5 ms·

Nanoparticle Temporarily Violates the Second Law of Thermodynamics

23 points by srikar 13y ago

infinity0 13y ago
It's not "violating" that law if it's only temporary. "In the long run" is part of the definition of that law.
- allthatglitters 13y ago
  One might also say that it's a "temporary" perpetual motion machine...
- adlpz 13y ago
  Additionally, the second "law" of thermodynamics doesn't even make sense at those scales. It pretty much just shows that, in a given (isolated) system, there are way more "unordered" possible states (degenerate) than "ordered" states, and due to basic statistics, in the long run the system will progress towards being in those more probable states. If the system is simple enough, the probability of jumping to a less-degenerate state is large enough, and eventually, will happen.
  - tormeh 13y ago
    Exactly. The probability that shards will meld into a glass pane and water will form a snowman is nonzero, but simply very low. There are no absolutes here.
    - logicchains 13y ago
      If the many worlds interpretation of waveform collapse is correct, it's possible that there's actually a universe somewhere in which the entire arctic is covered in such snowmen.
      - evanb 13y ago
        The many worlds interpretation of wavefunction NON-collapse, I think you mean :). And it is a guarantee that if it is not physically impossible for it to have happened, there is a branch of the universal wavefunction as you describe.
      - lloeki 13y ago
        I can't find the reference to the giant marshmallow hypothesis, stating that it perfectly probable (although possibly scarcely) that there exists a giant marshmallow that formed somewhere in space out of sheer luck. Probably Terry Pratchett or Douglas Adams.
Confusion 13y ago
That the 2nd law can be temporarily violated on nanometer scale is not news: that was already experimentally demonstrated years ago. The interesting thing in this publication is that they experimentally verified a certain theoretical description of that phenomenon.
ThePhysicist 13y ago
Well the second law of thermodynamics really isn't a law of physics but of probability, since it basically states that it is very improbable for a macroscopic system to go from a state with more disorder to a state with less. An example: If you take a glass chamber that is partitioned by a removable wall and where one side initially contains a given number N of non-interacting particles with random velocities, whereas the other side is empty. When you remove the wall between the two halves, the particles will start flying around freely in the chamber and will distribute roughly equally in the two halves. Now, the probability that they will again concentrate in only one of the halves of the chamber decreases exponentially with their number (as 2^N), so for macroscopic particle numbers (typically > 10^20) you would have to wait a VERY long time for this to happen. For a small number of particles, or a single nanosphere like in the article, it might well happen though.
- darkmighty 13y ago
  Well there's a little more physics to it, namely that biases towards certain distributions are small -- i.e. that systems always have paths to a large number of states. The laws of physics has to be such that they exhibit asymptotic equipartition. In your example, assuming that particles positions are iid over the entire container generates the second law, but only because the dynamics of the system allow such approximation -- imagine instead that particles liked to almost irreversibly "stick together", then the system would converge to most particles on a single side.
  - ThePhysicist 13y ago
    Yeah that's true of course and why I assumed they are non-interacting. It's of course a gross simplification of the real theory but it explains quite well why entropy increases in a closed system and as an explanation is not conceptually wrong.
interstitial 13y ago
When it comes to the 2nd Law of Thermodynamics, internet discussions are like the old biased coin toss: "Heads the 2nd law is true, Tails the 2nd law is not not true". I wish Karl Popper was still around.
mbrutsch 13y ago
> However, when we zoom into the microscopic world of atoms and molecules, this law softens up and looses its absolute strictness. Hard to take a science article seriously when they write like an 8th grader.

23 points by srikar 13y ago

infinity0 13y ago

It's not "violating" that law if it's only temporary. "In the long run" is part of the definition of that law.

allthatglitters 13y ago
One might also say that it's a "temporary" perpetual motion machine...
adlpz 13y ago
Additionally, the second "law" of thermodynamics doesn't even make sense at those scales. It pretty much just shows that, in a given (isolated) system, there are way more "unordered" possible states (degenerate) than "ordered" states, and due to basic statistics, in the long run the system will progress towards being in those more probable states. If the system is simple enough, the probability of jumping to a less-degenerate state is large enough, and eventually, will happen.
- tormeh 13y ago
  Exactly. The probability that shards will meld into a glass pane and water will form a snowman is nonzero, but simply very low. There are no absolutes here.
  - logicchains 13y ago
    If the many worlds interpretation of waveform collapse is correct, it's possible that there's actually a universe somewhere in which the entire arctic is covered in such snowmen.
    - evanb 13y ago
      The many worlds interpretation of wavefunction NON-collapse, I think you mean :). And it is a guarantee that if it is not physically impossible for it to have happened, there is a branch of the universal wavefunction as you describe.
    - lloeki 13y ago
      I can't find the reference to the giant marshmallow hypothesis, stating that it perfectly probable (although possibly scarcely) that there exists a giant marshmallow that formed somewhere in space out of sheer luck. Probably Terry Pratchett or Douglas Adams.

Confusion 13y ago

That the 2nd law can be temporarily violated on nanometer scale is not news: that was already experimentally demonstrated years ago. The interesting thing in this publication is that they experimentally verified a certain theoretical description of that phenomenon.

ThePhysicist 13y ago

Well the second law of thermodynamics really isn't a law of physics but of probability, since it basically states that it is very improbable for a macroscopic system to go from a state with more disorder to a state with less. An example: If you take a glass chamber that is partitioned by a removable wall and where one side initially contains a given number N of non-interacting particles with random velocities, whereas the other side is empty. When you remove the wall between the two halves, the particles will start flying around freely in the chamber and will distribute roughly equally in the two halves. Now, the probability that they will again concentrate in only one of the halves of the chamber decreases exponentially with their number (as 2^N), so for macroscopic particle numbers (typically > 10^20) you would have to wait a VERY long time for this to happen. For a small number of particles, or a single nanosphere like in the article, it might well happen though.

darkmighty 13y ago
Well there's a little more physics to it, namely that biases towards certain distributions are small -- i.e. that systems always have paths to a large number of states. The laws of physics has to be such that they exhibit asymptotic equipartition. In your example, assuming that particles positions are iid over the entire container generates the second law, but only because the dynamics of the system allow such approximation -- imagine instead that particles liked to almost irreversibly "stick together", then the system would converge to most particles on a single side.
- ThePhysicist 13y ago
  Yeah that's true of course and why I assumed they are non-interacting. It's of course a gross simplification of the real theory but it explains quite well why entropy increases in a closed system and as an explanation is not conceptually wrong.

interstitial 13y ago

When it comes to the 2nd Law of Thermodynamics, internet discussions are like the old biased coin toss: "Heads the 2nd law is true, Tails the 2nd law is not not true". I wish Karl Popper was still around.

mbrutsch 13y ago

> However, when we zoom into the microscopic world of atoms and molecules, this law softens up and looses its absolute strictness. Hard to take a science article seriously when they write like an 8th grader.