How To Dark matter: Agreed terms help sensible discussion

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Catastrophe

"There never was a good war, or a bad peace."
Sterile neutrino - Wikipedia
See 3.


Neutrinos and dark matter - AIP Publishing
https://aip.scitation.org › doi › pdf


by A Ibarra · 2015 · Cited by 4 — Neutrinos could be key particles to unravel the nature of the dark matter of the ... long-lived on cosmological time-scales and electrically neutral.


Connecting neutrino physics with dark matter - IOPscience
https://iopscience.iop.org › article


by M Lattanzi · 2014 · Cited by 39 — The origin of neutrino masses and the nature of dark matter are two in ... by an electromagnetically neutral component dubbed dark matter.


[1103.3261] Neutrino Physics with Dark Matter Experiments ...
https://arxiv.org › hep-ph


by M Pospelov · 2011 · Cited by 75 — ... Dark Matter Experiments and the Signature of New Baryonic Neutral ... If some fraction of solar neutrinos oscillate into \nu_b on their ...


DARK MATTER AND NEUTRINOS arXiv:1711.10564v1 ...
https://arxiv.org › pdf


PDF
by G Sharma · 2017 — Many experiments has been performed in search of dark matter candidates. Neutrinos, which are electrically neutral and tiny parti- cles, seem ...


Signal from sterile neutrino dark matter in extra U(1) model at ...
https://www.sciencedirect.com › science › article › pii


by O Seto · 2020 · Cited by 3 — Then, one RH neutrino could be a DM candidate if its lifetime is long enough, because it is electrically neutral [7]. Thus, three RH neutrino ...


A White Paper on keV Sterile Neutrino Dark Matter - OSTI.GOV
https://www.osti.gov › pages › servlets › purl


PDF
by R Adhikari · 2017 · Cited by 444 — we first review the physics motivation for sterile neutrino Dark Matter, based on ... Indeed, the neutral, weakly interacting, massive neutrino could in.


Cat :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Astronomy Now, October 2021 “Is dark matter real”, by Keith Cooper
Apologies for a repetition, but I really think this up to date assessment belongs in this thread,

After reviewing its origins (“It was named dark matter, though nobody really knew what it was”) and considering previous suggestions, such as MACHOs (Massive Compact Halo Objects) which are known objects such as neutron stars and black holes, attention has passed to new types of particles, distinct from normal matter – “cold, in that they have low energy and tend to sit in large clumps, and that they weakly interact with other forms of normal matter or electromagnetic radiation”. These are called WIMPS (Weakly Interacting Massive Particles).

Some possible modification of normal gravity is considered – MOND, or MOdified Newtonian Dynamics, but this does not currently compete with dark matter, in terms of explanations of observed phenomena. There is considerably more relevant discussion including coverage of the Bullet Cluster (collision between two galaxy clusters) and NGC 1052 –DF2 and –DF4Awithout dark matter) and evidence from the Cosmic Microwave Background radiation, provided by COBE, WMAP and Planck,

In conclusion: “Of course, what would really cement things in favour of dark matter would be if we could actually directly detect a bonafide particle of dark matter” and efforts are being made in this direction involving xenon atoms which, being relatively massive (atomic number 54) “have a greater chance of interacting . . . with a dark matter WIMP”. Whilst no dark matter particles have yet been found, “if dark matter really exists, and is a WIMP, then it is running out of places to hide.”

Cat :)
 

Catastrophe

"There never was a good war, or a bad peace."
Some really thought-provoking matters are raised in an article “Is the Big Bang in Crisis” by Dan Hooper (Astronomy May 2020). The author is a senior scientist at the Fermi National Accelerator Laboratory in Illinois, and a professor of Astronomy and Astrophysics at the University of Chicago; also author of At the Edge of Time: Exploring the Mysteries of Our Universe’s First Seconds. The article is sub-titled “Stubborn problems with dark matter, dark energy, and cosmic expansion have some astronomers re-thinking what we know about the early universe”.

Although science provides stunning agreement based on powerful observations, cosmologists have struggled – “if not outright failed –to understand essential facts of the universe” he suggests. These include dark matter and dark energy (which together make up more than 95% of the total energy in existence today); and how the universe’s protons, electrons and neutrons could have survived the effects of the Big Bang. “Everything we know about the laws of physics tells us that these particles should have been destroyed by antimatter long ago. And in order to make sense of the universe, cosmologists have been forced to conclude that space, during its earliest moments, must have undergone a brief and spectacular period of hyperfast expansion – an event known as cosmic inflation. Yet we know next to nothing about this key era of cosmic history”. Whilst it is possible that science may resolve these difficulties on further investigation, “we have not gained any substantively greater understanding of the nature of dark energy, the force that seems to be accelerating the expansion of the cosmos”. Or do these problems signify something more than just a few loose ends? Do they, perhaps, point us towards a very different picture of our universe and its early development?

View: https://imgur.com/a/qPCsZA7


QUOTE
This Hubble Space Telescope composite image shows a ghostly "ring" of dark matter in the galaxy cluster ZwCl0024+1652.

The ring-like structure is evident in the blue map of the cluster's dark matter distribution. The map is superimposed on a Hubble image of the cluster. The ring is one of the strongest pieces of evidence to date for the existence of dark matter, an unknown substance that pervades the Universe. [My emphasis]

The map was derived from Hubble observations of how the gravity of the cluster ZwCl0024+1652 distorts the light of more distant galaxies, an optical illusion called gravitational lensing. Although astronomers cannot see dark matter, they can infer its existence by mapping the distorted shapes of the background galaxies. The mapping also shows how dark matter is distributed in the cluster.

Astronomers suggest that the dark-matter ring was produced from a collision between two gigantic clusters.

Dark matter makes up the bulk of the Universe's material and is believed to make up the underlying structure of the cosmos.

The Hubble observations were taken in November 2004 by the Advanced Camera for Surveys (ACS). Thanks to the exquisite resolution of the ACS, astronomers saw the detailed cobweb tracery of gravitational lensing in the cluster.

Credit:

NASA, ESA, M.J. Jee and H. Ford (Johns Hopkins University)

QUOTE



Despite knowing little about dark matter, there is often speculation about what kinds of particle constitute dark matter. At first, WIMPs (weakly interacting massive particles) seemed a suitable candidate, but “increasingly sensitive dark matter detectors in deep underground laboratories that are capable of detecting individual collisions between a dark matter particle” and target atoms, have failed to produce the desired results. Although some form a WIMP remains a possible contender, some scientists are beginning to look elsewhere. One theory (https://www.scientificamerican.com/article/is-dark-matter-made-of-axions/#) has “yet to place very strict constraints on the properties of these particles”. The present author suggests that “another possibility that could explain why dark matter has been so difficult to detect is that the first moments of the universe may have played out much differently than cosmologists have long imagined”.

It has been calculated that the early universe should have produced vast quantities of WIMPs during approximately the first millionth of a second after the Big Bang. How these would . or would not, survive (and contribute to eventual dark matter) depends on their initial interactions. These calculations, in turn, depend on the assumption that space expanded steadily during the first fraction of a second, without any unexpected events or transitions. “It is entirely plausible that this simply was not the case”.

However much cosmologists know about the universe – its expansion and evolution – “they know relatively little about the first seconds that followed the Big Bang – and next to nothing about the first trillionth of a second. When it comes to how our universe may have evolved, or to the events that may have taken place during these earliest moments, we have essentially no direct observations on which to rely. This era is hidden from view, buried beneath impenetrable layers of energy, distance and time. Our understanding of this period of cosmic history is, in many respects, little more than an informed guess based on inference and extrapolation. Look far enough back in time and almost everything we know about our universe could have been different. Matter and energy existed in different forms than they do today, and they may have experienced forces that have not yet been discovered. . . . . . . Matter likely interacted in ways that it no longer does, and space and time themselves may have behaved differently than they do in the world we know.”

This may well lead to question what we do know about early expansion of the universe. The discovery of Edwin Hubble in 1929 that galaxies are moving apart at speeds proportional at speeds proportional to their distance from each other, provided the first clear evidence that the universe is expanding. The rate of this expansion, known as the Hubble constant is a key property in current Cosmology. Speed being proportional to separation (distance), we can write speed = k x distance. k is the Hubble Constant, and, in the graph, it is measured in (km per second) divided by megaparsecs



View: https://imgur.com/a/eUjIeDv

Graph (above) shows that the best fit line is far from perfect. It does not show perfect proportionality for all points – if fact, scarcely 2 or 3 out of 22.
The diagram below suggests alternative best fit lines, had some points been omitted or been only slightly different. Is this so unlikely if some distances turned out to be 10 times too small?
Would other fits be better if the straight line were not forced through the origin? After all, the original graph shows 3 points with zero velocity at a positive distance.
[Cat]


Graph (above) shows that the best fit line is far from perfect. It does not show perfect proportionality for all points – if fact, scarcely 2 or 3 out of 22.
The diagram below suggests alternative best fit lines, had some points been omitted or been only slightly different. Is this so unlikely if some distances turned out to be 10 times too small?
Would other fits be better if the straight line were not forced through the origin? After all, the original graph shows 3 points with zero velocity at a positive distance.
[Cat]


View: https://imgur.com/a/ws8B8fQ


(Above) As mentioned in the article, the ‘Hubble constant’ is not constant, suggesting that a simple straight line relationship may not be appropriate. “Although measurements of this so-called Hubble constant have grown more precise over the years, different methods yield different results. Direct observations of relatively nearby galaxies give significantly higher values than those deduced from observations of the cosmic microwave background”.


As mentioned in the article, the ‘Hubble constant’ is not constant, suggesting that a simple straight line relationship may not be appropriate. “Although measurements of this so-called Hubble constant have grown more precise over the years, different methods yield different results. Direct observations of relatively nearby galaxies give significantly higher values than those deduced from observations of the cosmic microwave background”.


“Assuming that these studies have correctly accounted for all the systematic uncertainties inherent in the observations, these two ways of determining the Hubble constant appear to be incompatible – at least within the context of the standard cosmological model. To make these discrepant results mutually consistent, astronomers would be forced to change how we think the cosmos expanded and evolved, or to reconsider the forms of matter and energy in the universe during the first few hundred thousand years following the Big Bang”.

Maybe all will come to rights with a few minor mods, but is it more likely that our present understanding is more analogous to that in 1904, when physicists had no idea what powered the Sun, or why various chemical elements emitted and absorbed light with specific patterns, none of which physicists had the slightest idea how to explain? In other words “the inner workings of the atom remained a total and utter mystery”.

There is so much more in this article, which is one of the best that I have read in some time, that I could not refrain from drawing it to your attention. Cat :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Thank you for your kind comments, but all credit is due to the author, Dan Hooper.

I have long had some reservations about the 'standard model', for example, when there is extremely rapid expansion postulated ('faster than light'?), and, if speed is proportional to distance, all galaxies will eventually be retreating faster than light'? -- especially if retreat is accelerating! Also, if there were this extremely rapid cosmic inflation, how do you reconcile this with a simplistic(?) straight line extrapolation on the graph - as if everything were uniform? When we know that the Hubble constant is not constant? And so on . . . . . . and on . . . , , , and on . . . . . . Invent one theory because it is expanding too much, and then another because it is contracting too much - all based on the less than 5% available to our observations.

Cat :)

One small addition. When all galaxies are retreating from one another faster than light, and all then each have (relatively) infinite mass, how come they can't see one another?

I do appreciate relativistic effects. However, there may also be a question of where this energy derives from if the mass of the galaxies is increasing towards 'infinity' approaching light speeds. Is this enough to retreat into a Big Crunch?
 
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A few points I’ll toss out....

It‘s all too common to credit Hubble with claims such as made in the image text. But Hubble never demonstrated or encouraged expansion to explain his data.

So he did not discover the “expanding universe in 1929.” In 1927, George’s Lemaitre published the first paper that argued for expansion along with his own expansion calculation. This was the paper that gave us the BBT. Lemaitre’s estimate was off since he only had Slpher’s few redshift data, along with Hubble’s few distance measurements. IIRC, Lemaitre’s estimate was less in error than those using Hubble’s distance and redshift data.

Also, regions that are currently moving away from us at faster than light speed will emit light that will actually reach us. At some greater distance, hence much greater than light speed, we will never see this light. This is mainstream science and demonstrable.
 

Jzz

May 10, 2021
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Universe - the definitive visual guide Gen ed Martin Rees Dark matter and dark energy DK 2012
There is far more dark matter in the Universe than that contained in stars and other visible objects. The invisible mass is called "dark matter". Its composition is unknown. Some might take the form of MACHOs (massive compact objects) - dark planet-like bodies - or WIMPs (weakly interacting massive particles) - exotic subatomic entities that scarcely interact with ordinary matter. . . . . . . . . . Cosmologists have proposed the existence of "dark energy", a force that counteracts gravity and causes the Universe to expand faster. The exact nature of dark energy is still speculative."
An excellent initiative.
 

Jzz

May 10, 2021
106
53
660
There's A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating Ethan Siegel, Senior Contributor Jul 26, 2018,10:00am EDT
"You'd wonder if we didn't have something fundamentally wrong. If we hadn't goofed something fundamental, like our theory of gravity. This is the heart of the debate over the existence of dark matter.
"On the scales of groups of galaxies, individual galaxy clusters, colliding galaxy clusters, the cosmic web, and the leftover radiation from the Big Bang, MOND's predictions fail to match reality, whereas dark matter succeeds spectacularly. . . . . . . . . . in the scientific realm, the evidence has already decided the matter, and 5/6ths of it is dark."
Present main-stream science, has a huge lacuna in not recognising the presence of ‘virtual’ particles. The existence of these ‘virtual’ particles was discovered during the middle of the Second World War, and so was highly classified, an injunction that was never removed, that the discovery never made it into main-stream science. although a vestigial reference to it exists in the form of the Lamb shift. The Lamb shift, which incidentally is a reproducible experiment, detected the fact that electrons in orbit ( I use the word purposely) around the nucleus were constantly emitting and absorbing what came to be known as ‘virtual’ photons. These were photons that were identical to normal photons but whose interactions took place over such an infinitesimal period of time that to all purposes they escaped the conservation of energy laws. This is in keeping with the Heisenberg Uncertainty principle as it applies to time and energy. Surely, a physics that can casually accept the existence of multiple Universe, super-position, dis-embodiment, quantum entanglement and other such exotic possibilities, should have no trouble in accepting that there exist energies smaller than we can detect or time periods smaller than we can discern? In any case the presence of these self-interactions by the electron as it rotates around the nucleus, offers the perfect classical physics explanation as to why the electron does not radiate away all of its energy and fall into the nucleus. The electron is in effect, by means of emitting and absorbing 'virtual' photons, self-regulating its energy.

If there exist ‘virtual’ photons that exist for such short periods of time that they escape the laws of conservation of energy and momentum, there also exist photons with such low energies that they can exist for practically ever. These are the ‘virtual’ photons that make up dark matter. If ‘virtual’ photons and ‘virtual’ interactions are recognised, as they should be given the evidence, then they completely negate the need for wave-particle duality, one of the very shaky corner stones of quantum mechanics.
 

Catastrophe

"There never was a good war, or a bad peace."
Present main-stream science, has a huge lacuna in not recognising the presence of ‘virtual’ particles. The existence of these ‘virtual’ particles was discovered during the middle of the Second World War, and so was highly classified, an injunction that was never removed, that the discovery never made it into main-stream science. although a vestigial reference to it exists in the form of the Lamb shift. The Lamb shift, which incidentally is a reproducible experiment, detected the fact that electrons in orbit ( I use the word purposely) around the nucleus were constantly emitting and absorbing what came to be known as ‘virtual’ photons. These were photons that were identical to normal photons but whose interactions took place over such an infinitesimal period of time that to all purposes they escaped the conservation of energy laws. This is in keeping with the Heisenberg Uncertainty principle as it applies to time and energy. Surely, a physics that can casually accept the existence of multiple Universe, super-position, dis-embodiment, quantum entanglement and other such exotic possibilities, should have no trouble in accepting that there exist energies smaller than we can detect or time periods smaller than we can discern? In any case the presence of these self-interactions by the electron as it rotates around the nucleus, offers the perfect classical physics explanation as to why the electron does not radiate away all of its energy and fall into the nucleus. The electron is in effect, by means of emitting and absorbing 'virtual' photons, self-regulating its energy.

If there exist ‘virtual’ photons that exist for such short periods of time that they escape the laws of conservation of energy and momentum, there also exist photons with such low energies that they can exist for practically ever. These are the ‘virtual’ photons that make up dark matter. If ‘virtual’ photons and ‘virtual’ interactions are recognised, as they should be given the evidence, then they completely negate the need for wave-particle duality, one of the very shaky corner stones of quantum mechanics.
Thank you for that most interesting post. I certainly need to study it carefully.
Cat :)
 

Catastrophe

"There never was a good war, or a bad peace."
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