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More on Spintronics
segment writes "'We have discovered the equivalent of a new 'Ohm's Law' for spintronics - the emerging science of manipulating the spin of electrons for useful purposes,' says Shoucheng Zhang, a physics professor at Stanford. 'Unlike the Ohm's Law for electronics, the new 'Ohm's Law' that we've discovered says that the spin of the electron can be transported without any loss of energy, or dissipation. Furthermore, this effect occurs at room temperature in materials already widely used in the semiconductor industry, such as gallium arsenide.'"
Ohm's law is "voltage dropped across a load is directly proportional to the current through the load, for a constant load". What does this have to do with the law the article talks about?
Jason
ProfQuotes
You think that a news release covering a article in Science isn't going to be dumbed down? Or that Dr.Shou-Cheng has managed to fool Stanford, Santa Barbara, and IBM with his slick descriptions of 'imagine a planet orbiting around the sun'. Or possibly you have a better explanation of quantum spin that will eludicate the masses in 30 words or less?
"A language that doesn't affect the way you think about programming, is not worth knowing" - Alan Perlis
Don't sound so final about your statements. This might be redundant by now but things can be 100% efficent at the atomic level, as someone else stated, they always are. The problem is that at the macroscopic level we can no longer control individual microscopic actions/reactions.
Sorry, no.
Entropy is not an absolute law, but a law based on extreme probabilities. In any reaction, certain quantities are completely conserved. One of these is energy.
The increase in entropy that occurs is due to energy being converted into less usable forms, such as from motion (kinetic energy) to heat (thermal energy).
It is not actually a decrease in total energy. Energy is perfectly conserved in any reaction.
In subatomic reactions, there is no place for energy to go, so to speak. In fact, the only thing energy really is is the motion (and mass, though those are remarkably interlinked) of subatomic particles.
When two subatomic particles collide, if neither of them splits or gives of any other particles, the energy remains entirely in the two particle system (that is, all that changes is kinetic energy; speed). Well, direction changes as well.
Mod parent down; he is incorrect. (or not, I'm actually in favor of the mod up only philosophy, but parent would be a good one to mod down if you believe in modding factually incorrect posts down).
For to end yet again.
I'll believe it when I can order one from Digi-Key. :-)
--- Ban humanity.
The discussion on spin is wrong. Spin has nothing to do with the rotation of macroscopic objects like the Earth, it's an intrinsic quantum property of particles like the electronic with no macroscopic analog. The best explanation I've heard of spin that doesn't involve explaining the details goes like this: spin is a measurement of the number of rotations required to bring a particle back to its initial state. One-half spin particles, like the electron, require, counterintuitively, two full rotations to go back to their initial state.
The physical situation seems to have very little to do with Ohm's Law except in the loosest sense. They're describing a current consisting of electron spins under an external electric field. This has some interesting properties (I'd like to poke at the math, if I could read the paper), one of which seems to be that it is predicted to persist at much higher temperatures than the best superconductors. If so, because this spin current seems to be dissipationless, this would allow information to be transmitted without generating heat.
Interesting stuff; a pity the article was so poor.
Currently, the only thing confirmed to move faster than the speed of light (confirmed via the "alan aspect" experiments, if you want to google it), is the spin on a pair of electrons. Two elextrons in a pair alwats spin in reverse directions. Even if the two electrons are 1000 miles apart, if you polarize one (change the spin), then the other spin will reverse itself instaneously.
Close, but not exactly. You are not changing the polarization. This is a really bizzare part of quantum mechanics, but neither of the photons have a polarization before the measurement. It's not just that it is unknown - it doesn't exist. After the measurement then both photons will have polarizations and they will be opposite.
Let me give an example from memory. I hope I don't butcher it. Lets look at polarization in a single axis. The two possibilities will be +1 and -1. We can generate three linked photons X, Y, and Z. If you measure any single photon you get a random result. If you multiply any pair without looking at them you always get +1 (you don't know if it was +1*+1 or -1*-1, you only get to see the final result) and if you multiply all three without looking at them you always get -1. If you think about it a bit you'll see that there is no pattern of actual X, Y, and Z values that can ever guarantee those results. Basic algebra immediately leads to a contradiction. The only way it can possibly work is if X, Y, and Z don't actually have values before the measurement. When you make any meaurement on any of the linked photons the unmeasured ones instantaneously go from not having a value to having the value the linkage says it must have.
On the quantum mechanics level the universe functions in a completely different way than we are familiar with. It does things that are "obviously" impossible. If you assume that photons have an actual polarization value before the measurement you get a violation of basic algebra.
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