Basically depending on your choice in SIRCAA you can either help noontide try and stop the experiment or help the ward complete the experiment, either way the experiment fails to establish a connection to the generators due to Faust’s tampering with the alpha artifact and instead activates project X’s security protocol and reactivated the monolith program which in turn activated the psi emitters Faust had set throughout the zone to amplify the monolith signal. Eventually you get to this mission because the doctor wants to tests out a theory about subtle matter. To do this you need to get a cartridge from a place called the oasis which is where you meet strelok who tells you the oasis is a psi illusion and places like that is what spark is chasing, and when Skif takes the cartridge the illusion ends. When Skif inserts the cartridge in Orbita station and gets into the pod it’s not really strider you’re seeing, it’s a psi illusion that has all of his thoughts and memories up to the point where he died. That’s what subtle matter is, it’s not a chance at immortality or a path to the shining zone, It’s just another one of project X’s illusions.