Dark Light Does Not Endanger Grandfather

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />why dismiss what is seen for what can be made from whatever information might found elsewhere when the data is just going to be filtered through theories?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Data is data. No honest scientist changes data based on theories.

The purpose of models is to make predictions. You could gather endless data about the time and place of solar eclipses without being able to predict one. So we develop models to predict eclipses using physics and mathematics, then test how well those models are doing by comparing their predictions with new data. At least, in honest science, that is how it is supposed to work.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">I know there is data coming in from other than vision but its distorted by models that are way over rated.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">The models may be overrated, but no data is distorted by them. Radio observations of objects near the Galactic center are just as valid as optical observations of objects there. But radio signals can penetrate the dense gas and dust far better than light can. Both types of data are then used to test models and try to understand what the data means; e.g., what type of objects are being seen in the data.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">There is a lot wrong in assuming a galatic structure is anything like the solar system.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">There are major differences. But you cited the disk shape, and that is a feature in common.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">the mass of the solar system is 99.8% located at the sun and the galaxy has all its mass spread all over the disk.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">But the Galaxy's mass is not spread evenly. Most of it is concentrated near the center, with the star density dropping off linearly with distance from the central bulge.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">Its a totally different dynamics when the mass location is no where near the geometric center even if the barycenter is located at the geometric center.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">A close Earth satellite responds exactly the same to an Earth spread out below it as it responds to an Earth concentrated at a point at its center. As a first approximation, our Galaxy can be considered as a having mass interior to the Sun that collectively acts just as if it was all concentrated at the Galaxy center; plus a smaller amount of mass exterior to the Sun that, on average, has zero effect on the Sun. Naturally, rigorous models take into account the actual mass distribution and actual forces. But the approximation just described is pretty good and a lot less calculating than the rigorous model.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">What happens when two or more stars are attracting each other and moving in the same direction at the same time?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">In general, single stars are too small to have much effect on their neighbors unless there is a close approach.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">There is no force in the disk structure pointing to the barycenter.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">That is untrue. The net force on the Sun is a single force pointing toward the Galactic center, and the Sun's orbit around the Galactic center is the rough equivalent of a planet's orbit around the Sun.

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote">All the force is pointing to all the stars all over the disks.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Again, stars interior to the Sun have a combined net force toward the center, and stars exterior to the Sun have a nearly zero combined net force. We've covered the following point before, but perhaps you missed it or didn't assimilate it: The net gravitational force of a uniform spherical shell of matter is everywhere exactly zero inside the shell, and acts as if all the shell mass was concentrated at its center everywhere outside the shell. -|Tom|-

The point about shells or layers of an onion was observed and processed and is a good point. The other point reguarding the distribution of mass in gravity forced structures is also understood but I don't see the distribution of mass that way. If you want to look at a galatic structure in the same way as a planetary system you get lots of details that don't connect whereas by looking at the distribution of mass being shared by all the 100 billion or so stars they attracting each other in ways very different than anything in a planetary system.

Doing a little math it is clear any star near by(5ly or so)will accelerate its neighbor to a speed of ~10m/s or so in a million years. That adds up to a lot of force does it not?

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Jim</i>
<br />Doing a little math it is clear any star near by(5ly or so)will accelerate its neighbor to a speed of ~10m/s or so in a million years. That adds up to a lot of force does it not?<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">No, the force remains miniscule at all times. A miniscule force applied continuously for a million years adds up to a not-so-miniscule velocity change. But that has practically no physical significance because everything in the solar system is accelerated equally, and we can't tell the difference if our interstellar velocity changes by such a small amount as 10 m/s.

And my calculations indicate the acceleration produces a speed change of 2 m/s in a million years, not 10. This assumes a solar-mass star at 5 ly.

But why choose a million years? Why not a billion or a trillion years? This shows how arbitrary your calculation is. A more appropriate choice of time would be ~ 60,000 years, which is the average time that a passing star can remain within or near 5 ly from the Sun. (The average velocity of passing stars is 25 km/s, which equals 80 ly per million years.) So no star can hang around long enough to exert its gravitational force for a million years.

The bottom line is that single stars have insignificant effects on other stars. Even in cases where the stars are packed into a cluster, encounters close enough to produce a significant speed change are the exception, not the rule. -|Tom|-

OK-this is good. Lets say on average stars are 5ly apart but in clusters stars are as near as 100AU or ~.0005ly and in some places more then 50ly in other areas of a galatic structure(subject to revision). The point is all these stars do effect the dynamics of the galatic structure in ways quite different than effects observed in a structure like the solar system.