Tired light and transverse waves

Quote:

>Gravitational redshift is a prediction of general relativity (GR),
>and MOND is an exception to GR, so the behavior of gravitational
>redshift in MOND is as yet unspecified. But it is certainly still
>negligible compared to cosmological redshift. -|Tom|-

This is from a FAQ page on the MOND pages at www.astro.umd.edu/~ssm/mond/faq.html :

Q: Does MOND contradict General Relativity?
A: It generally seems to be assumed that it must, but this is not true. GR and MOND apply in very different regimes. Relativity is what happens as v -> c; MOND is what happens as a -> 0. Empirically, these regimes couldn't be further removed.

However, this sounds more like special relativity so maybe its a bad example.

This next bit is from the MOND pages too:

Q: What is the acceleration scale [for MOND]?
A: a0 = 1.2 x 10-10 m s-2, i.e., about one Angstrom per second per second. This is one part in 1011 of what we feel on the surface of the earth. The precise value depends on the distance scale to galaxies, so perhaps it would be better to say a0 = 1.2 x 10-10 m s^-2 h(75)^2, where h = Ho/75 is the Hubble Constant (the expansion rate of the universe) in units of Ho = 75 km s-1 Mpc-1. (Currently, most measurements report values in the neighborhood of H0 = 72 km s-1 Mpc-1.)

Have a look at the FAQ page to get a better idea of what it looks like form a non-text cut n' paste.

The question is: what happens to the numbers for the acceleration scale if the universe is not expanding?

I'm sure others reading this thread must be as confused as I was until it found MOND in a dictionary of acronyms and Googled Modified Newtonian Dynamics . (Damn editor is not translating hyperlinks correctly!)

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by PhilJ</i>
<br />I'm sure others reading this thread must be as confused as I was until it found MOND in a dictionary of acronyms...<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Sorry. MOND comes up often in these discussions, and we sometimes forget the need to repeat definitions from time to time. MOND arose as a possible explanation (other than "dark matter") for the odd behavior of stellar velocities in galaxies. Those velocities do not drop with increasing distance from the galaxy center, the way planet orbital velocities must drop with increasing distance from the Sun.

In its essence, MOND postulates a minimum acceleration. But the model is primarily empirical. The Meta Model (the local preferred cosmology) predicts that, at some distance, gravitons must collide with other gravitons and scatter, thereby changing the character of gravitation from inverse square to inverse linear. That provides a sound theoretical basis for the MOND effect. -|Tom|-

<i>Originally posted by chriscurtis</i>
<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">[tvf]: Gravitational redshift is a prediction of general relativity (GR), and MOND is an exception to GR<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">[from a FAQ page on the MOND pages]:
Q: Does MOND contradict General Relativity?
A: It generally seems to be assumed that it must, but this is not true. GR and MOND apply in very different regimes.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">This statement is not inconsistent with mine. MOND does not contradict GR, but still represennts an exception or incompleteness to GR.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">what happens to the numbers for the acceleration scale if the universe is not expanding?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">They disappear. That was our cover story in <i>Meta Research Bulletin</i> v. 13 #2 (2004 June 15). A non-expanding, non-accelerating universe fits the data as is without need of any free parameters. The failure of a simple Hubble rate to fit the same data led the Big Bang to need a cosmic acceleration parameter and dark energy. -|Tom|-

Brilliant, thanks again. I'm glad we're singing from the same song sheet here!

An infinte universe... how else could irrational numbers like PI exist )

In his book, A Brief History of Time, Stephen Hawking claims that a static universe where gravity was always attractive would have galaxies collapse in on themselves. However, this does not take into account the likely state that stars, galaxies, galaxy clusters, super clusters, etc are all in motion with respect to each other, which is the reason the planets don't just fall into the sun. Conservation of momentum and angular momentum and all that!