Researchers blur the line between classical and quantum physics | Hacker News Reader

Researchers blur the line between classical and quantum physics

phys.org

82 pointsevo_924 comments

Here is a link to the arXiv page for the paper:

I never got past first-year physics in college, so hopefully you guys can help me understand these findings a bit more.

So, quantum entanglement is essentially the idea that the quantum state of a group particles cannot factored out individually. Chaos theory is the idea that complex systems are deterministic, but that even minute changes in the initial parameters of the system, or the forces applied to the system can cause dramatically different outcomes.

The issue with binding these models is that quantum mechanics operates on probabilities, which are fundamentally incompatible with the idea of determinism. It's impossible to call a quantum system deterministic when, for example, measuring the spin of a particle has a 50% chance of a different outcome each measurement, regardless of the initial state.

Is this understanding somewhat correct?

If so, the implication of this research is that quantum entanglement somehow produces a deterministic environment from a large collection of probabilities? Almost like a reverse monte carlo simulator?

> Chaos theory is the idea that complex systems are deterministic, but that even minute changes in the initial parameters of the system, or the forces applied to the system can cause dramatically different outcomes.

You can have chaotic deterministic dynamics, and this can help explain why formally deterministic systems are indeterministic in practice. But you can just as well have chaotic dynamics in a formally indeterministic system. Chaos is about (a) sensitive dependence on initial conditions and (b) bounded phase space (or some sort of other restriction that implies the "folding" phenomena when combined with (a)). In particular, there is a whole field of quantum chaos, and there's nothing contradictory about it.

> If so, the implication of this research is that quantum entanglement somehow produces a deterministic environment from a large collection of probabilities?

Nope.

If I may make a correlation to initial conditions and randomness: https://bl.ocks.org/mbostock/19168c663618b7f07158

>The issue with binding these models is that quantum mechanics operates on probabilities

>Is this understanding somewhat correct?

No! The schrodinger equation and the quantum state of a system is 100% deterministic. Probabilities only come into play during the observation step.

You might be interested in this view: http://www.scottaaronson.com/democritus/lec9.html

It basically views QM as a generalization of probability theory which allows negative probilities.

Not just negative, but complex. Also, not really probabilities, but probability-square-roots.

About chaos theory. You can experience it in playing Starcraft 2. In the very beginning make tiny decisions on workers vs soldiers. Or where to fortify or what to upgrade and see entire game getting influenced by it.

Have dusted it off after years. Still such a great game

So, entanglement could be said to be chaotic. Sounds more plausible than most attempts to bind these models together more succinctly.

Interesting, another link between classical thermodynamic processes, and quantum processes involved in non-locality. Speculation as to the nature of the arrow of time being a result of decoherence, and now a link between the behavior of entangled ensembles and chaotic systems thermalizing.

Could someone try to explain why "there's no idea of chaos in a quantum system"? To me that sounds weird -- I thought the entire premise behind quantum probabilities was our inability to get more definite answers from the subatomic world?

It is "chaos" in the mathematical sense, where two dynamic system with minute differences at t_0 end up diverging drastically as time passes.

For chaos to manifest itself you need at least two things. First, the equations of the dynamical system have to be nonlinear. Second, the dimensionality of the systems has to be greater than 3. In quantum mechanics, all the equations are linear, so there is no place for chaos in a strict mathematical sense.

I was really into physics in college. After taking a course on chaos theory and one on advanced quantum mechanics, I started getting a very strong feeling that whole quantum mechanics is kinda BS(like its just a mathematical model, not a representation of reality, ala GTR). And that chaotic systems is where the key to understanding the quantum world is.

So I took some time out to step back and see what my life would look like if I pursued physics, given the current state of affairs. Didn't like it at all.

Dropped out, learnt programming, started a company this year, finishing up the product for first 10 customers, and have a very strong feeling that we are onto something big!

Everything you could possibly use to describe reality is a model. What else could it possibly be?

A model which is, in some sense "particularly appropriate" in addition to making good predictions?

A model you can talk about without mathematics. Which doesn't need mathematics to form an intuition about.

STR and GTR are perfect examples of models which you can help even a layman develop an intuitive understanding of by just talking to them, without mathematics.

You can certainly explain even something as sophisticated as quantum field theory to laymen if you take the right approach. Feynman did just this in his lectures on QED, now available in book form. He didn't use any math, even though he talked about his own solution to the entirely mathematical problem of renormalization in QED.

Quantum mechanics (physics) makes lots of testable predictions and has many real world applications. Starting with black body radiation: https://en.m.wikipedia.org/wiki/Ultraviolet_catastrophe Double slit experiment, Solid state physics, semiconductors.

Mathematical models are not bs.

I think you will need some bs to be successful at sales, but I wouldn't try to use quantum mechanics in sales.

You can talk about GTR to someone without the use of mathematics and explain to them that time moves differently at different speeds, and that gravity effects time.

You cannot do that with quantum mechanics without bringing in a "probability wave", or a hypothesis that "maybe energy levels of systems are discrete", which anyone would agree doesn't make any sense by itself.

That's a really poor argument.

You can't demand that the universe works in easily comprehensible ways and discard a theory on how easy it is to explain without using math.

If you wanted to talk to someone about Quantum Mechanics you can start with black body radiation, the photoelectric effect and wave particle duality and the experiments that lead to these discoveries.

Then let's move on to precision tests of quantum electrodynamics done with low-energy atomic physics experiments, high-energy collider experiments, and condensed matter systems leading to the empirical evidence.

To me saying Quantum Mechanics could be BS is like someone saying evolution is BS because, well it's just a theory. Let's ignore all the facts that have been repeatedly confirmed through observation and experiment and pretend that "scientific theory" means the same thing as saying "it's just a theory".

ELI5 - please :)

Physicists are working, it's difficult, they might need help.

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