Many Worlds - Many Minds

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Many Worlds - Many Minds

• A view of our universe

Ingvar Lindgren
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Einstein
Bohr
God plays dice
God does NOT play dice
Dispute about the interpretation of QM
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...modern experiments and the discovery of
decoherence have shifted the prevailing quantum
interpretations away from wave function collapse
towards unitary physics,....
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Copenhagen school
Bohr, Heisenberg, Pauli
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Measuring process acc. to Cop. interpret.
Result
Wave function
?i
M
??? ci ?i
A measurement is performed by a macroscopic
apparatus System is instantaneously
and randomly transformed to an eigenstate of the
observable.
Wave function collapse
The probability for a certain result is ci2
God plays dice
Max Borns probalitity interpretation
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EPR paradox
Einstein-Podolsky-Rosen 1935
J0
J0
Two-photon decay
Photons of opposite polarization. Acc. to Cop.
interpret. the photons have no specific
polarization, before the pol. has been measured.
Superposition of states.
The measurement of photon 1 gives it a specific
polarization. Then also the
polarization of photon 2 will be given.
?i
? ? ? ci ?i
Hidden variables? Bells inequality
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Schrödingers cat
Radiation from a radioactive material initiates a
buttet that kills the cat.
Before the observation, the cat is acc. to
Copenhagen interpret. in a superposition of
dead and alive.
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Superposition -- entanglement
? ? ? ci ?i
Mathematically a state can be expanded in any
complete basis set.
Entanglement Coupling of physical states
(eigenstates of an observable)?
?i
? ? ? ci ?i
Collapse of wave function Abrupt destruction of
entanglement
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Problems with the Copenhagen interpretation

• The measurement process requires an macroscopic
  observer.

• Artificial border between micro and macro
  systems.

• The collapse of the wave function does not
  follow any known laws of physics.

• Borns statistical interpretation is an
  additional assumption that does not follow from
  the model.

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• Dropping collapse of wf

Entire world evolves accord. to time-dependent
Schrödinger eq.

• Also measuring device treated quantum
  mechanically (von Neumann)?

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Ygt (S ci Sigt) M0gt
S
M
No interaction between system and meas. device
No interaction between system and meas. device
Ygt S ci SiMigt
S
M
Interaction between system and meas. device
Measuring device affected by interaction with the
system under study
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S1M1
S
M
S2M2
S1M1O1
S
M
S2M2O1
Observer connected to ONE branch, sees only that
branch
Everett termed this relative-state model
DeWitt introduced around 1970 the term
Many-worlds interpretation
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Why no interference between the branches?
The Everett original model is incomplete.
Does not explain the emergence of
stable, non-interfering brances
Does not explain the emergence of classicality
Decoherence has to be considered
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Decoherens (W.H. Zurek, H.D. Zeh 1980)?
Zurek, Rev. Mod. Phys. 75, 715 (2003)?
Dynamical dislocation of quantum-mechanical
entanglements, destruction of quantum coherence
Wojciech Hubert Zurek
Purely quantum-mechanical phenomenon Caused by
interaction by the environment

Dieter Zeh
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S1M1
S
M
S2M2
Left alone, strong coherences between the branches
Complete entanglement
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S1M1
S
M
S2M2
Interaction with environment
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S1M1
S
M
S2M2
Entanglement with environment reduces
entanglement between branches
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S1M1
S
M
S2M2
Further entanglement with environment reduces
further entanglement between branches
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classicality
S1M1
pointer states stable, decoupled
S
M
S2M2
classicality
Eventually development of stable pointer states
Not further affected by environment
Branches completely decoupled
Emergence of classicality
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classicality
S1M1
pointer states stable, decoupled
S
M
S2M2
classicality
Zurek Einselection environment-induced
superselection
Preferred states Independent of
initial conditions
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classicality
S1M1
pointer states stable, decoupled
S
M
S2M2
classicality
This is the measurement process in MWI
No macroscopic observer
No collapse
Continuous transition to classicality No cat!
Observer in one branch not aware of the other
branches
Different worlds - different minds
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classicality
S1M1
pointer states stable, decoupled
S
M
S2M2
classicality
Compare Darwin's theory Origin of the spicies
Survival of the fittest
Quantum Darvinism
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S
M
S2M2
classicality
Copenhagen interpretation
Nature selects randomly ONE branch
God plays dice
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Extra detektor
Extra detektor
Stern-Gerlach magnet to measure spin orientation
Extra detector will destroy interference
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System (spin) detector (magnet)
F a sdgt b s-d-gt
Density matrix r F gt lt F
a2 sdgtlt sd absdgtlt s-d-ba
s-d-gtlt sd b2 s-d-gt lt s-d-
Interference terms
System (spin) detector (magnet) environment
(extra detektor)
Y asd e gt b s-d- e- gt
Reduced density matrix for sd system (lteiejgt
dij)
rr Se lte Y gt lt Y egt a2 sdgt lt sd
b2 s-d-gt lt s-d-
No interference
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H. D. Zeh The importance of decoherence was
overlooked for the first 60 years of quantum
theory precisely because entanglement was
misunderstood ....
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Quantum-mechanical decoherence has been verified
experimentally
Haroche et al, PRL 77, 4887 (1996)?
Zeilinger et al., Nature 401, 680 (1999)?
Serge Haroche
Anton Zeilinger
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Advantages with Everett-DeWitt model (with
decoherence)?
Schrödinger equation strictly valid. No collapse
of wave function. No classical observer needed.
No artificial border between micro and
macro systems. Decoherence leads to emergence of
classicality No cat states Borns statistical
interpretation follows from the model (Zurek
2005)?
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Many experts consider this to be the most or
even the only -- consistent interpretation of
mechanics quantum presented so far.
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Dieter Zeh 2000 The multi-universe
interpretation (which should rather be called
multi-consciousness interpretation) seems to be
the only interpretation of a universal quantum
theory (with an exact Schrödinger equation) that
is compatible with the way the world is
perceived. However, because of quantum
non-locality it requires an appropriate
modification of the traditional epistemological
postulate of psycho-physical parallelism. In
this interpretation, the physical world is
completely described by Everett's wave function
that evolves deterministically (Laplacean). This
global quantum state then defines an
inde- terministic (hence "branching") succession
of states for all observers. Therefore, the world
itself appears indeterministic subjective in
principle, but largely objective through
quantum correlations (entanglement).
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Dieter Zeh 2000 ... the Heisenberg-Bohr picture
of quantum mechanics is dead. Neither classical
concepts, nor any uncertainty relations,
complementarity, observables, quantum logic,
quantum statistics, or quantum jumps have to be
introduced on a fundamental level.
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Personal view
The decoherence leads ?to disentanglement of
entangled states. The branches still exist but
are not aware of each other.
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Universe a bifurcations tree
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Universe a bifurcations tree
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Universe a bifurcations tree
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Universe a bifurcations tree
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Universe a bifurcations tree
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Universe a bifurcations tree
Life
.......
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Universe a bifurcations tree
Homo sapiens
Life
.......
.......
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Universe a bifurcations tree
Homo sapiens
Life
.......
. . . . . .
I.L.
.......
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Universe a bifurcations tree
Homo sapiens
Life
.......
.......
. . . . . .
I.L.
.......
.......
Probability for Life ? Hom.sap. ? I.L extremely
small.
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Tage Danielssons statistik
Jag menar, före Harrisburg så var det ju ytterst
osannolikt att det som hände i Harrisburg skulle
hända, men så fort det hade hänt, rakade ju
sannolikheten upp till inte mindre än 100
procent, så det var nästan sant att det hade
hänt.
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Universe a bifurcations tree
Homo sapiens
Life
.......
.......
. . . . . .
I.L.
.......
.......
Probability for Life ? Hom.sap. ? I.L extremely
small.
Men när det väl har hänt, är sannolikheten 100
, och det är nästan sant att det har
hänt.
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Universe a bifurcations tree
Homo sapiens
Life
.......
.......
. . . . . .
I.L.
.......
.......
All branches remain no collapse of wave
function
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My universe
Homo sapiens
Life
.......
. . . . . .
I.L.
.......
All branches remain no collapse of wave
function
But each observer can see only one branch
Many minds
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My universe
Homo sapiens
Life
.......
. . . . . .
I.L.
.......
All branches remain no collapse of wave
function
But each observer can see only one branch
Many minds
Looks like a collapse of wave function for each
observer
Anthropic principle
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Anthropic principle
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Anthropic principle
(Dicke 1961, Brandon Carter, 1973)?
No coincidence that the universe has the
properties it has
Brandon Carter
Acc. to anthropic principle universe must have
exactly these properties in order for humans to
be created and to develop
If not, we would not exist and could not worry
about it.
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Stephen Hawking
A Brief History of Time (1988)? (9 mill.
copies)?
Universe in a nutshell (2001)?
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Hugh Ross Fingerprint of God
Creator and the Cosmos
Martin Rees Before the beginning
Barrow-Silk The left hand of
creation
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H. Dieter Zeh
The direction of time (5.ed.)?
Knowledge and the world
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Max Tegmark
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Further reading
Zurek, Rev. Mod. Phys. 75, 715 (2003)?
Zurek, Physics Today 44, 36 (1991)
Stanford Encyclopedia of Philosophy
D. H. Zeh, arXivquant-ph
Peter Byrne The Many Worlds of Hugh Everett,
Sci. Amer. Nov. 2007
Tegmark and Wheeler 100 years of the Quantum,
arXivquant-ph/0101077v1
I.L. Interpretation of Quantum Mechanics,
http//fy.chalmers.se/f3ail/