万物简史 第216期:把铅撵出去(5)

Chlorofluorocarbons are also not very abundantthey constitute only about one part per billion of the atmosphere as a wholebut they are extravagantly destructive. One pound of CFCs can capture and annihilate seventy thousand pounds of atmospheric ozon

万物简史 第217期:把铅撵出去(6)

Up to this time, the oldest reliable dates went back no further than the First Dynasty in Egypt from about 3000B.C. No one could confidently say, for instance, when the last ice sheets had retreated or at what time in the past the Cro-Magnon people h

万物简史 第218期:把铅撵出去(7)

Rather than restate every one, scientists decided to keep the inaccurate constant. Thus, Tim Flannery notes, every raw radiocarbon date you read today is given as too young by around 3 percent. The problems didn't quite stop there. It was also quickl

万物简史 第219期:把铅撵出去(8)

Finally, and perhaps a little unexpectedly, readings can be thrown out by seemingly unrelated external factorssuch as the diets of those whose bones are being tested. One recent case involved the long-running debate over whether syphilis originated i

万物简史 第220期:把铅撵出去(9)

Holmes was heroic as much for the obstacles he overcame as for the results he achieved. By the 1920s, when Holmes was in the prime of his career, geology had slipped out of fashionphysics was the new excitement of the ageand had become severely under

万物简史 第222期:把铅撵出去(11)

For seven years, first at the University of Chicago and then at the California Institute of Technology (where he moved in 1952), he worked in a sterile lab, making very precise measurements of the lead/uranium ratios in carefully selected samples of

万物简史 第223期:把铅撵出去(12)

As always, however, nothing was quite as straightforward as such a breezy description makes it sound. Meteorites are not abundant and meteoritic samples not especially easy to get hold of. Moreover, Brown's measurement technique proved finicky in the

万物简史 第224期:把铅撵出去(13)

His main work done, Patterson now turned his attention to the nagging question of all that lead in the atmosphere. He was astounded to find that what little was known about the effects of lead on humans was almost invariably wrong or misleadingand no

万物简史 第225期:把铅撵出去(14)

By counting back through these layers and measuring the amount of lead in each, he could work out global lead concentrations at any time for hundreds, or even thousands, of years. The notion became the foundation of ice core studies, on which much mo

万物简史 第226期:把铅撵出去(15)

Absurdly, he was excluded from a 1971 National Research Council panel appointed to investigate the dangers of atmospheric lead poisoning even though he was by now unquestionably the leading expert on atmospheric lead. 荒唐的是，一个美国研究委

万物简史 第227期:把铅撵出去(16)

On its website, a history of the company makes no mention of leador indeed of Thomas Midgleybut simply refers to the original product as containing a certain combination of chemicals. 在它的网站上，公司的历史没有提及铅──也没有提

万物简史 第228期:把铅撵出去(17)

So who is making it? We arethat is to say, many of our large corporations are still making it at their plants overseas. It will not be banned in Third World countries until 2010. 那么，是谁在生产含氯氟烃？是我们──那就是说，许多

万物简史 第237期:马斯特-马克的夸克(9)

It is all, as you can see, just a little unwieldy, but it is the simplest model that can explain all that happens in the world of particles. Most particle physicists feel, as Leon Lederman remarked in a 1985 PBS documentary, that the Standard Model l

万物简史 第238期:马斯特-马克的夸克(10)

In an attempt to draw everything together, physicists have come up with something called superstring theory. This postulates that all those little things like quarks and leptons that we had previously thought of as particles are actually stringsvibra

万物简史 第239期:马斯特-马克的夸克(11)

String theory has further spawned something called M theory, which incorporates surfaces known as membranesor simply branes to the hipper souls of the world of physics. I'm afraid this is the stop on the knowledge highway where most of us must get of

万物简史 第240期:马斯特-马克的夸克(12)

Almost at once the Bogdanov paper excited debate among physicists as to whether it was twaddle, a work of genius, or a hoax. Scientifically, it's clearly more or less complete nonsense, Columbia University physicist Peter Woit told the New York Times

万物简史 第241期:马斯特-马克的夸克(13)

Hubble realized that this could be expressed with a simple equation, Ho = v/d (where Ho is the constant, v is the recessional velocity of a flying galaxy, andd its distance away from us). Ho has been known ever since as the Hubble constant and the wh

万物简史 第242期:马斯特-马克的夸克(14)

This would mean that the universe was only half the size and age that Sandage believedten billion years. Matters took a further lurch into uncertainty when in 1994 a team from the Carnegie Observatories in California, using measures from the Hubble s

万物简史 第243期:马斯特-马克的夸克(15)

The difficulty in making final determinations is that there are often acres of room for interpretation. Imagine standing in a field at night and trying to decide how far away two distant electric lights are. Using fairly straightforward tools of astr

万物简史 第235期:马斯特-马克的夸克(7)

The charged pion and antipion decay respectively into a muon plus antineutrino and an antimuon plus neutrino with an average lifetime of 2.603 x 10-8 seconds, the neutral pion decays into two photons with an average lifetime of about 0.8 x 10-16 seco