<p>Just as with a spring, the process of conversion from potential to kinetic energy is never perfect, some of the energy is converted to heat which is lost to the environment. So even a spring in a vacuum will not continue to extend and shorten forever.</p>
<p>In a pulsating star there is a oscillation in which energy is repeatedly cycled between potential and kinetic energy, but these conversions are not perfect and some energy is converted to heat, which is ultimately lost by radiation from the star's surface. The process by which energy is wasted is the internal friction due to different motions of plasma inside the star (and probably other factors)  A gas or plasma is never frictionless. If the star was not powered (by fusion) the cycle could not continue indefinitely.</p>
<p>This is all in accordance with the second law of thermodynamics.  There are no &quot;soft violations&quot; of the second law of thermodynamics. It has a rather different nature than other physical laws, as it can be derived mathematically from statistical principles rather than being based on a descriptive model.</p>

CC BY-SA 4.0
2024-12-15T19:23:54.770Z
Thanks again for your explanation. It was very helpful., thanks James. Regarding rightness of the second law of thermodynamics, in my opinion, there is no absolute law. By observing nature and new experiments, possible exceptions would be found and then laws may need to be modified. The law is not wrong in many cases but not supposed to be true in all.  I think nature always surprises us by something unexpected and even more amazing than known theories.                   “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so. “ – Mark Twain
Reza Koohpaee
CC BY-SA 4.0
2024-12-15T19:38:33.363Z
This article regarding exceptions for the second law of thermodynamics was valuable. https://www.researchgate.net/publication/364655712_Beyond_the_Thermodynamic_Limit_Template_for_Second_Law_Violators
Reza Koohpaee
CC BY-SA 4.0
2024-12-16T04:12:54.667Z
@Reza The 2nd law is "only" statistically true, but 2nd law violations are *extremely* unlikely. Eg, take 60 coins and toss them all, once per second. You can expect the coins to all come up heads once per 36.5 billion years. And of course there are a lot more than 60 atoms in a star. :D
PM 2Ring
CC BY-SA 4.0
2024-12-16T08:51:17.137Z
The fact it is derived statistically makes it rather stronger than (say) F=ma law for motion.  The inverse square law is only an empirical observation, with no strong mathematical basis. Thermodynamic laws on the other hand can be deduced from mathematical principles (the law of large numbers) and the notion that "energy isn't sentient".  This means that while there are useful discussions about violations of the F=ma (Relativity, MOND etc) nobody can seriously doubt the thermodynamic laws.  There a quote from Eddington (or someone) about this.
James K
CC BY-SA 4.0
2024-12-18T16:50:23.180Z
@JamesK Except that "Boltzmann's H theorem" isn't a proper theorem, while Poincaré's recurrence theorem is a proper theorem, and contradicts it. So, what math do you accept? Well, if you spill your beer, Poincaré predicts that if you wait long enough it will unspill, while Boltzmann predicts it won't. The experiment has been performed countless times, and Boltzmann's prediction has always been right. So, the H "theorem", from which you may derive the second law, works *empirically*, in *contradiction* to the math.
John Doty
CC BY-SA 4.0
2024-12-18T18:15:41.477Z
You're using the wrong maths! The model is explicitly stochastic, not deterministic. This means that things like Poincare's theorem aren't really relevant here.  Important, since we suppose the underlying physics is deterministic. But irrelevant to statistical mechanics.  When  you model a die, you can treat it as a deterministic rigid body, or as a random number generator.  Neither model is "correct", both have their uses. But it's incorrect to say that the "random number generator" model is "wrong" just because the underlying physics is deterministic.
James K
CC BY-SA 4.0
2024-12-20T11:08:50.477Z
Thanks to all friends for your suggestions. I had a suggestion. You know, the second law has several definitions. One may ask, are all of them equivalent to each other, in experiments and or theories?  In addition, generally speaking, do you consider that nature has to obey theories, or what we calculate by mathematics?
Reza Koohpaee
CC BY-SA 4.0
2024-12-20T11:08:59.400Z
I remember a number of interesting old paradoxes from Zeno, one of the ancient Greek philosophers, which I think is relevant to this subject, (https://en.wikipedia.org/wiki/Zeno%27s_paradoxes). These deep thoughts are intriguing and remind us that if we don't think that we know all the things, there are always new things to learn from each other, a valuable blessing that brings joy and improvements.
Reza Koohpaee
CC BY-SA 4.0
2024-12-15T15:39:55.447Z
2024-12-15T15:39:55.447Z
James K
<p>Excuse me, I have a question regarding thermodynamics of stars. I know the mechanism of stellar pulsation is indeed complicated. But I was interested to think of it from the door of energy conservation. I was thinking in this manner. Consider a weight on a piston oscillating in a cylinder. In experiment, as there is always friction, this oscillation ends up by converting all mechanical energy to heat energy exiting from the system and spreading to the environment.</p>
<p>Now, can we consider that such an event is happening in those stars such as Betelgeuse?<br />
The interior temperature is increasing by contraction and decreasing by expansion, this is in agreement with changes that take place in gravitational potential energy of the star gas, when it expands or contracts.</p>
<p>In addition, as there is no piston wall in the star and not any loss of heat energy by friction from the system, such movement could continue without stopping, forever in theory.
Internal energy and potential energy are converting to each other and that results in oscillating temperature. Can this be thought as a soft volition of the second law of thermodynamics?</p>
<p>Does such oscillation happen in gas planets too?</p>
<p>Thanks a lot for your valuable suggestions, and it is of your kindness to let me know about any book or article regarding this subject.</p>
<p>Can we have a cycle such as this in nature, where heat is converted to work and vice versa, continuously?</p>

CC BY-SA 4.0
2024-12-14T17:05:31.110Z
While there is no "piston wall", there are frictional losses due to the relative movement of gas.  These might not be substantial (in comparison to the amount of energy flowing from the core) but they are not zero, and there is no "soft violation of the laws of thermodynamics".  The system would not keep oscilatting indefinitely, the oscilations would slow down and stop unless powered by some heat source, such as fusion in the core.
James K
CC BY-SA 4.0
2024-12-14T19:04:44.120Z
Thank you very much for your suggestion. I understand your point. But I still think there is an important difference between piston/cylinder example and stellar pulsation and that is: in cylinder/piston, the internal energy outspreads through the boundary of cylinder to environment which has a lower temperature.; this process continues until all potential energy of the weight on the piston has transmitted as heat to environment . However, in a star this increase in internal energy by compression (or friction as you have mentioned) is captured within system (maybe as how a spring acts).
Reza Koohpaee
CC BY-SA 4.0
2024-12-14T22:21:07.630Z
No. in each process entropy increases just as required by the second law. The state doesn't recur since after each cycle.  The energy isn't captured, the internal friction produces an excess of heat which ultimately escapes from the star as radiation. Springs are the same, there is internal friction which heats the spring. That heat escapes to the environment. In each step entropy increases.
James K
CC BY-SA 4.0
2024-12-15T10:12:04.927Z
Thank you very much for your response. Now, I understand. In that process, the heat energy is transferred by radiation during each cycle (system is not closed). It needs something for heat recycling, as internal energy is constantly spreading-out by radiation. Thanks a lot.
Reza Koohpaee
<star>
Stellar Pulsation
Reza Koohpaee
# Stellar Pulsation

(Asked by: username_0 on 2024-12-14)

Excuse me, I have a question regarding thermodynamics of stars. I know the mechanism of stellar pulsation is indeed complicated. But I was interested to think of it from the door of energy conservation. I was thinking in this manner. Consider a weight on a piston oscillating in a cylinder. In experiment, as there is always friction, this oscillation ends up by converting all mechanical energy to heat energy exiting from the system and spreading to the environment.

Now, can we consider that such an event is happening in those stars such as Betelgeuse?  
The interior temperature is increasing by contraction and decreasing by expansion, this is in agreement with changes that take place in gravitational potential energy of the star gas, when it expands or contracts.

In addition, as there is no piston wall in the star and not any loss of heat energy by friction from the system, such movement could continue without stopping, forever in theory.
Internal energy and potential energy are converting to each other and that results in oscillating temperature. Can this be thought as a soft volition of the second law of thermodynamics?

Does such oscillation happen in gas planets too?

Thanks a lot for your valuable suggestions, and it is of your kindness to let me know about any book or article regarding this subject.

Can we have a cycle such as this in nature, where heat is converted to work and vice versa, continuously?

**Tags:** star

> **Comments:**
> **username_1**: While there is no "piston wall", there are frictional losses due to the relative movement of gas.  These might not be substantial (in comparison to the amount of energy flowing from the core) but they are not zero, and there is no "soft violation of the laws of thermodynamics".  The system would not keep oscilatting indefinitely, the oscilations would slow down and stop unless powered by some heat source, such as fusion in the core.  
> **username_0**: Thank you very much for your suggestion. I understand your point. But I still think there is an important difference between piston/cylinder example and stellar pulsation and that is: in cylinder/piston, the internal energy outspreads through the boundary of cylinder to environment which has a lower temperature.; this process continues until all potential energy of the weight on the piston has transmitted as heat to environment . However, in a star this increase in internal energy by compression (or friction as you have mentioned) is captured within system (maybe as how a spring acts).  
> **username_1**: No. in each process entropy increases just as required by the second law. The state doesn't recur since after each cycle.  The energy isn't captured, the internal friction produces an excess of heat which ultimately escapes from the star as radiation. Springs are the same, there is internal friction which heats the spring. That heat escapes to the environment. In each step entropy increases.  
> **username_0**: Thank you very much for your response. Now, I understand. In that process, the heat energy is transferred by radiation during each cycle (system is not closed). It needs something for heat recycling, as internal energy is constantly spreading-out by radiation. Thanks a lot.  

---

## 1 answers

### Answer by username_1 on 2024-12-15. Score: 2 | Accepted answer

Just as with a spring, the process of conversion from potential to kinetic energy is never perfect, some of the energy is converted to heat which is lost to the environment. So even a spring in a vacuum will not continue to extend and shorten forever.

In a pulsating star there is a oscillation in which energy is repeatedly cycled between potential and kinetic energy, but these conversions are not perfect and some energy is converted to heat, which is ultimately lost by radiation from the star's surface. The process by which energy is wasted is the internal friction due to different motions of plasma inside the star (and probably other factors) A gas or plasma is never frictionless. If the star was not powered (by fusion) the cycle could not continue indefinitely.

This is all in accordance with the second law of thermodynamics. There are no "soft violations" of the second law of thermodynamics. It has a rather different nature than other physical laws, as it can be derived mathematically from statistical principles rather than being based on a descriptive model.

> **Comments:**
> **username_0**: Thanks again for your explanation. It was very helpful., thanks username_1. Regarding rightness of the second law of thermodynamics, in my opinion, there is no absolute law. By observing nature and new experiments, possible exceptions would be found and then laws may need to be modified. The law is not wrong in many cases but not supposed to be true in all.  I think nature always surprises us by something unexpected and even more amazing than known theories.                   “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so. “ – Mark Twain  
> **username_0**: This article regarding exceptions for the second law of thermodynamics was valuable. https://www.researchgate.net/publication/364655712_Beyond_the_Thermodynamic_Limit_Template_for_Second_Law_Violators  
> **username_2**: @username_0 The 2nd law is "only" statistically true, but 2nd law violations are *extremely* unlikely. Eg, take 60 coins and toss them all, once per second. You can expect the coins to all come up heads once per 36.5 billion years. And of course there are a lot more than 60 atoms in a star. :D  
> **username_1**: The fact it is derived statistically makes it rather stronger than (say) F=ma law for motion.  The inverse square law is only an empirical observation, with no strong mathematical basis. Thermodynamic laws on the other hand can be deduced from mathematical principles (the law of large numbers) and the notion that "energy isn't sentient".  This means that while there are useful discussions about violations of the F=ma (Relativity, MOND etc) nobody can seriously doubt the thermodynamic laws.  There a quote from Eddington (or someone) about this.  
> **username_3**: @username_1 Except that "Boltzmann's H theorem" isn't a proper theorem, while Poincaré's recurrence theorem is a proper theorem, and contradicts it. So, what math do you accept? Well, if you spill your beer, Poincaré predicts that if you wait long enough it will unspill, while Boltzmann predicts it won't. The experiment has been performed countless times, and Boltzmann's prediction has always been right. So, the H "theorem", from which you may derive the second law, works *empirically*, in *contradiction* to the math.  
> **username_1**: You're using the wrong maths! The model is explicitly stochastic, not deterministic. This means that things like Poincare's theorem aren't really relevant here.  Important, since we suppose the underlying physics is deterministic. But irrelevant to statistical mechanics.  When  you model a die, you can treat it as a deterministic rigid body, or as a random number generator.  Neither model is "correct", both have their uses. But it's incorrect to say that the "random number generator" model is "wrong" just because the underlying physics is deterministic.  
> **username_0**: Thanks to all friends for your suggestions. I had a suggestion. You know, the second law has several definitions. One may ask, are all of them equivalent to each other, in experiments and or theories?  In addition, generally speaking, do you consider that nature has to obey theories, or what we calculate by mathematics?  
> **username_0**: I remember a number of interesting old paradoxes from Zeno, one of the ancient Greek philosophers, which I think is relevant to this subject, (https://en.wikipedia.org/wiki/Zeno%27s_paradoxes). These deep thoughts are intriguing and remind us that if we don't think that we know all the things, there are always new things to learn from each other, a valuable blessing that brings joy and improvements.  

---

