Well, while we're on the topic of aliens, I've had a rather intense debate with a friend of mine about whether or not it's wise for us to send out radio broadcasts and do other things that could make first contact with aliens.
She maintains that aliens are likely predatory and aggressive, much like us. So such signals are tantamount to ringing the dinner bell. Think about what our own explorers did when they made contact. It would be much the same for us.
I agree that aliens would vaguely be like us, denizens of a planet or large moon - likely omnivorous generalists like us. They'd likely have a similar aggressive streak as us, though I'd like to think that total war is an alien (get it?) concept to them. And like us, they might've somewhat tempered their belligerent streak as they became more high-tech and learned to be a little bit more compassionate. Because a superbelligerent alien race would never make it into space at all - they'd simply bomb themselves into oblivion.
Given the vastness of space (space is really BIG), they would have plenty of resources and territory of their own (as would we), so we wouldn't necessarily have to fight over it. This galaxy is big enough for the both of us; neither of us would have any need to fight the other. In fact, we would literally have to go light years out of our way to fight each other. A rather absurd, though not impossible, situation.
Aliens wouldn't truly want our raw resources, the real treasure trove is in our life and its byproducts - culture and technology. Because that's certainly what we're interested in. Why come all that way to destroy when you can study?
And besides, our first contact would likely not be between us personally - but through our machine intermediaries - our probes - who definitely have no harmful intent.
So, instead of fearing aliens and going silent, we should do everything we can to be loud and noticeable to make first contact happen asap. Because any first contact would likely enable a huge technological leap for us, potentially saving countless lives. Imagine a new power source or new medical technology or new spaceflight technology. It's such a massive boost that it's worth betting that the aliens we do meet aren't genocidal.
I think dinnerbell is the wrong idea -- we'd need to be the same biology to be nourishing and the odds of evolution doing the same chemical thing twice are nearly, but not quite, zero.
Stephen Hawking was on the 'we should keep our heads down' side of the debate, of the opinion that we shouldn't draw attention to ourselves on the basis that the sort of aggression, tribalism and territoriality that still lurks (overtly or covertly) in the human animal might be evolutionarily common to sentient species, and the last thing we need is to meet an alien race as unpleasant as we are but with higher technology.
The fault with his reasoning is that it presupposes that they are nearby, and/or that they have broken the interstellar travel problem, either by circumventing the speed of light or by having a stardrive that pushes up close enough to
c that shipboard travel time is tolerable (and that you don't ever plan on going home again). Those are two
really big ifs.
Unless the galaxy is thickly populated, we're highly unlikely to be within thousands or even tens of thousands of lightyears to our nearest sapient neighbor. Now keep in mind that we ourselves have only been detectable for two hundred years (by spectrographic analysis of our atmosphere -- industrial pollution, ironically, would be the marker of "intelligence"), and broadcasting for one hundred. With the advent of cable, satellite, fiber optic, and other more finely focused data transmission means, our radio footprint is growing smaller. You don't need an AM antenna blasting 250,000 watts from just over the Mexican border to be heard nationwide anymore, you just need a wifi hotspot or a 3, 4 or 5g connection.
So instead of just blasting out a sphere across the electromagnetic spectrum, the Earth's radio signature is an expanding bubble about a hundred light-years thick, slowly attenuating into noise the further out it gets. A civilization fifty light years away that doesn't tumble across radio until 100 years from now will have missed us -- the easily-detectable stuff will have long since passed them by.
I am not convinced that as technology advances, races become more civilized. I mean, look at
us. We may be risen apes, but we're still apes deep inside our brains.
Of course, as you point out, space is really big. And the light barrier isn't an engineering problem like the sound barrier was -- it's built into the way reality works. Any first contact by radio will be a long, drawn out affair of slowly working out a mutual language to communicate with, and then gaps of centuries between questions and answers. The vastness of space makes for a quite efficient social condom. We would be
way out of the way for anyone to mount an expedition to come beat us up, enslave us, eat us, rob us, whatever, and the resources gained would not make up for the resources expended.
So I generally agree, we shouldn't worry about being heard. Besides, we're listening. Every argument against us making contact can be made by any other sentient race out there.
