Streams of electrons shoot at your monitor's
screen from behind, and where an electron hits, it kicks out
a packet of light energy. Energy is exchanged in fixed discrete
quantities, Einstein's "quanta." So a particular screen material,
hit by an electron, releases a light packet with a specific
amount of energy.
In the retina of your eye there are molecules
in which the links between atoms are under tension, like tiny
mousetraps that can be set off by a specific energy. (Different
energies will appear to you as different colors, red or blue
or green.) When a light packet of the right energy strikes a
molecule of the right type, it may trigger the molecule to straighten
out. This snap launches reactions that send a signal up a nerve
to your brain.
But the molecule is not always triggered.
Sometimes the light just goes on through, without transferring
its quantum of energy. Bohr held that it is a matter of pure
chance whether the interaction will happen in any particular
case. What can be calculated is the probability that
the energy will be exchanged--say, seven out of ten times that
a light packet meets a molecule of a given type. If your eyes
were more sensitive, at very low levels of light you would see,
instead of a constant image, a sparkling, "grainy" picture made
up of random flashes.
Is nature truly random at its foundations?
Recent experiments at extremely low light levels have found
examples of the strange behavior that Bohr's interpretation
predicts. Einstein lost the debate... But Bohr has not won it.
Physicists today continue to debate how to explain the intractably
weird laws of quanta.
You can EXIT to Todd's introduction to quantum mechanics.