flat rotation curves and 'foam' large scale struct

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Thomas</i>
<br />I don't see any point in adding effects that in my opinion are theoretically impossible (as explained on my page www.physicsmyths.org.uk/retard.htm for static forces in general).

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If you intend to dispute the universality of aberration, please make your argument succinctly here. But be warned that it will be quite an uphill battle because no one has successfully disputed aberration for the past few centuries.

Aberration (and therefore retardation) arises from the transverse motion of the target body relative to the source mass. It obviously exists for all kinds of "static" fields. For example, sunlight has aberration, and the force it applies on dust particles or balloon satellites is retarded.

In general, there are only two possibilities for "static" fields:
<ul><li>no moving parts -- like a frozen waterfall (in which case no momentum can be transferred from source to target, so no force can occur)</li><li>momentum carriers from the source to the target -- like a flowing waterfall, which appears unchanging, but every droplet is continually replaced by another from behind (in which case aberration applies -- see animation #4 and its caption at metaresearch.org/media%20and%20links/animations/animations.asp ) -|Tom|-

Thomas:"I am actually not sure if making the step-width proportional to Distance/Speed is the ideal solution here."

Very good you point this out. At different scales it doesn't work the same. It didn't bother me too much though since (for the time being) I only worked at one scale. It works fine and there are many other things to find out...

Thomas:"Also, did you ever try to couple the integration with a Runge-Kutta method? This might be more efficient than just using a simple Riemann or trapezoidal rule."

No, I didn't. Calculationtime efficiency is nice, but it's only part of the equation.
I think the leapfrog method is interesting. Is that the Runge-Kutta one?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by tvanflandern</i>
<br /><blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Thomas</i>
<br />I don't see any point in adding effects that in my opinion are theoretically impossible (as explained on my page www.physicsmyths.org.uk/retard.htm for static forces in general).

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If you intend to dispute the universality of aberration, please make your argument succinctly here. But be warned that it will be quite an uphill battle because no one has successfully disputed aberration for the past few centuries.
Aberration (and therefore retardation) arises from the transverse motion of the target body relative to the source mass. It obviously exists for all kinds of "static" fields. For example, sunlight has aberration, and the force it applies on dust particles or balloon satellites is retarded.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Aberration (of light) is related to electromagnetic waves which, unlike the electrostatic or gravitational force, are not static force fields. It is only for the latter that my argument regarding the impossibility of retarded forces applies.

Thomas

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Michiel</i>
I think the leapfrog method is interesting. Is that the Runge-Kutta one?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
I think the Runge Kutta method is a kind of improved leapfrog method.
(see en.wikipedia.org/wiki/Runge-Kutta_methods ,
monitor.admin.musc.edu/~cfs/datamodel/node30.html ).
I have personally never used the Runge Kutta method yet, but I intend to try it with my own orbit integration routine. It looks like a good compromise between simplicity and numerical efficiency.

Thomas

Thankyou all for your interesting comments so far.

There is some evidence from binary pulsars that GM is independent of the proximity of the two stars from each other, but as M increases as the stars approach each other, due to the velocity increasing (relativistic effect) - then this may be evidence for G decreasing, as the masses approach each other.

The trouble is that if a computer program is run with G decreasing and M increasing, the net result would be indistinguishable from a false conjecture, with constant M.

So if anyone is interested in testing the conjecture by computer simulation, it might be best to try a stationary star of mass near the schwarzshild limit, and see if it will explode, if true conjecture is used (instead of forming a black hole). Or to model a galaxy and see if true conjecture can lead to an explanation for jets.

All the best,

John Hunter.