Universe a grand tour of modern science Phần 9 docx

I n the late 1980s physicists at CERN, Europe’s particle physics lab in Geneva,

began a long series of experiments aimed at simulating the Big Bang in little

bangs hot and dense enough to set quarks free. These are the fundamental

entities that constitute the heavy matter in the atomic nucleus.

No one doubted by then that each of the protons and neutrons in a nucleus

consists of three fundamental entities called quarks. Various experiments with

particle accelerators had indirectly confirmed the presence of the quarks in the

nuclear material. But no one had seen any free quarks.

If you try to liberate a quark in ordinary reactions between particles, you

unavoidably create a new quark and an antiquark. One of them immediately

replaces the extracted entity. The new antiquark handcuffs the would-be escaper

in a particle called a meson. This is the trick by which Mother Nature has kept

quarks in purdah since the world began.

To be more precise, the confinement of quarks began about 10 millionths of a

second after the start of the Big Bang, at the supposed origin of the Universe.

Before then, in unimaginably hot conditions, each quark could whizz about

independently. Technically speaking, it was allowed to show its colour in public.

By the colour of a quark, physicists mean a quality similar to an electric charge.

But instead of just plus and minus, the colour charge comes in three forms,

labelled red, green and blue. The quarks are not really coloured, but it’s a

convenient way of thinking about the conditions of their confinement in

ordinary matter.

In a TV screen, a red, green and blue dot together make white, and the rule

nowadays is that nuclear matter, too, must be white. That’s why protons and

neutrons consist of three quarks apiece, and not two or four. One red, one

green and one blue quark within each proton or neutron are held loosely

together by particles called gluons.

The colour force carried by the gluons operates only over very short ranges.

Space is opaque to the colour force, in much the same way as frozen water is

impenetrable by fishes. But at a high enough temperature space melts, so to say,

and lets the colour force through. Then the quarks and gluons can roam about

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as freely as do the individual charged atoms and electrons in the electrified gas,

or plasma, of a neon lamp. The effect of the colour force is greatly weakened

because immediate neighbours screen each particle from the pull of distant

particles.

The resulting melee is called a quark—gluon plasma or, more colloquially, quark

soup. Extremely high pressure may have the same effect as high temperatures,

and physicists suspect that quark soup exists at the core of a neutron star, which

is a collapsed star just one step short of a black hole. That’s what the theory

says, anyway, but to set the quarks free experimentally required creating a new

state of matter never seen before.

I ‘A spectacular excess of strangeness’

A multinational team of physicists working at CERN set out to make quark

soup by using an accelerator, the Super Proton Synchrotron, to melt the nuclei

of heavy atoms. It was a matter of whirling heavy atoms up to high energy and

slamming them into a target also made of heavy atoms—lead onto lead, for

example. A direct hit of one nucleus on another would create a small fireball,

and might briefly produce the extreme conditions needed to liberate quarks.

The quarks would recombine almost instantly into a swarm of well-known

particles and antiparticles, and fly as debris out of the target into detectors

beyond. Only by oddities in the composition of the debris might one know

that a peculiar state of matter had existed for a moment. For example the

proportions of particles containing distinctive strange and charmed quarks

might change.

Charmed quarks are so heavy that they require a lot of energy for their

formation, in the first moment of the nuclear collision. They would normally

tend to pair up, as charmed and anticharmed quarks, to make a well-known

particle called charmonium, or J/psi. But if conditions are so hot that plasma

screening weakens the colour force, this won’t happen. The charmed quarks

should enjoy a brief freedom, and settle down only later, in the company of

lighter quarks.

In the next moment of the nuclear collision strange quarks, somewhat lighter,

are being mass-produced. By this time the colour force is much stronger, and it

should corral the strange quarks, three at a time, to make a particle called

omega. In short, the first signs of quark soup appearing fleetingly should be few

charmoniums and many omegas.

That was exactly what the CERN experimenters saw. By 1997 they were

reporting a shortage of charmoniums among the particles freezing out of the

supposed soup. Within a few years they had also accumulated ample evidence

for a surplus of the strange omega particles.

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quark soup

‘A spectacular excess of strangeness, with omega production 15 times normal, is

just the icing on the cake,’ said Maurice Jacob of CERN, who made a theoretical

analysis of the results of the nuclear collisions. ‘Everything else checks too—the

relative proportions of other particles, the size of the fireballs, and so on. We

definitely created a new state of matter, ten times denser than nuclear matter.

And the suppression of charmonium showed that we briefly let the charmed

quarks out of captivity.’

For the sake of only one criterion did the CERN team hesitate to describe their

‘new state of matter’ as quark soup, or to claim it as a true quark–gluon plasma.

The little fireballs were not sufficiently hot and long-lived for temperatures to

average out. It was like deep-frozen potage microwaved but not stirred, and in

Switzerland no self-respecting cook would call that soup.

I A purpose-built accelerator

In 2000, colleagues at the Brookhaven National Laboratory on Long Island, New

York, took over the investigation from CERN. Their new Relativistic Heavy Ion

Collider was expressly built to make quark soup. Unlike the experiments at

CERN, where one of the two heavy nuclei involved in an impact was a

stationary target, the American machine brought two fast-moving beams of gold

nuclei into collision, head-on.

It achieved full energy in 2001, and four experimental teams began to harvest

the results of the unprecedented gold-on-gold impacts. Before long they were

seeing evidence of better temperature stirring and other signs of soupiness.

These included a reduction in the jets of particles normally produced when very

energetic quarks try to escape from the throng. In quark soup, such quarks

surrender much of their energy in collisions.

‘It is difficult to know how the resulting insights will change and influence our

technology, or even our views about Nature,’ commented Thomas Kirk of

Brookhaven, ‘but history suggests there will be changes, and some may be

profound.’

E For more about quarks and gluons, see Particle families. The supposed sequence of

events at the birth of the Universe is described in Big bang.

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quark soup

I n a way , Relativita¨tstheorie was always a poor name for Albert Einstein’s ideas

about space, time, motion and gravity. It seemed to make science iffy. In truth,

his aim was to find out what remained reliable in physical laws despite

confusions caused by relative motions and accelerations.

His conclusions illuminate much of physics and astronomy. Taken one by one,

the ideas of relativity are not nearly as difficult as they are supposed to be, but

there are quite a lot of them. One of the main theories is special relativity (1905)

concerning High-speed travel. Another is general relativity (1915) about

Gravity.

Energy and mass appear in Einstein’s famous E ¼ mc2

, which was a by-product

of special relativity. It reveals how to get energy from matter, notably in

powering the Stars and also Nuclear weapons, which were a fateful by￾product. The equation implies that you can make new matter as a frozen form

of energy, but when Paul Dirac combined special relativity with quantum theory

it turned out that you inevitably get Antimatter too.

General relativity is another box of tricks, among which Black holes dramatize

the amazing effects on time and space of which gravity is capable. They are also

very efficient converters of matter into energy. Gravitational waves predicted

by general relativity are being sought vigorously. More speculative are

wormholes and loops in space, suggesting the possibility of Time machines.

Applied in cosmology, Einstein’s general relativity could have predicted the

expansion of the Universe, but he fumbled it twice. First he added a

cosmological constant to prevent the expansion implied by his theory, and then

he decided that was a mistake. In the outcome, his cosmological constant

reappeared at the end of the 20th century when astronomers found that the

cosmic expansion is accelerating, driven by Dark energy.

Special relativity seems unassailable, but doubts arise about general relativity

because of a mismatch to quantum theory. These are discussed in Gravity and

Superstrings.

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A t bogazko¨y in turkey you can still see the Bronze Age fortifications of

Hattusas, capital of the Hittites. Suppiluliumas I, who reigned there for 40 years

in the 14th century bc, refurbished the city. He came to a sticky end after the

widow of Tutankhamen of Egypt invited one of his sons to marry her and

become pharaoh.

Opponents in Egypt thought it a bad idea and assassinated the Hittite prince. An

ensuing conflict brought Egyptian prisoners of war to Anatolia. They were

harbouring smallpox, long endemic in their homeland. The result was an

epidemic in which Suppiluliumas I himself became the first victim of smallpox

whose name history records. That was in 1350 bc.

The last person to die of smallpox was Janet Parker of Birmingham, England, in

1978. She was a medical photographer accidentally exposed to the smallpox

virus retained for scientific purposes. In the previous year in Merka, Somalia, a

cook named Ali Maow Maalin had been the last to catch the disease by human

contagion, but he survived. In 1980, the World Health Organization in Geneva

formally declared smallpox eradicated, after a 15-year programme in which

vaccinators visited every last shantytown and nomadic tribe. This was arguably

the greatest of all the practical achievements of science, ever.

Individual epidemics of other diseases sometimes took a high toll, including the

bubonic plague that brought the Black Death to 14th-century Eurasia. Overall

smallpox was the worst. Death rates in infants could approach 100 per cent, and

survivors were usually disfigured by the pockmarks of the smallpox pustules,

and often blinded. The historian Thomas Macaulay wrote of smallpox ‘turning

the babe into a changeling at which the mother shuddered, and making the eyes

and cheeks of the betrothed maiden objects of horror to the lover.’

Populations in Eurasia and Africa were left with a level of naturally acquired

immunity. But when European sailors and conquistadors carried smallpox and

other diseases to regions not previously exposed to them, in the Americas and

Oceania, they inadvertently wiped out most of the native populations. One

victim was the Aztec emperor Ciutla´huac in 1520.

Nor was it always inadvertent. ‘The devastating effect of smallpox gave rise to

one of the first examples of biological warfare,’ noted the medical historians

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Nicolau Barquet and Pere Domingo of Barcelona. In 1763 General Jeffrey

Amherst, commanding the British army in North America, approved a proposal

by Colonel Henry Bouquet to grind the scabs of smallpox pustules into blankets

that were to be distributed among disaffected tribes of Indians. ‘You will do well

to try to inoculate the Indians by means of blankets,’ Amherst wrote, ‘as well as

to try every other method that can serve to extirpate this execrable race.’

By that time, many children in Eurasia were being deliberately infected with

smallpox from very mild cases, in the knowledge that most would survive with

little scarring and with acquired immunity. The practice of applying pus from a

smallpox pustule to a child’s skin, and making a small cut, may have originated

among Circassian women who supplied many daughters to Turkish harems. The

wife of the British ambassador in Istanbul introduced the practice to London in

1721. It killed one in 50 of the children so treated and could itself be a source of

contagion for others.

I ‘Such a wild idea’

The Circassians were not the only women with a special reputation for

beauty—meaning in those days, not pockmarked. Throughout rural Europe it

was common knowledge that dairymaids often escaped the smallpox. English

folklore attributed their good looks to their exposure to the morning dew when

they went to milk the cows. As one song had it:

Oh, where are you going, my pretty maiden fair,

With your rosy red cheeks and your coal-black hair?

I’m going a-milking, kind sir, says she,

And it’s dabbling in the dew where you’ll find me.

The dairymaids themselves had shrewder insight, and one of them pertly

assured a Bristol doctor that she would never have the smallpox because she’d

had the cowpox. This was a mild condition that produced sores on the hands of

those dealing with cattle. The doctor’s apprentice, Edward Jenner by name,

overheard this remark and remembered it.

Three decades later, when he had his own practice in Berkeley, Gloucestershire,

Jenner pursued the matter under the cloak of investigating diseases transmitted

from animals to human beings. Eventually he steeled himself and his patients to

see whether inoculation with the non-virulent cowpox might protect against

smallpox. In 1796, in an experiment that would nowadays be called heroic, i.e.

questionable, Jenner introduced matter from a sore on a dairymaid’s hand into

the arm of a healthy eight-year-old, James Phipps. Six weeks later he tried hard

to infect the lad with smallpox. Happily for young James and the rest of us, the

inoculation worked, as it did in further trials with cowpox.

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smallpox

‘This disease leaves the constitution in a state of perfect security from the

infection of the smallpox,’ Jenner reported. In an early manifestation of peer

review, the Royal Society of London refused to publish his manuscript.

Gratuitously it added the caution, ‘He had better not promulgate such a wild

idea if he valued his reputation.’

When Jenner issued a monograph at his own expense, the clerics joined the

medics in denouncing him. Nevertheless the treatment plainly worked, and

commended itself to the likes of the French and Spanish emperors and the US

president. By 1807 a grateful British parliament had rewarded Jenner with

£30,000, equivalent to about £1 million today. And in less than 200 years cowpox

had wholly extinguished smallpox.

I A biological weapon

Or had it? Alongside the dairymaid’s blessing, there remained General Amherst’s

curse. Nothing shows more graphically than smallpox how moral and political

issues are magnified and dramatized by the power of science.

The campaign against smallpox brought out the best in people. Thomas

Jefferson personally saw to it that Jenner’s vaccination was demonstrated to

Native Americans. And for the last big push, which occurred during the Cold

War, humanity was united as never before as a single species with a common

interest in eliminating smallpox from even the poorest and most remote parts of

the world—and damn the cost.

Yet smallpox also brought out the worst, in governments and their scientific

servants. What was superficially a scholarly argument within the World Health

Organization, about what should be done with laboratory stocks of smallpox

virus after eradication was certified in 1980, concealed a deeper anxiety. New

generations would grow up as immunologically naı¨ve in respect of smallpox as

the Aztecs were. They would then be sitting ducks for smallpox used as a

military or terrorist weapon.

Internationally approved stocks of smallpox virus were reduced to those at the

Centers for Disease Control and Prevention in Atlanta, and at the Ivanovsky

Institute for Viral Preparations in Moscow. The case for destroying these, too,

was that as long as they existed they could escape and cause an epidemic. A

minor argument for keeping them was that they might be needed for future

medical research. The main objection to their destruction was that no one knew

for sure if the Atlanta and Moscow stocks were the only ones. The destruction

of the smallpox virus was deferred repeatedly for want of consensus in the

World Health Organization’s multinational executive board.

Concern about a smallpox weapon was no paranoid fantasy. That became clear

when the Soviet Union collapsed. Ken Alibek (Kanatjan Alibekov) had been

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smallpox