Mapping the edge of reality

April 28, 2017
Credit: CC0 Public Domain

Australian and German researchers have collaborated to develop a genetic algorithm to confirm the rejection of classical notions of causality.

Dr Alberto Peruzzo from RMIT University in Melbourne said: "Bell's theorem excludes classical concepts of causality and is now a cornerstone of modern physics.

"But despite the fundamental importance of this theorem, only recently was the first 'loophole-free' experiment reported which convincingly verified that we must reject classical notions of causality.

"Given the importance of this data, an international collaboration between Australian and German institutions has developed a new method of analysis to robustly quantify such conclusions."

The team's approach was to use , a powerful machine learning technique, to automatically find the closest classical models for the data.

Together, the team applied machine learning to find the closest classical explanations of experimental data, allowing them to map out many dimensions of the departure from classical that exhibit.

Dr Chris Ferrie, from the University of Technology Sydney, said: "We've light-heartedly called the region mapped out by the algorithm the 'edge of reality,' referring to the common terminology 'local realism' for a of physics satisfying Einstein's relativity.

"The algorithm works by building through simulated evolution imitating natural selection - genetic programming.

"The generates a population of 'fit' individual causal models which trade off closeness to theory with the minimisation of causal influences between relativistically disconnected variables."

The team used photons, single particles of light, to generate the quantum correlations that cannot be explained using classical mechanics.

Quantum photonics has enabled a wide range of new technologies from quantum computation to quantum key distribution.

The photons were prepared in various states possessing quantum entanglement, the phenomenon which fuels many of the advantages in quantum technology. The data collected was then used by the to find a model that best matches the observed correlations.

These models then quantify the region of models which are ruled out by nature itself.

The research, "Explaining quantum correlations through evolution of causal models", has been published in Physical Review A and can be accessed online.

Explore further: Physicists demonstrate new way to violate local causality

More information: Robin Harper et al, Explaining quantum correlations through evolution of causal models, Physical Review A (2017). DOI: 10.1103/PhysRevA.95.042120

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14 comments

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sirdumpalot
not rated yet Apr 28, 2017
Relational quantum mechanics does fine with locality, but without ontological realism.
rogerdallas
3.7 / 5 (6) Apr 28, 2017
Can we finally dispense with a "first cause"? Could we finally stop asking how a "something" can arise from a "nothing"?
DonGateley
5 / 5 (4) Apr 28, 2017
The story gives no clue as to what their result was.
Da Schneib
5 / 5 (4) Apr 28, 2017
I would object that "classical causality" is merely another term for "local realism," and we've known that local realism is ruled out for decades; one can quibble and say that we didn't "really" have a "loophole free" Bell Test until recently (the last decade), but considering that we had 5σ tests thirty years ago and 30σ and greater tests twenty years ago, and that when we did the loophole free tests they came out the same, this is nothing but whining.

It's nice that they came up with a genetic algorithm to prove this, but it doesn't seem to me to be much of an advance.
Da Schneib
5 / 5 (3) Apr 28, 2017
@sirdumpalot, ontology is not physics. And Bell Tests show that ontology doesn't have much to do with QM, in any case, since either realism or locality must be rejected in order to be consistent with their results.

@rogerdallas, I don't see that this has much to do with first causes, or with something arising from nothing. It's got to do with Bell Tests, genetic algorithms, local realism, and entanglement.
rogerdallas
5 / 5 (2) Apr 29, 2017
@da schneib-- you are correct, yes. I was going more to the implications of the local realism issue. Confirmation of quantum oddities by genetic algorithm or by any other means seems to me to undercut conclusions reached by means of classical logical arguments using a classical notion of causality. I don't know whether it is even worth the effort to try to demonstrate that much of what passes as "philosophy" is naïve at best and crapola at worst, but I sometimes beat my head against that wall. It feels so good when I stop...
EyeNStein
4.5 / 5 (2) Apr 29, 2017
As it stands this research doesn't advance Quantum theory much. It just sets up classical real
ism for a fall by disproving any best fit classical solution it finds. Even in that endeavour their genetic algorithm isn't exhaustive as you cant prove it tried every possibility: (It just found some good near misses.)

However if their algorithm can seek out best solutions in non-Hilbert spaces where gauge forces could play; they might find some solution that looks like quantum causality. (i.e. entangled causality events between quantum particles 'behind the quantum curtain'.)

That would be a big step forward, and take the blind spookiness out of QM.
Da Schneib
5 / 5 (4) Apr 29, 2017
@rogerdallas, the first thing to do is stop beating your head against the wall and simply accept the Born Rule as descriptive of reality: uncertain is a state, neither this nor that, a percentage of both, not merely as a matter of perception but of reality. The point in this context is that this percentage represents a real state, not resolved until an interaction occurs. Examine this carefully and you will see that realism is debunked.

But examine locality, and you will see that Bell Test experiments deny that too. So the question is, which one is right, realism or locality, and more carefully examined, is it possible that reality is either one, just like the wave/particle or any of the other perceived dualities? Could it be that we can violate locality, or realism, and interpret the same experiment in both ways?

This is where it gets interesting.
Da Schneib
5 / 5 (3) Apr 29, 2017
@Eye, and feel free to save some typing and call me @Schneib,

We are faced with a situation where specific experimental results reject both realism and locality. This is a key unanswered question in physics, and many non-physicists do not perceive it. Symmetry of results appears to exclude this situation, and it therefore emerges as a bone of contention, with those whose experiments reject locality contending with those whose experiments reject realism.

My key prediction is that the ratio between proof of locality and proof of realism will turn out to be an uncertainty relation. I'll let you think about that.
EyeNStein
5 / 5 (2) Apr 29, 2017
@DS
the ratio between proof of locality and proof of realism

There are already many experiments which give ratios of results which are exactly related to the percentage of certainty that a particular experiment yields. The most obvious of which is the dual slit experiment fitted with detectors deliberately yielding only partial slit choice resolution.

My favourite manipulation of those ratios is when a partial measurement is immediately followed by a second measurement of equal strength but opposite polarity. (When within a predictable margin of quantum uncertainty the two disturbances to the system almost cancel out!)

There seems to be a very concrete (as in predictable) statistical process going on here. We just don't have a clue why yet.
Whydening Gyre
5 / 5 (1) May 01, 2017
@DS
the ratio between proof of locality and proof of realism

There are already many experiments which give ratios of results which are exactly related to the percentage of certainty that a particular experiment yields. The most obvious of which is the dual slit experiment fitted with detectors deliberately yielding only partial slit choice resolution.

My favourite manipulation of those ratios is when a partial measurement is immediately followed by a second measurement of equal strength but opposite polarity. (When within a predictable margin of quantum uncertainty the two disturbances to the system almost cancel out!)

There seems to be a very concrete (as in predictable) statistical process going on here. We just don't have a clue why yet.

Helicity?
And apologies for the 4 on one of your posts. we're travelling and wife can't seem to miss those rough spots...
Da Schneib
5 / 5 (3) May 01, 2017
But @Eye, this one is very specific, and not covered by a known uncertainty relation.

Realism is all about uncertainty relations; it says that even though we can't measure things closer than the uncertainty relation, those things still have definite values. This goes directly against the Born Rule.

Locality is not about uncertainty. It's about local causes having local effects (i.e. nothing happens faster than light moves from one location to another); that is, it's about causality. This goes directly against entanglement experiments, which appear to show that local causes appear to have non-local effects.

This is one of the central conundrums of quantum mechanics.
Da Schneib
5 / 5 (2) May 01, 2017
To put this another way, you can have locality, but only at the cost of the Born Rule; or you can have real values for Heisenberg uncertain parameters, but only at the cost of non-locality. Ultimately the question is, are these two completely opposed, or is there some compromise between realism and locality that gives a ratio between them? And if there is such a compromise, what does that tell us about what quantum mechanics really means?
sirdumpalot
not rated yet May 13, 2017
@Da Schneib you are right, realism - as Einstein envisioned it, is beyond the scientific method - as it talks about states independent of measurement, and the scientific method doesn't really make sense without measurement. But that's why any discussion of realism requires philosophy - it's a philosophical position, not a physics one.

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