Collapse of gravitational collapse

[james03]

James, a star is not a closed system. Why you would think so is beyond me. If you're going to attempt to argue against scientific theories you should at least have the basics down.

LOL.  GP you are boring.

[james03]

The problem I have is this doesn't pass the smell test.  Why not just have a solid or a liquid and your problem is solved. Jupiter for instance likely has a solid core.  It contains ammonia and water, which will be a solid at cold (space) temperatures.

I suspect the cosmologists have run into problems and are inventing crazy stuff again to get around God.

[Quaremerepulisti]

The system isn't closed; energy is radiated away to the rest of the universe.  The total entropy of the universe increases, but the entropy of the subsystem decreases, just like when water freezes.

Normally we ignore radiant heat transfer unless you get up to temperatures in the physical light spectrum.  I guess if this is a billion year process, you would have to consider it.  Except you have a problem, hydrogen does not emit light.  It is transparent being a non-polar gas.  This is why nitrogen is not a green house gas.

Energy is emitted in the form of electromagnetic waves - that is what is meant by "radiation".  Hydrogen emits light when the electron decays from a higher to a lower energy level.  This is all pretty basic.

Define "low temperature" and "high pressure".  Also what is the gas, i.e. helium, hydrogen, etc...

Imagine a gas cloud - the specific gas is irrelevant.  "Low" temperature means a temperature low enough such that the average velocity of molecules at the edge of the cloud is much less than the gravitational escape velocity.  In that you won't have a diffusing cloud of gas; it will collapse inwards.  "High" pressure means a pressure high enough such that collisions between molecules are no longer elastic -  they are close enough together that the attractive gravitational force becomes a similar order of magnitude as the repulsive force of the electron cloud.

The problem I have is this doesn't pass the smell test.  Why not just have a solid or a liquid and your problem is solved. Jupiter for instance likely has a solid core.  It contains ammonia and water, which will be a solid at cold (space) temperatures.

I suspect the cosmologists have run into problems and are inventing crazy stuff again to get around God.

Individual motivations are orthogonal to the objective truth of the matter.

[james03]

Energy is emitted in the form of electromagnetic waves - that is what is meant by "radiation".  Hydrogen emits light when the electron decays from a higher to a lower energy level.  This is all pretty basic.

Hydrogen is not an emitter below a few thousand K.  Emissivity is zero.  Especially at a temperature where the molecules have such a low velocity.  Now if you zap it with electrons, it will emit a photon due to electron decay, as you say.  But that is not what we are talking about.

[Quaremerepulisti]

Energy is emitted in the form of electromagnetic waves - that is what is meant by "radiation".  Hydrogen emits light when the electron decays from a higher to a lower energy level.  This is all pretty basic.

Hydrogen is not an emitter below a few thousand K.  Emissivity is zero.  Especially at a temperature where the molecules have such a low velocity.  Now if you zap it with electrons, it will emit a photon due to electron decay, as you say.  But that is not what we are talking about.

But the cloud heats up as it collapses - it is not an ideal gas and the closer the molecules are brought to each other the stronger the gravitational force thus the higher the velocities, so you will eventually reach a temperature where the kinetic energy of the molecules is the same order of magnitude as the binding energy of the electron.

I just don't see how gravitational collapse can be ruled out a priori on thermodynamic grounds.  It is conceptually not really different then a gas in a cylindrical container with a piston - the piston will fall and the volume will decrease until the upward pressure balances out the downward force from gravity.  This doesn't violate the first law - the gravitational potential energy is what was converted into work.  It doesn't violate the second law - this is an adiabatic process.

So, a similar thing will happen for a sphere of non-ideal gas where the inward attraction of gravity is stronger than the outward force from pressure.  Except it's not an adiabatic process, because the gas heats up, as I said (it would be adiabatic if the inward attraction were caused by attraction of another mass at the center rather than the attraction of molecules to each other).  But that doesn't violate the second law, because it's an entropy increase.  Entropy does decrease when the temperature becomes hot enough such that electrons are raised to higher energy states and then decay via emission of radiation.  But that's not a problem because energy is being lost to the rest of the universe.

[james03]

You are introducing "magic".  You have a state where the hydrogen is expanding outward.  Then things change.  I believe this is the point Dr. R. is making.  His solution is to introduce condensed matter.

Sure gases are attracted by gravity.  That is why we have an atmosphere.  I had thought of the counter example of Jupiter against Dr. R., however you realize you can SEE Jupiter, and further reading by me shows that Jupiter does have condensed matter including ammonia and water.

I do disagree with him on the Potential Energy part.  When you reduce a potential (in this case gravitational potential) entropy increases if it is not reversible, and gravitational attraction is not a reversible process.  It would be interesting to see him explain the formation of an atmosphere, even with condensed matter.

I think his sticking point is that the process won't initiate without having condensed matter.  I'll watch his series and see what he concludes.

[Quaremerepulisti]

You are introducing "magic".  You have a state where the hydrogen is expanding outward.  Then things change.  I believe this is the point Dr. R. is making.  His solution is to introduce condensed matter.

If the gas cloud is of uniform density, then definitely it can't be the case that the cloud is expanding outward then collapses.  If it is expanding, the outward pressure is bigger than the inward attraction.  But is this really what the theory says?

Dr. R. seems to be saying collapse is a priori impossible no matter what due to thermodynamics.  This is wrong.

I think his sticking point is that the process won't initiate without having condensed matter.  I'll watch his series and see what he concludes.

OK.

[Daniel]

Speaking of perpetual motion machines, just the other day I inadvertently created one. Right now I have it hooked up to my air conditioner and things are really heating up. But something tells me it's not working right...

[james03]

If the gas cloud is of uniform density, then definitely it can't be the case that the cloud is expanding outward then collapses.  If it is expanding, the outward pressure is bigger than the inward attraction.  But is this really what the theory says?

It seems you would have to have clumped matter, and now you are getting into magic.  Also, why limit the big bang to hydrogen and helium?  If you allow those to appear, then I can claim there was also iron.  Both are arbitrary speculations.

Back to Dr. R, I still am not getting his potential energy objection.  Suppose I have a tall cylinder filled with gas in orbit.  I define my closed system as the gas in the cylinder.  Note it is not isolated, so I can still radiate through the walls.  Now I measure the pressure at an arbitrary pressure of 2 "james".  However the pressure will be higher at the bottom of the cylinder, 2.5 "james", and lower at the top, 1.5 "james" due to gravity.  Now I lower the cylinder to the surface eliminating the gravitational potential.  This is irreversible, so entropy increases.  I remeasure the pressure and the bottom is 3.1 "james" and the top is 1 "james", with the overall pressure at 2.05 "james".  The rise in temperature comes from the heat of compression and entropy, which results in a higher pressure.  So instead of converting all the gravitational potential into usable pressure, I lose some to temperature increase.  Note I know the bottom of the cylinder has to increase in pressure because that is how we get atmospheric pressure.  "D" to the center of gravity decreases so the "weight" of gas increases.  I'm 99% certain this is true, otherwise a chimney wouldn't work.

Note also I have to either apply outside work to the cylinder to lower it controllably, which is wasted 100% to entropy, or let it crash into the earth which wastes energy into friction heat and impact heat.  That would not be an entropy increase on my defined system, so I believe I can ignore that.

His point on the gas not radiating is true, and maybe that's his main point.  Entropy is pretty much synonymous with molar volume, so as I compress and increase temperature I'm not getting the density I'd expect.  Don't know if that would be enough of a factor to preclude fusion.

My opinion now is that he is incorrect, but he raises some interesting questions.   If the big bang is a dispersed cloud of hydrogen, there's no way you would get stars, or perhaps you'd get one huge star at the center of the expansion after time.  If that is his point, I agree.