100th Anniversary of Quantum Physics

EricR writes "On December 14, 1900, Max Planck presented experimental results in front of the German Physical Society and announced that they could best be explained if energy exists in discrete packets, which he called "quanta." Today is the 100th birthday of Quantum Physics."

Comments

Enrico Fermi Institute - Dec 2nd

[VoidEngineer]

Gotta love quantum physics...

Check out the University of Chicago's Physics Department for all the information you could want to know about modern research in quantum physics.

Oh, and December 2, 2002 was the 60th Anniversy of the first self-sustaining controlled release of nuclear energy

Sorry about the spelling...

[VoidEngineer]

Since I goofed on the last post, I'll add the obligatory links to:

CERN
The Enrico Fermi Institute
Fermi National Accelerator Laboratories
Agronne National Laboratories
Los Alamos National Laboratories

Yep, all the information you could want on modern Quantum Physics.

What Planck actually discovered

[CactusCritter]

The wavelength distribution of blackbody radiation had been determined some (many?) years earlier. However, no one could figure out how to to explain how it could come about.

Somehow, Planck worked out an equation which yielded that wavelength distribution quite precisely. I believe that it is correct that his model was a "what if" conjecture about energy exisiting in discrete packets.

As discussed, the rest is history.

53 years of passing time has dimmed my memory, but I'm pretty sure that is the story.

Re:What Planck actually discovered

[Anonymous Coward]

wavelength distribution, while approximatedearlier than planck, wasn't known exactly. They just had some function(s) that fit the known data (ie, corrected the rayleigh-jeans ultraviolet catastrophe).

Plank showed, by solving statistically-mechanically, a series of independent discrete quanta(estimating the photon oscillation as simple-harmonic), the allowed spectrum was consistent with the observed data.

Lucky for him, simple harmonic oscillators have that exact energy spectra (E=hbar*omega(N+1/2)) where N is the energy-level (or quantum number) of the oscillator. Lucky guess, or insight of pure genious. No other (that i know of) systems have such an energy spectra (evenly-spaced, singly occupied). simple examples are particle-in-box and hydrogen atom.

This method of the blackbody radiation as quantum simple-harmonic oscillators is also very nearly similar to calculating the specific heat of crystals (Einstein method for independent oscillators, but corrected by Debye for coupled oscillators up to a sharp cutoff frequency).

This, though, ushered in new tidings, not just for pure quantum physics, but for statistical physics of quantum objects (bosons, fermions) which have different statistical distributions than classical particles (maxwell-boltzmann statistics). paved the way for solid-state physics to burgeon forth (hello transistors!!!)

Re:Quantum Physics -- entanglement

[etcshadow]

Wow... I don't even know where to start...

"it doesn't even matter how far apart they are in the universe; they'll always do the same things at the same times no matter where they are in the universe"

Wrong wrong wrong wrong wrong. Quantum entanglement says that the two particles *started off the same (or opposite or some such relationship of the initial states). It follows, then that if you do not *observe* either particle for quite some time, and take the two of them far distant from one another, then the instant that you *observe* the state of one particle, you immediately *know* the state of the other particle (wherever it is).

This gives at first pass the illusion that you have gotten information at faster than the speed of light... I mean, you did just *instantaneously* learn the state of a particle far, far away, right? That's gotta mean that you communcated with that thing way over there, right? No. Not at all.

Now, what makes this interesting is the fact that quantum mechanics tells us that if you don't *observe* either particle's state, then neither particle has actually "picked" a state yet. So, it's as though the one particle *told* the other one that "hey I was observed at state A, so you must now occupy state B". So, now it appears that information has traveled faster than the speed of light... and I won't argue that point, because last I knew better scientists than me were still duking that one out.

However, one thing that anyone with a basic understanding of this can agree upon is the fact that there is no way to *use* the possible information transfer involved in the collapse of a wave function to TRANSMIT INFORMATION. Why? Well, there is no way to observe a wave function directly. You can only measure some operator on a wave function (like energy, position, spin), and by doing so, you collapse the wave function into an eigenfunction of that operator. However there is no way to tell whether the eigenfunction you observe is the result of *your* observation or someone elses. In other words, you can't tell if you collapsed the wave function or if someone else did, and quantum entanglement doesn't *do* anything other than pre-collapse the wave-fcuntion for you.

Re:Richard P. Feynman said...

[grahamlee]

What Einstein disagreed with were things like the Uncertainty Principle, the EPR paradox (If he had lived to see it), and most likely even Schrodinger's Cat[1]. He disagreed with the assumptions that led to these conclusions.

I think his main problem was the idea of Universal instantaneous collapse of the wavefunction (which leads to "spooky action at a distance"[2] and God playing "dice with the Universe"). These concepts came from the Copenhagen Interpretation, and was the best way the Quantum theoreticians could think to explain the seemingly counterintuitive results of QM - it's pure philosophy and has nothing to do with the Physics.

Of course not everyone necessarily subscribes Copenhagen now. My personal favourite explanation is the proposition popular in the 80s and in Sliders - that multiple Universes are created at each instant multiple outcomes are possible, each reflecting the different outcomes.

So Einstein was most definitely NOT a supporter of quantum mechanics as we now know it.

Quantum mechanics as we currently know it includes Bose-Einstein statistics describing the behaviour of systems of integer-spin particles (which leads to the concept of a Bose-Einstein condensate - a highly active area of research today); Light Amplification by Stimulated Emission of Radiation (described at the atomic scale by the Einstein coefficients); quantisation of electromagnetic radiation (proposed by Einstein); Einstein's explanation of the photoelectric effect (for which he received the Nobel prize). Stretching the boundaries a little, there are equations for the equilibrium number of charge carriers in Solid State physics which rely on the quantisation of charge in the material. These are known as the Einstein equations.

Even the greatest can be mistaken.

Such as when he removed lambda from his equation on the state of the Universe (his "biggest blunder", indeed :-)).

[1]Point of order: even Schroedinger didn't believe in Schroedinger's Cat. He set it up as a thought experiment to show how absurd QM is (I mean, who could really believe in a dead/alive cat? Not him). The experiment has of course, since been done, sans cat.

[2]He believed that the "instantaneous" collapse of the wavefunction would lead to information being propagated instantaneously throughout the Universe. Of course, the wavefunction is not a measurable quantity so this does not occur.