Friday, April 17, 2015

Dark Matter and Energy: New Data, and a Map

Dark matter and dark energy will probably be in the news — science news, anyway — quite a bit over the next few months. CERN's upcoming research, using the Large Hadron Collider (LHC), pretty much guarantees that. (April 10, 2015)

The Dark Energy Survey, an international team of scientists, gave a second-year report on their five-year project this Tuesday. They are mapping the universe, tracing the effects of dark matter and dark energy: or whatever is pulling — and apparently pushing — galaxies and galactic clusters into position.

Other scientists, studying galaxies about 1,400,000,000 light-years away, collected and analyzed data that may help us understand dark matter.
  1. Shedding Light on Dark Matter
  2. Mapping Weak Gravitational Lensing: a Two-Year Report
I'll occasionally have something that belongs at the end of a post, but isn't quite related to the week's last news item. This is one of those times:

Living in a Big Universe

(From NASA/ESA Hubble Space Telescope, via Wikimedia Commons, used w/o permission.)
("...the rich galaxy cluster Abell 3827. The strange blue structures surrounding the central galaxies are gravitationally lensed views of a much more distant galaxy behind the cluster...."
"The heavens declare the glory of God; the sky proclaims its builder's craft."
(Psalms 19:2)
I've been over this before. The universe is big and old. We've known this for a long time.
"4 Indeed, before you the whole universe is as a grain from a balance, or a drop of morning dew come down upon the earth.

"But you have mercy on all, because you can do all things; and you overlook the sins of men that they may repent.

"For you love all things that are and loathe nothing that you have made; for what you hated, you would not have fashioned.

"And how could a thing remain, unless you willed it; or be preserved, had it not been called forth by you? "
(Wisdom 11:22-25)
As a Catholic, I must believe that God is creating the universe: which is changing as time proceeds. (Genesis 1:27-28; Catechism of the Catholic Church, 302373)

I also must believe that we're rational creatures, made in the image of God, responsible for the management of this world. (Genesis 1:27; Catechism, 16373, 1730)

The universe, although not yet perfect, is a place of beauty and order. Since part of our job is taking care of this world, learning how the universe works and developing tools is not just 'allowed.' It's part of being human. (Wisdom 7:17; Catechism, 341, 2292-2295)

Since the things of faith and the things of the world are all created by God, honest research cannot work against an informed faith. (Catechism, 159)

I like what Pope Leo XIII wrote: "truth cannot contradict truth." ("Providentissimus Deus," Leo XIII (November 18, 1893))
"...These discoveries invite us to even greater admiration for the greatness of the Creator, prompting us to give him thanks for all his works and for the understanding and wisdom he gives to scholars and researchers...."
(Catechism, 283)
On the other hand, some Catholics insist that God must conform to a 17th-century Calvinist's timetable, and that's another topic. Topics. (January 9, 2015; February 5, 2014)

1. Shedding Light on Dark Matter

(From EXO/R. Massey, via BBC News, used w/o permission/)
("The distribution of dark matter in the cluster is shown with blue contour lines"
(BBC News))
"Dark matter becomes less 'ghostly' "
Paul Rincon, BBC News (April 15, 2015)

"The mysterious stuff known as dark matter just became less ghostly.

"It makes up 85% of the total matter in the cosmos and comprises some 27% of the known Universe.

"For the first time, the enigmatic quantity may have been caught interacting with other dark matter in a cluster 1.4 billion light-years away.

"Previous studies of colliding galaxy clusters have shown that dark matter barely interacts with anything.

"And the finding, published in Monthly Notices of the Royal Astronomical Society, may hint at exotic physics - beyond the scope of current theories...."
This team was studying four bright galaxies in the Abel 3827 cluster.

I'm guessing that Paul Rincon got that "up to 85% of the total matter..." from Plank data. The number is a reasonable estimate: but it's far from carved in stone.

Scientists with the WMAP (Wilkinson Microwave Anisotropy Probe) project were very clear about how precise their numbers are. Or, rather, aren't:
"Warning! This graph will continue to change slightly as better and better data is collected This image is made with 5 year WMAP data. The final 9 year data produces a more accurate result...."
(WMAP (Wilkinson Microwave Anisotropy Probe): Content of the Universe; NASA)
Plank data suggests that today's universe is about 68.3% dark energy; 26.8% dark matter; and 4.9% atoms, the sort of matter we're made of.

That's some of the best data we have today, and some of the best analysis of that data. But it's still an estimate: an educated guess, based on observation and the best math we've developed.

Like I said last week, phlogiston was a pretty good explanation for how combustion works: but it doesn't exist. (April 10, 2015)

Unlike phlogiston, however — the more data they collect, the better dark matter and dark energy look as explanations for what scientists observe. I'm reasonably sure that dark matter, and dark energy are real: based on what we've been learning about the universe.

As I said last week, dark matter and dark energy are "dark" because they're frustratingly hard to observe. They're not dark-colored, at least not in the way we usually think of color. (April 10, 2015)

Observation and Analysis

Atoms are fairly easy to observe, particularly when they're clumped together in massive quantities and very hot: like stars.

Back in 1932, Jan Oort published "The force exerted by the stellar system in the direction perpendicular to the galactic plane and some related problems." I've talked about Ernst Öpik, Jan Oort, and the Oort cloud surrounding our star, before. (October 24, 2014)

Anyway, Jan Oort studied star motions near our galaxy: and figured that there was a lot more mass in the galactic plane than had been observed. His numbers weren't spot-on, but his math helped other astronomers analyze stellar motion. (Oort constants, Wikipedia)

Over the following decades, astronomers noticed that galaxies moved as if there was a whole lot more mass around and in them than we could observe.

Meanwhile, Horace W. Babcock noticed that the Andromeda galaxy's stars rotated a lot faster at the galaxy's edge than they would if the galaxy's mass was distributed like its stars were.

That was in 1939. Babcock suggested at least two explanations for this oddity: neither of which involved unobserved mass.

A lot more observation and analysis later, most scientists decided that the unexpected rotation rates in galaxies was due to "dark matter:" stuff they couldn't observe, but that had mass — and the gravity that goes with having mass.

Neutrinos, WIMPs, and All That

Scientists have known about one sort of dark matter, neutrinos, since 1956. Neutrinos are subatomic particles with no electric charge. They have mass, probably, but it's tiny even compared to other subatomic particles.

Since they're electrically neutral, magnetism won't affect neutrinos: but the weak subatomic force does, and so does gravity.

They're produced during radioactive decay and nuclear reactions, like what happens in our sun's core. I've talked about neutrinos and science — real and Hollywood versions — in another blog. (Apathetic Lemming of the North (November 22, 2013; November 16, 2009)

So far, scientists are pretty sure dark matter particles, or most of them, are WIMPs (Weakly Interacting Massive Particles).

We didn't realized that dark matter might exist until we started measuring things larger than star systems and smaller than atoms, though: so there's a very great deal left to learn.

As we learn more, we may learn that dark matter isn't what causes the effects we've observed.

Other explanations include mass in other dimensions, with gravity having an effect across all dimensions. This might explain why gravity is such a very weak force: it take moon- and planet-size concentrations of mass to produce serious gravity fields.

Or maybe we're looking at defects in quantum fields; or Newton and Einstein's descriptions of gravity need another major tweak, or Unruh radiation horizons generate inertia.

We don't know yet: and I've talked about that before. (November 7, 2014)


2. Mapping Weak Gravitational Lensing: a Two-Year Report

(From Dark Energy Survey, via BBC News, used w/o permission/)
("Warmer colours represent areas of higher density"
(BBC News))
"Dark matter map unveils first results"
Jonathan Webb, BBC News (April 13, 2015)

"A huge effort to map dark matter across the cosmos has released its first data.

"Dark matter is the invisible 'web' that holds galaxies together; by watching how clumps of it shift over time, scientists hope eventually to quantify dark energy - the even more mysterious force that is pushing the cosmos apart.

"The map will eventually span one-eighth of the sky; this first glimpse covers just 0.4%, but in unprecedented detail.

"It shows fibres of dark matter, studded with galaxies, and voids in between.

"The international collaboration, known as the Dark Energy Survey (DES), will present its preliminary findings on Tuesday at a meeting of the American Physical Society and publish them on the Arxiv preprint server.

"The survey involves more than 300 scientists from six countries and uses images taken by one of the best digital cameras in the world: a 570-megapixel gadget mounted on the Victor Blanco telescope at the Cerro Tololo Inter-American Observatory, high in the Chilean Andes.

"Incredible detail is required to detect dark matter, based purely on the way it warps the light from very distant galaxies...."
BBC News generally avoids the bombastic generalizations and factual errors that plague mainstream 'science' news. However, although saying that dark matter "is the invisible 'web' that holds galaxies together" may be true — the last I checked, scientists still weren't that certain.

And despite what the second paragraph says, these scientists didn't observe "fibres of dark matter, studded with galaxies," they mapped gravity lensing.

"Gravity lensing?"

Light travels in straight lines, but what's "straight" depends on the shape of space-time: which depends on gravity, so areas with lots of mass act like a lens, 'bending' the straight lines of light.

The colored part of that map is where they observed weak gravity lensing, with red representing lots of lensing. Assuming that stuff with mass makes the lensing, that's where the mass is. Black circles are galaxy clusters.
"...The clusters are overlaid as black circles with the size of the circles indicating the richness of the cluster. Only clusters with richness greater than 20 and redshift between 0.1 and 0.5 are shown in the figure. The upper right corner shows the correspondence of the optical richness to the size of the circle in the plot. It can be seen that there is significant correlation between the mass map and the distribution of galaxy clusters. Several superclusters and voids can be identified in the joint map."
("Wide-Field Lensing Mass Maps from DES Science Verification Data;" V. Vikram, C. Chang, B. Jain, and many others)
The team's map is a major accomplishment. They observed weak gravitational lensing, which shows where mass is: and isn't. It's not raw data. The 'mass map' is an analysis of 20 variables from DES (Dark Energy Survey) and South Pole Telescope data.

They started work two years ago, and have another five to go: according to BBC News. This map is a sort of sketch: a preliminary map, using their first set of data. Eventually, they hope this data will help them understand dark energy.
"...The full DES survey area will be ~ 35 times larger than that presented here, at roughly the same depth. The techniques and tools developed in this work will be applied to this new survey data, allowing significant expansion of the work here...."
("Wide-Field Lensing Mass Maps from DES Science Verification Data;" V. Vikram, C. Chang, B. Jain, and many others)

Dark Energy, an Expanding Universe, and Angst

Dark energy is the best explanation scientists have for another unexpected aspect of our universe. Back in the 1920s, physicists realized that what they were learning about space and time, together with Einstein's field equations, made a lot more sense if the universe is expanding.

Up to that point, scientists had assumed that the universe was basically static.

Oddly enough, strident rejection of an expanding universe hasn't been popular among religious zealots. Maybe that's because it was the 1920s. Europeans were recovering from the "Great War," America's government imposed the lifestyle preference we call prohibition, and angst was in the air:
"...Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world....
("The Second Coming," W. B. Yeats (1919))
I've discussed Lovecraft, flappers, Europe flambé, and getting a grip before. (November 21, 2014; August 31, 2014)

Cosmic Expansion: Making Sense of New Data

Where was I? Gravity lensing, dark matter, angst. Right.

Scientists on both sides of the Atlantic were trying to make sense of new data in the 1920s.

Georges Lemaître, a Belgian priest, astronomer and professor of physics at the Catholic University of Leuven, applied Einstein's theory of general relativity to cosmology in 1927. He estimated a value for the rate at which our universe expands. Two years later Edwin Hubble, an American astronomer; working with more data, published a more precise value: the "Hubble constant."

Some scientists thought that the universe was expanding, but that new matter popped into existence to 'fill in the gaps.' Sir James Jeans introduced Steady State theory in the 1920s. It satisfied the Perfect Cosmological Principle, the idea that the universe looks and acts the same everywhere: and everywhen. It's an attractive idea, but hasn't been a good match with observations.

My guess is that a thousand years from now, folks will have found a more complete explanation for what we've found than the Big Bang: but right now, it still looks pretty good.

Accelerated Expansion: Making Sense of Even Newer Data

(From Alex Mittelmann, Coldcreation, via Wikimedia Commons, used w/o permission.)

The Big Bang would result in a universe that's expanding. Some 13,798,000,000 (give or take 37,000,000) years later, it's still expanding. Since gravity exists, and presumably doesn't have a range limit, you'd expect that the rate of expansion is going down.

That makes sense, but it's not what astronomers observe. It looks like the rate of expansion is increasing. This is something that's been confirmed in my lifetime, so it's no surprise that scientists still aren't sure why it's expanding faster as time goes on.

They've come up with several explanations. Dark energy may be the best of the lot, or maybe phantom energy or quintessence: versions of dark energy. Sort of. Phantom energy is, or would be, a more potent form of dark energy; quintessence would be a fifth fundamental force.

So far, we don't know why the universe is expanding the way it is: but we're learning more, and discovering that the universe is even more astounding than we thought.

  • "Dark energy"
  • "Wide-Field Lensing Mass Maps from DES Science Verification Data"
    Cornell University Library; Astrophysics, Cosmology and Nongalactic Astrophysics; V. Vikram, C. Chang, B. Jain, D. Bacon, A. Amara, M. Becker, G. Bernstein, C. Bonnett, S. Bridle, D. Brout, M. Busha, J. Frieman, E. Gaztanaga, W. Hartley, M. Jarvis, T. Kacprzak, O. Lahav, B. Leistedt, H. Lin, P. Melchior, H. Peiris, E. Rozo, E. Rykoff, C. Sanchez, E. Sheldon, M. Troxel, R. Wechsler, J. Zuntz, T. Abbott, F. B. Abdalla, R. Armstrong, M. Banerji, A. H. Bauer, A. Benoit-Levy, E. Bertin, D. Brooks, E. Buckley-Geer, D. L. Burke, D. Capozzi, A. Carnero Rosell, M. Carrasco Kind, F. J. Castander, M. Crocce, C. B. D'Andrea, L. N. da Costa, D. L. DePoy, S. Desai, H. T. Diehl, J. P. Dietrich, C. E Cunha, J. Estrada, A. E. Evrard, A. Fausti Neto, E. Fernandez, B. Flaugher, P. Fosalba, D. Gerdes, D. Gruen, R. A. Gruendl, K. Honscheid, D. James, S. Kent, K. Kuehn, N. Kuropatkin, et al. (29 additional authors not shown) (Submitted on 12 Apr 2015)
    (From, (April 15, 2015))

Afterword: "...Like a Tent...."

The idea that this universe won't last forever is unsettling: to me, anyway. But I won't insist that the universe must be the way I want it. Taking reality 'as is' seems more prudent.

Besides, as a Catholic I must believe that God decides what's real and what's not — it's not up to me, or Aristotle, or anybody else. I've discussed 1277 and Aristotle's fan base before. (September 26, 2014; February 23, 2014)

We've known that the universe is like a tent, a garment, something useful but temporary, for millennia:
"He sits enthroned above the vault of the earth, and its inhabitants are like grasshoppers; He stretches out the heavens like a veil, spreads them out like a tent to dwell in."
(Isaiah 40:22)

"3 Raise your eyes to the heavens, and look at the earth below; Though the heavens grow thin like smoke, the earth wears out like a garment and its inhabitants die like flies, My salvation shall remain forever and my justice shall never be dismayed."
(Isaiah 51:6)

"and: 'At the beginning, O Lord, you established the earth, and the heavens are the works of your hands.

"They will perish, but you remain; and they will all grow old like a garment.

"You will roll them up like a cloak, and like a garment they will be changed. But you are the same, and your years will have no end.' "
(Hebrews 1:10-12)

"Then the sky was divided 13 like a torn scroll curling up, and every mountain and island was moved from its place."
(Revelation 6:14)
What's changed in the two-dozen-plus centuries since Isaiah's day is how much we know about this 'tent:' and how much we're discovering there is left to learn.

More of my take on reality and truth:


Brigid said...

Missing word? "the better dark matter and dark energy look explanations for what scientists observe."

The Friendly Neighborhood Proofreader

Brian Gill said...


Ri-i-ight. Got it. Thanks!

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From time to time, a service that I use will display links to - odd - services and retailers.

I block a few of the more obvious dubious advertisers.

For example: psychic anything, numerology, mediums, and related practices are on the no-no list for Catholics. It has to do with the Church's stand on divination. I try to block those ads.

Sometime regrettable advertisements get through, anyway.

Bottom line? What that service displays reflects the local culture's norms, - not Catholic teaching.