The Drake equation is all pretty flowers up until you get to the term which describes how long a technological civilization exists before it extinguishes itself. I imagine a picture of the galaxy moving through time with tiny flashes going off every second or so. The flashes represent the rise and fall of technology in civilizations. The flashes continue for billions of years but they are widely scattered and rarely occur close enough in time or space to enable the exchange of information.
They use Science.
While they don’t “know” know, scientists can reasonably infer what the Earth’s core is made of. Seismic devices used to measure large earthquakes can measure how long it takes vibrations to move through the surface and through the core of the Earth. That is one method they can use to calculate what the core might contain.
The Earth has a magnetic field. That generally means iron.
They can figure out the mass of the Earth and other objects from their orbits and gravitational effects on other objects in the solar system. If you know mass and volume, you can calculate density and figure out the corresponding material.
And they can make educated gueses based on chemistry and physics. It’s not going to be made of cottage cheese, obviously. Pretty sure it’s not hollow and filled with dinosaurs and Morlocks . It doesn’t have enough mass to be made of lead or uranium or something heavy like that.
Obviously it’s harder with objects like the sun or Jupiter that are further away.
Keep in mind astronomers have been fine-tuning their knowledge of how the stars and planets work for about three thousand years now.
I think it was The Hitchhikers Guide to The Galaxy books that suggested that in an infinite Universe, anything you would want likely grows on a planet somewhere in that Universe. There could be a planet that grows matresses or Volkswagon cars (well…I suppose Earth would be that planet) or whatever.
The point is, I think it’s entirely possible for self aware, reproducing, decision-making systems to evolve that would look absolutely like anything we would associate with “life”.
I’m surprised no one has made mention of the Drake equationyet.
It’s silly because we have nowhere near enough data points to figure out the elements of the equation. So we could be visited by aliens sometime between now and never.
I’m pretty confident there’s lots of life out there, and I’m hopeful we’ll get some real evidence for it during my lifetime, though that’s mostly wishful thinking, but it seems possible for (simple) life to exist on other bodies in our solar system.
If we actually find life on Europa, or someplace else in our system, that would up the estimates of life on other systems a lot. Right now, to my mind, the most convincing clue is that life started here on earth pretty much at the moment the whole thing cooled down enough.
Anyway, we don’t really know how easy it is to evolve intelligent life on par with ourselves. In some regards, humans are a pretty strange animal, and we’ve gone almost extinct at least once (and all the other Homo species are already extinct). It may even be that pretty much all life never makes it beyond single celled creatures or something equivalent. It took us quite a long time.
I’m cautiously optimistic about intelligent life, just because of the enormous scale of the universe. I’m not nearly as optimistic about the chances of humans ever making “contact” or finding any clue that would confirm their existence.
It is important to note that this picture, the Hubble Ultra Deep Field is a long exposure of a very small piece of aparently empty sky. There are about 10,000 galaxies in this picture. And it is like this in every direction. To cover the entire sky would take about 12.7 million more pictures, and they would all look a lot like this. So there is a lot going on out there.
My own opinion, as per the OP’s question, is that the universe will eventually be found literally infested with life, that it occurs wherever conditions allow. And that primitive forms will be found elsewhere in our own little solar system, probably in several locations.
The problem is that while there probably is life all over the universe, it’s likely the scale of the distances may render it such that none of them will ever meet. Then again, our civilization has only started going to space withing the past 50 years, which is like zero time in the grand scheme of things.
I think it’s certainly possible, though, like everyone else, almost impossible we’ve made contact or will anytime soon.
That’s because God hates… fuck it, too easy.
Oh, good lord. This HAD to be the day they did their GeoCities tribute. 
You do that. I’ll start carving the black monoliths.
I vote we wait until *after *Dick Cheney is dead before we start building temples to him. He might get the wrong idea.
The distances are so great that you have to start using Star Trek jibberish to explain how someone would get here in a time frame that makes it anything like worthwhile. This makes the whole topic moot to me (using a real definition of moot).
How are they so great? We could probably reach the next solar system within a thousand years with our current technology, and as far as the universe is concerned, a thousand years is no time at all. A civilization could easily spread across a significant portion of the galaxy in a million years - and in astronomical terms, what’s a million years?
A race that has mastered cryogenics, has uploaded their consciousness into computers, or is simply immortal and very, very patient can conquer space without much of a problem.
You don’t see at least 2 very improbable conditions in your scenario?
Plus, why do I want to spread out like this? I’m really asking. It’s an enormous hassle and a big risk. My home world has to really suck to go to this trouble. And I have to have the technical means, which are not trivial.
Because that’s how nature works. Species always spread as far as they are capable of.
That’s not true at all. Species spread by circumstance. If the ice/land bridge between North America and Asia had not still been in existence when hominids had developed enough to use fire and animal skins for warmth, there might not be any humans in North America (well, not until Columbus and/or the Vikings, at least).
Sure, but there’s every reason to believe that none of the above conditions are possible. I suspect that there probably is one or more intelligent species out there somewhere with no innate physical limits on its longevity- perhaps to compensate for a very low birthrate- though.
Species spread as far as their capabilities take them, until they are stopped by circumstance. If the land bridge hadn’t existed, humanity would have settled the Americas as soon as it evolved the ability to build transatlantic ships - which is indeed what happened. As soon as a species evolves the ability to perform and survive interstellar flight, it will spread to the stars. In the absence of natural predators or environmental limits (and let’s face it - space is pretty much the same everywhere; once you can travel between 2 stars, you can travel between a billion), such expansion is inevitable.
Space only seems vast and a million years only seems a long time because you and I have limited imaginations.
Have you ever noticed how modern scientists seem to take a perverse joy in telling us laymen how things are impossible? It used to be the other way around: science used to be about weaving dreams, not shattering them. Besides, saying something can’t be done is simply bad science - the most a real scientist can ever say is “we don’t know how to do that yet.”
Anyway - there’s no reason that a species with control of its own DNA can’t engineer immortality. Or is that impossible too?
I think we’re alone now.
There doesn’t *seem *to be anyone around.
I hate you.
I’ll take your word for it. That’s beyond my level of comprehension and the results are utterly irrelevant to my day to day life. Sounds cool but I have no way to assess it.
In some far-flung galaxy, most probably, but I don’t think there’s another planet in the Milky Way that has given rise to intelligent life.