Skyline is an above-average monster horror film. A film maker and a photographer with their families are living the high life in LA right up until aliens invade. Blue lights descend from the sky to capture humans. The lights are complex and play upon the human visual system. They are entrancing, hypnotic, and draw those who see them, towards them.
The lights collect a fair few of the inhabitants of LA, and disappear back into the sky. Hours later, they return, and this time, in the dawning light, the motherships follow. They descend from the sky, and suck any loose debris, including humans out in the open, into their gathering maws.
Smaller search craft and ground assault giants detach from the mother craft and search out hiding human survivors, taking them one by one. The bulk of the film is concerned with a small group of survivors including the above, trying to survive as they are picked by the aliens standard fare for this genre.
The military become involved, as the military are wont to do when aliens invade, and fight them in great swarms of fighters and bomber craft, ground troops and helicopters. They drop nukes on the invaders, and kill them in great numbers. Yet, more keep coming, and the motherships that are nuked, start to auto repair.
In the end it is down to the last two survivors, the photographer husband and his pregnant wife. Everyone else has been defeated; the other survivors are all gone, and even the military has withdrawn. Cut scenes show this happening to other cities all around the Earth. As they are sucked into the maw of the giant mothership above them, we near the closing minutes of the film, and things start to get really interesting. Everything that was hinted at or suggested earlier in the film comes into clear focus, and suddenly makes an awful lot of sense.
The aliens are not aliens. Well, the ships and equipment are, and there are undoubtedly a handful of real aliens left. However, this is not an invasion, well not in the traditional sense. This is a harvesting.
The equipment this species uses is all organic, or bio-mechanic in nature. They have been using modular control systems to run all their equipment their own brains. It is the epitome of augmented reality embodiment, really. Take a living brain and spinal cord, entirely intact.
Keep it stimulated with sensory data continually even when disembodied so it does not suffer sensory deprivation and go mad. They do this by surrounding the brains with the pulsating light, which, as the human brain is optogenetic responds to light pulses is theoretically capable of supplying sensory data, and even possible reprogramming the brain.
Then, when you are ready, slot that brain into a high-technology shell. The brain nestles gently in a prepared bay, and the spinal cord is pulled down inside where the individual nerve pairs are linked with the control systems for the equipment. It is way beyond our technological level of course, but the theory is sound.
Using this basis, when the brain is slotted in, and the protective covering closes, the body 'powers up' and disengages from it's life-support mechanism. The brain is now embodied in it's new form, and with the aid of the reprogramming it suffered earlier, knows the basics of how to move, although it will be clumsy and uncoordinated at first something the film showed with the early scouts and giants, which made little sense at the time. Like a baby learning to walk, they improve with time until they are extremely competent and capable, as if the body was naturally theirs.
Should the body become damaged beyond repair, carefully pop the brain and spinal cord out and insert them into a new body. If it is the same type, same size and arrangement of limbs, then the brain continues controlling it where it left off with the old. If it is a different type the brain has to adjust and learn how to move again.
On the flip side, should the brain become irreparably damaged, as occurred to one of the alien hunters in the film when a SUV rammed it into the wall, it doesn't matter. The brain is expelled, as it has suffered massive trauma and internal bleeding. Haemorrhages are triggering strokes and the cognitive capability of the brain as a control centre are rapidly diminishing. The body switches to it's own internal 'brain' which seems to be a very simple machine AI, not capable of very much in the way of thought or strategy. Not displaying any advanced functions at all, really.
Yet it can still function, with one simple driving purpose: To capture and reprogram a brain of sufficient complexity to serve as it's next control system. This the unit that was rammed by the SUV achieves, by using blue light to lure a survivor near, then stripping away the flesh it does not need, carefully removing the brain with the spine still attached. Blue lights flicker round the brain in complex patterns as the limb holding it, gently inserts the tissue into the receptacle it's old brain used to fill. Once all the connections are made, the body rises once again, able to continue it's work.
This also explains why the harvest took place the way it did. All throughout the film we see humans fighting these alien invaders, and killing a number, but finding a never-ending stream pouring from those ships. The more people are abducted, the more aliens there are to fight.
Of course what is really happening should by now, be obvious.
For whatever reason the ships that approached Earth found they had precious few remaining minds on board. They sought to replace what they had lost, and sent the initial probes down to the cities the blue lights that seemed to be all light and no ship, in the opening salvo. The mission of these small ships absolutely bristling with lights was simple; they landed at highly populated zones such as major intersections and lured humans driving their cars, into the light. There the probes sucked the organic beings inside until they reached capacity then took off again.
Other than the placement of the probes which was likely done before launch as quite a few missed, they did not show any intelligence at all. What they did do was gather many complex brains of what was obviously a technological civilisation.
The probes returned to the motherships with their precious cargo, and there the brains were carefully separated from their bodies. The brains were reprogrammed, and embodied in various machinery both separate from the ship and also to operate systems attached to the main ship, restoring full function.
Once this was done, the probes were sent out again, the process repeated until the ships had enough reprogrammed complex minds to fully function, and enough to run their initial war fleet. Only then did the motherships drop down to Earth and start vacuuming up bodies from the cities in great numbers.
At this point the humans had effectively lost. The bodies were stored internally, and rapidly sorted through to gain access to the brains they housed. These were removed, and the bodies tossed into waste pools, likely to be broken down to fuel the growth of more bio-mechanical equipment. Assorted debris that had risen with the humans was also sorted through ,and usable materials stripped to use to construct more equipment.
Every alien the humans fought against was basically a reprogrammed human brain in a plug-and-play body. There was a practically inexhaustible supply of humans, and a practically inexhaustible supply of basic raw materials to construct new units, so the ships could pump out as many as they desired, whilst storing yet more unused brains for future purposes.
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If you are willing to abandon all sense of morality or ethics, then the above scenario is in essence, quite plausible.
We know the brain is highly plastic, and can adjust or adapt to wildly different forms with ease. One arm, two arms, three arms, no arms. The brain will adapt within months to whatever body configuration it is presented with. We have attached additional robotic arms to primate bodies, wired them up to the primate's nervous system and watched as the primate learned to move the new arms like it was born with them.
Skyline is basically using this exact same process, speeding it up a little through optogenetic reprogramming. That is part of what makes this movie so scary and so fascinating at the same time. The scenario is wildly fanciful, but the technology of what the 'aliens' are doing, is realistic, and quite likely feasible to do on Earth once our neural interface technology advances sufficiently.
In addition, Skyline's 'aliens' are doing something much more complex and fiddly. They are reaching inside the brain with their light-based systems, and not just altering the input channels, but deleting and replacing memories as well. Change the memories, you change the person. You can turn an enemy into a loyal friend by changing what they remember.
We already know that memories can be removed through external means. Our own technology has shown that it is in-fact possible to remove a complete memory engram from a living brain, effectively permanently erasing that memory. Writing a new memory into the brain would be far more tricky but essentially possible. It is easier when you are rewriting the whole hippocampal formation of course. There will be no incompatible memories left to check the 'new' ones against.
On top of that, you would not even have to write all the new memories in. Get the major points right, and the brain will helpfully fill in the rest. It's own plasticity used against it.
Change the motor neurons and the cerebellum in the same manner as you altered the memories, and you have a much more interesting situation; you can in essence reprogram the brain to understand how it's new body works almost overnight, rather than waiting months for it to relearn how to walk (or learn how to fly).
This is something our science has never attempted, but in basic theory at least, it should be possible. If it is, that kind of technology would be a great asset to anyone who is relearning how to walk, or adjusting to a prosthetic or even an extra pair of arms.
We just have to bear in mind that we take the bad with the good, every time we advance a technology, and that a technology that peeks inside the brain, and plays about with connections inside it, has as many bad uses as it does good ones. Some of which are both insidious and devastating.
We don't have Skyline's technology yet, or anything close to it. However, we will get there one day, and it is on that day the lessons that Skyline and it's ilk are trying to teach had best be remembered.
If they are not, we may find ourselves in a situation where whole identities can be rewritten, not just leaving a friend where an enemy once stood, but being able to do such in bulk, and at speed.