Billy Brown wrote:
> Bryan Moss wrote:
> > Wouldn't the fact that we're here so early account for us being rare?
> No, it just explains why we aren't surrounded by billion-year-old elder
> races. If Earth's evolution is exactly average, and life is fairly common,
> we would still expect there to be lots of other races that beat us out by a
> few tens of thousands of years. So, at least one of those assumptions must
> be false.
Lets run a simulation.
Keep in mind that all stars in our local area of the galactic arm that are stable main sequence stars like ours are roughly of samilar age and size. Lets say that there are 1000 other civilizations that have arisen within 10 million years of each other in time in this area of the galaxy, which has some 20-50 million stars in it, is rougly 20 million light years in diameter. Also assume that each time a group colonizes from one star to the next nearest habitable star system (lets say one every 50 light years), traveling at sublight speeds, taking an average of 53 years objective time each jump, but also 100 years to terraform the new planet, and 200 years to build up enough industrial base to support launching the next large colonizing jump. This gives us an expansion rate of 0.14 c. It takes a race that emerged 10 million years ago in the center is still only 13% of the way from the center to the edge of the stellar cluster.
Also assume a relative level of coexistence when spacefaring races meet and intermingle. The densest center of the stellar cluster is the most likely point where the earliest races would erupt and eventually contact and intermingle. Their intermingling would slow things down a bit, and the edges of the stellar cluster would be least likely to see early civilizations emerge. We must also see that the gaps between galactic arms are really rather wide and are a hindrance to expansion.
Now, what about civilizations which die off? its an interesting thing to think about, but also think that the radio silence has a net positive evolutionary benefit to the existing starfaring races - since pre-starfaring but radio capable civilizations have no evidence of other races out there, they would be less motivated to become starfaring than if there were a measurable level of radio communications across the stars. This tends to dampen out the number of spacefaring races emerging a bit, especially the reducing the number of more agressive and violent races who would be more likely to self annihilate before reaching stardrive capability.
Now, considering that we were emitting measurable radio signals for some 40 years before we actually decided to start listening with any amount of focus, we gave starfarers a 40 year head start to set up jamming stations capable of nulling out their own emissions in our local area, while not interfering with the broadcasting elsewhere... Its really simply a matter of real estate. If I were them thats what I would do if I were even here yet.