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Entropy: A little understood concept in physics [video]

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Re: Entropy: A little understood concept in physics [video]

#101

Post by mNovak »

credit_guy wrote: post #51
sghiassy wrote: post #22

Earlier quoted context omitted.

Not really - look up “heat death” of the universe.

The "heat death" of the universe is a concept that deserves to die. The second principle of thermodynamics is true only if you ignore gravity. In the presence of gravity, systems tend to go towards lower entropy, just see how a planetary system can form out of a gas cloud.

Not my area of expertise, but in the video at least, they indicate that black holes have very high entropy. So if we imagine gravity eventually pulling all those planetary systems together into some number of black holes, isn't gravity indeed pulling the system towards a high entropy state?

The video actually directly addresses the gas cloud question, saying basically that a gas cloud is actually a highly improbable distribution of matter, whereas the eventual planetary system is much more probable. The claim being, that trend towards expected state is entropy increasing.

Re: Entropy: A little understood concept in physics [video]

#102

Post by kikokikokiko »

kgwgk wrote: post #55
cshimmin wrote: post #52

Earlier quoted context omitted.

"information" is not a good term for the opposite. Entropy is a well defined concept in information theory (and can be connected to the physical concept). More entropy means more information, not less.

> Entropy is a well defined concept in information theory (and can be connected to the physical concept). More entropy means more information, not less. More entropy means more missing information. https://iopscience.iop.org/book/mono/978-0-7503-3931-5/chapt...

As I understand it in information theory, "more entropy" equals "more information is necessary to fully describe this thing", but I may be wrong.

Re: Entropy: A little understood concept in physics [video]

#103

Post by JumpCrisscross »

dahart wrote: post #57
lisper wrote: post #11

A pithier way to introduce this topic: the first law of thermodynamics, a.k.a. the law of conservation of energy, is that energy cannot be created nor destroyed, only transformed from one form to another. In light of this, how can there ever be a shortage of energy? [Note that this is intended to be a rhetorical question advanced for the purposes of pedagogy. If you find yourself wanting to post an answer, you have m…

Why is this pithier than the video? I’m not entirely sure I see added pedagogical value. Asking the rhetorical question how can there be a shortage of energy sounds a little like someone sort-of intentionally misunderstanding what that phrase “energy shortage” means in any practical economic context. “Energy shortage” is an economics phrase, not a physics phrase. The first law of thermodynamics doesn’t suggest there…

It’s pithy, but in the way of word play. Energy, colloquially, means useful energy. The question collides the conventional and technical definitions to create the illusion of profundity.

Re: Entropy: A little understood concept in physics [video]

#104

Post by martythemaniak »

Great video, but very wrong to cite Jeremy England. Ilya Prigogine came up with the concept of Dissipative Structures and won the Nobel Prize in Chemistry in 1977 for that work. He also has a couple of pop-sci books on he subject that I found super illuminating. They are a little bit challenging to read, but they're very thorough and Order out of Chaos in particular has a fantastic summary of 400 years of philosophy of science. Highly recommend reading the OG.

Re: Entropy: A little understood concept in physics [video]

#105

Post by kledru »

spuz wrote: post #27

I think the concept would be easier for me to understand if we talked about the inverse of entropy - i.e. some kind of measurement for the concentration of useful energy or "order". I think it would then be more intuitive to say that this measurement always decreases. Do we even have a word for the opposite of entropy?

we do have a word -- "negentropy". Physicists also sometimes find it easier to talk about "negentropy" instead of entropy.

Re: Entropy: A little understood concept in physics [video]

#106

Post by kgwgk »

kikokikokiko wrote: post #102
kgwgk wrote: post #55

Earlier quoted context omitted.

> Entropy is a well defined concept in information theory (and can be connected to the physical concept). More entropy means more information, not less. More entropy means more missing information. https://iopscience.iop.org/book/mono/978-0-7503-3931-5/chapt...

As I understand it in information theory, "more entropy" equals "more information is necessary to fully describe this thing", but I may be wrong.

“more [additional] information is necessary to fully describe this thing” = “more missing information [in the incomplete description of the thing]”

Re: Entropy: A little understood concept in physics [video]

#107

Post by ithkuil »

guga42k wrote: post #98
javajosh wrote: post #38

Entropy only made sense when I learned it from the perspective of statistical thermodynamics. It's a very programmerly understanding, IMHO, and it's quite intuitive. EXCEPT that the language used is ridiculous: grand canonical ensemble indeed! Anyway, the idea that a system can be in some number of specific states, and that equilibrium is that unique situation where the number of possible specific states is at its ma…

If somebody needs to build an intuition about entropy he could think about simple problem. You are given insulated cylinder with a barrier in the middle. Left side of the cylinder filled with ideal gas A, and the right side filled with gas B. If given a particle one can distinguish A from B. The pressure and temperature on both sides are the same. Then you remove the barrier and gases mix. Question: how much work you…

If you need to do work in order to revert to the previous state, does it imply you can extract work when going to the first to the second state?

Given the scenario you just laid out it seems no work can be extracted just by letting mix two substances that are at the same temperature and pressure. But there is something about it that doesn't quite add up to my intuition of symmetry and conservation laws. Could you please elaborate more on that?

Re: Entropy: A little understood concept in physics [video]

#108

Post by kgwxd »

antimora wrote: post #92

The video did not explain why the sun is a low entropy source. I found this explaining what I am sharing with you: So, the sun is a low-entropy source of energy, and Earth (and everything on it) increases that entropy as it uses and then reradiates that energy. This process is entirely consistent with the second law of thermodynamics. The relationship between light frequency and entropy comes from the fact that entro…

> The video did not explain why the sun is a low entropy source.

Laymen to the extreme but, didn't it? The thing about the low entropy of the universe near the big bang, gravity naturally bringing things together, and such?

Re: Entropy: A little understood concept in physics [video]

#109

Post by cubefox »

Balgair wrote: post #87
semi-extrinsic wrote: post #75

Earlier quoted context omitted.

No. Entropy can be used to explain the direction of time, as a kind of symmetry breaking of all the microscopic laws that are symmetric in time. But it does not say anything about the "speed of time". Relativity does tell us the speed of time - it's the speed of light.

To be suuuuuuper pedantic here: Relativity tells us that time is a dimension, one that is a bit unique. In that it has a constant attached to it. So, the 3 dimensions you're used to are just normal, they have no constants. (x,y,z) Meters of x are meters of z and meters of y. Relativity (and I'm really simplifying a lot by just saying 'relativity'), well relativity comes along as says that time is also a dimension, ju…

The last sentence surprised me.

Re: Entropy: A little understood concept in physics [video]

#110

Post by ctafur »

According to entropy, and thermodynamics in general, I can't recommend enough the notes [0] of prof. Zhigang Suo of Harvard. It's a new way of presenting thermodynamics and I finally get it... contrary to when I took a thermo course at university.

[0]: https://docs.google.com/document/d/10Vi8s-azYq9auysBSK3SFSWZ...

Also prof. Suo puts entropy as the main character of the "play". The other concepts (temperature, etc.) are defined from entropy.

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