Lawrence Krauss: Quantum Mechanics is deterministic (video)

[Pleonasm]

I understand partly what he is saying, but can you discount the measurement effect as a feature of the world? Aren't measurement effects going on all the time between macroscopic and microscopic systems, making it in practice, at times, an indeterministic world? Or is he assuming that decoherence removes all possibiities of indeterminism in the external world (that is the world outside of their labs)?

 

[A. Neumaier]

He also wrote a book ''The Universe from Nothing''. Being deterministic, it would mean that the universe is still nothing...

But all he says is that the state developes deterministically by Schrödinger's equation and the measurements behave probabilistically, without any clear connection between the two. This was known since 1926.

 

[Pleonasm]

all he says is that the state developes deterministically by Schrödinger's equation and the measurements behave probabilistically, without any clear connection between the two. This was known since 1926.

A significant portion of physics graduates see a connection between the two and extrapolate that the world is indeterministic due to the findings of QM. They are found in no large part on sites such as these. Could this video by one of the most foremost particle physicists put to rest this notion?

 

[A. Neumaier]

A significant portion of physics graduates see a connection between the two and extrapolate that the world is indeterministic due to the findings of QM. They are found in no large part on sites such as these. Could this video by one of the most foremost particle physicists put to rest this notion?

No. The connection is called Born's rule and is known since 1926.

To get rid of the observed indeterminism one would have to explain how it arises from the deterministic laws for the quantum state, as in the thermal interpretation. . But Krauss just utters some nearly 100 year old statements without giving any explanation or even references.

 

[Pleonasm]

No. The connection is called Born's rule and is known since 1926.

The Einstein-Bohr debates, which most people reference to as reinforcement of "the death of determinism in modern physics", took place in 1925... That's partly the problem.

 

[Pleonasm]

To get rid of the observed indeterminism one would have to explain how it arises from the deterministic laws for the quantum state,

How about an analogy then: If a spinning dice was observed with no possible tools to measure its future motions, it would appear to behave indeterministicly as to when and how it lands, right? That doesn't mean however that it exhibits indeterministic behavior. The question of why we can't measure it perfectly is not an argument against the laws that governs its motions. Krauss asserts that it is simply a fundamental feature of the quantum world. It does however run counter to the determinism that we are accustomed to, which is precise trajectory of a given objects future motions.

 

[Pleonasm]

He also wrote a book ''The Universe from Nothing''. Being deterministic, it would mean that the universe is still nothing...

That is an incorrect deduction. A perfectly deterministic universe could arise from an indeterministic source.

 

[A. Neumaier]

That is an incorrect deduction. A perfectly deterministic universe could arise from an indeterministic source.

But the source here is ''Nothing'', without any information content.

 

[Pleonasm]

But the source here is ''Nothing'', without any information content.

Nothing is the "absence of everything", according to Krauss. My objection was at any case to your contention that deterministic systems can't be sprung out of non-deterministic ones. That is not sound logic.

 

[A. Neumaier]

Nothing is the "absence of everything", according to Krauss. My objection was at any case to your contention that deterministic systems can't be sprung out of non-deterministic ones. That is not sound logic.

A deterministic system that begins in a state of absence of everything cannot evolve into a state of any complexity, unless you place this complexity explicitly into the dynamical law.

 

[Pleonasm]

A deterministic system that begins in a state of absence of everything cannot sensibly evolve into a state of any complexity, unless you place this complexity explicitly into the dynamical law.

Suppose that to be true, that has no bearing on whether it is a deterministic or indeterministic universe. A indeterministic universe cannot "sensibly evolve" from nothing either. This thread was about a deterministic universe in particular, and quantum mechanics.

 

[A. Neumaier]

A indeterministic universe cannot "sensibly evolve" from nothing either.

Of course it can, because then the future is not determined by the initial state.

 

[Pleonasm]

Of course it can, because the future is not determined by the initial state.

There is no working model for such a system. Contrary to popular belief, QM does not dispatch with causality. It is a very different type of causality, however. There is a source from which things spontaneously (to our minds) arrise. It is not randomness. It is however random in the sense that we cannot have absolute knowledge about its positions more than the probability distributions.

As for Krauss's views on the possible beginnings of the universe, you will have to ask him how he reconciles it with the knowledge we have about QM.

 

[Pleonasm]

So how many people in here would agree with Krauss's conclusion that the underlying world based on QM is deterministic (interpretation neutral, he says)?

 

[DarMM]

So how many people in here would agree with Krauss's conclusion that the underlying world based on QM is deterministic (interpretation neutral, he says)?

Well not me. There's no way being interpretation neutral that it's deterministic. You have the Born rule with no account for how that arises dynamically.

 

[Pleonasm]

There's no way being interpretation neutral that it's deterministic.

"Calculations of quantum decoherence predict apparent wave function collapse when a superposition forms between the quantum system's states and the environment's states. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation."

Which is deterministic...

 

[DarMM]

"Calculations of quantum decoherence predict apparent wave function collapse when a superposition forms between the quantum system's states and the environment's states. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation."

Which is deterministic...

Decoherence reduces the density matrix for the relevant observables to one without interference/coherent mixing. It still doesn't tell you which outcome occurred it only gives you a probability distribution of outcomes.

 

[Pleonasm]

Decoherence reduces the density matrix for the relevant observables to one without interference/coherent mixing. It still doesn't tell you which outcome occurred it only gives you a probability distribution of outcomes.

Deterministic probabilities is still determinism. It is not randomness/indeterminism.

 

[PeroK]

Deterministic probabilities is still determinism. It is not randomness/indeterminism.

Perhaps you need to define ( what you mean by):

Determinism
Probability
Randomness

 

[Pleonasm]

Perhaps you need to define ( what you mean by):

Determinism
Probability
Randomness

Determinism: if you know the state ket at one point in time, then you can predict the state ket at all future times. This is still true of the probability distributions in quantum mechanics during (apparent) wave function collapse.. You just know them in terms of (extremely) precise probability amplitudes this time.

 

[DarMM]

Deterministic probabilities is still determinism. It is not randomness/indeterminism.

Well yes you can determine the probabilities for the outcomes. Those outcomes still happen probabilistically not deterministically.

 

[PeroK]

It does however run counter to the determinism that we are accustomed to, which is precise trajectory of a given objects future motions.

I'm not accustomed to determinism outside of a few simple systems. The universe around us, regardless of any appeal to QM, is fundamentally not deterministic.

If you take Newton's laws, for example, then there is a fundamental determinism at the heart of nature. But, in a way, that runs counter to our experience. And, there's no way to tell directly whether the lack of determinism is due to the sheer complexity of the universe or because the universe lacks that fundamental determinism.

 

[bhobba]

The Einstein-Bohr debates, which most people reference to as reinforcement of "the death of determinism in modern physics", took place in 1925... That's partly the problem.

As great as those important debates were things have moved on a lot since then eg see Weinberg:
https://physicstoday.scitation.org/doi/10.1063/1.2155755
'The Copenhagen interpretation describes what happens when an observer makes a measurement, but the observer and the act of measurement are themselves treated classically. This is surely wrong: Physicists and their apparatus must be governed by the same quantum mechanical rules that govern everything else in the universe. But these rules are expressed in terms of a wavefunction (or, more precisely, a state vector) that evolves in a perfectly deterministic way. So where do the probabilistic rules of the Copenhagen interpretation come from?'

It was thought even though we now know both are 'wrong' Bohr was 'more' right and correctly, for his time, won the debates. I personally do not agree - I think Bohr was too philosophical and Einstein was more coherent with the Ensemble Interpretation that I personally hold too. I also think there is the possibility it may be resolved just using the formalism itself with simple a conceptualization of things like probability. As an aside a lot of the arguments simply rehash those about ordinary probability: http://math.ucr.edu/home/baez/bayes.html.

Gell-Mann and Hartle have made interesting progress in that direction:
https://www.sciencenews.org/blog/context/gell-mann-hartle-spin-quantum-narrative-about-reality

Bottom line here is become acquainted with the more modern ideas before forming any views in this area. And please, just some pleading from a mentor, do not get worked up about it. I am very sure in time it all will be sorted out - no need to worry. It may turn out is is simply just semantics - but I don't really know. Formally we know what's going on:
https://arxiv.org/abs/quant-ph/0101012

Thanks
Bill

 

[DarMM]

I think the Colbeck-Renner theorem is interesting here. If you have Bell violating correlations between two systems you can show that the outcomes for a single system conditioned on any set of events in spacetime is indeterministic.

(Technically this is a corollary of the theorem)

 

[DrChinese]

... Contrary to popular belief, QM does not dispatch with causality. It is a very different type of causality, however. There is a source from which things spontaneously (to our minds) arrise. It is not randomness. It is however random in the sense that we cannot have absolute knowledge about its positions more than the probability distributions.

As for Krauss's views on the possible beginnings of the universe, you will have to ask him how he reconciles it with the knowledge we have about QM.

You are espousing opinions that are very much interpretation dependent. Specifically, what you are claiming is very much like the Bohmian interpretation, which is fully deterministic but nonlocal.

At any rate, there is no evidence whatsoever that in the quantum world, any specific (previously unknown) measurement outcome can be predicted in advance. Regardless of the Schrodinger equation. So ultimately, you assuming that which you seek to prove.

As you are a long time member, I assume you have read some the dozens of recent discussions of determinism, interpretations, etc. which have previously been presented here. So I really don't follow what your point is. Regardless of what Krauss' opinion is (or his professional reputation), physicists' opinions tend to cover the spectrum on this subject.

 

[Pleonasm]

You are espousing opinions that are very much interpretation dependent. Specifically, what you are claiming is very much like the Bohmian interpretation, which is fully deterministic but nonlocal.

At any rate, there is no evidence whatsoever that in the quantum world, any specific (previously unknown) measurement outcome can be predicted in advance. Regardless of the Schrodinger equation. So ultimately, you assuming that which you seek to prove.

As you are a long time member, I assume you have read some the dozens of recent discussions of determinism, interpretations, etc. which have previously been presented here. So I really don't follow what your point is. Regardless of what Krauss' opinion is (or his professional reputation), physicists' opinions tend to cover the spectrum on this subject.

It is not interpretation dependent. I have read the litterature. "Main stream" interpretations of QM does not part with causality.

 

[DarMM]

The outcomes of experiments are not determined in standard textbook QM. It's that simple.

 

[A. Neumaier]

"Main stream" interpretations of QM do not part with causality.

Bohr and Heisenberg, and with them generations of physicists thought otherwise.

 

[Pleonasm]

Well yes you can determine the probabilities for the outcomes. Those outcomes still happen probabilistically not deterministically.

"Happen probabilistically"? What does that mean..? The probabilities arise from a deterministic evolution.

 

[Pleonasm]

Bohr and Heisenberg, and with them generations of physicists thought otherwise.

Because it is not classically conceived causality. But it is still causality. Things are caused from a source. I know the analogies from the textbook

 

[Nugatory]

This thread has reached the point of diminishing returns so it is closed.

As with all such closures, if there is something to say that has not already been said you may PM me or any other mentor and ask that it be reopened.