Life on other planets would likely be brief and become extinct very quickly

And how long does an average civilization broadcast radio?

On the "life is safe" end of the spectrum, maybe there's much better technology to be discovered. On the "life is dangerous" end, maybe you learn pretty fast not to broadcast your location to the galaxy.

I think that one advantage of interstellar distance is we can effectively look back in time a great distance, so in effect we don't have a visible radius, but a combination of time and distance.

We can see thousands of light years back in time, thousands of light years away. However, we don't have that picture of Tau Ceti at 11 light years away. Perhaps thousands of years ago there was a civilization there that flourished and died - and we'll never know because their signs of life are outside our distance/time perception.

A graph of Time/distance would be Time one axis, distance on the other and a diagonal line stretching up and to the right, showing what we could see at any given time.

Thoughts?

[edit: comment formatting ate my pretty ascii chart]

Given the timeframes involved it's entirely likely that any 'aliens' are half a billion years ahead or behind us. Our first encounter with life will likely be one of three things.

1. Pond scum millions of years away from being anything else.

2. Aliens who have been extinct for millions of years.

3. Aliens so hopelessly advanced they are deities

Even just a million year gap would be insurmountable. Which is nothing on the universe's timeline.

Depressing, but it seems more plausible than things like "Great Filters of DOOM". It would predict that there is a lot of intelligence in the entire universe, but each cluster of intelligence is profoundly alone.

So it seems like it was a close call. Life needed almost the full extent of that interval of stability to create an (arguably) intelligent species. There can be no reset and start over. This is it, for the solar system. If we fail to survive, this whole star and its planets have failed to produce viable intelligence.

If Earth turns out to somehow be unusually stable as a life-bearing planet, this might explain a large portion of the Fermi paradox. This might be a large chunk of the Great Filter.

So true. We are really bad at looking at things outside the lens of our own experience. Why would life evolve in exactly the same fashion? Would it even have DNA as we know it? There is life that could form in ways we cannot even perceive - intelligence of a type that is so completely alien that neither could every notice or understand the other.

The universe may simply be filled with life, but because it evolves so differently it may simply be impossible to see most of it.

Controversial assertion. There's a lot of evidence that we've been able to rank on the level of forces of nature for quite a while now. The disappearance of megafauna, the desertification of Western China and Saharan Africa. There's even evidence that the Amazon rainforest may have been a massive human silviculture project that had been going on for 10,000 years.

I mean, scenarios can be imagined where an alien would want to destroy life on Earth, but they seem far fetched.

It's unclear whether that's actually feasible from an energy balance perspective. You'll need a lot of energy to re-arrange things on that scale. Each star is already sitting at the bottom of its own local energy well.

Maybe the far future will discover radically new ways to produce energy - but until then, this whole thing about the wave of computronium flooding the universe is pure speculation.

What tells us this is the case?

How do we know there isn't an upper limit on the amount of computing resources a civilization desires, even if it's an absurdly high limit like "disassemble all the inner planets"? How do we know there is an incentive to build interstellar civilizations, versus independent civilizations? Is computronium even worth spreading?

Analogous to r/K selection, is there more incentive to replicate a particular way of life (eg civilizations uploaded to a particular computronium implementation), or is it more beneficial to simply shotgun probs with very primitive seeds capable of bootstrapping new implementations of life? Is the interstellar competition between civilizations, or is the competition between different fundamental forms of life where civilizations simply mark a system developing to the point it can reproduce?

Given the distances between solar systems, why would a civilization span multiple systems? Wouldn't each system become culturally and economically isolated, evolving independent from the parent civilization? If that's the case, why invest in cloning the parent civilization when they could bootstrap native life from-scratch?

PS: Sorry; accidental mobile downvote when trying to upvote :(

E.g., we have big Jupiter. We don't know exactly what it does, but it might have helped the Earth survive its early days. Therefore, it might be the case that the rise of complex life needed Jupiter. Yadda yadda, multiply a dozen of these things, and suddenly life on Earth looks like an incredible stroke of luck.

The problem is, we don't know enough to make that verdict. What if the existence of Jupiter actually postponed the rise of life by sending big comets along our way?

I enjoyed "Life Everywhere" by Darling much more, though it is probably too dated to recommend in 2016. (Astrobiology is a rapidly changing field, I suppose.)

If you meant intelligent life, then nevermind :)