But what if it's 0.5c travel?

That's a massive difference from 0.99c travel

Agree, visitors may have traveled for millions of years to get here. We should not project human timescales on aliens.

Humans as we know them today will never visit other galaxies, but our AI descendants almost certainly will.

If you have 20 million years and don't mind waiting, you can send probes to every system in the galaxy at sub-light speeds.

Idk what’s so special about the speed of light/causality, in an alien universe it may not even be relevant. When talking about alien intelligence and technology literally everything is on the table.

> literally everything is on the table

Right, they could have ridden dragon-unicorn hybrids through a magic portal made from the dust of black hole centers.

That's what you mean when you say "literally everything is on the table."

Or, start drawing lines for me if you disagree.

There is only one universe

I'm not sure we will ever know if this is the only universe. However it seems highly unlikely that aliens could travel from another universe and, even if they could, bring their own laws on physics with them.

with coldsleep technology, or a species evolved or self-engineered for ultralongterm hibernation, speed might not matter.

Having just finished Iain Banks excellent The Algebraist, this is immediately what came to mind: we have no idea what timescales aliens would operate on.

Machines would be more likely than anything biological in any case. Not implying this is what we have here, just a general observation. It's weird people believe space travel requires pilots.

> Machines would be more likely than anything biological in any case.

Counterpoint: biology is a machine in itself.

Our machines of metal and microchips are incredibly primitive compared to where they'll be in 100, 500, 1000, 10K+ years from now - and when a machine has the ability to to self-replicate, have autonomy, and to protect itself from microscopic threats, then it sure looks a lot like life-as-we-know it.

Extend that too: a) An alien civilization has overcome the massive problems of interstellar travel and is able to visit in a manner that doesn't create a second sun in the sky b) then crash

Why near c travel is assumed?