X-ray survey of galaxy clusters challenges dark energy models

[meteor]

Elastic dark energy:
http://arxiv.org/abs/astro-ph/0405096
Well, being this model correct or no, advice to you, dark energy: we will finally discover your nature, so your slippery behaviour will not be of utility for you

 

[meteor]

k-essential phantom energy

http://arxiv.org/abs/astro-ph/0312579
K-Essential Phantom Energy: Doomsday around the corner?
Authors: Pedro F. Gonzalez-Diaz (IMAFF, CSIC, Madrid)
Comments: 10 pages, Latex, 1 Figure, to appear in Physics Letters B
Report-no: IMAFF-RCA-03-10
Journal-ref: Phys.Lett. B586 (2004) 1-4

In spite of its rather weird properties which include violation of the dominant-energy condition, the requirement of superluminal sound speed and increasing vacuum-energy density, phantom energy has recently attracted a lot of scientific and popular interests. In this letter it is shown that in the framework of a general k-essence model, vacuum-phantom energy leads to a cosmological scenario having negative sound speed and a big-rip singularity, where the field potential also blows up, which might occur at an almost arbitrarily near time in the future that can still be comfortably accommodated within current observational constraints.

 

[wolram]

http://www.physics.ucla.edu/hep/dm04/talks/yunwang.pdf

a pencil survey of 100 type 1A supernova will help in solving dark
energy problem.

 

[wolram]

an april 2004 review of dark matter energy.

http://arxiv.org/abs/astro-ph/0403324

I briefly review our current understanding of dark matter and dark energy. The first part of this paper focusses on issues pertaining to dark matter including observational evidence for its existence, current constraints and the `abundance of substructure' and `cuspy core' issues which arise in CDM. I also briefly describe MOND. The second part of this review focusses on dark energy. In this part I discuss the significance of the cosmological constant problem which leads to a predicted value of the cosmological constant which is almost $10^{123}$ times larger than the observed value $\la/8\pi G \simeq 10^{-47}$GeV$^4$. Setting $\la$ to this small value ensures that the acceleration of the universe is a fairly recent phenomenon giving rise to the `cosmic coincidence' conundrum according to which we live during a special epoch when the density in matter and $\la$ are almost equal. Anthropic arguments are briefly discussed but more emphasis is placed upon dynamical dark energy models in which the equation of state is time dependent. These include Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model independent methods to determine the cosmic equation of state and the Statefinder diagnostic are also discussed. The Statefinder has the attractive property $\atridot/a H^3 = 1 $ for LCDM, which is helpful for differentiating between LCDM and rival dark energy models. The review ends with a brief discussion of the fate of the universe in dark energy models.

 

[wolram]

http://physicsweb.org/article/world/17/5/7

Dark energy
Feature: May 2004

New evidence has confirmed that the expansion of the universe is accelerating under the influence of a gravitationally repulsive form of energy that makes up two-thirds of the cosmos

It is an irony of nature that the most abundant form of energy in the universe is also the most mysterious. Since the breakthrough discovery that the cosmic expansion is accelerating, a consistent picture has emerged indicating that two-thirds of the cosmos is made of "dark energy" - some sort of gravitationally repulsive material. But is the evidence strong enough to justify exotic new laws of nature? Or could there be a simpler, astrophysical explanation for the results?

 

[meteor]

http://arxiv.org/abs/hep-th/0405054
"Dilatonic ghost condensate as dark energy"

 

[meteor]

http://arxiv.org/abs/gr-qc/0405038
SO(1,1) dark energy model and the universe transition
Authors: Yi-Huan Wei, Yu Tian
Comments: 11 pages

 

[kurious]

WOLRAM

"Or could there be a simpler, astrophysical explanation for the results?"


What if some parts of the universe are contracting faster than others - wouldn't that give the illusion of accelerating expansion?

 

[wolram]

Hi kurious.
The data from supernova red shift is compelling evidence for expansion,
Adam Riess used the Hubble telescope to discover 42 new ones including
6 of the most distant known, if some parts of the U are contracting
i think that would show up in the data collected from these S Nova.

Red shift is not the only method used to demonstrate that the U is
expanding, a team lead by Prof G Efstathiou used clustering patterns
of 25000 galaxies and compared it to the CMBR, and found a good
match with S Nova data.

so everything points to an expanding U accelerated by Dark Energy,
a most unintuitive scenario and the only one on offer to date.

 

[wolram]

http://www.space.com/scienceastronomy/astronomy/universe_expansion_020320.html
Now, a team of 27 astronomers led by Professor George Efstathiou of the University of Cambridge has published strong evidence for the existence of dark energy using an entirely different technique. They used the clustering pattern of 250,000 galaxies in a large volume of the universe surveyed with the Anglo-Australian Telescope at Siding Spring in New South Wales, Australia. By comparing the structure in the universe now, some 15 billion years after the Big Bang, with structure observed in the cosmic microwave background radiation, which preserved information about what the universe was like when it was only 300,000 years old, the Anglo-Australian team could apply a simple geometrical test to elucidate the composition of the universe.

 

[Mike2]

If the nature of the universe at the very first is for accelerated expansion (inflation), even before there were any kind of particles, then doesn't that imply that there is something inherent is space itself that accelerated expansion is a property of space? I can imagine that the creation of matter might slow this process down for a while. But I don't see why the expansion should continue to accelerate.

 

[wolram]

astro-ph/0305179] Inflation and the Cosmic Microwave Background.

Is continued acceleration "natural", i don't know, this paper
by Lineweaver goes some way in explaining inflation,
unfortunately these thing can not be tested in a laboratory
and can only be deduced from observations.

 

[meteor]

http://arxiv.org/abs/astro-ph/0405232
"Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy"

SNAP: A space-based experiment to study the nature of the "Cosmic yeast"

 

[kurious]

Can't dark energy just be electric charges of the same sign repelling one another -
even if the charge has to be on a massless wave of some sort.Repulsion of charges would stop a singularity from forming too if there were enough of them.

 

[meteor]

vector dark energy

http://arxiv.org/abs/astro-ph/0405267

There are various models that assume that dark energy is a scalar field, for example the models of quintessence and k-essence, but this paper explores the possibility that dark energy could be a vector field. An interesting reading without a doubt

 

[kurious]

There are various models that assume that dark energy is a scalar field, for example the models of quintessence and k-essence, but this paper explores the possibility that dark energy could be a vector field. An interesting reading without a doubt

The three vectors in this paper are all at right angles to one another to guarantee isotropy.Usually vectors in phenomena associated with energy, such as photons,
are at right angles when they represent different kinds of field.Is dark energy a collection of fields.

 

[meteor]

Hi kurious, I tend to prefer the idea that dark energy is due to a single field, but is because I always tend to simplicity, and I may be biased. In concrete, my favourite model of dark energy is that called quintessence.
Perhaps the most important quantity defining dark energy is the value of its equation of state. If dark energy is the cosmological constant, then the dark energy equation of state takes a fixed value always, this value is -1. However, if it's quintessence, the value of the equation-of-state varies over time. This is very important. But in general, the models of quintessence have a great difficulty, and is that they need that the initial conditions of the quintessence scalar field must have a very precisses values in order to obtain the energy density and the value of the equation of state at present time. In other words, they require fine tuning. This has been alleviate with the appearance of some models called "tracker quintessence", in these models the initial conditions are not important, a wide range of initial conditions converge to a common evolutionary track, hence the name tracker.

 

[kurious]

The difficulties dark energy is causing theorists may mean that we do not currently understand what a scalar field is - the dark energy problem may only be solved if we modify our beliefs about more familiar scalar fields.

 

[meteor]

Hello!
In 2001, a person called Wetterich wrote this paper
http://arxiv.org/abs/hep-ph/0108266
"Cosmon dark matter?"
where he proposes that quintessence, the scalar field driving the acceleration of the universe, it's not uniformly distributed throughout the U, but its more concentrated at certain points, so these "quintessence lumps" can account for the dark matter of the universe. He dubs this kind of dark matter with the original name of Cosmon dark matter.

I want to present also another version of quintessence, gauge quintessence
http://xxx.arxiv.cornell.edu/abs/hep-ph/0302087
"Gauge quintessence"

 

[kurious]

The gauge quintessence paper mentions that the flatness of a quintessence
field is difficult for physicists to model in a natural way.It makes you wonder if dark energy is a scalar phenomenon.I'm more inclined to think of it as a vector phenomenon that seems to be scalar.A vector has magnitude and direction.But if a vector was spinning quickly it would behave like a scalar. There would be a difference
though - the rotating vector should give rise to a small force in all directions.

 

[meteor]

phantom bounce

http://arxiv.org/abs/astro-ph/0405353
"The Phantom Bounce: A New Oscillating Cosmology"



-----------------------------------------------------------
Perhaps is time to give a bit of attention to another model of dark energy, the Generalized Chaplygin gas. This model was proposed in this paper

http://arxiv.org/abs/gr-qc/0202064

"Generalized Chaplygin Gas, Accelerated Expansion and Dark Energy-Matter Unification"
Authors: M. C. Bento, O. Bertolami, A. A. Sen


and is a generalization of the Chaplygin gas model of dark energy, proposed some time before by other people

 

[kurious]

"The phantom bounce" was very interesting reading. I didn't know that oscillating universe theories were constrained by Hawking's idea that black holes would grow
as large as the horizon and make the cosmological equations invalid.The paper
says that dark energy needs to tear the black holes apart before a bounce occurs for the equations to be useful.In a particular case the author says that the energy density of dark energy can be inversely proportional to the energy density of radiation.
This would be the case if the dark energy was absorbing energy from the radiation.
Is the cosmic microwave background redshifted because dark energy absorbs energy from photons? If Dark energy absorbs photon energy and undergoes a phase change it would be analagous to what water vapour is to ice and water -Give dark energy some input energy and it "evaporates" and yields a higher "vapour pressure."
If the photons and dark energy are exchanging quanta of energy this would mean
electromagnetic theory needs revising and also we would be able to introduce quantum mechanics into the friedman equations.
One of the arguments against tired light theories of redshift is that
there would be blurring because of the change in momentum of photons
interacting with other particles.But dark energy is unusual, perhaps there would be no blurring involved.And what's more explaining redshift with dark energy means the universe is still expanding and so the microwave background is the afterglow of a Big Bang.

 

[kurious]

Does dark energy absorb energy from photons and cause them to redshift?
Someone told me that the redshift would probably be higher than is experimentally observed if this idea was right, but they didn't give details of why. Can someone tell me why the redshift would be higher? And if dark energy isn't uniformly distributed at every point in space - if it was distributed like a uniform volume of atoms- could that reduce the redshift back to the experimentally observed redshift?
Can dark energy consist of individual quantized particle pairs of
some kind?
Apparently quintessence models have difficulty producing the supposed
flatness of the dark energy distribution in a natural way.There is a
paper on the arxiv that models dark energy as phenomenon with three mutually orthogonal Vectors to guarantee isotropy.Is dark energy a
vector phenomenon?
If dark energy absorbs energy from photons and expands it would keep its density constant - in other words, can dark energy be space-time?

 

[wolram]

If dark energy absorbs energy from photons and expands it would keep its density constant - in other words, can dark energy be space-time?
-----------------------------------------------------------------------
photon energy reduces as space expands also photon density,
but i think photon numbers stay constant, i think your suggestion
is close to the tired light theory which has not found favor.
I'm not even sure if total photonic energy is sufficient to power
accelerated expansion, maybe METEOR has some ideas?

 

[marcus]

Wolram have you seen
www.cosmologystatement.org[/URL]
it seems that a number of academic folk (some
emeritus) and technically trained brethren
have decided to rain on the dark energy parade
but I have not checked, just saw this

doesnt mean BB is wrong and they are right, just healthy skepticism
on their part, I suppose.
you tend to maintain a skeptical attitude, even while
getting into the details, so this should not seem all that different

I don't like their statement myself, but there it is
published 22 May in New Scientist

 

[kurious]

photon energy reduces as space expands also photon density,
but i think photon numbers stay constant, i think your suggestion
is close to the tired light theory which has not found favor.
I'm not even sure if total photonic energy is sufficient to power
accelerated expansion, maybe METEOR has some ideas?


Tired light arguments don't apply.The dark energy might not have momentum to cause blurring of photons and time dilation would be fine too because the universe is still expanding but the redshift is caused by space-time (dark energy?) absorbing energy from photons.
If rest masses are also supplying energy to dark energy then they might make up the shortage.We could all be evaporating slowly!

As for the cosmology statement: alternative theories to the big bang hypothesis should get funding.When any scientific investigation is done
it usually yields posititve or negative results that help scientists decide what the right answer is.

 

[wolram]

Thanks MARCUS, several learned people giving ms science an itch, i can
only say---------
Good old Halton Arp," I am unsure about others," he keeps banging his drum, maybe some will start to like his music, i think he should not be dismissed
as he has some valid reasons for disputing m/stream science, if i were a scientist i would sign his paper, for no other reason than opening the debate.

KURIOUS seems i misunderstood you how could your theory
be tested?

 

[Chronos]

the fluctuations are required by quantum physics. nothing, including consciousness, can remain fixed. universal expansion requires exansion on all levels, including the spectators

 

[kurious]

how could your theory
be tested?

--------------------------------------------------------------------------------
Need to know accurately the acceleration rate of the expansion of the universe and the change in that rate.
Then the amount of mass/energy turning into dark energy could be deduced.
If a planet is losing mass/energy to space-time/dark energy then the radius of its orbit
would change slightly.Perhaps a gyroscope would spin more slowly or the magnetic moment of an electron which is known to 11 decimal places might change.But any measurement of the acceleration rate of the expansion of the universe has a high
degree of uncertainty in it.Maybe the way a photon redshifts in the Earth's atmosphere
could help out.

 

[wolram]

KURIOUS, i do like your theory, if anything it is more tangible
than some and seems to have a nice intuitive feel to it, maybe
someone will come along and poke holes in it, but i think it is
a theory worth pursuing.