Welcome to Quantum Mechanics 101:
Just as physicists today wonder why there seems to be more gravity holding our Milky Way galaxy and the whole universe together than there should be, the big question in physics at the turn of the 20th century was the problem of "Cavity Radiation", more commonly called "Black Body Radiation".
Here is the problem that was keeping physicists awake at night:
If you take any hollow object and heat it until it glows, the spectrum of the electromagnetic energy (heat, light, etc.) that comes off the outer surface of that object will depend on both it's temperature and what it's made of.
But, if you drill a hole into that object, and measure the spectrum of the electromagnetic energy coming out of the hole, the spectrum you get depends only on the temperature, and is the same for all materials.
WTF?
The light, heat and everything that comes out of the hole had to originate at the interior surface of that hollow body, which is the same material as the outside surface, so why wouldn't the energy coming out the hole be the same regardless of what the object is made of?
In 1896, a german physicist by the name of Wilhelm Wien used theories of heat and electromagnetism that were current at his time to derive a theoretical equation which predicted experimental measurements of cavity radiation. Wien's theoretical equation was:
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The problem was that Wien's equation really didn't work well for all temperatures. That is, it was great theory, but it just didn't jive well with experimental data.
A young physicst by the name of Maxwell Planck was working on the problem of cavity radiation at the time and had developed an "emperical" equation which gave results that matched experimental results very accurately at all temperatures.
(An "emperical" equation is one that isn't based on any theory at all. You come up with an emperical equation by doing experiments, plotting the results on a graph to find out what kind of a curve you get looks like, and then coming up with an equation that matches that curve as closely as possible. Your equation might predict experimental results very accurately, but there's no reason why it should, so you can't learn anything from that equation.)
The emperical equation Max Planck had developed based on experimental data was:
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And it wasn't lost on Max Planck that the two equations were astonishingly similar!
When Planck read Wien's paper describing the derivation of his theoretical equation, Planck decided to work backward through Wein's derivation using his emperical equation as a starting, ...errr... ending point, to see if he could come up with a similar theoretical derivation of his emperical equation.
And, within two months he found he could do it. All he had to do was make two unsettling assumptions at the beginning of his derivation:
- that an atom could not have ANY amount of energy, only certain discreet amounts of energy. This is very much like saying that you cannot have ANY amount of money in your wallet, only multiples of the smallest amount of money, the penny. So, you can have .14 in your wallet or .15 in your wallet, but not pi dollars in your wallet. Similarily, you can't have a third of a dollar in change; you can only have 33 cents or 34 cents, but not 33.33333...... cents.
- that the vibration of atoms at any frequency neither consumed nor released any energy. Energy was released when an atom dropped from a high energy level to a lower energy level, and it was absorbed when an atom jumped from a lower energy level to a higher energy level, but the vibration of the atom at any given energy level required no energy at all.
On December 14, 1900, Max Planck presented the derivation of his equation to the Berlin Physical Society, but to physicist that were used to thinking about atoms as billiard balls and energy as waves, Planck's theoretical derivation seemed completely implausible because of the bizarre assumptions about matter and energy he had to make. So, prominant physicists of the time took no notice of him or his equation.
Unbeknownst to them, Max's presentation on December 14, 1900 turned out to be time and place of birth of the branch of physics that has come to be known as "Quantum Mechanics".
Subsequent experiments over the course of the next 17 years proved Max's "quantized" version of energy to be correct, and in 1918 Max Karl Ernst Ludwig Planck was awarded the Nobel Prize in Physics "in recognition of the services he rendered to the advancement of Physics by his discovery of energy quanta."
That is, if energy were money, Planck had discovered the penny.
Using Planck's new "quantized" version of electromagnetic energy, in the 1920's Neils Bohr was able to calculate what the light spectrum of monotomic hydrogen gas should be. And, he got it right. To four decimal places. That gave the Max Planck's version of things some serious credibility.
The discovery of the "energy quanta" put the first crack in our understanding of matter as being a particle and energy as being a wave. Subsequent experiments have proved conclusively that if you set up an experiment to prove that electromagnetic energy is a wave, you'll prove conclusively that it's a wave and not a particle. But, if you set up an experiment to prove that electromagnetic energy is a particle, you'll prove conclusively that it's a particle and not a wave. Today we have less confidence in our understanding of what matter and energy are than we did in 1900.
The only thing we know for sure is that the world of the very very small, the atom and smaller, is every bit as strange as Prof. Emlyn Hughes stripping down to his underwear and remaining in a fetal position as two assistants dressed up as ninjas blindfold stuffed animals against a backdrop of 9/11 and holocaust images played on a screen behind them...
.. and I applaud Dr. Hughes for being bold enough to teach that lesson to his students in such a spectacular and memorable way. No one who was there will ever forget it.