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[Morrigi]

A bit like submarines.  If you can be stealthy, be very stealthy. If you can't then push everything to the limit and get very noisy indeed. 

The problem with that is that you can't even think about hiding your heat signature without very large, heavy, and expensive heat sinks, and even then it won't do jack shit if your ship is manned, because it will have to be kept within tolerable temperature limits for the crew... which are much, much higher than the background temperature of space. Provided you know which general direction to look in, it's also extremely easy to detect thrusters firing, even from across a solar system.


Now, as for conflict between entire civiliations, The Killing Star has a very interesting take on things.

The great silence (i.e. absence of SETI signals from alien civilizations) is perhaps the strongest indicator of all that high relativistic velocities are attainable and that everybody out there knows it.

The sobering truth is that relativistic civilizations are a potential nightmare to anyone living within range of them. The problem is that objects traveling at an appreciable fraction of light speed are never where you see them when you see them (i.e., light-speed lag). Relativistic rockets, if their owners turn out to be less than benevolent, are both totally unstoppable and totally destructive. A starship weighing in at 1,500 tons (approximately the weight of a fully fueled space shuttle sitting on the launchpad) impacting an earthlike planet at "only" 30 percent of lightspeed will release 1.5 million megatons of energy -- an explosive force equivalent to 150 times today's global nuclear arsenal...

I'm not going to talk about ideas. I'm going to talk about reality. It will probably not be good for us ever to build and fire up an antimatter engine. According to Powell, given the proper detecting devices, a Valkyrie engine burn could be seen out to a radius of several light-years and may draw us into a game we'd rather not play, a game in which, if we appear to be even the vaguest threat to another civilization and if the resources are available to eliminate us, then it is logical to do so.

The game plan is, in its simplest terms, the relativistic inverse to the golden rule: "Do unto the other fellow as he would do unto you and do it first."...

When we put our heads together and tried to list everything we could say with certainty about other civilizations, without having actually met them, all that we knew boiled down to three simple laws of alien behavior:

THEIR SURVIVAL WILL BE MORE IMPORTANT THAN OUR SURVIVAL.
If an alien species has to choose between them and us, they won't choose us. It is difficult to imagine a contrary case; species don't survive by being self-sacrificing.

WIMPS DON'T BECOME TOP DOGS.
No species makes it to the top by being passive. The species in charge of any given planet will be highly intelligent, alert, aggressive, and ruthless when necessary.

THEY WILL ASSUME THAT THE FIRST TWO LAWS APPLY TO US.
...

Your thinking still seems a bit narrow. Consider several broadening ideas:

Sure, relativistic bombs are powerful because the antagonist has already invested huge energies in them that can be released quickly, and they're hard to hit. But they are costly investments and necessarily reduce other activities the species could explore. For example:
Dispersal of the species into many small, hard-to-see targets, such as asteroids, buried civilizations, cometary nuclei, various space habitats. These are hard to wipe out.
But wait -- while relativistic bombs are readily visible to us in foresight, they hardly represent the end point in foreseeable technology. What will humans of, say, two centuries hence think of as the "obvious" lethal effect? Five centuries? A hundred? Personally I'd pick some rampaging self-reproducing thingy (mechanical or organic), then sneak it into all the biospheres I wanted to destroy. My point here is that no particular physical effect -- with its pluses, minuses, and trade-offs -- is likely to dominate the thinking of the galaxy.
So what might really aged civilizations do? Disperse, of course, and also not attack new arrivals in the galaxy, for fear that they might not get them all.   Why? Because revenge is probably selected for in surviving species, and anybody truly looking out for long-term interests will not want to leave a youthful species with a grudge, sneaking around behind its back...
I agree with most parts of points 2, 3, and 4. As for point 1, it is cheaper than you think. You mention self-replicating machines in point 3, and while it is true that relativistic rockets require planetary power supplies, it is also true that we can power the whole Earth with a field of solar cells adding up to barely more than 200-by-200 kilometers, drawn out into a narrow band around the Moon's equator. Self-replicating robots could accomplish this task with only the cost of developing the first twenty or thirty machines. And once we're powering the Earth practically free of charge, why not let the robots keep building panels on the Lunar far side? Add a few self-replicating linear accelerator-building factories, and plug the accelerators into the panels, and you could produce enough anti-hydrogen to launch a starship every year. But why stop at the Moon? Have you looked at Mercury lately? ...

Dr. Wells has obviously bought into the view of a friendly galaxy. This view is based upon the argument that unless we humans conquer our self-destructive warlike tendencies, we will wipe out our species and no longer be a threat to extrasolar civilizations. All well and good up to this point.

But then these optimists make the jump: If we are wise enough to survive and not wipe ourselves out, we will be peaceful -- so peaceful that we will not wipe anybody else out, and as we are below on Earth, so other people will be above.

This is a non sequitur, because there is no guarantee that one follows the other, and for a very important reason: "They" are not part of our species.

Before we proceed any further, try the following thought experiment: watch the films Platoon and Aliens together and ask yourself if the plot lines don't quickly blur and become indistinguishable. You'll recall that in Vietnam, American troops were taught to regard the enemy as "Charlie" or "Gook," dehumanizing words that made "them" easier to kill. In like manner, the British, Spanish, and French conquests of the discovery period were made easier by declaring dark- or red- or yellow-skinned people as something less than human, as a godless, faceless "them," as literally another species.

Presumably there is some sort of inhibition against killing another member of our own species, because we have to work to overcome it...

But the rules do not apply to other species. Both humans and wolves lack inhibitions against killing chickens.

Humans kill other species all the time, even those with which we share the common bond of high intelligence. As you read this, hundreds of dolphins are being killed by tuna fishermen and drift netters. The killing goes on and on, and dolphins are not even a threat to us.

As near as we can tell, there is no inhibition against killing another species simply because it displays a high intelligence. So, as much as we love him, Carl Sagan's theory that if a species makes it to the top and does not blow itself apart, then it will be nice to other intelligent species is probably wrong. Once you admit interstellar species will not necessarily be nice to one another simply by virtue of having survived, then you open up this whole nightmare of relativistic civilizations exterminating one another.

It's an entirely new situation, emerging from the physical possibilities that will face any species that can overcome the natural interstellar quarantine of its solar system. The choices seem unforgiving, and the mind struggles to imagine circumstances under which an interstellar species might make contact without triggering the realization that it can't afford to be proven wrong in its fears.

Got that? We can't afford to wait to be proven wrong.

They won't come to get our resources or our knowledge or our women or even because they're just mean and want power over us. They'll come to destroy us to insure their survival, even if we're no apparent threat, because species death is just too much to risk, however remote the risk...

The most humbling feature of the relativistic bomb is that even if you happen to see it coming, its exact motion and position can never be determined; and given a technology even a hundred orders of magnitude above our own, you cannot hope to intercept one of these weapons. It often happens, in these discussions, that an expression from the old west arises: "God made some men bigger and stronger than others, but Mr. Colt made all men equal." Variations on Mr. Colt's weapon are still popular today, even in a society that possesses hydrogen bombs. Similarly, no matter how advanced civilizations grow, the relativistic bomb is not likely to go away...

We ask that you try just one more thought experiment. Imagine yourself taking a stroll through Manhattan, somewhere north of 68th street, deep inside Central Park, late at night. It would be nice to meet someone friendly, but you know that the park is dangerous at night. That's when the monsters come out. There's always a strong undercurrent of drug dealings, muggings, and occasional homicides.

It is not easy to distinguish the good guys from the bad guys. They dress alike, and the weapons are concealed. The only difference is intent, and you can't read minds.

Stay in the dark long enough and you may hear an occasional distance shriek or blunder across a body.

How do you survive the night? The last thing you want to do is shout, "I'm here!" The next to last thing you want to do is reply to someone who shouts, "I'm a friend!"

What you would like to do is find a policeman, or get out of the park. But you don't want to make noise or move towards a light where you might be spotted, and it is difficult to find either a policeman or your way out without making yourself known. Your safest option is to hunker down and wait for daylight, then safely walk out.

There are, of course, a few obvious differences between Central Park and the universe.

There is no policeman.

There is no way out.

And the night never ends.

[Graknorke]

Who would even want to put humans on a vehicle intended for fighting? They're far too squishy and sensitive to make anything practical. Do you know how much acceleration a human can withstand? Not enough, that's how many.

[Dorsidwarf]

"The most powerful laser ever is 150000J

I know this was said some time ago but really?

https://lasers.llnl.gov/about/what-is-nif

1,850,000Joules, at more that 500,000,000,000,000W

[mainiac]

The problem with that is that you can't even think about hiding your heat signature without very large, heavy, and expensive heat sinks,

Yes I can, I just thought about it several posts ago.  I may have thought about it incorrectly but I certainly demonstrated that I can think about it.

[i2amroy]

-snip-

See, the problem I have with that is that it assumes that for some reason just having the capability to travel like that suddenly makes us all into immoral logical monsters.

In a lot of ways it comes across no different than the "if there was no god then we would all be murdering and raping each other", arguments. I mean honestly when was the last time you thought "oh gee, I really wish I could go murder and genocide those people over there"? I don't murder people and attempt to exterminate entire groups because I don't want to, not because I can't.

[Nick K]

It doesn't assume anything about humans - the argument is about aliens. Some people assume that advanced aliens would have to be benevolent just because they're advanced, but there isn't really much evidence to support that. It doesn't really matter if humans are "immoral logical monsters" or not, just that an alien race might well be.
The real assumption it makes is that futuristic weapons can wipe out a civilisation without any defences being possible and without leaving them the opportunity to strike back. This is much more questionable, and I personally think it probably isn't true. If we do accept that assumption though, then it makes a strong case against active SETI - where humans make an effort not just to detect alien races but to send out communications that unknown aliens might intercept.

In fact, even if we do consider humans, it seems quite possible that we'd pull the trigger in that situation. Humans aren't particularly benevolent towards non-human species, and when we are it's usually because we think they're 'cute' - usually because they have traits like big eyes etc that remind us of human children.
Imagine if we became sufficiently advanced to create relativistic warheads, but were largely still confined to a few planets. Imagine we then found out there was a nearby planet of aliens. Initial scans of their broadcast shows that they are a creature we consider almost instinctively disgusting - let's say they resemble cockroaches. Their behaviour also has some aspects that we don't understand, and that makes them confusing and unpredictable. Plus, they break some of our deeply held moral beliefs or cultural taboos - perhaps they practice regular infanticide, maybe they genocided another species that we consider intelligent, perhaps they keep another species that we consider cute, likable, or human-like as food and slaughter them in what we consider a cruel way, perhaps one of their genders violently subjugates the other(s) and routinely kills them in unpleasant sexual practices.
From analysing their broadcasts, we can't get full understanding of how they think or if they're likely to be aggressive towards us, but we do know that they act in a warlike and aggressive way towards each other and that they are very willing indeed to slaughter other species in vast numbers if it'll benefit them.

Luckily, the cockroach aliens are less developed than us. They don't have relativistic weapons and can't threaten earth. However, at their current rate of advancement our scientists believe in a century or so they will develop them.
The government has a choice. Send over a warhead and it'll wipe them out. They'll be rendered extinct and can never threaten earth. Alternatively, we could let them develop or even help them. In that case they're sure to discover us, sure to develop relativistic weapons, and sure to realise that we could develop such weapons and thus pose a threat to their existence.
Would they choose to wipe us out? They might. They're unpredictable and aggressive creatures, their governments often have periods of upheaval and even when stable are known to break treaties, many of them are xenophobic and violent towards outsiders even of their own kind, and it's not uncommon for individuals who are insane even by the confusing standards of their species to gain power.

So, does the human government spare them the baby-killing cockroaches and gamble with the very survival of the human race? What if there are many human governments with the technology to launch such warheads - do all of them spare the cockroaches? Does future Bush? Future Putin? Future Bashar al-Assad? Future Kim-Jong-Un? Future Hitler? All it takes is one of them to decide to attack.

[mainiac]

Because you know so much about alien psychology that you can predict how they estimate Knightian uncertainty estimates of other races?  Why dont you apply to perform psychology at three k iterations to the bond market and become a billionaire?

[Egan_BW]

It's natural selection; if there's a technology capable of destroying civilizations, then presumably the civilizations willing to use have already wiped out all the ones who aren't.

[Nick K]

Because you know so much about alien psychology that you can predict how they estimate Knightian uncertainty estimates of other races?  Why dont you apply to perform psychology at three k iterations to the bond market and become a billionaire?

I don't follow. My whole point was that we don't understand how aliens might think, and so it's dangerous to assume that they'll be benevolent.

It might be that humans are unusually aggressive and most aliens are in fact peaceful and friendly. It might be that humans are unusually benevolent and most aliens wouldn't understand concepts like mercy or altruism that we take for granted. It could be anything in between. We don't really know, and that makes it a risky gamble to blindly signal who and where we are without any knowledge of who or what could receive the message.

[GiglameshDespair]

"The most powerful laser ever is 150000J

I know this was said some time ago but really?

https://lasers.llnl.gov/about/what-is-nif

1,850,000Joules, at more that 500,000,000,000,000W

As I said, casual google.

[mainiac]

I don't follow. My whole point was that we don't understand how aliens might think, and so it's dangerous to assume that they'll be benevolent.

And it's exactly as dangerous to assume they are malicious.  Maybe they have an immortality serum for all you know.  You are using Knightian uncertainty as evidence when it's the exact opposite of evidence.

[Culise]

It's natural selection; if there's a technology capable of destroying civilizations, then presumably the civilizations willing to use have already wiped out all the ones who aren't.

Alternately, the ones who used it indiscriminately were already wiped out by those who didn't trust the sort of civilization that wipes out anything in their vicinity indiscriminately.  The Killing Star is an interesting story, but one of the key issues in its logical analysis is that it assumes a two-party problem: you have only two sets of aliens, each with a gun at the other's head (or whichever housing for the cognitive organ of choice).  Now, contrast this with the following: you have three sets of aliens, termed A, B, and Doom, none of which know each other, none of whom have FTL or other soft-SF techs, but all of whom have telescopes powerful enough for regular wide-sky exoplanet -searches for alien life (say, Kepler+SETI in another century or three) and the ability to accelerate projectiles to relativistic velocities.  Doom meets A but not B, and immediately pulls the trigger (we'll assume an effectively 100% kill rate, which is another major issue with the Killing Star's assumptions).  B watches one of their neighbor's orbiting worlds get a bit brighter briefly, investigates, and finds craters and the ruins of a civilization in whatever outposts were too small to exterminate out of hand, and what little they piece together indicates A had no idea what was coming.  By tracking back (assuming here that they didn't already spot the "muzzle flash" originally), they identify where the shot came from.  Suddenly, Doom is at a disadvantage - they have an enemy with a strongly vested interest in attacking them (out of self-defense, if nothing else) that they don't even know about.  This enemy knows exactly where they are, and they don't even know that it exists.  The other issues are the light-speed barrier to the propagation of information.  If your target is in Proxima Centauri, your targeting information is four years old by the time you load it into your weapon, and eight years old by the time your shot actually arrives.  That's all and good if your target is limited to a single solar system (EDIT: Planet, sorry. If they're scattered throughout a solar system, it's already too late) with very limited space travel, but what happens if it's already a multiplanetary polity?  What if your target is not literally the next star system over?  If you plant your weapon somewhere outside your home system to avoid it being tracked back to you, you've extended your command loop even further, worsening the information gap. 

In other words, the primary defense is dispersion and secrecy, not a preemptive strike.  You do not want aliens to know where your homeworld is, as this is likely to be the most-developed and most-populous world in any multiplanetary polity for the near future, by analogy the metropole of the historical colonial empire, and exploration in the name of first contact is likely to be done in part to encourage this - contact is to be established as far away from the metropole as possible, in places where an RKV won't necessarily wipe out the locus of your civilization and industry.  Finally, you do not want to embark on a policy of extermination unless you're absolutely positive that no one's in a position to return the favor, and you're absolutely certain you can wipe out the targets in one go, because if you give them a motivation that strong, they can and will return the favor.  Even a single missed colony, given time, will be able to do the exact same thing to you that you just did to them.

[mainiac]

As a follow up, would you imagine that a genocidal or a non-genocidal race is going to do a better job spreading themselves out?

Or how about having a head start.  Imagine that the first spacefaring race in the galaxy is ethical.  By the time they go to space, war is completely foreign to them.  They have literally a 10 million year head start on the next spacefaring race.  They see this race around the time it's inventing fire and psychoanalyze it.  They decide that this race is dangerous.  As a result they never allow this race to advance in spacetravel too much.  But then a third race develops sentience and they are psychoanalyzed and found to be hippies so their advanced cousins give them a friendly hello to the neighborhood.

Hey, maybe we are the second race and FTL travel is actually really easy to do but aliens dont trust us so they have us under the FTL equivalent of radio static until our race matures into something less dangerous.

Maybe there is one other civilization out there and they are moral but their scientific development is radically different from ours but the two science systems together would be miraculous.  If we knew their information or they knew ours civilization would be revolutionized.  If we cautiously talked it would take tens of thousands of years to learn due to the lightspeed delay.  But if we just send them what we know they would reciprocate and we could revolutionize mankind.  The sooner we contact them the better then.

Maybe there are advanced aliens out there who would be altruistic towards us poor starving humans but dont even know we exist.

If we dont know between any of the possibilities, being "cautious" might be the exact worst thing to do.

[Egan_BW]

What if all the life in the universe is different enough that we can't reason with them?

[Cryxis, Prince of Doom]

What if we are the only sentient life? I don't care how unlikely it is but just think about it what if we truely are the only sentient life that will ever travel the stars and see and learn and live the wonders of this massive universe