Schrodinger's Cat and The Universe

[1977ub]

The cat waits by the mouse hole until it comes out, pounces on it, injures it, plays with it for a while, then kills it, brings it to your front door, then eats it. If two cats become entangled, it was probably proceeded by arched backs, bristled fur and hisses, not because some creature decayed into two cats or the cats are near absolute zero temperatures. A cat is way more like a human than a particle.

A cat or a human is made of particles ... in physics terms is there any evidence that an animal is more than the sum of its parts?

 

[PeroK]

A cat or a human is made of particles ... in physics terms is there any evidence that an animal is more than the sum of its parts?

Yes and no. At some indeterminate point systems of particles no longer show quantum properties directly, but have classical characteristics. For example, electrons are truly indistinguishable; whereas red snooker balls are only practically indistinguishable.

The cat has a huge number of degrees of freedom that "wash out" the quantum properties of its particles.

Where this split between quantum and classical takes place is not well defined and is essentially part of the measurement problem.

 

[Michael Price]

Yes and no. At some indeterminate point systems of particles no longer show quantum properties directly, but have classical characteristics. For example, electrons are truly indistinguishable; whereas red snooker balls are only practically indistinguishable.

The cat has a huge number of degrees of freedom that "wash out" the quantum properties of its particles.

Where this split between quantum and classical takes place is not well defined and is essentially part of the measurement problem.

Decoherence defines how this split manifests itself and is not mysterious any more. We have different interpretations of how the measurements get into our brains, but the classical-quantum split is not mysterious. The "washing out" is a quantifiable process, with the aid of decoherence lengths and times.
https://en.m.wikipedia.org/wiki/Quantum_decoherence

 

[GlenLaRocca]

Funny you should ask. As an animal that is a sum of its parts. As Decarte would say "you ask therefore you are more than the sum of your parts".

I think all of the "magic" happens with 1) a hierarchy 2) simple things get complex 3) computation is easy to implement in nature.

All those particles play particle games making atoms. All those atoms play atoms games making molecules. All off those molecules play small and large molecule games. Large molecules make building blocks for life. We have things like membranes, then cell organelles., then cells, …. They each play with each other with rules that apply to entities at their level.

The next two things are related, its just the math. Consider he study of all things exactly the same. That should be the easiest thing there is. we ignore all differences between them. The study of the unit. What can you do with units. You can count them, add them, ask if you can equally distribute them. You get number theory in a hurry. The simple processes that lead to the Mandelbrot and Julia sets show how complexity can emerge from simplicity.

Finally the computer thing. Automata theory shows that you can form a general purpose computer in very simple ways

Finally, I think, therefore I am able to sum my particles at 10^26 or so.

A cat or a human is made of particles ... in physics terms is there any evidence that an animal is more than the sum of its parts?

 

[vanhees71]

A cat or a human is made of particles ... in physics terms is there any evidence that an animal is more than the sum of its parts?

Well, even a stone (in physics language any many-body system of interacting elementary quanta) is way more than the sum of its parts.

 

[Elias1960]

Wouldn't it make more sense to accept QM on it's face without interpretations?

This was what has been the mainstream position. It is named "shut up and calculate" or "minimal interpretation".

In itself, the minimal interpretation is quite useful for all those not interested in speculations about interpretations. It allowed them to do exactly that - to calculate predictions of QM for all the various experiments, without having to be afraid that the result would depend on all those highly speculative claims made by various interpretations.

To restrict oneself to computations and to ignore interpretational discussions was a quite reasonable decision in the past, when there were a lot of things not yet computed, a lot of new, unexpected quantum effects waiting for discovery. But "shut up and calculate" was more, it was not simply a reasonable decision made by many researchers, but a sort of command not to discuss interpretations at all, obligatory for all. A command which has essentially stopped the development of interpretations of quantum theory. Here, the baby was thrown out with the bathwater. As a consequence, all the interpretations discussed today were developed by research groups consisting of at most 1 person (usually with that person working only part-time on that interpretation). This changed only as a long-term consequence of Bell's theorem (with Bell being at that time de facto the only supporter of Bohmian mechanics).

Fortunately, for quantum theory, this period is over now, with this subforum being part of the evidence. Unfortunately, it is not yet over for relativity, questioning the spacetime interpretation with other interpretations of SR or GR, say, the Lorentz ether, remains forbidden yet. Probably we have to wait another 30 years of failure of quantum gravity based on the spacetime interpretation until this will be allowed. (The optimistic variant would be that discussion about the viability of realistic quantum interpretations in the relativistic domain will be allowed here, and they automatically lead to a discussion about the viability of interpretations of relativity with preferred coordinates/frames.)

Wouldn't it be easier to accept QM as universal and we're just a subsystem of some larger system in thermal equilibrium therefore whatever happens in our subsystem isn't objective? If you accept QM as universal do you really need interpretations?

To accept QM as universal already is an interpretation. Or at least an essential and nontrivial part of it.

In particular, if QM is universal, one would plausibly have to accept that there has to be a universal wave function, or a wave function of the universe, not? Given that this object cannot be known by anybody except God, this wave function would have to be part of the objective, observer-independent reality, not? Anyway, this object is not part of the minimal interpretation, where the wave function is defined as a state of a subsystem of the universe prepared by some measurement external to the subsystem.

 

[EPR]

Every physical theory must have an interpretation and ontology. Or refer to reality - the established reality. So far qt does not conform to an ontology and it's obvious that we are missing something fundamental in our understanding of how the world works. But one day it will have an ontology.

 

[vanhees71]

Every physical theory must have a minimal interpretation in the sense that it allows to describe in sufficient detail what we objectively observe (i.e., measure) in nature. The ontology is provided by what's observable. Everything else is metaphysics and nice to have for some people but irrelevant for science.

 

[EPR]

No doubt. Everything is okay in the physics of today as long as physicists do not insist on having realism in the physics sense in the micro scale. Everything checks out. Every theory and practice works flawlessly. Some are bothered, some not so much. Yet curiosity is screaming

 

[Elias1960]

Everything else is metaphysics and nice to have for some people but irrelevant for science.

No, interpretations are relevant for science.

Of course, given that they make the same empirical predictions, they seem irrelevant for the actual physical predictions of the theory which is interpreted. But, sorry, this is only one particular theory, and in no way the final truth. (The claim that that theory is the final truth would be only a particular interpretation.)

So, as long as we do not have a theory of everything which satisfies at least the mainstream of physics as the final ultimate truth, the search for theories beyond the theory under consideration is an essential part of science.

Searching for such theories has always the problem that it needs guiding principles, non-trivial hypotheses, and the requirement that these hypotheses should be compatible with the existing empirical evidence does in no way allow to identify them. So, the choice of these hypotheses is necessarily a guess, and different guesses define different research programs for the more fundamental theory.

But for each such guess, there is the obvious requirement of compatibility with the established theory. So, we have, as a natural part of every research program for a more fundamental theory, the question if some particular set of general principles is compatible with the existing established theory. And a positive answer for a particular research program - that means, a proof that a particular set of general principles is compatible with the established theory - is nothing but an interpretation of that theory.

In other words, interpretations can be understood as research programs for a more fundamental theory, and are, in some sense, a necessary part of such a research program, and therefore also a legitimate part of science.

 

[bhobba]

But "shut up and calculate" was more, it was not simply a reasonable decision made by many researchers, but a sort of command not to discuss interpretations at all, obligatory for all. A command which has essentially stopped the development of interpretations of quantum theory. Here, the baby was thrown out with the bathwater.

That is wrong. Its was simply a free choice. Some didn't worry about it, some did. Its exactly the same situation now. It gets discussed a lot on forums like this, but its more of a backwater for professional physicists. I have been reading lately a number of papers by philosophers/historians of physics on QM. They can't agree on anything - even something as fundamental as did Einstein understand Bohr's ideas such as complementary, or even what it is, but do be fair I don't understand it either. According to Pais, Einstein did understand his good friend quite well, and he wrote THE book on Einstein, Subtle Is The Lord, so I am with him. But others disagree. The reason it is a backwater is physicists like actually making progress, not endless debate not really going anywhere. But to each to his/her own. And while not an area with a lot of active researchers, many physicists have dabbled in it - but usually as a sideline and often not for long.

Thanks
Bill

 

[A. Neumaier]

Every physical theory must have a minimal interpretation in the sense that it allows to describe in sufficient detail what we objectively observe (i.e., measure) in nature. The ontology is provided by what's observable. Everything else is metaphysics and nice to have for some people but irrelevant for science.

Thus in your minimal interpretation, most of the interior of the Earth is metaphysical since we can observe it only very coarsely!?

 

[A. Neumaier]

But "shut up and calculate" was [...] a command which has essentially stopped the development of interpretations of quantum theory.

A command issued in 1989, at a time when the development of interpretations of quantum theory had already evolved tremendously into quite a number of distinct species, and nothing stopped it from blossoming further.

 

[mattt]

Actually, what we "observe", and really, everything that we experience, is just (apparently) different states of our own nervous system. Anything different than that, that we say about it, it's just inference and convenience.

 

[bhobba]

A command issued in 1989, at a time when the development of interpretations of quantum theory had already evolved tremendously into quite a number of distinct species, and nothing stopped it from blossoming further.

Usually attributed to Feynman or sometimes Dirac - but of course, as you correctly point out, it was actually Mermin. To be honest I do not think anyone heeded it - they simply researched what they wanted to anyway.

Thanks
Bill

 

[DarMM]

Just to be clear Mermin wasn't commanding anybody. He was saying that the Copenhagen Interpretation seemed to him to say "Shut up and calculate", which he didn't like.

However later he considered that summary of Copenhagen to be unfair and simplisitic.

 

[vanhees71]

Thus in your minimal interpretation, most of the interior of the Earth is metaphysical since we can observe it only very coarsely!?

This is of course also nonsense. The interior of the Earth is not metaphysical since it's observable in principle. You can just drill a hole, though it's pretty difficult the deeper you want to get.

What I consider metaphysical are using notions like "realistic" in the sense of some philosophers if it was something beyond what's observable (at least in principle). The same holds for "consciousness" and "free will", which are all subjective emotions but not subject of clearly defined scientifically accessible phenomena. That doesn't meant that they are not important, but they are simply not the subject of objective science. It can even be pretty dangerous to take such notions as scientific and then claim, e.g., by using some MRI you can "prove" that there's no "free will"...

 

[PeterDonis]

The same holds for "consciousness" and "free will", which are all subjective emotions but not subject of clearly defined scientifically accessible phenomena.

Really? Your posts here are not scientifically accessible evidence that you are conscious and freely chose to post them?

 

[A. Neumaier]

This is of course also nonsense. The interior of the Earth is not metaphysical since it's observable in principle. You can just drill a hole, though it's pretty difficult the deeper you want to get.

And the interior of the sun? Or that of a black hole inside its horizon?

 

[Elias1960]

A command issued in 1989, at a time when the development of interpretations of quantum theory had already evolved tremendously into quite a number of distinct species, and nothing stopped it from blossoming further.

No, that command was given much earlier, it was the rejection of Bohmian mechanics on quite superficial grounds. Recommended reading about this:

Freire, O. (2005) Science and exile: David Bohm, the hot times of the Cold War, and his struggle for a new interpretation of quantum mechanics. Historical Studies on the Physical and Biological Sciences 36(1), 1-34, arXiv:physics/0508184

Mermin naming this "shut up and calculate" was already a satirical attack against it, at a time when the discussion about Bell's inequalities already showed that the ban against discussing interpretations is artificial and hampering the development of physics.

That is wrong. Its was simply a free choice. Some didn't worry about it, some did. Its exactly the same situation now. It gets discussed a lot on forums like this, but its more of a backwater for professional physicists.

In modern professional physics with physicists living from grant to grant in a publish or perish environment, there is no longer any free choice. To survive, you have to work in a direction that gets many grants, has many journals, conferences and so on, independent of the scientific value of all this. Freedom of choice is restricted to those who have a permanent position and don't have to care about getting grants for their own university.

I don't remember where I have read the anecdote that Aspect has asked Bell if he recommends him to start doing such experiments. Bell asked him first if he has a permanent position. Only after Aspect said that he has one, Bell gave a positive answer.

The reason it is a backwater is physicists like actually making progress, not endless debate not really going anywhere. But to each to his/her own. And while not an area with a lot of active researchers, many physicists have dabbled in it - but usually as a sideline and often not for long.

Since the creation of the SM, the other parts of fundamental physics beyond the SM have not made any progress too. The fundamental research has, last but not least, given Bell's theorem with all that followed. Bell was at that time essentially the only proponent of dBB theory. Compare with the number of string theory researchers and what they have given to physics (not mathematics).

Doing research with zero financial support in the free time, as a sideline and not for long, is the natural reaction of physicists. They do what they think is interesting as far as they can afford it.

 

[vanhees71]

Really? Your posts here are not scientifically accessible evidence that you are conscious and freely chose to post them?

Well, my posts are evidence that I communicate with you, and as far as my subjective feeling goes, I do this freely.

On the other hand, couldn't my postings also come from some algorithm? Does then the computer have consciousness and free will?

 

[vanhees71]

And the interior of the sun? Or that of a black hole inside its horizon?

The interior of the Sun as well as that of Earth is of course also accessible by observations of waves of their surface (seismology, astero seismology):

https://en.wikipedia.org/wiki/Seismology#Mapping_the_earth's_interior
https://en.wikipedia.org/wiki/Asteroseismology

Of course, here we also use models, based on general physical laws to draw conclusions about the interior of the Earth and the Sun.

The question about the black holw inside its horizon is of course more tricky. In one sense its unobservable, i.e., we cannot say anything about what's going on beyond the event horizon as outside observers we only can observe the behavior of matter and radiation falling into the black hole, but then all its properties are just subsumed into the fundamental properties of the singularity, i.e., total energy or mass, electric charge, and angular momentum of the black hole. On the other hand in principle we could just "dive" beyond the event horizon (despite the fact that maybe we'd get destroyed due to the large tidal forces) and look what is there. The only trouble is we couldn't communicate it outside and write a paper or adventure book about our journey ;-)). Whether you can consider it as accessible to the scientific method or not is not so clear.

 

[PeterDonis]

couldn't my postings also come from some algorithm?

Only if there is some algorithm that can pass the Turing test.

Does then the computer have consciousness and free will?

If its behavior was indistinguishable from that of a human (and a human with expertise in science at that, if we're talking about posts here on PF), then that would be the natural inference, yes.

 

[DarMM]

Wait is vanhees realism being debated here?

I assert priority when the Nobel committee come around.

 

[vanhees71]

I guess, with this topic you have some chances for a literature Nobel ;-)).

 

[A. Neumaier]

The interior of the Sun as well as that of Earth is of course also accessible by observations of waves of their surface (seismology, astero seismology):

But only very summarily, based on simplified models. Measurability is always very limited compared to what is assumed in the associated physical models. Thus one cannot equate physical reality with measurability.

 

[vanhees71]

It's typical that one can only say what "physical reality" is not, but there seems to be no clear definition of it. If it's not the sum of (at least in principle possible) objective observations of phenomena, what is it then? Some ideal idea a la Plato, which we can never really grasp?

 

[A. Neumaier]

It's typical that one can only say what "physical reality" is not, but there seems to be no clear definition of it. If it's not the sum of (at least in principle possible) objective observations of phenomena, what is it then? Some ideal idea a la Plato, which we can never really grasp?

Even though I cannot specify clearly what "physical reality" is, it is clear to me that physics is supposed to
describe what happens in Nature everywhere, not only where it can be measured. Otherwise it would be impossible to base successful technology on advances in physical understanding.

 

[vanhees71]

To develop successful technology it's sufficient to successfully describe what's observable, and that's what science is all about. It's the strength (and maybe at the same time the weakness) of the scientific method to describe and only describe what can be subject to empirical investigation. As far as we know today, QT describe what happens in Nature everywhere as far as we can observe it.

 

[Emelda]

It isn't. Schrodinger created the cat in a box thing to show how silly such a concept IS, NOT to show that that's actually how it is. Pop-science has been misrepresenting it ever since.

You could tell by the box.. a live cat in a box would cause box oscillation