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Roamer
Post  Post subject: Does this thought experiment break 2nd law of thermodynamic?  |  Posted: Sun Nov 20, 2016 5:18 pm

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"As time progresses, the second law of thermodynamics states that the entropy of an isolated system never decreases." - wiki

This is a thought experiment.
You have an impossible box.
The walls of this box prevent any external energy from entering, or any internal energy from escaping.
There are 100 atoms in the box.
They start arranged in a specific order, with a specific velocity.
The time starts playing.
The atoms start bouncing around in a fashion that makes it look disordered.
X seconds later, all atoms end up in their original order, with their original velocity.
This never-ending loop happens with a period of every X seconds.
This system does not evolve toward thermodynamic equilibrium between certain two points in time.
Repeat this thought experiment, but instead of 100 atoms, try any arbitary big number.

Did entropy increase between any 2 points of time in this closed system?
Is the 2nd law of thermodynamics broken?


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Sun Nov 20, 2016 6:01 pm
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"X seconds later, all atoms end up in their original order, with their original velocity."

If zero energy is added, by what mechanism do you propose this happens?

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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Sun Nov 20, 2016 6:14 pm

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iNow wrote:
"X seconds later, all atoms end up in their original order, with their original velocity."

If zero energy is added, by what mechanism do you propose this happens?


The mechanism of random chance.
X seconds can be any arbitarily large number, even a zillion years or so.


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Sun Nov 20, 2016 6:48 pm
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Increases in velocity are unrelated to chance. The amount of time that's passed is also irrelevant. It requires the addition of energy, as does achieving order from disorder.

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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Sun Nov 20, 2016 7:27 pm

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"As time progresses, the second law of thermodynamics states that the entropy of an isolated system never decreases." - wiki

Image

Let me give a simple example of my thought experiment to make it easy to understand.

You box has just 18 atoms bouncing around.
When t=0 seconds, there is disorder, as shown by the squares on the left.
When t=X/2 seconds, there is order, as shown by the squares on the right.
When t=X seconds, the position of the atoms become disordered again, with each atom being at its exact same position when t=0.

"It requires the addition of energy, as does achieving order from disorder."
The disorder decreases between t=0 and t=X/2 even though no energy is added to this isolated system. Isn't the 2nd law of thermodynamics broken?

I admit the I'm not a physics genius, but am I misunderstanding the 2nd law?
I'm open to learn.


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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Sun Nov 20, 2016 7:58 pm

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"As time progresses, the second law of thermodynamics states that the entropy of an isolated system never decreases." - wiki

After reading carefully, I think I get it. The point is "as time progresses".

I can't just take any two points I favor and say that the 2nd law of thermodynamics is broken.


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 1:34 am
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How are you defining order?

To simplify, are you thinking a broken coffee mug will suddenly reassemble, or are you thinking its broken fragmented shards will eventually get spread out evenly given enough time?

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g o r t
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 8:29 am

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Roamer wrote:
"As time progresses, the second law of thermodynamics states that the entropy of an isolated system never decreases." - wiki

After reading carefully, I think I get it. The point is "as time progresses".

I can't just take any two points I favor and say that the 2nd law of thermodynamics is broken.


Making limited quotes allows you to roam off the subject. :lol:

Entropy in thermodynamics is about the availability of energy to do work.
Since no work is being done your example is non sequitur.
From a perspective of order, no order is built and maintained for any time.
Your idea is for randomness to look like order on a repeating basis, which in reality would drift off
due to quantum effects anyway and not cycle.


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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 10:29 am

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"To simplify, are you thinking a broken coffee mug will suddenly reassemble, or are you thinking its broken fragmented shards will eventually get spread out evenly given enough time?"

The shards are flying around chaotically, and I am thinking that (if the initial conditions allow it) if both the disassembling, and reassembling, can happen, given sufficient time.


Last edited by Roamer on Mon Nov 21, 2016 10:30 am, edited 1 time in total.


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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 10:29 am

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"Entropy in thermodynamics is about the availability of energy to do work. Since no work is being done your example is non sequitur."

What do you mean by "availability of energy to do work"? If lets say there are 10^27 atoms in the box, and then between two points in time, the atoms form both a tiny slab of butter, a tiny butter knife, and an intelligent tiny homunculus. The humonculus, uses his muscles (available energy) to cut the butter with his butter knife (do work). The closed box demonstrates the creation of availability of energy to do work, thus breaking the 2nd law of thermodynamics. Right?

"Your idea is for randomness to look like order on a repeating basis, which in reality would drift off due to quantum effects anyway and not cycle."
This is a thought experiemnt. The box cannot exist in reality.
The box is to demonstrate a closed cyclic system, meaning you must ignore both quantum effects and the ability for energy to enter or escape.


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 4:44 pm
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Roamer wrote:
The shards are flying around chaotically, and I am thinking that (if the initial conditions allow it) if both the disassembling, and reassembling, can happen, given sufficient time.

Not on any timescale that's relative to the age of the entire universe itself, or even a few hundred times the age of the universe. The chance of this happening is not exactly zero, but it is about as close to zero as you can get without actually reaching it.

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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Mon Nov 21, 2016 5:32 pm

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iNow wrote:
Not on any timescale that's relative to the age of the entire universe itself, or even a few hundred times the age of the universe. The chance of this happening is not exactly zero, but it is about as close to zero as you can get without actually reaching it.


I must emphasize this again.
This is a thought experiement.
The box cannot exist in reality.
The box is to demonstrate a closed cyclic system.
This is a thought experiement that is not meant to be done in reality.

What if the mug is made up of only 16 atoms?

Is the chance of this happening not exactly zero, but about as close to zero as it can get without actually reaching it?


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g o r t
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Tue Nov 22, 2016 10:57 am

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Roamer wrote:
What do you mean by "availability of energy to do work"? If lets say there are 10^27 atoms in the box, and then between two points in time, the atoms form both a tiny slab of butter, a tiny butter knife, and an intelligent tiny homunculus. The humonculus, uses his muscles (available energy) to cut the butter with his butter knife (do work). The closed box demonstrates the creation of availability of energy to do work, thus breaking the 2nd law of thermodynamics. Right?

No, "availability of energy to do work" (as in the definition of entropy), as in forming a tiny slab of butter or a tiny butter knife or even an intelligent tiny homunculus. All of which would stay what they are because there is no more energy (energy difference) to disassemble them again.

Basically, any chemical reactions possible would simply happen until no more could happen. Same as throwing a blanket over the Earth and waiting for chemical reactions to stop. They are currently powered by the sun, tidal heating, thermal and chemical location differences. Without new energy from the sun and radiation to space, everything becomes the same temperature, all iron rusts and stays rusted, bacteria digest all organic matter and then die, even the winds would stop. And there you go, even if it's a hundred degrees, eventually there is no energy difference to do work.

Taken as originally written, separate atoms of a gas could reach maximum entropy and still move around for a time creating a fleeting resemblance to "order".


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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 8:23 am

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g o r t wrote:
No, "availability of energy to do work" (as in the definition of entropy), as in forming a tiny slab of butter or a tiny butter knife or even an intelligent tiny homunculus. All of which would stay what they are because there is no more energy (energy difference) to disassemble them again.

Is extra energy really needed to disassemble them again? The velocities and positions of each atom could cause a disassemble of the atoms in the tiny picnic in a million years.

g o r t wrote:
Basically, any chemical reactions possible would simply happen until no more could happen. Same as throwing a blanket over the Earth and waiting for chemical reactions to stop. They are currently powered by the sun, tidal heating, thermal and chemical location differences. Without new energy from the sun and radiation to space, everything becomes the same temperature, all iron rusts and stays rusted, bacteria digest all organic matter and then die, even the winds would stop. And there you go, even if it's a hundred degrees, eventually there is no energy difference to do work.

This is a good example that I am hoping to make illustrate my point.
Let's start with the final state of "heat death" of that blanket-covered earth in your quote.
Please correct me if I'm wrong, but I'm not breaking any law of physics by reversing the velocities of every atom in that blanket.
Now, we play time, and let the atoms start bouncing around.
We find that the winds start moving, bacteria starts to appear, which creates organic matter, all iron unrusts, and stays unrusted, and temperature becomes different everywhere.
Doesn't that demonstrate order coming from disorder, the breaking of the 2nd law of thermodynamics?


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g o r t
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 10:43 am

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Changing the velocity of any mass requires energy.
Undoing a chemical reaction requires energy.
Breaking atomic bonds requires energy.
Moving an object against gravity requires energy.


These things cannot be undone by reversing "atomic velocities".
In such a heat death, no atoms would have velocities.
Only heat, the same heat everywhere which would no longer be able to move and do work.


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PhDemon
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 12:30 pm

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g o r t wrote:
Changing the velocity of any mass requires energy.
Undoing a chemical reaction requires energy.
Breaking atomic bonds requires energy.
Moving an object against gravity requires energy.


These things cannot be undone by reversing "atomic velocities".
In such a heat death, no atoms would have velocities.
Only heat, the same heat everywhere which would no longer be able to move and do work.


I'd disagree with your last point... "Heat" IS the movement of atoms and molecules. The key point is at heat death with the same temperature everywhere the distribution of velocities is at equilibrium, there is no way for a system at equilibrium to do work.

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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 8:46 pm
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PhDemon wrote:
g o r t wrote:
Only heat, the same heat everywhere which would no longer be able to move and do work.

I'd disagree with your last point... "Heat" IS the movement of atoms and molecules.

No, it's not. You appear to be confusing heat with temperature. They are often related, but are not the same concept. GORT is entirely correct.

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PhDemon
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 8:52 pm

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Oops my bad, I misread (or probably replied to without thinking while doing something else) his post...

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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Wed Nov 23, 2016 11:00 pm

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https://en.wikipedia.org/wiki/Entropy_(arrow_of_time)

Quote:
Entropy is the only quantity in the physical sciences (apart from certain rare interactions in particle physics; see below) that requires a particular direction for time, sometimes called an arrow of time. ... No physical laws are broken in the reverse movie except the second law of thermodynamics


I once heard someone saying that time is weird, and no laws of physics are broken when time (velocities) is reverse (except this one). Glad to learn something cool today.

g o r t wrote:
No, "availability of energy to do work" (as in the definition of entropy), as in forming a tiny slab of butter or a tiny butter knife or even an intelligent tiny homunculus. All of which would stay what they are because there is no more energy (energy difference) to disassemble them again.

External energy isn't required to disassemble them again.
Given the correct initial conditions were right, the velocities and positions of each atom in the closed cyclic system would disassemble those objects again.


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Thu Nov 24, 2016 1:04 am
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PhDemon wrote:
Oops my bad, I misread (or probably replied to without thinking while doing something else) his post...

No worries. It's a common issue. I used to conflate them myself until someone was kind enough to correct me. In its barest form, heat is a transfer of energy wherein temperature is a measure of it.

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g o r t
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Thu Nov 24, 2016 7:12 am

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Roamer wrote:
External energy isn't required to disassemble them again.
Given the correct initial conditions were right, the velocities and positions of each atom in the closed cyclic system would disassemble those objects again.


Anyone have a name for this process? Spontaneous disintegration?

Disintegration being the removal of molecular bonds allowing the constituent atoms to again roam free.

Citation needed.


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Thu Nov 24, 2016 4:23 pm
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I'm not certain, but Roamer seems to be discussing the slow release of energy and how objects tend toward a state of equilibrium. Not sure how this relates to the previous points specifically, though.

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Roamer
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Thu Nov 24, 2016 6:30 pm

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iNow wrote:
I'm not certain, but Roamer seems to be discussing the slow release of energy and how objects tend toward a state of equilibrium. Not sure how this relates to the previous points specifically, though.


"External energy isn't required to disassemble them again.
Given the correct initial conditions were right, the velocities and positions of each atom in the closed cyclic system would disassemble those objects again."

Instead of tending to reach a state of equilibrium, and ending in heat death...
Isn't there another possible outcome?
Given the just right initial conditions and enough time, isn't it possible for a microscopic closed system to be cyclic? (which also includes the forming and breaking of atomic bonds in this nanoscopic system)


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iNow
Post  Post subject: Re: Does this thought experiment break 2nd law of thermodyna  |  Posted: Thu Nov 24, 2016 7:27 pm
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No. As far as we know, absent some energy from another source, entropy increases with time.

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