A Lonely Universe

> But if abiogenesis happened more than once, and we don't see any alternate-root lineages, then we've admitted the possibility that major advances towards complex life can have a resource lock out effect leading to the extinction of alternates; this could apply to any or all of the critical steps towards technological intelligence

I have often wondered if this is not exactly what occurred on earth, basically immediately after life first appeared. That direct ancestor to modern humans, maybe not even a real unicellular organism yet, won that very first resource race and extinguished any/all other contenders. That distant ancestor would have suffocated any possibility for carbon-based abiogenesis to occur again, leaving us with the tree of life we have today.

"Just the milky way"

You mean the collection of stars that's 100,000 light years across?

How long has life existed on Earth?

Of that time, how long has life on Earth been generating signals that could be detected elsewhere?

How much of the Milky Way has recieved those signals by now?

50,000 light year radius squared (let's favor your argument by calculating the milky way disc as 2D area) = 2.5 billion square light years

Area our signals could have reached in the milky way over the past century of broadcasting: ~10,000 square light years

So the intelligent life here and now, only a fraction of the life that's existed (much of which has had some degree of intelligence) has only reached about 0.0004% of the Milky Way by now, to say nothing for the drop of signal to CMB noise as it propagates.

There's extensive discussion about the fine tuning argument for Earth regarding our gravity/propulsion to even be able to enter outer space, a threshold other intelligent life on a different planet may never be able to cross.

Fermi's Paradox is silly when you dive into the nuances.

Maybe intelligent life isn't so rare, but technologically advanced intelligent life is exceedingly rare? It's possible that there could be planets where life emerged, evolved to an intelligent species that didn't have to compete for resources, maybe there were no large carnivores to worry about, maybe resources are even less scarce than they are here, maybe they developed a very collective culture and thus no concept of war, whatever - some scenario where technology doesn't really develop very far. It would never occur to this species to want to leave their planet to go exploring. They could be quite content to live this way for millions of years. We'd never see any signals from them.

When it comes to questions like the one posed in the fermi paradox we always seem to assume that all intelligent lifeforms would be very much like us with similar drives and culture. But it seems exceedingly unlikely.

Theoretically if you could travel very close to the speed of light time dilation would make the trip fairly short. Of course it’s one way since it would take hundreds of thousands to millions of years for everyone else. If you came back you would be returning to a different geological epoch.

Of course the energy requirements are insane and would require some kind of physicists nightmare propulsion system like antimatter rockets. Lose reactor containment and you are instantly converted into plasma and gamma rays. If you hit something the size of a dust particle it will destroy your spacecraft.

A bit hard.

Near light speed is a requirement for intergalactic travel because even solid state machines will not last long enough to make it without time dilation to shorten the trip.

Interstellar travel could theoretically be achieved with 1960s tech. Look up Project Orion. It could even be done with chemical rockets if you could hibernate, greatly extend life span, build a generational ship, or be an AI and just turn yourself off for the trip.

> Theoretically if you could travel very close to the speed of light ... Of course the energy requirements are insane

Yeah, this is why I don't think we'll ever achieve this and I very much doubt other species have or will either. I don't think the incentives are there to expend this kind of energy (and capital) trying to get to another galaxy - especially since it would a very, very long time before anyone would know if the project succeeded (if it would ever be known at all)- there's no success feedback for a project like that. Interstellar travel will be difficult enough and the feedback time there would likely be at least a couple generations (longer depending on where the travel is to).