How does time function in quantum mechanics and its multiverse implications?

[hellfire]

When you say that position is not an observable within the field theory (I believe you) this means that a position has no correlated operator in this theory. I suppose you refer effectively to one of the difficulties that Carlip is enouncing in his book 2 + 1 Quantum Gravity page 2: “Ordinary Quantum field Theory is local but the fundamental observables in quantum gravity are necessarily non local.”…

Position is only a label in quantum field theory, same as time. The question about the position of a particle at a given time seams not to be really meaningful in a strict sense. Instead, one asks about the value of the field at a given label (position and time) and makes use of the notion of propagators as correlation functions of the values of the field for different labels.

In my opinion Carlip's claim that you are quoting here seams not to be related to this. I would guess that the fact that observables in quantum gravity are postulated to be non-local might be related to the holographic principle (the real degrees of freedom and the physics take place at the boundaries of volumes), but this is far beyond my knowledge.

 

[CarlB]

How does time work in QM?

Here's my(speculative) version of how time works in QM. The official version is satisfactory for producing predictions but somewhat lacking in ontological interpretation.

Both QM and QFT can be put into a wave / particle duality. The connection between the wave and the particle is probabilities is defined by the squared magnitude of probability wave. For the relativistic theory, the wave function is defined in space-time.

To an experimenter, it is clear whether to use the particle model (i.e. probabilities of various outcomes) and wave model for an experiment. If the experiment has already been performed, then its results must be thought of in terms of probabilities of various particle results. If the experiment has not yet been performed, then probabilities will not do because of the possibility of quantum interference. For experiments still in the future, the wave description of the situation must be used.

If by "passage of time" we mean the stuff we experience as we grow older, that must be modeled in physics by wave function collapse. If, instead, by "passage of time" we mean the method we use to extend a solution to Schroedinger's equation at time t to time to a solution at time t+dt, then we must mean the unitary operator of quantum mechanics.

These two definitions of "passage of time" imply that we really need two temporal dimensions to fully describe a point in an experiment. One of the time dimensions, say t_1, gives a measure of time in the second sense given above. It refers to the number of seconds since the big bang. The other time dimension, t_2, gives the number of seconds between "now" and the big bang. If t_1 > t_2 then we must use a particle method of describing the event because it is in the past as compared to now. If t_1 < t_2, then we must use the wave method because the event is still in the somewhat indefinite future.

This sort of thinking implies that there must be a continuous deformation of a wave function description of an experiment to a particle description. This can be done if one rearranges quantum mechanics a bit.

Carl

 

[Juan R.]

So far I understand QM (only; = not Q Gravity), we have:
1°) Physically observable phenomenon; e.g.: a particle.

Wery well!

2°) Parameters and variables that help us to describe the physical situation or state in which the phenomenon is; e.g.: its position, its momentum, …

ONLY on nonrelativistic quantum mechanics. Only observable on R-QFT is the S-matrix and properties directly derived from them, for example energy.

3°) In fact a certain probability to really measure a given value for a given variable. In QM this is obtained with the introduction of the wave function [I note that it depends on the position and on the time Y(r, t)];

In relativistic QM (R-QFT), there is not wave-functions. The quantum state is represented by a funtional Y (phy_1, phy_2, phy_3... ) of field configurations phy_j at spacetimes points. Position is not a dynamical variable. Time enter as a parameter. I am talking of special relativity + QM (R-QFT). In quantum gravity, time dissapears.

4°) This proceeding leads to the notion of operator associated with an observable variable; e.g. for the position and (h/2pi). Ñ for the momentum
5°) this concept can be (and is) generalized and an operator can be (and is) represented by a matrix
When you say that position is not an observable within the field theory (I believe you) this means that a position has no correlated operator in this theory. I suppose you refer effectively to one of the difficulties that Carlip is enouncing in his book 2 + 1 Quantum Gravity page 2: “Ordinary Quantum field Theory is local but the fundamental observables in quantum gravity are necessarily non local.”…

Even ignoring some basic thecnical details you are simply ignoring (take a course in the topic) when 'I' say that position is not an observable is because in R-QFT position is not a dynamical variable. I am not talking about quantum gravity just about standard R-QFT. The nondynamical character of position follows from uncertainty relations in the relativistic regime. This is the reason that only scattering amplitudes are defined in R-QFT and particle physics.

Carlip's appeal to 'locality' is irrelevant for this discussion.

In Carlip’s book it is written (page 2 point 6; difficulties) that “perturbative quantum field theory depends on the existence of a smooth, … but there is no reason to believe that the short distance limit of quantum gravity even resembles a smooth manifold”…

Just speculation.

I would be happy if some one could give me his impression concerning my essay to demonstrate the Lorentz –Einstein Law (see my homepage). This essay is actually under consideration by the administrators of this Internet site at independent Research and I am waiting for the judgment.

Good luck!

 

[member 11137]

Wery well!
ONLY on nonrelativistic quantum mechanics. Only observable on R-QFT is the S-matrix and properties directly derived from them, for example energy.
In relativistic QM (R-QFT), there is not wave-functions. The quantum state is represented by a funtional Y (phy_1, phy_2, phy_3... ) of field configurations phy_j at spacetimes points. Position is not a dynamical variable. Time enter as a parameter. I am talking of special relativity + QM (R-QFT). In quantum gravity, time dissapears.
Even ignoring some basic thecnical details you are simply ignoring (take a course in the topic) when 'I' say that position is not an observable is because in R-QFT position is not a dynamical variable. I am not talking about quantum gravity just about standard R-QFT. The nondynamical character of position follows from uncertainty relations in the relativistic regime. This is the reason that only scattering amplitudes are defined in R-QFT and particle physics.
Carlip's appeal to 'locality' is irrelevant for this discussion.
Just speculation.
Good luck!

Thank you for the extensive answer. I understand now better the difference between my approach and the conformal approaches QM, R-QFT, ... In fact trying to think about what an impermanent geometric background could be (this is the -perhaps false- representation that I develop concerning the context for a quantum gravity theory), I inconsciently incorporate the idea that the backgrounds moves and with this kind of though, position becomes evidently a dynamical variable... That's my error; ok. Best regards.

 

[setAI]

the best beginning of a description of Time I have seen- [and am currently trying to grok the best that I can]- which stems from Everett MWT- conjectured by Page and Wooters in 83 and currently being supported by David Deutsch/et al at the Centre for Quantum Computation- is the idea that the 'past' and the 'future' are special cases of different universes in the Multiverse where the laws of physics-principally Entropy- establish a causal relationship with an observer and their world that restricts the possible states that could causally result in the current observer's state to very specific cases which emerge/appear as the 'fossil record/memory' of an observer's 'fixed past'- and that because of the randomness of entropy the 'future' does not have such a specific set of possible states- so an infinitude of different universes will diverge out from what were once nearly identical states and the 'future' that the observer sees is simply the state that that single instance of the observer happened to find themselves in- but ALL the possibilities [according to many worlds interpretations] occurred and each of these universes has a divergent copy of the observer with a different 'future' outcome that all share the same 'past' due to the causal constraints of entropy-

this system of specific universes with a causal construction defined by Entropy emerges subjectively to each instance of an observer as a fixed past/present with an open non-deterministic future [well actually each and every future is rigorously deterministic- but there is no way to predict which of the transfinite outcomes a single instance of the observer will subjectively find themselves in] and a subjective sensation of forward moving change as a result of the observer [and other clock-like systems] continuously comparing their current state with previously remembered states-

the thinking goes that if we can construct a workable theory of Quantum Gravity- that the details of the apparent flow of time and the relationship of universes connected by causality and entropy in this way will be much better understood