslave us; if they
had the necessary know-how to invade a planet, they could instead build a
simple robot to make the tea and fetch their slippers for them. They
wouldn't want the planet for its natural resources; if they've just
travelled N light years to get here, expending <large-number> terajoules of
energy in the process, they're not going to want Earth's <small-number>
joules of fossil fuel energy.
Conclusion
==========
For those high-powered executives among you who haven't had time to read
this entire article and have instead skipped straight to the conclusion,
here is the bulk of the article presented in one easy-to-digest sentence:
If the occurrence of alien invasions of Earth is random, Earth has not
undergone alien invasion yet, and the Earth has been around for a long time,
the probability of alien invasion over a small time scale is minute.
So, throw away your T-shirt emblazoned with the slogan "the End of the World
is Nigh", and invest in some lottery tickets! That'll give you a better
chance of getting it right.
[1] Conspiracy theorists might point out that this is precisely what
the government wants us to think. But then, this is precisely what
conspiracy theorists would want us to think. (Perhaps the conspiracy
theorists are hatching a conspiracy to make us believe we are being
conspired against?)
[2] In his book, Cosmos, the late Dr Sagan puts forward a formula for
estimating the number of technologically advanced civilisations in our
galaxy:
N* x fp x ne x f1 x fi x fe x fL
Where:
* N* is the number of stars in our galaxy (about 400 billion);
* fp is the fraction of stars with planetary systems (about 1/3);
* ne is the number of planets per system that are suitable for life
(about 2);
* f1 is the fraction of suitable planets on which life actually
arises (about 1/3);
* fi is the fraction of planets containing life on which intelligent
life evolved;
* fe is the fraction of planets with intelligent life on which
technical civilisations developed (where fi x fe =~ 1/100); and
* fL is the fraction of the planet's lifetime for which the technical
civilisation existed (less than 0.0000001%).
This apparently comes out to 10,000,000 civilisations. (However, that's
not what I get, which may be due to the fact that my source of this
information is a small text file containing information regurgitated
from the book. I make the number to be about 0.9 civilisations, which
seems considerably more accurate, fitting in as it does with our current
knowledge.)
[3] However, it has been found that million-to-one chances crop up nine times
out of ten.
[4] Or the year 2001, if the alien race really gets it right.
[5] 45,000,000 x 100 x 365.25 x 24 x 60 = 2.367 x 10^15 (3 sf)
[6] The basic idea is that if you could travel faster than light, you could
overtake the light rays that left the Earth all those billions of years
ago, and when you looked back at the Earth, you would see what was going
on down there all that time ago (so long as you had a really powerful
telescope with you as well). It's not very easy though, folks.