5 ms·

What does entropy have to do with anything?

by vecter 12y ago

lutusp 12y ago
Entropy = the inverse of available energy to do anything at all. EDIT: Look -- if you don't understand physics, don't compound your ignorance by downvoting the posts of people who do. Instead, post a written objection, and I will explain why you're wrong.
- vecter 12y ago
  I'm pretty sure entropy isn't what's stopping us from probing high energy levels.
  - lutusp 12y ago
    That's true -- we're a long way from being limited by entropy in experimental physics.
- possibilistic 12y ago
  I don't like that definition. I like to consider ∆S the result of a smoothing operation over energy differentials. You can put work into a system to reestablish an energy differential. It just necessitates obtaining that other energy differential with which to do the work.
  - lutusp 12y ago
    >> Entropy = the inverse of available energy to do anything at all. > I don't like that definition. Physics isn't a popularity contest. http://en.wikipedia.org/wiki/Entropy http://en.wikipedia.org/wiki/Entropy > You can put work into a system to reestablish an energy differential. Yes, but that doesn't change the definition of entropy -- it just borrows energy from somewhere else.
    - possibilistic 12y ago
      I feel like you're being that guy. Forgive me if I come across the same way. Why link me to the Wikipedia article or insinuate I'm pulling this out of--to put it more politely--ex culo? Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived. To be pedantic for a bit, Entropy is an abstract mathematical state function useful for the prediction of thermodynamic systems. Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you. Mathematically speaking, I think you got your equality / definition wrong. Which energy function do you refer to? If you are still convinced about an error on my part, you can demonstrate in classical thermodynamics that, S = "the inverse of available energy to do anything" Or stats thermo, if that's how you roll. (Mine isn't that great anymore, sadly.)
      - lutusp 12y ago
        > I feel like you're being that guy. What's my incentive to continue a discussion with someone who has abandoned the topic? In a closed system, the amount of exploitable energy, and the quantity called entropy, move in opposite directions. > ... or insinuate I'm pulling this out of--to put it more politely--ex culo? Point to where I said this. If you can't, then you have abandoned the topic. > Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you. Nonsense. Entropy is clearly understood, it's not a philosophical puzzle as you suggest. It's easily quantifiable. It's science, not philosophy. > Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived. Anyone can adopt the notations used in science. This doesn't tell me anything about their knowledge of the topics under discussion. You simultaneously apply standard terminology, but you go on to say that explaining entropy is "not unlike looking for God or faeries or what have you", which means you don't understand the significance of the symbols you used. Entropy = k log(n) k = Boltzmann's constant. n = number of states the system can be in. How difficult is that? http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper2.html http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper2.ht... Quote: "Temperature is expressed as the inverse of the rate of change of entropy with internal energy, with volume V and number of particles N held constant. This is certainly not as intuitive as molecular kinetic energy, but in thermodynamic applications it is more reliable and more general."
  - coldtea 12y ago
    >I don't like that definition. Yeah, but physics aren't a la carte. Either prove it wrong (and get a nobel) or accept it.
    - possibilistic 12y ago
      See my reply to sibling comment.
- lifeisstillgood 12y ago
  Well, I don't think I understand entropy - even after Wikipedia. So is there somewhere in universe some energy that is not available to do anything at all? How does that work? Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? If so how did it get to that state?
  - lutusp 12y ago
    > Well, I don't think I understand entropy - even after Wikipedia. Okay, here's a commonly used explanation. Entropy and time are bound together -- as time passes, overall entropy increases (with local violations like us). This is one idea about why time "moves" in the direction it does -- if time were to reverse, we could tell because some classic entropy results would run in reverse, violating common sense. Imagine that there's a room, and in one corner of the room there's a perfume bottle. At time zero, the cork is removed from the perfume bottle. Because of entropy, the tendency of isolated systems to move from order to disorder, the perfume disperses through the room. Ask yourself what the probability is for the perfume to spontaneously recombine in the bottle, versus the probability that it will disperse through the room. That probability differential is a measure of entropy. > So is there somewhere in universe some energy that is not available to do anything at all? Sure -- any isolated system can eventually get to a point where no useful work can be performed. Imagine an engine without any temperature differentials anywhere, or any way to acquire a temperature differential from an external source. Such an engine cannot do useful work. A steam engine requires a heat source and a heat sink. Without a temperature differential, the engine cannot function. Same with a gas engine. > Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? But without tapping an external energy source, the energy in an isolated system won't concentrate itself or spontaneously create a temperature differential suitable for exploitation. In an isolated system, the level of disorder always increases over time. > If so how did it get to that state? Simple physics. For two masses having a temperature difference, one with temperature "a", the other "b", and a temperature conductivity of "k", they will eventually reach the same temperature this way: Δ = (b-a) e^(-t k) Δ (delta) = temperature difference at time t a = temperature a b = temperature b t = time k = energy transfer coefficient The above refers to an isolated system with an initial temperature difference. As time passes, that difference declines.
dspillett 12y ago
If the available energy is dispersed and chaotic, we won't be able to concentrate enough to perform the experiments? Though I doubt that'll be the case at any time while the human race is in existence... (caveat: I know very little of real physics)
- lutusp 12y ago
  > If the available energy is dispersed and chaotic, we won't be able to concentrate enough to perform the experiments? That's a layman's definition of entropy, but we're a long way from that state.
- Drakim 12y ago
  If humanity lives to a point where entropy becomes a problem, I'm pretty sure our lives would be the first to go, not our "ability to perform experiments".
  - serf 12y ago
    that entirely depends on the magnitude of the experiment. If we were approaching any "universal energy" limitations, it'd stand to reason that our technology would be very much different than our technology now -- perhaps universe sized experiments would be feasible by that point, at which time we may hit a limit imposed on us not by anything other than the length of time since the last universe formation event, and our poor luck in meeting that point in technology at a time where the energy no longer exists to fuel it. Unlikely, and I think your idea of life being threatened before science is probably much more rational, but it's fun to think about. Plus, if we were using that much energy for a single experiment, one would wonder about that experiments' safety.
- mwest 12y ago
  You might enjoy Isaac Asimov's short story: The Last Question http://www.multivax.com/last_question.html http://www.multivax.com/last_question.html I recommend you read the whole thing, but if you're looking for a plot summary: http://en.wikipedia.org/wiki/The_Last_Question#Plot_summary http://en.wikipedia.org/wiki/The_Last_Question#Plot_summary

What does entropy have to do with anything?

by vecter 12y ago

What does entropy have to do with anything?

Entropy = the inverse of available energy to do anything at all. EDIT: Look -- if you don't understand physics, don't compound your ignorance by downvoting the posts of people who do. Instead, post a written objection, and I will explain why you're wrong.

vecter 12y ago
I'm pretty sure entropy isn't what's stopping us from probing high energy levels.
- lutusp 12y ago
  That's true -- we're a long way from being limited by entropy in experimental physics.
possibilistic 12y ago
I don't like that definition. I like to consider ∆S the result of a smoothing operation over energy differentials. You can put work into a system to reestablish an energy differential. It just necessitates obtaining that other energy differential with which to do the work.
- lutusp 12y ago
  >> Entropy = the inverse of available energy to do anything at all. > I don't like that definition. Physics isn't a popularity contest. http://en.wikipedia.org/wiki/Entropy http://en.wikipedia.org/wiki/Entropy > You can put work into a system to reestablish an energy differential. Yes, but that doesn't change the definition of entropy -- it just borrows energy from somewhere else.
  - possibilistic 12y ago
    I feel like you're being that guy. Forgive me if I come across the same way. Why link me to the Wikipedia article or insinuate I'm pulling this out of--to put it more politely--ex culo? Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived. To be pedantic for a bit, Entropy is an abstract mathematical state function useful for the prediction of thermodynamic systems. Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you. Mathematically speaking, I think you got your equality / definition wrong. Which energy function do you refer to? If you are still convinced about an error on my part, you can demonstrate in classical thermodynamics that, S = "the inverse of available energy to do anything" Or stats thermo, if that's how you roll. (Mine isn't that great anymore, sadly.)
    - lutusp 12y ago
      > I feel like you're being that guy. What's my incentive to continue a discussion with someone who has abandoned the topic? In a closed system, the amount of exploitable energy, and the quantity called entropy, move in opposite directions. > ... or insinuate I'm pulling this out of--to put it more politely--ex culo? Point to where I said this. If you can't, then you have abandoned the topic. > Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you. Nonsense. Entropy is clearly understood, it's not a philosophical puzzle as you suggest. It's easily quantifiable. It's science, not philosophy. > Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived. Anyone can adopt the notations used in science. This doesn't tell me anything about their knowledge of the topics under discussion. You simultaneously apply standard terminology, but you go on to say that explaining entropy is "not unlike looking for God or faeries or what have you", which means you don't understand the significance of the symbols you used. Entropy = k log(n) k = Boltzmann's constant. n = number of states the system can be in. How difficult is that? http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper2.html http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/temper2.ht... Quote: "Temperature is expressed as the inverse of the rate of change of entropy with internal energy, with volume V and number of particles N held constant. This is certainly not as intuitive as molecular kinetic energy, but in thermodynamic applications it is more reliable and more general."
- coldtea 12y ago
  >I don't like that definition. Yeah, but physics aren't a la carte. Either prove it wrong (and get a nobel) or accept it.
  - possibilistic 12y ago
    See my reply to sibling comment.
lifeisstillgood 12y ago
Well, I don't think I understand entropy - even after Wikipedia. So is there somewhere in universe some energy that is not available to do anything at all? How does that work? Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? If so how did it get to that state?
- lutusp 12y ago
  > Well, I don't think I understand entropy - even after Wikipedia. Okay, here's a commonly used explanation. Entropy and time are bound together -- as time passes, overall entropy increases (with local violations like us). This is one idea about why time "moves" in the direction it does -- if time were to reverse, we could tell because some classic entropy results would run in reverse, violating common sense. Imagine that there's a room, and in one corner of the room there's a perfume bottle. At time zero, the cork is removed from the perfume bottle. Because of entropy, the tendency of isolated systems to move from order to disorder, the perfume disperses through the room. Ask yourself what the probability is for the perfume to spontaneously recombine in the bottle, versus the probability that it will disperse through the room. That probability differential is a measure of entropy. > So is there somewhere in universe some energy that is not available to do anything at all? Sure -- any isolated system can eventually get to a point where no useful work can be performed. Imagine an engine without any temperature differentials anywhere, or any way to acquire a temperature differential from an external source. Such an engine cannot do useful work. A steam engine requires a heat source and a heat sink. Without a temperature differential, the engine cannot function. Same with a gas engine. > Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? But without tapping an external energy source, the energy in an isolated system won't concentrate itself or spontaneously create a temperature differential suitable for exploitation. In an isolated system, the level of disorder always increases over time. > If so how did it get to that state? Simple physics. For two masses having a temperature difference, one with temperature "a", the other "b", and a temperature conductivity of "k", they will eventually reach the same temperature this way: Δ = (b-a) e^(-t k) Δ (delta) = temperature difference at time t a = temperature a b = temperature b t = time k = energy transfer coefficient The above refers to an isolated system with an initial temperature difference. As time passes, that difference declines.

dspillett 12y ago

If the available energy is dispersed and chaotic, we won't be able to concentrate enough to perform the experiments? Though I doubt that'll be the case at any time while the human race is in existence... (caveat: I know very little of real physics)

lutusp 12y ago
> If the available energy is dispersed and chaotic, we won't be able to concentrate enough to perform the experiments? That's a layman's definition of entropy, but we're a long way from that state.
Drakim 12y ago
If humanity lives to a point where entropy becomes a problem, I'm pretty sure our lives would be the first to go, not our "ability to perform experiments".
- serf 12y ago
  that entirely depends on the magnitude of the experiment. If we were approaching any "universal energy" limitations, it'd stand to reason that our technology would be very much different than our technology now -- perhaps universe sized experiments would be feasible by that point, at which time we may hit a limit imposed on us not by anything other than the length of time since the last universe formation event, and our poor luck in meeting that point in technology at a time where the energy no longer exists to fuel it. Unlikely, and I think your idea of life being threatened before science is probably much more rational, but it's fun to think about. Plus, if we were using that much energy for a single experiment, one would wonder about that experiments' safety.
mwest 12y ago
You might enjoy Isaac Asimov's short story: The Last Question http://www.multivax.com/last_question.html http://www.multivax.com/last_question.html I recommend you read the whole thing, but if you're looking for a plot summary: http://en.wikipedia.org/wiki/The_Last_Question#Plot_summary http://en.wikipedia.org/wiki/The_Last_Question#Plot_summary