| Topic: |
Science > Philosophy |
| User: |
"Sir Frederick" |
| Date: |
11 Jul 2004 11:29:37 AM |
| Object: |
On Vacuum Energy |
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5). The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
.
|
|
| User: "Immortalist" |
|
| Title: Re: On Vacuum Energy |
11 Jul 2004 11:46:09 AM |
|
|
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:40F16AF1.28BF7C29@fuzzysys.com...
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5).
I recently read that spacetime is a "feild" and even if there were no object to
warp it it would be something to "push against" and create centripital force as a
zero valued gravitational feild.
The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
.
|
|
|
| User: "Tim" |
|
| Title: Re: On Vacuum Energy |
11 Jul 2004 12:38:20 PM |
|
|
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:27WdnUXst46K8mzdRVn-sA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:40F16AF1.28BF7C29@fuzzysys.com...
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5).
I recently read that spacetime is a "feild" and even if there were no
object to
warp it it would be something to "push against" and create centripital
force as a
zero valued gravitational feild.
Yeah right Spok. But you forgot to mention the dilythium crystals and the
warp flux capacitor.
Can one grow crops in a "feild"? And would zero valued be identical to the
worth of your posts?
The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
.
|
|
|
| User: "Immortalist" |
|
| Title: Re: On Vacuum Energy |
12 Jul 2004 10:04:41 AM |
|
|
"Tim" <nospam@spam.sp> wrote in message
news:y-idnQHeTvoL5mzd4p2dnA@edaptivity.com...
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:27WdnUXst46K8mzdRVn-sA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:40F16AF1.28BF7C29@fuzzysys.com...
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5).
I recently read that spacetime is a "feild" and even if there were no
object to
warp it it would be something to "push against" and create centripital
force as a
zero valued gravitational feild.
Yeah right Spok. But you forgot to mention the dilythium crystals and the
warp flux capacitor.
Can one grow crops in a "feild"? And would zero valued be identical to the
worth of your posts?
Remember you have to open your mouth very wide when you deep throat because you
can scrape the base with your teeth.
The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
.
|
|
|
| User: "Tim" |
|
| Title: Re: On Vacuum Energy |
12 Jul 2004 03:44:02 PM |
|
|
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:vaWdndx4H4VSNW_dRVn-gw@comcast.com...
"Tim" <nospam@spam.sp> wrote in message
news:y-idnQHeTvoL5mzd4p2dnA@edaptivity.com...
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:27WdnUXst46K8mzdRVn-sA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:40F16AF1.28BF7C29@fuzzysys.com...
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5).
I recently read that spacetime is a "feild" and even if there were no
object to
warp it it would be something to "push against" and create centripital
force as a
zero valued gravitational feild.
Yeah right Spok. But you forgot to mention the dilythium crystals and
the
warp flux capacitor.
Can one grow crops in a "feild"? And would zero valued be identical to
the
worth of your posts?
Remember you have to open your mouth very wide when you deep throat
because you
can scrape the base with your teeth.
I wouldn't know - but obviously you do as you "remember" it. I always
thought you were a ***** now I know it. Don't get lost in the "feild"
without your tricorder smokee.
The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
.
|
|
|
| User: "Immortalist" |
|
| Title: Re: On Vacuum Energy |
12 Jul 2004 05:44:02 PM |
|
|
"Tim" <nospam@spam.sp> wrote in message
news:HvmdnVK6-b4BZW_dRVn-ig@edaptivity.com...
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:vaWdndx4H4VSNW_dRVn-gw@comcast.com...
"Tim" <nospam@spam.sp> wrote in message
news:y-idnQHeTvoL5mzd4p2dnA@edaptivity.com...
"Immortalist" <Reanimater_2000@yahoo.com> wrote in message
news:27WdnUXst46K8mzdRVn-sA@comcast.com...
"Sir Frederick" <mmcneill@fuzzysys.com> wrote in message
news:40F16AF1.28BF7C29@fuzzysys.com...
COSMOLOGY: VACUUM ENERGY AND HIGH-REDSHIFT SUPERNOVAE
ScienceWeek http://scienceweek.com
The following points are made by Bertram Schwarzschild (Physics
Today 2004 June):
1) Since 1998, overwhelming evidence has been accumulating that
distant type Ia supernovae appear systematically dimmer than one
would expect from their redshifts in a Universe whose expansion
is slowing down. One infers the distance of such a supernova from
its apparent brightness, and its redshift is a direct measure of
the total expansion of the Cosmos since the light was emitted.
The relation between redshift and distance over a large range of
redshifts traces the history of cosmic expansion.
2) The supernova data -- bolstered by an imposing variety of
other, less direct evidence -- have led to an evolving consensus
called the "concordance model", which asserts that the Cosmos is
currently in an epoch of accelerating expansion driven by a
pervasive dark vacuum energy dense enough to overcome the
gravitational braking of all the mass in the Universe. The model
is agnostic about the nature of the dominating vacuum energy, so
long as its pressure is sufficiently negative. Somewhat
counterintuitively, general relativity asserts that negative
pressure would act as a repulsive counterpoise to gravity on the
cosmological scale.
3) The energy of ordinary electromagnetic radiation won't do; its
pressure is positive. The dark energy might be manifesting the
optional cosmological constant (Lambda) allowed by the field
equations of general relativity. But the magnitude of (Lambda)
inferred from the observations is implausibly small by many
orders of magnitude. Alternatively, the dark energy might be more
dynamical, its density varying in time and space as imagined in a
number of "quintessence" theories.
4) In any case, a cosmology dominated by vacuum energy of unknown
character has profound implications for fundamental physics. So
supernova observers have been at great pains to seek out, or
eliminate, more prosaic astrophysical explanations for the
anomalous faintness of high-redshift supernovae -- for example,
obscuring dust or possible evolutionary differences between
recent supernovae and those of earlier epochs.
5) The recent report of 16 new type Ia supernovae discovered with
the Hubble Space Telescope (HST) by a team led by Adam Riess of
the Space Telescope Science Institute in Baltimore, largely
forecloses such astrophysical alternatives to accelerated cosmic
expansion.(1) The new supernovae also shed some light on the dark
energy's equation of state. Of the several hundred type Ia
supernovae previously reported by groups seeking to trace the
history of cosmic expansion, all but three had been discovered
with ground-based telescopes. And the limitations of ground-based
observation severely inhibit the discovery of supernovae with
redshift z greater than one.(2-4)
References:
1. A. G. Riess et al., Astrophys. J. In press, available at
http://arXiv.org/abs/astro-ph/0402512
2. G. Goldhaber et al. (Supernova Technology Project), Astrophys.
J. 558, 359 (2001)
3. R. A. Knop et al. (Supernova Technology Project), Astrophys.
J. 598, 102 (2003)
4. R. Caldwell, M. Kamionkowski, N. Weinberg, Phys. Rev. Lett.
91, 071301 (2003)
Physics Today http://www.physicstoday.org
--------------------------------
Related Material:
THEORETICAL PHYSICS: ON THE SPACE-TIME VACUUM
The following points are made by R. B. Laughlin (Science 2004
303:1475):
1) In discussing cosmic matters it is impossible not to draw
analogies with science fiction from time to time, for the issues
are as large as those depicted in science fiction and equally
mysterious, despite being experimentally constrained.(1) Our
knowledge of the cosmos is still very primitive, and much of our
thinking about it correspondingly speculative, more along the
lines of what might plausibly have been than what is so.
Plausibility is an interesting concept in theoretical physics,
usually amounting to either a physical analogy with something
observed to occur elsewhere in nature or a mathematical
extrapolation of microscopic law. The latter, however, is
actually a shibboleth, for the things that matter are nearly
always collective organizational phenomena that cannot be
reliably predicted from microscopics. The shapes of galaxies and
the behavior of cosmic jets are simple cases in point, but the
observation also applies to the grandest issues of modern
cosmology: inflationary expansion and the hierarchical
consolidation of matter after the big bang (2-4). The absence of
predictive power is actually self-evident, because there would be
no point in measuring these things if one could calculate them.
As a practical matter, all plausibility arguments that count are
analogies.
2) It may seem shocking to speak of the vacuum of space-time as
an organizational phenomenon, but this is actually just a matter
of semantics. The idea behind the words is mainstream and fully
consistent with the facts. It has been known since the 1950s, and
routinely verified by accelerator experiments since then, that
empty space is a kind of matter quantum-mechanically similar to a
rock (5).
I recently read that spacetime is a "feild" and even if there were no
object to
warp it it would be something to "push against" and create centripital
force as a
zero valued gravitational feild.
Yeah right Spok. But you forgot to mention the dilythium crystals and
the
warp flux capacitor.
Can one grow crops in a "feild"? And would zero valued be identical to
the
worth of your posts?
Remember you have to open your mouth very wide when you deep throat
because you
can scrape the base with your teeth.
I wouldn't know - like I asked you in another post
I want to learn how to give good blow jobs, so please
just describe how women blow you because I
have never been with a woman.
Well son, it comes with experience, just practice blowing strangers and then when
you learn how to tickle a guys fancy you can find the guy, I geuss, you can fall
in love with? However you guys do it, its OK by me even though I'm straight.
The standard model of elementary particles is grounded
firmly on the idea of space as a phase. A multiplicity of such
phases and a complex sequence of transitions among them in the
early universe are corner-stones of modern particle cosmology.
The existence of such phases is implicated in the structure one
sees on intergalactic scales, and the heat released in the
transition between two of them is the ostensible power source of
inflation. Inflation itself is partly motivated by these phases,
because they make the observed uniformity of the universe
unnatural and something requiring explanation.
3) The semantic incongruity, however, like the sublimated worries
about modern life that give us science fiction nightmares, belies
something important -- unfinished business of the 1970s that has
been slowly and systematically tearing physics apart. Stripped of
their confusing mathematical descriptions, the phases of the
vacuum boil down to physical analogies with phases of ordinary
matter, natural phenomena observed to exhibit universality. That
means that their properties at long length and time scales, where
we normally do experiments, do not depend on microscopic details
at all, and thus do not constrain them when measured. A simple
example of emergent universality would be sound propagation in
fluids and solids, an effect perfectly well accounted for as the
motion of atoms, but also a generic property of the phases not
requiring atoms to make sense. Sound is an especially pertinent
example because it has a second identity at low temperatures as
an emergent elementary particle with properties identical to
those of particles of light. Insensitivity to microscopic detail
thus turns the concept of fundamental on its head, in that it
makes principles of self-organization the truly important thing,
rendering the quantum underpinnings of the Universe, whatever
they are, unknowable in the absence of experiments that reach
shorter scales and irrelevant to behavior we presently see.
Little wonder that physicists remain bitterly divided over full
acceptance of the vacuum as a phase.
References (abridged):
1. Akira, 124 min, directed by Katsuhiro Otomo (Kodansha Ltd.,
Japan, 1988)
2. S. Weinberg, The First Three Minutes: A Modern View of the
Origin of the Universe (Basic Books, New York, 1994)
3. M. Rees, New Perspectives in Astrophysical Cosmology
(Cambridge Univ. Press, Cambridge, 2000)
4. A. H. Guth, A. P. Lightman, The Inflationary Universe: The
Quest for a New Theory of Cosmic Origins (Perseus, New York,
1998)
5. M. E. Peskin, D. E Schroeder, An Introduction to Quantum Field
Theory (Westview, Boulder, CO, 1995)
Science http://www.sciencemag.org
--------------------------------
Related Material:
ON QUINTESSENCE AND THE EVOLUTION OF THE COSMOLOGICAL CONSTANT
The following points are made by P.J.E. Peebles (Nature 1999
398:25):
1) Contrary to expectations, the evidence is that the Universe is
expanding at approximately twice the velocity required to
overcome the gravitational pull of all the matter the Universe
contains. The implication of this is that in the past the greater
density of mass in the Universe gravitationally slowed the
expansion, while in the future the expansion rate will be close
to constant or perhaps increasing under the influence of a new
type of matter that some call "quintessence".
2) Quintessence began as Einstein's cosmological constant,
Lambda. It has negative gravitational mass: its gravity pushes
things apart.
3) Particle physicists later adopted Einstein's Lambda as a good
model for the gravitational effect of the active vacuum of
quantum physics, although the idea is at odds with the small
value of Lambda indicated by cosmology.
4) Theoretical cosmologists have noted that as the Universe
expands and cools, Lambda tends to decrease. As the Universe
cools, symmetries among forces are broken, particles acquire
masses, and these processes tend to release an analogue of latent
heat. The vacuum energy density accordingly decreases, and with
it the value of Lambda. Perhaps an enormous Lambda drove an early
rapid expansion that smoothed the primeval chaos to make the near
uniform Universe we see today, with a decrease in Lambda over
time to its current value. This is the cosmological inflation
concept.
5) The author suggests that the recent great advances in
detectors, telescopes, and observatories on the ground and in
space have given us a rough picture of what happened as our
Universe evolved from a dense, hot, and perhaps quite simple
early state to its present complexity. Observations in progress
are filling in the details, and that in turn is driving intense
debate on how the behavior of our Universe can be understood
within fundamental physics.
Nature http://www.nature.com/nature
--------------------------------
Notes by ScienceWeek:
Active vacuum of quantum physics: This refers to the idea that
the vacuum state in quantum mechanics has a zero-point energy
(minimum energy) which gives rise to vacuum fluctuations, so the
vacuum state does not mean a state of nothing, but is instead an
active state.
If a theory or process does not change when certain operations
are performed on it, the theory or process is said to possess a
symmetry with respect to those operations. For example, a circle
remains unchanged under rotation or reflection, and a circle
therefore has rotational and reflection symmetry. The term
"symmetry breaking" refers to the deviation from exact symmetry
exhibited by many physical systems, and in general, symmetry
breaking encompasses both "explicit" symmetry breaking and
"spontaneous" symmetry breaking. Explicit symmetry breaking is a
phenomenon in which a system is not quite, but almost, the same
for two configurations related by exact symmetry. Spontaneous
symmetry breaking refers to a situation in which the solution of
a set of physical equations fails to exhibit a symmetry possessed
by the equations themselves.
In general, the term "latent heat" refers to the quantity of heat
absorbed or released when a substance changes its physical phase
(e.g., solid to liquid) at constant temperature.
The inflationary model, first proposed by Alan Guth in 1980,
proposes that quantum fluctuations in the time period 10^(-35) to
10^(-32) seconds after time zero were quickly amplified into
large density variations during the "inflationary" 10^(50)
expansion of the Universe in that time frame.
ScienceWeek http://scienceweek.com
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