Timeline for Is entropy physical or idealistic?
Current License: CC BY-SA 4.0
13 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Mar 13 at 13:36 | comment | added | armand | @leftaroundabout analogies break, that's life. A reader who does not have the notion that closed systems do not lose energy and can't have "low energy states" is indeed very unprepared. I can't take the responsibility to babysit people. | |
| Mar 13 at 8:57 | comment | added | leftaroundabout | @armand but "oh, it's just the energy" is exactly what an uprepared reader would take away from the analogy. Which is why it's no good. Basically the problem is that you're trying to use heaps of sand as a standin for abstract PDFs of statistical distributions. It's not a bad idea, but it breaks horribly if you don't take care to avoid bringing in physical connotations, dynamics that sand grains are subject to but don't make sense for general PDFs. | |
| Mar 13 at 1:08 | comment | added | armand | @LiamClink "ergodicity", "noncollisional gas"... i get your point but you have lost all the casual readers by the third line of your comment. This is an analogy to drive the point that entropy is about the natural evolution of a system, not some mystical "order and chaos" metric, and it's flawed AF but it does not claim to provide an understanding of physics. | |
| Mar 13 at 1:02 | comment | added | armand | @leftaroundabout except we are not talking about energy here. It's not the thermodynamics of sand heaps we are discussing. That's the point of an analogy. | |
| Mar 12 at 22:49 | comment | added | Kaia | @Howwhye For the record; the first few chapters of an introductory statistical mechanics textbook won't have math more complicated than a few derivatives. If you're curious about entropy, I'd highly suggest working through the derivation of entropy as a concept yourself! I haven't read it, but this book is CC-BY-SA and gets to a derivation of entropy by page 20. | |
| Mar 12 at 17:42 | comment | added | Liam Clink | Something to add: Entropy increases not just because there is a very sharply defined region in state space that contains almost all of the probability, but also because ergodicity is a valid assumption. That is, that the system has no preference for any particular state. Also necessary is the assumption that the system randomly wanders around state space in the first place. If you had a noncollisional gas in a balloon in space, and then popped it, the gas molecules would move in straight lines without acceleration, which is not random at all. Core to entropy is the notion of randomness. | |
| Mar 12 at 17:15 | comment | added | leftaroundabout | You could make the analogy work by talking not about heaps but instead assuming all sand grains are sitting on a glass plate (never two on top of each other) and comparing the state where all the grains are snugly pushed to one corner of the plate, to the state where they're spread out across the whole plate, though this too has caveats (e.g. if they're arranged on a perfect square grid). | |
| Mar 12 at 17:06 | comment | added | leftaroundabout | No, Bill K is right, this is not a good analogy because it suggests that a high-entropy state is a low-energy state, which is much more wrong than suggesting a low entropy corresponds to well-ordering. In fact, if the sand is spread out perfectly flat on the ground then this has the same low entropy as a maximum steep heap or even an intricate sand castle. What would have high entropy is if the sand is spread out but not evenly but with lots of random mounds and ripples. But that doesn't match your "lower is more likely than higher" explanation. The highest entropy meanwhile is a sandstorm! | |
| Mar 12 at 0:14 | comment | added | armand | that's the problem with analogies, if you stretch them to much they tend to burst. I guess one could build on the sand (pun intended) and move to a steam engine or something. Maybe use the image of an hourglass with a small mill wheel. I suspect creationists would also jump on to suggest that this is proof that someone had to put the heap together in the first place, etc. But I think the sand example is enough to dispel the whole "order/chaos" misconception, which was the original goal. | |
| Mar 11 at 21:38 | comment | added | Bill K | That is a good analogy but you might also point out that without intervention, given bounded area (let's say a pile in a sealed box) it will, over time, only flatten, never grow back into a mound. This seems a strange thing to say for sand, but the sand is representative of energy. All "Work" done with the energy leads towards the "Flat sand" state, and once it's at the "Flat" state no more work can be done (Nothing can happen) for that isolated area without external input. | |
| Mar 11 at 19:21 | comment | added | Philip Roe | Nice indeed! I would add that when the sand is in a heap there exists the possibility of doing something with it, like letting it run through a funnel and drive a tiny machine. In general, what happens to the heap reduces it usefulness. | |
| Mar 11 at 2:13 | comment | added | How why e | +1 What a beautiful analogy, I can say this is the closest I have come to completely grasping the idea of entropy. | |
| Mar 11 at 1:57 | history | answered | armand | CC BY-SA 4.0 |