Who Wins in the Galaxy: Attackers or Defenders?

Suppose you envision a contact between two alien civilizations somewhere in our galaxy.  As noted in a previous blog, both should have the same technology development, asymptotic technology.  That means that the weapons, both offensive and defensive, that each could possess would not be different in technology.  One civilization may have more resources, and therefore could have quantitatively more, but they cannot have qualitatively more that the other civilization could possess. 

Let’s also suppose that one of them was a predator, and wanted to boot out the other one from their own home planet, or planets, or world satellite, or moons, or wherever they lived.  Making this supposition is a bit chancy, because the two civilizations would be near identical, as discussed in that very same previous blog.  For the purpose of this blog, let’s assume the first one is a predator for some reason to be determined later, and the other is not.  The first one wants the resources, say the home solar system or systems, of the second.  They want to get rid of the other civilization.  The other civilization will be assumed to have some self-preservation desires, and wants to prevent the first civilization from eradicating it. 

Let’s consider first attacks with explosive devices.  If civilization I amasses enough of them, and can transport them to the home world of civilization II, and then drop them on appropriate points and they go off, civilization II dies off and some time later, civilization I can come and occupy that home world.  That’s the assumed plan of civilization I.  Will it work?  We here on Earth are still pretty close to the caveman era of weaponry, only able to make thermonuclear bombs in the hundred megaton class, but we might assume that civilization I, with a thousand years of more technology, can make them much larger if needed.  If civilization II is living on reasonably small artificial worlds, this might destroy them in a short time, along with civilization II itself.  If civilization II is living on a planet or a moon, on the surface, then these bombs might also do the trick.  If civilization II is living on a planet or a moon, deep under the surface, the bombs would have to be much larger to shatter the infrastructure of civilization II.  Here is the tradeoff: Does making such bombs and transporting them across interstellar space, along with the control equipment, and delivering them precisely have a cost which is more than the planet is worth?  It is hard to see how the bomb cost would not be less than the planet’s worth, as if civilization II is eradiated, civilization I lives there for countless millennia. 

Other means of eradicating civilization II might be tried.  We are familiar with weapons of mass destruction of various kinds other than nuclear bombs, such as lethal contagious viruses.  These would be well understood by the aliens in civilization II, and means of stopping the contagion applied rapidly, as soon as the attack was recognized and the virus diagnosed.  Some sort of cyberattack could be tried, but all of the possible cyberattacks could be just as easily figured out by civilization II and defenses built in to their systems.  It’s hard to imagine what another thousand years of hacking will lead to, but the basic principles of defending a communication and resource transmission architecture should be completely understood, and if the costs of defense are not too great, they could be done.

Mass assault is probably not feasible, as civilization II’s home world will have billions of residents, and being able to drop in enough warriors to kill all of them one by one is likely so expensive that it is not possible.  So, from our caveman perspective, bombs are the thing.

Can civilization II defend itself against such an attack?  First to be considered is the element of surprise.  Can civilization I pull off a surprise attack on civilization II so that civilization II does not know it is going to be attacked until the bombs start detonating? 

Asymptotic technology plays a role here.  Civilization II knows how life originates, and can figure out that there are planets within some radius, maybe a thousand  light years, that could harbor life.  They know the optimal way to build large bombs, how to transport them, how to disguise their approach, and how to detect the approach of the disguised bombs.  They know the exact technology of civilization I and all the possibilities that civilization I might try, because they have the same knowledge.  Both sides can figure out the other’s best strategy.  So, what is the cost of detecting the incoming bombs far enough away so that whatever defensive reaction is best can be done?  Does it sap all the energy of civilization II to protect itself?  Very likely not.  Detection of a swarm of objects coming toward the home planet at a large distance, even if the signatures have been concealed, should be a small cost compared to running the civilization.  Signatures are all those emissions which are detectable, and as we know them, involve electromagnetic emissions from the microwave range up to X-ray.  To reduce those signatures, civilization I will try to make the outer surface of the bombs cold and black, so they neither radiate their own heat signature nor reflect sunlight.  In asymptotic technology, we can expect them to be at the best temperature, that of its background, and completely black.  Civilization II might be watching for transit effects, when one of the bombs obscures the light of a star of the galaxy, so the incoming trajectory would have to be chosen to reduce this possibility.  They would not be large enough to provide gravitational disturbances to other objects in the home solar system of civilization II.  So, detection is possible, but the range is likely to be short, with a warning time of the travel time from nearby, maybe only a few days. 

Given a minimal warning, what options does civilization II have for an active defense?  Active defense involves defeating the attack, as opposed to a passive defense which means absorbing it with reduced damage.  The success of active defense depends on the warning time.  If we assume that the bombs are not braked upon entering the solar system, but are still traveling at interstellar speeds, a fraction of the speed of light, material defense with some sort of projectile is unlikely.  Beam defense with an electromagnetic or particle beam might work, but the difficulty is having enough time for these types of defenses to work.  They involve an integrated effect.  In other words, they do not blow up like an interceptor projectile, but erode the surface of the incoming weapon.  At a good fraction of light speed, there would have to be a tremendous transmitter to make enough erosion of the bombs’ forward surface to destroy it.  Clearly civilization I would make a thick shield there.  Other types of active defenses have similar problems.  So, active defense is not very promising.

Passive defense of some or all of civilization II’s aliens and infrastructure by deep burial is possible.  Shock isolation technology would be at its asymptotic limit, and if the aliens can go deep enough or have a planet with an outer layer that is sufficiently absorbent of shock waves, like sand, they might survive the attack.  However, they would lose communication with anything outside their buried structures, meaning they would be mostly defenseless against any later attacks or an occupation, which might start once the effects of the initial attack abated.  The contest between a buried group of defenders, using only resources obtained from minerals deep within the crust, and a group of occupiers on the surface is an interesting one.  It might come down to growth rates, which would be small for the defenders, having little energy at their disposal, and the occupiers, who have all the resources available on the surface and from the rest of the solar system.  The economic advantage indicates that the defenders would not win over the long run. 

For a first look at the problem of a war between two civilizations with asymptotic technology, it appears that the attackers have the advantage, and are likely to overwhelm the defenders.  This is exactly analogous to our Cold War standoff, and requires us to think of the solution that was found for this threat: deterrence.  If civilization II knew about civilization I, and could build an identical set of attacking weapons, they could threaten civilization I with mutual destruction.  This worked during the Cold War, and perhaps it would work in our current imagined situation. 

In order for deterrence to work, a civilization would need to be able to do two things.  First, they must be able to target their attackers.  In other words, they would need to be able to tell where the home world of civilization I was and be able to send information to their deterrent weapons on where it is and the details they need to attack it.  Second, they must be able to defend their deterrent weapons against being destroyed in the attack of civilization I.  They must also ensure that those weapons are not destroyed shortly after being launched toward civilization I by any devices that civilization I arranges to simultaneously arrive at the home world of civilization II. 

If there are many possibilities for a home world for civilization I, civilization II would have to decide to annihilate all of them for deterrence to work, or to figure out from the attack, during the warning time, which one it was.  For the defense of their deterrent weapons, they would have to have a base for them that was either dependent on concealment for survival, or on being able to survive the attack using passive defense.  With passive defense, digging out is a large problem.  If the weapons are capable of interstellar travel and attack, they would not be particularly small and concealing them or excavating them would be a challenge.  Either way, deterrence is difficult.

There is one saving feature that has not been discussed.  That is reconnaissance.  If civilization II is able to continuously monitor the home worlds of civilization I, they might have much more warning and a much greater ability to deter.  This is a topic worthy of a separate blog.