Then, without warning, all hell breaks loose, and the ships begin using devastating weapons and power to destroy everything around them -- people, buildings, military resistance.
This continues for about two hours of popcorn-eating enjoyment until the Earthlings on screen somehow come up with a miracle to stop these unwelcome invaders from laying waste to our beloved planet.
From "The War of the Worlds," "Independence Day," "Mars Attacks!" "Transformers," "Invasion of the Body Snatchers," "The Day the Earth Stood Still," "V" and the current box office favorite, "Battle: Los Angeles," alien invasion is most definitely part of our culture -- and maybe our fears.
But, in the real world, if predatory ETs come to Earth to take us over, for whatever their reasons, could we, in fact, prevent it from happening? Could we actually survive such an attack?
"The bottom line for a hostile engagement between aliens and humans is not a pretty picture, and there is no happy ending for us," according to John Alexander, a retired Army colonel who spent 25 years searching top levels of the U.S. government for evidence of a reported UFO cover-up -- and couldn't find one.
From a military point of view, Alexander, author of "UFOs: Myths, Conspiracies and Realities" (Thomas Dunne Books), says entertainment depicting alien invasions of Earth is pretty much just a vehicle to blow stuff up.
"Fundamentally, if aliens wanted to take over the world, why fight us? All of the Hollywood movies are based on the paradigm that if you're going to fight someone, you're going to have to use physical violence to do that, which involves risk," Alexander told AOL News.
|Retired Army Col. John Alexander outlines|
reasons why a real alien invasion of Earth
-- unlike those depicted in movies --
would turn out very badly for us.
So, what could Earth or Earthlings have that could be of any interest to space-faring creatures?
"It's a typically human response that anything that comes is going to attack. So the storyline where aliens come down and someone grabs a shotgun and starts shooting at them -- that's probably not the most appropriate thing," Alexander said.
"We know how we and animals respond when threatened -- they don't try to negotiate, they attack and defend themselves. If we're supposed to be above that, then it ought to be handled a little bit more cognitively."
From a strategic point of view, Alexander suggests that invading aliens wouldn't simply "resort to fighting our military forces directly" when there are so many easy ways to accomplish that mission.
"If they chose to use physical force, they would simply destroy our infrastructure, power, communications, transportation and economic systems. While a terribly blunt approach, it could be accomplished without any danger to the aliens, or direct confrontation with any military system."
As long as we're offering a sober, logical, strategic scenario in which unfriendly extraterrestrials want to take over our home turf with the least amount of destruction possible, Alexander speculates there's a much easier way to do it.
"If depopulation of Earth is an objective, the simplest way to accomplish that would be to introduce one or more biological organisms that kill humans.
"There is no reason for them to engage in the time-consuming effort to physically eliminate the armed forces of Earth. Biological warfare would be the most efficacious, energy-efficient and safest means for them to conquer Earth. For the aliens, this is a no-risk option."
OK, you say you want yet another reason why we might be targets of an otherworldly takeover?
Try this: The aliens need our DNA.
Vivid accounts of UFO encounters in both the Old and New Testaments, where creatures descended from the sky and intermingled with humans, are similar to modern-day stories where people report being abducted into UFOs by ETs who allegedly conduct some kind of biological experiments on them.
But why would aliens do that? Alexander suggests a genetic reason.
"Human DNA might be necessary to rejuvenate their genetic lines. However, if the aliens understood DNA sequencing, they would certainly comprehend the cloning process. They would only need a few samples of human DNA in order to create a population that meets their requirements for regeneration.
"It would be far easier to grow their own population that would have no propensity for violence towards them, than to subjugate inherently impetuous and pesky humans."
All of these reasons seem to support the belief by some scientists that we really shouldn't be trying to contact any other civilizations that live in the Milky Way galaxy.
Last year, renowned British astrophysicist Stephen Hawking warned everybody of the potential dangers of interacting with an alien species.
"If aliens ever visit us, I think the outcome would be much as when Christopher Columbus first landed in America, which didn't turn out very well for the Native Americans," Hawking said.
And yet, other scientists actively looking for extraterrestrial signals from deep space take a different approach.
"Hawking is concerned about the possibility of betraying our presence, that if they were to come here, it might not be good for us," said Seth Shostak, senior astronomer at the SETI Institute in Mountain View, Calif. "It's hard for me to believe that they actually have (hostile) intentions on us."
Alexander acknowledges Hawking's fear of ET contact.
"According to his hypothesis, there may be marauding bands of ETs that scour the universe for the raw materials they need to survive. Therefore, inhabitants of any planet possessing those substances would be merely inconveniences, subject to removal."
It's a less-than-utopian view of an alien invasion presented by Alexander. And regardless of what we try to do to save ourselves -- in the movies or in real life -- any kind of hostile intentions toward us by aliens is going to turn out badly for us.
Could I have extra butter on my popcorn, please?