[palmotea]

>> According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years

> ...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0].

I guess it depends on whose hundred million years you're talking about: the colonists' or those who stay home's. I don't know how to do the calculations, but it seems plausible that you could traverse the entire observable universe at near light-speed in 100 million years ship time.

[grvbck]

You need ridiculous speeds for time dilation to really kick in though. Mathematically, it starts as soon as an object moves. But if a spaceship travels at 90 % of light speed (0.9 c), their local time moves just approximately at half speed compared to local time on earth. A year for the astronauts is just over 2 years on earth.

At 0.995 c, the ship clock runs 10 x slower.

At 0.999 c, 22 x slower. Then if you push the turbo button to 0.9999 c, 71 x slower.

The fastest man-made object to date is the Parker Solar Probe, at 0.059 c.