Tuesday, June 28, 2016

Independence Day and Alien Invasions

So I saw Independence Day: Resurgence. To put it simply, it was really stupid. When I was kid, I think part of what made the first film kind of scary was the feeling that aliens may actually exist, that something like that could happen. Of course I've long since realized that the events depicted in the film are far from realistic, but what would a real alien invasion be like? Is it even possible?

Let's assume for the moment that spacefaring alien civilizations exist. We don't need to invoke faster-than-light travel or anything, just aliens that can move from planetary system to planetary system over thousands of years. Let's also assume there is a sufficiently large number of them such that there is a non-zero probability that one of their ships could arrive in orbit around Earth. There is nothing impossible about such a scenario, and this is how movies like Independence Day usually start, but how likely is it? Consider that there is no compelling evidence that aliens have colonized the Earth in its 4.5 billion year history, and the galaxy itself is over 13 billion years old. Therefore the probability of them arriving as part of some colonizing wave front during this incredibly small window of our existence seems exceedingly small.

However, an interstellar civilization that is actively colonizing the galaxy would be able explore more rapidly than its colonization wave front expands. While a colony would probably have to grow to a certain size to produce more daughter colonies, an exploration ship traveling at relativistic velocities, perhaps with the ability to refuel in situ, could travel system to system, exploiting time dilation to slow the aging of the crew. Such a ship could circumnavigate the Milky Way in a few hundred thousand years. There would be perhaps tens of billions of habitable worlds to explore, so the chances of one of these ships finding Earth by accident may still be small. However, our expanding bubble of radio transmissions might be detected and divert a ship to our otherwise unremarkable system. This is partly why some scientists, such as Stephen Hawking, fear that deliberately broadcasting our presence may be dangerous.

So how does this line up with Independence Day so far? About the only thing we know about the aliens in the first film is that they're nomadic and that they strip worlds of their resources before moving on to another system. This isn't too far off from the scenario I laid out above. We could say that the reason the aliens are nomadic is because they're explorers of some kind, and that since their ship isn't a perpetual motion machine, they would need to refuel and resupply periodically. But why would they need resources from Earth? Why would they attack? This is where things get dumb real fast, especially for the second film.

**Spoilers Below**

Firstly, if the aliens have reactionless drives (what I'm assuming the "antigravity" system is), we must assume they have the ability to harness enormous amounts of energy and could easily destroy every major city on Earth from orbit. This is one thing I think the Halo series got right with the Covenant's method of "glassing" entire planetary surfaces from space. They could also cripple our civilization by detonating nuclear weapons at high altitudes to produce a series of electromagnetic pulses. They certainly wouldn't use our primitive satellites to communicate. Secondly, why the hell would aliens with fusion reactors, and likely even more advanced methods of energy production, use magma to power their ships? Do they use geothermal steam engines? Why would they need to blow up our cities before retrieving the magma? They could have just dropped a very large asteroid, or given the size of the mothership in the second film, tugged the Moon out of its orbit and into the Earth, producing a big ball of liquid rock! They wouldn't need our water, because contrary to a common misconception, water is quite abundant in the universe. Some of the gas giant moons such as Europa are essentially giant balls of ice and liquid water.

As I explained in my previous post about the xenomorphs, I'm a big believer that science fiction movies can be made with some scientific rigor without spoiling the fun, so lets construct a "realistic" Independence Day. The story begins with our nomadic alien mothership exploring the galaxy, for the benefit of some distant interstellar empire, when it picks up broadcasts from Earth. The ship changes course towards the source of the signals, and along the way the aliens decipher some of them, seeing our wars, atrocities, and ecological destruction in the process. As a highly unified, eusocial species, they determine that we pose a threat to their expanding empire if allowed to "metastasize". Moreover, they have more to gain from studying the rich biodiversity of Earth than from humans themselves, and fear we may destroy most of it. The ship arrives in orbit and it is so large that it looks like Earth has acquired a new moon. It detonates nuclear weapons at high altitudes around the globe, cripplingly communications and travel. At this point, the story could focus on a group of people trying to escape from a darkened city while directed energy weapons systematically destroy major population centers around the globe. Cut to several months after the invasion, after human civilization has been virtually destroyed and no longer deemed a threat by the aliens. The invaders begin landing to establish research outposts all over the world. The story could focus on a band of survivors fighting a guerrilla war. They reverse engineer some of the invader's technology and eventually capture some aliens and one of their ships and use it to infiltrate the mothership. It's not perfect, but it's about as close as I can get to a version of Independence Day that doesn't severely strain my ability to suspend disbelief.