I just woke up from a nightmare that terrified me to my core. I had recently seen this video from Sixty Symbols regarding the apparent paradox of time dilatation http://goo.gl/dwOvg1 on a train moving near the speed of light heading towards a tunnel with guillotines at each end. The nightmare was that i was watching this same experiment unfold, but in a way that challenged causality. Maybe I just need someone who really knows to tell me it'll be ok. In my dream I was watching the experiment unfold, except this time the observer at rest (relative to the mountain tunnel) used entangled particles. Depending on the state of the particle the guillotine it arrived at would operate or not. On one end, however, the particle was received into a new entangled set that was kind of like a quantum computer where each qbit had its probability adjusted and more-or-less controlled into a pre-determined state regardless of the original input value. The other entangled particle of the original pair was just held at the other end of the tunnel guillotine for the pre-determined amount of time before a measurement was made. The experiment played out pretty much as it does in the video, with both sides agreeing that regardless of the fact that one event happened before the other, that both events happened. Only because of the "delayed quantum choice" the probability was shifted from an even 50/50 to something more like a 25/75. But both observers still agreed. Then it started up again and I found myself riding on a new train, also going near the speed of light from the OPPOSITE direction. In that moment I realized that the events that had played out in one direction were now reversed so that the cause and effect looked to be opposite from that perspective. Except, because of the entangled particle being "modified" at the destination, I realized that the results were now different since the particle that was being observed without the extra "tweaking" was happening first, supposedly changing the entangled particle at the other end of the tunnel before it could be "adjusted" to be something different. So I awoke in a cold sweat and I tried to find an answer online, but couldn't. If Train A sees the probability as 25/75, and train B sees it as more like 50/50, what does that say about causality? Doesn't everything all fall apart? Need help on this one so I can sleep at night. And really, I did dream this. I suppose I've been struggling with the twists of science a bit much. I take it as a sign of my science muscle growing.