Physics Needs a Physical Theory of Observation by Chris Fields

I called the trace operation unphysical because it is something we do by fiat. I agree there is something going on, but we in effect "trace over it." It is rather similar to the problem of metric back reaction with Hawking radiation. This is something one imposes, using classicality of spacetime, which is suggestive of some quantum gravity process. In fact the problem of measurement in quantum mechanics and the problem of quantum black holes share some remarkable similarities.

I am not as heavily marinated in problems on the foundations of quantum physics as apparently you are, and certainly not as much as Chris Fuchs. I do find something odd about this. I maintain that quantum mechanics is as simple a physics as one could ever want. It involves state spaces that are linear, linear operators, basic vector space operations of diagonalization, eigenvalues and eigenvectors and so forth. Nature could not possibly be any simpler. The problem is not the quantum but the classical. The existence of a classical world is the big mystery. All of the strangeness about quantum mechanics stems from the fact we observe things from a classical perspective.

I think it comes down to the fact that quantum mechanics describes states that have a representation in configuration variables, but quantum states or Hilbert space has no explicit dependency upon them. As a result we make measurements, such as "the electron appeared here" according to such variables in a way that quantum mechanics is blind to, or at least blind to as we understand. We measure these according to classical systems or represent them according to classical information.

If one were to quantize the observer, which I think requires understanding how quantum mechanics "builds up" the classical world, this seems to me to get into the problem of self reference. A self referential physics, one where maybe quantum numbers are Godel numbers, strikes me as the last possible theory after all else has been exhausted. We may well be heading in this direction though, with what ever dragons might appear.

Cheers LC

Dear Lawrence,

"The existence of a classical world is the big mystery." Indeed.

It is an irony of history that physicists, with the notable exception of Helmholtz, never seem to have become very interested in the "measurement problems" of classical physics - the problems of how observers differentiate systems from their environments and of how they determine that multiple observations are observations of the same system. Had they been, the variations introduced by quantum theory might not have seemed so surprising or shocking.

As far as I know, the first experimental studies of the object identification problem were those of Burke, who showed in the 1950s that how an object moves in part determines whether humans see it as remaining the same object over time. The frame problem wasn't formulated as such until McCarthy and Hayes in 1969. Now, however, these questions are an industry - much larger than the foundations of physics! If you really want to understand how humans implement the trace operator, you use an fMRI machine, or study the cytology of Alzheimer's disease.

Self-reference enters into this as the question: how does an observer know that part of the observation is observation of a memory? How is this tag implemented? It seems obvious when you're looking at your instrument and looking at a logbook page. But it's less obvious when the memory is in your head.

So yes, it is the classical versions that are the really hard ones. When we understand how someone knows that her coffee cup is the same thing as it was 10 minutes ago - really understand it - we'll be making progress.

Cheers,

Chris

Hi Chris,

I really enjoyed reading your essay. I'll have to give it a second read to wrap my head around it, but the question of the meaning, import and ontology of systems is fascinating. What are your thoughts on Carlo Rovelli's relational quantum mechanics? I've been impressed by the clarity of his thinking on this issue - in a nutshell, that quantum physics is about what information one system has about another, and that such relations exhaust what we can say about the world. In any case, you've put forward some intriguing ideas.

If you have a moment to look at my essay, it may be of some interest to you. While very different, it focuses on a kind of radical frame-dependence that also invokes a relational view of systems, and of the boundary between observer and observed, which clearly is itself frame-dependent. I'd love to hear your thoughts.

Best,

Amanda

Chris,

An observer can include any classical information recording system. Consider a cosmic ray that interacts with the atmosphere, scatters and its muon decay product is caught in a piece of flint. The rock has a path of the muon recorded in it, and serves as a type of particle detector. The set of possible quantum amplitudes for the cosmic ray interaction and subsequent decays has been in part recorded by this rock. The rock is in some sense a "classical observer." Of course the human geologist looking at the rock under a microscope constitutes a conscious observer.

BTW, I have proposed that if a spacecraft were to land on the Jovian moon Europa that possibly high energy cosmic ray events could be studied in the hard ice of the moon. Cosmic ray tracks could be frozen in place and "log" some very high energy physics.

The classical world, in the large N limit S = Nħ in a path integral setting

Z[φ] = ∫δ[φ] e^{-iS[φ]}

has a wild set of oscillations. The e^{-iS[φ]} is interpreted in the Euclidean Wick rotated form as a real valued function that becomes very small, and thus the quantum fluctuations around a classical trajectory become insignificant. Of course this assumes there is a classical trajectory, which is some stable eigenvalue in the large N limit. This is a sort of argument, but it is not entirely satisfactory. In part we don't entirely understand path integrals, the euclideanization is a bit of a sleight of hand, and the existence of this large N stable eigenvalue = classical trajectory is not proven.

Actually my essay involves degrees of freedom fundamental in a physical system. An elementary particle, such as an electron, is just a projection of one particle state in different configuration variables. This is a brane holography result. So ultimately there is only one electron in the entire universe, but multiple projections of it. If this is correct it is ultimately what Feynman initially thought of with respect to the path integral.

The role of a brain or conscious beings such as ourselves makes the issue far more difficult. Of course we have a poor idea about how the brain generates this subjective experience we call consciousness. It is maybe at this point one is thinking about some self-referential foundation to reality. The piece of rock above, or a computer memory that places a detector click into a histogram bin, or the manual written notes of an experimenter are classical information. The brain acting to understand this; to have some awareness of this information at least subjectively appears different. How does one know that a conscious perception is real? We all have those moments of doubt, such as walking back into the house to really check you turned off the stove, even if you have some memory of it. Some people in fact go a bit dysfunctional over this.

Cheers LC

Dear Chris,

your approach is very interesting to me. The idea that even in a single-"particle"-experiment the degrees of freedom aren't what we assume to be is really new to me. In fact, to model a realistic information transfer of Qubits on has to define things in a classical manner: environment, measurement device and the object of measurement (and probably the final observer). From a classical point of view this seems to be easily feasible. But as you outlined in your essay from the view of QM it is non-trivial.

So, in my own essay i come to similar conclusions as you ("Treating such boundaries as "given" distorts physical theory: it renders our perspective special, turns the universe into a multiverse and makes time appear objective.").

This non-triviality may be one reason why Hawking stated that, for him, "many-worlds" are "trivially true". In my own essay i refute the MW-assumption in favour of a more non-trivial explanation: Namely that entanglement does render every measured system to be consistent with logic and our trivial understanding of physical causality. I differenciate between this causality and non-physical reassons because i think to have found a new explanation of QM that at least is isomorphic to some other attempts here at fqxi and because i also think that Wheeler's "utterly simple idea" could be that the very framework of physics - the causality-concept - does no more fully hold in the domain of QM. How it can be nonetheless, that we experience strong causal effects in our classical world is outlined in my essay.

I would be happy if you could take a look at it!

Best wishes,

Stefan

Dear Chris Fields,

I agree very much with the title of your essay. I did read what I could of your essay but I'm afraid it became very difficult for me to follow as I got further into it. It is an interesting subject and no doubt those with an adequate training in the background science and mathematics will get far more from it than I managed.

Good luck in the competition. Kind regards Georgina.

"Neither the prestige of your subject, and the power of your instruments, nor the extent of your erudition and the precision of your planning, can substitute for the originality of your approach and the keeness of your observation."(Hans Selye)

Dear Chris,

That's a very interesting essay! You brought light and focus to a subject that is often overlooked by physicist: the Hilbert space itself. What defines what is the Hilbert space of a system? How do we know what is the Hilbert space of the specified system? I think almost nobody asks these questions, but they are very important. I wouldn't say I agree with all your answers, however, the most important here is not giving the right answers, but asking the right question. This is questioning the foundations. You have shown that there many problems on a fundamental notion that are often overlooked.

I have also tried to answer some of these questions in a previous work of mine (aXiv: 1208.4474). I suggest you using the identity of the Hilbert space as a mathematical tool for understanding these notions. The many Hilbert space can all be identified by their associated identities, which are projectors. Knowing which is the Hilbert space means knowing which is the identity associated with it. I also suggest you visiting and rating my essay: The Final Theory and the Language of Physics , you might find it interesting...

Great work! Regards,

Frederico

Dear Chris Fields,

I'm sorry if my review sounded unkind, it was not meant so. It was unnecessarily honest. My lack of comprehension is not any reflection on the quality of the material you have presented. Your reply to Lawrence Sep. 28, 2012 @ 10:44 GMT is really interesting to me. I also think Lawrence's point about observer's not having to be human is important. I talk about the output generated by artificial devices and sensitive materials as well organisms. The most important feature in all cases is the function of a Reality Interface, that converts input data into an output that is distinct from the source of the data and the data itself. That is what I regard the classic space-time to be, an emergent output reality. That overcomes a lot of problems in physics.

Just noticed this in your biography. "His current research focuses on describing how humans identify systems across observations at the implementation level, and on building a realistic representation of observation into a physical formalism." That sounds fascinating. How physics and the output of observation are related has been an interest of mine for a number of years. It has been mostly a philosophical/problem solving inquiry rather than the sort of in depth practical work I am imagining you are engaged upon.

I have enjoyed seeing how evidence from the study of biology, such as presented by David Eagleman at the last FQXi conference, fits with the "Reality in Physics" framework.I would very much appreciate you opinion of the summary of that framework, used in my essay to answer the essay question. There is a high resolution version in my essay discussion thread which is the correct way around. Kind regards Georgina

If you do not understand why your rating dropped down. As I found ratings in the contest are calculated in the next way. Suppose your rating is [math]R_1 [/math] and [math]N_1 [/math] was the quantity of people which gave you ratings. Then you have [math]S_1=R_1 N_1 [/math] of points. After it anyone give you [math]dS [/math] of points so you have [math]S_2=S_1+ dS [/math] of points and [math]N_2=N_1+1 [/math] is the common quantity of the people which gave you ratings. At the same time you will have [math]S_2=R_2 N_2 [/math] of points. From here, if you want to be R2 > R1 there must be: [math]S_2/ N_2>S_1/ N_1 [/math] or [math] (S_1+ dS) / (N_1+1) >S_1/ N_1 [/math] or [math] dS >S_1/ N_1 =R_1[/math] In other words if you want to increase rating of anyone you must give him more points [math]dS [/math] then the participant`s rating [math]R_1 [/math] was at the moment you rated him. From here it is seen that in the contest are special rules for ratings. And from here there are misunderstanding of some participants what is happened with their ratings. Moreover since community ratings are hided some participants do not sure how increase ratings of others and gives them maximum 10 points. But in the case the scale from 1 to 10 of points do not work, and some essays are overestimated and some essays are drop down. In my opinion it is a bad problem with this Contest rating process. I hope the FQXI community will change the rating process.

Sergey Fedosin

Dear Georgina,

Thanks for your comments; please see mine on your essay.

Thinking about physics from a more biological viewpoint may indeed be useful. We as observers are in the position of individual neurons trying to figure out what the brain they are part of is doing. The brain is thinking about something or other, but all the neurons see are superimposed patterns of local excitation. What kinds of theories can such neurons build?

Cheers,

Chris

Dear Chris Fields,

In Coherently-cyclic cluster-matter paradigm of universe, as the source and observer are two independent systems, the emergence of time is expressional with two series of events by eigen-rotational quanta, in that a third series of reference time is imperative for both series. With this framework we may develop a physical theory of observation.

With best wishes

Jayakar