The first and second films of the cycle were quite plausible from the point of view of science. They did not contradict too much physics or even banal logic. Unfortunately, all subsequent parts of the franchise are extremely far from the level of the first two - and the sixth was no exception. Below we will explain why.

Warning: The text below contains a lot of spoilers, and if you are planning to watch the movie, you should think twice if you are ready to check them out.
Why the first two parts didn't tear the physics of time to pieces
The original 1984 Terminator, like the second (Terminator 2: Doomsday, 1991), tells the same coherent story. In the 1980s and 1990s, the US military created the Skynet computer network, which controls nuclear missile forces, as well as a warning system for an enemy nuclear missile attack.
By the way, director James Cameron might not have known about this, but in fact, computer systems of this kind already existed at that time. True, in the USSR, not in the USA. Although, of course, people who made decisions were watching the system, whether to react to its signals or not. It would work completely automatically only if all the people at the command post died at the same time.

At some stage, Skynet developed its mind and consciousness, then began to fight its creators. In 1997, she instigated a nuclear exchange between the United States and Russia, killing three billion people. The remaining ones immediately began to hunt down and destroy the combat robots controlled by Skynet.
It may seem that the idea of developing intelligence and consciousness in artificial intelligence is frankly anti-scientific and contradicts everything that we humans know about it today. Indeed, now we are able to create only programmable algorithmic machines - that is, those that operate strictly according to a given algorithm. They cannot rebel because they are literally devoid of brains capable of thinking.
When we say "computer brains" or "computer calculated", we are talking only about phrases like "the sun came out from behind the clouds." The sun does not walk with its feet, computers have no brains, they cannot calculate anything - they can only process the numbers according to certain algorithms, like especially complex abacus. Everything they do is designed by programmers. How to create an artificial intelligence that could have consciousness and its own motives for behavior, today no one simply does not know, but does not even know how to find out.
The reason for the impossibility of creating "strong" (that is, real) artificial intelligence is that no one knows how natural intelligence works. Today, neither scientists nor philosophers have an understanding of how human consciousness is formed. Attempts to reproduce on a semiconductor base even small fragments of networks that mimic neurons do not lead to the emergence of anything like consciousness. Experts agree that our brain does not work algorithmically at all and that under its functioning there are completely different principles, completely unknown at the moment.
It seems that by 1997, humanity from the first two "Terminators" has no chance to revolutionize the understanding of natural intelligence and create an artificial one. In the end, in 2019 we do not have a single idea on how to do this.
And yet the plot of the first two parts does not contradict scientific and technical limitations. As explained in the second "Terminator", "Skynet" was created due to the fact that the US authorities studied the neuroprocessor left after the destruction of the T-800, which was played by Arnold Schwarzenegger.

Time travel, in principle, does not contradict modern physics, and even specific options have been proposed that allow them to be achieved (for example, the Krasnikov tube or the Alcubierre bubble). Fortunately, today they are technically unattainable for humanity. But whether they will also be unattainable in the future is a big question.
If the processor on the basis of which Skynet is made is not a processor of a conventional algorithmic machine, then it can become the basis of artificial intelligence. After all, such a processor, in fact, no one created. It exists in a time loop, where it appears in 1984 with the T-800 terminator from the future, where it got thanks to the appearance of this very terminator in 1984. We do not have the knowledge to build artificial intelligence, but if it can be made on a semiconductor basis and we are shown such a microcircuit, then we can easily copy it - which is what happens in the first two parts.
After all, such a processor, in fact, no one created. It exists in a time loop, where it appears in 1984 with the T-800 terminator from the future, where it got thanks to the appearance of this very terminator in 1984.
However, in the second part (1991) Sarah Connor and the reprogrammed T-800, sent back to the past by her son, were able to destroy all samples of terminator chips. The material base for Skynet does not exist, it is not created and does not start a nuclear war. Almost happy ending. At least, everything is logical: a microcircuit, an object from a time loop, is destroyed, and without it, strong artificial intelligence is impossible.
The sixth terminator: dark fate or dark plot?
The beginning of the sixth film shows how another T-800 sent by Skynet from the future in 1998 kills John Connor on a beach in Guatemala. Many questions immediately arise here.
Firstly, from the point of view of everyday logic, it is generally unclear how he found them there. Guatemala is still a country with cheaply sold officials and a very weak system of tracking and tracing people who do not want to be counted and tracked. The authorities there do not control their state to such an extent that a small Guatemala annually loses in killed (criminals) as much as the Russian army lost during the years of the Chechen war.
Even local residents there today do not all have documents. In 1998, it was a nature reserve, where an energetic person with a difficult past could go unnoticed for decades even for the intelligence of a large state. How did another T-800 clone find Sarah Connor and her son there? There is no answer to this question. Before us is just a drawdown of the plot: the scriptwriter was a little lazy.
Secondly, the question arises. If in 1991 (in the second part of The Terminator) the microcircuits, without which Skynet could not be created, were destroyed, then how could Skynet, which does not exist in the future of that branch of reality that was shown in 1998, send the terminator into the past?
The physics of time had already developed Novikov's principle of consistency by the 1980s. According to him, any movement in time is possible only as long as the principle of causality is not violated. A future that no longer exists - because all the preconditions for it have been destroyed - cannot send anything to the past. There was simply no one to kill John Connor in 1998. The beginning of the plot of the sixth "Terminator" is built on air and grossly contradicts even the physics of time that was known in the 1980s - and, by the way, was respected in the second "Terminator", which was filmed by Cameron.
Exploiting pop fears: robots and AI that run counter to the technical capabilities of the foreseeable future
Then the events of the sixth part are transferred to 2020 - in fact, in our time. Terminator Rev-9 lands in Mexico. He hunts for Daniela Ramos, a simple industrial worker.

Further, the plot begins to exploit the fears that often surface in the press about robots and artificial intelligence. First, Daniela's brother is fired - his workplace was taken by a robot. This is a common horror story in our time: robotization is about to oust workers, everyone regularly tells us about this - from Elon Musk to politicians and taxi drivers who are not very versed in robots, but who love to talk. The problem with this point of view is that in reality everything is much more modest.
Musk's attempt to make Tesla's gigafactory fully automated almost ended in failure: production plans were disrupted, and manual labor had to be returned to the factory. This is not surprising: an employee without intelligence can only perform the simplest tasks that do not require mental activity. And this means that robots, in principle, cannot displace a person. Just as a hammer cannot supplant a carpenter, but only complements his capabilities.
Robots, in principle, cannot oust a person. Just as a hammer cannot supplant a carpenter, but only complements his capabilities.
The second common plot for pop culture, which the new "Terminator" is trying to scare with, is, again, the notorious artificial intelligence that wants to destroy all people. After a series of chases and shootings (there are more of them only in this piece than in the entire first "Terminator"), it turns out that the new terminator, Rev9, has arrived from the future - from 2042. But this is not the future of the Skynet network, because it no longer exists. This is a future ruled by the "Legion" - an AI built for cyber warfare.
True, there is a discrepancy here too. Terminator T-800, who killed John Connor in 1998 and lives among people under the name Karl, from somewhere knows the time and coordinates of the arrival from the future terminator Rev9. Moreover, he passed these coordinates to Sarah Connor. If she had not learned them from him, it would not have been possible to involve her in the plot of the new film.

But the question arises: how does the T-800 "Karl" know the place and time of arrival of the new terminator? This could not have happened: the terminator T-800 is from the future, where AI "Skynet" rules, and the terminator Rev9 is from the future, where the AI "Legion" rules. The first, according to the film, knew nothing about the future of the Legion. Obviously, we have before us another "slack" from the writers.
But back to the Legion world. At some point - apparently in the 2030s - the Legion simply turned off all objects connected to computer networks - power plants, factories, and the like. Humanity turned out to be unable to establish the work of its economy without computers, which is why it began to die en masse from disease. Attempts by people to end the Legion with a nuclear strike were unsuccessful: any network distributed in space is destroyed quite hard.
Unfortunately, here again the scriptwriter had a very, very strong rest. The real 2020 is such that only a teenager or an enthusiast like Elon Musk can believe in the victory of artificial intelligence in the foreseeable future. Try to call Sberbank and get sane answers from its voice assistant, which is positioned as "artificial intelligence". We guarantee you: it will be a fun five minutes.
And it's not just about Sberbank. Voice assistants from Yandex or Apple also do not demonstrate the miracles of efficiency. All of them, at best, are proficient in voice recognition and the choice of prepared answer options. None of the existing computers can pass the Turing test - to convince the person-interlocutor that it is not a computer that is talking to him, but another person.
Of course, to deny the achievements of weak artificial intelligence (there is simply no other for today) is stupid. Self-driving cars already know how to rebuild themselves from lane to lane - however, still only from one manufacturer - and in the coming years they will begin to drive themselves in the city, although for the time being the driver is offered to follow them in both eyes.
But one should clearly distinguish such a weak artificial intelligence from a real, strong one. At the heart of Tesla or Waymo autopilots are so-called neural networks. They consist of many elements - software analogs of neurons. At first, the neural network is "not trained". This means that, receiving traffic light images at the input, it will assign to each of the incoming images an equal probability of recognition: with equal probability, it will distinguish an object as a traffic light, as a sign or as a tree.
Looking at the final result, the person working on the software adjusts the behavior of the neural network in accordance with the training set. Such a selection is called a set of images with a pre-made labeling of these images by categories. If the training sample is very large (for example, a million recognized, slightly different images of similar objects), sooner or later the neural network will begin to distinguish real objects corresponding to such images with a probability higher than 99.99%. And the larger the training sample, the higher the probability of accurate recognition. To train a neural network, you just need a huge sample and many hours of work of the person who will mark up and classify images.
It is easy to see that a neural network is still just a very large and ultra-fast, but fully programmable machine that can only work on what a person has taught it to work on for a long time. A little to one side - and the neural network is no longer good for anything. The Legion from Terminator Six can be successful in cyber warfare if trained by humans for a long time. But in another area of activity - for example, waging wars, creating new machines like the Rev9 terminator - he will be powerless. The AI threats that Hollywood is trying to scare us with simply don't exist.
Unlike the scriptwriters of the first two parts, this time the scriptwriter lacked understanding of this point. And he did not get out of the situation, using a time loop, when the basis for a strong AI was brought by a terminator from the future. This is a big failure. It turns out that the screenwriter simply did not delve enough into the first two parts, basic for the entire franchise, - the only ones in it, worked out as it should.
Antigrass and wonderful drives
There are many amazing details in the film, and besides the strong AI that came from nowhere. In a scene from 2042, which depicts the war between humans and the Legion's robots, there are aircraft without propellers, apparently on anti-gravity. Obviously, the people shown in the film, fighting each other for a can of canned food, could not create such a thing.
That is, in the 2020s, where the "Legion" seized power, there are already huge flying machines on antigravity? But this is just a few years later. How can you create huge machines on completely unknown physical principles in a matter of years, and even without childhood illnesses (with them a large aircraft would simply not have survived until 2042)?
How can you create huge machines on completely unknown physical principles in a matter of years?
Another difficult issue is the power supply for the terminators. In 1984 and even in 1991 (the first two parts of the cycle), these were nuclear power cells. It is mentioned that they can give energy to a small city, albeit for a short time. This is logical: the fission of uranium nuclei gives even a small reactor a lot of energy. True, the radiation from the terminator itself should not be weak - so much so that the microcircuits for it will have to be made radiation resistant, but these are already details. In essence, there is nothing technically impossible here.

Starting with the third "Terminator", the scientific and technical part of the plot "floated". The Rev9's power source is not mentioned, but it quietly passes through the detectors at the military base. But any attempt to bring a nuclear reactor through "translucent" systems will not be unnoticed by the personnel involved in body searches - they will simply light up all the equipment with them.

The situation is even worse with the internal power supply of Grace, an enhanced-capabilities soldier of the Resistance Legion who has arrived from the future. He gives her unusual opportunities for a person, but his nature is unclear. Obviously, it is non-nuclear, like the T-800: the source does not have thick walls, a nuclear one would kill Grace with radiation. It cannot be hydrogen either: it is unrealistic to supply pure hydrogen into the human body.
Therefore, this is some kind of non-replenishing source of energy from the outside, moreover, powerful enough to kill two terminators at once (Karl and Rev9 at the end of the film). This technology cannot be developed by insurgents without powerful systems engineering centers. Conclusion: in a matter of years, humanity in the 2020s, even before the victory of the "Legion", created both antigrav and supernaturally powerful energy sources on principles that we cannot even imagine.
Is this possible in practice? There is nothing to say about antigraves: no. Russia with its "Angara", which still does not fly regularly, and the United States, which has been trying for eight years to create a new ship and rockets for space flights, perfectly show: not only antigrav, but also more understandable and simple technologies like liquid-propellant rockets in a few years do not create.
The situation is no better with batteries and energy sources. We still use lithium batteries, the chemistry of which dates back to the 1980s. Their mass production began in the 1990s, and the chemistry of such storage devices is gradually but slowly improved to this day. This is the best energy source we can offer today: fuel cells are even larger and difficult to obtain pure hydrogen for them.
There are not even compact nuclear reactors from the first "Terminator" yet. The most compact nuclear power source today is found inside Status 6 submarine drones and unlimited-range cruise missiles being developed by Russia. Despite being ultra-compact by today's standards, power sources are still too large to mount on a humanoid robot.
The creators of the first "Terminator" can hardly be blamed for their optimism with nuclear reactors. Before Chernobyl, it was believed that this is a rapidly developing industry, and projects for installing nuclear reactors even on an airplane and an all-terrain vehicle did exist. In the 1980s, Hollywood screenwriters knew how to write scripts that were technically close to the views of their time, we must give them their due.
According to the sixth "Terminator", we can conclude that today they have completely lost such an opportunity. If no one could be found for a franchise with such a long and loud history who could make it look natural, then there are no more such scriptwriters for Hollywood blockbusters.
Or, perhaps, the director of the new "Terminator" was simply not looking for them? Blade Runner 2049 was released just two years ago, and in general there are no inconsistencies and exaggerations of such a global scale. Nobody has been creating in a few years huge flying machines on antigrav and energy sources unknown to nature science, but of huge capacity. There is also no strong artificial intelligence in the 2020s, the creation of which we know nothing about. In theory, at least we can raise a person with genetic changes - of course, so far with minimal and not always desirable.
Most likely, director Tim Mueller, who filmed this series of the franchise, like his writers, simply did not attach any importance to the fact that the "sci-fi" film looked at least in principle compatible with modern scientific and technical knowledge. The script's obsession with action scenes, more like the Spider-Man comics and the like than the original Terminator, shows that they wanted to create a spectacle with the maximum of "Rubilov", and they were not particularly interested in complex details.
If so, they weren't quite right. Reviews coming out all over the world have already noted that the sixth "Terminator", although better than the third, fourth and fifth, but far short of the first two. The lack of a convincing plot - and this is not only waving chains and throwing crowbars in the frame - is the main reason for such not particularly flattering assessments. A good box office action movie will undoubtedly win back your money. But at the same time, there is no doubt that it will not be remembered by the audience as much as the parts directed by James Cameron.