On Friday, March 1, 2019 at 8:53:00 AM UTC-6, Bruno Marchal wrote:
>
>
> On 1 Mar 2019, at 09:20, Philip Thrift <cloud...@gmail.com <javascript:>>
> wrote:
>
>
>
> On Thursday, February 28, 2019 at 6:42:07 PM UTC-6, Lawrence Crowell wrote:
>>
>>
>>
>> On Monday, February 25, 2019 at 9:42:01 AM UTC-6, Bruno Marchal wrote:
>>>
>>>
>>> On 25 Feb 2019, at 12:39, Lawrence Crowell <goldenfield...@gmail.com>
>>> wrote:
>>>
>>> On Monday, February 25, 2019 at 2:44:14 AM UTC-6, Bruno Marchal wrote:
>>>>
>>>>
>>>> On 24 Feb 2019, at 15:24, Lawrence Crowell <goldenfield...@gmail.com>
>>>> wrote:
>>>>
>>>> On Friday, February 22, 2019 at 3:18:01 PM UTC-6, Brent wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2/22/2019 11:39 AM, Lawrence Crowell wrote:
>>>>>
>>>>> This sounds almost tautological. I have not read Masanes' paper, but
>>>>> he seems to be saying the Born rule is a matter of pure logic. In some
>>>>> ways
>>>>> that is what Born said.
>>>>>
>>>>> The Born rule is not hard to understand. If you have a state space
>>>>> with vectors |u_i> then a quantum state can be written as sum_ic_i|u_i>.
>>>>> For an observable O with eigenvectors o_i the expectation values for that
>>>>> observable is
>>>>>
>>>>> sum_{ij}<u_j|O|u_i> = sum_{ij}<u_j|o_i|u_i> = sum_ip_io_i.
>>>>>
>>>>> So the expectations of each eigenvalue is multiple of the probability
>>>>> for the system to be found in that state. It is not hard to understand,
>>>>> but
>>>>> the problem is there is no general theorem and proof that the eigenvalues
>>>>> of an operator or observable are diagonal in the probabilities.
>>>>>
>>>>>
>>>> I am not sure I understand this.
>>>>
>>>>
>>>>
>>>>
>>>> In fact this has some subtle issues with degeneracies.
>>>>>
>>>>>
>>>>> Doesn't Gleason's theorem show that there is no other consistent way
>>>>> to assign probabilities to subspaces of a Hilbert space?
>>>>>
>>>>> Brent
>>>>>
>>>>
>>>> It is close. Gleason's theorem tells us that probabilities are a
>>>> consequence of certain measurements. So for a basis Q = {q_n} then in a
>>>> span in Q = P{q_n}, for P a projection operator that a measure μ(Q} is
>>>> given by a trace over projection operators. This is close, but it does not
>>>> address the issue of eigenvalues of an operator or observable. Gleason
>>>> tried to make this work for operators, but was ultimately not able to.
>>>>
>>>>
>>>> It should work for the projection operator, that this is the
>>>> yes-no-experiment, but that extends to the other measurement, by reducing
>>>> (as usual) the question “what is the value of A” into the (many) question
>>>> “does A measurement belong to this interval” … Gleason’s theorem assures
>>>> that the measure is unique (on the subspaces of H with dim bigger or equal
>>>> to 3), so the Born rule should be determined, at least in non degenerate
>>>> case (but also in the degenerate case when the degeneracy is due to
>>>> tracing
>>>> out a subsystem from a bigger system. I will verify later as my mind
>>>> belongs more to the combinator and applicative algebra that QM for now.
>>>>
>>>>
>>>>
>>>>
>>>> Many years ago I had an idea that since the trace of a density matrix
>>>> may be thought of as constructed from projection operators with tr(ρ_n) =
>>>> sum_n |c_n|^2P_n, that observables that commute with the density matrix
>>>> might have a derived Born rule following Gleason. Further, maybe operators
>>>> that do not commute then have some dual property that still upholds Born
>>>> rule. I was not able to make this work.
>>>>
>>>>
>>>> I will think about this. Normally the measure is determine by the
>>>> “right" quantum logic, and the right quantum logic is determined by the
>>>> any
>>>> “provability” box accompanied by consistency condition (like []p & p, []p
>>>> &
>>>> <>t, …). The main difference to be expected, is that eventually we get a
>>>> “quantum credibility measure”, not really a probability. It is like
>>>> probability, except that credibility is between 0 and infinity (not 0 and
>>>> 1).
>>>>
>>>> Bruno
>>>>
>>>>
>>> I think I ran into the issue of why Gleason's theorem does not capture
>>> the Born rule. Not all operators are commutative with the density matrix.
>>> So if you construct the diagonal of the density matrix, or its trace
>>> elements, with projector operators and off diagonal elements with left and
>>> right acting projectors (left acting hit bra vectors and right acting hit
>>> ket vectors) the problem is many operators are non-commutative. In
>>> particular the usual situation is for the Hamiltonian to have nontrivial
>>> commutation with the density matrix.
>>>
>>>
>>>
>>> It seems to me that Gleason theorem takes this into account. It only
>>> means that the probabilities does not make the same partition of the
>>> multiverse, but that is not a problem for someone who use physics to see if
>>> it confirms or refute the “observable” available to the universal
>>> numbers/machines in arithmetic.
>>>
>>
>> Gleason's theorem applies for just one set of commuting operators, and in
>> particular those that commute with the density matrix. The Born rule holds
>> for all operators, and especially the Hamiltonian that does not commute
>> with the density matrix.
>>
>>
>>>
>>> I am not completely sure. You raise a doubt, and I’m afraid it will take
>>> some time I come back to Gleason theorem. But I appreciate. My conversation
>>> with Bruce and Brent makes me think that the notion of multiverse is far
>>> from clear. At least with mechanism things are crystal clear! There is only
>>> the sigma_1 sentences, and the nuances imposed by incompleteness for the
>>> “Löbian number” who “lives” through them (them for the sigma_sentences,
>>> which “realises” the computations).
>>>
>>
>> I would not confuse the multiverse with this. There are several levels of
>> multioverse. The first is just the world beyond what we can ever observe
>> due to the cosmic horizon. The second is the vacuum pocket worlds in an
>> inflationary de Sitter spacetime. A third may be how these are connected to
>> anti-de Sitter spacetimes and how the landscape or swampland is generated.
>> The fourth is the idea that many worlds interpretation is the grand or
>> ultimate many worlds. This last one I would not take that seriously. Many
>> worlds interpretation, as with all interpretations, is an addition to
>> quantum mechanics that is less about physics and more about metaphysics.
>>
>>
>>>
>>> Of course I come from the other side, but if mechanism is correct, I can
>>> only cross physics when and where physics is correct. For now, physics is
>>> not yet a solved problem, as GR does not fit with QM. The very notion of
>>> “force” or “interaction” seems conceptually very different in GR and QM. We
>>> can expect surprise, but with Mechanism, the quantum weirdness is welcomed,
>>> and we are far from having any notion of physical space, and why 3D or 11D
>>> or 26D. Mechanism is a 0 dimension theory of the mind, à la Plato, where
>>> the ideas are the numbers i, and the partial recursive function phi_i, and
>>> the operator phi_phi_i, etc.
>>>
>>
>> Spacetime is likely emergent from quantum entanglements. Quantum
>> entanglements are entirely nonlocal, so it seems strange that something
>> that is local should be so defined. However the Einstein field equation
>> R_{ab} - 1/2Rg_{ab} = T_{ab} has a curious duality about it. It says that
>> high energy quantum gravity on the left is equal to low energy ordinary
>> quantum fields. Further, the T_{ab} is for local quantum fields and these
>> are dual to nonlocal physics as gravitation in the spacetime bulk.
>>
>> LC
>>
>>
>>>
>>> Space, like in Kant, is a universal pattern of the universal machine,
>>> although this is not yet proved, only suspected, as it could still be that
>>> even space is “geographical” and that consciousness can survive without it.
>>> Well, the theology of the numbers is in its infancy, if not still an
>>> embryo: but the propositional parts is given by the two arithmetical
>>> completeness theorem of Solovay, leading to G and G* describing all what
>>> can be said on this. G gives the part that all sound machine can justify,
>>> and G* gives the true, but non justifiable part. In between the rational
>>> and the irrational there is a “surrational part”: what science can learn
>>> from experience but never rationally justify.
>>>
>>> Bruno
>>>
>>>
>>>
>
>
>
> Reading all the above in the context of
>
> *Naturalness and Emergence*
> David Wallace
> February 20, 2019
> http://philsci-archive.pitt.edu/15757/1/naturalness_emergence.pdf
>
> leads to the conclusion that *our current language(s) of physics is(are)
> most likely wrong.*
>
>
>
> A proposition can be wrong. I am not sure what you or Wallace would mean
> by a language being wrong. Perhaps Wallace meant that our metaphysics (most
> of the time the materialist one) is wrong, which makes more sense. Perhaps
> he does not dare to say so. It is not well seen in some circles.
>
> Bruno
>
>
>
>
By 'language' in the above paper he means 'mathematical language' and he
means precisely the language in which QFT an GR are actually written in
(seen when you look at them on paper or on a screen): Sentences are made of
mathematical symbols and variables, but the basics begin with a selection
of sentences (axioms) from which a theory is made. So he is really saying
the axioms are likely wrong, and even new primitives (mathematical symbols)
may have to be invented.
- pt
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