Great article, reminds me of the “big chill” or the heat death of the universe:
https://en.wikipedia.org/wiki/Heat_death_of_the_universe
What is entropy? A measure of just how little we know
131–140 of 169 posts
Re: What is entropy? A measure of just how little we know
#132What about the efficiency to remove entropy? Is there a threshold our combined efforts called science cannot surpass? Do we need Frank Herbert’s spice to progress?
A localized reduction of entropy will always result in an increase of entropy in the larger system. It doesn't matter how efficient your process is, the entropy of the surrounding system will ALWAYS increase as the result of the work needed to effect a localized reduction.
Yes, so we should bundle the excess entropy into a rocket and shoot it into space. As Futurama showed, this is perfectly fine!
Re: What is entropy? A measure of just how little we know
#133I remember that somewhere during my physics degree this idea of the article clicked with me. Entropy is just a simpler way of manifesting properties of a system that we didn’t measure because it is too difficult (when I was still at classical physics level) or it’s not possible to measure (when quantum mechanics became present in everything we learned). We use it because we can’t measure the position and momentum of…
The chart of "Thermodynamic Beta" on wikipedia is great. I like to think about the big bang as a population inversion where the entropy temporarily becomes negative leading to the hyperinflationary epoch as the universe "collapses" into existence finally cooling to a near "infinite" temperature making the CMB nice and smooth.
The big bang clearly defies thermodynamic laws so why wouldn't be a negative entropy and temperature phenomenon? It's the "cheat code" the "primordial universe" uses to dodge problems like realities popping into existence.
Re: What is entropy? A measure of just how little we know
#134Entropy got a lot more exciting to me after hearing Sean Carroll talk about it. He has a foundational/philosophical bent and likes to point out that there are competing definitions of entropy set on different philosophical foundations, one of them seemingly observer dependent: - https://youtu.be/x9COqqqsFtc?si=cQkfV5IpLC039Cl5 - https://youtu.be/XJ14ZO-e9NY?si=xi8idD5JmQbT5zxN Leonard Susskind has lots of great talks…
why is it exciting at all? it is the most depressing concept i have ever heard.
What's depressing about it?
Re: What is entropy? A measure of just how little we know
#135Earlier quoted context omitted.
First, when I joined the project, it wasn’t clear how it would be published. Svelte, which outputs compiled JavaScript, can fit into many CMS workflows that newspapers/publishers use. I believe Svelte was developed by Rich Harris at the NY Times for this very reason. We ended up using iFrames, so other frameworks like React could have been used. Second, Svelte is very well suited for these small interactives because…
> We ended up using iFrames, so other frameworks like React could have been used. Wait, wasn't one of the original selling points of React that it could be embedded piecewise to enhance interactivity of the parts of pages that needed it? It should certainly not need a separate page!
It was, but it also feels like there's now a very large gulf between React's original selling points and the mess we have today.
You definitely can do it (I've done it myself including SSR hydration) but it was a massive pain to do.
Re: What is entropy? A measure of just how little we know
#136I don't get the example under "What is entropy?". This works only under the assumption that reality (phase space in particular) is somehow "pixelated". If reality is continuous, 9 particles that are clumped together can already be in uncountalbly many states.
Isn't that the whole point of quantum theory, it's quantized? Or did I get that wrong?
Re: What is entropy? A measure of just how little we know
#137Earlier quoted context omitted.
> entropy is the ability to extract useful work from a system https://www.damtp.cam.ac.uk/user/tong/statphys/jaynes.pdf The amount of useful work that we can extract from any system depends - obviously and necessarily - on how much “subjective” information we have about its microstate, because that tells us which interactions will extract energy and which will not; this is not a paradox, but a platitude. If the entro…
I think this is a very weird thought experiment, and one that is either missing a lot of context or mostly just wrong. In particular, if two people had access to the same gas tank, and one knew that there were two types of argon and the other didn't, so they would compute different entropies, one of them would still be wrong about how much work could be extracted out of the system. If whifnium did exist, but it was c…
> unless of course you tautologically define entropy as the amount of work the experimenter/humanity can extract from the system
Do you have a different definition? (By the way the entropy is the energy that _cannot_ be extracted as work.) The entropy of the system is a function of the particular choice of state variables - those that the experimenters can manipulate and use to extract work. It’s not a property of the system on its own. There is no “true” entropy anymore that there is a “true” set of state variables for the “true” macroscopic (incomplete) description of the system. If there was a true limiting value for the entropy it would be zero - corresponding to the case where the system is described using every microscopic variable and every degree of freedom could be manipulated.
Re: What is entropy? A measure of just how little we know
#138Earlier quoted context omitted.
Agreed, sure. Of course it's not subjective. Is there a concrete physical example where the information-theory definition of entropy conflicts with experiment?
Others in this thread do believe that entropy is a subjective measure, or more precisely a measurement of the information that an observer has about a system instead of a measurement about the state of the system itself. Information theory easily leads to this interpretation, since for example the informational content of a stream of bytes can very much be observer-dependent. For example, a perfectly encrypted stream…
I feel that my careful distinction between "information theory" entropy and "physical" entropy seems to vanish in your first sentence.
Re: What is entropy? A measure of just how little we know
#139My perspective: 1) entropy is a mathematical concept. Physics apply it, like any other mathematical one 2) math entropy does not change, everything is reversible, as it is based on known quantities 3) entropy measures how far we are from perfectly knowing a system 4) logarithm is chosen to measure entropy because of its convenient properties, not because of any deeper law. It could be a sum, a product etc 5) the Seco…
Thermodynamics is a young and poorly thought out science.
My beef is the adoption of bad names and pseudo-philosophy. In Gibbs free energy equation, there is a term called entropy but it is nothing more than the value for heat transferred for the given elements and given constant temperature and derived from experimental observation. Instead of calling it entropy, they could have called it Clausius constant. No need to confuse generations of students.
Re: What is entropy? A measure of just how little we know
#140Earlier quoted context omitted.
> Fundamentally, entropy depends on the probability distribution, not the observer. Right but a probability distribution represents the uncertainty in an observer so there is no inconsistency here (else you're falling for the Mind Projection Fallacy http://www-biba.inrialpes.fr/Jaynes/cc10k.pdf ).
This is only true if one assumes that (a) physical processes are fundamentally completely deterministic, and that (b) it is possible to measure the initial state of a system to at least the same level of precision as the factors that influence the outcome. Assumption (a) is currently believed to be false in the case of measuring a quantum system: to the best of our current knowledge, the result of measuring a quantum…
The idea that entropy represents the uncertainty in our description of a system works perfectly well in quantum statistical mechanics (actually better than in classical statistical mechanics where the entropy of a system diverges to minus infinity as the precision of the description increases). The entropy is zero when we have a pure state, a state perfectly defined by a wave function, and greater than zero when we have a mixed state.
Regarding your second point, how does the practical impossibility of measuring the initial state invalidate the idea that there is uncertainty about the state?