Well, I didn't know it until I looked at the American Association of Physics Teachers calendar on my refrigerator today, but yes, it is Max Carl Ernst Ludwig Planck's birthday! He's got more middle names than Paul Adrian Maurice Dirac! I wonder who has the record for most middle names?
Yesterday was J. Robert Oppenheimer's birthday, which I already knew but is also noted on the calendar (as is Earth Day). He'd be 111. Julius is his first name. He went by Robert, or for some friends, Oppie. Maxie and Oppie were temperamental opposites. They died 20 years apart, MCELP in 1947 and JRO in 1967.
Planck won the 1918 Nobel Prize for his work, but Oppenheimer never did work deemed worthy of a Nobel. Of course, Oppenheimer's career took a sharp turn toward technological physics and administration duties during WWII, even though his talent was in theory. For instance: "In 1939, working with graduate student Hartland S. Snyder, Oppenheimer
discovered a solution of Einstein's equations of general relativity
describing the gravitational collapse of a massive star. This solution
shows how the star can end its life as a collapsed object. Such objects
were later observed and given the name "Black Holes." They are now known
to play an important role in the evolution of the universe." From Institute for Advanced Study website. Black holes, by the way, were named (1960s) long before their presence was observed indirectly (1990s) from the behavior of stars and gas whose orbital motion can only be explained (so far) by an invisible object with a very strong gravitational field. Observational evidence is now considered to be sufficient to confirm the existence of black holes.
(On second thought, Oppenheimer might have won a Nobel prize for his black hole prediction if he'd lived 10 or so years longer. But maybe not. Hawking's significant work on black holes has not yet resulted in a Nobel for him. Many people think he deserves one, and if he does, Oppenheimer and Snyder would have deserved one even more.)
Back to The Planck. One thing to keep in mind about Planck's derivation in 1900 of the correct black-body spectrum formula is that he didn't assume discrete frequencies, he assumed discrete energies, according to the relation E = nhf, where f is not restricted to integers, but because of that little n in there, E is. Because frequencies are not restricted to integers, there is a continuum of frequencies in black-body or thermal radiation emission and absorption.
Discrete or integer-related frequencies are emitted by isolated atoms, however, as first described theoretically for the hydrogen atom in 1913 by Niels Bohr.
Planck and Bohr were both trying to understand and mathematically describe the physical interactions responsible for already-known electromagnetic spectra. In Planck's case, it was the spectrum of heated solid objects. In Bohr's case, it was the "line spectrum" of discrete frequencies of light produced by individual hydrogen atoms. They succeeded where others had failed.
Planck in 1900 assumed a quantization of the energy levels in the material (the energy levels of the abstract oscillators of the material). He did not allow himself to think of light itself as being quantized. Einstein was the first modern physicist to suggest it was necessary to consider light itself to consist of quanta. He made this intellectual leap in 1905, in his theory of how electrons can be ejected from a clean metal surface by ultraviolet light, a process that was already known experimentally as the photoelectric effect.
Bohr's model of the atom also is based on the idea that light itself is emitted and absorbed as electromagnetic quanta. Bohr showed how discrete energy levels in the atom result from assuming that an electron's orbital angular momentum is quantized and equals integer multiples of Planck's constant h. He then applied Planck's formula in a new way to calculate how an electron going from one discrete energy level to another would absorb or emit a single frequency of light.
Bohr's model explains the spectrum of isolated hydrogen atoms, such as atoms in a gas discharge tube, where energy levels, and thus the frequencies of light seen in emission and absorption, are widely spaced. Planck's model applies to solids (or even near-solids such as molten metal), where atoms are packed together, meaning their collective energy levels are packed together. Arising from transitions between these slightly separated energy levels, the frequencies of emission and absorption of light are "packed together" also, giving a continuous spectrum. Graphs of this spectrum for different black-body temperatures can be seen in the next-to-last link in my previous post. You see light--mainly reflected from your surroundings--with this type of spectrum when you're in sunlight or in a room lit by an incandescent bulb. An electric heating element on a stove also produces this type of spectrum. (By the way, how hot do these get?)
My next post will discuss the equivalence of black-body radiation to radiation inside a certain kind of enclosure or "cavity".
Back to The Planck. One thing to keep in mind about Planck's derivation in 1900 of the correct black-body spectrum formula is that he didn't assume discrete frequencies, he assumed discrete energies, according to the relation E = nhf, where f is not restricted to integers, but because of that little n in there, E is. Because frequencies are not restricted to integers, there is a continuum of frequencies in black-body or thermal radiation emission and absorption.
Discrete or integer-related frequencies are emitted by isolated atoms, however, as first described theoretically for the hydrogen atom in 1913 by Niels Bohr.
Planck and Bohr were both trying to understand and mathematically describe the physical interactions responsible for already-known electromagnetic spectra. In Planck's case, it was the spectrum of heated solid objects. In Bohr's case, it was the "line spectrum" of discrete frequencies of light produced by individual hydrogen atoms. They succeeded where others had failed.
Planck in 1900 assumed a quantization of the energy levels in the material (the energy levels of the abstract oscillators of the material). He did not allow himself to think of light itself as being quantized. Einstein was the first modern physicist to suggest it was necessary to consider light itself to consist of quanta. He made this intellectual leap in 1905, in his theory of how electrons can be ejected from a clean metal surface by ultraviolet light, a process that was already known experimentally as the photoelectric effect.
Bohr's model of the atom also is based on the idea that light itself is emitted and absorbed as electromagnetic quanta. Bohr showed how discrete energy levels in the atom result from assuming that an electron's orbital angular momentum is quantized and equals integer multiples of Planck's constant h. He then applied Planck's formula in a new way to calculate how an electron going from one discrete energy level to another would absorb or emit a single frequency of light.
Bohr's model explains the spectrum of isolated hydrogen atoms, such as atoms in a gas discharge tube, where energy levels, and thus the frequencies of light seen in emission and absorption, are widely spaced. Planck's model applies to solids (or even near-solids such as molten metal), where atoms are packed together, meaning their collective energy levels are packed together. Arising from transitions between these slightly separated energy levels, the frequencies of emission and absorption of light are "packed together" also, giving a continuous spectrum. Graphs of this spectrum for different black-body temperatures can be seen in the next-to-last link in my previous post. You see light--mainly reflected from your surroundings--with this type of spectrum when you're in sunlight or in a room lit by an incandescent bulb. An electric heating element on a stove also produces this type of spectrum. (By the way, how hot do these get?)
My next post will discuss the equivalence of black-body radiation to radiation inside a certain kind of enclosure or "cavity".
