INFLU

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SEMINÁRIO UFES
Vitória, agosto 2013
The quantum-to-classical transition of primordial
cosmological perturbations.

• Nelson Pinto Neto
• with Grasiele Santos and Ward Struyve

CBPF ICRA
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THE STANDARD COSMOLOGICAL MODEL
(FRIEDMANN-1922)
Copernicus Principle space homogeneous and
isotropic.
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But where the structures come from?

• In the standard Friedmann model the Universe was
  always decelerated
• p??, ? gt 0 ? atq with qlt1 (?0, q2/3
  ?1/3, q1/2)

• Scales of different structures grow with a
  lphys a l
• Curvature scale grows with a1/q H-1 RH ? t ?
  a1/q

ln(lphys) ln(l) ln(a)

In the past, observed large scales where much
greater then the curvature scale. Impossible to
justify initial spectrum in terms of local
physical arguments, unless there is an
inflationary phase in the past or a bounce
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Evolution of scalar perturbations
F(x) is the inhomogeneous perturbation, related
to theNewtonian potential in the nonrelativistic
limit, df is the scalar field perturbation.
Mukhanov-Sasaki variable ?
Hamiltonian for the perturbations from GR ?
Equations of motion ?
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IN TERMS OF THE FOURIER MODES
The classical solutions
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QUANTIZATION
In the Schroedinger picture ?(y,?)
lty0,?gt

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THE PROBLEM
0gt is homogeneous and isotropic, and
so is lt0y(x)y(x)0gt ( lt0y(xd)y(xd)0gt)

• Attempts for solving
  the problem
• squeezing ? positive Wigner distribution in phase
  space
• quantum distribution looks like classical
  stochastic distribution of
• realizations of the Universe with different
  inhomogeneous configurations.
• decoherence avoids interference among
  realizations.

Severely criticized by
Sudarsky and many others The state is still
homogemeous and isotropic In the standard
interpretation, different potentialities are not
realities How ONE of the potentialities become
our real Universe? What makes the role of a
measurement in the early Universe? (we cannot
collapse the wave function because we could not
exist without stars!)
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The de Broglie-Bohm interpretation
The guidance relation allows the determination
of the trajectories (different from the
classical)
If P(x,t0) A2 (x, t0), all the
statistical predictions of quantum mechanics are
recovered.
However, P(x,t0) ? A2 (x, t0), relaxes rapidly
to P(x,t) A2 (x, t)
(quantum H theorem -- Valentini)
Born rule deduced, not postulated
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SOLUTION OF THE MEASUREMENT PROBLEM
de Broglie-Bohm particles and fields have
actual trajectories, independently of any
observation (ontology). One trajectory enter in
one branch and singularize it with respect to
the others.
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Measurement problem position in configurations
space determines choosen branch (depends on X0)
?
?
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Some remarks
a) Q is highly non-local and context
dependent! It offers a simple characterization of
the classical limit
Q0
b) Probabilities are derived in this theory. The
unknown variable is the initial position.
c) With objective reality but with the same
statistical interpretation of standard quantum
theory.
d) One postulate more (existence of a particle
trajectory) and two postulates less (collapse
and Born rule) than standard quantum theory 1-2
-1 postulate
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QUANTIZATION
In the Schroedinger picture ?(y,?)
lty0,?gt

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The de Broglie-Bohm solution

• The existence of an actual field configuration
  breaks
• translational and rotational invariance.
• It obeys guidance equations.
• Its initial condition satisfies Born rule at
  initial time.

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The quantum-to-classical transition
y(?) a f(?) a f(?)
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In terms of the quantum potential
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FOR THE BOUNCE
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Statistical predictions the two point
correlation function
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V - CONCLUSION
Bohm-de Broglie interpretation is very suitable
for quantum aspects of cosmology! It explains in
a very simple way a very old controversy
concerning cosmological perturbations of quantum
mechanical origin. What about the other
interpretations?
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"To try to stop all attempts to pass beyond the
present viewpoint of quantum physics could be
very dangerous for the progress of science and
would furthermore be contrary to the lessons we
may learn from the history of science. This
teaches us, in effect, that the actual state of
our knowledge is always provisional and that
there must be, beyond what is actually known,
immense new regions to discover."
Louis de Broglie
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THE PROBLEM OF INTERPRETATION
The problem of quantum measurement
Wave function of system apparatus interaction
-gt bifurcation but only one branch is observed.
Copenhaguen interpretation Actual facts take
place in the classical world. The classical
apparatus realizes the collapse of the wave
function and turn the quantum potentialities
into actual and unique facts.
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We would like that quantum theory could help
cosmology!
Within the Copenhaguen interpretation we are
stuck no further developments. Contemporary
quantum theory constitutes an optimum
formulation of certain connections but
offers no useful point of departure for future
developments. Albert Einstein.
Fortunately, there are alternative quantum
theories! Many Worlds Consistent
Histories Spontaneous collapse de
Broglie-Bohm ..........
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Decoherence explain why we do not see
macroscopic superpositions, but... IT DOES NOT
EXPLAIN THE UNICITY OF FACTS!
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FOR THE UNIQUE FACT A COLLAPSE OF THE WAVE
FUNCTION IS POSTULATED!
X
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MANY WORLDS
(Everett, DeWitt, Deutsch)
All possibilities are realized,
but they are not aware of each
other. THERE IS NO UNIQUE FACT!
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SPONTANEOUS COLAPSE
(Pearle, Ghirardi, Rimini, Weber, Penrose)
Non linear evolution suplemented to Schrödinger.
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THE DE BROGLIE-BOHM THEORY

• The kinematics of the world, in this ortodox
  picture, is given by a
• wave function for the quantum part, and classical
  variables
• variables which have values - for the classical
  part
• (?(t,q ...), X(t) ...). The Xs are somehow
  macroscopic. This is not
• spelled out very explicitly. The dynamics is not
  very precisely
• formulated either. It includes a Schrödinger
  equation for the
• quantum part, and some sort of classical
  mechanics for the
• classical part, and collapse recipes for their
  interaction.
• It seems to me that the only hope of precision
  with the dual (?,x)
• kinematics is to omit completely the shifty
  split, and let both ? and x
• refer to the world as a whole. Then the xs must
  not be confined to
• some vague macroscopic scale, but must extend to
  all scales.
• John Stewart Bell.

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Bell in Speakable and unspeakable in quantum
mechanics
In 1952 I saw the impossible done. It was in
papers by David Bohm. the subjectivity of the
orthodox version, the necessary reference to the
observer, could be eliminated. . . . But
why then had Born not told me of this pilot
wave? If only to point out what was wrong with
it? Why did von Neumann not consider it? . .
. Why is the pilot wave picture ignored in text
books? Should it not be taught, not as the only
way, but as an antidote to the prevailing
complacency? To show us that vagueness,
subjectivity, and indeterminism, are not forced
on us by experimental facts, but by deliberate
theoretical choice? (Bell, page 160) I have
always felt since that people who have not
grasped the ideas of those papers. . . and
unfortunately they remain the majority . . . are
handicapped in any discussion of the meaning
of quantum mechanics. (Bell, page 173)