Friday, May 20, 2005

More Quantum Causality

I have suspected that modern quantum theory contains the seeds of a new theory of causality. I did a search on Google scholar looking for more papers. I thought this one, by mathematical physicist V.P. Belavkin, was interesting, and I offer the briefest of summaries below. As usual, I was limited in my ability to follow the formalism, and therefore will “bleg” anyone with expertise in this area to comment or offer references which help explain this in layman’s terms.

Belavkin says that “the latest developments in quantum probability, stochastics, and in quantum information theory” make it possible to bypass the paradoxes of the measurement problem in the traditional quantum theory. The original theory divides the world into an external observer and a closed quantum system to be observed, which results in the problem.

It goes something like this: Belavkin analyzes open quantum systems using a dynamical approach which gives the output statistics of continuous quantum measurements which result from the solution of a stochastic differential equation. He then applies a special filtering method or superselection rule – which he calls a causality principle – which imposes a past-future boundary. The past consists of classical particle trajectories, the future are the quantum probabilities compatible with these trajectories. The statistical results obtained are consistent with experiment, just as in the traditional formulation.

Now it seems we haven’t gotten “something for nothing” here. In exchange for getting rid of the seemingly subjective observer problem in the original theory and making things more objective, he had to insert “by hand” a boundary defining the arrow of time. Still, it is appealing to think that time and causality are in an objective way intimately bound up with the transformation of quantum potentials into classical realities, as is the case with this proposal.


Steve said...

[1 Feb.2010] Question to visitors: why are you searching on the term 'quantum causality'. If you have a quick moment please let me know. Thanks,
- Steve Esser

Silver Hawk said...

I came here because of this wonderful little number


Anya said...

Actually, I am as well. It seems very interesting, but unfortunately I don't really know much about quantum theory..

Steve said...

Thanks. It may be that people have some different ideas about what is meant by quantum causality. Here's my take:

In a quantum measurement event, a variety of possible outcomes (say, for the position of a particle) are resolved (or "collapsed") into a single outcome. If we take this as a simple model for general causal processes in nature, we would say that causation is the process whereby the various potential futures are resolved into a fixed past.

Causation is a topic which is historically surprisingly difficult in philosophy, and it is also hard to locate the concept in classical physics (where dynamic laws are typically reversible in time). This quantum-inspired version is a very simple idea which seems to fit pretty well with our intuitions.

Joselyn Neon said...

I wanted to know more about the term "Quantum Causality" because of an article I read that argued that Einstein wasn't to blame for the devastation of the Atomic Bomb.

Steve said...

Thanks - I wonder if it this same one that silver hawk pointed out?

While the tongue-in-cheek style makes me unsure the author is serious, his point about how we often over-assess credit and blame is fine. I don't see anything "quantum" there, however.

But I can cook better than you :) said...

Oddly enough I was following an argument I was having with myself about cause and effect. I too am a layperson interested in philosophy and science. My career is Hospitality and Restaurant services. Specifically I'm a cook.

Unknown said...

I came to find out why I thought dividing the light from the darkness was a good idea ;-)

And the link I found on Stumbleupon about Silver Hawk's number.

It made for a interesting blog post.

jdecaro said...

I discovered the same article as "SilverHawk". I thought it was quite interesting, and wanted to see the theory behind Robert Anton Wilson's writing.

Steve said...

Wilson seems like an interesting figure. I've never read him.

Lintropy said...

In response to your first question: I came across the idea on a post and wanted to look into it, mostly because I'm looking for metaphors that might be useful for my dissertation introduction. I'm trying to describe a process of reading literary texts that doesn't assume that they reference previous ones (or contemporary ones) in a neatly causal way.

Steve said...

That's interesting. Previous texts would inform, perhaps constrain the new -- but it is not a deterministic process. The quantum event has a notion of spontaneity, of creativity.

matt said...
This comment has been removed by the author.
Unknown said...

I am an independently educated quantum physics geek looking for further theories that integrate causality in a non-deterministic reality with the probabilistic science we can currently test. I want to understand how to integrate the ideas of observer independent relativity theories and quantum mechanics. I want new ideas on how humans percieve time that have a sold scientific foundation; though i don't expect to find any empirical evidence that could negate our perception of causality being a straight line through space time of cause and effect. If you come across anything besides quantum loop gravity, let me know!

Steve said...

It seems like we're interested in some of the same questions -- I'll post on the blog if I come across some good ideas. Thanks for commenting.

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Anonymous said...

I searched for quantum caSUality actually. I just went with this idea that undeterminism on a quantum level is just due to a lack of computational power that forced the programmers to approximate that part of reality with a pseudo-random function. Of course this came after i read Nick Bostrom's theories :p

Anonymous said...

Me too! I love Einstein and was intrigued by this little gem, which led me here.

Anonymous said...

The Cosmological Argument for the existence of (a) God rests on the assumption that everything (except the special case of the first cause) is the result of a prior cause. But quantum theory brings the very notion of causality into doubt.

Steve Esser said...

You have a point, when causation is seen as strongly determining the effect (necessitation). But there are weaker notions (e.g. causation as a constraining influence) which I think can be compatible with QM.

James said...

Why I am searching on "quantum causality"? I'm trying to find a cohort for setting up experimentation.

My evolved present perspective.

Quantum Mechanics uses probability to assign the likelihood of an event occurring. In so doing, that system of mathematics obscures causal relationships; generally grouping causality into containers of mathematics, with causality hidden from observable experimentation.

However, quantum mechanics can explore quantum causality by observing the differences between “systems” of experimental outcomes.

E = mc^2 throughout the universe

For the mathematics to hold true, everything observable must have connectedness; if not connected, independent results would be observed.

Mathematics infers causality.

Relativity as an implicate of any one entity in the universe subtends those influences throughout the Universe, such as gravity.

Therefore all observable physics has causal Relativity as an underlying foundation.

Observable relativity are systems of non-relativistic causality quanta, not individual observable causal outcomes.

Relativistic Quantum Entanglement can be explained as Systems of Non-relativistic Causal connectedness that differentially produce causal Relativity and the related Observable qualities.

Create experiments where a physics constant of observable relativity is neutralized (some form of balancing a unitary operator like
E/m = E/m e^(+1) * E/m e^(-1)

Relative to angular acceleration for instance. The difference between two experimental systems that neutralize the Newtonian physics constant relative to the Universe may allow for deducing the non-relativistic quantum causality characteristics.

Neutralizing or Differentially Biasing influences of physics constants (scalar causal constants, i.e. singularities).

To create tools for manipulating space-time, the manipulation of non-relativistic quantum causality must be characterized.

Suspected is that Relativity floats upon a sea of quanta. So for an experiment from moment to moment, different causal quanta would be involved. Characterization requires neutralization and/or biasing then differentiation.

Proposed are three types of causality: simple conditional, recurrent, and evolutionary. Their interplay creates the foundation for relativity; and observable physics.

Is this at all interesting for anyone to discuss setting up experimentation?