- #1

marcus

Science Advisor

Gold Member

Dearly Missed

- 24,738

- 785

## Main Question or Discussion Point

Around 1998 we got the estimate of 71 from Wendy Freedman's Hubble Space Telescope team. That was called the "key project" of the HST program and was one of the main reasons for HST. So much depends on it that it is important to keep trying to improve the accuracy.

That 71 has stood for 10 years.

Now it looks like Adam Riess' team has a more accurate figure of 74, based on HST observations since Freedman 1998.

74 point something, with some confidence interval or error range. Like +/- 3. So we will have a little turbulence around this for a while.

Ned Wright has put Riess et al's figure in his News of the Universe page on the web.

http://www.astro.ucla.edu/~wright/cosmolog.htm

It behoves us to consider the possibility that 74 might be righter than 71.

Let's recalculate the critical density. It will come out in nanopascal, which is the same as nanojoules per cubic meter.

I put this into the google window and press return

(74 km/s per megaparsec)^2*3*c^2/(8 pi G)

and it tells me 0.92 nanopascal.

That is the average density around us----0.92 nanojoules per cubic meter.

It has to be that, because we can see that it is flat or nearly flat.

So if the Riess figure is accepted, this is what you take 73 percent of, and 27 percent of, and 4 percent of, etc. Talking about the makeup of the universe.

Wright's news item sounds like Riess figure will be accepted, and he's where he should know. He says:

That 71 has stood for 10 years.

Now it looks like Adam Riess' team has a more accurate figure of 74, based on HST observations since Freedman 1998.

74 point something, with some confidence interval or error range. Like +/- 3. So we will have a little turbulence around this for a while.

Ned Wright has put Riess et al's figure in his News of the Universe page on the web.

http://www.astro.ucla.edu/~wright/cosmolog.htm

It behoves us to consider the possibility that 74 might be righter than 71.

Let's recalculate the critical density. It will come out in nanopascal, which is the same as nanojoules per cubic meter.

I put this into the google window and press return

(74 km/s per megaparsec)^2*3*c^2/(8 pi G)

and it tells me 0.92 nanopascal.

That is the average density around us----0.92 nanojoules per cubic meter.

It has to be that, because we can see that it is flat or nearly flat.

So if the Riess figure is accepted, this is what you take 73 percent of, and 27 percent of, and 4 percent of, etc. Talking about the makeup of the universe.

Wright's news item sounds like Riess figure will be accepted, and he's where he should know. He says:

**More Accurate Hubble Constant**

07 May 2009 - Riess et al. report a new value for the Hubble constant of Ho = 74.2 +/- 3.6 km/sec/Mpc based on Cepheid measurements in galaxies that have hosted Type Ia supernovae, including the nuclear ring maser galaxy NGC 4258 which has a very precise distance determined by geometric means.07 May 2009 - Riess et al. report a new value for the Hubble constant of Ho = 74.2 +/- 3.6 km/sec/Mpc based on Cepheid measurements in galaxies that have hosted Type Ia supernovae, including the nuclear ring maser galaxy NGC 4258 which has a very precise distance determined by geometric means.

Last edited: