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symmetry (and relative simplicity), of his equation. He noticed that the
equation would work just as well for positively charged particles as for the
negatively charged electrons. He then proposed that for every particle there
exists a corresponding anti-particle, with nearly identical properties to the
original particle, except that it has the opposite electric charge. This led to
the concept of antimatter, which consists of anti-particles in the same way
that matter is constructed from ordinary particles.
As a result, in the first few decades of the 20th Century physicists (and
chemists alike) had arrived at a fairly consistent picture of the structure of
matter. All substances were composed of chemical compounds, whose basic
building blocks were molecules, which were themselves constructed from an
arrangement of atoms. The simplest possibility was a material (known as an
element ) constructed from only one type of atom. The atoms were not indivisible, as had been assumed by Democritus and Dalton, but were composed
of a nucleus surrounded by a cloud of electrons. The nucleus was made
up of neutrons and protons. It appeared that protons, neutrons and electrons, together with photons, were all that was necessary to explain the world
around us. Physicists at this time had reason to feel well-satisfied, even smug
with their achievements.
However, this happy state of self-congratulation lasted only for a short
time before other particles began to be discovered, demanding an explanation
for their existence. Also, one would expect the positively charged protons to
repel each other electrostatically and fly apart, rather than suffer confinement
within the bounds of the nucleus, unless there were some stronger, as yet
unknown, nuclear forces binding them together.
Before addressing these problems, however, we must digress to explore how
particles interact with each other. Besides the direct collision of one particle
with another, it was clear that particles must also interact in a more indirect manner. This phenomenon was dubbed action at a distance, and it takes
place when the like poles of two magnets repel each other, or two electrically charged objects deflect each other. It involves ideas gradually developed
over many years, until coming to fruition in the 19 th Century with the new
concept of a field . 2
We have already explored gravitational “action at a distance”, aka the gravitational field, in the last Chapter, and seen how Einstein explained this
phenomenon as a consequence of the warping of the fabric of space–time
by the large mass of heavy objects. An analogous explanation does not exist
for electromagnetic fields, or the fields produced by nuclear forces. This is
2 Michael Faraday coined the term “field” in 1849. A field can be defined as the region in which the
effect of a given force is felt. It extends throughout a large region of space.
R. Barrett and P. P. Delsanto
symmetry (and relative simplicity), of his equation. He noticed that the
equation would work just as well for positively charged particles as for the
negatively charged electrons. He then proposed that for every particle there
exists a corresponding anti-particle, with nearly identical properties to the
original particle, except that it has the opposite electric charge. This led to
the concept of antimatter, which consists of anti-particles in the same way
that matter is constructed from ordinary particles.
As a result, in the first few decades of the 20th Century physicists (and
chemists alike) had arrived at a fairly consistent picture of the structure of
matter. All substances were composed of chemical compounds, whose basic
building blocks were molecules, which were themselves constructed from an
arrangement of atoms. The simplest possibility was a material (known as an
element ) constructed from only one type of atom. The atoms were not indivisible, as had been assumed by Democritus and Dalton, but were composed
of a nucleus surrounded by a cloud of electrons. The nucleus was made
up of neutrons and protons. It appeared that protons, neutrons and electrons, together with photons, were all that was necessary to explain the world
around us. Physicists at this time had reason to feel well-satisfied, even smug
with their achievements.
However, this happy state of self-congratulation lasted only for a short
time before other particles began to be discovered, demanding an explanation
for their existence. Also, one would expect the positively charged protons to
repel each other electrostatically and fly apart, rather than suffer confinement
within the bounds of the nucleus, unless there were some stronger, as yet
unknown, nuclear forces binding them together.
Before addressing these problems, however, we must digress to explore how
particles interact with each other. Besides the direct collision of one particle
with another, it was clear that particles must also interact in a more indirect manner. This phenomenon was dubbed action at a distance, and it takes
place when the like poles of two magnets repel each other, or two electrically charged objects deflect each other. It involves ideas gradually developed
over many years, until coming to fruition in the 19 th Century with the new
concept of a field . 2
We have already explored gravitational “action at a distance”, aka the gravitational field, in the last Chapter, and seen how Einstein explained this
phenomenon as a consequence of the warping of the fabric of space–time
by the large mass of heavy objects. An analogous explanation does not exist
for electromagnetic fields, or the fields produced by nuclear forces. This is
2 Michael Faraday coined the term “field” in 1849. A field can be defined as the region in which the
effect of a given force is felt. It extends throughout a large region of space.