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Tiniest Lamp Spans Quantum, Classical Physics 59

Posted by kdawson
from the just-small-enough dept.
Urchin writes "Physicists in California have made the smallest ever incandescent lamp using a carbon nanotube as the filament. The nanotube is so small it behaves as a quantum mechanical system but it's just large enough that the classical physics rules of thermodynamics should apply. Analyzing the light emitted from the tiny light will give the team a better picture of what happens in the twilight zone between the quantum and classical worlds." The New Scientist article doesn't mention the researchers' surprise, as the abstract does: "Remarkably, the heat equation and Planck's law together give a precise, quantitative description of the light intensity as a function of input power, even though the nanotube's small size places it outside the thermodynamic limit."
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Tiniest Lamp Spans Quantum, Classical Physics

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  • by A beautiful mind (821714) on Friday May 01, 2009 @10:27AM (#27786729)
    ...of course. It's just that the rules we recognize as classical laws of physics work well enough at that scale for us not to notice the effects that had to be explained by quantum physics.
  • by pablomme (1270790) on Friday May 01, 2009 @10:42AM (#27786861)

    Obviously. Which isn't to say that the concept of a classical regime versus a quantum one isn't useful. You wouldn't describe the motion of a baseball using Schroedinger's equation: it's perfectly possible, but impractical.

    Any information we can get about the transition between the two regimes is very valuable indeed.

  • by DriedClexler (814907) on Friday May 01, 2009 @10:54AM (#27787009)

    Obviously. Which isn't to say that the concept of a classical regime versus a quantum one isn't useful. You wouldn't describe the motion of a baseball using Schroedinger's equation: it's perfectly possible, but impractical.

    Good point. I was browsing Douglas Hofstadter's I Am a Strange Loop recenlty, and he made a great point about levels of description. He notes that when we discover "X is reducible to the more fundamental phenomenon of Y", people seem to think that means Y is more important and useful. But, he says, that discovery is equivalent to "Y can be ignored at the level X". That is, even though there might be a lower-level description, the discovery of enough regularity at that level is also useful since it means a simpler way to describe what's going on.

  • by Rich0 (548339) on Friday May 01, 2009 @12:25PM (#27788619) Homepage

    Agreed. If quantum mechanics were truly practical then we chemists would be out of jobs. :)

  • The history of science suggests that exploring the intersection of two bodies of theory is a very important kind of experiment. It was Thomas Young's double slit experiments [wikipedia.org], Planck's study of blackbody radiation [wikipedia.org], and Einstein's work with the photoelectric effect [wikipedia.org] that revealed the necessary clues to the quantum theory that resolved the paradox of the apparent wave/particle duality of electromagentic radiation.

    It took 19th century classical physicists an entire century to resolve this issue, so long that the discipline became a little stagnant and some folks were beginning to claim that physics had explained everything there was to explain. However, Planck's work was especially important in revealing the quantized energy nature of light that was the key to opening up 20th century physics. [wikipedia.org]

    Anyway, to keep this short, I suggest that we find ourselves in a similar situation. Our current models have been played out, and are leaving a lot of important questions unanswered. There are a few candidate theories that hold promise but aren't supported by observations. Looking at the cracks between our building blocks worked before -- it opened up whole universes of possiblility. We need to keep doing it. This experiment is a great example of that kind of work.

  • by plasmacutter (901737) on Friday May 01, 2009 @01:59PM (#27790223)

    They would make a lot more money by making the world's tiniest violin with nano-tubes, and mailing it to, in order:

    bank executives
    auto executives
    the **AA and member companies
    right-wing talking heads seen in recent clips on episodes of the daily show.

  • by radtea (464814) on Friday May 01, 2009 @03:28PM (#27791547)

    that resolved the paradox of the apparent wave/particle duality of electromagentic radiation.

    We didn't actually resolve the paradox, we just showed that we didn't have to resolve it to do useful calculations. The legacy of positivism and the Copenhagen Interpretation has been to simply sweep the whole question under the carpet.

    Even modern approaches that attempt to explain the central question of quantum theory, which is "How does the classical world arise out of quantum phenomena?" don't actually answer it. They just make you feel better about it, distracting you from the fact that they have explained nothing. The whole Many Worlds approach is like this: it actually says nothing about why consciousness experiences only one of the many possible outcomes, despite its rather clever intellectual edifice.

    To look at it another way, if all you knew about was the quantum universe of smoothly evolving probability densities, you would never guess at the existence of the classical universe at all. You would never suspect there was such a thing as "wavefunction collapse" (or any of its conceptual equivalents in different interpretations.) You would simply be aware (insofar as awareness might be possible in such a universe) that the various components of wavefunctions decohere smoothly over time due to interactions and entanglements with systems that have many degrees of freedom. You would not under any circumstances say, "Hey, all the components of that wavefunction just vanished except for this one!" Yet that is what WE say all the time, and no one has a clue as to why it happens.

    My own take on this is that far from being some bizarre quantum phenomenon, consciousness is fundamentally classical in a way that physics is not. This is a Kantian view, that there are necessary conditions to consciousness that are more restrictive than the general conditions of existence.

    So far, no empirical test of any interpretation of quantum mechanics (except experimental violations of Bell's Inequalities, which rule out any local causal interpretation) have been proposed. It may be that systems like this one will allow for novel tests, and in any case they are likely to put a finer point on the fundamental question even if they get us no closer to answering it.

"A great many people think they are thinking when they are merely rearranging their prejudices." -- William James

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