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If there are a bunch of other earths out there, and even if only a few of them are populated, how come none of them has advanced enough to contact us? I mean, are homo sapiens on this planet the most advanced, or even nearly the most advanced, species in the universe? I figure within a 1,000 years or so, we'll know a lot more than we do now. The way technology is progressing, we should definitely be able to send probes to some distant systems, use radio waves to signal other planets, etc. So how come no one has contacted us?

And 1,000 years, or even 10,000 years, is not much in the human time scale. We've been walking around on this planet for what, a few million years? So isn't it feasible that somewhere, some civilization could have just been a slight bit faster? Or are we really the fastest, or nearly the fastest. I just don't understand why no one has contacted us if there are so many civilizations out there.

We've only been transmitting to the universe for a few decades, so almost certainly none of them would have any idea we're here. Even if there are 10,000 detectable civilizations in the galaxy, the galaxy is so big that the nearest one on average would be about 1,000 light years away. Any civilization further than 120 light years away would hear nothing but silence coming from our direction, no matter how sensitive their instruments.

I just don't understand why no one has contacted us if there are so many civilizations out there.

The ability to receive radio transmissions is fairly new. Even newer is the ability to discern that radio transmissions might be sent to us from other civilizations.

Figure, SETI has actively been looking for intelligent life via radio transmissions since 1984. This gives us a 21 light-year range of possible places in the universe that might be sending us messages via light-speed radio transmissions.

21 light years is pretty small.

Furthermore, while intelligent, even highly advanced cultures may thrive on other worlds, intergalactic travel at speeds faster than light may indeed be impossible as currently theorized. Like us, these other civilizations might be unable to develop spacecraft capable of travelling through the vastness of our galaxy (not to mention the universe). This could explain why aliens aren't dropping by daily.

Or maybe we are alone (though I believe this is unlikely).

Good questions! Personally, I'm leaning more and more to the view that intelligent life -- never mind technologically advanced civilizations -- is exceedingly rare. Earth was around for four billion years before life ever evolved beyond the single cell stage, and of the perhaps billions of higher forms of life that have existed on Earth, only one has ever achieved high intelligence, despite its obvious evolutionary advantages, etc.

I just don't understand why no one has contacted us if there are so many civilizations out there.

The Mayans, Toltecs, Aztecs, Souix, Cheyenne, Chippewa, etc.. never discovered the wheel...
The advent of Islam (eventually) destroyed Arab culture..

Without say, Newton, how much longer would it have taken to understand the laws of gravity?
Without Maxwell, would Einstein have deduced the theory of relativity?
Without Tesla, would we have slogged along with a direct current technology? ( He was the inventor/discoverer of alternating current, and the AC generators that provide our electrical services )

What's my point?
There are many things that can go wrong..
The Axis powers might have won WW2, changing the entire direction of world history..
Stalinism, instead of collapsing from economic and social failure, might have succeeded in gaining world control instead..

Politics can guide scientific endeavor.. So can religion, or the dictates of an insane tyrant..
Or, a Natural Disaster, catastrophic in proportion can set everything back to square one..

Even given the number of inhabitable worlds and the possibilities of intelligent life, technology, advanced civilization, War, some alien Bill & Hillary.. ... well, it's just too awful to consider..
They probably are too busy handling their own problems..

There's no guarantee that advanced civilizations mean that all problems are solved..
Just that there are new, and unforseen problems..

Think!

If you were from a technologically advanced civilzation many, many light years distant from here, would you waste you time on this violent collection of scientific wannabes, when in all probablilty there's so much more to be had out there?

How could you trust a "civilization" that is brutal to it's own?

How could you approach a people who have seen fit to irridate their own planet - not just once, but many times?

How comfortable could you feel with an ignorant mass of collected races that seemingly have been thrown together haphazardly, and can't find it in themselves to get along?

How confident would you be with a world that has just scratched the surface of scientific possibilities and whose first option to your visit is more likely than not going to be militaristic?

With each passing year I become more and more convinced we live in a really bad galactic neighborhood, and until such time as we get our sh*t together, we won't be graced with a visit from these guys any time soon.

And in passing, I don't think warp technology is the answer to interstellar apace travel. At some point it might serve as a semi-useful bridge technology, but I really think they'd use something else more efficient.

Just my thoughts...

CA....

Humans are a lot more than just an excellent brain. We possess the finest construct found anywhere in nature. There's one at the end of each arm. The hand has made all of our technology possible. The dolphin could be three times smarter than we are and never achieve more than it already has. It can't use fire, metals or electronics. It can't manipulate stones so as to create a sharp edged tool and couldn't use one if it could produce one.

Then there are the imponderables. Maybe we are a rare species not bothered by radio waves. Maybe other intelligent species find it carcinogenic or simply obnoxious to be around. Maybe we possess more curiousity than most and the vast majority of intelligent species simply don't care.

There are probably a million reasons why we are not yet in contact with other species first among them is we simply may not be paying attention to what they think is an obvious message. Frustrating isn't it?

I forget where I heard this, but this is the explanation for lack of contact that I like best: (although it does rely on human nature, which may not apply to an alien species). If we simply scan the sky for a radio message from an alien civilization, if there is one, we will know immediately, or at least in the amount of time it will take for us to recognize the alien signal as such. If we broadcast a message on the other hand, we must wait for the message to get to its target civilization and then wait for a reply. It's possible that we wouldn't know for several hundred years or more if we were successful. Humans naturally would rather do the former and just listen rather than broadcasting and leaving the question open until our descendants hear an answer. However, what if other species think the same way? It's possible that no other species is broadcasting for the same reason that we choose to just listen.

One "why no contact" theory is that developing scientific cultures tend to go thru the same process of discovery and engineering ... eventually reaching a point where they invent something that wipes out the whole dang planet.

When the first atomic bomb was detonated on Earth, scientists gave it a non-trivial probability that, considering they knew they didn't fully understand what would happen, the detonation's chain reaction might just continue until the whole planet was consumed.

Recently there was news that a black hole (just a little one) may have been created in a lab. Had it been of self-sustaining size (and not promptly evaporate due to Hawking radiation), it could have plummeted thru the floor, began an oscillating path thru the Earth's core, and increasingly hoovered up the planet.

Other doomsday technologies are conceivable: cobalt-caked nukes (radiation & distribution balanced to give _everyone_ terminal radiation poisoning), genetically engineered ultrabugs (stabilized Ebola turns everyone to goo), physics experiments gone haywire (quark-level chain reaction breaks down all Earth matter), MAD nuclear war (nuclear winter starves all), and so on.

Obviously we haven't gotten there yet ... but technology advances mean smaller packages can adversely affect more people. One good solid technological mistake, statsitically inevitable, could mean every intelligent species in the universe invariably wipes itself out before contacting anyone else. Those first interstellar warp drive tests just _never_ go right...

Or maybe they just have a habit of creating the "history eraser button" and there's always some bozo who actually pushes it: