can we talk about the aliens

[Person Man]

There is definitely life and even intelligent somewhere out there unless of course we do live in a simulation or that some variation of creationism is true (where life on Earth just was there and had no natural beginning). The chance of even intelligent life being a one and done thing in a natural world approaches infinity. We have a better probability of floating off into space suddenly than being "alone".

That said, it is very unlikely that something relatively close to us in time and space would be there to visit or contact us. We probably have already been visited but probably by beings who have been intelligent for millions of years. That means we probably would never be able to find them or know they are here because we are unable to detect their past or present presence.

In order to have a chance to see little grey or green men, they would have to be close and advanced enough to find us and come here yet not too advanced or different that we can't detect them.

[Person Man]

I do think it's possible (though I wouldn't bet on it) that we're the only intelligent life in the observable universe (parts old enough that we can see light from them). We just don't know enough about how likely life is to occur, much less intelligent life, in order to know otherwise.

But if the universe is infinite, as it appears to be, then it is a sure thing that there is other intelligent life. In fact, it's a sure thing that there are identical copies of Earth and everything on it, infinitely many in fact. But since they're not observable in principle, it's somewhat of a philosophical question whether they should be considered real to us or not.

I think it was Hawking that said (paraphrasing) "there are two possibilities, we're alone or we're not and both are awesome".  If we're alone, then that makes us super special (and we should probably be better stewards).  If we're not alone, great, more to discover!  Breaking each down further, are we alone because we're the first?..the last? maybe the only, ever?  Each of those is pretty cool too.  If we're not alone, are we one of just a few locations with life? or maybe one planet of billions?  I think the most likely is the most boring, the universe is teeming with life, but 99.8% of planets with life have only microbial creatures.  Only 1 in 800 have anything bigger than a lady bug and only 1 in 5000 have something advanced as a dolphin and life that creates any kind of advanced tech is extraordinarily rare.


...but that just makes us super special.  We've sent sh**t out of our star system, I'd bet that doesn't happen very often in the universe.

I imagine that there are probably a few dozen civilizations in our galaxy with perhaps none of them being at any point of history close to ours. My guess is a new civilization comes into being maybe every 10000 years in the Milky Way. There are about 10 billion planets capable of supporting life based on the evidence we have but this assuming the confidence we don't have. If about 1 in 10000 develop intelligence over the course of 10 billion years, that's about one civilization forming every 10000 years.

[Person Man]

That sounds reasonable...and if we did the math the closest one would still be really really really far away.

If we assume a normal "best case scenario" for the evolution of life is what's happened on Earth, then it takes about 4.5 billion years for a solar system to go from early planets to life that can go into space.  The Milky Way is pretty much as old as the universe itself at ~13billion years, but, if I remember correctly, the heavier elements required for life took two or three cycles of stars forming and blowing up before they existed in quantities enough to form rocky/metalic planets big enough to form life (as we know it).  Lets say that's only been true for the last 6 billion years, that still leaves some plausible life (as we know it) bearing planets that are more than a billion years old.  If FTL travel is possible, they could be all over the galaxy.  Even if it's not, they could be all over a small corner of it.

Of course stars blow up, or otherwise die out.  Unless life is super advanced and can GTFO, it's not going to survive that very well.  Sometimes planets collide or other big thing from space hits it, or really, a million other things could stop early/non-advanced life on a planet.  It's a tough universe and we (probably) live on a rare Eden.

Although I've heard chances aren't bad for a planet to survive until it dies of the natural lifecycle of the star is over and that probably hasn't happened to any one civilization yet unless it was orbiting a white to blue star.