The Centenary Of Quantum Physics 8
OCatenac writes: "This article at the Economist regarding the 100th anniversary of Max Planck's discovery of Quantum Physics is interesting. Thought other /. readers might find it interesting too."
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The Centenary of Quantum Physics
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Re:The author of this article... (Score:1)
Thereby ending all reporting on physics, politics, and life in general.
Re:The author of this article... (Score:1)
You say: I wonder if the author of this article can tell me how the wave-nature of electrons is used to make lasers and LED's?
The author says:
Solutions to the Schrödinger wave equation dictate that an electron, no matter how smeared-out, can reside only within such a band
Put it another way: The existence of discrete electron orbitals is a consequence of the wave-nature of electrons. (It is an if-and-only-if consequence)The solutions of the Schrödinger equation describe these orbitals although it gets kinda hard to solve for extended materials.
Think about ruby or He-Ne lasers. There can only be population inversions in the energy levels if discrete (quantized) orbitals existed - or as the author says:
Solutions to the Schrödinger wave equation dictate that an electron, no matter how smeared-out, can reside only within such a band.
You Again:
but there is no way to prevent there from being a gradient in between these regions.
The existence of conduction/valence bands (and the gradient)is an IFF consequence of the existence of quantized electron orbitals due to the wave nature of electrons.
If the wave nature did not exist (and therefore no discrete orbitals), then electrons could assume any energy value and the band gap between the P-N junction would not exist. No PN junction, no diode, transistor, or LED.
The story of wondering about the light bulb is apocryphal but not wrong if you consider that Wien's displacement law predicts a different color for radiating bodies than what is observed. So, what the author is saying is that the yellow that is observed for the typical light bulb is not what is predicted by theory. Why should the author spend another page explaining the black-body radiation problem (linear Temp/Freq relationship for low temps and exponential relationship for high temps) when a concrete physical example exists?
You again:
First of all, Planck did not discover quantum mechanics. He postulated quantized energy levels.
You are right about that, but I'm mystified about your rant as the article nowhere says that "Planck discovered quantum mechanics".
It said:
For to solve his problem, Planck had had to invent the notion of the quantum.
The author did have this to say as well:
But, although he was the first to be confounded by quantum mechanics, he would not be the last.
Re:The author of this article... (Score:2)
Actually, you are a bit mistaken
ultraviolet catastrophe . . . exponentially more radiation as the wavelength got shorter.
You mean the infra red catastrophe. but names make no difference. what is important is that classical calculations predict exponential increases in radiation at longer wavelengths. This is in fact why light bulbs are yellow, and not more red. It is because the peak of the plank spectrum at the temperature that incandescant bulbs are at is in the yellow part of the spectrum
there are also some minor problems with your other explanations, however, I do agree with you that journalists should know what they are talking about before they write.
OT: Account Logged In! (Score:1)
Interesting (Score:1)
Re:The author of this article... (Score:1)
Schroedinger OTOH, engaged in a pretty nasty philosophical debate over the fundamentals of quantum mechanics with Bohr and went and attempted to back up his position by looking for a reformulation of quantum mechanics as a differential equation. Philosophically he turned out to be incorrect, but the work and effort that he put forth advanced quantum mechanics both mathematically and philosophically. The math he did was much nastier than de Broglie's, and the philosophical debate he was engaged in was a lot more advanced than what I see in de Broglie's suggestion that matter was a wave and a particle.
I guess I'm just more impressed by hard work than by insight.
Re:The author of this article... (Score:2)
The Rayleigh-Jeans spectral distribution of blackbody radiation has the form required by Wein's law: the energy density varies with the inverse fifth power of the wavelength. This leads to an exponential increase in energy density with decreasing wavelength, which is referred to as the "ultraviolet catastrophe," just as the previous poster said (what's catastrophic is the complete failure of the Rayleigh-Jeans spectrum, which is a necessary consequence of classical physics).
Pick up any introductory modern physics text -- it will say precisely what I (and dmatos) just did.
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The author of this article... (Score:3)
First of all, Planck did not discover quantum mechanics. He postulated quantized energy levels. That's all. Of course, perhaps he did discover quantum mechanics. I can see him now, in a dusty library, in some dark corner that no-one has been in for centuries. He trips on a tome that someone has carelessly left in the middle of the aisle, and crashes into a bookcase. After the ensuing chaos, what lands on his lap but the volume "Quantum Physics, a Beginner's Guide." Perhaps then you could say he "discovered" quantum physics.
Secondly, anyone who has ever looked at a physics text book knows that quantized energy levels explain the ultraviolet catastrophe, not why a light bulb is yellow, for chrissake! Classical calculations show that a radiating blackbody would have exponentially more radiation as the wavelength got shorter. Not only is this not what is observed, but it would lead to infinite energy being radiated by the blackbody. It was Planck's postulation that energy levels were quantized that resolved this.
Now, I wonder if the author of this article can tell me how the wave-nature of electrons is used to make lasers and LED's? LED's work as they do because Gallium Arsenide is a direct bandgap material, meaning that in order to transition from the valence band to the conduction band (take a course on the electrical properties of materials) the electron only needs energy, as opposed to in silicon where it needs both energy and momentum. That means that it is easier for an electron to drop back down from conducting band to valence band in GaAs, emitting only energy - read this as light. Nowhere does the wave nature of the electron come into this. Laser diodes are based on the same principle. Go read a book.
As for the description of how a transistor works, that is a hell of a lot of bullshit. He's correct in the fact that a transistor consists of electron rich and electron poor (commonly called n-type and p-type doped semiconductors) regions, but there is no way to prevent there from being a gradient in between these regions. His Schrodinger equation explanation is also crap. Apart from the infinite potential well problem, there is a solution to the Schrodinger equation for every point in space. It is just required to be continuous and smooth (ie, first and second derivatives must exist). Right now, transistors work because of potential. When you apply the necessary voltage to the gate of a transistor, it attracts enough electrons or holes (opposite of electrons when studying materials) to allow a conductive pathway between the source and the drain. This is true for BJT's and most FET's. The other option is that the gate voltage will drive away the electrons or holes, and "pinch off" the current. This is how a JFET works.
Dammit, I really wish that these "journalists" would pick up a text book before they write crap like this.