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When you think of the butterfly effect, I'm guessing you're probably thinking of the 2004 film of the same name by Ashton Kutcher and Amy Smart, but right?
The butterfly effect is the concept that seemingly insignificant little things can eventually lead to huge consequences – in other words, these small things have a non-linear effect on extremely complex systems. To take a classic example: when a butterfly flapps its wings in India, a small change in air pressure can end up causing a tornado in Iowa.
In the film mentioned at the beginning, Kutcher's character finds a way to return to his childhood. Every time he travels through time, there are some small changes in his actions – but those small changes end up having a significant (and terrifying) impact on his adult life.
Figure 1. "Butterfly Effect" movie poster | The picture comes from the Internet
The term "butterfly effect" was coined in the 60s of the 20th century by Edward Lorenz, a professor of meteorology at the Massachusetts Institute of Technology, when he was studying meteorological models. He devised a model to describe the fact that if there were two close to each other that indicated the current weather, the two points would quickly separate, and then one of the points would represent an area that could be subject to severe storms, while the other would be calm.
At the time, meteorological statisticians believed that people should be able to predict future weather by querying historical records, seeing what happened in the past and when things were the same now. Lorenz is skeptical. He ran a computer program to simulate various weather conditions, and he found that if a variable was rounded from 0.506127 to 0.506, the program's weather forecast for the next two months would change dramatically.
His view is that long-term weather forecasting is almost impossible, largely because humans do not have the ability to measure nature's extraordinary complexity. There are too many tiny variables that can be called pivot points that lead to greater consequences.
As science journalist Peter Dizikes wrote in the Boston Globe: "Lorenz points out that the 'myriad' interconnectedness of nature means that the flapping of a butterfly's wings could trigger a tornado – or, conversely, could stop one." In the same way, if we make super-small changes to nature, 'we will never know what would have happened if we hadn't interfered', because subsequent changes are too complex and entangled to revert back to the previous state. ”
So, while it's often thought that the butterfly effect means that small changes can have serious consequences (and that we can tease out the cause and effect by going back in time), Lorenz is trying to say that we can't track these changes. We are not sure what would cause weather patterns to develop in different directions.
女孩的脸上落了一只绿帘维蛱蝶，图源：CARL COURT/GETTY IMAGES
Lorenz presented his work to the public in a 1963 paper entitled "Determined Aperiodic Flow Fields" and referred to the aforementioned concept as "initial conditional sensitivity" (the term "butterfly effect" was coined in a subsequent lecture). The paper used to be rarely cited (at least at first).
The Butterfly Effect and Chaos Theory
Later, other scientists realized the importance of Lorenz's discovery. His keen insight laid the foundation for a branch of mathematics called chaos theory, which sought to predict the behavior of systems that were inherently unpredictable.
You see examples of the butterfly effect every day. Weather is just one example, and so is climate change. It turns out that climate warming – by chance – is affecting alpine butterfly species in North America.
"Climate change is expected to have some major impacts, such as the climate becoming too hot for some species or too dry for others, while at the same time there will be a myriad of smaller indirect impacts. Alessandro Filazzola, a community ecologist and data scientist and postdoctoral researcher at the University of Alberta, wrote in an email.
"In our study, we investigated one of the indirect effects and found that future climates will gradually lead to non-overlapping habitats for butterflies and their host plants. In the larval stage (caterpillar), since the butterfly eats only one plant, any misalignment of the habitat of the two will lead to a decline in the butterfly population. ”
If we pause to consider all the other species in the food chain, he adds, we suddenly see that there are many species that could be affected – not just a small butterfly. This is the application of the butterfly effect on a larger scale. "For example, what about the animals that used to feed on butterflies and the animals that fed on those animals, or other insects, or other butterflies (which can all be affected)? The project that we did was very manageable because the butterfly species we were studying ate only one plant, and when you were looking at the whole ecosystem, the same logic (just more difficult to measure). "When we start thinking about how quickly a small change can lead to a lot of unintended consequences, it naturally becomes worrying.
For example, restricting the construction of hydropower plants may reduce certain types of environmental damage. But while reducing this potentially clean energy, we have become more dependent on fossil fuels that accelerate global warming. Biofuel subsidies, while designed to reduce our dependence on fossil fuels, have actually exacerbated the destruction of rainforests, the waste of freshwater, and the rise in food prices, affecting the poorest of humanity.
So how do we live freely in our lives without fear of harm? Firazzola uses butterflies as an example. "Probably one of the most important things to do to mitigate these indirect effects is to better understand them. Simply put, keeping nature pristine is the most important thing," he said. "Ecosystems are very complex, and the disappearance of one species may not have a noticeable impact, but it may have a knock-on effect on the entire system. "For example, the reintroduction of wolves to Yellowstone has not only increased beaver populations, but also willow and aspen trees, and provided food for animals such as birds, coyotes and bears, among other benefits.
Second, let's think about how the butterfly effect affects our personal lives. With a planet of nearly 8 billion people, can one person's actions trigger change on a global scale?
Firazzola says he does think about the indirect effects of individual actions. "The items I buy, the people I come into contact with, the words I say, I believe that everything has the potential to have a ripple effect in society," he said. "That's the important thing about trying to be a good person: making a positive impact on society. In addition, I think that these indirect effects are often not as small and isolated as many people think. ”
NASA wants to use the butterfly effect to guide spacecraft. The International Cometary Explorer, launched in 1978, became the first spacecraft to intercept a comet, passing through the tail of Comet Giacobini-Zinner and collecting valuable data. Using chaotic system calculations, the researchers learned that with just a little fuel at exactly one moment, a spacecraft could get to the right place quickly and accurately—and it all worked perfectly.
作者：Nathan Chandler
Translation: Machine Seven
Reviewer: Yue Yue
原文链接：What Is the Butterfly Effect and How Do We Misunderstand It? | HowStuffWorks
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The views expressed in the translation are solely those of the author
It does not represent the position of the Institute of Physics of the Chinese Academy of Sciences