This is Scientific American — 60-Second Science. I'm Julia Rosen.
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Isaac Newton said, "I can calculate the motion of heavenly bodies, but not the madness of people." He meant that while people can be unpredictable, the planets are just the opposite—they glide through space in orbits defined by the laws of physics. But that view's been changing and a new study bolsters a more complex outlook.
"The big finding of this paper was the discovery of the first real firm, unambiguous geologic evidence to confirm this idea that the solar system is chaotic."
Stephen Meyers, a geoscientist at the University of Wisconsin–Madison.
By chaotic, Meyers doesn't mean that the planets zoom around wildly on random paths. Rather, he's referring to the mathematical meaning of the word, in which the future state of a complex system depends strongly on its initial conditions. In this case, it means that seemingly random changes in planets' orbits can occur because of subtle gravitational interactions between objects in the solar system.
"It's also known as the butterfly effect. This is the exact same phenomenon. The idea that a butterfly flapping over the Indian Ocean could influence weather patterns over North America a week later."
The idea has been proposed before, but Meyers and his team found supporting evidence in a surprising place: a rock formation in Colorado. The formation is made up of sedimentary layers deposited when a vast inland sea covered parts of North America. These layers contain a record of regularly paced climate changes that were triggered by fluctuations in the amount of sunlight hitting Earth as a result of variations in its orbit.
For at least the last 50 million years or so, Earth's orbit has cycled between a more circular shape and a more elliptical shape every 2.4 million years, producing climate changes with the same timing. However, by independently dating the rocks in Colorado with other methods, Meyers and his colleagues found that before about 85 million years ago, this cycle took 1.2 million years. The cycle time changed because Mars and Earth tugged on each other—just the kind of thing you would expect to see in a chaotic system. The findings are in the journal Nature.
Meyers says the results have several implications. One is that they will help scientists to date ancient rocks and understand the link between orbital changes and climate. But the other potential implication is somewhat more disturbing: billions of years from now, there's a very small chance that Mars could crash into Earth.
"That certainly is a rather dramatic demise to the Earth that would be a consequence of the chaos."
But that's just life—or the end of it—in a chaotic solar system.
Thanks for the minute for Scientific American — 60-Second Science Science. I'm Julia Rosen.
艾萨克·牛顿曾说：“我可以计算天体的运动，但却算不出人类的疯狂 。”他的意思是, 人类可能是无法预测的，而行星却恰恰相反，行星是按照物理定律规定好的轨道在宇宙中运行 。但是这种观点正在发生变化，一项新研究证实了一个更复杂的观点 。
迈耶斯认为，“混沌”的意思并不是说行星在随机疯狂地运动 。相反，他指的是数字意义上的“混沌”，也就是复杂系统的未来状况在很大程度上取决于它的初始状态 。在这种情况下，由于太阳系物体间的轻微引力交互作用，行星轨道的随机改变是可能发生的 。
“这也被称为蝴蝶效应 。这是完全相同的现象 。也就是：一只蝴蝶在印度洋上空扇动翅膀，可能会影响北美一周后的天气模式 。
这个想法之前就被提出来过，但是迈耶斯和他的团队在一个令人吃惊的地方发现了支持证据：科罗拉多州的岩层 。北美部分地区被广阔的内陆海覆盖时形成了沉积层，而科罗拉多岩层就由这些沉积层沉淀而成 。这些岩层记录了节奏固定的气候变化，这些变化由照耀地球的阳光量的波动而引发，而阳光量的变化取决于地球轨道的变化 。
至少在过去5000万年这段时间里，地球轨道一直在圆形和椭圆形之间循环，周期为240万年，而气候变化也在同样的时间产生 。但是，用其他的方法独立确定科罗拉多州岩石的年代以后，迈耶斯和他的同事发现，在大约8500万年前，循环周期为120万年 。循环周期的变化是火星和地球互相拖拽造成的，就像你期待在混沌星系中看到的情况 。这项研究结果发表在《自然》期刊上 。
迈耶斯表示，研究结果有几点启示 。其一，这可以帮助科学家确定古代岩石的年代，并理解轨道改变与气候之间的关系 。但是另一个潜在的含义则令人更加不安：数十亿年以后，虽然机率很小，但火星可能会撞上地球 。
谢谢大家收听科学美国人——60秒科学 。我是朱莉娅·罗森 。
1. refer to 指的是；
例句：In some contexts it can be used to refer to any sort of occlusive vascular disease anywhere in the body, except the heart.
2. be made up of 组成；构成；
例句：Life is made up of little things.
3. or so …左右；…上下；
例句：Though rates are heading down, they still offer real returns of 8% or so.
尽管利率在下降，它们仍然能提供 8%左右的实际收益率 。
4. each other 彼此；互相；
例句：We looked at each other in silence.