Author Topic: Entropy  (Read 8292 times)

Offline stephako

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Entropy
« on: July 07, 2012, 04:52:37 AM »
yeah ben,

how about a show about entropy?
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Offline bn

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Re: Entropy
« Reply #1 on: July 07, 2012, 04:58:20 AM »
yeah!
that's a really good idea.
entropy is awesome.

right now, i'm trying to snag a politician to be on the show.
and if i manage to hook this politician, i'll try to explain entropy to them
because politicians, of all people, need to understand entropy :p
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Offline bn

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Re: Entropy
« Reply #2 on: July 07, 2012, 05:00:37 AM »
although...
I'm kind of having trouble putting together a list of topics for that show.
like... we could talk about thermodynamic entropy. that's nice.
and then statistical mechanics entropy. that's really good.

but then aside from the usual explanations and examples (balls bouncing around rooms, drops of ink in glasses of milk)

are there any super sexy but also intuitively appealing examples where entropy is the important thing?
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Offline stephako

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Re: Entropy
« Reply #3 on: July 07, 2012, 11:42:56 AM »
I haven't thought about analogies yet, but what about information entropy and Maxwells demon? Or the hydrophobic collapse in protein folding?
For the latter one a Highschool analogy could maybe be usefull, but I have to think about how to do it correctly

If I come up with good analogies I'll post them
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Offline bn

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Re: Entropy
« Reply #4 on: July 07, 2012, 12:42:20 PM »
hydrophobic collapse in protein folding?
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Offline Jacob Stump

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Re: Entropy
« Reply #5 on: July 08, 2012, 03:20:43 PM »
This is how the interview with the politician would go

Politician: "I think I know about as much Science as the average citizen"
Ben: "So, you know very little Science, then?"
Politician: "Listen, Science is important... The children are our future... We must invest in the future... uh, um..."
Ben: "CAN I EXPLAIN ENTROPY TO YOU?"
Politician: "Can you do what?"
Ben: "OK, so...Entropy is like, this thing...this idea...that the entire universe tends towards DISORDER. And the only way to bring ORDER to the universe is to add ENERGY to the system..."
Politician: "And this is exactly why I've advocated federal incentives to our nation's oil exporters...to bring ORDER to our universe, and prove those anarchists wrong!"
Ben: "Hahahah, well...um... no that's not what I meant..."
Politician: "Well this has been great, I think that's all I have time for tonight. Thank you very much Benjamin. Vote conservative!"

Offline Ed Lolington

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Re: Entropy
« Reply #6 on: July 08, 2012, 03:34:08 PM »
Titanium Physicists has a pro-bee-analogy agenda. That's certainly no secret.

Offline bn

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Re: Entropy
« Reply #7 on: July 08, 2012, 03:47:14 PM »
Titanium Physicists has a pro-bee-analogy agenda. That's certainly no secret.
that's my new signature.
Titanium Physicists has a pro-bee-analogy agenda. That's certainly no secret.

Offline stephako

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Re: Entropy
« Reply #8 on: July 10, 2012, 11:33:03 AM »
hydrophobic collapse in protein folding?

On second thought that probably wouldn't be the best option. But in general structure formation or demixing would be a nice phenomena to explain. I thought about something like:

Think about a schoolyard with teenage boys. They all want to run around each other and show the teachers how little they care about the rules and behaving in an orderly fashion. But you have two kinds of boys, lets say bullies and nerds (or any other stereotypes). In general they both want to run through each other , but a bully has to bully a nerd when he can reach him, because otherwise he will lose the respect of the other bullies. Depending on how strong the desire to beat up a nerd is compared to the desire to run around with the other bullies and high five and how many nerds you have different structures will form on the yard. If you have only a few nerds the bullies always get to each one and can bully each of them. But if you add more nerds they will start to form groups and the bullies can only get to ones standing on the edge of the group. At first you might form several little circles, and then form more complex structures, until you reach a point where you have only a small circle of bullies, surrounded by nerds.

And this is why you get these little blobs of oil when you drop it onto water. (nerds being hydrophobic as we all know, like oil and bullies are hyrdophylic like water)


This might need some streamlining, but do you think this could work? Instead of the oil you could use other examples, like the folding of a protein, but I guess people are not familiar with that sort of thing.

Another fun thing for entropy could be the purely entropic pressure you get when compressing an idealized version of a polymer (one where the polymer doesn't interact with itself). Maybe a worm analogy could be used: If you have a worm in a large box it can wriggle around all it wants and not touch the wall, but when you make the box smaller the worm touches the walls more often as it moves, until the box is so small that the worm is pressing strongly against the wall just to keep moving.

I'm sorry that I couldn't come up with any bee metaphors, but maybe some else has an idea.

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Politician: "And this is exactly why I've advocated federal incentives to our nation's oil exporters...to bring ORDER to our universe, and prove those anarchists wrong!"

Oh man that would be a terrible lesson to draw from physics...
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Offline bn

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Re: Entropy
« Reply #9 on: July 10, 2012, 06:46:37 PM »
@_@ i don't know enough chemistry to make use of any of your entropy examples.

which is too bad. because they sound awesome.
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Offline stephako

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Re: Entropy
« Reply #10 on: July 11, 2012, 12:46:27 AM »
@_@ i don't know enough chemistry to make use of any of your entropy examples.

hmm... I learned that stuff in physics classes, our university has kind of an affinity to polymer and soft matter physics.
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Offline Lynx Cat

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Re: Entropy
« Reply #11 on: July 11, 2012, 07:22:32 AM »
I'm very interested on the topic of entropy, because I think its importance in the formation of the world around us is very underrated. But the one specific thing I really, desperately want to know more about is the whole "arrow of time" thing. Well, it's not specifically about entropy, but as I understand it, the concept of which direction the arrow of time points to (i.e. what's "past", what's "future", and what's the difference between the two) is mostly informed by entropy. And I think that's a fascinating discussion - what makes "going forward" in time any different than "going backward"? If you looked at physical phenomena with the clock running "backwards", would they still conform to all the same laws of physics? If not, why not? And what's the role of entropy in all that - is it merely statistical? Does it make any qualitative, rather than quantitative difference? Those are questions I still understand very little, and I'd love to know more.

p.s. I'm the guy who was having trouble getting to the board... apparently it works anywhere but at home. Weird - as I said, I don't have a proxy at home, and I've got one here... well, anyway, glad it worked somehow.
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Offline stephako

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Re: Entropy
« Reply #12 on: July 11, 2012, 08:47:04 AM »
Well, it's not specifically about entropy, but as I understand it, the concept of which direction the arrow of time points to (i.e. what's "past", what's "future", and what's the difference between the two) is mostly informed by entropy.

That is correct. The thing is this: In statistical mechanics and thermodynamics (so the physics of systems with a lot of particles in them) you can show that processes should only happen if the entropy increases which gives a prefered direction in time. Of course this is a statistical statement and it can be violated in individual cases. The point is that these fluctuations become more and more rare the larger you system gets. So once you are at the level that we can observe with our senses you wouldn't expect to see any such thing. On the other hand if you go to microscopic systems you wouldn't necessarily expect that.

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If you looked at physical phenomena with the clock running "backwards", would they still conform to all the same laws of physics?

Yes, most of the laws of nature stay unchanged if you change the direction of time (there is some weird thing when magnetic fields are involved, but I'm not sure if that is just a problem of the law not being the most fundamental version).
So these microscopic processes are all reversible. However in my statistical physics class we had an example of a system of particles, that each follow a reversible law of motion, but once you look at the whole system of many such particles the behaviour starts to become irreversible. Unfortunately I haven't understood that beyond the level of "the equations say so"....

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is it merely statistical? Does it make any qualitative, rather than quantitative difference? Those are questions I still understand very little, and I'd love to know more.
As I said above, entropy is a statistical quantity, but you can derive qualitative results. In the macro world that's not so surprising, considering that you have almost no fluctuations. It is a bit more complicated once you get to smaller systems. As far as I know the field of micro-thermodynamics is just a bit over a decade old. Micro thermodynamics deals with systems which are large enough to use a statistical description, but not so large that you can neglect fluctuations. This is for example the case when you do experiments on single, large molecules (e.g. proteins or polymers). Then you can derive a distribution your measurements should follow and compare that to what you actually measured. I think one could still call this qualitative, in the same sense that quantum mechanics can also only give you a statistical description of what is happening.
In these cases one actually can violate the second law of thermodynamics (that is only things that increase the entropy happen) as long as one stays within the statistical fluctuations....

I hope this was what you meant and that it was not to much jargon to be understandable (I only noticed in this forum how little I talk to non scientists about science...)
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Offline Lynx Cat

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Re: Entropy
« Reply #13 on: July 11, 2012, 12:21:57 PM »
Thanks for your reply! What you wrote is pretty much what I understood from other sources. I'd still like to hear more about this (hence this being in "topic suggestions"), especially "why" entropy has a preferred direction in time. I hear that's one of the big unknowns in modern physics, but I wonder if there are any theories...

I don't have any formal schooling in hard sciences beyond high-school, but they've always fascinated me, so I've always been reading about them. (And I paid close attention to high-school physics too... one of my favorite subjects.) Since about last year, I'm trying to teach myself more advanced physics (special & general relativity and quantum physics), but it's sometimes hard to find the time to do that, so I'm still struggling with the mathematical foundations. Well, there's "popular science" stuff like books and Titanium Physics, which I gobble up like there's no tomorrow, but I wanna see physics "from the inside"...
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Offline stephako

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Re: Entropy
« Reply #14 on: July 11, 2012, 01:40:37 PM »
Since about last year, I'm trying to teach myself more advanced physics (special & general relativity and quantum physics), but it's sometimes hard to find the time to do that, so I'm still struggling with the mathematical foundations.

Wow that is impressive! I imagine this to be some pretty hard work. Most of the stuff is difficult to understand even if you are in a university with teachers and students around you who do nothing else all day... You Sir or Madam have my respect

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especially "why" entropy has a preferred direction in time

I am not sure I completely understand what you mean by that. Do you want to understand why processes only happen when the entropy increases? Or do you want to know why the entropy increases always in the direction of positive time?
Null results, open questions and a bit of my writing: JUnQ