Ever since the rapid rise of digital special effects in the 1980s there have been a number of sci-fi Hollywood films presenting elaborately illustrated farfetched alien invasions of Earth with city-sized motherships (Independence Day, 1996), beachfront storming aliens (Battle Los Angeles, 2011) and sea attacking aliens (Balttleship, 2012).
Even esteemed astrophysicist Stephen Hawking got a lot of press attention when he warned that we should not attempt to contact alien civilizations because it may lead to an invasion of Earth.
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However, in a recent paper, Janne Korhonena of the Aalto University, Espoo, Finland argues that it is unlikely that humanity would be attacked by renegade aliens. We have no interstellar "weapon of mass destruction," that might present a future threat as possibly perceived by some extraterrestrials. Smart aliens would likely avoid unprovoked, preemptive invasions until then.
"Destroying a species that cannot harm the invader would not improve the invader's security at all, and the gain of a single planet would seem to be a trivial advantage to a civilization that already has the capability to live in space," writes Korhonena.
He cautions that aliens may become hostile if we reached the ability to launch Star Trek-style space battle cruisers. "Any spacecraft capable of interstellar voyages in reasonable time is by itself a weapon of mass destruction," he writes. Even worse, a starship would show up without warning. The infrared signature from an alien vehicle heading towards the Earth at ten percent the speed of light might be detectable no farther than 2 billion miles from Earth. We'd only have 12 to 24 hours of warning before arrival (or impact!).
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There is a long list of arguments for aggressive societies: eagerness to consume our resources, a belligerent ideology, a desire to be the sole galactic power, indifference to our existence, or a combination of the above. What's more, some alien societies might just be pathologically xenophobic.
My best guess is that they could have purely unfathomable motives behind our elimination.
Korhonena says that a scenario not widely talked about is an alien first strike aimed at eliminating competitors. This buries deep in the Darwinian psyche. A lesson learned from the Cold War is that two fundamentally antagonistic civilizations with the capability of destroying each other had a rationale for launching a preemptive first strike.
In 1954, a Joint Chiefs of Staff advance study group briefed President Eisenhower on a plan to initiate a war with the USSR before the Soviets could achieve a large enough thermonuclear capability to be a real menace to the continental U.S. In the end fear of retaliation, nuclear winter, and mass deaths far exceeding those of WWII, made the plan seem suicidal. It was nicknamed MAD for Mutually Assured Destruction.
But in interstellar wars, the home base biospheres of the enemy planets are separated by light-years. Even if the defending planet had the technological prowess to strike back, it would take decades or centuries - not minutes - for a counterblow. The enemy would have plenty of time to prepare for whatever counter invasion was coming!
In practicality the attacker would be so overwhelmingly superior the defender could not retaliate in any meaningful way.
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But hold on. The limitations imposed by the speed of light make attacking a very dicey gamble for a bellicose civilization. By the time the alien warships arrive at a target planet they may find themselves outclassed by decades or even centuries of accelerated technological development by the formerly "backwards" victim civilization. Imagine their surprise to be immediately decimated by some super weapon they had not anticipated. It would be like a Spanish Galleon fleet taking so long to get to Hawaii that they wind up sailing into a fleet of battleships at Pearl Harbor.
The most likely reality is that galaxy is so vast that interstellar civilizations have ample space and do not have to risk antagonizing or crushing emerging species. That is, unless they had a purely fiendish desire to do so. And, given the age of the galaxy, any Darth Vader and Imperial Battlestar would have come by this way already.
However, such civilizations might seed the galaxy with robotic sentinels that send an alert home if an emerging society crosses a significant technological threshold. This idea is rampant in UFO mythology that blames the flying saucer scares of the 1950s on the first detonation of the Trinity atomic bomb in 1945. UFO believers overlook the fact that the electromagnetic alarm signal from that blast would have only reach a range of a few light-years by the 1950s.
Even with these exceptions, Korhonena concludes that interstellar conflicts between alien civilizations are rare, but not impossible. He writes, "if interstellar travel proves to be feasible, there is always the non-zero probability of humanity harming ETIs." But I'd say more likely vice versa!
We could never eavesdrop on star wars taking place elsewhere in the galaxy. The universe is so naturally destructive that any oddball high-energy radiation from mega-weapons would be interpreted as simply more natural chaos in the cosmos.
Publication: "MAD with Aliens? Interstellar deterrence and its implications," arXiv:1302.0606 [physics.pop-ph]
Image credit: Discovery Channel