天体迟早撞地球 自身活动是人类灭亡主因？ Is the end of the world really nigh? Science is moving ever closer to understanding how, and when, humanity may be extinguished Alok Jha The Observer, Saturday 19 November 2011 Article history An exceptionally strong magnetic storm would have deadly effects. Photograph: Alamy Judging by the run of successful natural disaster films in the past few years, people are fascinated by the idea of the end of the world. In Danny Boyle's 28 Days Later, a virus ravaged the UK and beyond; an asteroid was the world-ending threat in Deep Impact and Armageddon; and climate change got a starring role in The Day After Tomorrow. The Doomsday Handbook: 50 Ways to the End of the World by Alok Jha Buy it from the Guardian bookshop Search the Guardian bookshop Tell us what you think: Star-rate and review this book In the real world, we don't know how the Earth (or humanity) might meet its end or when that will happen. Pondering and predicting the event has usually been a job for the world's great religions: all of them have some idea about how humans will meet their maker. Indeed, "the end" (or judgement day) is usually a deity's way of cleansing our planet, to allow a fresh race of people who are morally purer to repopulate the resulting clean slate. Usually, there is too much sin or debauchery and the time has come to start again. Stories of brimstone, fire and gods make good tales and do a decent job of stirring up the requisite fear and jeopardy. But made-up doomsday tales pale into nothing, creatively speaking, when contrasted with what is actually possible. Look through the lens of science and "the end" becomes much more interesting. Since the beginning of life on Earth, around 3.5 billion years ago, the fragile existence has lived in the shadow of annihilation. On this planet, extinction is the norm – of the 4 billion species ever thought to have evolved, 99% have become extinct. In particular, five times in this past 500 million years the steady background rate of extinction has shot up for a period of time. Something – no one knows for sure what – turned the Earth into exactly the wrong planet for life at these points and during each mass extinction, more than 75% of the existing species died off in a period of time that was, geologically speaking, a blink of the eye. One or more of these mass extinctions occurred because of what we could call the big, Hollywood-style, potential doomsday scenarios. If a big enough asteroid hit the Earth, for example, the impact would cause huge earthquakes and tsunamis that could cross the globe. There would be enough dust thrown into the air to block out the sun for several years. As a result, the world's food resources would be destroyed, leading to famine. It has happened before: the dinosaurs (along with more than half the other species on Earth) were wiped out 65 million years ago by a 10km-wide asteroid that smashed into the area around Mexico. Monica Grady, an expert in meteorites at the Open University, says it is a question of when, not if, a near-Earth object (NEO) collides with our planet. "Many of the smaller objects break up when they reach the Earth's atmosphere and have no impact. However, a NEO larger than 1km wide will collide with Earth every few hundred thousand years and a NEO larger than 6km, which could cause mass extinction, will collide with Earth every hundred million years. We are overdue for a big one." Other natural disasters include sudden changes in climate or immense volcanic eruptions. All of these could cause global catastrophes that would wipe out large portions of the planet's life, but, given we have survived for several hundreds of thousands of years while at risk of these, it is unlikely that a natural disaster such as that will cause catastrophe in the next few centuries. In addition, cosmic threats to our existence have always been with us, even thought it has taken us some time to notice: the collision of our galaxy, the Milky Way, with our nearest neighbour, Andromeda, for example, or the arrival of a black hole. Common to all of these threats is that there is very little we can do about them even when we know the danger exists, except trying to work out how to survive the aftermath. But in reality, the most serious risks for humans might come from our own activities. Our species has the unique ability in the history of life on Earth to be the first capable of remaking our world. But we can also destroy it. "Existential risks are a relatively novel phenomenon," writes Nick Bostrom, a philosopher and director of the Future of Humanity Institute at Oxford University, in the World Economic Forum's annual publication, Global Agenda. "With the exception of a species-destroying comet or asteroid impact (an extremely rare occurrence), there were probably no significant existential risks in human history until the mid-20th century and certainly none that it was within our power to do anything about." All too real are the human-caused threats born of climate change, excess pollution, depletion of natural resources and the madness of nuclear weapons. We tinker with our genes and atoms at our own peril. Nanotechnology, synthetic biology and genetic modification offer much potential in giving us better food to eat, safer drugs and a cleaner world, but they could also go wrong if misapplied or if we charge on without due care. Martin Rees, Britain's astronomer royal and former president of the Royal Society, warned in his 2003 book, Our Final Century?, that the odds of human civilisation surviving beyond 2100 are no more than 50%, given the easy access to technologies that could have global impacts, such as biological terrorism, or the potential adverse impacts of molecular nanotechnology. The first manmade existential risk, said Bostrom, might have been the first detonation of the atomic bomb. "At the time, there was some concern that the explosion might start a runaway chain-reaction by 'igniting' the atmosphere. Although we now know that such an outcome is physically impossible, an existential risk was nevertheless present then." Potential points of danger continue to come from the more successful achievements of our recent past. Our society is connected and computerised like never before and this has brought us big benefits in terms of trade, access to knowledge and education and better communications. But those same interconnections can spread viruses (human and computer) ever faster. A skilled terrorist cell (or intelligent machine) could compromise power systems, steal or delete financial data and wreck supply chains, all of which are crucial for the modern world to function. A failure in a digital system in the United States can spread to China or Australia in seconds. It is perhaps ironic that the shadow of potential threats becomes ever longer the more light we shed on our understanding of the universe. Imagine that we took some of the most learned figures of the enlightenment period in western Europe – Isaac Newton, say, or Francis Bacon, or Bishop George Berkeley – and asked them how they thought the world would come to an end. There might be tales of divine intervention (Newton believed doomsday would be in the 21st century, calculated from clues in the Bible), or the idea that a bloody war would end up causing so many casualties that nations would suffer and wither away. There might be serious consideration of other fantastical theories, but none of these clever people could have told you about the doomsday potential of nuclear bombs, or black holes, or rising sea levels due to climate change. You can only know that the world could pop out of existence in a bout of vacuum decay, and be wiped out in a blink, if you know about quantum particles and the evolution of the universe since the big bang. We are beginning to understand that what we conceive of as "time" might one day disappear from our universe, giving us no sense of movement or direction. And let us hope we never run into a clump of the deadly strangelet matter anywhere in the universe. This is a substance nominally so very close to being made of the same stuff that makes up everything we see around us, yet coldly destructive of our way of life. Jason Matheny, a program manager at the US **'s Intelligence Advanced Research Projects Activity, routinely considers potential ways that humanity might be threatened. In a 2007 article for the journal Risk Analysis, he pondered the inevitable death of the sun. "In one billion years, the sun will begin its red giant stage, increasing terrestrial temperatures above 1,000 degrees, boiling off our atmosphere, eventually forming a planetary nebula, making Earth inhospitable to life," he wrote. "If we colonise other solar systems, we could survive longer than our sun, perhaps another 100 trillion years, when all stars begin burning out. We might survive even longer if we exploit non-stellar energy sources." Which all sounds very positive. But the universe has some further tricks up its sleeve. It is hard to imagine, wrote Matheny, how humanity will survive beyond the decay of nuclear matter, which is expected in 1032 to 1041 years. "Physics seems to support Kafka's remark that there is infinite hope, but not for us. While it may be physically possible for humanity or its descendents to flourish for 1041 years, it seems unlikely that humanity will live so long. Homo sapiens has existed for 200,000 years. Our closest relative, Homo erectus, existed for around 1.8 million years. The median duration of mammalian species is around 2.2 million years." Should any of this doomsaying concern us, particularly in a credit-crunched world? Yes, argues Bostrom. "Attempts to quantify existential risk inevitably involve a large helping of subjective judgment. And there may be a publication bias in that those who believe that the risk is larger might be more likely to publish books," he writes in Global Agenda. "Nevertheless, everybody who has seriously looked at the issue agrees that the risks are considerable. Even if the probability of extinction were merely 5%, or 1%, it would still be worth taking seriously in view of how much is at stake." It is sad, he concludes, that humanity as a whole does not invest much in improving its thinking on how to enhance its own survival against the threats about which we might do something (vacuum decay and the death of the sun notwithstanding). Addressing the World Economic Forum's 2006 panel, which was convened to consider global catastrophes, he gave this advice: "A great leader acts in awareness of the big picture and accepts responsibility for the long-term consequences of the policies he or she pursues. With regard to existential risks, the challenge is neither to ignore them nor to indulge in gloomy despondency, but to seek understanding and to take the most cost-effective steps to make the world safer." In short, better safe than sorry. • Alok Jha is a Guardian science correspondent and author of The Doomsday Handbook: 50 Ways to the End of the World (Quercus, ￡9.99) and How To Live Forever And 34 Other Really Interesting Uses for Science (Quercus, ￡9.99) Strange ways to go DEATH BY EUPHORIA Many of us use drugs such as caffeine or nicotine every day. Our increased understanding of physiology brings new drugs that can lift mood, improve alertness or keep you awake for days. How long before we use so many drugs we are no longer in control? Perhaps the end of society will not come with a bang, but fade away in a haze. Danger sign: Drugs would get too cheap to meter, but you might be too doped up to notice. VACUUM DECAY If the Earth exists in a region of space known as a false vacuum, it could collapse into a lower-energy state at any point. This collapse would grow at the speed of light and our atoms would not hold together in the ensuing wave of intense energy – everything would be torn apart. Danger sign: There would be no signs. It could happen half way through this… STRANGELETS Quantum mechanics contains lots of frightening possibilities. Among them is a particle called a strangelet that can transform any other particle into a copy of itself. In just a few hours, a small chunk of these could turn a planet into a featureless mass of strangelets. Everything that planet was would be no more. Danger sign: Everything around you starts cooking, releasing heat. END OF TIME What if time itself somehow came to a finish because of the laws of physics? In 2007, Spanish scientists proposed an alternative explanation for the mysterious dark energy that accounts for 75% of the mass of the universe and acts as a sort of anti-gravity, pushing galaxies apart. They proposed that the effects we observe are due to time slowing down as it leaked away from our universe. Danger sign: It could be happening right now. We would never know. MEGA TSUNAMI Geologists worry that a future volcanic eruption at La Palma in the Canary Islands might dislodge a chunk of rock twice the volume of the Isle of Man into the Atlantic Ocean, triggering waves a kilometre high that would move at the speed of a jumbo jet with catastrophic effects for the shores of the US, Europe, South America and Africa. Danger sign: Half the world's major cities are under water. All at once. GEOMAGNETIC REVERSAL The Earth's magnetic field provides a shield against harmful radiation from our sun that could rip through DNA and overload the world's electrical systems. Every so often, Earth's north and south poles switch positions and, during the transition, the magnetic field will weaken or disappear for many years. The last known transition happened almost 780,000 years ago and it is likely to happen again. Danger sign: Electronics stop working. GAMMA RAYS FROM SPACE When a supermassive star is in its dying moments, it shoots out two beams of high-energy gamma rays into space. If these were to hit Earth, the immense energy would tear apart the atmosphere's air molecules and disintegrate the protective ozone layer. Danger sign: The sky turns brown and all life on the surface slowly dies. RUNAWAY BLACK HOLE Black holes are the most powerful gravitational objects in the universe, capable of tearing Earth into its constituent atoms. Even within a billion miles, a black hole could knock Earth out of the solar system, leaving our planet wandering through deep space without a source of energy. Danger sign: Increased asteroid activity; the seasons get really extreme. INVASIVE SPECIES Invasive species are plants, animals or microbes that turn up in an ecosystem that has no protection against them. The invader's population surges and the ecosystem quickly destabilises towards collapse. Invasive species are already an expensive global problem: they disrupt local ecosystems, transfer viruses, poison soils and damage agriculture. Danger sign: Your local species disappear. TRANSHUMANISM What if biological and technological enhancements took humans to a level where they radically surpassed anything we know today? "Posthumans" might consist of artificial intelligences based on the thoughts and memories of ancient humans, who uploaded themselves into a computer and exist only as digital information on superfast computer networks. Their physical bodies might be gone but they could access and store endless information and share their thoughts and feelings immediately and unambiguously with other digital humans. Danger sign: You are outcompeted, mentally and physically, by a cyborg. 世界末日真要来了吗？ (作者阿洛科·杰哈) 自从35亿年前地球上出现生命以来，脆弱的世间万物就一直生活在灭绝的阴影中。在这个星球上，灭绝是常态———在已知进化而成的40亿个物种中，有99%已经灭绝，特别是在过去5亿年中，不为人察觉的物种灭绝速度加快了5倍。某种东西(没有人知道到底是什么)把地球变成了完全不适合生命存在的星球。在每一次大灭绝中，有75%以上的现有物种会在一段时期内灭亡，而从地质学上来说，这样一段时期只是一瞬间。 英国开放大学的陨石专家莫妮卡·格雷迪认为，近地天体与地球相撞只是个迟早的问题，而不是会否的问题。她说：“大多数小天体在到达地球大气层时会化为灰烬，不会撞上地球。但每隔几十万年就会有一个直径超过1公里的近地天体与地球相撞，每几亿年就会有一个直径超过6公里、可能引发大灭绝的近地天体与地球相撞。我们早该撞上一个大家伙了。” 改造世界毁灭地球 但事实上，人类面临的最大风险也许来自我们自身的活动。我们这个物种具有地球生命史上独一无二的能力，是第一个能够改造这个世界的物种。但我们也可能毁灭这个世界。 人类造成的威胁是实实在在的，这些威胁来自气候变化、过度污染、自然资源枯竭以及疯狂的核武器。我们自冒风险，胡乱修补我们的基因和原子。纳米技术、合成生物学和转基因技术很可能给我们带来更好的食物、更安全的药品和更加干净的世界，但如果滥用或贸然行事的话，它们也可能出问题。 英国皇家学会前主席、皇家天文学家马丁·里斯在2003年的《我们的最后一个世纪？》一书中警告，鉴于我们可以轻而易举地获得能够产生全球影响的技术，比如生物**主义和可能产生反作用的分子纳米技术，人类文明延续到2100年之后的几率不超过50%。 人类近期取得的更伟大成就不断地带来潜在的危险。我们的社会以前所未有的方式电脑化并联系在一起，在贸易、学习、教育和沟通方面令我们获益匪浅。但这样的相互联系也可能以前所未有的速度传播病毒(不管是人类病毒还是电脑病毒)。一个掌握技术的**组织(或智能机器)就能够破坏电力系统，窃取或删除金融数据，切断供应链，而所有这些对于现代社会的运转都是至关重要的。美国的数字系统故障可能在几秒钟之内蔓延至中国或澳大利亚。 人类灭亡方式多样 美国情报高级研究计划署的项目主管杰森·马西尼常常思考人类可能面临灭绝之虞的方式。在2007年为《风险分析》杂志撰写的一篇文章中，他探讨了太阳不可避免的灭亡问题。他写道：“十亿年后，太阳将进入红巨星阶段，导致地球的温度升至1000摄氏度以上，烤化我们的大气层，最终形成一个行星状星云，把地球变成一个不宜居的星球。如果我们移居到其他星系，或许能够比太阳活得更长久。我们可能再活100万亿年，直到所有恒星都开始燃烧殆尽。如果我们能够利用非恒星能源，或许还能再活长一些。” 这听上去都充满了希望，但宇宙还留了几手。马西尼写道，很难想象人类怎样才能在核物质衰变后继续存活下去。核物质被认为将在1032年至1041年后衰变。 他写道：“物理学似乎支持卡夫卡说的那句话，‘希望是无限的’，但对我们来说并非如此。虽然从物理学的角度来说，人类或人类的后代再活1041年是可能的，但人类似乎不大可能活那么长时间。现代人已经存在了20万年，我们最近的近亲直立人存在了180万年左右。哺乳动物物种存在时间的中位数为220万年左右。” 我们是否应该为这些末日预言感到担心，特别是在一个信用缩水的世界里？英国牛津大学人类未来研究所所长、哲学家尼克·博斯特罗姆认为答案是肯定的。在世界经济论坛2006年探讨全球灾难的小组讨论会上，博斯特罗姆给出的建议是：“就生存风险而言，我们需要做的既不是置之不理，也不是灰心丧气，而是努力认清它们并采取最有效的措施使世界变得更加安全。”一句话，防患于未然。 查看更多0个回答 . 2人已关注
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