Is Carlos Barcelo's Research Redefining Cosmology and Gravity?

[George Jones]

Yes, of course. There is no argument there. Even if the Hubble constant were to decrease with time, the simple fact that space is expanding with time means that galaxies pick up speed with time which is an acceleration.

Not necessarily.

This much was know when the Hubble law was first discovered.

No, before the (1998) supernova data, it was widely believed that the universe was decelerating (near t = now). This is why people found the supernova data to be so surprising.

So am I now to believe that the supernova data just now discovered this effect? I don't think so. I'm sure they were pointing to an apparent increase in the Hubble constant when they say the word "acceleration".

No. I think people participating in this thread have tried repeatedly to tell you that this is not the case.

As an example of a decelerating (but still expanding) universe that has a Hubble constant that decreases with time, Consider a toy universe and galaxies A, B, C, D at three differents instants of cosmological time.

Table of proper distances D from Milky Way:

<br /> \begin{matrix}<br /> &amp; | &amp; A &amp; B &amp; C &amp; D \\<br /> -- &amp; | &amp; - &amp; - &amp; - &amp; - \\<br /> t = 1 &amp; | &amp; 1 &amp; 2 &amp; 3 &amp; 4 \\<br /> t = 2 &amp; | &amp; 1.4 &amp; 2.8 &amp; 4.2 &amp; 5.7 \\<br /> t = 3 &amp; | &amp; 1.7 &amp; 3.5 &amp; 5.2 &amp; 6.9<br /> \end{matrix}<br />

Table of recessional speeds v from Milky way:

<br /> \begin{matrix}<br /> &amp; | &amp; A &amp; B &amp; C &amp; D \\<br /> -- &amp; | &amp; - &amp; - &amp; - &amp; - \\<br /> t = 1 &amp; | &amp; 0.5 &amp; 1 &amp; 1.5 &amp; 2 \\<br /> t = 2 &amp; | &amp; 0.35 &amp; 0.71 &amp; 1.1 &amp; 1.4 \\<br /> t = 3 &amp; | &amp; 0.29 &amp; 0.58 &amp; 0.87 &amp; 1.2<br /> \end{matrix}<br />

The Hubble constant equals 1/2, 1/4, and 1/6 at times 1, 2, and 3.

Also, as can be seen, the universe is decelerating.

This toy model is a Freidman-Robertson-Walker universe that has its scale factor given by a(t) = t^{1/2}, and, qualitatively, echos the way we thought the universe behaved (near t = now) before we had the 1998 supernova data.

 

[hellfire]

So now I'm not sure that the graph does indicate an increase of the Hubble parameter with time.

Clearly it is not.

If the Hubble parameter would be currently increasing (\dot H_0 &gt; 0) then in our flat universe:

q_0 &lt; - 1

And therefore the curve relating luminosity distance and redshift:

d_L = \frac{1}{H_0} \left(z + \frac{1}{2} (1 - q_0) z^2 + ...\right)

would be below the blue one here, which corresponds to the de-Sitter model in which:

q_0 = - 1

In encourage you to check that an increasing Hubble parameter implies q_0 &lt; - 1 in a flat space. It is not a difficult task and I already pointed out how to proceed.

 

[Mike2]

So after the luminosity distance is corrected for redshift, is there not even an appearent increase in the Hubble constant.