Scientists use quasars to probe dark energy over 10 billion years in the past

Nov 13, 2012
Light from distant quasars (dots at left) is partially absorbed as it passes through clouds of hydrogen gas. A "forest" of hydrogen absorption lines in an individual quasar’s spectrum (inset) pinpoints denser clumps of gas along the line of sight, and the spectra are collected by the telescope’s spectrograph (square at right). Before BOSS, the Sloan Digital Sky Survey had collected spectra from 10 times fewer quasars (yellow dots) per square degree of sky in the accessible redshift range, which corresponds on average to about 10 billion years ago. By measuring the spectra from many more quasars in this range (red dots), BOSS can reconstruct a three-dimensional map of the otherwise invisible gas, revealing the large-scale structure of the early universe. Illustration by Zosia Rostomian, Lawrence Berkeley National Laboratory; Nic Ross, BOSS Lyman-alpha team, Berkeley Lab; and Springel et al, Virgo Consortium and Max Planck Institute for Astrophysics

BOSS, the Baryon Oscillation Spectroscopic Survey, is mapping a huge volume of space to measure the role of dark energy in the evolution of the universe. BOSS is the largest program of the third Sloan Digital Sky Survey (SDSS-III) and has just announced the first major result of a new mapping technique, based on the spectra of over 48,000 quasars with redshifts up to 3.5, meaning that light left these active galaxies up to 11.5 billion years in the past.

"No technique for dark energy research has been able to probe this ancient era before, a time when matter was still dense enough for gravity to slow the , and the influence of dark energy hadn't yet been felt," says BOSS principal investigator David Schlegel, an astrophysicist in the Physics Division of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab). "In our own time, expansion is accelerating because the universe is dominated by dark energy. How dark energy effected the transition from deceleration to acceleration is one of the most challenging questions in cosmology."

Two ways to measure the expanding universe

As an , many of whose leading scientists are present or former members of Berkeley Lab, BOSS studies dark energy by mapping baryon acoustic oscillations (BAO) – the large-scale network of variations in the distribution of visible galaxies and hard-to-see clouds of intergalactic gas, which also reveal impossible-to-see dark matter. The regular spacing of peaks in originated in primordial density variations, whose remnants are visible in the . This spacing provides a cosmic ruler for calibrating the rate of expansion wherever BAO can be measured.

Using the Sloan Foundation Telescope at the Apache Point Observatory in New Mexico, BOSS has mounted a two-pronged spectroscopic investigation of BAO. The first priority is to survey normal bright galaxies with redshifts up to 0.8, some seven billion years in the past; first results of the galaxy survey, which included over 300,000 galaxies, were announced in March, 2012. But collecting enough galaxies at redshifts high enough to map BAO in the very early universe can't be done with a 2.5-meter telescope. Thus BOSS's second target: quasars.

"Quasars are the brightest objects in the sky, and therefore the only credible way to measure spectra out to redshift 2.0 and beyond," says Schlegel. "At these redshifts there are a hundred times more galaxies than quasars, but they're too faint to use for BAO."

Quasars are too sparse to measure BAO directly, but there's another way they reveal BAO at high redshifts. As the light of a quasar passes through clouds of intergalactic gas on its way to Earth, its spectrum develops a plethora of hydrogen absorption lines known as a Lyman-alpha forest. Ideally, each absorption line in the "forest" reveals where the quasar's light has passed through an intervening gas cloud. Like a single flashlight seen through the fog, the different prominences and redshifts of the individual absorption lines in a single quasar's spectrum reveal how the gas density varies with distance along the line of sight.

With enough quasars, close enough together and covering a wide expanse of sky, the distribution of intervening gas clouds can be mapped in three dimensions. The idea was first advanced in the early 2000s by Patrick McDonald, then at the Canadian Institute for Theoretical Astrophysics, and Martin White, both now at Berkeley Lab.

"When I presented this idea to a conference of cosmologists in 2003, they thought it was crazy," says White, who is also a professor of physics and astronomy at the University of California at Berkeley and the chair of the BOSS science survey teams. "Nine years later, BOSS has shown that it's an amazingly powerful technique. It has succeeded beyond our wildest dreams."

Until recently, three-dimensional maps by BOSS (red dot, right of center) and other surveys were able to measure the regular distribution of galaxies back to an average of only about five and a half billion years ago, a time when the expansion of the universe was already accelerating. BOSS's quasar measurements (red dot, left), by measuring the distribution of intergalactic gas, have now probed the structure of the early universe at a time when expansion was still slowing under the influence of gravity. The quasar data gives new access to the transition from deceleration to acceleration caused by dark energy. Graph by Zosia Rostomian, Lawrence Berkeley national Laboratory, and Nic Ross, BOSS Lyman-alpha team, Berkeley Lab

SDSS-III's far more sophisticated spectrograph, whose construction was directed by Berkeley Lab's Natalie Roe, allows much better coverage and resolution than earlier surveys, but searching for BAO in the Lyman-alpha forest was still a high-risk proposition for many reasons. Lyman-alpha absorption lines occur in the ultraviolet part of the spectrum, which is absorbed by Earth's atmosphere; from the ground, only those quasars whose spectra are redshifted the right amount are useful. The lines tag only neutral hydrogen; most hydrogen in the universe is ionized. Among other uncertainties, irregular heating of hydrogen clouds, or too many quasars too close together, could distort the clustering signal.

"Compared to a galaxy survey, looking for BAO in the Lyman-alpha forest is cool – high-risk, but high-reward," says Berkeley Lab's Nicholas Ross, who led the target selection team. To catch enough quasar spectra to map clustering – a minimum of 15 to 20 quasars per square degree of the sky – BOSS would have to devote 10 percent of the two million individual targets during its five-year run to possible quasars. The targets had to be chosen from photometric data (an object's brightness in different colors), but only after the spectra were taken would the team be sure which targets were real quasars and which were stars or some other quasar mimic. BOSS took the chance.

"We had one thing in our favor," Ross says. "It didn't matter what type of quasar it was, as long as it was high redshift. To identify them we could use ultraviolet data, near-infrared data – any method, any trick – because we were only going to use them as backlights to probe the intervening clouds of gas. Ultimately we found that all our selection algorithms worked well."

Searching for the signal

The initial Lyman-alpha result – the first map of BAO at this very early stage of the universe's evolution – is based on just a third of the volume of space that BOSS will ultimately map, and includes 60,369 quasars confirmed by visual inspection of their spectra. But to simplify the search for BAO, many of these were discarded.

"To get BAO out of the data, we have to remove artifacts that distort the signal we're looking for," says Berkeley Lab's Bill Carithers. One class of rejects is broad-absorption line quasars, whose spectra have been smeared out by extremely fast-moving gas from the quasar's active center. Another class are quasars whose spectra have "damped Lyman-alpha troughs," which happens, Carithers says, "when the light from the quasar runs into a very, very large clump of gas, so large it wipes out the forest."

With unhelpful spectra removed, BOSS was left with 48,129 quasars. In May of 2011, a team led by Anže Slosar of Brookhaven National Laboratory, formerly at Berkeley Lab, had demonstrated the practicality of measuring the varying density of intergalactic hydrogen gas at cosmological distances using just 14,000 BOSS quasars – enough, said Slosar, "to establish a proof of the concept."

"We don't use the specific information in a single line of sight, we look at the correlations among many," says Carithers. "BOSS is the first to do this because we have enough quasars – with too few, you can't see the pattern."

In addition to helping convert the raw data from the telescope into useful scientific information, Berkeley Lab's Stephen Bailey was in charge of generating simulated data sets – called "mocks" – to make sure the analysis was dependable.

"Mocks are important when you're trying to measure something that's never been measured before," says Bailey. "We know where the real quasars are and we know what the physics of the gas is, but we don't know where the gas is. Our simulations were based on the positions and redshifts of the real quasars, but with mock spectra that gave different gas distributions. If we could see the simulated distribution in one analysis, we should see it in all."

In the end, after data processing and generation of mock spectra on the Riemann Linux cluster of computers provided by Berkeley Lab's High-Performance Computing Services Group, the competing analyses of the Lyman-alpha forest of over 48,000 quasars all gave similar results.

The analytic techniques used in this report were developed by Andreu Font-Ribera and his collaborators among BOSS's French Participation Group. Applied to the real quasar spectra, they produced a picture of density distributions that, Bailey says, "gives us a first look at BAO in this previously hidden region."

Schlegel says, "There is no other credible way we could have measured BAO at redshifts of two or more. Five years ago it was chancy, but it was the only proposal on the table. We could have failed in any number of ways, but nature was good to us."

White says, "We are seeing back to the matter-dominated universe, when expansion was decelerating and dark energy was hard to see. The transition from decelerating expansion to accelerating expansion was a sharp one, and now we live in a universe dominated by . The biggest puzzle in cosmology is, why now?"

It's a question BOSS will go far to illuminate as it collects more than a million and a half galaxies and more than 160,000 before SDSS-III is complete. Meanwhile, the Lyman-alpha forest has opened a new view of the ancient universe, one that may come to full fruition with future, more powerful surveys like the proposed BigBOSS.

Explore further: Eclipsing binary stars discovered by high school students

More information: "Baryon Acoustic Oscillations in the Lyα forest of BOSS quasars," by N.G. Busca et al., has been submitted to Astronomy & Astrophysics and is available on the arXiv preprint server.

BigBOSS survey bigboss.lbl.gov/

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Torbjorn_Larsson_OM
3.7 / 5 (3) Nov 13, 2012
A veritable tour de quasars.

As for puzzle, I would like to retain that for baffling (and/or difficult) problems. The coincidence isn't baffling, since it has long been suggested to be a natural consequence of eternal inflation. EI would have to be ruled out to make it a baffling problem once more.
david_templeton
2.3 / 5 (3) Nov 13, 2012
Could someone please explain why the universe is expanding (via dark energy) rather than evaporating?
cantdrive85
1.2 / 5 (18) Nov 13, 2012
"Quasars are the brightest objects in the sky, and therefore the only credible way to measure spectra out to redshift 2.0 and beyond," says Schlegel.

Halton Arp has produced a great deal of info on quasars that contradicts this assumption, conveniently this info is ignored and disregarded due to the implications it has on many aspects of the standard theory.
http://www.halton...articles
GSwift7
3.6 / 5 (17) Nov 13, 2012
Could someone please explain why the universe is expanding (via dark energy) rather than evaporating?


It sounds like you might be confusing terms here. The Universe (space and time) are expanding. Objects inside the Universe evaporate. Evaporation has no meaning outside the context of the Universe.

Halton Arp has produced a great deal of info on quasars that contradicts this assumption, conveniently this info is ignored and disregarded due to the implications it has on many aspects of the standard theory


Flat Earth models of our planet have many contradictions with the assumptions of the spherical Earth model. Conveniently, this info is ignored and disregarded due to the implications it has on many aspects of the spherical Earth theory.

Why, oh why are they SO blind? A round Earth just doesn't make any sense!! One day the dogmatic oppression of the round Earth conspiracy will be shown for what it is!!
cantdrive85
1.3 / 5 (15) Nov 13, 2012

Flat Earth models of our planet have many contradictions with the assumptions of the spherical Earth model. Conveniently, this info is ignored and disregarded due to the implications it has on many aspects of the spherical Earth theory.

Why, oh why are they SO blind? A round Earth just doesn't make any sense!! One day the dogmatic oppression of the round Earth conspiracy will be shown for what it is!!


Typical straw man, usually observation is a tool for falsification. Edwin Hubble wrote in "The Observational Approach to Cosmology";
"Most of the theoretical investigators adopt this point of view, and accept without question the interpretation of red-shifts as velocity-shifts. They are fully justified in their position until evidence to the contrary is forthcoming."

Evidence which his protege Halton Arp has produced, first is his book 'Atlas of Peculiar Galaxies' and in several papers since. However, the "theoreticists" were firmly entrenched by the time of his discoveries.
lengould100
2 / 5 (4) Nov 13, 2012
I just have a problem with the two hypotheses "dark matter" and "dark energy". I grant the observations which stimulated their invention are correct, but not that the presently generally accepted inventions are unarguably the only possibilities, or even the most probable. Re dark matter for example, it simply looks obvious to me that all observations to date can be more logically explained by a modification of the equations of gravity than by hypothesising some undetectable matter particle which doesn't fit any model. John Moffat's work is my current choice re dark matter.

http://www.johnwm...ers.html

On dark energy, is there any observation we have which would rule out a simple modification to our theories of gravity, which modification would apply a reduction in field strength beyond a certain distance?
RealityCheck
1.9 / 5 (14) Nov 13, 2012
Hi GSwift7. In fairness, CD85 points out that observations (and their interpretational basis) are crucial. He also points out the 'interpretational meme' that has insidiously entrenched itself in theoretical/cosmological physicist mainstream which seems unwilling to actually question which is the 'cart' and which is the 'horse' when it comes to their observations and interpretations. Redshift values have for too long been automatically interpreted/associated as/with expansion-related 'recession velocity' rather than just distance. Latest observations/discoveries about intervening space and galactic dynamics and local evolutions over time and space may help explain (interpret/associate) the CMB and redshifts in a new light. But still redshift is automatically attributed to 'expansion' instead of local dynamics/evolution of actual material features/gravity etc, so all observations/alternatives to expansion hypothesis may be improperly dismissed/ignored due to 'meme' not fact. Cheers!
Q-Star
3.4 / 5 (15) Nov 13, 2012
Re dark matter for example, it simply looks obvious to me that all observations to date can be more logically explained by a modification of the equations of gravity


Every time a modification has been tried, it causes the physics of the things at hand, that we can see directly, measure directly, and examine by direct experiment to fail. So by the 1st Principle, "the laws of physics must be the same, regardless of location". What we see over there, has to be constrained by the same reality as that which we see here.
antialias_physorg
4 / 5 (8) Nov 13, 2012
I just have a problem with the two hypotheses "dark matter" and "dark energy". I grant the observations which stimulated their invention are correct, but not that the presently generally accepted inventions are unarguably the only possibilities

Dark matter and dark energy are just placeholders. Since the properties of these are rather undefined they are not some sort of 'defined possibilities' that you need to agree with or not.
At present they're just names given to observed phenomena.
Shinichi D_
2.8 / 5 (4) Nov 13, 2012
RealityCheck: Cepheids!
cantdrive85
1.4 / 5 (9) Nov 13, 2012
RealityCheck: Cepheids!


Shinichi: Assumptions!
Shinichi D_
4.2 / 5 (5) Nov 13, 2012
RealityCheck: Cepheids!


Shinichi: Assumptions!


There are a lot of methods. All of them are wrong in a strange way, to lead to the same wrong assumption? How difficult that would be. The clusters/galaxies somehow ("light scattering"?) would 'mimic' greater redshift, and the same time sporting generally dimmer supernovae and false cepheids with different periods? And always the same combination of false signs. Never a different, wrong combination of them.
How complex delusion that is. Strange man.
RealityCheck
1.9 / 5 (10) Nov 13, 2012
Hi Shinichi D_.
RealityCheck: Cepheids!


Parallax. No use for far distant. Also different cepheids/processes. Also, from Wiki:
Uncertainties in Cepheid determined distances. Chief among the uncertainties tied to the Classical and Type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination (blending) and a changing (typically unknown) extinction law on Cepheid distances. All these topics are actively debated in the literature. These unresolved matters have resulted in cited values for the Hubble constant (established from Classical Cepheids) ranging between 60 km/s/Mpc and 80 km/s/Mpc. Resolving this discrepancy is one of the foremost problems in astronomy since the cosmological parameters of the Universe may be constrained by supplying a precise value of the Hubble constant.


So careful, mate! Cheers!
barakn
4.4 / 5 (7) Nov 13, 2012
I love it when people trot out Halton Arp. It's a good measure of how desperate they are, by seeing how far into the dustbin of history they'll reach. Arp was a decent astronomer and did have access to the Hale Telescope, the largest telescope in the world for 45 years. Part of his argument was statistical, but much broader surveys since then rule statistically against him. Part of his argument was due to alleged visible links between quasars and galaxies (light-bridges and whatnot). However, film - as was used in his time - is famous for its non-linear response to light, and even the Hale Telescope's resolution was limited by seeing from the bottom of our atmosphere. Better, higher resolution images are driving nails into this coffin also.
Psiotic
1.5 / 5 (8) Nov 13, 2012
Reading some of these comments reminds me that Scientists or those in "training" have Egos that are far too big for a field that should be open minded and questioning everything.

If something new makes an old 'rule' cease to function, then it simply proves you're missing something... Science has been dismantled and propagated by decades of "them" controlling what you're "educated" with.
RealityCheck
1.5 / 5 (8) Nov 13, 2012
Hi barakn. The latest astronomical observations show that on the larger scales the universal distribution is somewhat like 'soap bubble' agglomeration. It's 'filaments and nodes' like where the 'bubble-walls' meet in three dimensions. Imagine this pattern repeated again and again at ever smaller scales (at which lesser scales most such 'structures' like bridges and filaments and nodes are not so easily discerned unless they are close enough to us). The universe if replete with gas jets and streaming energy-mass and clouds etc (both visible and invisible). Don't be so sure and kneejerkingly/personally dismissive/disparaging. Take the time to review the latest astronomical articles/discoveries which give rise to all these speculations old and new. Cheers!
Psiotic
1.6 / 5 (7) Nov 13, 2012
The 'ranking' system will prove my point. Ego.
rubberman
2.3 / 5 (6) Nov 14, 2012
Re dark matter for example, it simply looks obvious to me that all observations to date can be more logically explained by a modification of the equations of gravity


Every time a modification has been tried, it causes the physics of the things at hand, that we can see directly, measure directly, and examine by direct experiment to fail. So by the 1st Principle, "the laws of physics must be the same, regardless of location". What we see over there, has to be constrained by the same reality as that which we see here.


By this rationale, if what we observe causes the standard theory to break down, insertion of a gravity only particle to bolster it back up, and then claim that the majority of matter in the universe is composed of these particles only detectable by their gravitational effect, which they produce en masse, without interacting with each other or "normal" matter in any other way, just to preserve the theory in it's present form is...questionable.
rubberman
1.7 / 5 (6) Nov 14, 2012
White says, "We are seeing back to the matter-dominated universe, when expansion was decelerating and dark energy was hard to see. The transition from decelerating expansion to accelerating expansion was a sharp one, and now we live in a universe dominated by dark energy. The biggest puzzle in cosmology is, why now?"

This article was also covered in R & D mag, they referred to dark energy as "turning on"...here it goes from deceleration to acceleration. I would hypothesize that "dark energy" reared it's head at about the same time that enough galaxies became populated with enough stars for each galaxy to generate magnetic field structures that began to interract, and this is what overwhelmed the force of gravity. Yes, my crank hypothesis is that electromagnetic repulsion drives the expansion of the universe (along with gravitational interactions).

I will abandon this when/if the dark brothers are more tangible than just their observed effects that we attribute to them.
rubberman
2 / 5 (4) Nov 14, 2012

I will abandon this when/if the dark brothers are more tangible than just their observed effects that we attribute to them.


Or, of course, if one of the resident Physicists can explain why it IS a grank hypothesis, I would welcome this as well. I would rather learn from being wrong than chain my cart to a hypothetical horse with no legs.
Q-Star
3.3 / 5 (12) Nov 14, 2012
By this rationale, if what we observe causes the standard theory to break down, insertion of a gravity only particle to bolster it back up, and then claim that the majority of matter in the universe is composed of these particles only detectable by their gravitational effect, which they produce en masse, without interacting with each other or "normal" matter in any other way, just to preserve the theory in it's present form is...questionable.


Not at all. Unless you can find a model that works, better in all circumstances to replace the one currently being used,, then you use the one that works best. Is gravity an inviolate constant? No one can say that it is with 100% certainty. It is 100% certain is that NO ONE has yet produced a model that supports that it is not. Many have tried, many very smart people.

A model must be consistent with what we observe. And it must predict. You can't have a force that acts one way here and yet another way when you move it "over there".
lengould100
1 / 5 (1) Nov 14, 2012
You can't have a force that acts one way here and yet another way when you move it "over there".

I was thinking of an issue while reading the comments, then came on yours, which dovetails neatly. What I was wondering is "How precisely identical are each example of the fundamental particles?"

Is every up quark precisely identical to every other up quark? Every down quark exactly identical to every other down quark? etc. At every level of observation above the atom (molecule), we are accustomed to a statistical variation in the properties of the basic particles we deal with. We don't expect every stone of the nominal 3/4" crushed rock in concrete to be identical to every other stone.

What proof have we that every (eg. up) quark is identical? How have we verified this? What level of precision? Even if they are now identical by some unexplainable magic, has this always been true since the beginning of the universe?

Of course, just spouting off. LOL.
rubberman
1.8 / 5 (5) Nov 14, 2012
" Unless you can find a model that works, better in all circumstances to replace the one currently being used,, then you use the one that works best."

I agree. There isn't one (yet) that performs as well as the standard theory/dark matter/dark energy hypothesis.

My issue with it is this:

We can measure, detect and observe enough of the overall energy spectrum of the universe that to attribute so much gravitational force to dark matter without being able to detect even a hint of it in this spectrum is not logical. We don't understand 100% of how gravity "works", so for lack of a better word, to "invent" a particle and attach a force to it that we don't fully understand and claim that it is the dominating factor in what we observe is akin to admitting "it's a guess". It may make the theory work, but now the theory works on a 75% fudge factor because that is what is required to explain our observations if we use this theory....sorry Q, in my head it is still questionable.
antialias_physorg
5 / 5 (5) Nov 14, 2012
so for lack of a better word, to "invent" a particle and attach a force to it that we don't fully understand and claim that it is the dominating factor in what we observe is akin to admitting "it's a guess"

And that's exactly what it is. No one is claiming otherwise. We know it's has an effect - and an effect means that there is a cause. We call a cause a 'force', and a force needs an energy behind it.

Then there's the gravity issue. We can see gravitational effects and we currently only know that matter has gravity: Since something must be responsible for the non unifiormity in the gravity observed we call that something 'dark matter'

That's really all there is too it. The trick now is to devise experiments to see what kinds of properties these causes have and fill in the blanks.

It's like with the particle zoo: You see a new effect that doesn't match observed particles you attribute it to a new particle. It's just how we model stuff. Don't get hung up about the words.
Q-Star
3 / 5 (10) Nov 14, 2012
We don't understand 100% of how gravity "works", so for lack of a better word, to "invent" a particle and attach a force to it that we don't fully understand and claim that it is the dominating factor in what we observe is akin to admitting "it's a guess".


We understand gravity very well, that is why we keep it in the models as is. The "invented" stuff is merely a place holder until we can measure and detect the "invented" stuff more definitively.

Of course the "stuff" is only a guess, the guess is getting more and more precise as we accumulate more data. Gravity is well known. The "invented" stuff is what we don't understand completely.

Suggest equations or models that make gravity act differently and agree with all we see and test them.
rubberman
1.7 / 5 (6) Nov 14, 2012
For the record, I am spouting off as well. I had 100% faith in gravity at one time...I also believed in Santa, until the physics of that gift bag fitting down the chimney made me stay up all night...only to watch my parents fill my stocking.

I only hope that this is solved/identified in my lifetime...i may refuse to die until it is.
rubberman
2 / 5 (4) Nov 14, 2012
AP and Q- One question, why not electromagnetism? As i said if I am chasing my tail with that one then snip the bastard off so I stop chasing it.
antialias_physorg
5 / 5 (6) Nov 14, 2012
why not electromagnetism?

What about it?

The problem with electromagnetism is that it's so much stronger than gravity. That means that different charges will try to get on top of one another VERY quickly (much more quickly than stuff collapses due to gravity)

I've got here a lecture by Feynman and in it he says that if he and another guy in the room had each just 1% more of one type of charge (and the other uy the othertype of charge) they'd attract each other with the force of an Earth standing next to the Earth.

That's why protons and electrons make up such an incredibly dense mixture (atoms)

For electromagnetism to stay separate throughout the course of the universes existence at such scales that they could drive expansion there would have to be some force that keeps them apart. A 'cosmic dielectricum' if you so wish. No such substance (or its effects) is observed. It would be easily visible since it would massively affect the paths of charged particle jets.
yyz
4.4 / 5 (7) Nov 14, 2012
"It may make the theory work, but now the theory works on a 75% fudge factor because that is what is required to explain our observations if we use this theory"

I think the same type of argument you give here could have been used concerning the existence of the neutrino back in 1930. But, we all know how that story came out.

Perhaps dark matter will turn out not to be composed of WIMPS. Maybe a low mass particle like axions will prove to be DM. Or possibly some combination of the two (or something else altogether). But for now, observations are consistent with DM being a weakly interacting massive particle, so until it's ruled out or a more likely candidate is found, the search goes on.
Q-Star
2.8 / 5 (9) Nov 14, 2012
AP and Q- One question, why not electromagnetism? As i said if I am chasing my tail with that one then snip the bastard off so I stop chasing it.


Me too, why not what? Look, if you are so sure gravity is doing something different "out there" than it is doing "here", all you have to do show us the model you propose.

Just saying "that must be wrong", without any explanation of why it is wrong, or any viable explanation that can be shown to be a better explanation.

Electromagnetism IS a fundamental force, as is gravity. But they do different things. They do what they do, they don't do what the other does.
ValeriaT
1.5 / 5 (8) Nov 14, 2012
We understand gravity very well, that is why we keep it in the models as is ..the "invented" stuff is what we don't understand completely..
..which is apparently the reason, why only 4% of observable matter in the Universe follows these models...;-) The fact some phenomena is well known doesn't imply it's well understood. Even the best gravity theory has no better explanation for gravity than just four hundred years old Newton's gravitational law.
Suggest equations or models that make gravity act differently and agree with all we see and test them.
LeSage shielding model works definitely better for gravity, when dark matter is considered. It requires superluminal speed of gravity propagation and it allows both gravitational shielding with massive bodies, both shielding of this shielding with another massive bodies. It's the only model which not only postulates the Newton's gravitational law, but which explains it too.
cantdrive85
1 / 5 (9) Nov 14, 2012
The mental masturbation and the waste of scientific funding continues, in the face of observational evidence that proves expansion is nothing more than a theoreticist's wet dream.
lengould100
1 / 5 (2) Nov 14, 2012
I'm still curious, as previous.

"On dark energy, is there any observation we have which would rule out a simple modification to our theories of gravity, which modification would apply a reduction in field strength beyond a certain distance?"

And what refutation supports everyone's ignoring of John Moffat's work, MOG? What observation prove it is wrong?

From About.com physics

"{MOND and MOG} falls in the informal category of a "fringe theory." Specifically, it falls in the somewhat less-informal category of an "alternative gravity theory," because it proposes fundamental changes to our understanding of the way gravity works (as opposed to dark matter theory, which supposes that our understanding of gravity is fine, but we're missing some physical substance that needs to be included in the calculations).


Moffat, in his book "Reinventing Gravity", states that his new equation of gravity fits every observation of Einstein's gravity, and ALSO explains away the need for DM.
rubberman
2.6 / 5 (5) Nov 14, 2012
Apologies Q star. I don't think gravity works differently anywhere, I should have specified that. Thanks AP, i do know more about EM as it is something i deal with occasionally....and how strong a force it is compared to G....hence my theory. Q, i'll see what i can do with math. Thanks again guys.
lengould100
1 / 5 (4) Nov 15, 2012
So someone is willing to down-rate my post, but not to respond to the request for justification for doing so? Are your credentials as good as Mr. Moffat?

John W. Moffat, Cambridge educated, is a Professor Emeritus in physics at the University of Toronto. He is also an adjunct Professor in physics at the University of Waterloo and a resident affiliate member of the Perimeter Institute for Theoretical Physics.
antialias_physorg
4.2 / 5 (6) Nov 15, 2012
On dark energy, is there any observation we have which would rule out a simple modification to our theories of gravity, which modification would apply a reduction in field strength beyond a certain distance?

No, there is no reason against doing that. But you always have to ask yourself: "Now you add this extra term - why?". Just adding a term is not a solution (e.g. Relativity added the square root of 1-v^2/c^2...but not out of thin air. )

As always you first use the simplest explanation and try to figure out if that works. Adding a term "out of thin air" to an equation is the most complex explanation (dark energy and dark matter are - fom a theoetical standpoint - vastly simpler constructs). Let's first ztry (and posibly eliminate) the simple ones before we move to the complex ones.

That doesn't mean Moffat is wrong. It's just that it's unlikely that he's right (compared to other theories). And we should look at the likely ones first.
GSwift7
2.1 / 5 (7) Nov 15, 2012
Is every up quark precisely identical to every other up quark? Every down quark exactly identical to every other down quark? etc.


That's a good question.

When two of these quasi particles are entangled, they act as though they are the same particle (or as though a single particle is in two places at the same time), but that state doesn't last long.

I would say that the location in spacetime of any given thing is a property of its existence, and therefore that any two distinct 'objects' are by definition different. If you can define them as two different things, then they are not identical. That's kinda open to philosophical debate though.

That also leads into the question of whether anything beyond the Plank limit is actually 'real'.
lengould100
1 / 5 (2) Nov 15, 2012
antialias -
As always you first use the simplest explanation and try to figure out if that works. Adding a term "out of thin air" to an equation is the most complex explanation (dark energy and dark matter are - fom a theoetical standpoint - vastly simpler constructs). Let's first ztry (and posibly eliminate) the simple ones before we move to the complex ones.


It seems to me the opposite. Declaring the existence of an undetectable non-interacting mass particle making up almost 6 times the mass of all detectable matter in the universe, being at a specific location in every galaxy (why at the periphery of galaxies exactly where it needs to be, and not, as more logical for a gravity-only particle, at the centre?) .... well, that's just right out of a fairy tale compared to declaring a slight added complexity to the operation of the gravity force, which we must admit, we know almost nothing about.
lengould100
1 / 5 (3) Nov 15, 2012
quote from Wikipedia
The observed "value" of the background vacuum energy is so small, it is involved in one of the largest discrepancies in the history of physics (which is often accurate to 10 decimal places). Particle physicists, in their calculations, somehow come up with an estimate that is 120 orders of magnitude too large. Understandably, this research area is one of the least understood and most active in physics, astronomy, astrophysics, and cosmology.


Only off by 120 decimal places eh? Well, of course then, declare all alternative proposals definitely wrong. LOL. (I know, this refers to dark energy rather than dark matter, but IMHO given the length of time this has been around, with zero progress, isn't it time to start re-thinking the basics, such as Einsteins gravity equation?
Q-Star
2.8 / 5 (11) Nov 15, 2012
isn't it time to start re-thinking the basics, such as Einsteins gravity equation?


Where have you been? Very smart people having been doing just that thing for a century now. So far they haven't come up with anything that works as well.

General Relativity is one of the most (if not the most) tested theories going. It's passed every test. The only problem anyone has found in it is when it applied outside of the framework in which it was developed.

Every alternative has either broken down when tested, or can not be subjected to testing by experiment.

If you can't conduct an experiment to test it, it is a philosophical construct, not a physical science theory.

But too many people these days seem to think philosophy is a good enough process for making progress in science without experiment. It then turns into metaphysical sophistry.

Unless an idea can be tested, it is only an idea, a pondering, a question without an answer. It's certainly not a science theory.

antialias_physorg
4.4 / 5 (8) Nov 15, 2012
Declaring the existence of an undetectable non-interacting mass particle making up almost 6 times the mass of all detectable matter in the universe, being at a specific location in every galaxy (why at the periphery of galaxies exactly where it needs to be, and not, as more logical for a gravity-only particle, at the centre?) .... well, that's just right out of a fairy tale

Look at it this way: We currently know only of one source of gravity: matter

So which one is more complicated:

a) Positing that the observed gravity effects are caused by some form of matter

OR

b) Positing that there is an unknown, second mechanism of gravity
AND that that mechanism is distance dependent
AND that that mechanism is also not uniformly distance dependent (because the gravity effect seems to bunch up)
AND that the effect isn't detectable at close ranges at all
AND ...

Not saying it certainly isn't b). But checking out a) first seems a lot easier.
yash17
1 / 5 (4) Nov 15, 2012
"To probe dark energy over 10 billion years in the past"

That energy wasn't & isn't dark. We can watch its effect. We can trace its source. Its source (N) hides around behind Ursa Major & Leo constellation. It has pushed low redshift galaxies/quasars (z around <1.4) away from it. It has pulled at least 10 high redshift quasars (z > 5) back toward it. The appearing of other at least 7 high redshift quasars (z > 6) at north of Galactic Coordinate System also support that. It leaves some of high redshift galaxies/quasars (z > 5) at south of Galactic Coordinate System, as signal of belated light phenomenon. And the appearing of NGC 3314a & NGC 3314b at Hydra, http://en.wikiped...alaxies, also gives another positive signal of belated light phenomenon. It is expected on surface of ball with diameter MW-N. And plus ghost galaxy at Leo Minor, http://astrobob.a...c-2497/.

Too many festivity there, around Ursa Major & Leo.
lengould100
1 / 5 (2) Nov 16, 2012
Antialias
So which one is more complicated: a) Positing that the observed gravity effects are caused by some form of matter OR b) Positing that there is an unknown, second mechanism of gravity
It appears you misunderstand my (eg. Mr. Moffat's) position. Option b) does NOT involve any "second mechanism" of gravity, simply increases the complexity of Einstein's equations (no mean feat, given how complex they already are see http://en.wikiped...quations

From Moffat et. al. paper "Applying MOG to lensing: Einstein rings, Abell 520 and the Bullet Cluster" at http://arxiv.org/...2985.pdf

This equation formed the basis of much of our investigation to date, including our successful modeling of the detailed rotation curves of spiral galaxies [7, 8].


Does anyone who hasn't read the material matter?
justinthyme
1 / 5 (2) Nov 16, 2012
So does this rule out the big bang theory? ;P
justinthyme
not rated yet Nov 16, 2012
Declaring the existence of an undetectable non-interacting mass particle making up almost 6 times the mass of all detectable matter in the universe, being at a specific location in every galaxy (why at the periphery of galaxies exactly where it needs to be, and not, as more logical for a gravity-only particle, at the centre?) .... well, that's just right out of a fairy tale

Look at it this way: We currently know only of one source of gravity: matter

So which one is more complicated:

a) Positing that the observed gravity effects are caused by some form of matter

OR

b) Positing that there is an unknown, second mechanism of gravity
AND that that mechanism is distance dependent
AND that that mechanism is also not uniformly distance dependent (because the gravity effect seems to bunch up)
AND that the effect isn't detectable at close ranges at all
AND ...

Not saying it certainly isn't b). But checking out a) first seems a lot easier.


Occam's Razor anyone :P
lengould100
1 / 5 (2) Nov 16, 2012
IMHO Occam's Razor argues for modified gravity equations rather than some imaginary matter which fits no model and is defined as undetectable LOL.

Is the resistance based in Einstein's declaring gravity to be matter warping spacetime, and you cannot imagine spacetime being warped according to the MOG equations? If so, perhaps that is the part to be re viewed.
rubberman
2 / 5 (4) Nov 16, 2012
why not electromagnetism?
What about it?

The problem with electromagnetism is that it's so much stronger than gravity...

For electromagnetism to stay separate throughout the course of the universes existence at such scales that they could drive expansion there would have to be some force that keeps them apart. A 'cosmic dielectricum' if you so wish. No such substance (or its effects) is observed. It would be easily visible since it would massively affect the paths of charged particle jet.

Kind of had to snicker a bit, even though I know it's not what you meant.

http://phys.org/n...ack.html
rubberman
2 / 5 (4) Nov 16, 2012
It would be easily visible since it would massively affect the paths of charged particle jets.-AP

The field that produces the jet will over power any other field that could effect the jet until the field strengths equal out. I should have realized this before I read the article linked above.
antialias_physorg
5 / 5 (1) Nov 17, 2012
The field that produces the jet will over power any other field that could effect the jet until the field strengths equal out.

Think of a black hole that spews out a jet.
Now think of all black holes that are sideways to your predominant field.
Now think what those jets would look like (the field creating the jet is at right angles so it doesn't 'overpower' anything of your universe-wide field because it has no component in that direction)

Now look at the jets we observe. Compare them to your scenario. See how that doesn't match what we observe at all?
antialias_physorg
4.2 / 5 (5) Nov 17, 2012
IMHO Occam's Razor argues for modified gravity equations rather than some imaginary matter which fits no model and is defined as undetectable

True. But since dark matter is not defined as fitting no model and also is not defined as undetectable: what's your point?

If anyone WOULD posit such unfitting/undetectable stuff then that would certainly not be a theory worth pursuing. But since no one is doing so. Meh - Strawman.

So I think the problem you're having here is not that you don't understand which one of the two approaches is more complicated - rather:

a) you don't actually know what the dark energy/dark matter theories are (and what they aren't)
b) you VASTLY underestimate how complicated a modification to gravity would make things.
rubberman
2 / 5 (4) Nov 19, 2012
"Now look at the jets we observe. Compare them to your scenario. See how that doesn't match what we observe at all?"

Well, the only answer I can speculate on to this one is that we are talking about active galactic nuclei in the neighbourhood of a billion solar masses and the jets are composed of neutral ions and extend thousands of light years. Any imaging I have seen has the jets slowing and ending in lobes or HH structures. But the neutrality allows for the field penetration.

http://www.efda.o...jection/
becomes active, this would support my guess.
Widdekind
1 / 5 (5) Nov 27, 2012
Denser regions collapse quicker. Cosmically, denser clumps tend to be more massive. So, more massive clumps collapsed quicker -- large Clusters of galaxies were the first galactic-scale structures to form (z~3). Eons later, Filaments formed bridging between Clusters (the net gravity, exerted by a pair of Clusters, on matter residing in between them, pulls matter towards the line between their centers.)

So, perhaps the "forest" of Lyman-alpha absorption lines, at high redshift, corresponds to HI clouds (proto-galaxy clumps) in Clusters; whereas lines, at low redshift, correspond increasingly, to clouds (proto-galaxy clumps) in Filaments ?

Swaths of spectrum lacking lines could conceivably correspond to Voids
Widdekind
1 / 5 (5) Nov 28, 2012
Sound waves in space gas are quenched, by gravity collapse, at the Jeans wavelength. Neglecting the expansion of space-time, the Jeans wavelength, at the very high redshift of the CMB, would have been about ~1kpc. That size scale (and the corresponding Jeans mass scale) resemble globular star clusters; but is much much smaller, than the ~100Mpc "BAOs" (which correspond to the CMB 1-degree anisotropies). Inexpertly, actual sound waves, in normal baryonic space gas, can account for the formation of ancient globular star clusters at high redshift (z~(30-6)); but cannot account, for the ~100Mpc "BAOs" of Large Scale Structure in the Cosmic Web. Are not those structures larger, representing longer-wavelength perturbations, than can be explained, by simple sound waves (which gravity quenches, via collapse, at the much smaller Jeans wavelength)?
Widdekind
1 / 5 (5) Nov 29, 2012
In the early universe, baryons were ionized, and the primordial space plasma (H,He,e) coupled to photons (CMB, albeit blue-shifted at earlier epochs). With matter coupled to energy, radiation pressure augmented particle pressure, in support of sound (acoustic) waves. In fact, radiative pressure was thousands of times stronger than particle pressure, in supporting clumps against gravitational collapse -- the effective sound speed, resulting from radiation, was thousands of times faster than the sound speed, of massive particles alone. Thus, the radiation-supported primordial plasma, having a trans-luminal sound speed, could propagate long wavelength "bass notes" w/ Jeans' wavelengths comparable to Hubble lengths. Then universal expansion diffused energy & cooled matter; primordial plasma de-ionized. Neutral space gas, oblivious to photons, lost P_rad support, drastically reducing Jeans' wavelengths, to ~kpc scales, of globular star clusters, tiny to ~100Mpc "BAOs"=CMB 1-deg. anstrp