Not the photon is in both arms, but its wave-function. In Bohr's philosophy there is no photon, until it is measured. But I prefer the David Bohm's interpretation, see file paperBell7.pdf in my publications.

Thank You very much, Remi. Quote arXiv:0808.3316: "the speed of this spooky influence would have to exceed that of light by at least 4 orders of magnitude." Me: suppose the experimentalists arrived not at v > 10^4 c, but there is a typing mistake and they meant v < 10^4 c for spooky action. Such a disaster for David Bohm! It turns out, that his "interpretation of QM" is in fact very well refutable. Thus, it is not something stupid the Bohm did. Bye!

Dear all,

"The problem of spooky action at a distance" is we look to the problem from our space time which is only real space time. The relation between elementary particles and classical observers is not a real relation. Its a complex relation as can be noted from the complexity of wave function and from uncertainty principle that makes any real transformations of time and position between classical observers and quantum particles a forbidden one. There is a new theory that manipulated this in the following paper 

https://www.researchgate.net/publication/259996539_Solving_the_instantaneous_response_paradox_of_entangled_particles_using_the_time_of_events_theory

This theory assume a dynamic space time that leads to such complex relation. if the complex relation is found between the quantum particles and classical observers then any action that appeared to be spooky from our sight it's indeed happened locally from the frame of the quantum particles.

Article Solving the instantaneous response paradox of entangled part...

I am not really good at this, but if I recall it properly, your question is similar (in a way) to something which was attempted by Wheeler and Feynman way back in 1945 in the following paper:

http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.17.157 

Dmitri do you mean that the photon is passing tru the left arm in this case i have proposed.

And does the wavefunction has a separate physical existence since passing tru both arms

Dear Remi

Its not easy to knock out the time, because its the origin of all the mysteries in physics. Even if we consider the mass as the real source of all the noted time dilation and length contraction. But time is still playing the major rule indeed. Because everything in the universe is moving and nothing is stationary, so there is no absolute stationary frame. Even the stationary observer assumed in special theory of relativity is indeed a moving one in practice. 

Hi, Actually if the two different states of the above quantum system are equally likely to be observed (for example existence of photon in left or right arm) then an act of measurement will show it in one of the states. The act of measurement realizes the position but it does not infer where the photon was before it was measured. Before it the photon was measured it was in both the arms.

You cannot confuse the act of measurement with the existence of multiple states and probabilistic envelope. The act of measurement realizes the observable into one unique measurement but it does not disallow the existence of system to be in multiple co-existing states. A single observation in a unique state does not imply determinism.

In you above setup if you push many photons one by one through the MZI and have a counter for photons coming from left hand and right hand then you will roughly count them as equal. This means the result and the internal state is not deterministic but the act of observation determines it into one of the states.

Remi that's nice 

but it will be more effective if you assume a dynamic ether instead of stationary one.

its a suggestion

regards

In order to infer something that happens now with possible consequences in the past, we need a realistic temporal theory that unfortunately goes beyond traditional quantum mechanics.

The present discussions in quantum interferometry, however interesting and fruitful lacks spatio-temporal "reality" and needs a rigorous treatment in the framework of general relativity.

Remi 

the problem is ether itself is not stationary, its moving in conjunction  with universe expansion. It could be stationary if the universe does not expand, but its actually keep expanding.

Are You sure in space and time, Remi?

One radical viewpoint about it and Aether: My paper without any assumption, using existing equation with a scenario of continuum of observers shows that there a problem with conservation of relativistic energy and momentum. Furthermore if any interaction needs to take place by converting potential energy to kinetic energy then the potential energy should also have momentum. It also shows that we can derive infinite linearly independent conservation equations. This also implies that normal day phenomena like elastic collision will not take place unless somehow space-time compensates for the deficit in the infinite conservation equations. https://www.researchgate.net/publication/265643349_Problem_in_the_relativistic_energy_and_momentum_conservation

Does it by any chance proves existence of Aether?

P.S.

-----------------------------------------------------------------

Robert B. Laughlin, Nobel Laureate in Physics, endowed chair in physics, Stanford University, had this to say about ether in contemporary theoretical physics:

It is ironic that Einstein's most creative work, the general theory of relativity, should boil down to conceptualizing space as a medium when his original premise [in special relativity] was that no such medium existed [..] The word 'ether' has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum. . . . Relativity actually says nothing about the existence or nonexistence of matter pervading the universe, only that any such matter must have relativistic symmetry. [..] It turns out that such matter exists. About the time relativity was becoming accepted, studies of radioactivity began showing that the empty vacuum of space had spectroscopic structure similar to that of ordinary quantum solids and fluids. Subsequent studies with large particle accelerators have now led us to understand that space is more like a piece of window glass than ideal Newtonian emptiness. It is filled with 'stuff' that is normally transparent but can be made visible by hitting it sufficiently hard to knock out a part. The modern concept of the vacuum of space, confirmed every day by experiment, is a relativistic ether. But we do not call it this because it is taboo.

-----------------------------------------------------------------

Article Problem in the relativistic energy and momentum conservation

I added a new question for the above response: https://www.researchgate.net/post/Does_this_paper_in_anyway_prove_existence_of_Aether

Hi Shalender

in a previous post you said

"Before it the photon was measured it was in both arms." Suppose the two arms of MZI are in opposite directions and the measurement takes place when the 'left part' of the photon is at the end of Universe. Then 'its part' in the other arm must receive a hyperluminal immidiate signal and vanish without any trace.

Why not ascribe a physical meaning to the wavefunction (WF) -- very different from the physical meaning of the particles indeed!!! (Such step has anology in physics -- the field form of matter (photons) which was introduced centuries after ordinary matter (atoms)) but is well accepted now.

So then the photon is in one arm and the WF (or somethig which WF describes!!) is in both arms. WF can interract only with its own photon (particle). When we measure the photon the WF does not vanish but its connection with the particle is lost (something analogues to disentanglement). When we try to measure WF (in the empty arm) also its connection with the photon is broken.

If we bring WF and its photon in contact (as in ordinary MZI with a second beamsplitter) it will interract as well known with the photon.

Note that we can even change WF with phase plates etc.

So I beleive WF describes something real but different from current notion of matter (atoms and fields). If we accept that - all paradoxes in QM disapear.

Postscript: A rather speculative guess of mine is that WF might be somehow connected with dark matter.

Dear Remi,

Traditional QM is unfortunately not better here, since time is only treated as a parameter without an interpretation of any realistic time evolutions. True that a stationary state can be trivially propagated by en evolution operator, but extra assumptions are needed to get relevant lifetimes from e.g. the Fermi Golden rule and then finding the associated decay laws.

Whenever we ask a boolean question in quantum mechanics, we have to be careful about what exactly we are asking. A yes/no question is associated with a projector and its orthogonal complement on the Hilbert space. Now, consider combining two such questions, i.e. is the conjunction A and B true or false? The problem that arises here is that A and B are projectors that may not commute, so A and B (which corresponds to the product of the projectors AB) is different from B and A (which corresponds to the product of the projectors BA), that is AB != BA. This is a striking difference between boolean logic (in which A and B = B and A) and the so-called quantum logic. So, combining questions in QM may give rise to these kinds of issues, and these are at the roots of absolutely all paradoxes. 

An approach that solves this issue a bit brutally is the "decoherent histories" or "consistent histories" interpretation of quantum mechanics, http://en.wikipedia.org/wiki/Consistent_histories ,introduced by Griffiths and Omnes, which basically considers the types of questions above "meaningless", i.e. it makes no sense of asking them because there is no projector in the Hilbert space that corresponds to the question being asked. See also http://quantum.phys.cmu.edu/CHS/histories.html for more details and a now free book by one of the original authors, in which your question has a very detailed explanation (there is a chapters about interferometers etc).

Your case is of this kind, the question itself (although seems OK in our boolean and classical way of thinking), does not make sense in quantum mechanics, so apparently you have a paradox. But again, if you try to formalize it mathematically (as a series of question asked at different times), you will realize that you end up with what is called a "in-consistent history", so the question you are asking is in fact meaningless. It gives rise to the same type of paradox as the double slit experiment etc.

Vlad Gheorghiu> What you are saying is correct. Shor prime factorization in polynomial time algorithm has used the very nature of multi-quantum path for Period-finding subroutine. One can analyze that algorithm backwards from the output and deduce similar Boolean logic paradoxes. A QM system co-exists in all states but only one state of them is observed as a observable.

Another Boolean paradox can be deduced if we observe the system at a in-between time and the final time. At a in-between time we may observe the system in a different path and at the final the observance may be on another path, which are completely separated in space. This is because even though we observed the system on a certain path in-between, it also had non-zero finite weight (probability) to be on the other path.

Dear Vlad

I dont understant what does not commute here. I am doing one measurent A and not two. Even if i am assumed tacitly to ask where is the photon before the measurement am not asking it then in

@Ilian, you are asking more than one question (at difference sequences in time), and you model this as a tensor product of projectors. These sequences of projectors do not commute. You may take a look at the link of the book I wrote you about, it is in my opinion one of the best introduction to the Consistent History formalism.

Dear all,

Here are some comments to the "past" discussion.

1. It is our rulers and clocks that materially change, not the space!

"Rulers" and "clocks" are material objects and such objects are physically perceived in terms of energy and momentum (variables or operators).

2. Space and time is ideal, platonic, immutable, the background. The thing that affects our measurements is an ether that resides in space and time (3 + 1).

Space and time are conjugate variables (operators), that forms the perception. A relevant physical description must treat both variables (operators) and their conjugates in a consistent fashion. GR does that although in a somewhat limited fashion, since QM is not yet considered to be correctly incorporated.

Changes in momentum-energy should be automatically commensurate with corresponding changes in space time. Alterations in one and not the other is wrong and inconsistent. This conclusion is not dependent on any additional concepts like an ether.

The paradox arises in the (usual) predictive formalism of quantum mechanics in which the state is assumed to be determined by the preparation procedure.  In the retrodictive formalism (see e.g. D.T. Pegg and S.M. Barnett, J. Opt. B: Quantum Semiclass. Opt. vol.1 pp 442-445 (1999), D.T. Pegg, Foundations of Physics, vol. 38, 648-658. (2008)) the state is determined by the measurement.  It is easy to show that both both formalisms predict the same experimental results.  In this case there is a paradox in the predictive formalism but none in the retrodictive formalism.  It is not that a future measurement changes the past, the future measurement determines the past.  As there is no way that this effect can be used to send a message into the past or even faster than light there is no difficulty with causality.

Your question is equivalent to the question asked by Weeler in devising the so called delayed choice gedanken experiment. Recently this experiment was realized and authors concluded that the present influences the past. We published the paper in Physica Scripta in which we critically analyzed this conclusion.

Phys. Scr. T143 (2011) 014007

The two state vector formalism attempts to answer this type of question. 

http://arxiv.org/abs/quant-ph/0105101v2