Dark matter and dark energy

Chalnoth

Then what, pray tell, is the explanation?

This is pure, unadulterated fantasy. The dark matter model used in nearly all WMAP data analysis is the simplest possible: zero-temperature dark matter. This model fits the data exceedingly well. There is no curve fitting done with respect to dark matter in analyzing the WMAP data, except in terms of estimating the values of the various parameters. The simplest model for WMAP uses the following parameters:

1. Dark matter density.
2. Normal matter density.
3. Hubble expansion rate.
4. Scalar spectral index (an inflation parameter).
5. Optical depth to the CMB (basically, how transparent the universe is between us and the CMB).
6. Amplitude of fluctuations.

Each one of these parameters is physically-motivated. There is no "curve fitting" going on. Each one of the parameters which can be estimated independently with other experiments shows the same result for those parameters. The various extensions of this minimalist model, such as allowing spatial curvature to vary, or allowing the scalar spectral index to change with scale, so far show no evidence of deviation from this simplest description.

juanrga

What you call «pure, unadulterated fantasy» is just the orange line in the next figure.



The orange line is the prediction done by the dark-matter model before WMAP data (and Boomerang data) was known. The dark matter model was clearly falsified... unless you are blind.

The prediction done by the non-dark matter model for both first and second peaks was remarkably verified... unless again you are blind. The third peak could not be explained because the model used then was non-relativistic, but some recent relativistic extensions seem to fit the third as well.

Once the WMAP data was known, DM cosmologists did an exercise in curve fitting (all of dark matter is pure curve fitting) and changed the parameters of the dark matter model until fitting the data.

Moreover, when forcing the dark matter model to fit the available data, DM cosmologists chose values for its free parameters that contradict other independent tests. For example, the baryon density assumed in the current dark matter cosmological model is much larger (about 3x) that the baryon density measured from other independent tests.

However, if you do not assume this high value of the density then you cannot fit the WMAP data using the dark matter cosmological model, generating a contradiction.

Therefore we have a contradictory dark matter model, which fails to explain many data (TFL, fine tunning of galactic rotation curves...) and whose hypothetical new kind of matter has been systematically not found in a large list of experiments performed since the 80s. I cited the recent results of Fermi not finding any evidence of the hypothetical dark matter, but before Fermi was Xenon100 the experiment that found nothing and before was...

Chalnoth

Two points on this:
1. Did you even look at the parameters for the no dark matter case? Generally the parameters for these types of "alternative" theories are completely and utterly falsified by other observations.
2. WMAP has since measured the third peak pretty accurately, completely breaking the degeneracy between dark matter and the other parameters. The dark matter model fits, models without dark matter do not.

Edit: Oh, and let me just point out that the baryon density discrepancy is trivially explained by just noting that most of the normal matter has not fallen into gravitational potential wells and is thus invisible.

juanrga

This remind me of a typical anti-evolutionist argument that says that fossils were put by God for testing the faith of the Christians.

It is not fascinating that whereas the DM prediction (red orange) failed miserably, the non-DM theorists were so lucky that used false values of parameters just to predict the result of the WMAP before was known. Those non-DM guys would play bonoloto all the weeks

As you said the evidence for dark matter is firm. It is so firm that numerous experiments designed to find it have all failed to find it merely for improving the true faith of DM-believers.

The measurement of the third peak is not so accurate as you believe and new experiments are being prepared to measure it with more accuracy. Of course, the third peak in no way proves that the dark matter is correct.

Edit: Oh and I believed that the baryon density discrepancy still remains unexplained in the literature, but you can give a reference on the contrary please.

jtbell

juanrga, please provide citations to demonstrate that your view has at least some currency in professional circles. If this is just your view, then publish it somewhere and make it part of professional discussion, and then we can consider it here.

If legitimate controversy already exists in professional circles, then it is fair game for discussion here; but this is not the place to start such controversy.

Chalnoth

You are truly demonstrating a shocking ignorance of the science you are so keen to criticize.

There is no unique power spectrum predicted for the CMB given the existence of dark matter. The specific power spectrum you get depends upon the amount of dark matter (and other things). However, dark matter produces an extremely distinct signature on the CMB power spectrum: it suppresses the even-numbered peaks with respect to the odd-numbered peaks.

This is why I went on about the third peak and why its measurement is important. It is possible to fudge the first and second peaks merely by adjusting the parameters which control how rapidly the overall power spectrum drops at smaller angular scales. But once you've measured the third peak, this degeneracy is broken, as now you can directly measure the overall decay of the power spectrum (by comparing the first and third peaks), and then if the second peak is comparatively low against this overall decay, then that is a definitive and conclusive signature of dark matter.

And that is precisely what we see in the data.

juanrga

What you call «my view» is a well-known astrophysics/cosmological topic that has received large coverage even in science news services.

For instance, you can find some coverage about the most recent evidence against dark matter

http://news.sciencemag.org/scienceno...te.html?ref=ra

http://blogs.nature.com/news/2011/02/post_73.html

Regarding the figure in my post #19 and my claim that the dark matter model predictions were falsified (orange line in that figure), take a look to http://xxx.lanl.gov/abs/astro-ph/0008188 (Astrophys.J. 541, 2000, L33-L36), you would find the first figure in page 10, which gives the correct prediction using a model without dark matter (No-CDM), whereas the second figure gives the well-known fiasco of the prediction done using a dark matter model (Lambda-CDM).

A review of a cosmology without dark matter is given in Class. Quant. Grav. 26: 143001, 2009 (http://arxiv.org/abs/0903.3602) although I do not like TeVeS.

If you search in this thread you would find my posts alluding to the null results by Xenon100 and by Fermi experiments in their search for the aether dark matter. If you do not know what Fermi is or what measures, please search my posts here and follow the link to Physics World.

Now, it would be fine if you also ask to Chalnoth to provide references supporting his many bold claims. He has just replied now to me but once again he refuses to provide references albeit I am asking to him for at least one...

Chalnoth

What a bunch of steaming crap. Not one shred of evidence is presented here.

Except it doesn't fit. Not when you include the third peak. It is simply not possible to fit the first three peaks without dark matter.

I'd also point out that he simply has the wrong parameter values. That can be forgiven the paper's author because these parameters were not known in detail when this paper was written. The parameters are, however, known in detail today.

What, you want a textbook in basic cosmology? Here is how the various parameters impact the power spectrum of the CMB:
http://space.mit.edu/home/tegmark/cmb/movies.html

juanrga

Unfortunately my «shocking ignorance» will remain because in each occasion that I ask you for a specific reference you offer me none...

It seems that you want to put in my writings stuff that I have never said (you can offer quotations if you believe the contrary), whereas you decidedly ignore what I have really said .

As said before the third peak is still a bit controversial (foreground subtracting). As said also new experiments as PLANCK presumably will clarify this. Although you take WMAP third peak as gospel.

Moreover, the no-CDM model predicted the correct first and second peaks BEFORE the data was known. Whereas the Lambda-CDM model was falsified (see the orange line in the figure in #19).

AFTER and only AFTER the data was known the Lambda-CDM model was changed. I would not call that a prediction...

You go on and say that «is possible to fudge the first and second peaks merely by adjusting the parameters» in the dark matter model. I wonder if you read my posts because I already said this to you, but I added the important point of that values incompatible with other independent tests were assumed for the parameters. You claim that the «baryon density discrepancy is trivially explained» but then you fail to provide me a single reference showing that the discrepancy is solved.

You then go far and claim that overall measurement of the three peak ratios is «a definitive and conclusive signature of dark matter». Again this is another bold claim without support. First and second peaks are already obtained without appeal to dark-matter (in fact both peaks were predicted by a no-CDM model, see references given). The third peak can be explained without dark mater also, in fact you only need a source for gravity that propagates independently of the baryons. Precisely, this is the role played by the scalar field in TeVeS (although I dislike this theory by several reasons)

juanrga

Yes Physical Review Letters and the several cosmologists and astrophysicists quoted in Science and Nature are well-known for their «bunch of steaming crap»:

He is merely a scientist and could not fit a, then inexistent, peak. Do you see the third peak in some figure in that paper?

It is possible to fit the three peaks without dark matter. But it is not possible to explain the other tests and observations that I cited before using a dark matter model.

As already said you this guy would be playing bonoloto , because he is so lucky that using 'wrong' parameters he was able to predict exactly what would be observed in the experiment BEFORE the experiment was done.

He is so lucky that using a 'wrong' theory (i.e., one without aether dark matter) and using 'wrong' parameters, he has been able to predict what has been after observed in hundred of observations/experiments. He has worked a whole spectrum from galactic scale to cosmos, and all his predictions have been posteriorly verified. ALL

Is not truly fantastic? Specially when his successes are compared with the failed dark matter predictions done about the same observations/experiments

Thanks by the laugh . Now when you find some free time, please give me the specific reference asked. One is enough, do not send me 30 or 40, please

Chalnoth

No. That is my entire point. I see it in papers released today. For example:
http://arxiv.org/abs/1001.4635

The most recent WMAP data release shows a relatively tight measurement of the third peak, and a weak measurement of the fourth. Gone are the types of heuristic data checks performed by McGaugh: today we do full bayesian parameter estimation, and a universe without dark matter is conclusively ruled out.

This is simply a blatant, unadulterated lie. He absolutely, positively, did not predict what the experiment would observe, because as you can see in the paper I linked above, the second and third peaks have nearly the same amplitude, while with McGaugh's parameters the third peak would have a much lower amplitude. He was wrong. And not slightly wrong. Completely wrong.

As for Planck, yes, Planck will improve our estimate of the CMB power spectrum, as well as shining light on quite a bit of other science. But WMAP measurements alone are more than detailed enough to answer the dark matter question.

cristo

This thread is done. The article that juanrga is referring to is over 10 years. But, as Chalnoth says, we now have a lot more data giving us a far more detailed picture of the CMB power spectrum which simply cannot be fitted without CDM. As for MOND, I think very few people take this theory seriously anymore, and its relativistic generalisation also does not fit the data (e.g. http://arxiv.org/abs/0907.1463).