# Physicists measure the loss of dark matter since the birth of the universe

Discussion in 'Astronomy, Exobiology, & Cosmology' started by paddoboy, Dec 28, 2016.

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Physicists measure the loss of dark matter since the birth of the universe
December 28, 2016

The discrepancy between the cosmological parameters in the modern Universe and the Universe shortly after the Big Bang can be explained by the fact that the proportion of dark matter has decreased. The authors of the study could calculate how much dark matter could have been lost and what the corresponding size of the unstable component would be. Researchers may explore how quickly this unstable part decays and say if dark matter is still disintegrating. Credit: MIPT
Russian scientists have discovered that the proportion of unstable particles in the composition of dark matter in the days immediately following the Big Bang was no more than 2 percent to 5 percent. Their study has been published in Physical Review

"The discrepancy between the cosmological parameters in the modern universe and the universe shortly after the Big Bang can be explained by the fact that the proportion of dark matter has decreased. We have now, for the first time, been able to calculate how much dark matter could have been lost, and what the corresponding size of the unstable component would be," says co-author Igor Tkachev of the Department of Experimental Physics at INR.

Astronomers first suspected that there was a large proportion of hidden mass in the universe back in the 1930s, when Fritz Zwicky discovered "peculiarities" in a cluster of galaxies in the constellation Coma Berenices—the galaxies moved as if they were under the effect of gravity from an unseen source. This hidden mass, which is only deduced from its gravitational effect, was given the name dark matter. According to data from the Planck space telescope, the proportion of dark matter in the universe is 26.8 percent; the rest is "ordinary" matter (4.9 percent) and dark energy (68.3 percent).

danshawen likes this.

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http://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.023528

Dark matter component decaying after recombination: Lensing constraints with Planck data

ABSTRACT
It has been recently suggested [Z. Berezhiani, A. D. Dolgov, and I. I. Tkachev, Phys. Rev. D 92, 061303 (2015)] that emerging tension between cosmological parameter values derived in high-redshift (CMB anisotropy) and low-redshift (cluster counts, Hubble constant) measurements can be reconciled in a model which contains a subdominant fraction of dark matter decaying after recombination. We check the model against the CMB Planck data. We find that lensing of the CMB anisotropies by the large-scale structure gives strong extra constraints on this model, limiting the fraction as F<8% at 2σconfidence level. However, investigating the combined data set of the CMB and conflicting low-z measurements, we obtain that the model with F≈2%–5% exhibits better fit (by 1.5–3σ depending on the lensing priors) compared to that of the concordance ΛCDM cosmological model.

5. ### danshawenValued Senior Member

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Awesome observation! 2016 was a great year for science, even if we lost a few great scientists.

7. ### The GodValued Senior Member

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It is needed to explain DM = 0.

8. ### karenmanskerKSMRegistered Senior Member

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Question: How can 'we' measure DM when it has NOT yet been established (i.e., 'proven' experimentally) that DM even exists. I appears (to me) that DM is hypothesized only by default . . . that there are yet shown-to-be any viable alternatives. The model is based on their "hypothesis" - no experimental data (other than 'mental' cogitations) has been based on any real observations - BTW: Is DM really observable (physically detectible) - or, is it only inferred based on mental and mathematical constructs?. Are we forgetting the accepted steps in the Scientific Method? Just sayin' . . . ya' know . . . .

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DM was certainly a fudge factor to explain rotational curves of some galaxies.
That does not make it wrong.
Since those days, more and more evidence has been observed to support the DM concept.
Fudge factors in other areas of science and cosmology are also evident, and now accepted.
Einstein's CC was a fudge factor, which he declared as his greatest blunder, which strangely enough, is now once again, back in vogue.

10. ### karenmanskerKSMRegistered Senior Member

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Good points Paddoboy . . . .

I pretty much agree with you. 'fudge factor' (FF) does not make it (e.g., DM concept) wrong . . . .but it (FF) does not necessarily make it correct either.
More and more evidence? . . . . .Would that be "observational evidence" (Step 1 of Scientific Method, SM) . . . or "experimental evidence" (Step 3 in SM) How does one perform experiments on something that hasn't been proven yet to exist? At best one can make only observations and try to 'fit' them into a preconceived/hypothetical model.
Just because a fudge factor is evident . . . (sic, via SM?) . . . . though it may be accepted, it is not necessarily correct . . . rather, simply that the FF appears to work for mathematicians/modelers.

YES! Einstein's CC was a FF - that now (again) appears to actually be real mechanism; but he certainly received a lot of grief from his peers at the time he proposed it! However, there may yet be viable alternatives how his CC is manifest and how it operates.

[BTW: This goes to a deeper, more philosophical concept that can be discussed elsewhere/elsewhen - can scientific truths be evident from simply mental constructions (i.e., simply thinking about the issue) . . . bypassing the early stages of the Scientific Method (i.e., by intellect alone?) - and the inferences for metaphysical solutions]

Regards . . . y Prospero Ano Nuevo

11. ### iceauraValued Senior Member

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Almost every factor, force, pattern, or explanation of anything ever discovered was, in the first place, hypothesized - that is, it was a member of that class of possibilities you have apparently decided to call "fudge factors" (illiterately, btw - "fudging" involves introduction of ambiguity, smearing, soft manipulation, adjustment of data on a more or less continuous scale).

Some restrictions on the term "fudge factor", even in its new disembodied usage, might be useful. Newton's introduction of a "force" he called "gravity" was not the employment of a fudge factor - agreed?

12. ### SchmelzerValued Senior Member

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We do measure dark matter in a very simple way: The Einstein equations tell us $G_{mn} = T_{mn}$. What we can measure is $G_{mn}$ and $T^{visible}_{mn}$. The difference is dark matter:
$T^{dark}_{mn} = G_{mn} - T^{visible}_{mn}$. So we can see where it is located, and even how it changed in time.

Of course, the problem remains if the difference is really some "dark matter" or, instead, a wrong theory of gravity. But this can remain open to speculation. It is independent of the question how we measure DM. The method to measure it is quite certain and well-defined, but it is, of course, based on the assumption that GR is correct and that the error in $G_{mn} \neq T^{visible}_{mn}$ is caused by dark matter.

There are other attempts to "measure" dark matter, but they are based on something different, namely some particular theories about what this dark matter really is. And such theories are usually based on some assumptions that this dark matter is not completely dark, but somehow interacts with usual matter. And these additional assumptions sometimes allow to predict some other effects, which could be measured. This measurement usually fails, and the journalists then write "dark matter not found". The usual way to measure dark matter described above has nothing to do with this.

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http://chandra.harvard.edu/press/06_releases/press_082106.html

NASA Finds Direct Proof of Dark Matter
For Release: August 21, 2006

NASA RELEASE 06-297

X-ray/Optical Composite of 1E 0657-56
Press Image and Caption
Dark matter and normal matter have been wrenched apart by the tremendous collision of two large clusters of galaxies. The discovery, using NASA's Chandra X-ray Observatory and other telescopes, gives direct evidence for the existence of dark matter.

"This is the most energetic cosmic event, besides the Big Bang, which we know about," said team member Maxim Markevitch of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

Gravitational Lensing Explanation
These observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.

"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."

Animation of Cluster Collision
In galaxy clusters, the normal matter, like the atoms that make up the stars, planets, and everything on Earth, is primarily in the form of hot gas and stars. The mass of the hot gas between the galaxies is far greater than the mass of the stars in all of the galaxies. This normal matter is bound in the cluster by the gravity of an even greater mass of dark matter. Without dark matter, which is invisible and can only be detected through its gravity, the fast-moving galaxies and the hot gas would quickly fly apart.

The team was granted more than 100 hours on the Chandra telescope to observe the galaxy cluster 1E0657-56. The cluster is also known as the bullet cluster, because it contains a spectacular bullet-shaped cloud of hundred-million-degree gas. The X-ray image shows the bullet shape is due to a wind produced by the high-speed collision of a smaller cluster with a larger one.

4-Panel Illustrations of Cluster Collision
In addition to the Chandra observation, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes were used to determine the location of the mass in the clusters. This was done by measuring the effect of gravitational lensing, where gravity from the clusters distorts light from background galaxies as predicted by Einstein's theory of general relativity.

The hot gas in this collision was slowed by a drag force, similar to air resistance. In contrast, the dark matter was not slowed by the impact, because it does not interact directly with itself or the gas except through gravity. This produced the separation of the dark and normal matter seen in the data. If hot gas was the most massive component in the clusters, as proposed by alternative gravity theories, such a separation would not have been seen. Instead, dark matter is required.

Animation: Galaxy Cluster in Perspective
"This is the type of result that future theories will have to take into account," said Sean Carroll, a cosmologist at the University of Chicago, who was not involved with the study. "As we move forward to understand the true nature of dark matter, this new result will be impossible to ignore."

This result also gives scientists more confidence that the Newtonian gravity familiar on Earth and in the solar system also works on the huge scales of galaxy clusters.

"We've closed this loophole about gravity, and we've come closer than ever to seeing this invisible matter," Clowe said.

These results are being published in an upcoming issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass.

Additional information and images can be found at:

http://chandra.harvard.edu
and
http://chandra.nasa.gov
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My only criticism of the article is the "headline" and the use of the word "proof" as per the definition of any scientific theory and the scientific method.

14. ### karenmanskerKSMRegistered Senior Member

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I believe you mis-attributed the usage of "fudge factor" to me . . . . it was Paddoboy who initiated that terminology in this thread . . . BTW: I actually like fudge (factors) - especially as candy during the holidays - except for the dearth of calories! (HAHA!)

Also . . . I don't recall mentioning Newton in this thread . . . besides IMO, Newton did not need a "fudge factor" to describe the force of gravity - "proof" of gravity is intuitively obvious - fateful experiments involving the experimenter jumping-off a cliff are fairly (and objectively) conclusive (again, HAHA!) - not much room for peer argument here! Plus, such experiments are objectively 'repeatable' and very often yield the same result (then it becomes a theory).

Happy New Year!

15. ### karenmanskerKSMRegistered Senior Member

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185

I DO fail to 'see' in the image what is (except for inference based on preference) actual 'dark matter'.

BTW: Digression - tangent to the OP: I have determined - to my satisfaction - over a period of more than 50 years as a scientist, that the 'X and millenial generations'- i.e., the current flock of scientists - are professionally trending toward accepting much as (proven) fact that is actually inferred conclusion based on a preferred point-of-view (POV). Such POVs are quite often grounded in hypothetical preference and not proven fact - i.e. no actual physical (repeatable) experimnetal data - but are seeming accepted as fact. Pls note that I am not necessarily opposed to such approaches, since hypothesis is an important aspect of the Scientific Method that promulgates the next step (experiment]; however, reliance at the hypothetical step - and exclusion of the experimental - seems to nowadays to be the norm, and distracts from the purpose and intent of the Scientific Method - Scientific Truth! "Hypothesis alone does not a fact make!" . . . .but (Sigh!) . . . I ramble on.

Happy New Year!

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Happy New Year to you too.

17. ### iceauraValued Senior Member

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I quoted the post I was replying to - no misattribution of usage involved.
I introduced Newton, to illustrate - and the "force of gravity" was introduced by him as exactly the kind of thing you are calling a "fudge factor", in your posts here. I think that leads to confusion.

18. ### danshawenValued Senior Member

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Mia culpa. Paddoboy and I have discussed this at some considerable length in dozens of threads. I hope it was a positive influence, but I can explain:

The Universal Gravitational Constant, G = 6.67408 × 10-11 m3 kg-1 s-2

is a "fudge factor", meaning that it is 100% empirical (measured, by means of something like the Cavendish experiment), as opposed to the rest of Newton's expression for gravity, which is indeed justifiable by means of manipulating proportional relationships involving masses and accelerations subject to the assumption that gravity behaves as though all of the mass of a planet behaved as though it were concentrated at a single point center of mass where, according to Newton, the 1/r^2 force of gravity should be infinite because r = 0. The reason this doesn't happen most likely has to do with the fudge factor G STEADILY DECREASING as a result of having more of the mass in outer shells of the planet exerting forces in opposing directions so that they will cancel out each other at the geometric center. In actual fact, the force of gravity at the geometric center is zero. Looks like mathematical fudge to me. It doesn't have any component that indicates a direction to the force it predicts.

19. ### danshawenValued Senior Member

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And the field equations for Einstein's General Relativity also contain G, and it is no more a derived constant there than it was by Newton. Still a constant to be determined; a "fudge factor" with all mitigating or confounding factors such as density, mass distribution and geometry lumped into a single constant not physically explained in any real measure of detail.