CHRISTMAS LECTURE
SEVEN WONDERS OF SCIENCE
A Lecture by Professor Sir Michael Berry FRS on 9 December 1998
Professor Sir Michael Berry is the Royal Society Research Professor
of the University of Bristol.
The speaker was introduced to a packed house by Mr Victor Suchar who
outlined his distinguished career. The seven wonders were, of course,
a personal choice but Professor Berry was able to show that it illustrated
some of the great principles of physics. In his introduc tion, Sir
Michael pointed out that he was attracted to the topic by a series
on television, produced by Christopher Sykes, in which several eminent
scientists discussed seven aspects of science, and occasionally the
arts, which have inspired or influenced them.
The first topic was the Severn bore near Gloucester which Sir Michael
has seen on numerous occasions. He pointed out that tides are caused
by the gravitational pull of the moon and the sun on both the earth
and the sea, the effect of the moon being roughly twice that of the
sun. The net effect is of an outwards tide- raising force at points
both nearest and furthest from the moon which accounts for the two
tides per day. He pointed out that the Severn bore is a good example
of the flrst great unification in physics due to Newton who showed
that it was the universal force of gravitation which held us to the
ground, kept the moon in its orbit and created the tides.
His second example was the super numerary rainbow in which a dark
region separates the main rainbow from a second bright bow. Theories
of the rainbow go back as far as Descartes in 1638. To understand
it requires a knowledge of refraction and reflection of light as well
as the fact that light of different colours refract by different amounts.
This is known as dispersion of light and was first discovered by Sir
Isaac Newton who also proposed that the laws of reflection and refraction
could be explained in terms of rays. However, the supernumerary rainbow
cannot be explained by Newton's ideas but instead requires a wave
model in order to explain it since it involves light interference
effects. Sir Michael showed a fine picture of a supernumerary rainbow
taken at Newton's birthplace at Woolsthorpe in Lincolnshire.
His third example was an intriguing plastic boat-shaped object which
could only spin in one direction. This one-way spinner is a good example
of an object which is not quite symmetric and it is this small asymmetry
which gives rise to the striking effects observed. Despite its simple
appearance, the dynamics of the system is still not understood and
the one-
way spinner has proved to be a most intractable problem to analyse
mathematically. It received the attention of several mathematicians,
including an extensive analysis by G. H. Walker in 1899 which was
completed by Hermann Bondi in 1986. This proved that one direction
of
spin was stable while the other was unstable. Professor Berry pointed
out that symmetry breaking is an important aspect of modern physics.
The green flash is a striking and dramatic effect which can occasionally
be seen as the sun is setting, provided there is a clear, distant
horizon. It is generally seen if the sun is setting over water. It
is exactly what its name
implies: as the sun sinks below the horizon, there is a sudden green
gleam. It is a colour distortion or chromatic aberration due to the
earth and the air acting as a lens. It is a good example of the different
scales at which physics operates. According to legend, those who are
fortunate
enough to observe the green flash are supposed be lucky in love, although
Sir Michael did dispute this idea!
The fifth example is the mathematics of prime numbers which finds
important applic ations in the apparently completely unrelated area
of quantum chaology. Riemann zeros, so-called after the 19th century
mathematician who first studied them, are a set of of numbers derived
from the set of prime numbers.Years later, it was found that these
numbers were the same as the quantum energy levels of a chaotic system.
His penultimate example, related to a revealing analysis of fuel consumption,
which is expressed as a value C = miles/gallon i.e.
dimensionally as length/volume = L/L3 from which it can be calculated
that L=C-½ . Considering a typical car with a fuel consumption
of 40 miles/ gallon, and imagine the one gallon of petrol to be contained
in a tube 40 miles long, then the diameter of the tube would have
to be 0.25mm - not much more than a hair's breadth.
His final example related to the area of quantum exchange which is
fundamental to quantum mechanics. The question asked is what .happens
when two particles are exchanged. The problem embraces the Pauli Exclusion
Principle which is fundamental to the whole of chemistry and most
of biology. Professor Berry showed that one could make mechanical
analogies which are used in conjuring tricks such as balancing a glass
of water on one’s hand as your arm is turned through 360 degrees
vertically, without spilling it. He emphasised that there are
hidden solutions when two objects are exchanged.
This was the first Christmas lecture to be held by the BRLSI and was
indeed a tour de force. It will be a hard act to follow having been
given by a person who combines being a brilliant physicist and a brilliant
lecturer. In
a brief vote of thanks, Dr Peter Ford complimented Sir Michael on
his wit, erudition and deep insight into physics.
Peter Ford
