Marginal evidence for cosmic acceleration from Type Ia SNe

[wabbit]

This is neither the paper we were talking about, nor the same model. You are deliberatelly confusing different things and ideas just to desprestige a model that fits the data as well as LCDM.

You cannot say it fits the data as well, that is not what any of the papers quoted here show.

 

[Chalnoth]

This is neither the paper we were talking about, nor the same model. You are deliberatelly confusing different things and ideas just to desprestige a model that fits the data as well as LCDM.

When the model describes the CMB data well (meaning a prediction of the full power spectrum out to $\ell=3000$ or so), then it would make sense to say it fits the data. But right now, this model is tens if not hundreds of standard deviations away from fitting the CMB data without adding some dynamics to make the late universe approximately linear in growth but the early universe following CDM + inflation.

 

[JuanCasado]

When the model describes the CMB data well (meaning a prediction of the full power spectrum out to $\ell=3000$ or so), then it would make sense to say it fits the data. But right now, this model is tens if not hundreds of standard deviations away from fitting the CMB data without adding some dynamics to make the late universe approximately linear in growth but the early universe following CDM + inflation.

But this is the point: The Steady Flow model is linear in growth in recent times, while it follows standard dynamics for the early universe.

 

[Chalnoth]

But this is the point: The Steady Flow model is linear in growth in recent times, while it follows standard dynamics for the early universe.

Except with a very different matter density. I just don't think that's going to work. I'll believe it when I see it.

The issue here is that the CMB constrains the matter density very tightly. The baryon density is the tightest constraint as the baryon density is largely determined by the magnitude of the first acoustic peak. The ratio of dark matter to normal matter is then determined by the ratio of the heights of the even an odd acoustic peaks*.

The CMB itself doesn't actually constrain the dynamics of the expansion since it was emitted, but changing those dynamics has very little impact on the estimated matter and dark matter density from the CMB. For example, compare these parameters, which are WMAP 9-year only using $\Lambda$CDM with no spatial curvature:
http://lambda.gsfc.nasa.gov/product/map/dr5/params/lcdm_wmap9.cfm

To these parameters, which use the same data and assumptions except for relaxing the assumption of flat space:
http://lambda.gsfc.nasa.gov/product/map/dr5/params/olcdm_wmap9.cfm

In particular, the $\Omega_\Lambda$ and other density fraction parameters are extremely poorly constrained in the second case: $\Omega_\Lambda$ has 95% confidence limits between 0.22 and 0.79. When flat space is assumed, this tightens to $0.732 \pm 0.025$ (68% confidence limits, making this somewhat confusing).

But if you compare this to the measures of the cold dark matter and baryon density ($\Omega_ch^2$ and $\Omega_bh^2$, respectively), those remain very tightly constrained and are largely unaffected by the assumption of flatness. In fact, the errors on the density parameters barely budge.

* This isn't how it's done when people are doing CMB parameter estimates, of course. But it does illustrate why the constraints on these parameters are so tight.