170
R. Barrett and P. P. Delsanto
on a billiard table, we cannot tell if the video is running forwards or backwards. We also cannot tell whether the video has been left-right reflected,
i.e. whether we are actually watching a mirror image of the collision. This is
because all the laws of classical physics are symmetric with respect to these
types of interchange.
This symmetry can manifest itself in many ways. For instance, suppose
we wish to communicate to another intelligence in a faraway galaxy, and tell
them that we drive on the left-hand side of the road 4 , how can we do it by
words alone? Concepts such as left or right are mere conventions, and classical
physics does not offer us any experiment that we could ask our far-off friends
to perform which might help them distinguish left from right. The weak
interaction, however, provides us with a solution. An experiment to measure
the spin of the electrons emitted in beta decay, a process that involves the
weak interaction, will show an asymmetry that enables us to define the left
and right directions unambiguously [1].
It is also interesting to note that complex biological molecules have a lefthandedness, which may be a consequence of their all being descended from
an original left-handed molecule aeons ago. Chemicals manufactured in the
laboratory normally have equal numbers of left and right-handed molecules.
It is worth debating whether extra-terrestrial life, if we discover it sometime in
the future, will display a similar left-handedness in its constituent molecules.
As its name suggests, the strength of the weak interaction is much less than
that of the strong interaction, by a factor of approximately 10 -6. (Because the
weak force decays much more quickly with distance than the strong force, this
factor is hard to define precisely.) It is also only about 10 -4 times as strong as
the electromagnetic interaction. Its range is of the order of 10 -18 m, which is
1/1000 that of the strong force.
Following the same methodology used by Feynman in QED, and by
Yukawa for the strong force, Sheldon Lee Glashow, Abdus Salam, and Steven
Weinberg in the 1960s independently proposed a scheme for the weak force,
analogous to QED. However, a particular symmetry requirement could only
be met if the electromagnetic force were also included into their scheme. The
result is a composite electroweak interaction. This development generated great
excitement at the time, as it was seen as the first step towards a Theory of
Everything, an overarching theory, uniting all four forces into one. This was
the goal pursued in vain by Einstein for the latter half of his life. It seemed
the journey he had been seeking had at last begun, and excitement was in the
air.
4 Well, some of us do, anyway.
R. Barrett and P. P. Delsanto
on a billiard table, we cannot tell if the video is running forwards or backwards. We also cannot tell whether the video has been left-right reflected,
i.e. whether we are actually watching a mirror image of the collision. This is
because all the laws of classical physics are symmetric with respect to these
types of interchange.
This symmetry can manifest itself in many ways. For instance, suppose
we wish to communicate to another intelligence in a faraway galaxy, and tell
them that we drive on the left-hand side of the road 4 , how can we do it by
words alone? Concepts such as left or right are mere conventions, and classical
physics does not offer us any experiment that we could ask our far-off friends
to perform which might help them distinguish left from right. The weak
interaction, however, provides us with a solution. An experiment to measure
the spin of the electrons emitted in beta decay, a process that involves the
weak interaction, will show an asymmetry that enables us to define the left
and right directions unambiguously [1].
It is also interesting to note that complex biological molecules have a lefthandedness, which may be a consequence of their all being descended from
an original left-handed molecule aeons ago. Chemicals manufactured in the
laboratory normally have equal numbers of left and right-handed molecules.
It is worth debating whether extra-terrestrial life, if we discover it sometime in
the future, will display a similar left-handedness in its constituent molecules.
As its name suggests, the strength of the weak interaction is much less than
that of the strong interaction, by a factor of approximately 10 -6. (Because the
weak force decays much more quickly with distance than the strong force, this
factor is hard to define precisely.) It is also only about 10 -4 times as strong as
the electromagnetic interaction. Its range is of the order of 10 -18 m, which is
1/1000 that of the strong force.
Following the same methodology used by Feynman in QED, and by
Yukawa for the strong force, Sheldon Lee Glashow, Abdus Salam, and Steven
Weinberg in the 1960s independently proposed a scheme for the weak force,
analogous to QED. However, a particular symmetry requirement could only
be met if the electromagnetic force were also included into their scheme. The
result is a composite electroweak interaction. This development generated great
excitement at the time, as it was seen as the first step towards a Theory of
Everything, an overarching theory, uniting all four forces into one. This was
the goal pursued in vain by Einstein for the latter half of his life. It seemed
the journey he had been seeking had at last begun, and excitement was in the
air.
4 Well, some of us do, anyway.