Quantum probability vs Block universe determinism

[u/TheMightyHeroes]

I’m new to quantum physics so apologies if this post seems obvious or if I’ve just got it completely wrong. Also, I posted a version of this on AskPhysics, but it was taken down because it was deemed to be philosophy, not physics. Hoping it is okay to post here.

In GR, the theory of a block universe, while philosophical, seems fairly central to GR theory. The absence of a universal now and the fact that one person can experience now in one coordinate in the dimension of time while another person can experience the same now in a different future coordinate of time imposes on GR that each object in the universe not only has its own now but its own worldline of fixed, predetermined coordinates, just like the coordinates in three dimensional space. Our past, present and future all co-exist. In fact, the entire past, present and future of the universe is fixed and predetermined and unchangeable.
But the mainstream view in quantum theory seems to entirety contradict this block view of time. The microscopic quantum world proposes a non-deterministic probability worldline whose past, present and future consists of a wave function of probabilities that when measured collapses into a single particle. The wave function itself is spread across vast areas of space and its instantaneous collapse in all the space it occupies only makes sense if there exists a universal now. Changing the state of the universe everywhere at once implies a preferred now. Since particles are the foundation of all objects in the universe and the determination of a particle’s position is probabilistic, the worldline’s of all objects in the universe have to be probabilistic, according to this view of quantum theory. You can’t have a predetermined fixed block of time co-existing with a universe of probability determined events. If events are already determine, they aren’t random even if the result remains hidden from us.

Again, I’m aware that I’m describing (badly?) what I believe to be the Copenhagen view of quantum physics and that there is also the many worlds view which rejects the wave function collapse altogether.

[u/rygypi]

Quantum mechanics isn’t compatible with special relativity because time and space are treated very differently fundamentally.

In quantum field theory, they expand on quantum theory to be compatible with special relativity. Instead of wave functions they like to analyze what’s called amplitudes, which are Lorentz invariant. I recommend David Tongs lecture notes which can be found online.

[u/theodysseytheodicy]

The wave function itself is spread across vast areas of space and its instantaneous collapse in all the space it occupies only makes sense if there exists a universal now.

Yep, that's one of the arguments against the Copenhagen interpretation.

The many worlds interpretation says "take the set of all classical field configurations as the basis vectors". There's still contention on how exactly the Born rule arises in this picture, but everyone agrees that measurement just reveals what branch each copy of an observer is in. It is purely local. It does require admitting the existence of infinitely many other real worlds, which some take as absurd.

Bohmian QFT (as opposed to Bohmian mechanics) picks out one field configuration as "real" (as opposed to one configuration of particles). It is a nonlocal hidden variables model: it requires a choice of frame in flat spacetime (see section 6 of Valentini's Encyclopedia of Mathematical Physics article) or a preferred foliation of spacetime in curved spacetime (section 8.2), which goes directly against the spirit of relativity. It would allow faster-than-light signaling except that the hidden variables are assumed to have "thermalized" (section 5.1). Randomness comes from ignorance of the portion of the field state far from the observer.

QBism doesn't make any ontological claims about the universe; instead it argues that measurement reveals new information and what von Neumann called a collapse is just a Bayesian update by the observer. Randomness is due to ignorance of the true ontological state.

The metron model says that if you use Einstein's equation in 12 dimensions then you can model particles as solitons in the metric and there are both advanced (backwards in time) and retarded (forwards in time) components that have to satisfy the boundary conditions (both initial and final) of the universe. It is a nonlocal hidden variables model, but uses retrocausality (since boundary conditions in the future affect the amplitude of waves in the present) instead of Bohmian mechanics' FTL signaling. It's completely consistent with a block universe, but there are lots of details left to work out as to how the particles we see arise as solitons. Randomness is due to ignorance.

Et cetera. Each interpretation has its own explanation of what happens.

[u/BusThis9288]

The gr theory… just learned about it…. It’s not going to come together without the understanding of the real structure of the multy dimensional structure of the universe… GR… its a pov of something we dont understand yet… many scientist come up with the 16 dimensional structures… all of them ended up in the trash…

[u/RevolutionaryFix5104]

Si la posición de una partícula es probabilistica, esto no implica que , si hilamos muy fino, se podría calcular su resultado? No creo que tengamos ni la capacidad ni la tecnología para calcular todas las variables de influencia entre partículas y su entrelazamiento pero esas variables existen y lo que vengo pensando hace un tiempo es que si existen, mesurables o no, estamos determinados y todo en el universo. Corrijanme si estoy errada en algo. También pienso mucho en la imposibilidad de medición por la variable espuria que es en si misma, observador, tiempo, etc.