# B Is expansion the same Throughout the Universe

1. Feb 3, 2017

### wolram

I have just found this paper that states the universe is expanding faster the further we look back, Different than the Hubble measured.?

https://www.sciencedaily.com/releases/2017/01/170126132624.htm

The new measurement is completely independent of -- but in excellent agreement with -- other measurements of the Hubble constant in the local Universe that used Cepheid variable stars and supernovae as points of reference heic1611.

However, the value measured by Suyu and her team, as well as those measured using Cepheids and supernovae, are different from the measurement made by the ESA Planck satellite . But there is an important distinction -- Planck measured the Hubble constant for the early Universe by observing the cosmic microwave background.

2. Feb 3, 2017

### Staff: Mentor

I don't see any links to the actual paper in the article. Is it on arxiv?

Also, the general answer to all papers of this type is that this is ongoing research and we don't know what the final answer is going to be.

Finally, the question of what the rate of expansion was in the far past does not seem to be the same as the title question of this thread. The title question of this thread seems to be asking whether, at the present time, the universe is expanding at the same rate everywhere. The answer is that that is true by definition: we purposely choose the coordinates we use in cosmology so that this is true.

3. Feb 3, 2017

### Chronos

This is not unlike asking if a really long rubber band stretches by the same amount at various intervals along its entire length. It's not an easy question when the rubber band itself is the only reference available. This is one of the questions cosmologists hope to answer with the Dark Energy Survey, http://www.darkenergysurvey.org/the-des-project/overview/.

4. Feb 3, 2017

5. Feb 4, 2017

### Jorrie

The reported value of Ho does seem to jump up and down around the 70 km/s/Mpc mark, depending on the data-set and the analysis used. This is not of too much of a concern, as long as it is the same for all distances. It is a bit worrying that such small error margins are quoted, but the Hubble and Planck error bars do not overlap.

We know that H(t) in the early universe was much higher than H(t) later, but this is compensated for when Ho is determined. It looks suspiciously much like an artifact of the different analysis techniques.

Last edited by a moderator: May 8, 2017
6. Feb 4, 2017

### Chronos

It's unclear what it might mean if Ho varies with the age of the universe. Does it herald new physics or just a misapplication of existing physics?

7. Feb 4, 2017

### m k

A triangle that has matter around its sides that can beat dark energy but center can't.
How is it expanding?

Same triangle.
A photon straight from the center of the base to opposite vertex and another photon detouring around other vertex.
(no gravity well between start and end)
How their redshifts differ?

8. Feb 4, 2017

### wolram

Thank you for replies and your patience.

9. Feb 4, 2017

### Staff: Mentor

It can't; $H_0$ is the Hubble constant "now". Unless I'm misunderstanding the terminology being used in these papers.

Different measurements of $H_0$ whose error bars don't overlap suggests to me that there is a model assumption being made that is not quite correct, since as I understand it all of these measurements require some assumption about the cosmological model (LCDM being the usual one).