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
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.
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:
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:
And it wasn't lost on Max Planck that the two equations were
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:
1. 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 $3.14 in your
wallet or $3.15 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.
2. 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
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
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
.. 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.