Consider a force like gravitation which varies predominantly inversely
as the square of the distance, but which is about a billion-billion-billion-billion
times stronger. And with another difference. There are two kinds of "matter",
which we can call positive and negative. Like kinds repel and unlike kinds attract -
unlike gravity where there is only attraction. What would happen?
A bunch of positives would repel with an enormous force and spread out
in all directions. A bunch of negatives would do the same. But an evenly mixed bunch
positives and negatives would do something completely different. The opposite pieces
would be pulled together by the enormous attraction. The net result would be that the terrific
forces would balance themselves out almost perfectly, by forming tight, fine mixtures of the
positive and negative, and between two separate bunches of such mixtures there would
be practically no attraction or repulsion at all.
There is one such force: the electrical force. And all matter is a mixture of positive protons
and negative electrons which are attracting and repelling with this great force. So
perfect is the balance, however, that when you stand near someone else
you don't feel any force at all. If there were even a little bit of unbalance you would know
it. If you were standing at arms length from someone and each of you had one percent
more electrons than protons, the repelling force would be incredible. How great?
Enough to lift the Empire State Building? No! The repulsion would be enough to lift
a "weight" equal to that of the entire earth.
You know, of course, that atoms are made with positive protons in the nucleus and with
electrons outside. You may ask: "If this electrical force is so terrific, why don't the protons
and electrons just get on top of each other? If they want to be in an intimate mixture, why isn't it
still more intimate?" The answer has to do with quantum effects. If we try to confine our
electrons in a region that is very close to the protons, then according to the uncertainty
principle they must have some mean square momentum which is larger ther more we try
to confine them. It is this motion, require by the laws of quantum mechanics, that keeps the
electrical attraction from bringing the charges any closer.