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Boyle's Gas Law, What is it?

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#321 Richard Townsend

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Posted 31 July 2009 - 10:45 AM

Back to gas.....

There's an interesting subject relating to this discussion that I'd like to get people's perspectives on.

To me, simulations of the formation of the first generations of stars or other processes involving gravitational collapse of gas are pretty convincing, because they are based on known laws of physics. (For me the caveat on them is that they make assumptions about dark matter).

Any simulation that builds in the conclusions upfront by special choice of starting conditions or selective use of some physical laws but not all the relevant ones would be useless in terms of increasing understanding. I don't believe that physicists would do that - what would they gain? Even if they did, sooner or later, someone would challenge their results.

What is it about these simulations that others find unconvincing?

#322 CTD



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Posted 31 July 2009 - 02:52 PM

Now, since CTD responded, I'll go ahead and address his post:  Gravity is not calculated as proceeding from an infinitely dense point, he's trying to confuse the issue.

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I confuse nothing. Every time this issue comes up, we get the same tricks. You talk as if you have experience, but you need to demonstrate some. You're welcome to badmouth me 'til the cows come home for exposing the childish mistakes; I don't plan on stopping.

Oh, and new stars, which are new according to spectrum analysis, absolute magnitude, and solar mass, always appear in nebulae.  And dense gas bubbles (gravitationally contracted) appear in nebulae.  And many new stars can be seen with halos of dust around them.  Go figure.  It's because stellar synthesis happens.

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You overpropagandize. A gas bubble in space is a nebula. :) And designating a star "new" doesn't reduce its age by a single day.

#323 Adam Nagy

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Posted 04 August 2009 - 11:53 AM

Okay, I split a topic from here because there was a parallel discussion occurring regarding the frustrating and fascinating principles of The 2nd Law of Thermodynamics:


#324 MarkForbes


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Posted 05 March 2011 - 07:15 AM

The Universe, by definition, IS a closed system. Any outside influence would be chalked up as supernatural in both of our books. The only difference is that we acknowledge supernatural markers and naturalists ignore them and/or equivocate about them.

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Can I briefly summarize here, as I am following the debate.
The basic question is:
How could stars have formed from loose gas clouds in the universe?

Materialistic Hypothesis:
Stars form by themselves from natural gravitation in the gas cloud.

a) There is no gravitation worth mentioning present in gas clouds .
:( Compression of the gas cloud would lead to increase in pressure/temperature
c) Increase in temperature/pressure would lead to extension of the volume again.

The last two arguments would be derived from the gas laws.
Two form a star from a gas cloud would require the work of directed forces to compress the gas cloud to a concentrated mass that has got it's own gravity to keep it together.

#325 adsummum



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Posted 05 March 2011 - 11:41 AM

a) There is no gravitation worth mentioning present in gas clouds .
b.) Compression of the gas cloud would lead to increase in pressure/temperature
c) Increase in temperature/pressure would lead to extension of the volume again.


a.) No, the gravitational force present in gas clouds is worth mentioning. You could just as easily state that the gas pressure isn't worth mentioning, as both are extremely small. There is a marked difference between a small force and a non-existent force, and in this case it plays a vital role maintaining hydrostatic equilibrium in gas clouds. One could for instance make the simple observation that in the absence of any force opposing the diffusion of the high pressure system represented by the gas cloud into the low pressure system represented by the vacuum of space, the gas clouds would have since dissipated, moreover, more condensed particular agglomerations such as Bok globules (I will discuss these later) would not be observed.

b/c.) Yes, but this process eventually reaches an equilibrium point, where the gas pressure balances the internal gravitational force. This point is described in gas mechanics by the virial theorem ( 2<T>=n(Vtot), where n is some power of the inter-particle distance). A more pertinent equation which describes the system is given by the differential equation;
where G is the gravitational constant and p® and M® represent functions of pressure and mass in terms of radius respectively. For equilibrium, this must be zero. If however the mass is increased, as a consequence of a collision with another cloud, galactic collisions, local aberrations etc. the cloud reaches its Jeans mass, a quantity specific to the radius, mass, temp of a given cloud. It begins a process of runaway collapse - smaller agglomerations of mass and turbulence within the cloud fragment it, creating individual stars (and as such multiple stars can be born from the one cloud).

As an aside, Bok globules are significantly smaller than interstellar gas clouds, (though operate on the same mechanism i have outlined above) and consist primarily of gas and dust. The have a radius of about 1 light year, and a mass ranging from 2-50 solar masses. Infrared telescopes have observed stellar formation within such clouds.

#326 Stripe



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Posted 06 February 2012 - 05:40 AM

It will fall together until it reaches equilibrium in its pressure against its gravity.

Why is it not already at equilibrium?

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