Many Worlds - Many Minds

A view of our universe

Ingvar Lindgren

Einstein

Dispute about the interpretation of QM

Bohr

”God plays dice” ”God does NOT play dice”

...modern experiments and the discovery of decoherence have shifted the prevailing quantum interpretations away from wave function collapse towards unitary physics,....

Copenhagen school

Bohr, Heisenberg, Pauli

Result

i

Wave function

ci i

M

Measuring process acc. to Cop. interpret.

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 |ci|2 ”God plays dice”

Max Born’s probalitity interpretation

EPR paradoxEinstein-Podolsky-Rosen 1935

Hidden variables? Bell’s inequality

Two-photon decay

J=0

J=0

Photons of opposite polarization. Acc. to Cop. interpret. the photons have no specific polarization, before the pol. has been measured. Superposition of states.

ci i i

The measurement of photon 1 gives it a specific polarization. Then also the polarization of photon 2 will be given.

Schrödinger’s 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.

Superposition -- entanglement

ci i

Mathematically a state can be expanded in any complete basis set.

Entanglement: Coupling of physical states (eigenstates of an observable)

Collapse of wave function: Abrupt destruction of entanglement

ci i i

Problems with the Copenhagen interpretation

• The measurement process requires an macroscopic observer.

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

• Born’s statistical interpretation is an additional assumption that does not follow from the model.

• Artificial border between micro and macro systems.

H u g h E ve r e tt

J o h n W h e e le r

H u g h E v erett ’s in terp reta t io nR e v. M o d . P h y s ic s 2 9 , 4 5 4 ( 1 9 5 7 )

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

• Also measuring device treated quantum mechanically (von Neumann)

• Dropping collapse of wf

ci |

Si

0>No interaction between system and meas. device

Measuring device affected by interaction with the system under study

ci |S

i

i>

No interaction between system and meas. device

Interaction between system and meas. device

S M

S M

Everett termed this ”relative-state model”

DeWitt introduced around 1970 the term ”Many-worlds interpretation”

Observer connected to ONE branch, sees only that branch

S M

S1M1

S2M2

S M

S1M1O1

S2M2O1

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

Why no interference between the branches?

Dynamical dislocation of

quantum-mechanical entanglements,

destruction of quantum coherence

Decoherens (W.H. Zurek, H.D. Zeh ~1980)

Zurek, Rev. Mod. Phys. 75, 715 (2003)

Purely quantum-mechanical phenomenon

Caused by interaction by the environment

Wojciech Hubert Zurek

Dieter Zeh

Left alone, strong coherences between the branches

Complete entanglement

S M

S1M1

S2M2

S M

S1M1

S2M2

Interaction with environment

S M

S1M1

S2M2

Entanglement with environmentreduces entanglement between branches

S M

S1M1

S2M2

Further entanglement with environmentreduces further entanglement between branches

Eventually development of stable pointer states Not further affected by environment Branches completely decoupled

Emergence of classicality

S M

S1M1

S2M2

pointer statesstable, decoupled

classicality

classicality

S M

S1M1

S2M2

Zurek: Einselectionenvironment-induced superselection

Preferred states: Independent of initial conditions

pointer statesstable, decoupled

classicality

classicality

S M

S1M1

S2M2

This is the measurement process in MWI

Different “worlds” - different “minds”Observer in one branch not aware of the other branches

No macroscopic observerNo collapse

Continuous transition to classicality – No cat!

pointer statesstable, decoupled

classicality

classicality

S M

S1M1

S2M2

Compare Darwin's theory:Origin of the spicies

Survival of the fittest

”Quantum Darvinism”

pointer statesstable, decoupled

classicality

classicality

S M

S2M2

classicality

Copenhagen interpretation:

Nature selects randomly ONE branch

”God plays dice”

Extra detektor

Extra detektor

Stern-Gerlach magnet to measure spin orientation

Extra detector will destroy interference

System (spin) – detector (magnet) – environment (extra detektor)

System (spin) – detector (magnet):

= s+d+ e+ > + s-d- e- >

|s+d+><s+d+| +s+d+><s-d-|+s-d-><s+d+| +|s-d-> <s-d-|

Density matrix = | > < | =

Interference terms

= s+d+>+ s-

d->

Reduced density matrix for sd system (<ei|ej> = ij):

r= e <e| > < |e> = |s+d+> <s+d+| + |s-d-> <s-

d-| No interference

H. D. Zeh:The importance of decoherence was overlooked for

the first 60 years of quantum theory precisely

because entanglement was misunderstood ....

Quantum-mechanical decoherence has been verified experimentally

Zeilinger et al., Nature 401, 680 (1999)

Haroche et al, PRL 77, 4887 (1996)

Serge Haroche Anton Zeilinger

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

Born’s statistical interpretation follows from the model (Zurek 2005)

Many experts consider this to be the most – or even the only -- consistent interpretation of mechanics quantum presented so far.

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 quantumcorrelations (entanglement).

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.

The decoherence leads to disentanglement of entangled states. The branches still exist but are not aware of each other.

Personal view

Universe – a bifurcations tree

Universe – a bifurcations tree

Universe – a bifurcations tree

Universe – a bifurcations tree

Universe – a bifurcations tree

Life

.......

Universe – a bifurcations tree

Life

..............

Homosapiens

Universe – a bifurcations tree

Life

..............

. . . . . .

Homosapiens

I.L.

Universe – a bifurcations tree

Life

..............

Homosapiens

..............

Probability for Life Hom.sap. I.L extremely small.

. . . . . . I.L.

Universe – a bifurcations tree

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.”

Life

..............

Homosapiens

..............

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.”

I.L.

Universe – a bifurcations tree

Life

..............

Homosapiens

..............

. . . . . .

All branches remain – no collapse of wave function

I.L.

Universe – a bifurcations tree

My universe

..............

. . . . . . I.L.

LifeHomosapiens

But each observer can see only one branch –

”Many minds”

All branches remain – no collapse of wave function

..............

. . . . . .

LifeHomosapiens

”Anthropic principle”

Looks like a collapse of wave function for each observer

I.L.

All branches remain – no collapse of wave function

My universe

But each observer can see only one branch –

”Many minds”

Anthropic principle

Anthropic principle

No coincidence that the universe has the properties it has

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.

(Dicke 1961, Brandon Carter, 1973)

Barrow and Frank, Oxford 1988

Brandon Carter

A Brief History of Time (1988) (9 . )mill copies

Stephen Hawking

Universe in a nutshell (2001)

Hugh Ross: Fingerprint of God Creator and the Cosmos

Martin Rees: Before the beginning

Barrow-Silk: The left hand of creation

The direction of time (5.ed.)

Knowledge and the world

H. Dieter Zeh

Max Tegmark

Commentary

Natu re 448 , 2 3- 2 4 (5 J u ly 2 0 0 7 )

Many lives in m any w orlds

Max Tegm ark1 1. I n this Universe , Max Tegm ark is a physicist a t the Massa chusetts I nstitute o f Techno logy , C am bridge,

Massachusetts, US A . Top o f page

Abstract

Accepting quantum physics to be universally true, argues Max Tegmark, means that you should also believe in parallel universes.

M I R A G E EN TER PR I S ES / R G A

I s it only in fiction that we can experience parallel lives? I f atom s can be in two places at once, so can you.

I.L. Interpretation of Quantum Mechanics, http://fy.chalmers.se/~f3ail/

Peter Byrne: The Many Worlds of Hugh Everett, Sci. Amer. Nov. 2007

Stanford Encyclopedia of Philosophy

Zurek, Rev. Mod. Phys. 75, 715 (2003)

Further reading

D. H. Zeh, arXiv:quant-ph

Tegmark and Wheeler: 100 years of the Quantum, arXiv:quant-ph/0101077v1

Zurek, Physics Today 44, 36 (1991)