杏吧原创

POPULAR belief has it that science is the preserve of logical Mr Spocks. A
great scientific discovery must surely spring from a series of logical steps,
each taken coolly and calmly, in the rational order. But take some time to leaf
through the pages of history and you will find the surprising truth. Some of the
greatest discoveries in science were only made because logic fell by the wayside
and some mysterious intuition came into play.

Fortune has occasionally smiled on those who abandon all reason, and what
better year to celebrate them than 1996? For it is exactly 100 years since the
French chemist Henri Becquerel was led鈥攂y an unfounded belief that certain
rocks emit X-rays and some inexplicable experiments in his laboratory in
Paris鈥攖o one of the most monumental discoveries in history: that of
radioactivity.

Like his father and grandfather before him, Becquerel had an obsessive
interest in minerals that glowed, or fluoresced, after exposure to sunlight. He
was trying to get to the bottom of this in January 1896 when he heard the
sensational news of the discovery of X-rays by the German physicist Wilhelm
R枚ntgen. Becquerel was struck by the thought that the fluorescent minerals
he had been studying might react to sunlight not only by glowing with visible
light, but also by emitting invisible X-rays.

He set out to test this by wrapping a photographic plate in dark paper, so
that light could not get at it, and placing it on a sunlit windowsill. On top of
the plate he arranged various fluorescent minerals. He reasoned that if sunlight
triggered a mineral to produce X-rays, in addition to visible light, then the
X-rays should easily penetrate the paper and blacken the photographic plate.

Flash of genius

To Becquerel鈥檚 disappointment, a whole series of fluorescent minerals failed
to blacken the wrapped plate. Nonetheless, he persisted for weeks with various
samples and got round to the uranium salt potassium uranyl disulphate. Here he
came up trumps. On 24 February 1896, he reported to the French Academy of
Sciences that this uranium mineral emitted rays that penetrated paper and
blackened a photographic plate.

Without firm evidence that the mystery rays were actually X-rays, Becquerel
set about finding their properties. He began another windowsill experiment in
which he placed a small copper cross between the sample and the wrapped
photographic plate. If the rays travelled in straight lines, as R枚ntgen鈥檚
X-rays did, then the developed plate would show the shadowed outline of the
cross.

On 26 February, much to Becquerel鈥檚 frustration, the Parisian sky was
completely overcast and he was unable to carry out his experiment. Instead, he
took the entire apparatus鈥攗ranium salt, wrapped photographic plate and
copper cross鈥攁nd placed it in the drawer of a cabinet. There it remained,
in total darkness, for several days during which time the Sun made only fleeting
appearances in the wintry sky above the city. Eventually Becquerel鈥檚 impatience
got the better of him. On 1 March he removed his apparatus from the dark drawer
and developed the photographic plate.

Why he did this is a fascinating question worthy of an article in itself.
Becquerel was studying an effect which he believed was triggered by sunlight,
yet he developed the plate knowing full well that it had languished for days in
complete darkness. Perhaps he had a hunch. Perhaps it was a sixth
sense鈥攖he flash of unpredictable genius that separates the few scientists
who make great discoveries from the many who do not.

Whatever his motivation, Becquerel developed the plate. And what he saw left
him open-mouthed in disbelief. Shining out in brilliant white against the black
background was the image of the copper cross. The rays that he had reported to
the Academy of Sciences barely a week before were still emitted, in the dark,
with undiminished intensity.

There was only one explanation. The rays coming from the uranium mineral were
not triggered by sunlight or by any other obvious external agent. They had
nothing to do with fluorescence. Instead, they were intrinsic to the uranium
salt. What Becquerel had discovered was an entirely new phenomenon鈥攐ne
which Marie Curie would two years later christen 鈥渞adioactivity鈥�.

Bottomless energy

The characteristic of radioactivity that Becquerel found most astonishing was
its persistence. Becquerel could detect no weakening in the 鈥渦ranium rays鈥�, as
he called them. They poured out in an unending stream, week after week, month
after month, drawing on an apparently bottomless source of energy. It was the
first indication that inside ordinary matter is a mind-boggling energy supply.
For his epoch-making discovery, Becquerel shared the 1903 Nobel Prize for
Physics with Marie and Pierre Curie.

Becquerel is not alone in being led to a major scientific discovery by a
faulty chain of logic. Take the case of William Harvey, the 17th-century English
physician who discovered the circulation of the blood. Harvey, who treated James
I and Charles I, saw the human body as a microcosm of the Universe. He believed
that the same 鈥渁bsolute ruler鈥� governed both, and so he looked to the heavens
for insights into the workings of the body.

And so, bizarre as it may sound, the orbits of the planets inspired Harvey鈥檚
triumphant discovery of the circulation of the blood. 鈥淚 began to think whether
there might be a motion of the blood as if it were in a circle,鈥� wrote Harvey.
He then pondered the discovery made a century earlier by Nicolaus Copernicus
that the planets did not circle the Earth but instead orbited the Sun, the
life-giving source of energy in the Solar System. The energy source for the
circulation of the blood then seemed clear to Harvey鈥攊t must be a central
organ, most likely the heart. 鈥淭he heart,鈥� he wrote, 鈥渋s the Sun of the
尘颈肠谤辞肠辞蝉尘.鈥�

Harvey went on to test his ideas on circulation by dissection and experiment.
He demonstrated, for instance, that blood flows through arteries, veins and
heart valves in one direction only. He showed that the heart is a muscular pump
that expels blood by contracting, and that blood returns to the heart through
the veins. Yet Harvey made his great discovery鈥攁nd in the process founded
the science of modern physiology鈥攐n the basis of a fallacious theory that
there was an intimate connection between blood and the planets.

In common with physiology, the modern theory of the origins of the
Universe鈥攖he big bang鈥攈ad some rather dubious early days. The big
bang theory was first suggested by Soviet-American physicist George Gamow. In
the late 1930s, Gamow set out to explain where the chemical elements had come
from. What was the origin of the iron in our blood, the calcium in our bones,
and the oxygen that fills our lungs?

When Gamow began thinking about this, scientists had already found an
important clue. Astronomers had examined the spectra of countless stars and from
the patterns of missing colours they had deduced not only which elements were
absorbing the light but how common each element was. They had concluded that
everywhere in the Universe the elements existed in roughly the same relative
proportions.

To some this was an indication that a common process had built up all the
elements, starting perhaps from the simplest, hydrogen. Indeed, there was a
precedent for such an element-building process. In 1919, the New Zealand
physicist Ernest Rutherford had bombarded a light element (nitrogen) with alpha
particles and turned it into a heavier element (oxygen). Could nature have done
the same thing?

The obvious site for building elements was inside stars. In the 1930s, the
German physicist Carl-Friedrich von Weizs盲cker had investigated plausible
element-building nuclear reactions. He concluded that synthesis of all the
chemical elements from hydrogen would require a furnace with a very wide range
of densities and temperatures, increasing to billions of degrees. However, at
that time everyone thought, incorrectly, that all stars were much the same as
the Sun, which has a core temperature of only 15 million 掳C.

It was against this backdrop that Gamow began looking for an alternative site
that could have forged the chemical elements. Where in the Universe was there a
鈥渇urnace鈥� that could reach a temperature of billions of degrees? Gamow realised
the entire Universe must have been such a furnace when it was very young.

Over the previous decade or so, it had become clear the Universe is
expanding. Run this expansion backwards, and the Universe would become hotter as
it became denser, just as air in a bicycle pump heats up when it is
compressed.

This led Gamow to suggest that the Universe was born in a 鈥渉ot鈥� big bang. He
envisaged the early Universe as a searing hot mass of protons, neutrons and
electrons compressed into a tiny volume. Something then triggered this mass to
start expanding and cooling, and as it did so nuclear reactions among the basic
ingredients forged all the elements. This must have happened in the first few
minutes of the Universe鈥檚 existence before the fireball became too cool and
rarefied for nuclear reactions to continue.

But this theory didn鈥檛 entirely fit the evidence. Although Gamow found that
it was possible to make helium and other light elements in this way, it proved
impossible to build the heavy elements鈥攚hatever mixes of initial
ingredients he chose. The early Universe simply did not stay hot and dense long
enough for a succession of nuclear reactions to build up elements such as oxygen
and calcium. Gamow鈥檚 theory was a miserable failure.

Inside stars

By the 1950s, however, the way that stars generate energy was better
understood. Their interiors supported a far wider range of densities and
temperatures than anyone had dreamed was possible. In fact, the hot interiors of
stars have manufactured virtually every element heavier than helium.

Gamow鈥檚 big bang theory had risen from the ashes of an idea about the cores
of stars that was entirely wrong. Nevertheless, his achievement was immense. He
was the first person to think seriously about the conditions in the early
Universe. He also laid the foundations of the modern view that only particle
physics can provide answers to the ultimate questions about the first few
minutes after the Universe was born.

Gamow, Becquerel and Harvey were just three of many scientists who were right
for the wrong reason. Evidence, if evidence were needed, that great scientific
discoveries often come about in the most unexpected of ways and that the
progress of science is not as logical as the textbooks would have us
believe.