What does a local non-realistic theory look like?

[Jilang]

Time is not well defined in QM. We can only assume trajectories moving forward and backward -- retrodiction. If we interpret Time to have that property then the natural and direct consequence is that will be having mixed realities -- time moving forward which we are in and time moving backward that is hidden from us. But we can't say much about it.

http://www.dailymail.co.uk/sciencet...m-experiment-suggests-time-run-backwards.html

Indeed. My question was whether is was the change in entropy that separated the classical from the quantum? In QM it seems that there is a reversibility with no change in entropy. Is it when entropy increases there is no going back?

 

[RUTA]

If the entropy of the system changes do you still have the backwards evolved time component?

Yes, the change of entropy due to the exchange of energy (source to sink) isn't affected by the information exchange from the forward and backward-time evolved wavefunction.

 

[DrChinese]

If the arrow of time were somehow an illusion, or is a local effect, it's hard to see why vastly separated sections of the universe would have their arrows of time aligned. The argument that every time you measure entropy, you're at a local minimum of entropy, doesn't sound like it would explain why distant stars have their arrows of time aligned, or why they all have their arrows of time aligned with the cosmological arrow of time.

Sure, I agree with this. But I think it is a bit different question than asking why the elements of the future are participating (if they are) in observations made in the present. In other words, I don't see understanding the arrow of time as an impediment to a time symmetric theory.

I will give you a speculative hypothesis that embodies this. (Yes, I know speculation is bad - but there is no physical evidence pro or con here so I would call it no more speculative than MWI.) Suppose at the big bang, time symmetry was evidenced as follows: half the mass-energy went in one time direction T=+1, and the other half went in the other T=-1. The net "time momentum" is zero. So our observable universe is only one of two halves, and each starts out with a preferred time direction. That would neatly explain the arrow of time, and would be consistent otherwise with what we know. And would provide a basis for an interpretation involving time symmetry.

In RUTA's terms, the block world would be a bit bigger as it extends in a second direction. :)

 

[Jilang]

Yes, the change of entropy due to the exchange of energy (source to sink) isn't affected by the information exchange from the forward and backward-time evolved wavefunction.

Thanks, but I think I didn't express myself properly. If there is a change of entropy between source and sink does that preclude the backward-time evolved wavefunction?

 

[zonde]

Another example of an adynamical global constraint is the least action principle applied to the path of a refracted light ray.

Can't agree with this. I don't see the "global" part in least action principle applied to the path of a refracted light ray.

 

[julcab12]

In QM it seems that there is a reversibility with no change in entropy.

Reversibility has very little meaning in QM since time is just a parameter, in addition to the inherent non-deterministic property of the system(standard). We can assume also that particle does not have entropy.

Is it when entropy increases there is no going back?

Going back in what manner? The increase in entropy makes the state mixed and it is impossible to ever go back to the ordinary notions where things had position and momentum that had exact, well-defined values. Either it goes branching forever or some dynamic is introduced -- bounce/cyclical which is speculative at the moment.

 

[Jilang]

Going back in what manner? The increase in entropy makes the state mixed and it is impossible to ever go back to the ordinary notions where things had position and momentum that had exact, well-defined values. Either it goes branching forever or some dynamic is introduced -- bounce/cyclical which is speculative at the moment.

I was referring to the reverse causality/ backwards time evolution of the wavefunction. If entropy can only increase in either direction would not a change in entropy in the forwards direction put the blockers on a time-reversed component?

 

[Ilja]

Local non-realistic interpretations simply look like the minimal interpretation. They make only the predictions - the probabilities - but do not aim of finding a causal explanation for observable correlations. So, if there is a 100% correlation between A and B, one is not allowed to conclude that A causes B or B causes A or that there has to be a common cause C for A and B. There is such a correlation, fine, so what?

In my opinion, this simply means giving up doing science in this particular direction. It is not very dangerous, because it is restricted to a single domain - the foundations of physics - and the existing theories in this domain are already nice enough that any lack of scientific progress in the direction of the foundations of quantum theory is not necessary. But imagine, say, medicine without the obligation for science to find causes for observed correlations. One observes that smokers often die because of lung cancer. The tobacco lobby could, then, argue: So what? We have no explanation for this? So what, physicists have also no explanation for the violations of Bell's inequalities, the only possible causal explanations would violate relativity, but nobody cares about this and doubts that relativity is wrong. No, they say we should not search for hidden causes. So, let's follow the physicists and give up the search for causal explanations for the correlations between smoking and lung cancer.

 

[Jilang]

So, let's follow the physicists and give up the search for causal explanations for the correlations between smoking and lung cancer.

Ilja, I don't think you need to worry on that score. I think it is pretty much accepted that on an everyday scale we we live a classical world.

 

[Dale]

Closed pending moderation