aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?
These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?

--
Rich

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun < M < 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]

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In article <d6c00c23-a17d-4b1a-b7c4-d93015466000@googlegroups.com>, <rdelaney2001@gmail.com> writes:

aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?

No.

These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?

There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun < M < 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

Right.

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]

I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/helbig/research/publications/abstracts/microlensing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

[[Mod. note -- URL corrected with author's permission. -- jt]]

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter.

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On November 27, Phillip Helbig (undress to reply) wrote:

Is it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?
These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.
What are the counter-arguments?

There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun < M < 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

Right.
I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/helbig/research/publications/abstracts/microlensing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

I'm unfamiliar with this technique - microlensing refers
to the occlusion of distant bright objects, by nearer objects?
Thus gravitational lensing effects?

I don't understand the primacy of the masses.
Wouldn't the statistics depend on the volume of
the 'dark' objects? That is, their solid angle arc,
how much of the sky they cover?

I don't find the reasoning compelling. You looked
at quasar variability, and concluded that MACHO
doesn't explain it. Isn't it a big leap to say such
objects don't exist at all?

Also, big-bang nucleosynthesis tells us what fraction of the universe
is in baryons; there is no way that stars, being baryonic, could make
up a significant fraction of dark matter.

Seeing that 80% of the mass of the mass is 'missing', of
unknown character, all such origin theories are suspect.

--
Rich

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Le 26/11/2018 à 19:49, rdelaney2001@gmail.com a écrit :

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun < M < 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

That study assumes a spherical halo around the galaxy. It measures the
events when a massive body passes between us and stars in the small and
large maghellanic clouds, two satellite galaxies of our own galaxy.

IF the halo is spherical THEN the study is right.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, that
study proves nothing.

If we suppose that the galaxy is old, very old, a lot of star corpses
should be around within the plane of the galaxy where they spent all
their relatively short lives...

Now, most stars that go supernovae have non-symmetrical explosions that
could propel their "dead" corpses in random directions, but the galaxy's gravity should hold most of them back and keep them within the galaxy
plane.

To prove/disprove this hypothesis we should look for einstein rings
within our own galaxy.

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In article <a5fd3c7c-d62c-47c4-94f0-6618b669727d@googlegroups.com>, rdelaney2001@gmail.com writes:

I'm unfamiliar with this technique - microlensing refers
to the occlusion of distant bright objects, by nearer objects?
Thus gravitational lensing effects?

Yes. Not necessary occlusion, though; it's enough if a background
object is near the line of sight to a foreground object. Due to proper
motion, the proximity changes with time, and since the amplification
depends on the radial distance, one sees a typical brightening then
dimming of the background object.

[[Mod. note -- To the original poster (and anyone else unfamiliar
with the technique): The Wikipedia article
https://en.wikipedia.org/wiki/Gravitational_microlensing
is an excellent introduction.
-- jt]]

I don't understand the primacy of the masses.
Wouldn't the statistics depend on the volume of
the 'dark' objects? That is, their solid angle arc,
how much of the sky they cover?

Not so much their own solid angle, but rather the solid angle within
which an appreciable gravitational-lensing effect occurs.

I don't find the reasoning compelling. You looked
at quasar variability, and concluded that MACHO
doesn't explain it. Isn't it a big leap to say such
objects don't exist at all?

The conclusion is not that they don't exist at all, but rather that
they cannot explain most of the long-term variability of quasars.
This contradicts a claim that most long-term variability of quasars
is due to microlensing, which in turn would imply that they make
up at least most of the dark matter in the universe. Executive
summary: Yes, at first glance long-term quasar variability is
compatible with microlensing, if one looks at individual light
curves. However, this hypothesis makes predictions about the
distribution of amplifications which are in conflict with
observations.

Also, big-bang nucleosynthesis tells us what fraction of the universe
is in baryons; there is no way that stars, being baryonic, could make
up a significant fraction of dark matter.

Seeing that 80% of the mass of the mass is 'missing', of
unknown character, all such origin theories are suspect.

Why? If you have a theory which predicts what all the matter in
the universe is composed of, let us know. Otherwise, we discover
it, component by component. We know more about some components
than about others. For example, we know how many baryons there can
be at most. This is not enough to explain most of the dark matter,
so there must be some other component. What is surprising or suspect
about that?

If one thinks that dark matter is somehow strange, one assumes, for
no good reason, that all components of the mass of the universe
must be detectable via our senses, or by astronomical techniques
at the stage they were during the second half of the twentieth
century.

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In article <ptjv8u$c8s$1@dont-email.me>, jacobnavia
<jacob@jacob.remcomp.fr> writes:

That study assumes a spherical halo around the galaxy. It measures the
events when a massive body passes between us and stars in the small and
large maghellanic clouds, two satellite galaxies of our own galaxy.

IF the halo is spherical THEN the study is right.

There is much evidence that galactic halos are spherical.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy,
that study proves nothing.

Note that there are similar studies lucking along the plane of the
galaxy towards the bulge. Same result: the bulk of the dark matter
cannot be in compact objects of around a solar mass.

If we suppose that the galaxy is old, very old,

Older than it is normally thought to be? On what grounds?

a lot of star corpses
should be around within the plane of the galaxy where they spent all
their relatively short lives...

Star corpses are baryonic, and hence ruled out due to upper limits on
the total amount of baryons.

To prove/disprove this hypothesis we should look for einstein rings
within our own galaxy.

One won't see Einstein rings, since a) they are too small and b) occur
only when there is (nearly) perfect alignment. Rather, such
microlensing surveys look for the brightening then dimming of background objects caused by the gravitational-lensing effect when they pass near
the line of sight of a foreground object

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On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

In article <d6c00c23-a17d-4b1a-b7c4-d93015466000@googlegroups.com>, <rdelaney2001@gmail.com> writes:

aIs it possible that the missing mass, the 'dark matter',
consists of two generations of burned out stars?

No.

These would be short lifetimes, hence large masses,
according to star formation theory, hence mostly black holes
or neutron stars. I don't see that as a problem.

What are the counter-arguments?

There are several.

[[Mod. note -- Microlensing studies show that at most a small fraction
of the dark matter in the Milky Way's halo can be in compact objects
of stellar mass. For example, the EROS project
https://arxiv.org/abs/astro-ph/0607207
concluded that "machos in the mass range 0.6e-7 M_sun < M < 15 M_sun
are ruled out as the primary occupants of the Milky Way Halo".

Right.

I don't know offhand what (if any) limits there are for M31 or maybe
other galaxies.
-- jt]]

I was co-author on a paper which pointed out that a significant fraction
of dark matter can't be on compact objects between us and quasars (i.e.
in most of the observable universe), otherwise this would be seen in
quasar light curves (which, despite some claims to the contrary, is not
the case):

http://www.astro.multivax.de:8000/helbig/research/publications/abstracts/microlensing_qsos.html
http://adsabs.harvard.edu/abs/2003A&A...408...17Z

[[Mod. note -- URL corrected with author's permission. -- jt]]

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter.

The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2
RDS

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On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:

On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is
in baryons; there is no way that stars, being baryonic, could make up a significant fraction of dark matter.

The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts https://arxiv.org/abs/1810.05976v2
RDS

This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the dark-matter density, more or less by definition. -P.H.]

At the beginning of the article we reed: "Nevertheless, it is physics
that needs to be considered in any calculation of BBN."
I agree if you want to understand the early evolution of the universe
it is physics.
At the end we read: "The revised abundances exacerbate the deviation
of BBN etc perhaps suggesting a crucial greater need for new physics
and/or astrophysical explanations."
My interpretation is that the birth of non-baryonic matter is not part
BBN and started later.

[Moderator's note: We don't know what dark matter is, but as far as I
know there is no plausible scenario where it forms after BBN. -P.H.]

Secondly any explanation requires a definition what darkmatter
(i.e. non-baryonic matter) physical is.

[Moderator's note: Here: whatever is not baryonic. -P.H.]

The title of the article https://arxiv.org/abs/astro-ph/0501171 is:
"Detection of the Baryon Acoustic Peak in the Large-Scale
Correlation Function of SDSS Luminous Red Galaxies"
Baryon fraction = Omegab/Omagam is dicussed at page 2.
Here we read:
"A simple way to understand this is to consider that from an initial
point perturbation common to the dark matter and the baryons,
the dark matter perturbation grows in place while the baryonic
perturbation is carried outward in an expanding spherical wave"
IMO this is not simple.

[Moderator's note: While the process is relatively simple compared to
some other things, what is meant is that this is an easy-to-understand
rough sketch, not that the entire process is extremely simple. -P.H.]

Nicolaas Vroom

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On 11/30/18 4:16 PM, Nicolaas Vroom wrote:

On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:

On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is >>> in baryons; there is no way that stars, being baryonic, could make up a
significant fraction of dark matter.

The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS

This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the dark-matter density, more or less by definition. -P.H.]

[Moderator's note: Quoted text snipped. -P.H.]

Ref 1 https://arxiv.org/abs/1810.05976v2
Ref 2 https://arxiv.org/abs/1811.04932
There was a very vigorous response[2] to [1]
defending the current BBN calculation
"The detailed and correct computation
of big-bang nucleosynthesis (BBN) dates
back 51 years to the seminal papers of Wagoner, Fowler and Hoyle"
(also referenced in 1)
but in their conclusions[2];
"We have not been able to identify
the source of the discrepancy with [1]"

Apparently it comes down to:
How do BBN classical Maxwell-Boltzmann plasma
baryon relativistic velocity distributions
affect nuclear reaction rates?
rds

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On 01/12/2018 23:00, Richard D. Saam wrote:

On 11/30/18 4:16 PM, Nicolaas Vroom wrote:

On Wednesday, 28 November 2018 21:49:18 UTC+1, Richard D. Saam wrote:

On 11/27/18 1:03 PM, Phillip Helbig (undress to reply) wrote:

Also, big-bang nucleosynthesis tells us what fraction of the universe is >>>> in baryons; there is no way that stars, being baryonic, could make up a >>>> significant fraction of dark matter.

The Big-bang nucleosynthesis hypothesis does not warrant
such an absolute telling baryon fraction statement
in terms of on going BBN mechanistic derivation efforts
https://arxiv.org/abs/1810.05976v2
RDS

This interesting (up to date) article mentions the word baryonic,
however nothing about darkmatter and baryon fraction.

[Moderator's note: Since we have a pretty good idea of the total
density, the difference between that and the baryonic density is the
dark-matter density, more or less by definition. -P.H.]

[snip]

At the risk of opening up a new can of worms what do people think of the
new paper from Jamie Farnes at Oxford which seeks to unite dark energy
and dark matter as a negative mass fluid filling all of empty space (if
I have understood his paper correctly). It seems to work... title:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

--
Regards,
Martin Brown

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In article <puavjn$1pl9$1@gioia.aioe.org>,
Martin Brown <newspam@nezumi.demon.co.uk> writes:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

Paper link is at https://www.aanda.org/articles/aa/full_html/2018/12/aa32898-18/aa32898-18.html

A&A site was flaky the last day or two, but eventually it served the
paper.

As I wrote on sci.astro, the paper seems highly unconventional but mathematically consistent. It requires _two_ unconventional
hypotheses -- existence of negative mass and continuous creation of
it -- so skepticism on that basis is warranted.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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In article <ptjv8u$c8s$1@dont-email.me>,
jacobnavia <jacob@jacob.remcomp.fr> writes:

IF the halo is spherical THEN the study is right.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, that study proves nothing.

Aren't there also microlensing studies towards the Galactic bulge?

Now, most stars that go supernovae have non-symmetrical explosions that
could propel their "dead" corpses in random directions, but the galaxy's gravity should hold most of them back and keep them within the galaxy
plane.

How would motion perpendicular to the plane be damped out?

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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[[Mod. note -- This article arived in my moderation mailbox with a
number of garbled non-ASCII characters, and many excessively-long
lines. I have "tidied up" and reformatted the text; my apologies
to all if I've garbled the author's intended meanings.

Memo to all newsgroup participants: Usenet isn't fully 8-bit-clean,
so it's much safer to restrict your postings to plain ASCII. Notably,
avoid "smart quotes" -- they are almost always garbled somewhere before
the moderators ever see your submission.
-- jt]]

1:13 AMMartin Brown

At the risk of opening up a new can of worms what do people think of the
new paper from Jamie Farnes at Oxford which seeks to unite dark energy
and dark matter as a negative mass fluid filling all of empty space (if
I have understood his paper correctly). It seems to work... title:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

--

Regards,
Martin Brown.

For what my opinion is worth, I'm glad to see it. I've long been
of the opinion that looking for exotic matter or applying modifications
to GR were futile. They both ignore published work by W. Israel,
H. Sato, K. Maeda among others whose work could potentially be
generalized to explain Dark Matter.

If we consider that gravity is actually a configuration of space
time we must wonder what types of relevant physics we can expect
from other types of configurations. And most especially when two
different types abut one another, as when expanding Voids interact
with stationary matter structures and their associated gravitational
fields. In other words when two different metrics are involved.

I'm particularly encouraged by this:
"It seems that the proposed negative mass fluid can be modelled
as either matter or vacuum energy. It has previously been proposed
that space-time arises as a form of large-scale condensate of more
fundamental objects, that are typically of an unknown nature
(e.g. Liberati & Maccione 2014). One could therefore speculate
that the negative masses could be interpretable as a quantised
form of energy associated with space-time itself".

That, _that energy_, is natural to spacetime in the absence of
matter. That matter inhibits this energy by its presence.

Furthermore,

H.Sato and K. Maeda (here)
Humitaka Sato Kei-ichi Maeda
Progress of Theoretical Physics, Volume 70, Issue 1, 1 July 1983,
Pages 119--127, https://doi.org/10.1143/PTP.70.119

offer an idea whereby expansion of a Void causes matter to cluster
along the void perimeter and ultimately to form structures via
gravitational collapse.

With these ideas and Israel's formalism (snowplow effect of expanding
space time metric during a supernova) we could ask if: matter
structures are, in effect, 'confined' to the filaments because of
expanding Voids and cannot escape that confinement? can enough
centrifugal acceleration be imparted to disrupt structure? that
is : can stars in the outer galaxy even leave bound structure without
giving up their energy and "falling back" ? if voids are constraints
and they didn't exist would galaxies be larger in breadth? And would
their outer components then follow Newtonian mechanics? are DM and
DE two sides of the same phenomenon? (To me that seems most plausible, especially when the expansion is accelerating.)

Ultimately I don't like the idea of negative mass unless it is in
the idea of Dirac's anti electron. That is, more like a "hole" in
a sea of normal mass. Also I wonder if negative mass is electromagnetically responsive. I'm more inclined towards any theory explaining the
Dark phenomena that invokes, or at least recognizes "metric
confinement".

Brad

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On Thu, 06 Dec 2018, Martin Brown wrote:

new paper from Jamie Farnes at Oxford which seeks to unite dark energy
and dark matter as a negative mass fluid filling all of empty space

Unimaginative. Dark energy & dark matter are just quantifications of
the discrepancy between physical law and our models of it. I prefer a dimensional interpretation where additional dimensions have as-yet
unmodelled qualities like "scale" or "Mach's Law". Try explaining
colors to a totally color-blind person to get a glimpse of this task.

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[[Mod. note -- My apologies for the delay in processing this article,
which was submitted on 2018-12-08.
-- jt]]

In article <puetbc$jgf$2@dont-email.me>, Steve Willner <willner@cfa.harvard.edu> writes:

In article <ptjv8u$c8s$1@dont-email.me>,
jacobnavia <jacob@jacob.remcomp.fr> writes:

IF the halo is spherical THEN the study is right.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, tha=

t

study proves nothing.

Aren't there also microlensing studies towards the Galactic bulge?

Yes, including some by the MACHO collaboration.

Now, most stars that go supernovae have non-symmetrical explosions that could propel their "dead" corpses in random directions, but the galaxy'=

s

gravity should hold most of them back and keep them within the galaxy plane.

How would motion perpendicular to the plane be damped out?

I think he is saying that while supernovae might cause stellar remnants
to move in any direction, the gravity of the galaxy would cause them to concentrate in the plane. (I'm just explaining what I think the
original poster meant.)

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[[Mod. note --
My apologies for the delay in processing this article, which the
author submitted on 2018-12-09.
-- jt]]

On 12/8/2018 7:38 PM, Steve Willner wrote:

In article <ptjv8u$c8s$1@dont-email.me>,
jacobnavia <jacob@jacob.remcomp.fr> writes:

IF the halo is spherical THEN the study is right.

If the halo is NOT spherical but follows the plane of the milky way,
i.e. most dead stars are in the galaxy plane and WITHIN the galaxy, that
study proves nothing.

Aren't there also microlensing studies towards the Galactic bulge?

Now, most stars that go supernovae have non-symmetrical explosions that
could propel their "dead" corpses in random directions, but the galaxy's
gravity should hold most of them back and keep them within the galaxy
plane.

How would motion perpendicular to the plane be damped out?

If they oscillate up and down the plane, then each time they go through
the plane and traverse the denser regions, the elastic collisions with
other stars create friction, just like atoms in a gas see friction by
the collisions with other atoms (or molecules).

This does not seem to be different from what happens before they go
supernova, of course..

--
Jos

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In article <puavjn$1pl9$1@gioia.aioe.org>, Martin Brown <newspam@nezumi.demon.co.uk> writes:

At the risk of opening up a new can of worms what do people think of the
new paper from Jamie Farnes at Oxford which seeks to unite dark energy
and dark matter as a negative mass fluid filling all of empty space (if
I have understood his paper correctly). It seems to work... title:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

There is some blog discussion at

https://telescoper.wordpress.com/2018/12/07/negative-mass-phlogiston-and-cosmology

and

https://backreaction.blogspot.com/2018/12/no-negative-masses-have-not.html

[[Mod. note --
1. My apologies for the delay in processing this article, which the
author submitted on 2018-12-08.

2. I strongly agree with the author's recommendation -- those are
*excellent* blog discussions.
-- jt]]

--- SoupGate-Win32 v1.05
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[[Mod. note -- I apologise for the delay in processing this article,
which the author submitted on 2018-12-09.
-- jt]]

Steve Willner
In article <puavjn$1pl9$1...@gioia.aioe.org>,
Martin Brown <new...@nezumi.demon.co.uk> writes:

A Unifying Theory of Dark Energy and Dark Matter: Negative Masses and
Matter Creation within a Modified =CE=9B CDM Framework

https://arxiv.org/abs/1712.07962

Arxiv link but now also in A&A'. It makes some testable predictions.

Paper link is at >https://www.aanda.org/articles/aa/full_html/2018/12/aa32898-18/aa32898-18.html

A&A site was flaky the last day or two, but eventually it served the
paper.

As I wrote on sci.astro, the paper seems highly unconventional but >mathematically consistent. It requires _two_ unconventional
hypotheses -- existence of negative mass and continuous creation of
it -- so skepticism on that basis is warranted.

As I understood it he ran simulations. At the end of the paper he
states that the negative mass energy could instead be vacuum energy.
So my question is...suppose one postulates a field associated with
negative mass. Would it be the opposite of a normal gravitational field?
Would it take kinetic energy from anything that entered it? Would
geodesics diverge?

Aren't those qualities associated with an expanding space time metric?
Can't we model Voids in such a way?

Brad

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In article <5c0cf368$0$22357$e4fe514c@news.xs4all.nl>,
Jos Bergervoet <bergervo@iae.nl> writes:

If they oscillate up and down the plane, then each time they go through
the plane and traverse the denser regions, the elastic collisions with
other stars create friction, just like atoms in a gas see friction by
the collisions with other atoms (or molecules).

This called "dynamical friction." (I expect Jos knows that, but some
readers may not.) The question is how long it takes for this process
to damp out the vertical motion. If not very long, why do the thick
disk and halo stars still have the orbits they do?

This does not seem to be different from what happens before they go supernova, of course..

The progenitors of core-collapse SNe are massive, therefore young,
stars and therefore presumably belong to the thin disk population.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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