Scientists Watch as Heat Moves at the Speed of Sound
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Scientists Watch as Heat Moves at the Speed of Sound
1–10 of 33 posts
Re: Scientists Watch as Heat Moves at the Speed of Sound
#2As I understood the article, in one part of the experiment they set up alternate regions of heat and cold within a sample of graphite using interference patterns from two laser sources. When they turned off the lasers, instead of the hot regions dispersing their energy until the troughs were the same temperature, the hot regions "overshot", becoming cooler than the (former) troughs, with wave-like behaviour.
This seems to me like energy is momentarily flowing from a cooler region (the former "peaks") to a hotter area (the former "troughs").
Would a Real Physicist be kind enough to explain to me why this doesn't violate the 2nd law? Probably the answer is "you misunderstood".
Re: Scientists Watch as Heat Moves at the Speed of Sound
#3As I understood the article, in one part of the experiment they set up alternate regions of heat and cold within a sample of graphite using interference patterns from two laser sources. When they turned off the lasers, instead of the hot regions dispersing their energy until the troughs were the same temperature, the hot regions "overshot", becoming cooler than the (former) troughs, with wave-like behaviour. This see…
Not a "Real Physicist" but the information is not being lost, it's only being kept static-ish. This is the same as that waves don't violate the 2nd law (it's telling that they being called the phenomenon second sound.)
> The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time.
So instead of entropy increasing, it's hanging around for a while. No violation, still unusual though.
Re: Scientists Watch as Heat Moves at the Speed of Sound
#4This is the theory of phonons: pseudo particles which transfer heat in materials.
Re: Scientists Watch as Heat Moves at the Speed of Sound
#5As I understood the article, in one part of the experiment they set up alternate regions of heat and cold within a sample of graphite using interference patterns from two laser sources. When they turned off the lasers, instead of the hot regions dispersing their energy until the troughs were the same temperature, the hot regions "overshot", becoming cooler than the (former) troughs, with wave-like behaviour. This see…
Not a "Real Physicist" but the information is not being lost, it's only being kept static-ish. This is the same as that waves don't violate the 2nd law (it's telling that they being called the phenomenon second sound.) > The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. So instead of entropy increasing, it's hanging around for a while. No violation, sti…
Doesn't seem as if total entropy is increasing, simply rebalancing to the other side (which is still kind of interesting, like a wave in a pool).
Re: Scientists Watch as Heat Moves at the Speed of Sound
#6So the effect was known for a long time, and the new development is that it was now observed at higher temperatures. But 120 K is still pretty cold, so it doesn't really matter much for practical applications.
Re: Scientists Watch as Heat Moves at the Speed of Sound
#7Earlier quoted context omitted.
Not a "Real Physicist" but the information is not being lost, it's only being kept static-ish. This is the same as that waves don't violate the 2nd law (it's telling that they being called the phenomenon second sound.) > The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. So instead of entropy increasing, it's hanging around for a while. No violation, sti…
Doesn't seem as if total entropy is increasing, simply rebalancing to the other side (which is still kind of interesting, like a wave in a pool).
Yep, and energy is lost in the rebalancing process, and it oscillates until equilibrium, just like a pendulum.
Re: Scientists Watch as Heat Moves at the Speed of Sound
#8The effect appears at 120 Kelvin, or -240°F, so the article's assertion that this could revolutionize microelectronics seems like a stretch
Re: Scientists Watch as Heat Moves at the Speed of Sound
#9A quick first impression question: how important is the laser interference? Could you do this with a multi-centimeter graphite rod, by heating one end?
Re: Scientists Watch as Heat Moves at the Speed of Sound
#10The effect appears at 120 Kelvin, or -240°F, so the article's assertion that this could revolutionize microelectronics seems like a stretch
Right, and the article says you wouldn't need to do it at "cryogenic" temperatures. I thought this was funny: "Nobody ever thought that you would actually be able to do this at such high temperatures."