Entropy

[zong]

The second law of thermodynamics does not state that entropy must increase. It states that overall entropy of the whole system increases, but entropy will increase in some places and decrease in others. The second law of thermodynamics is not a certainty but possibilities. There is a greater possibility of entropy increasing then decreasing, therfore overall it increases but in some places it decreases.

For example a box with a pendulum swinging freely without resistance from air or friction. let's say there are 3 particles of gas in box and 11 units of energy in the box. All 11 units of energy comes from the pendulum at the start. If we have 10 units of energy in the pendulum and one in the particles of gas, we have 1 state, being (1,0,0). 1 in the 1st particle 0 in the other 2. if we have 2 units of energy in the particles and 9 in the pendulum, we have 2 possible states. (2,0,0) and (1,1,0). but if we have all 11 units in the particles and none in the pendulum, we will have a total of 16 possible states. The total number of states is calculated to be 83. 1/83 would be 1 unit of energy in particles. 16/83 would be 11 units in particles. THerfore, there is a higher possibility that the final result would be 11 units in the particles and none in the pendulum. BUT it is still possible that the pendulum has more energy at the end. But there is no space with only 3 particles of gas. The more particles the greater the possibility that the particles will have the energy and pendulum none.

Hello whiteholes, thank you for posting these theory stuff out here. However, not many in this forum are really interested in theory.. We prefer looking at real things that show colours lol..

But that is not to say what you post is not appreciated. Please do not just post for the sake of posting. On reading the post in more detail, i realise that you are posting your idea of what entropy is all about. This is a good topic for dicussion, but please state it before you start blabbering all about entropy and make people lose interest in your post.. Everyone wants to enjoy their stay in this forum, right? So please post with responsibility ^^

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Ok, so a proper reply to your idea. I think you do not yet have a firm grasp of what entropy is all about. In your example, you talked about energy and the possible states. To link to your example, entropy is about the increase in work done to put energy and particles back in order. Your example does not show entropy at all, but rather teaches very well the topic of probability in mathematics!

So entropy (as i remember, i am too lazy to google out sources, so i shall explain in my own words), is defined as the amount of disorder in a certain system we define. The whole universe is the system as described in the law of thermodynamics. But to show you why you cannot disobey the laws of entropy, here is an example.

Suppose you have a nice room with nicely placed tables and chairs. A certain somebody comes in, sits on the chair, and breaks it, and leaves. The entropy in the room increases.

Now you can argue that to decrease the entropy in the room, you just have to remove the broken chair, which results in the room being in order again. But, where is the broken chair now? In the rubbish dump? So the rubbish dump has gained entropy. In fact, a rubbish dump, which is already chaotic, becomes even more so! Therefore, to count overall entropy, you have to add the initial entropy of both the room and the rubbish dump, and compare it with the final entropy of the room (which remains the same) and the rubbish dump (which increases). Therefore entropy can only increase. The "decrease" in entropy is only an illusion, because the decrease is just a transfer in entropy to other places, which overall causes entropy to increase further.

I hope you have learnt something, both in the area of astrophysics and entropy, and that of learning how to post such that people will not get confused by what you are trying to get across in your post.

[whiteholes]

Hello whiteholes, thank you for posting these theory stuff out here. However, not many in this forum are really interested in theory.. We prefer looking at real things that show colours lol..

Yep. i realised that. No one here is really interested in the theory stuff, which i am interested in. I thought that staring up into the sky is quite meaningless, though i would as a pastime. I prefer the theory part of astronomy. I find it more interesting. Sorry, but i would rather be honest than tactful.

But that is not to say what you post is not appreciated. Please do not just post for the sake of posting. On reading the post in more detail, i realise that you are posting your idea of what entropy is all about. This is a good topic for dicussion, but please state it before you start blabbering all about entropy and make people lose interest in your post.. Everyone wants to enjoy their stay in this forum, right? So please post with responsibility ^^

lol. yea, maybe i did not state clear my point of my posts. :oops:

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Ok, so a proper reply to your idea. I think you do not yet have a firm grasp of what entropy is all about. In your example, you talked about energy and the possible states. To link to your example, entropy is about the increase in work done to put energy and particles back in order. Your example does not show entropy at all, but rather teaches very well the topic of probability in mathematics!

oh. so entropy has nothing to do about energy and the possible states? Or maybe its the way i phrase?

So entropy (as i remember, i am too lazy to google out sources, so i shall explain in my own words), is defined as the amount of disorder in a certain system we define. The whole universe is the system as described in the law of thermodynamics. But to show you why you cannot disobey the laws of entropy, here is an example.

Suppose you have a nice room with nicely placed tables and chairs. A certain somebody comes in, sits on the chair, and breaks it, and leaves. The entropy in the room increases.

Now you can argue that to decrease the entropy in the room, you just have to remove the broken chair, which results in the room being in order again. But, where is the broken chair now? In the rubbish dump? So the rubbish dump has gained entropy. In fact, a rubbish dump, which is already chaotic, becomes even more so! Therefore, to count overall entropy, you have to add the initial entropy of both the room and the rubbish dump, and compare it with the final entropy of the room (which remains the same) and the rubbish dump (which increases). Therefore entropy can only increase. The "decrease" in entropy is only an illusion, because the decrease is just a transfer in entropy to other places, which overall causes entropy to increase further.

Is it anything like the Maxwell's demon though experiment? Where entropy seems to decrease. But actually, it is not. The expenditure of energy by the demon will cause an increase in the entropy of the demon, which will be larger than the lowering of the entropy of the gas.

Now you can argue that to decrease the entropy in the room, you just have to remove the broken chair, which results in the room being in order again. But, where is the broken chair now? In the rubbish dump? So the rubbish dump has gained entropy.

"It states that overall entropy of the whole system increases, but entropy will increase in some places and decrease in others."

Do they mean the same thing? :?

[chrisyeo]

It's not true that there is no one interested in the theory stuff, it's just that no one comes forward to talk about it, that's why it seems like there's no one interested.

I'm sure there are many people interested to discuss astrophysics. This forum has enough space for all things astronomy.

Just try to be clearer about what you are trying to discuss about.

Cheers,

[weixing]

Hi,

Yep. i realised that. No one here is really interested in the theory stuff, which i am interested in.

As what Chris Yeo had mention, it's not that people are not interested in theory here... just that most of the active members here are working people who just don't have time (and energy) reading about theory... some of us may fall asleep very fast seeing those theory books... ha ha ha

I thought that staring up into the sky is quite meaningless

Hmm... without people like us who look at the "quite meaningless" sky, those theory that you happen to be interested will only still be consider as someone else's imagination, science fiction and may be people will still think that the earth is the centre of universe and the Sun Revolve Around the Earth....

Have a nice day.

[whiteholes]

Hmm... without people like us who look at the "quite meaningless" sky, those theory that you happen to be interested will only still be consider as someone else's imagination, science fiction and may be people will still think that the earth is the centre of universe and the Sun Revolve Around the Earth....

But do you use such powerful telescopes? Or do you have time to study thousands of photos to discover a planet? In order to get accurate data, telescopes have to be sent to space as the atmosphere of the earth will distort light coming into the earth.

[jermng]

Maybe other than theory, do read up on a little history as well.

Find out what scope Galileo used .. Also, in more recent times, read up how David Levy discovered his first comets ..

And other than

staring up into the sky

, many pple have taken beautiful pictures of the universe ..

Also, on a more related note, our very own "Starfinder", Gavin, was one of the first few pple who reported the thickening and change in Jupiter's belts right here on SingAstro! Using "just" an 8" SCT and commonly available commercial imaging equipment.

How's that for 'meaningful'??

[weixing]

Hi,

But do you use such powerful telescopes?

Most of us may not have the big "bucket", but we make it up with numbers and telescope time... those big "bucket" can't point at a star for continous observation, but our small "cups" all around the world can help them to do that.

Or do you have time to study thousands of photos to discover a planet?

I don't have the time (I think most professional astronomer don't have time to do that too) to do that, but there are something call computer and software which can be use to do that.

In order to get accurate data, telescopes have to be sent to space as the atmosphere of the earth will distort light coming into the earth.

Err... the last time I heard was that most telescopes are still earth base and also there is something call "calibration" which can used to obtain accurate data even from a small telescope.

Anyway, there are quite a number of discoveries were make by amateur, so amateur can still contribute and help to make "some imagination idea" become a theory or facts.

By the way, it's getting off-topics... may be you can start a new topics to discuss how amateur can help the professional astronomer in scientific work if you are interested.

Have a nice day.

[zong]

oh. so entropy has nothing to do about energy and the possible states? Or maybe its the way i phrase?

It does, but not in the way you mentioned. The link has nothing to do with possible states, because states are decided before entropy can be "calculated". It is not a factor, but a cause.

Is it anything like the Maxwell's demon though experiment? Where entropy seems to decrease. But actually, it is not. The expenditure of energy by the demon will cause an increase in the entropy of the demon, which will be larger than the lowering of the entropy of the gas.

Sorry, might have seen this experiment, but forgot about it, What you say is roughly true.

It states that overall entropy of the whole system increases, but entropy will increase in some places and decrease in others.

Do they mean the same thing? :?

Yes this sentence means what i say. But your next line: "The second law of thermodynamics is not a certainty but possibilities. There is a greater possibility of entropy increasing then decreasing, therfore overall it increases but in some places it decreases." is wrong. When in calculation, you cannot assume an open system (ie. in my case you forget the rubbish dump and only calculate the room's entropy). You can only calculate entropy in closed system (ie rubbish dump AND room in my case). Anything can happen in open systems, so if we assume open systems then we might as well say the whole of physics can be proven wrong..

[Canopus Lim]

Starring at the sky is not meaningless...... there are thousands of objects to be seen with our 'small telescopes'.

Also, if you have a chance, go to somewhere that is far from a city and take a look at the night sky. In Singapore, I guess you get the notion of meaningless sky especially without a telescope to see the craters on the moon or the rings of Saturn. You could join the Mersing trip this 17th March or observations conducted by some Singastro members. The beauty of the night sky is better than all those man made things you see everyday. To me meteors look better than fireworks which are predictable. There are really lots of things to see.

[whiteholes]

Yes this sentence means what i say. But your next line: "The second law of thermodynamics is not a certainty but possibilities. There is a greater possibility of entropy increasing then decreasing, therfore overall it increases but in some places it decreases." is wrong. When in calculation, you cannot assume an open system (ie. in my case you forget the rubbish dump and only calculate the room's entropy). You can only calculate entropy in closed system (ie rubbish dump AND room in my case). Anything can happen in open systems, so if we assume open systems then we might as well say the whole of physics can be proven wrong..

For example a box with a pendulum swinging freely without resistance from air or friction.

In the example i gave, it is a close system. Its a box which is isolated so that it cannot exchange matter or energy with its surroundings. Please correct me if i might be wrong.