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From: Saibal Mitra <smitra.domain.name.hidden>

Date: Fri, 12 Jul 2002 14:11:13 +0200

This all assumes that photons, electrons, etc. are real. We don't know that.

If you were Einstein, and you were faced with Bell's result, you could have

concluded that the nonexistence of local hidden variables implies that

elementary paricles don't exist. They are mere mathematical tools to compute

the outcome of experiments. The real underlying theory of Nature could be

still be deterministic. Recently 't Hooft has shown how QM can emerge out of

a deterministic theory. In this case QM has to be interpreted according to

the Copenhagen interpretation.

----- Oorspronkelijk bericht -----

Van: "Bruno Marchal" <marchal.domain.name.hidden>

Aan: "scerir" <scerir.domain.name.hidden>

CC: <everything-list.domain.name.hidden>

Verzonden: vrijdag 12 juli 2002 12:44

Onderwerp: Re: "Morality" in a Block Multiverse

*> Hi Serafino,
*

*>
*

*> At 23:00 +0200 10/07/2002, scerir wrote:
*

*> > > Hal
*

*> >> You can also have a "block universe" in QM with the many-world
*

*> >> interpretation. It has a more complicated geometric structure but
*

*> >> philosophically it is deterministic, with the same issues regarding
*

*> >> changes, free will, etc.
*

*> >
*

*> >I'm not an Everettista, anyway let us try. Alice has photon 1, which is
*

in a

*> >certain quantum state, unknown to Alice and unknown to anyone else.
*

*> >Let us say that this unknown quantum state is
*

*> >|psi>_1 = a |0>_1 + b |1>_1
*

*> >with |a|^2 + |b|^2 = 1
*

*> >and where |0>_1 and b |1>_1 represent two orthogonal quantum states
*

*> >and a and b represent complex amplitudes.
*

*> >
*

*> >Now Alice wants to "transfer" (I say: "transfer") her quantum state to
*

Bob,

*> >which is remote, so she can not directly deliver it to him. But,
*

fortunately,

*> >Alice also has a pair of entangled photons, let us say the photon 2 and
*

the

*> >photon 3, and she already gave the photon 3 to Bob, who still has
*

*> >this particle.
*

*> >Leaving apart normalization factors we can write that the total
*

*> >state of those 3
*

*> >photons is
*

*> >|psi>_1,2,3 =
*

*> >( |0>_1 |1>_2 - |1>_1 |0>_2 ) (- a |0>_3 - b |1>_3 ) +
*

*> >( |0>_1 |1>_2 + |1>_1 |0>_2 ) (- a |0>_3 + b |1>_3 ) +
*

*> >( |0>_1 |0>_2 - |1>_1 |1>_2 ) ( a |1>_3 + b |0>_3 ) +
*

*> >( |0>_1 |0>_2 + |1>_1 |1>_2 ) ( a |1>_3 - b |0>_3 )
*

*> >
*

*> >Alice now performs a measurement on photons 1 and 2 and she "projects"
*

her

*> >two photons onto one of these four states below:
*

*> >( |0>_1 |1>_2 - |1>_1 |0>_2 )
*

*> >( |0>_1 |1>_2 + |1>_1 |0>_2 )
*

*> >( |0>_1 |0>_2 - |1>_1 |1>_2 )
*

*> >( |0>_1 |0>_2 + |1>_1 |1>_2 )
*

*> >
*

*> >And consequently Bob will found his photon in one of these four states
*

below

*> >(- a |0>_3 - b |1>_3 )
*

*> >(- a |0>_3 + b |1>_3 )
*

*> >( a |1>_3 + b |0>_3 )
*

*> >( a |1>_3 - b |0>_3 )
*

*> >
*

*> >Now Alice, who wants to "transfer" the unknown quantum state of photon 1
*

to

*> >Bob, must inform Bob, via a classical channel, about her measurement
*

*> >("projection")
*

*> >result (on photons 1 and 2). So Bob can perform (25% of times it is not
*

*> >required)
*

*> >the right simple unitary transformation on his photon 3, in order to
*

*> >obtain the
*

*> >initial
*

*> >quantum state |psi>_1 = a |0>_1 + b |1>_1
*

*> >
*

*> >Note that Alice does not get any information, from her measurement, about
*

the

*> >quantum state she wants to "transfer" and about the values of those a and
*

b

*> >amplitudes. Note also that during Alice's measurement photon 1 loses his
*

*> >original quantum state, as required by the no-cloning theorem.
*

*> >
*

*> >Ok, that was the basic teleportation (= trasportation) of a quantum state
*

from

*> >Alice to Bob.
*

*> >
*

*> >Now something strange happens in the MWI version. Alice's measurement
*

does not

*> >"project" the superposition of
*

*> >( |0>_1 |1>_2 - |1>_1 |0>_2 )
*

*> >( |0>_1 |1>_2 + |1>_1 |0>_2 )
*

*> >( |0>_1 |0>_2 - |1>_1 |1>_2 )
*

*> >( |0>_1 |0>_2 + |1>_1 |1>_2 )
*

*> >onto just one of these quantum states (above). They all exist. And all
*

these

*> >quantum
*

*> >states (below) also exist
*

*> >(- a |0>_3 - b |1>_3 )
*

*> >(- a |0>_3 + b |1>_3 )
*

*> >( a |1>_3 + b |0>_3 )
*

*> >( a |1>_3 - b |0>_3 )
*

*> >and one of them (1 over 4 = 25% of times) is the same quantum state that
*

Alice

*> >wanted to "transfer" to Bob.
*

*> >
*

*> >Thus it seems that in the MWI of teleportation the quantun state it is
*

not

*> >"teleported" or "trasported" but it is already "there", and it is already
*

*> >"there", in one of those branches, from the beginning. This stuff
*

*> >reminds me of
*

*> >the "block universe", at least a bit.
*

*> >
*

*> >s.
*

*> >
*

*> >[still not an Everettista] :-)
*

*>
*

*>
*

*>
*

*> Still not? Even after this nice presentation of (quantum) teleportation
*

*> in the MW view? Your last remark confirms my feeling that quantum
*

information

*> is "just" classical information about which partition of the multiverse
*

*> we belong (and measurement is always sort of self-localisation).
*

*> Do you know the paper by Peres http://xxx.lanl.gov/abs/quant-ph/9904042
*

*> Peres shows how to teleport entanglement in the past! In the MW view there
*

*> is no problem at all, neither non-locality, nor 3-indeterminacy. But Peres
*

*> concludes its paper by insisting on keeping the Copenhague view. It's
*

*> quite mysterious.
*

*> If you have time to look at it I would appreciate your opinion.
*

*>
*

*> Bruno
*

*>
*

*>
*

Received on Fri Jul 12 2002 - 05:12:57 PDT

Date: Fri, 12 Jul 2002 14:11:13 +0200

This all assumes that photons, electrons, etc. are real. We don't know that.

If you were Einstein, and you were faced with Bell's result, you could have

concluded that the nonexistence of local hidden variables implies that

elementary paricles don't exist. They are mere mathematical tools to compute

the outcome of experiments. The real underlying theory of Nature could be

still be deterministic. Recently 't Hooft has shown how QM can emerge out of

a deterministic theory. In this case QM has to be interpreted according to

the Copenhagen interpretation.

----- Oorspronkelijk bericht -----

Van: "Bruno Marchal" <marchal.domain.name.hidden>

Aan: "scerir" <scerir.domain.name.hidden>

CC: <everything-list.domain.name.hidden>

Verzonden: vrijdag 12 juli 2002 12:44

Onderwerp: Re: "Morality" in a Block Multiverse

in a

Bob,

fortunately,

the

her

below

to

the

b

from

does not

these

Alice

not

information

Received on Fri Jul 12 2002 - 05:12:57 PDT

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