| Interview
with Sir Martin Rees
The Times
Educational Supplement (Dec 1999)
Catching up with the Astronomer
Royal proved to be harder than I imagined. Unlike most
astrophysicists, Sir Martin Rees does not spend his
entire life nuzzled next to a telescope or sat behind
a computer, but rather travels whenever possible, extolling
the wonders of astronomy and the mysteries of cosmology
to the public. In between speaking at the British Association
Meeting in Sheffield, a Cambridge bookshop and in Barcelona,
he managed to spare a moment to meet for afternoon tea
following his talk at the Cheltenham Festival of Literature.
His Cheltenham lecture, which
had been sold-out days in advance, was given in a hall
filled with three hundred people, ranging from teenagers
attending Cheltenham Ladies’ College to dozens of gentile
Gloucestershire pensioners. They listened keenly to
a vivid explanation of the Big Bang and cosmological
evolution, illustrated with snapshots of the most distant
galaxies in the universe. He presents astrophysics with
wit and charm, ultimately giving the impression of a
humble man exploring the wonders of the universe, rather
than an arrogant master of the cosmos.
As well as giving him a greater
opportunity to speak to the public, the title of Astronomer
Royal also allows him to speak out about the issues
that concern him. For example, he feels that there is
some excellent science reporting, but he is currently
annoyed by the lack of coverage of British science,
a problem that is compounded by the regular reporting
of breakthroughs made in the United States. He acknowledges
that this is partly the fault of British scientists,
who can sometimes be rather diffident, and university
press offices, who sometimes be less than proactive,
but in the main he blames the British media.
“For instance, the BBC gives the impression that all
the
exciting advances are coming
from the United States,”
Sir Martin complains, “When
in fact there are equally
articulate and capable people
in this country who have
contributed to the subject.
To give one example,
“The Planets” series on BBC2
was rightly primarily
about NASA’s success, but the
Cassini mission was
a collaboration between the
European Space Agency
and America, whereas the programme
gave the
impression that it was an entirely
American mission.”
Although he would like to influence
how science is perceived and conducted, especially,
to ensure that the UK maintains its strong astronomical
tradition, he is well aware that the title of Astronomer
Royal does not have the same clout as other titles,
such as Poet Laureate.
“To
some extent it’s an embarrassment,” he says. “People
think the title gives
me some special influence, whereas in
particular with
PPARC (the astronomy funding committee)
I have had frustratingly little
influence on many of their
decisions, which I feel
have been sub-optimal over the years.”
The fact that Sir Martin is
a great populariser and politically active within
the astronomy community does not mean that he has neglected
research. His career has spanned four decades, and he
continues to be one of the most respected and eminent
astronomers in the world. However, he embarked on his
career with no real passion for the subject, and it
took an inspirational professor and a remarkable series
of astronomical discoveries to make him realise that
he should devote his life to exploring the universe.
As an undergraduate, Sir Martin
had studied pure mathematics, and upon graduating he
considered pursuing careers in both statistics and economics.
However, he was taken under the wing of Dennis Sciama,
a Cambridge astronomer responsible for nurturing many
of the great figures in modern cosmology. Sciama worked
closely with the young Roger Penrose, now Sir Roger,
and he supervised Stephen Hawking, George Ellis and
Brandon Carter, before taking on Sir Martin as a PhD
student.
It soon became clear that Sir
Martin had stumbled into a rich and vibrant area of
physics, in which revolutionary discoveries were opening
new lines of research. During the latter half of the
1960s’s, astronomers discovered quasars, pulsars and
the microwave background radiation, forcing a radical
reshaping of astronomical and cosmological models, which
in turn heavily discounted the experience of established
physicists and created a level playing field for younger
researchers.
Quasars and pulsars were exciting
because they provided the first real testing ground
for Einstein’s theory of general relativity, the more
accurate successor to Newton’s theory of gravity, which
has only been useful for three centuries because our
experiences have been limited to small gravitational
forces. Newton’s law of gravity is satisfactory for
describing the orbit of planets in the weak gravity
of the Sun, and they are fine for calculating the consequences
of the even weaker gravity here on Earth, but the bizarre
astronomical objects discovered in the 1960s are held
together by such intense gravitational forces that Newton’s
theory has to be abandoned in favour of Einstein’s theory.
For example, a pulsar (a form
of neutron star) is the superdense core that remains
after a large star implodes in a supernova event. The
most spectacular confirmation of this scenario is the
Crab Nebula, which consists of debris flying away from
a central neutron star, the remnant of a supernova that
was observed by the Chinese in 1054 AD. The density
of a neutron star is such that the force of gravity
is a million million times greater than on Earth. This
force crushes anything on the surface of a neutron star,
so that all mountains are less than one millimetre in
height. However, climbing such a one millimetre mountain
would require an immense amount of energy, greater than
the energy required to launch a person on Earth into
orbit. These gravitational forces can only be explained
within the context of general relativity.
Prior to the 1960s, general
relativity described only hypothetical objects, but
now there existed real relativistic objects. At the
time, the astrophysicist Thomas Gold summarised how
the community reacted to the emerging field of relativistic
astrophysics and the changing role of relativity theorists:
“The relativists with their sophisticated work are not
only
magnificent cultural ornaments but
might actually be
useful
to science!”
Over the last thirty years,
Sir Martin has continued to study the physics of extreme
astronomical phenomena, including black holes and active
galactic nuclei. Most recently, he has focussed his
attention on gamma ray bursts, flashes that are incredibly
intense when they strike the Earth, even though they
originate from far across the universe. The flashes
last only a few seconds, and their power is equivalent
to the output of millions of galaxies. Sir Martin explains,
“We
believe that gamma ray bursts are connected with
either a peculiar kind
of supernova or perhaps two
neutron stars spiralling
together and merging. In either
case we are witnessing the formation
of a black hole
and the energetics of the material falling into it.”
Typically, astronomers detect
one gamma ray burst per day somewhere in the universe.
In addition to trying to explain
the physics of specific astronomical objects, Sir Martin
has also studied broader cosmological questions, namely
the evolution of the universe and the formation of galaxies.
He is particularly interested in the so-called Dark
Age, the period between the brilliant early phase of
the universe and the moment when stars ignited. Half
a million years after the Big Bang, the universe cooled
enough so that light shifted to a lower infra-red frequency,
which is beyond the visible spectrum. Visible light
was created once again roughly a billion years later
when first stars formed and began to shine. In other
words, Sir Martin is interested in what happened during
this phase of darkness – how did a cooling, largely
formless universe transformed itself into a structured
universe with stars?
The evolution of the universe
is, in part, the subject of Sir Martin’s new book, “Just
Six Numbers”, in which he points out how every
aspect of the universe’s evolution depends on the eponymous
six numbers. For example, one number, N, reflects the
strength of gravity relative to the strength of strength
of electrical forces. N is roughly 10^36, which means
that gravitational forces are a million million million
million million million times weaker than electrical
forces. This number is important, because had the force
of gravity been stronger, then stars would be formed
more quickly, and would also die more quickly. Stars
in this universe burn for roughly ten billion years,
but stars in a different universe, one with gravity
that is one million times stronger, would live for only
ten thousand years, which is not long enough for life
to evolve.
The other five numbers are
also critical to the fate of the universe, and the likelihood
of life is even more sensitive to changes in these numbers.
In other words, if the numbers that define our universe
were slightly different, then it would be a sterile
space, which prompts us to ask whether there is some
deeper significance to these numbers. Are we simply
lucky or is there a Creator who selected the numbers
in order to create a universe capable of sustaining
life?
According to Sir Martin, there
is a third possibility. He suggests that there is a
myriad of universes, collectively known as the multiverse,
each with its own values for the six numbers. The vast
majority of universes are sterile, but a few of them
can contain life. As we are alive, then we must, by
definition, find ourselves in a universe with the right
six numbers. The book is a digestible and engaging exposition
of this astonishing theory,
Evidence in favour of the multiverse
theory might be too long in coming, particularly as
Sir Martin feels that we are in another Golden Age of
astronomical discovery, similar to the mid-1960s when
he began his research. For example, physicists are working
on superstring theories that might help describe the
earliest phase of the universe, while experimentalists
are hunting down the so-called dark matter. Furthermore,
ground-based telescopes and the Hubble Space Telescope
have observed galaxies that are further away and younger
than any previously seen, which may provide vital clues
to illuminate the Dark Age.
However, regardless of any
potential discoveries, Sir Martin is confident that
there will always be a healthy stock of unsolved problems.
He is fond of Richard Feynman’s analogy between physics
and chess:
“Imagine you’d never seen chess being played before,
then by watching a few games,
you could infer the
rules. Physicists, likewise,
learn the laws that
govern the universe. In chess,
learning the
moves is just a trivial preliminary
on the
absorbing progress from novice
to grand
master; similarly, even if
we knew the basic
laws, exploring how their consequences
have
unfolded over cosmic history
is an unending quest.” |
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