[quote=AlienBastard]Although there lies a new issue; What about self replicating probes? A civilization that used such probes would be able to easily comb the galaxy in a mere 10 million years.[/quote]

**IGNORING BALKANIZATION EFFECT OR NATURAL DISASTERS**

1 Cycle = 1,000 years. (Travel + colonization.) Each cycle, the number of colonies doubles, assuming that each colony sends out one ship per thousand years.

[hider=Maths]NUMBER OF COLONIES
1 (Starting homeworld. Thrown in for funsies.)
2
4
8
16
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
2,097,152
4,194,304
8,388,608
16,777,216
33,554,432
67,108,864
134,217,728
268,435,456
536,870,912
1,073,741,824
2,147,483,648
4,294,967,296
8,589,934,592
17,179,869,184
34,359,738,368
68,719,476,736
137,438,953,472
274,877,906,944
[b]549,755,813,888[/b] = 40 Cycles.[/hider]

40 Cycles = 1,000 Years (per cycle) = 40,000 Years.

[b]Milky Way Age:[/b] 13.2 billion years.
[b]Time to complete colonization of the entire galaxy:[/b] 40,000 years, given no natural disasters and assuming they found a way around the Balkanization effect.

Forget self replicating probes. Even assuming the slowest possible speeds (sub-light) a civilization could colonize every single planet in the entire galaxy in less than 40,000 years.

If there are aliens out there, colonizing shit, in my humble opinion, the most likely solutions to the Fermi Paradox are...
[b]#1:[/b] The aliens (regardless of the numbers) have a Star Trek like no interference policy on developing civilization.
[b]#2:[/b] There are no aliens capable of spaceflight. We were the first to win the genetic lotto race in terms of intelligence.
[b]#3:[/b] They colonize planets which are utterly inhospitable to us, therefore why we simply don't encounter them.
[b]#4:[/b] They don't use our ancient methods of communication, so our every attempt to contact them has of course failed as a result.
[b]#5:[/b] Balkanization took them down: Every civilization manages to get a few dozen colonies out and then fails to upkeep any sort of coherent empire due to the inability to send communication faster than the speed of light. Resulting in fighting amongst the colonies at worst, or a genuine feeling of not needing to proceed further out into the galaxy at best.
[b]#6:[/b] The chance for intelligent life to crop up is simply so insanely low that if there are other alien civilizations, they're simply off in other [i]galaxies[/i] and haven't figured out how to traverse the abyss between galaxies in any remotely safe or viable manner.
[b]#7:[/b] The chance for a hospitable planet is simply so low that the odds of mass colonization are very low.
[b]#8:[/b] The odds of a successful colonization might actually be very crapshoot at best. (IRL, colonizing North America from Europe had a lot of failed colonies. Imagine that, but worse, out in space.)