# Dark Energy’s Clues

Fifty years ago, our understanding of space included only some of the properties we now find most intriguing from the standpoint not only of physics but also of potential propulsion. Dark energy was not suspected then, while Fritz Zwicky’s inference of dark matter (1933) wouldn’t really inspire a wave of investigations until the 1970’s. The presence of the quantum fluctuations that would later be dubbed Zero Point Energy had only recently been examined. For that matter, the cosmic microwave background was still almost a decade from discovery.

Knowing that such properties exist out there in the cosmos offers the potential of future technologies that might be able to make use of them. But clearly, we are a long way from understanding whether or if such phenomena could eventually be harnessed. Just how far becomes apparent every time we get new dark energy news, as we recently did from the University of Toronto, where astronomers studying supernovae in nearby galaxies found when comparing them to far more distant ones that the older supernovae were brighter.

That adds yet another problem to the dark energy picture, because the assumption of uniform brightness in these exploding stars has been helpful in understanding the universe’s accelerated expansion. Correcting for varying brightness could be a thorny problem, says Andrew Howell, lead author of the study:

“You can think of supernovae as light bulbs. We found that the early universe supernovae had a higher wattage, but as long as we can figure out the wattage, we should be able to correct for that. Learning more about dark energy is going to take very precise corrections though and we aren’t sure how well we can do that yet.”

We’d also like to know whether dark energy varies over cosmic time. After all, the term in play is ‘cosmological constant,’ but just how constant is it? Trying to figure out how dark energy behaved in the early universe may require studying radio emissions from neutral hydrogen, redshifted by the expansion of the universe. Stuart B. Wyithe (University of Melbourne) and Avi Loeb (Harvard-Smithsonian Center for Astrophysics) want to study such emissions, believing that although most hydrogen from that era was ionized, surviving neutral clumps may still be detectable.

Does neutral hydrogen show the same kind of distribution patterns as galaxies, caused by early fluctuations in energy density and pressure? Studying its distribution should provide clues as to dark energy’s role in the first few billion years. Wyithe and Loeb believe instruments now being built such as the Murchison Wide-field Array could detect the faint signals from the neutral hydrogen that could tell the tale.

Given the revolution in our understanding of the universe’s expansion, we can assume that the investigation of dark energy will continue to be a primary thrust of modern physics. Which reminds me that a focus of the Breakthrough Propulsion Physics program at NASA was to introduce a targeted perspective — applications to spaceflight — within which recent physics advances could be studied, in hopes of generating new lines of inquiry. The hope: Even if propulsion breakthroughs do not emerge, their study may add to the pool of scientific knowledge.

That’s a worthy goal, and we will need all the perspectives we can find to approach problems as thorny as dark energy. The Toronto paper is Howell et al., “Predicted and Observed Evolution in the Mean Properties of Type Ia Supernovae with Redshift,” Astrophysical Journal 667, pp. L37-L40 (abstract). You can find Loeb and Wyithe’s paper “Fluctuations in 21cm Emission After Reionization” here. The mind boggles at how vast the future bibliography of dark energy studies will become.

Comments on this entry are closed.

• Peter Fred October 20, 2007, 18:42

Mr. Centauri Dreams writes:

“The mind boggles at how vast the future bibliography of dark energy studies will become”

Of course, if the dark energy does not exist, then one should expect for that bibliography for something that can not be found to be vast.

The same sort expectation should go for the dark matter. Since the need for the dark matter has been around longer then the need for the dark energy, the literature is now quite large.

Of course this recent “cosmic train wreck” observation of Abell 520 where the blob of hot gas gets most of the weak gravitational lensing is just a fluke and soon the anomaly will be cleared up by some right thinking theorist.

With main sequence stars there is a high correlation between the log of the luminosity of the star and the log of its mass. Which could mean that this incredible belief in the magical powers of some yet-to-be specified property of mass to attract other mass, that we have held for 300 years could quite possibly be do to an artifact in much the same way that Ptolemaic astronomy was based on the artifact of due to the the earth rotating on its axis.

There is an incredible coincident between the dimming of the universe and its acceleration–they both occurred around z = 1. They could not be causally related could they?

I am getting 3%, 11%, 23% and more increase of test masses that radially spew out infrared radiation just like the planets and stars do. Can this amount of change of weight be observed in a Cavendish type experiment?

The Tully Fisher relation tells us that the luminosity of a galaxy is proportional to its orbital velocity. In deference to Newton and Einstein we take a mass to light ratio and change the TF relation so that it conforms to our belief the its the mass of a galaxy and not its luminosity that that is responsible for that galaxy’s attractive ability.

• forrest noble November 4, 2007, 0:29

Dark Energy unfortunately is another false start in Cosmology. The Dark Energy Theory is based upon very distant events which have, I believe, been misinterpreted for more than just one reason. But primarily, the farther away a galaxy (and therefore the stars within it) the more their appearance is masked. In this case intervening intergalactic “clouds” and dust obscure the apparent brightness of any distant galaxy– following the general rule, the farther away the object is the more the discrepancy between real and apparent brightness. They did consider this possibility but discounted it based upon current paradigms (not observations) of how the universe is structured.

The second problem, unrelated to dark energy interpretations, is that the further away a galaxy is the more its radiation is absorbed by these same intergalactic gases and re-radiated in the radio frequency range. Therefore the further away a galaxy is the more radio waves it will appear to emit. This gives the false impression that the universe was different in the observable past.

These misinterpreted observations along with many others helped catapult the Big Bang Theory into what I believe now is a collection of ad hoc ideas/ theories with zero chance of being true. At least I think their theory of Dark Matter is generally correct. However, unfortunately they still don’t have the correct understandings of gravity. What will be the next big misinterpretation? Of course some day, I hope soon, we will “see the unobscurred light” as a result of correct/ better theories.

• ljk November 28, 2007, 1:13

Dark energy as a mirage

Authors: Teppo Mattsson

(Submitted on 27 Nov 2007)

Abstract: We show that the observed inhomogeneities in the universe have a quintessential effect on the observable distance-redshift relations. The effect is modeled quantitatively by an extended Dyer-Roeder method that allows for two crucial physical properties of the universe: inhomogeneities in the expansion rate and the growth of nonlinear structures. On large scales, the universe is homogeneous, but due to the forming nonlinear structures, the regions the detectable light traverses get emptier and emptier compared to the average. As space expands the faster the lower the local matter density, the expansion can then accelerate along our line of sight. This phenomenon provides both a natural physical interpretation and a quantitative match for the observations from the cosmic microwave background anisotropy, the position of the baryon oscillation peak, the magnitude-redshift relations of type Ia supernovae, the local Hubble flow and the nucleosynthesis, resulting in a new concordance model with 90% dark matter, 10% baryons, no dark energy and 14.8 Gyr as the age of the universe. The model is based only on the observed inhomogeneities so, unlike a large local void, it respects the cosmological principle, further explaining the late onset of the perceived acceleration as a consequence of the forming nonlinear structures. Altogether, the results seem to imply that dark energy is a mirage.

Subjects: Astrophysics (astro-ph)

Report number: HIP-2007-64/TH

Cite as: arXiv:0711.4264v1 [astro-ph]

Submission history

From: Teppo Mattsson [view email]

[v1] Tue, 27 Nov 2007 20:47:32 GMT (122kb)

http://arxiv.org/abs/0711.4264

• ljk November 30, 2007, 12:36

Dark Energy in Light of the Cosmic Horizon

Authors: Fulvio Melia

(Submitted on 29 Nov 2007)

Abstract: Based on dramatic observations of the CMB with WMAP and of Type Ia supernovae with the Hubble Space Telescope and ground-based facilities, it is now generally believed that the Universe’s expansion is accelerating. Within the context of standard cosmology, the Universe must therefore contain a third dark’ component of energy, beyond matter and radiation.

However, the current data are still deemed insufficient to distinguish between an evolving dark energy component and the simplest model of a time-independent cosmological constant. In this paper, we examine the role played by our cosmic horizon R0 in our interrogation of the data, and reach the rather firm conclusion that the existence of a cosmological constant is untenable. The observations are telling us that R0=c t0, where t0 is the perceived current age of the Universe, yet a cosmological constant would drive R0 towards ct (where t is the cosmic time) only once, and that would have to occur right now. In contrast, scaling solutions simultaneously eliminate several conundrums in the standard model, including the coincidence’ and `flatness’ problems, and account very well for the fact that R0=c t0.

We show here that for such dynamical dark energy models, either R0=ct for all time (thus eliminating the apparent coincidence altogether), or that what we believe to be the current age of the universe is actually the horizon time th=R0/c, which is always shorter than t0.

Our best fit to the Type Ia supernova data indicates that t0 would then have to be ~16.9 billion years. Though surprising at first, an older universe such as this would actually eliminate several other long-standing problems in cosmology, including the (too) early appearance of supermassive black holes (at a redshift greater than 6) and the glaring deficit of dwarf halos in the local group.

Subjects: Astrophysics (astro-ph); General Relativity and Quantum
Cosmology (gr-qc); High Energy Physics – Phenomenology (hep-ph); High Energy Physics – Theory (hep-th)

Cite as: arXiv:0711.4810v1 [astro-ph]

Submission history

From: Fulvio Melia [view email]

[v1] Thu, 29 Nov 2007 19:50:17 GMT (119kb)

http://arxiv.org/abs/0711.4810

• ljk December 4, 2007, 12:36

Dark passions

Understanding the accelerating universe is almost as difficult as deciding
who should gain credit for its discovery

http://physicsworld.com/cws/article/print/31904

A dark future for cosmology

Lawrence Krauss on why we will never understand the true nature of
dark energy

http://physicsworld.com/cws/article/print/31905

Dark Energy

Robert P. Crease describes the discovery of the accelerating universe

http://physicsworld.com/cws/article/print/31908

The enduring mystery of the accelerating universe

http://physicsworld.com/cws/article/print/31910

• ljk December 5, 2007, 14:12

General relativistic velocity: the alternative to dark matter

Authors: F.I. Cooperstock, S. Tieu

(Submitted on 30 Nov 2007)

Abstract: We consider the gravitational collapse of a spherically symmetric ball of dust in the general relativistic weak gravity regime. The velocity of the matter as viewed by external observers is compared to the velocity gauged by local observers. While the comparison in the case of very strong gravity is seen to follow the pattern familiar from studies of test particles falling towards a concentrated mass, the case of weak gravity is very different. The velocity of the dust that is witnessed by external observers is derived for the critically open case and is seen to differ markedly from the expectations based upon Newtonian gravity theory. Viewed as an idealized model for a cluster of galaxies, we find that with the general relativistic velocity expression, the higher-than-expected constituent velocities observed can be readily correlated with the solely baryonic measure of the mass, obviating the need to introduce extraneous dark matter. Hitherto unexplained and subject-to-reinterpretation astrophysical phenomena could also be considered within this context. It is suggested that an attempt be made to formulate an experimental design at smaller scales simulating or realizing a collapse with the aim of implementing a new test of general relativity.

Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Theory (hep-th)

Cite as: arXiv:0712.0019v1 [astro-ph]

Submission history

From: Fred Cooperstock I [view email]

[v1] Fri, 30 Nov 2007 22:48:04 GMT (15kb)

http://arxiv.org/abs/0712.0019

• ljk December 14, 2007, 12:34

Dark Energy: back to Newton?

Authors: Lucy Calder, Ofer Lahav (University College London)

(Submitted on 13 Dec 2007)

Abstract: Dark Energy is currently one of the biggest mysteries in science. In this article the origin of the concept is traced as far back as Newton and Hooke in the seventeenth century. Newton considered, along with the inverse square law, a force of attraction that varies linearly with distance. A direct link can be made between this term and Einstein’s cosmological constant, Lambda, and this leads to a possible relation between Lambda and the total mass of the universe. Mach’s influence on Einstein is discussed and the convoluted history of Lambda throughout the last ninety years is coherently presented.

Comments: 14 pages; to appear in the Astronomy & Geophysics journal of the Royal Astronomical Society

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2196v1 [astro-ph]

Submission history

From: Ofer Lahav [view email]

[v1] Thu, 13 Dec 2007 20:50:06 GMT (221kb)

http://arxiv.org/abs/0712.2196

• ljk December 19, 2007, 12:42

Addressing the Crisis in Fundamental Physics

Authors: Christopher W. Stubbs

(Submitted on 18 Dec 2007)

Abstract: I present the case for fundamental physics experiments in space playing an important role in addressing the current “dark energy” crisis. If cosmological observations continue to favor a value of the dark energy equation of state parameter w=-1, with no change over cosmic time, then we will have difficulty understanding this new fundamental physics. We will then face a very real risk of stagnation unless we detect some other experimental anomaly. The advantages of space-based experiments could prove invaluable in the search for the a more complete understanding of dark energy. This talk was delivered at the start of the Fundamental Physics Research in Space Workshop in May 2006.

Comments: 11 pages, Opening talk presented at the 2006 Workshop on Fundamental Physics in Space. Submitted to Int’l Journal of Modern Physics, B

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2876v1 [astro-ph]

Submission history

From: Christopher Stubbs [view email]

[v1] Tue, 18 Dec 2007 04:40:52 GMT (6kb)

http://arxiv.org/abs/0712.2876

• ljk December 20, 2007, 11:01

Dark Energy and the Hubble Constant

Authors: H. Arp

(Submitted on 19 Dec 2007)

Abstract: Dark energy is inferred from a Hubble expansion which is slower at epochs which are earlier than ours. But evidence reviewed here shows $H_0$ for nearby galaxies is actually less than currently adopted and would instead require {\it deceleration} to reach the current value.

Distances of Cepheid variables in galaxies in the Local Supercluster have been measured by the Hubble Space Telescope and it is argued here that they require a low value of $H_0$ along with redshifts which are at least partly intrinsic. The intrinsic component is hypothesized to be a result of the particle masses increasing with time.

The same considerations apply to Dark Matter. But with particle masses growing with time, the condensation from plasmoid to proto galaxy not only does away with the need for unseen “dark matter” but also explains the intrinsic (non-velocity) redshifts of younger matter.

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.3180v1 [astro-ph]

Submission history

From: Halton Arp [view email]

[v1] Wed, 19 Dec 2007 13:10:02 GMT (29kb)

http://arxiv.org/abs/0712.3180

• ljk January 21, 2008, 10:59

Agegraphic dark energy as a quintessence

Authors: Jingfei Zhang, Xin Zhang, Hongya Liu

(Submitted on 18 Jan 2008)

Abstract: Recently, a dark energy model characterized by the age of the universe, dubbed “agegraphic dark energy”, was proposed by Cai. In this paper, a connection between the quintessence scalar-field and the agegraphic dark energy is established, and accordingly, the potential of the agegraphic quintessence field is constructed.

Comments: 9 pages, 3 figures; accepted by Eur. Phys. J. C

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0801.2809v1 [astro-ph]

Submission history

From: Jingfei Zhang [view email]

[v1] Fri, 18 Jan 2008 03:37:49 GMT (108kb)

http://arxiv.org/abs/0801.2809

• ljk January 30, 2008, 13:55

The bang of a white hole in the early universe from a 6D vacuum state: Origin of astrophysical spectrum

Authors: Mauricio Bellini (Mar del Plata University – CONICET)

(Submitted on 15 May 2007 (v1), last revised 29 Jan 2008 (this version, v4))

Abstract: Using a previously introduced model in which the expansion of the universe is driven by a single scalar field subject to gravitational attraction induced by a white hole during the expansion (from a 6D vacuum state), we study the origin of squared inflaton fluctuations spectrum on astrophysical scales.

Comments: Final version to be published in Eur. Phys. J. C

Subjects: Astrophysics (astro-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Theory (hep-th)

Cite as: arXiv:0705.2223v4 [astro-ph]

Submission history

From: Mauricio Bellini [view email]

[v1] Tue, 15 May 2007 22:21:31 GMT (21kb)

[v2] Tue, 25 Sep 2007 16:11:31 GMT (21kb)

[v3] Mon, 14 Jan 2008 13:50:56 GMT (21kb)

[v4] Tue, 29 Jan 2008 19:13:18 GMT (21kb)

http://arxiv.org/abs/0705.2223

• ljk January 9, 2009, 20:59

Palomar Skies has a link to several articles on Fritz Zwicky:

http://palomarskies.blogspot.com/2009/01/fritz-zwicky-father-of-dark-matter.html

• Richard Benish July 11, 2009, 21:46

Peter Fred boldly acknowledged that

“… this incredible belief in the magical powers of some yet-to-be specified property of mass to attract other mass, that we have held for 300 years could quite possibly be due to an artifact in much the same way that Ptolemaic astronomy was based on the artifact of the earth rotating on its axis.”

I would add that faith in this belief is based almost entirely on observations of phenomena beyond the surfaces of large gravitating bodies (e.g., common orbiting and falling phenomena, as well as light propagation and clock behavior). There is a huge gap in empirical evidence for gravitational attraction INSIDE gravitating bodies.

Given that the mysteriousness of gravity has been perennially asserting itself not only with respect to unification with other forces, but lately also with respect to cosmological and astrophysical phenomena, perhaps we are well advised to finally make a local test of gravity inside massive bodies. Specifically, useful light may be shed on the nature of gravity, dark matter and dark energy by testing the common thought problem of dropping a test object into a hole through a uniformly dense spherical mass. The “well known” Newtonian (and General Relativistic) answer, of course, is that the test object will harmonically oscillate from one side of the sphere to the other.

But we have no empirical evidence backing up this prediction. It could be tested by one of two methods: 1) With a satellite laboratory (on a trajectory taking it far from Earth) using a whole sphere, much like the idealized problem. Or 2) In an Earth-based laboratory using a modified Cavendish balance. The large masses would need to have a channel and slice cut out of them to allow passage of the small masses and the arm that connects them.

Though much less expensive than the space experiment (1), the Cavendish balance (2) would also require a novel suspension system. The usual torsion fiber would need to be replaced with a magnetic or fluid suspension, so as to allow free movement of the arm through a wide angular range.

One’s first guess may be that we already “know” what the result of this experiment would be (simple harmonic motion). Upon deeper reflection, we have to admit that we really do not know, and that, if an unexpected result were to occur, it may reveal something to help us understand the “magic” of gravity and give us a new perspective on the cosmological conundrums discussed here.