Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-l] A New Way To Understand Gravity?




"In 1967 Sakharov published a very interesting article titled " Vacuum
Quantum Fluctuations in Curved Space and the Theory of Gravitation."
In order to understand its meaning , it is important to recall that ,
according to Einstein , gravity is the curvature of space caused by the presence
of matter; that is by the presence of real particles and fields ( which
have some energy density) The curvature is proportional to the energy density ,
and the proportionality coefficient is Newton's gravitational constant G,
divided by the velocity of light raised to the fourth power.


Curvature ~ G/c^4 X energy density


This is the famous Einstein equation.
In his work , Sakharov asserted that this equation has a dynamic
interpretation: that the curvature multiplied by c^4/G is the change in the energy
density of the vacuum due to the curvature of space. Therefore in Sakharov's
view there is hope that with quantum field theory it is possible to find the
energy of the quantum vacuum fluctuations as a function of the curvature of
space. "


From "What Else If Not Me? by V.I Ritus Lebedev Physical Institute ,
Moscow



))))))))))))))))))))))))

A New Way to Understand Gravity? .






The great physics theory divide between gravity and the quantum field theory
is the certainly the most pressing problem in fundamental physics. There is
something very different about gravity. Unlike the other forces of nature, it
is universal. No species of matter evades it effect.
So the great quest in physics is for a quantum theory of gravity. But this
goal has proved illusive. This is because the gravity field itself is space
time, the background on which all of physics is written. In order to have a
quantum field theory of gravity, it seems likely that the clear separation
between matter and geometry may be lost. Rather we may need a new model with pre-
geometric degrees of freedom.
However, the commonality of gravity to all matter states suggests that it
may, in fact, not be a fundamental force at all. Rather gravity may be an “
induced force” which emerges from quantum field theory like hydrodynamics emerges
from molecular physics. One such gravity model is Sakharov’s induced gravity
theory. This model incorporates Lorentz’s vision of the possibility of
gravity merely being an effective force induced by residual electromagnetic
forces. Since in this model the action terms would contain both classical and
quantum terms, this model leads to a “semi-classical quantum “gravity theory.
In the sense that space time may be quantized, (seemingly required by the
Holographic principle) it would be the quantization of collective excitations of
the vacuum state. Because gravity is the result of the mutual interaction of
the fundamental quantum fields we could retain space time as background,
avoiding the objection to semi classical models raised by Terno.
Sakharov’s starting point is to notice that gravitation consists, not in the
existence of space curvature, but in the existence of a large “metrical
elasticity” which opposed the curvature of space, except near concentrations of
matter. The equations of general Relativity arise from the action principle
obtained by adding to the action of the matter fields the Einstein Hilbert
action. The action is then the proportional scalar curvature term multiplied by
the inverse of Newton’s constant. Therefore the unification scale, the mass
cutoff value is a property of the collective excitations of the vacuum states.
Continuing with this line of reasoning, Sakharov was able to show that in
simple models of matter fields, the proportionality constant in the effective
action is given by an infinite sum over masses of the fluctuation quanta (the
virtual ZPE quanta) which are present. When space is curved, Sakharov argues,
the action arising from quantum fluctuations is altered and is only
partially canceled by the renormalization constant computed in flat spacetime.
Obviously this has important consequences for the quantum theory treatment
of the vacuum especially as it relates to the Higgs field and gravity. This
may call into question the whole program of quantization of these fields from
first principles. Rather, the quantum model of the degrees of freedom utilized
in condensed matter physics may be more appropriate.
Recently, a new paradigm has been introduced into physics which may modify
our understanding of the ZPE fluctuations of the vacuum. This basic model
proposed by Klauber, Moffat, t Hooft, Sundrum and others , resurrects the
discarded “unphysical” negative energy states of the relativistic equations (
Klein Gordon, Proca and Dirac equations) in an attempt to solve the infamous
zero point energy problem, the prediction of an immense unobserved vacuum energy
density.
While the application of these negative energy states to solve the ZPE
problem varies in detail in the various proposals, the basic idea is the same for
all of them. In addition to the matter states normally described in Quantum
Field Theory, which Klauber calls the traditional states and Moffat the positon
particles, we double the number of possible matter states by including the
negative energy quanta which Klauber calls the supplemental states and Moffat
labels as the negaton particles.
This would seem to add ammunition to the idea that the condensed matter
physics paradigm may be usefully applied to vacuum physics. Given that at some
fundamental level spacetime and matter may be the emergent properties of
pre- geometric degrees of freedom, we can view the entities of quantum field
theory as collective excitations of this underlying pre geometric structure.
Therefore it may be possible to model the positon and negaton virtual states of
the vacuum in a way which is similar in principle to the electron and hole
model used in solid state physics.
In a vacuum absent any gravitational effect ( zero cc) all the models
utilizing these negative matter states postulate a perfect canceling balance
between the virtual positon ( positive cc contribution) and the negatons (
negative cc contribution). In other words a space time with zero curvature.
However, in our Universe the observed cc is not zero. This would mean, based
on the models utilizing these negative energy states, that there are more
positon virtual states than negaton virtual states in
the vacuum with negative space time curvature. Using the solid state
analogy, we can view this as a “depletion” of negaton virtual states.
But what process can effect this depletion? I think the answer to this
question points to the Davies –Hawking-Unruh effect as the process in question.
Non inertial frames “promote” virtual particles into real particles. The
gravity field is by definition an acceleration field. By the equivalence
principle they are the same thing.
So using this proposal we can say that negative curvature depletes negaton
virtual states and positive curvature depletes positon states. The application
of these negative energy states provides a mechanism to alter the action
density arising from quantum fluctuations. Therefore we can describe gravity as
a field induced by the collective action of the quantum states.
This is made very clear when we consider the vacuum energy density in the
presence of event horizons. Given a past event Horizon we see the depletion of
traditional virtual states ( positon) creating a negative vacuum energy
density while the presence of a future horizon creates a depletion of the
supplemental virtual states ( negatons) creating a positive vacuum energy density.
Therefore the Davies-Hawking -Unruh effect may be viewed as a measurement
process of the vacuum states. The local concentrations of real matter results in
this vacuum measurement process creating an effect we call gravity.
Bob Zannelli


" A Large part of history is replete with the struggle for Human rights, an
eternal struggle in which a final victory can never be won. But to tire in
that struggle would mean the ruin of society."

Albert Einstein





************************************** See what's free at http://www.aol.com.