Hot answers tagged

80

No, it's not possible. See, there's a problem with the English word "possible": it's an English word. Even in the best cases it's hard to translate technical, scientific ideas into English sentences. You're asking us to choose between two English words, "possible" and "impossible", to describe an event where a broken egg ...


49

It's possible, but won't happen anywhere within even one universe lifetime, not even close. Physicists often hate saying it is technically possible because the process is so mind bogglingly unlikely, that really it should always be emphasized just how unlikely it is. But yes it is possible.


40

Up to the limits of our theoretical understanding, yes, there is nothing in principle wrong with seeing what happens in the video happen for real in the sense that you can formulate this entire scenario in principle in such theory without running into any contradiction, whereas something like a perpetual motion machine would (namely, that would require ...


21

A few days ago I was watching a few YouTube videos about reversing entropy and how it was impossible. I think you might mean "decrease entropy", and it's perfectly possible for the entropy of a system to decrease. Only the entropy of an isolated system is required to never decrease (which you state later in your post). But the entropy decreases ...


9

All these answers that say "yes it is possible ... but very very unlikely" are failing to take into consideration the limits of human knowledge itself. In dealing with something as extraordinary as a broken egg getting reassembled, one misleads oneself if one says either "yes it is possible" or "no it is impossible" because in ...


7

I think a way of looking at the stat mech here is to convert it over to billiards. Take a shot where you launch one ball at two stationary balls. The shot is calibrated just so that the cue ball stops, and the other two balls go off at some angle $\theta$ with some speed $v$ (we can use conservation of energy and momentum to compute what values $v$ and $\...


7

When gas collapses to form a star, it will increase in temperature. If we ignore radiation and any interaction of the gas with its surroundings, this will be an adiabatic compression where entropy remains constant. The loss of entropy due to the confinement of the gas molecules into a smaller space will be offset by the increase in entropy due to the broader ...


6

It is, of course, within the realm of possibility that any of the laws of physics, as we presently understand them, is only true overwhelmingly often, rather than always. However, if we are going to start dealing with an epistemology of absurdly unlikely events, we should also remember David Hume's point that there is no sure knowledge that the laws of ...


5

To complete, @The_Sympathizer, you can calculate (or, better said, estimate) the entropy with Boltzmann formula $S=k_B\log N$, with $N$ the number of states. From the initial (i) state to the the broken final state (f), the change in entropy is $$\Delta S=k_B\log N_f/N_i$$ So, $$N_f=N_ie^{\Delta S/k_B}$$ and the probability of the transition from initial to ...


5

Gravity does not reverse an increase of entropy. If a ball rolls of a shelf, gravity will pull it down, converting potential energy into kinetic energy. If the ball hits a perfectly bouncy floor, it will bounce up to the same height as before. In thermodynamics this is considered reversible because there is no change in entropy. The ball will continue to ...


4

I wondered about this myself. Especially after reading a book by Brian Greene (I don't remember if it was "the elegant universe" or "The fabric of the cosmos"), in which it was stated that gravity indeed contributes negatively to unfolding chaos. On can read here: The first stars did not appear until perhaps 100 million years after the ...


4

I want to establish some baseline definitions. As some have pointed out, english is not very precise. Definition Possible - A non-zero probability value. Impossible - Probability=0 exactly. Never going to happen, ever - Probability is less than $ 10^{-15}$ (about 1 in 1 quadrillion odds) Egg spontaneously reassembling itself has a non-zero probability, but ...


4

The electrical load, if it is not at 0 K, will also generate noise current through the coil, which will produce a magnetic field, which will do work on the magnetic particle, which will then transfer energy back to the particles of the fluid that it interacts with. Ultimately, if the fluid is hotter than the load, energy will transfer from the fluid to the ...


3

There are many processes which move entropy around, so that some parts end up with less entropy than they started with, and the entropy in the other parts increases. So overall the net total entropy of the global system goes up, but it is very significant that within this there can be regions of low entropy, such as planets and living things (which have low ...


3

There is something I miss in the other answers: they do not take into account that the egg did actually spontaneously assemble itself in the first place. However, it did not assemble in a way that looks anywhere close to what the video shows, but something that involves chicken, reproductive organs, nutrition, etc. This is the point where most will probably ...


3

There is no way this could happen. Statistical thermodynamics can be applied to free particles (atoms, molecules, but elementary particles are somehow never involved), some chemical interactions (by introducing the chemical potential), but not to complex interactions in which a complex compound of a high variety of bound structures is involved, like in a ...


3

The change in entropy of the hot bath has to be negative since heat transfers out of the bath. They are wrong. I also object to them calling this engine a Carnot engine. A Carnot engine operates in a reversible cycle. The processes in a reversible cycle have to be carried out very slowly (quasi-statically). A 0.5 sec cycle is hardly a cycle carried out very ...


2

$\newcommand{\mean}[1] {\left< #1 \right>}$ $\DeclareMathOperator{\D}{d\!}$ $\DeclareMathOperator{\pr}{p}$ Proof that $\beta = \frac{1}{k T}$ and that $S = k \ln \Omega$ This proof follows from only classical thermodynamics and the microcanonical ensemble. It makes no assumptions about the analytic form of statistical entropy, and does not involve the ...


2

Suppose we mix two gases that initially have different temperatures. Higher temperature gas molecules move faster than lower temperature gas molecules. Collisions occur between the molecules of one gas and the other. Part of the energy from the faster molecules passes to the slower molecules. Gradually the temperature of both gases equalize. We have called ...


2

The zeroth law basically states that systems being at equilibrium with each other is a transitive property. if A is at equilibrium with B, and B is at equilibrium with C, then A is at equilibrium with C. From this we can map equivalence sets of systems at equilibrium onto the real numbers. If you do it in a particular way, you get "temperature." ...


2

and so the direction of heat flow was just a matter of definition. It is not just a matter of definition. It's a matter of observation. Heat is never observed to flow naturally or spontaneously from a low temperature substance to a high temperature substance. For that to happen, work must be done (as, for example, in the case of refrigerators and heat pumps....


2

Hint: You have to use $$dE=TdS-PdV+\mu dN$$ $$\frac{P}{T}= \left. \frac{\partial S}{\partial V}\right|_{N,E}$$ Where $$S=k_B\ln\Omega$$


2

Entropy is a starting point for many advanced theoretical statistical mechanics books but beyond it just being negative or positive, what does it actually tell you? Specifically, what does the magnitude of it's change tell you? For one thing, it tells you if a process is irreversible the entropy generated due to the irreversible process results in less ...


2

Let's do some quantitative answer for those interested in more in-depth discussion. I'll just follow the discussion in Gravity, Entropy, and Cosmology: In Search of Clarity arxiv paper. We start with a spherical volume of gas of radius $R$ that contains $N$ particles and that have total energy $E$. The standard expression for entropy of such gas is: $$S = ...


2

So where does the extra work that I get go? You didn't get any extra work in scenario 2, if that's what you meant by "extra work". See the Figures below. FIG 1 is based on my understanding of your two scenarios (if it is incorrect, let me know and I will either edit or delete my answer). The additional work output you got when you operate the heat ...


2

From my point of view this mechanism violates 2nd law of thermodynamics, because it converts internal energy to electricity, which in a closed system will become heat which will then be converted to electricity again. What am I missing? There is nothing that violates the 2nd law of thermodynamics about converting thermal energy into electricity. Indeed, ...


1

I don't see how the example of merging N galaxies to form a bigger galaxy means a decrease of disorder. We have before a situation where stars $X_1$, $X_2$, ...,$X_n$ are in a region of space (galaxy $X$), that is completely separated from other region where stars $Y_1$, $Y_2$,...,$Y_n$ are in the galaxy $Y$. After merging, the stars are no longer organized ...


1

I remember I read in Thirrings book 'mathematical physics' probably vol 1 or 2. Something like this: If you have two cluster of gravitational matter at different temperature (measured by the kinetic energy, I think) and they pass through each other then we know from numerical experiment, that the cluster that was cooler before the 'collision' is even more ...


1

As a chemical engineer, I regard this from a very different perspective. Entropy and entropy change are a critical part of the definition and change in Gibbs free energy. Gibbs free energy is the basis in chemical engineering for not only assessing whether a mechanical process or work can be done. It is critical in the quantification of the behavior of ...


1

The entire gas does not heat up to Th all at once. First the boundary is at Th, and then the heat penetrates in further and further by (transient) heat conduction into the interior. So initially, the interior portion of the gas is still cold. It is like baking a turkey in the oven. First the outside heats up, and then the heat flows toward the middle. ...


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