Comments on: Escape from the clutches of the dark sector?

By: Maybe it’s not dark matter, just gravity leaking in « Later On

Maybe it’s not dark matter, just gravity leaking in « Later On — Sat, 11 Nov 2006 15:28:27 +0000

[...] UPDATE: That last link references a paper that has serious problems. So we do need dark matter—or some other explanation—after all. [...]

By: Dark matter is still needed « Later On

Dark matter is still needed « Later On — Sat, 11 Nov 2006 15:22:11 +0000

[...] I have linked to this post previously, which suggests that general relativity explains the rotation of the galaxies, with no need for hypothesized dark matter. But that paper has serious problems, so one can safely ignore it. So we’re left with dark matter—or with even stranger ideas. [...]

By: Danger, Phil Anderson | Cosmic Variance

Danger, Phil Anderson | Cosmic Variance — Tue, 03 Jan 2006 18:54:52 +0000

[...] Well, not so much “radical” as “incorrect.” Anderson doesn’t mention the fact that the universe is accelerating, which is curious, since that’s the best evidence for dark energy. His offhanded proposal that density fluctuations are somehow responsible is similar in spirit to the original proposal of Kolb, Matarrese, Notari, and Riotto, that ultra-large-scale inhomogeneities could mimic the effects of dark energy. Everyone now agrees that this idea doesn’t work, although the authors are trying again with small-scale fluctuations. While that hasn’t been cleanly ruled out, it’s a long shot at best; most folks agree that we either need dark energy, or somehow to modify gravity. [...]

By: Scott

Scott — Fri, 09 Dec 2005 02:35:32 +0000

background i have in

By: Scott

Scott — Fri, 09 Dec 2005 02:34:47 +0000

Eagerly awaiting the response of the Dark Forces

or simply an expert in GR. It seemed to refute the non-physical argument, but I had trouble following all the math, as the only background in GR is what I taught myself from Sean’s book this summer not to mention the fact that I am drained from lack of sleep and finals.

By: Dissident

Dissident — Thu, 08 Dec 2005 16:51:00 +0000

…and here’s the latest from Cooperstock & Tieu: no “thin sheet of infinite density”.

http://arxiv.org/abs/astro-ph/0512048

Eagerly awaiting the response of the Dark Forces…

By: Arun

Arun — Mon, 14 Nov 2005 13:14:27 +0000

Thomas, how does the conclusion – dark matter is not a perfect fluid lead to the conclusion that dark matter doesn’t exist?

By: Count Iblis

Count Iblis — Mon, 14 Nov 2005 12:50:41 +0000

Here are some interesting papers by M. Reuter and H. Weyer: M. Reuter and H. Weyer, Running Newton Constant, Improved Gravitational Actions, and Galaxy Rotation Curves, Phys. Rev. D 70, 124028 (2004). M. Reuter and H. Weyer, Quantum gravity at astrophysical distances?, JCAP 0412, 001 (2004). M. Reuter and H. Weyer, Do we Observe Quantum Gravity Effects at Galactic Scales?

By: Dissident

Dissident — Mon, 14 Nov 2005 10:49:17 +0000

Far from being an expert, I’d still expect those who claim such lofty status to focus on assumption #2: “in the limit of no rotation halo spacetime is Minkowski spacetime”. Why this should be more “likely” than assumption #4 (perfect fluid) is not obvious, at least to me.

But for the time being, I’ll be doing my usual excited-jumping-around-routine. Thanks for pointing out this paper – I had (again!) completely missed it!

By: Thomas Larsson

Thomas Larsson — Mon, 14 Nov 2005 07:53:40 +0000

Another paper has appeared:

astro-ph/0511241

Let me quote the entire section 4, Conclusion:

“Dark matter does not exist.”

Do the experts have an opinion about this paper?

By: Arun

Arun — Sat, 05 Nov 2005 15:24:48 +0000

Another paper has appeared:

http://arxiv.org/abs/astro-ph/0510750

Presence of exotic matter in the Cooperstock and Tieu galaxy model

Authors: D. Vogt, P. S. Letelier
Comments: 4 pages

We analyze the presence of an additional singular thin disk in the recent General Relativistic model of galactic gravitational field proposed by Cooperstock and Tieu. The physical variables of the disk’s energy-momentum tensor are calculated. We show that the disk is made of exotic matter, either cosmic strings or struts with negative energy density.

By: Bloggernacle Times » This Week in Science and Religion

Bloggernacle Times » This Week in Science and Religion — Fri, 21 Oct 2005 19:02:04 +0000

[...] Dark matter often pops up in unexpected places in LDS discussions. I’ve mentioned it myself a few times. There are some new arguments coming out for why we should reject dark matter entirely. It’s an interesting and controversial topic. [...]

By: Dissident

Dissident — Wed, 19 Oct 2005 19:23:37 +0000

Oh oh… here we go again:

http://arxiv.org/abs/astro-ph/0510523

Off to jump all over the place.

By: Sean

Sean — Wed, 19 Oct 2005 14:58:11 +0000

Shantanu, I am not an expert. But as it says in the link you included, a consensus of people who are experts agree that this is not a measurement of something we would call “the speed of gravity.” I would tend to believe them.

By: Shantanu

Shantanu — Wed, 19 Oct 2005 05:23:41 +0000

Thanks a lot Sean for the detailed description. This was helpful for
non-experts like me. On a related note I am very curious to know
your take on the speed of gravity/speed of light controversy from two years ago.
http://wugrav.wustl.edu/people/CMW/SpeedofGravity.html
In the last two weeks itself there have been many more papers on this.
What is your take on it? If Kopeikin’s claims are correct, then does that
mean that some brane/string based models which predict speed of gravity
to be different from speed of light are ruled out? Note same question also
holds for Mark, Risa, Clifford and Joanne and (other experts who read this blog).
(If you have discussed this before, could you point me to the link?)
Thanks

By: Kaleberg

Kaleberg — Wed, 19 Oct 2005 03:13:00 +0000

And it might just turn out that these second order effects that play hob with applying perturbation theory ARE dark matter. Why do I keep thinking of that GR paper, was it by Wisdom, about how one can flap one’s wings in empty space and push oneself forward? It seems that it isn’t just quantum theory that says that there is something in a vacuum.

Then again, I’m not a physicist. I sell vacuum cleaners.

By: agm

agm — Tue, 18 Oct 2005 06:18:23 +0000

for example, there could be “non-perturbative effects” that this procedure simply can’t capture, or the perturbation series itself could be sick, for example if the function f2(x) were so huge itself that it overwhelmed the extra factor of Îµ it comes along with.

Still, the skepticism from most people stems from the simple fact that first-order perturbations are quite small, so second-order perturbations should be even smaller!

I agree that in a given application of perturbation theory, a second order effect is likely to be small, if perturbation is valid way of looking at something. And since I know crap all about GR, I’m gonna take your word for it. However, you’re logic is truly dizzying. You are saying that it’s unlikely that Kolb et al are correct because their results are inconsistent with perturbation theory, after explaining that perturbation theory doesn’t apply when perturbative effects are hair on the back of the non-perturbative effects doing the heavy lifting.

By: Brad Holden

Brad Holden — Mon, 17 Oct 2005 23:58:57 +0000

How funny, today’s CosmoClub was on this very subject. We had a speaker from the University of Florida, named Ethan Siegel, who talked about doing a better calculation like that of Kolb et al.

The gist of it was that you need to calculate the scale factor evolution to arbitary order in density contrast but most other terms can be done to linear order. The original Seljak result was wrong, according to our speaker, but not very wrong. He had interesting things to say about super-horizon perturbations as well, namely that most inflationary models would require a fair bit of fine-tuning to produce the observations.

The paper is published and, of course, on astro-ph.

By: citrine

citrine — Mon, 17 Oct 2005 23:35:06 +0000

How will the non-linear effects modify the (interpretation of the?) metric components?

By: Plato

Plato — Mon, 17 Oct 2005 18:25:54 +0000

The fundamentally new science of gravitational wave astronomy opens up a new window on the universe. Up until now, astronomy has relied on observations of electromagnetic wave signals (e.g. visible light, radio waves). The detection of gravitational waves offers a completely new perspective on the universe: they will enable us to “hear” the cosmic orchestra as well as to see it! GR17 will provide the scientific community with one of the earliest opportunities to discuss the first scientific results of this era.

http://www.dcu.ie/~nolanb/gr17.htm

If you did not have a leading perspective in GR, to the conclusions of a cosmic scenario, as such with elliptical valuation might we ever discerned in global perspective (we know gravity waves are theoretical right?)[Taylor and Hulse]

Then how indeed would any valuation on dark energy suffice us to say, that “Omega” would have a value in the expansitory situation at the edge of that same universe? Would also lead us to the “edge” on questions about the blackhole horizon?

Something had to be created out of “nothing” right? Or was there something always there, that we never wanted to take to a limit in terms of theoretical developement?

The circle/sphere being very large ( our cosmos), had to signal somekind of collapse, or could we ever find this association in what happens to the blackhole circle valuation in energy detrmination, would also define some edge for the universe?

Tegmark said no to the “soccer ball”, maybe he might say no to the circles too?