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[经济学人] [2011.10.08]Expanding horizons2011诺贝尔奖:不断扩大的视野









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发表于 2011-10-13 14:31 | 显示全部楼层 |阅读模式
The 2011 Nobel prizes

Expanding horizons
This year’s prizes were awarded for work on the immune system, the expansion of the universe and quasicrystals

THE rules say it is not allowed. But this year a Nobel prize was awarded to a dead man. Ralph Steinman of Rockefeller University in New York, who discovered the role of dendritic cells in activating the immune system, died on September 30th. That news did not, however, make it across the Atlantic Ocean in time, and on October 3rd the Karolinska Institute in Stockholm honoured Dr Steinman with half of this year’s prize in physiology or medicine.

The other half went to Bruce Beutler, from the Scripps Institute in San Diego, and Jules Hoffmann, from Strasbourg University, for work on the way the immune system boots up in the face of invading pathogens. Dr Hoffmann found in fruit flies, and Dr Beutler subsequently discovered in mice, a crucial protein-binding mechanism that helps the immune system recognise invaders and trigger an immune response against them.

This done, Dr Steinman’s dendritic cells then stimulate some of the immune system’s main cellular troops, known at T-lymphocytes, into action. Some T-cells go on to kill infected body cells. Some act as part of the immune system’s memory, so that it can respond quickly to the recurrence of an infection. And some help regulate the activities of other cells in the immune system.

Champagne supernovae

The physics prize was awarded for what, in one sense, might reasonably be viewed as the biggest discovery ever made in that subject—that the universe is not only expanding (which had been known since the 1920s), but that the rate of expansion is increasing. Something, in other words, is actively pushing it apart.

This was worked out by two groups who, in the 1990s, were studying exploding stars called supernovae. One was the Supernova Cosmology Project, led by Saul Perlmutter of the Lawrence Berkeley National Laboratory, in California. The other was the High-z Supernova Search Team, an international collaboration led by Brian Schmidt and involving Adam Riess, both then at Harvard University. It is these three gentlemen who have shared the prize.

Supernovae come in various types. One particular sort, though, known as type Ia, always explode with about the same energy and are therefore equally bright. That means it can be estimated, with reasonable precision, how far away they are. In addition, the speed at which an object such as a star or galaxy is moving away from Earth, because of the expansion of the universe, can be worked out from its redshift. This is a fall towards the red end of the spectrum in the frequency of its light. It is caused by the Doppler effect (something similar happens when a police car or fire engine drives past you with its siren blaring, and the pitch of the sound suddenly drops).

What both groups found was that the light from distant supernovae was fainter than predicted. In other words, the supernovae were farther away than their redshifts indicated they should be, based on the existing model of the universe. Something, then, was pushing space itself apart.

What that something is, remains conjecture. It has been labelled “dark energy”, but that is really physicists’ shorthand for “we haven’t got a clue”. It may, though, relate to a mathematical term called the cosmological constant that appears in Einstein’s general theory of relativity, and which Einstein thought, before the discovery of the expansion of the universe, was necessary to stop the universe collapsing.

Crystal tips

Unlike the medicine and physics prizes, the chemistry prize went to an individual. The winner was Daniel Shechtman of Technion, a technology institute in Haifa, Israel. On April 8th 1982 Dr Shechtman fired a beam of electrons at a slice of aluminium-manganese alloy, in order to understand its crystal structure. Electrons, being waves as well as particles, produce a diffraction pattern when transmitted through a crystal. Analysis of that pattern can tell you the details of how a crystal’s atoms are arranged. One of the most basic parts of that arrangement, though, is immediately obvious from the picture of spots in the pattern. This is the order of symmetry of the crystal (in other words, the number of ways it can be rotated to produce a pattern identical to the original).
和诺贝尔医学奖和物理学奖不同,诺贝尔化学奖由一个人独享。获奖者是以色列  海法一家技术学院——Technion的达尼埃尔·谢赫特曼。1982年4月8号,谢赫特曼在一片铝锰合金中燃烧一束电子,想观察它的晶体结构。电子和粒子同时产生波动,当电子穿过一块晶体时产生衍射模式。通过对衍射模式的分析可以观察晶体中的原子是如何排列的。其中最本质的一部分可迅速从衍射模式的空间点镇排列图中清楚看到。这就是晶体的对称体的顺序(换句话说,就是使其旋转后能和原型完全重合有多少种方法)。

In this case the order of symmetry Dr Shechtman saw was tenfold. That is impossible. Geometry dictates that only two-, three-, four- and sixfold rotational symmetry can exist. At least, those are the possibilities if the material really is a crystal. What Dr Shechtman had discovered, he realised, was a new sort of material called a quasicrystal. Quasicrystals have regular elements, like normal crystals. But these elements fit together in ways which never properly repeat themselves. The two-dimensional equivalent is known as Penrose tiling (see picture above), after Sir Roger Penrose, the mathematician who put this form of geometry on a formal footing. Penrose tiling has, however, been widely used in the past for decoration, particularly by Islamic artists.

The discovery of quasicrystals—in effect, three-dimensional Penrose tiles—has revolutionised materials science. Others, with eight- and 12-fold symmetry are now known. They often have interesting properties, such as poor heat conductivity (which makes them good insulators) and low friction (which makes them slippery). This makes them useful for certain sorts of coating. Liquid crystals, often used in display screens, are sometimes quasicrystals, too. And they have even turned up in a type of hard, specialised steel made by Sandvik, a Swedish engineering firm. Alfred Nobel, Sweden’s most famous industrialist, would have been proud.
Time can both ruin everything and build everything-It depends on you

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