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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