The Misunderstood Nature of Entropy | Space Time



Entropy and the second law of thermodynamics has been credited with defining the arrow of time.

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Previous Episode:
Quantum Invariance & The Origin of The Standard Model

Entropy is surely one of the most intriguing and misunderstood concepts in all of physics. The entropy of the universe must always increase – so says the second law of thermodynamics. It’s a law that seems emergent from deeper laws – it’s statistical in nature – and yet may ultimately be more fundamental and unavoidable than any other law of physics.

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23 thoughts on “The Misunderstood Nature of Entropy | Space Time

  • July 21, 2018 at 1:34 am
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    "…the ultimate heat death of the universe."
    Glad to know that science has weighed in on the end of eternity, having gathered the data to support – what – forty years ago? Science! We observe, then extrapolate, project by a few quadrillion millennia, and state as fact. Yep! We're waaaay better than religion.

    Reply
  • July 21, 2018 at 1:34 am
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    Money is a measure of how much work I can get someone to do for me. Since energy is the capacity to work, and money is proportional to how much work I can get done by proxy, does that prove communism, socialism, and other "share the wealth" systems are doomed to failure because they seek to distribute wealth evenly?

    I hate to bring politics into this, but if science is to reconcile our model of the world with the actual world, it is going to have to account for a political world.

    Reply
  • July 21, 2018 at 1:34 am
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    If Universe start in an Homogenous Distribution of Highly Uniform environment(High Energy) and expand to a Homogenous Distribution Highly Uniform (Low Energy) after expansion and Black Hole evaporation etc.. Shouldn't the Entropy be equal at the end vs at the beginning based on Botlzmann Definition of Microstate vs Macrostate possibility since there's no Gradient of energy to provide useful Work in both state and both are at the same probability state?

    Reply
  • July 21, 2018 at 1:34 am
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    This should be required study for creationists. They like to argue that evolution from single-celled organisms to multi-cellular ones, and on to, oh, say, humans, violates the "increasing disorder" misconception of entropy.

    Reply
  • July 21, 2018 at 1:34 am
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    By this definition of entropy, the probability of the entropy of a system spontaneously decreasing is not zero right? Although incredibly low. The probability of all gas particles in a room to (randomly) go back into a bottle is not zero, just incredibly small. And if we define the arrow of time as the direction in which entropy increases, then there is a non-zero probability for all time in the universe to reverse?

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  • July 21, 2018 at 1:34 am
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    Now I understand entropy and have stopped understanding energy. You introduced energy as a hand wave at the end of the episode without tying it to the statistical mechanics and macro states of entropy.

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  • July 21, 2018 at 1:34 am
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    At 6:16 or so you state that the microstate with all of the stones at the upper left " is 2*10^107 less likely than one of the many smoothly mixed microstates." This is incorrect. It's exactly as likely as any ONE of the many smoothly mixed microstates. The difference is that there are many more smoothly mixed microstates. But any given one of them is as unlikely as the one with all of the stones on and above the diagonal. Also, you mention "heat must flow…." relying on the incorrect concept that heat is a substance. I understand that you're trying to put things in a simple and comprehensible form but please don't do so by making false statements.

    Reply
  • July 21, 2018 at 1:34 am
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    Why is there a division by T in Clausius entropy equation (ΔS=ΔQ/T) ? In a higher temperature, entropy would increase less for the same amount of added heat? Why???

    Reply
  • July 21, 2018 at 1:34 am
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    Ok.. but, what happens after heat death? Eventually all the fundamental forces will tear themselves apart as the expansion of the universe continues unabated, right? Like.. eventually everything gets reduced to essentially just a bunch of individual massless particles moving at the speed of light but isolated causally from everything else. Therein lies the problem, because causality only makes sense if there is time. Distance and time lose scale entirely once everything is massless.. Wait, does that mean the end and the beginning are the same thing? Statistically speaking, if time and distance no longer have scale it'll essentially just immediately run through every possible configuration instantly.

    Wait wait.. What about the strong force? That increases in strength over distance to such an extent that pulling two quarks apart causes two new quarks to spontaneously pop into existence to fil the gap. If the space between those particles were expanding faster than the speed of light, wouldn't that just cascade into.. well.. a shitload of quarks?

    Reply
  • July 21, 2018 at 1:34 am
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    Note that entropy can decrease from time to time, just shortly, but it happens. From Quora (Jack Wimberley, Ph.D.): The second law of thermodynamics does not absolutely state that the entropy of a finite system cannot decrease – only that the probability of it doing so vanishes in the limit that its size becomes infinite.

    Reply
  • July 21, 2018 at 1:34 am
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    I know that you are trying to make things understandable through analogy, but comparing a Go board to the molecules in a room is just simply wrong. When randomly placing pieces on a board, you get 1X10^107 possible combinations because that's what statistics tells you. In order to get all the molecules in the room to move to one side you would have to physically introduce order which takes energy equal to or greater than the average energy of the system. Only if the age of the universe could be infinite would you get that result randomly. NOT because of random chance, but because of physical characteristics of air molecules and ambient energy in the room. The universe is not a Go board, don't dumb down a topic to the point of absurdity.

    Reply
  • July 21, 2018 at 1:34 am
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    Does this mean that in any particle space one cannot use a limit to infinity argument since you then have to deal with a non enumerable number of substates? How then do you apply calculus to statistical mechanics?

    Reply

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