DEWs, heliobeams, or gravity weapons---those destroy the universe!

Second, there could be so many different species and civilizations in the future that determining who exactly perpetrated an attack could pose an impossibly complicated forensic challenge. This too could undercut the threat of retaliation.

And third, so could the weapons available to technologically advanced future civilizations. For example, the US military is already experimenting with “direct-energy weapons” (DEWs) like laser and particle-beam weapons that can attack a target at or nearly at the speed of light. Since nothing travels faster than light — not even a message saying, “Help us, we were just attacked!” — the use of powerful DEWs by a Kardashev type II civilization, for example, could eliminate the threat of a counterstrike.

This differs from the Cold War situation in which each side could detect nuclear missiles traveling through the air with enough time to consult the relevant decision-making bodies and determine whether or not to strike back. Civilizations couldn’t possibly see a deadly laser beam that destroys crucial infrastructure coming; the damage would occur before a warning message from allies could ever reach them.

There are also biological and nanotech agents that civilizations could launch across the galaxy at each other, martial von Newman probes that are aided by metamaterial invisibility cloaks, “heliobeams” that concentrate large amounts of solar radiation on targets, and maybe even “gravity weapons” that use gravitational waves to create black holes (a speculative idea that appears to fall within the realm of physical possibility). Even more, the universe is teaming with asteroids and comets that could be catapulted toward planets or spaceships, with more destructive consequences than a swarm of hydrogen bombs. Some have called these “planetoid bombs,” since asteroids and comets are “planetoids.”

We also shouldn’t overlook the possibility that future civilizations devise entirely novel “weapons of total destruction” (WTDs). Just as our Paleolithic ancestors would be dumbstruck by the extraordinary mechanisms of mass death available to modern humans, so too might we be horrified by the weapons that our spacefaring children invent — say, WTDs that move at close to lightspeed and wreak galactic- or cosmic-scale hazards.

The cherry on the cake is that even a perfectly peaceable civilization might have strong incentives to obliterate its neighbors. For example, imagine two civilizations with radically different political, cultural, and religious traditions. They can’t even communicate very well because they speak entirely different languages and have evolved, through natural selection and cyborgization, divergent emotional repertoires and mental categories. They have different internal models of the world, distinct perceptual and phenomenological experiences, and incompatible “normative” worldviews.

Consequently, neither is able to trust the other. The result is that it would be rational for each to annihilate the other merely to ensure that the other doesn’t annihilate one first. Worse, if a civilization X believes that a civilization Y is rational, then X will believe that Y believes that it should annihilate X so that X doesn’t annihilate Y, since X annihilating Y would be the rational thing to do. (Whew!) This line of reasoning provides X an even stronger reason to annihilate Y, and therefore Y an even stronger reason to annihilate X — thus yielding a “spiral” of escalating tensions that ultimately culminates in war, despite both X and Y wishing for peace. Scholars know this as the “Hobbesian trap.”

But civilizations may have an equally strong incentive to destroy their neighbors even if they believe that those neighbors are irrational (rather than rational). For example, consider a civilization A that is full of irresponsible particle physicists. Civilization A has no bad intentions, yet it conducts physics experiments that could inadvertently end the universe. Another civilization B might try to reason with A not to conduct these experiments, but let’s imagine that A ultimately resists. In order to save A from annihilating the universe by accident, B may thus opt to launch a preemptive attack against A to avert a cosmic disaster.

Generalizing this case, since any given civilization will have some probability of accidentally destroying the universe, it would be in every civilization’s self-interest to destroy everyone else merely to obviate accidental cosmic calamities. This may be especially true if evolutionary adaptive radiation produces numerous species unable to fully grasp each others’ intentions, cognitive abilities, or moral values. The possibilities for miscommunication here are immense — and this should worry rather than reassure us.