[cdn-nucl-l] Science: The Most Versatile Physicist of His Generation

["Adam McLean" <adam.mclean@utoronto.ca>]

Printed in Science Magazine, volume 296, Number 5565, Issue of April 5,
2002, pp. 49-50 and at:
http://www.sciencemag.org/cgi/content/full/296/5565/49

Adam

-------------

PORTRAITS OF SCIENCE:
"The Most Versatile Physicist of His Generation"
Mary Jo Nye*
"The most versatile and the best loved physicist of his generation": so
said the British geophysicist Sir Edward Crisp Bullard in remembrance of
P. M. S. Blackett (1897-1974) (1).

Bullard had known Blackett at the Cavendish Laboratory, where Blackett
had supervised Bullard's experiments on electron scattering in hydrogen
gas, before Bullard left particle physics for geophysics in 1931.
Bullard and Blackett worked together in the 1940s in operational
research at the British Admiralty, and Bullard afterward observed
Blackett shift his laboratory research from particle physics and cloud
chambers to the Earth's magnetic field, paleomagnetism, and
magnetometers. Widely admired for his craft as an experimental
physicist, Blackett was noted, too, for his broadly ranging theoretical
interests in quantum electrodynamics, gravitation, and continental
drift. A war veteran, Blackett had served in the Royal Navy during the
first world war, and he was a civilian founder of operational research
during the second world war. Blackett's range of expertise was truly
unusual.

However, if Blackett was versatile, he also was controversial. This is
the same Blackett who was said by the Times [of London] in 1974 to have
been a "Radical Nobel-Prize Winning Physicist" who had been "committed
too far to the [political] left for [even] a Labour Government to employ
with ease" (2). Although many regarded Blackett as a hero for his
achievements as a British physicist and his wartime role in operational
research, others villified him for his postwar criticism of British
wartime and Cold War military strategy. On facing pages of his local
newspaper, the Manchester Guardian, appeared two articles about Blackett
on 5 November 1948. One news item reported that Blackett had won the
Nobel Prize in Physics. On the opposite page stood a review by the
American sociologist Edward Shils of Blackett's book, The Military and
Political Consequences of Atomic Energy. Shils baldly characterized
Blackett's opposition to development of atomic weapons as a Stalinist
apology in which Blackett's analytical powers had fallen sway to
political prejudices (3).

At root in the controversy over Blackett was not simply his political or
military point of view, but his very right to express a strong opinion
outside the field of physics. To Blackett, the objection that "science
and politics do not mix" made no sense, especially with regard to
military questions: "Why I should stick to Physics ... I cannot quite
conceive. Anyway I have spent eleven years of my life in warfare. That
gives me a title to talk about it" (2, 3). In feeling that he had an
obligation to speak out, Blackett shared the perspective of British
scientists in the leftist and sometimes marxist "social relations of
science" movement of the 1930s and, for that matter, of French
scientists engaged in 1930s Popular-Front politics. The French physicist
Paul Langevin remarked of his own political activism, "The scientific
work that I do can be done by others ... but unless the political work
is done there will be no science at all" (4).

Blackett had a commanding presence in British scientific life. It was a
physical and social presence, as well as an intellectual and political
one. Tall and slim, always described as "handsome," admired for dressing
well, Blackett entered Ernest Rutherford's Cavendish Laboratory in 1921
as one of the few physicists of his generation to have served and
survived in combat during the first world war before beginning studies
at the University of Cambridge (5). He had seen action in the Falklands
in 1914 and at Jutland in 1916, serving as First Lieutenant controlling
gunnery fire on the H.M.S. Sturgeon off Terschelling in 1918. In his
naval education at Osborne and Dartmouth naval colleges during
1910-1914, Blackett had enjoyed what was probably the most intensive
physical science and engineering secondary education available in
England. While on wartime duty, Blackett obtained his first (jointly
authored) patent, which described an instrument for measuring the rate
of change of bearing in order to compute the firing of guns. By the time
he walked into the Cavendish, he was considerably accomplished in tools,
inventions, and instruments, but also in self-discipline, self-reliance,
and experience of leadership (6). Then, as later, he was a man of strong
opinions and apparent confidence.

Assigned by Rutherford in 1921 to modify an automatic cloud chamber,
Blackett worked diligently to perfect the instrument in the face of
Rutherford's impatience for results. In the summer of 1924 Blackett
obtained eights tracks (from 23,000 photographs), confirming a nuclear
transformation. His photographs showed the paths of an incident alpha
particle that was captured by a nitrogen nucleus; an ejected proton; and
the recoiling oxygen nucleus. These photographs have been widely
reprinted ever since (7).

Blackett spent the 1924-25 academic year with James Franck in Göttingen
and returned to Cambridge with new expertise from theoretical
discussions with Paul Dirac and members of the informal physics club
that met in the rooms of Peter Kapitza. Blackett's next set of
path-breaking experiments came in the early 1930s when he collaborated
with Giuseppe Occhialini to devise a cloud chamber controlled by a
Geiger-Müller counter, in which expansion of the cloud chamber was
triggered by passage of charged particles through the chamber.

In late 1932, Carl D. Anderson at Caltech published an observation of a
positively charged particle, with mass smaller than a proton, in cosmic
radiation. He initially characterized its production as a rare event. By
February 1933, Blackett and Occhialini had completed a paper summarizing
their analysis of some 500 tracks of cosmic-ray particles, of which 14
tracks were evidence of an anti-electron or positive electron, which
they explicitly linked to Dirac's relativistic electron theory. Some
physicists thought it unfortunate that Blackett and Occhialini appeared
to have delayed publication, in order to get firmer data on the positive
electron within the framework of Dirac's theory, so that it was Anderson
who received the Nobel Prize in Physics for the "discovery of the
positron" in 1936.

In 1933, Blackett moved to Birkbeck College in London and, in 1937, to
Manchester, returning to London in 1954 to Imperial College. His
research groups gathered evidence for the cosmic-ray cascade or shower
effect, which he and Occhialini had first noted in their February 1933
paper. Lively debate occurred in the mid-1930s over the identity of a
particle that Anderson and Seth Neddermeyer interpreted as a "mesotron"
or heavy electron and that Robert Serber and Robert Oppenheimer
suggested was the theoretical particle predicted by Hideki Yukawa in
1935. Cecil Powell and colleagues at Bristol found Yukawa's particle
(the pi-meson) in cosmic radiation in 1947, demonstrating that the
particle decayed into the mesotron (mu-meson) and a neutrino. In the
same year, at Blackett's Manchester laboratory, George Rochester and
Clifford Butler announced discovery of another new particle, evidenced
by a V-shaped track, which they interpreted, with Blackett's advice, as
the result of decay of a heavy neutral ("strange") particle (8).

At this time Blackett moved away from cosmic-radiation studies, when he
became intrigued by an old hypothesis that the magnetic fields of the
Sun, stars, and Earth are a fundamental property of their rotating mass.
In 1952, Blackett announced that he had failed to confirm this theory
following a series of experiments using a magnetometer, which he
designed, to detect minuscule magnetic effects in a rotating cylinder.
Blackett noted the suitability of his magnetometer for a new field of
investigation and turned his research group's efforts to measurement of
remanent magnetism (paleomagnetism) in sedimentary rocks, leading to a
new kind of evidence for Alfred Wegener's hypothesis (1912) of
continental drift. Stanley Keith Runcorn, Edward A. Irving, and John A.
Clegg were among those who worked at some point with Blackett's
magnetometer and its successor instruments, contributing to a new
geophysics based on the theory of the continents' past motions in
relation to the Earth's magnetic pole (8).

Magnetic effects and magnetic mines had been a practical concern of
Blackett's during the war. He had been recruited by Henry Tizard in
early 1935 to join an Air Ministry committee charged with investigating
the use of radio waves in air defense. At the time, the political Left,
with which Blackett was sympathetic, was largely pacifist, but pacifism
was a sympathy that Blackett did not share. In 1940, Blackett was
scientific adviser to the Army's anti-aircraft command, organizing a
group of scientists to study the operational use of radar, guns, and
mechanical calculators for anti-aircraft fire. In the Royal Air Force's
Coastal Command, he headed a group that recalculated depth settings for
antisubmarine explosives. At the Admiralty from 1942 to 1945, his
operational research group brought about significant improvement in the
use of airborne radar for finding German submarines that were sinking
merchant ships in the Atlantic (7).

At war's end, Blackett made public his wartime arguments against
saturation bombing of German cities. As demonstrated by Shils's review,
Blackett's 1948 book, republished in 1949 in the United States under the
title, Fear, War and the Bomb, excited anger and invective because of
its sympathy with Soviet objections to American plans for control of
atomic energy, its criticism of the bombing strategy during the war
(escalated at Hiroshima and Nagasaki), and its debunking of claims that
bombs and the air force alone can win a war (3).

During the next decade, Blackett excoriated applications of game theory
to nuclear war by scholars at the RAND Corporation, the Hudson
Institute, and Princeton University. By the time that Blackett's
collection of essays, Studies of War: Nuclear and Conventional, was
published in 1962, many of his arguments no longer seemed radical,
especially his reiterated warnings that nuclear weapons would not make
conventional war outmoded and that cutbacks in nuclear and conventional
weapons should be negotiated in tandem (9).

Blackett's postwar publications and speeches gained scrutiny from
American embassies, the American FBI, and, likely, British security's
MI5. He came under suspicion, too, for his Third-World sympathies. In
particular, he was criticized by many members of his scientific audience
for using the occasion of his Presidential Address at the Dublin Meeting
of the British Association for the Advancement of Science in 1957 to
advocate massive foreign aid to underdeveloped countries, particularly
from the UK to former colonies. Scientists and engineers had a
particular responsibility in this matter, Blackett argued, because "it
is their genius and their skill which alone can bring the material basis
of happiness within reach of all.... The uneven division of power and
wealth, the wide differences of health and comfort among the nations of
mankind, are the sources of discord in the modern world, its major
challenge and, unrelieved, its moral doom" (7).

In a recent political history of the Nobel Prizes, Robert Marc Friedman
suggests that Blackett received the physics award in 1948 partly because
of Swedish Social Democrats' sympathy with scientific planning and with
international controls on nuclear weapons, as well as admiration for
Blackett's achievements in operational research (10). Of course, it was
Swedish physicists and members of the Swedish Academy of Sciences who
decided the award, not the Social Democratic leadership. In the official
presentation speech for Blackett in Stockholm, the experimental
physicist Gustaf Ising noted that the physics prize may be awarded for
"discovery or invention" and that the award to Blackett was motivated on
both grounds: Blackett's leadership in the development of the Wilson
cloud chamber and the discoveries that he had made with the method. If
Blackett's politics won him some sympathy in Sweden, it was his
versatility and distinction in the practice of physics that gained him
the Prize, as well as the admiration of physicists and geophysicists
such as Bullard.

References

E. C. Bullard, Nature 250, 370 (1974). 
M. J. Nye, Phys. Perspect. 1, 136 (1999). 
P. M. S. Blackett, Military and Political Consequences of Atomic Energy
(Turnstile, London, 1948). 
B. Swann, F. Aprahamian, eds., J. D. Bernal: A Life in Science and
Politics (Verso, London, 1999). 
A. Brown, Phys. World (April), 35 (1998). 
P. Hore, ed. Patrick Blackett: A Biography (Frank Cass, London, in
press). 
B. Lovell, Biograph. Memoirs Fellows R. Soc. 21, 1 (1975). 
M. J. Nye, Br. J. Hist. Sci. 32, 69 (1999). 
P. M. S. Blackett, Studies of War: Nuclear and Conventional (Oliver and
Boyd, Edinburgh, 1962). 
R. M. Friedman, The Politics of Excellence: Behind the Nobel Prize in
Science (Freeman, New York, 2001). 

------------------------------------------------------------------------
--------
The author is in the Department of History, Oregon State University,
Corvallis, OR 97331, USA. E-mail: nyem@ucs.orst.edu