Why are there tape recordings of just about everything that happened on the island? Because it was the USSR at the time, and everyone was being spied on. The only thing different about Katorga-12 is that all of the facilities were built in the 1940s, and so probably had recording devices built right into them.
Katorga-12 is the only place on Earth with this rare, time-bending element. Why? Because natural fluctuations in time around the island mutated the material of the island itself, just as E99 mutates living creatures.
Alternatively, Katorga-12 is an astroid, possible the one that wiped out the dinosaurs or caused some similarly large impact. It's the only place on Earth that you can find E99, because E99 could not form on Earth.
Okay, so having an E99-armed Soviet Union curbstomp the world in the 1960s without anyone coming up with any deterrents is implausible, right? It seems like it...until you realize that not only is the USSR's new power coming from a line of research that no one else in the 1950s has imagined, let alone done basic theoretical work in, but said research has literally given the Soviet Union time machines. If a defector steals some samples or someone at Los Alamos starts making independent discoveries, Moscow can just send someone back in time to kill them before they've done any damage. And they can do this as many times as they want.
Hey, why is the pathfinding function made out of footprints? They're yours.
The explosion at the Singularity that wrecked the island and spread E99 radiation everywhere is your fault. It's the E99 bomb you set off; You Already Changed the Past and Demichev just rebuilt the generator afterward.
To clarify: in the unaltered timeline, the Barisov reactor was never finished, and the island was devastated by an experiment gone wrong as a result of political pressure to produce some sort of result, after which the Politburo shut down the research program on the island. When you save Demichev, he lives to change their minds, allowing the Singularity to be built. Then you blow it up, causing the mutations and everything else. Supposedly, the ghost-imprints and the time waves that crash your helicopter and bring you to 1955 for the first time are either natural on the E99-addled island, or a result of the original experiment.
Why does the description for the futuristic-looking assault rifle say it's built in the USSR? Because you changed history, and now the USSR rules the entire world in 2010!
Additionally, the Valkyrie is very clearly modeled on the AK-47, which not only parallels how Russian rifles have evolved in reality, but explains why you can find ammo for it in 1955.
Why do the Phase Ticks, when mutated and inflated with the TMD's de-aging function, begin to attack their own kin? Why, it's the same with humans: Reverts are universally aggressive toward all humans as well.
Here's something that will only become apparent upon multiple playthroughs: Those hidden messages scrawled in E99 dust that you reveal with the TMD? On a replay, the ones you have uncovered will remain uncovered, and any you haven't yet found will remain obscured. The messages are written by yourself from the future, who has repeatedly gone back in time to try to fix things. And you've started the game over. Congratulations, you, the player, are now complicit in creating your own time loop!
Furthermore the hidden messages are both conflicting and suggestive of madness. Some of them have tick marks as if it were counting something, and one specifically writes "the many deaths me". What if what happens when the player dies is the same thing that happens to Renko himself. He's trying various ways to fix the timeline and keeps dying over and over in the process, but every time he dies his vision just fades to white and he wakes a few minutes earlier and tries again. The messages conflict because they're written in different iterations of the time loop, and Renko is desperately trying to overturn his previous failed attempts to chance history. Hence messages that say the opposite of previous messages and finally one that cries "Don't trust me!"
This troper had a moment of boredom near the end of the game. Specifically, after killing Demechev, and figuring he could just take potshots at the good professor, assuming there would be some sort of immortality clause. Then he fell over, dead, and the third ending initiated.
At first, when I had all three endings done, I got really confused about why I couldn't restore the original timeline, in fact, I was confused about the way time travel had worked in general, but then I realised that the game has a ridiculously well-developed, original and downright sophisticated time travel mechanic. The truth is that the original timeline is necessarily terminated at the point where Renko travels back in time. Why? Because time travel in Singularity only goes between the present moment (not the present generally, but specifically the exact moment when the traveler uses a rift encounters a rift or gets thrown back by a wave of chrono-energy) and 1955, when the Singularity was created. As a result of this, "our" timeline became irreparably unreachable by time travel when Renko traveled back in time and saved Demichev, because Renko can never not change the past in 1955 - if he's not shot by his future self, then he saves Demichev out of heroism and if he does get shot by his future self then he leaves behind the TMD for Barisov to use. There is the question of what would happen if future Renko shot Demichev and let himself live but that's by no means certain - there are plenty of ways this action could still result in Renko dying and leaving the TMD, like if the impact of the bullet in Demichev knocks him over and the dead weight stops him escaping the burning building. The only way to restore the original timeline would be to travel back to some time between 1955 and 2010 and stop Renko, or anyone else, for that matter, going to Katorga-12 and being sent back in time, where they potentially rescue Demichev or drop a TMD but this can't be done because the game's time-travel mechanic only allows transition between the present moment and the creation of the Singularity. — AnCeithreMarcach
Now, what really got to me when I started to realise this is how this seems to be happening to a Renko who hasn't gone through the loop dozens of times already - he seems to be experiencing this for the first time. Then I realised this is actually perfectly consistent with the rules of time travel used throughout the game. The changes you make by travelling through time are not understood by the people you're working with when you get back to 2010, because they sent you back in a timeline that didn't have that change, but you return to a timeline where that change has already been made. This is why you've been caught in a loop and, for the very same reason, all the loops you've gone through have actually already happened. The reason this seems to be a first-time experience for you is because you're the first Renko in the final loop, because all the others have already happened. Basically, you're playing the iteration of the loop where everyone finally realises that you've been caught in a self-created, self-sustaining loop, which means that you finally figure out how to break it, thus creating one of the three endings. — AnCeithreMarcach
At first I thought how stupid it was that a game with such a well thought time travel story had Barisov be there every time after a time travel to 1955 and know exactly what Renko had accomplished, because if Renko had changed anything, the present day Barisov wouldn't have sent Renko back to change it. But then it hit me- Renko had already done it all and Barisov was aware of his actions because they had all already happened and didn't matter as revealed at the end.
While English writings alongside Russian ones are unodubtedly a translation convention for the player, hearing Russian characters speaking in English may be not. The protagonist's last name is Renko: even if not explicitly stated, it's easy to assume he's of Russian origin and bilingual. So when he hears Russian, it's like English to him: he perfectly understands it. That would also explain why he was on a mission on Katorga, he may be sent often on Russian-speaking territories because of his fluency.
Problem being their firefight banter is still in Russian, not in English. Only their cutscene speech is in English. Maybe Renko isn't fluent enough to internally translate it under fire?
The island is called "Katorga 12." The "Katorga" was a system of penal colonies. How many of the people working on the island were actually volunteers?
It was a penal colony during the '40s, when they were mining for Uranium (a job usually delegated first and foremost to those people you wouldn't miss). When they found E-99 and set up the facilities, it's pretty clear that everyone was enthusiastic with the project, and their families were there as well.
Zek is the Russian for "prisoner". The "Zeks" in the game were created by "complications with the teleportation experiments". Clearly, they were not willing volunteers.
On a vastly more massive scale, imagine the effects an all-powerful Soviet Union has on the world.
It's revealed at the end that all the faded notes written on the walls were written by you. And every single one of them is true. You're pretty much stuck in a hellish cycle of death and destruction on Katorga-12 till the end of time.
Why is the Russian spoken by enemy soldiers so painfully bad at times? Because it's Soviet Union! A multilanugaged country with obligatory Russian in schools, yet not known for teaching languages well. They may be Baltic.
Presumably the footprints you've been following around are a previous Renko's footprints who was doing what you did on a different loop. However these footprints sometimes appear in areas where he was never able to walk (like a flooded vent that you have to swim through).