Is the next state of the universe only dependent on the current state or is every state before the future have some play on the future state?

(other than forming the states between them and the future state)

  • I mean, this strikes me as asking after a metaphysical interpretation of the wavefunction (and its collapse); In other words -- I'm not sure exactly what you'd be expecting someone to explain (what problem you're trying to solve) other than survey various interpretations of QM... – Joseph Weissman Jun 16 '13 at 18:43
  • tbh I am asking these questions so I can take a stance (one way or the other) on a Priest's (logics) explanation of the existence of God. (not the question of existence of God itself) if it requires Quantum Mechanics to answer this then so be it. I will study up. – 0xFFF1 Jun 16 '13 at 18:48
  • @0xFFF1 I'm interested in this priest's explanation... – commando Jun 17 '13 at 17:04

In Quantum Mechanics the wave-function of a system is also known as the state of the system. This state is not static but evolves in time. The evolution is only dependent on the present time, so is not historical. It is exactly deterministic.

(Exactly the same holds for all Classical theories including Newtonian Mechanics and General Relativity).

However, in the classical Copenhagen Interpretation introduced by Bohr, a measurement provokes the collapse of the state into an eigenstate. This introduces a stochastic element into the physics. After the collapse the State evolves as before.

This was a tactical manouver by Bohr to separate the classical & quantum worlds so that the physics of the quantum world could develop without a thick fog of interpretational issues.

Notably Heisenberg did not see the collapse as real, preferring to see the physics describe a kind of objective epistemology. That is the collapse of the state indicates a jump in our knowledge of the system.

Bohm taking his cue from Heisenberg introduced quantum decoherence, so that the state never actually collapses, but is seen to have done so by the environment surrounding the system. The state itself is always hidden from the measurer and only the decohered state is seen.

This allowed Bohm to introduce a wholly determinsitic account of QM called Bohmian Mechanics. It is non-local, so the evolution is not just determined by the present time but also by previous times.

Quantum Decoherence is also used in conjunction with a temporal logic in the Consistent Histories approach to QM where what is predicted is the set of consistent histories for a system. In this interpretation both the measurement process and collapse are not neccessary. One could consider this a revision of Everetts many-worlds interpretion except consistent histories are not real alternate worlds. Here, the world doesn't fracture and isn't fractal.

So, to be recap:

  1. In the Copenhagen interpretation, the State evolves deterministically punctuated by a non-deterministic collapse.

  2. In the Consistent Histories interpretation, the State evolves deterministically but is inaccessible, one measures the probability for a consistent set of histories which are decoherences of the State with the environment.

In both of these interpretations the State never depends on past states.

However the Bohmian interpretation does, but this is due to its non-locality which is controversial to theorists, being attractive to some and deeply unattractive to others.

Of course once one introduces special relativity one has problems with the idea of simultaniety. General Relativity brings along its own confusion with time as spacetime becomes dynamic.


The premise is flawed: there is no "current state" due to relativity. You have your current local state, but what has affected that state is potentially anything in the light-cone into the past (basically, what could have affected you spreads out at the speed of light backwards into the past--so if you care about what affected you within the last nanosecond, you only have to consider things about a foot away).

There are, thanks to quantum mechanics, various instances of "spooky action at a distance", some of which are apparently (but not actually, in an information-transmitting way, anyway) faster than light, and because of the equivalence between space and time, it's not exactly clear to me how to answer the question (or if it even has an answer--the premises may be so flawed that it doesn't really have an answer, as with "how duplicitous is the moon?").

Let me give an example of why reality doesn't play nice with questions like these. Certain processes can result in the emission of a pair of photons which are entangled, meaning that some of their properties are randomly chosen but correlated with each other. (For example, they may have been generated with a random polarization, but the same polarization.) Now you have two ways to interpret their behavior: either at t = now they are in a state of being entangled, or they are both impacted by what happened at t = when they were produced.

My general advice with philosophical questions like these is: it doesn't work enough like that to even ask the question, and the answer isn't as important as you think because of how it does work.


I assume you mean physical states. It is worth noting that not all views about Physics accept that any collection of facts about present or previous facts will determine every fact about future states. It's also not entirely clear what counts as forming states between the present and past. If states are discrete objects then it should be pretty clear, but if they're continuous (a not entirely settled matter) then what this means exactly may be unclear. For instance, if states are continuous then an object may have an instantaneous position and velocity and acceleration. Velocity and acceleration are usually conceived of as a change in some magnitude over time, but we permit ourselves to talk about their instantaneous values given a differentiable function that models position. If we take this model to model the position in a very literal sense, then does instantaneous velocity encode some information about previous states?

If we count instantaneous velocity and acceleration as properties of a single time state, then classical mechanics requires only knowledge of the present. If they do not, then you need at least some sort of information about the past.

I don't understand quantum mechanics or string theory enough to blather about what those disciplines would say.

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