Greetings OAs

[Tony6Whiskeys]

Welcome to the group those are some great interests, especially the wine lol.

How fast a space faring civilisation might colonise the galaxy is a question with no clear answer, it depends on a lot of assumptions such as reasonable interstellar velocities, time between colony ship launches, cultural factors etc. I've seen estimations anywhere between 0.2 to 100 million years! For an in-depth look at the later I'd recommend looking into the 2019 Global Trajectory Optimisation Competition. It's an annual competition affiliated with the European Space Agency where groups around the world are tasked with finding optimum, efficient interplanetary transfer methods. In that year for their 10th anniversary they made it a competition to simulate colonising the galaxy. The rules were that Sol could launch two kinds of spacecraft: a fast runner that can't change course and colonises one system, and a mothership that travels slowly but has delta-V to adjust course and drops off colony pods to nearby systems as it passes. The emphasis on this competition is efficiency, and the ground rules were quite conservative by sci fi standards;

• Sol can only launch 5 ships: 3 motherships and 2 fast ships.
  
• Motherships carry 10 settlement pods that they can drop by nearby systems as they pass by
  
• Fast ships travel to one system only and colonise it.
  
• After 2 million years of being colonised a system can launch up to 3 settlement ships, which travel slow and colonise one system.
  
• Motherships and settlement ships travel at ~0.05% light speed, fast ships at 0.5% light speed.
  

The teams focused on the optimum way to colonise the galaxy with these constraints. Most went for sending the fast ships on trips far across the galaxy so that a wave of colonisation could happen backwards. The winning team had the galaxy colonised fully after 90 million years. This is part of the simulation of the team that placed third in the competition (yellow dot is sol, green lines are the path of fast ships, purple lines are the motherships, red lines are the settlement ships);



Obviously these are very conservative figures. There are speculative but realistic designs for interstellar drives that can manage 1-10% of light speed, and there's no physical reason why a colony would be restricted to only a few launches every million years. You could likely cut an order of magnitude or more from the winning team's speed by swapping these figures, colonising the galaxy in less than a million years, but the purpose of this competition was efficiency so that would kind of defeat the point

What this shows though is that on "merely" geological time frames a space faring species could colonise the whole galaxy with minimal effort.

Appreciate it.... so much to dig into here it's a bit overwhelming so thanks for the pointers!