Actual reason for 2nd law of thermodynamics

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Discussion Overview

The discussion revolves around the second law of thermodynamics, exploring its proof, implications, and potential exceptions. Participants examine the law's foundational role in thermodynamics, its statistical nature, and its relationship with concepts like entropy and time. The conversation includes both theoretical and experimental perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Some participants question the proof of the second law, particularly regarding hypothetical scenarios where particles could reverse direction to create lower entropy.
  • Others assert that the second law is a foundational postulate in thermodynamics, supported by extensive experimental evidence.
  • A participant suggests that the inability to observe spontaneous reformation of a broken vase serves as a proof of the second law, while also noting that other proofs require deeper knowledge of thermodynamics.
  • There is a discussion about the statistical nature of entropy, with some arguing that while such reversals are theoretically possible, they are statistically improbable within the lifespan of the universe.
  • One participant illustrates the second law using the example of ships and energy, explaining that heat cannot spontaneously flow from a colder to a warmer body without external work.
  • Another participant mentions the use of the second law in discussions surrounding creationism, suggesting a caution against oversimplification of the concept.
  • A participant shares an ongoing classroom experiment involving food coloring in water, claiming that if the coloring separates back into its original state, it would disprove the second law.
  • Some participants note that while the second law is robust, it is based on specific axiomatic conditions and may not hold in extreme or unusual situations, particularly in quantum contexts.

Areas of Agreement / Disagreement

Participants express a mix of agreement on the validity of the second law while also raising questions about its implications and potential exceptions. The discussion remains unresolved regarding the hypothetical scenarios posed and the nature of entropy.

Contextual Notes

Limitations include the dependence on classical definitions of thermodynamics and the acknowledgment that extreme conditions may challenge the applicability of the second law.

jeffceth
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Hi, I was just wondering what the actual proof is for the second law of thermodynamics that would disprove a situation where all particles are simply reversed in direction creating lower entropy? Is it a consequence of another scientific principle or where does it come from?

sincerely,
jeffceth
 
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Its so important of a concept that its used as a postulate: a starting assumption for theories, but it is easily tested, so its backed up by pretty much every thermodynamics experiment ever done.
 
Originally posted by jeffceth
Hi, I was just wondering what the actual proof is for the second law of thermodynamics that would disprove a situation where all particles are simply reversed in direction creating lower entropy? Is it a consequence of another scientific principle or where does it come from?

The fact that you do not see a broken vase spontaneously reform back into the original vase without any input in energy is a proof for the 2nd Law. Other types proofs are more esoteric - heat engine, etc. - and requires some knowledge of classical thermodynamics.

Whether it is a consequence of another principle is hard to say. There are many speculations that it is tied to our time arrow, but saying that will get us into the chicken or the egg question, i.e. is entropy the consequence of our 1D time arrow, or is the 1D time arrow the consequence of entropy?

There is a very good website that describes and, more importantly, debunk several myths regarding entropy (i.e. entropy and "disorder"):

http://www.entropysite.com/

It may not answer your question directly, but it's still a fun read! :)

Zz.
 
Originally posted by jeffceth
Hi, I was just wondering what the actual proof is for the second law of thermodynamics that would disprove a situation where all particles are simply reversed in direction creating lower entropy? Is it a consequence of another scientific principle or where does it come from?

sincerely,
jeffceth
Ok, think for just a minute...where does the energy come from, to make the particles change direction?
 
Really there is no reason in physics preventing any of these things from happening, we can even compute the likelihood of such events occurring. When all is taken into consideration, the time time you would have to wait for these unlikely events exceeds the life time of the universe, thus are considered impossible.

Entropy is statistical in nature, but in the statics of large numbers, such as the number of particles which constitutes the universe, the events that are most probable are what happens.
 
Integral,
Perfectly worded.
-Mike
 
An illustration of the 2nd law that I like to think about is ships sailing across the Ocean. Underneath them, there is a vast source of energy - the heat in the water amounting to billions of Joules of energy. So why don't ships use heat pumps to get hold of this free energy?
The 2nd law tells us that heat flows from a warmer environment, to a colder one, never the other way round. The only way to tap into the sea's free energy therefore, involves having a colder heat sink for the heat to flow into. Other than towing an iceberg behind the ship, this is impossible.

It is a bit like a wind powered sailing ship sailing over a Pacific ocean of free Diesel fuel, but not being able to use it!
 
I've noticed that entropy and the Second Law are favorite topics in some Creationist tracts and articles--which brings to mind the saying, "A little learning is a dangerous thing."
 
Originally posted by Janitor
I've noticed that entropy and the Second Law are favorite topics in some Creationist tracts and articles--which brings to mind the saying, "A little learning is a dangerous thing."

You'll like this then from this weeks Onion:
http://www.theonion.com/news/index.php?i=1&n=3
:smile:
 
Last edited by a moderator:
  • #10
Funny stuff, Adrian.

I think I recognize Cosmic Stan as one of our members.
 
  • #11
I have a "2nd Law" experiment in my classroom that has been ongoing for three years now: a sealed jar of water with food coloring in it. As soon as the coloring separates into a "clear" half and "green" half of the jar (as was the original condition), then the 2nd law will be disproved. I'll keep you posted.
 
  • #12
It should be said that while the 2nd Law of Thermodynamics is a solid and verified principle, it is built on several major axiomatic conditions, one of which is that it isn't in a "transient" regime, or that it assumes a classically-defined space/vacuum configuration. Once we understand those boundaries, physicists, being the curious beings that they are, will always try to test the validity of anything beyond those boundaries and see where such thing will fail.

.. and such things have been done, especially in the quantum critical regime, and when vacuum fluctuations effects are significant:

http://www.nature.com/nsu/020722/020722-2.html

I was hesitant to post this because there is always the potential "abuse" of such reports. The fact that this occurs in only very extreme and unusual situation where the 2nd Law wasn't meant to be applied should always be kept in mind. The 2nd Law reminds valid and fully intact.

Zz.
 
  • #13
Originally posted by Chi Meson
I have a "2nd Law" experiment in my classroom that has been ongoing for three years now: a sealed jar of water with food coloring in it. As soon as the coloring separates into a "clear" half and "green" half of the jar (as was the original condition), then the 2nd law will be disproved. I'll keep you posted.

It might do it at night when you aren't looking!:smile:
 
  • #14
Originally posted by Adrian Baker
It might do it at night when you aren't looking!:smile:

Adrian,
Are you saying that you are the kind of person that would turn off a guy's fuel petcock on the starting grid? lol. -Mike
 
  • #15
Originally posted by Michael D. Sewell
Adrian,
Are you saying that you are the kind of person that would turn off a guy's fuel petcock on the starting grid? lol. -Mike


Me? As if!
A long time racer told me a good trick of his for unnerving the opposition... if you get past someone you are having a real battle with on the track, point at his engine and shake your head as you go past...

Nothing to do with the 2nd law, but a good tip nonetheless!
 
  • #16
The practical application of physics is a blast! I'm too old for racing now, but I have many fond memories of Thompson, Ct Laconia, NH
and Bridgehampton, NY. I still have a Suzuki GS 1000. The footpegs are about 1/2" long(That's the way I like them).

We've gotten pretty far off subject. We should do this in the general discussion area.

Cheers,
-Mike AAMRR #984
 

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